A new 1,5-to I,ll-carbonyl transposition protocol involving ...nopr.niscair.res.in/bitstream/123456789/22416/1/IJCB 40B...Indian Journal of Chemistry Vol. 40B, October 2001, pp. 937-947

Indian Journal of Chemistry Vol. 40B, October 200 1 , pp. 937-947

A new 1,5- to I,ll-carbonyl transposition protocol involving ketene dithioacetal chemistry: an efficient polyene synthesist

C V Asokan, Janhvi Shukla, U K Syam Kumar, H Ila* & H Junjappa* Department of Chemistry, Indian Institute of Technology, Kanpur, V.P. India

E-mail: [email protected]

Received 16 March 2001; accepted 4 July 2001

An efficient strategy for alternative 1 ,5-, 1 ,7-, 1 ,9- and 1 , 1 1 - carbonyl transposition has been developed via 1 ,2-reductive or alkylative addition to 5,5-bis(methylthio)-2,4-pentadienals 3a-b, 7,7-bis(methylthio)-2.4,6-heptatrienones 5, 9,9-bis(methylthio)-2,4,6,8-nonatetraenones 8 and 1 I , I I -bis(methylthio)-2.4,6,8,lO-undecapentaenones 11 followed by BF3.Et20 induced methanolysis of the resulting carbinols to the corresponding polyene esters. The synthesis of the novel polyene aldehydes 3a-b, 7a-b, lOb and polyenones 5, 8, 1 1 precursors has also been described following iterative Vielsmeier-Haack reaction and aldol condensation.

The term carbonyl transposition\,2 is generally defined to mean the effective movement of the carbonyl functionality from one position to another within the same carbon framework. Theoretically it is possible to move a carbonyl functionality from one carbon to another carbon either in an acyclic or cyclic product via appropriate reagents or by the appropriate design of the substrate or the combination of both. The 1 ,2-carbonyl transposition protocol has been by far the largest group of reactions described in the literature2. The I ,3-carbonyl transposition in a,�-unsaturated ketones, �-alkylthioenones and a-oxoketene dithioacetals3 have also been examined extensively in recent years. However, only limited number of 1 ,4-carbonyl transposition reactions were found in the literature while 1 ,5- and I ,6-carbonyl transpositions are confined only to the intramolecular hydride shift I . Recently 1 ,7-carbonyl transposition has been reported in the literature which involves the conversion of 3,4-dehydro-�-ionone to megastigma-4,6,8-triene- I -one through a series of 2,3-sigmatropic rearrangements of the intermediate allylic sulfoxide4• Duhumel and coworkers5 have also reported the reaction of functionalized silyloxy and alkoxypolyenyl lithium and other organometallic reagents with aldehydes and ketones followed by hydrolysis to yield the corresponding polyenals. These examples clearly demonstrate the synthetic usefulness of 1 ,5- and 1 ,7-carbonyl transpositions. Apparently, there has been no

tDedicated to Prof. V. R. Ghatak on his 70th birthday

example beyond I ,7-carbonyl transposItIOn in the literature. Thuillier and coworkers6 and also Dieter and coworkers7 have studied the transformation of carbinol dithioacetals in the presence of sulphuric acid6 and HgO/AcOH in HBF/ to afford the corresponding thiol esters which can be considered as examples of I ,3-carbonyl transpositions. We have reported in our earlier publications,8.,9a-d that the carbinol thioacetals obtained by the I ,2-addition of sodium borohydride or alkyl Grignard reagents to aoxoketene dithioacetals undergo BF3.Et20 assisted methanolysis to yield the corresponding ene- esters 2c-d in high yields (Scheme I). The overall transformation can be recognized as the homologation of the active methylene ketones at the a-position involving I ,3-carbonyl transposition. The formation of a,�-unsaturated methyl esters from active methylene ketones via a-oxoketene dithioacetals has emerged as a new general method for the synthesis of cinnamates, a-substituted cinnnamates and the corresponding crotonates9a. Subsequently in our preliminary communication I I we have reported 1 ,5- to I , ll-carbonyl transposition via bis(methylthio)polyenals and their enones and we now describe these results in detail in the present paper.

Synthesis of 2,4-pentadienals 3a-b Our strategy to 1 ,5-, 1 ,7-, 1 ,9- and I , ll-carbonyl

group transposition involves the synthesis of the appropriate bis(methylthio)enals 3a-b (Scheme I), 7a-b (Scheme III), lOb (Scheme V) and the

938 INDIAN J CHEM, SEC. B, OCTOBER 2001

o SMe

Me¥SMe R

OH SMe .1 � POCI3/DMF Me/l� 'SMe ________ � •• H R

o SMe

H�SMe R

4 a b c d e f 9 h i

1a-b

1-3a, R = H b, R = CH3

o

2a-b

I BF3:EtP/ t MeOH

Me 0

HYOMe R

Scheme I

2e, R = H d, R = Me

o SMe

3a-b

3a-b + R'� NaOMe/MeOH. U2

R'�SMe U2 R

4a-i 5

R R2 5 R R' R2 5 R R' CsHs H aa H CsHs H ea H 2-Thienyl 4-MeCsH4 H ab Me CsHs H eb Me 2-Thienyl 4-0MeCsH4 H 4-CICsH4 H 2-Thienyl H 2- Furyl H C(J H

Meo-C(J H

ba H 4-MeCsH4 H fa H 2-Furyl bb Me 4-MeCsH4 H fb Me 2-Furyl

H 4-0MeCsH4 H ga H C(J ca C(J cb Me 4-0MeCsH4 H gb Me ha H Meo-C(J da H 4-CICsH4 H

MeO-C(J hb Me Me H db Me 4-CICsH4 H ib Me Me

Scheme II

o SMe

R2

H H H H

H

3a-b _M __ e_M..::.g�\.. lH2//'o. /lMe POCI 3 �

Et20 Me/ � � "'f 'SMe DMF H R

H�SMe R

7a-b +

6a-b 3,6, 7a, R = H

b, R = Me Scheme III

NaOMe MeOH ..

4a,4d,4h

Scheme IV

7a (56%) b (80%)

ASOKAN et al.: AN EFFICIENT POLYENE SYNTHESIS

Sib NaBH",EtOH OH SMe POCIa

Me�SMe DMF--H Me 9b

o SMe

H�SMe 10b (70%)

Me 7b

MeMglIEt 20 NH4CI

o SMe I NaOMe/MeOH Jl � � � � .l.. � 4a,4h 11ab,R1 = H,R2= CsHs 1 2 .cu hb,R = R = I R

1- � ��� y -SMe �2 Me MeO "" Scheme V

1,5-Carbonyl Transposition

3a-b

OH SMe CsHsMgBr __ � u-... 1--. BF3·EbOI __ Et20 CsHs � '"' Y -SMe MeOHI t::. H

R 12a, R = H

b, R = H

Scheme VI 1,7- Carbonyl Transposition

H 0

CsHs�OMe 13a, R = H (90%)

b, R = Me (85%)

R Rl

R2 Yo yield 5,14,15 R R' R2 % !seld 5,14,15 15 aa H CsHs H 80 ea H 2- Thienyt H 70 ab Me CsHs H 87 eb Me 2-Thienyt H 79 ba H 4-MeCsH4 H 78 fa H 2-Furyt H -bb Me 4-MeCsH4 H 85 fb Me 2-Furyl H -ca H 4-0MeCsH4 H 76 ga H C(J 78 cb Me 4-0MeCsH4 H 84 gb Me C(J 78 da H 4-CICsH4 H 75 ha H MeO.c0 76 db Me 4-CICsH4 H 82 ib Me MeOOO 76

Scheme VII

939

corresponding enones 5 (Scheme 11);8 (Scheme IV) and 11 (Scheme V). We first describe the synthesis of these enals and enones from the basic three carbon active methylene ketones as described in the Schemes l -S. Thus the S,S-bis(methylthio)-2,4-pentadienal 3a and S,S-bis(methylthio)-4-methyl-2,4-pentadienal 3b (Scheme I) were prepared starting from ketene dithioacetals la-bll•12 (Scheme VII) derived from acetone and ethyl methyl ketone respectively. These ketene dithioacetals la-b were subjected to sodium borohydride reduction in ethanol to afford the

corresponding carbinol thioacetals 2a-b in nearly quantitative yields. The transformation of 2a to methyl crotonate 2c under BF3.EtzO assisted methanolysis has been reported in our earlier papers8a-d• The carbinol acetals 2a and 2b were subjected to Vilsmeier-Haack reaction (POCI/DMF)13a-b to afford the corresponding dienealdehydes 3a and 3b in 70% and 74% yields respectively. On the basis of their IH NMR data, the dienealdehydes were assigned 2E geometry. These intermediates 3a-b are not only the candidates for 1 ,S-carbonyl transposition but also

940 INDIAN J CHEM, SEC. B, OCTOBER 2001

used as a precursors for the synthesis of the corresponding 7,7-bis(methylthio) -2,4,6-heptatrienones S and heptatrienals 7a-b (Schemes II-III). Thus 3a was condensed with acetophenone in the presence of sodium methoxide in methanol to afford the corresponding 7,7 -bis(methylthio )-I -phenyl-2,4,6-triene- I -one Saa in 95% yield. The dienealdehyde 3b was similarly condensed with acetophenone under the identical conditions to afford the corresponding 7,7-bis(methylthio )- I -phenyl-6-methyl-2,4,6-trien- I -one Sab in 90% yield (Scheme 2). On the basis of their IH NMR spectral data, the 2E,4E configuration was assigned for both the compounds. The other 7,7-bis(methylthio )-2,4,6-trien- I -ones S and the corresponding 6-methyl analogs (Scheme II) were similarly obtained by condensing 3a and 3b with various active methylene ketones under identical reaction conditions (Scheme II).

Synthesis of 2,4,6-heptatrienals 7a-b (precursors for 1,7- and 1,9-carbonyl transposition)

The dienealdehyde 3a was reacted with methylmagnesium iodide to afford the carbinol thioacetal 6a in nearly quantitative yield, which was then subjected to Vilsmeir-Haack (POCh/DMF) reaction to give the corresponding 7,7-bis(methylthio)-2,4,6-heptatrienal 7a in 56% yield (Scheme III). Similarly the corresponding 6-methyl-2,4,6-heptatrienal 7b was obtained from 3b under identical conditions in 80% yield. From their IH NMR data, both 7a-b were assigned the 2E,4E configuration. These aldehydes apart from being precursors for the I ,7-carbonyl transposition, they are also starting materials for the synthesis of nonatetraenones 8 (Scheme IV). Thus 7a was condensed with acetophenone in the presence of sodium methoxide in methanol to afford the corresponding 9,9-bis(methylthio)-2,4,6,8-nonatetraenone 8aa in 92% yield. Similarly the other nonatetraenones 8ab-8hb were obtained under the described reaction conditions in 70-78%overall yields (Scheme IV). The stereochemical assignment for these tetraenones were in conformity with the 2E,4E,6E configuration on the basis of their IH NMR data. These tetraenones were few selected candidates for I ,9-carbonyl transposition in our subsequent studies (Scheme IX).

Synthesis of 2,4,6,8-nonatetraenals lOb (precursors for I,ll-carbonyl transposition) (Scheme V)

The 9,9-bis(methylthio )-8-methyl-2,4,6,8-nonatetraenal lOb was the sole polyenealdehyde prepared for

our I , l l -carbonyl transposition study. It was possible to prepare lOb from both trienone Sib (Scheme II) or tetraenaldehyde 7b (Scheme V). Thus the enone Sib was reduced with NaBH4 to give the carbinol thioacetal 9b in nearly quantitative yield which was also prepared in identical yield by adding methylmagnesium iodide to 7b. The carbinol thioacetal 9b was subjected to Vilsmeier-Haack reaction to afford the corresponding 9,9-bis(methylthio )-8-methyl-2,4,6,8-nonatetraenal lOb in 70% yield which was assigned 2E,4E,6E configuration on the basis of IH NMR data (Scheme V). The aldehyde lOb is our precursor for 1 ,9-carbonyl transposition as well as for synthesizing higher homologues 2,4,6,8,1 O-undecapenten- I -ones 11 for 1 , 1 1 carbonyl transposition. Thus lOb was condensed with acetophenone in the presence of methanolic NaOH to afford the corresponding 1 1 , 1 1 -bis(methylthio)- I -phenyl-2,4,6,8 , 1O-undecapenten- I one (llab) in 90% yield. Similarly the pentaenone llhb was prepared in 95% yield by condensing lOb with 6-methoxytetralone under identical conditions. These pentaenones 11 are our precursors for 1 , 1 1 -carbonyl transposition and we have tentatively assigned 2E,4E,6E,8E geometry for the double bonds in these compounds on the basis of preceding examples. We have thus synthesized appropriate polyene precursors bearing a carbonyl and bis(methylthio) functionality at the two terminal end of a conjugated polyene which are suitable precursors for our 1 ,5-, 1 ,7-, 1 ,9- and I , l l -carbonyl transposition studies.

1,S-Carbonyl transposition from S,S-bis(methylthio)-2,4-pentadienals (3a-b) (Scheme VI)

Although in principle, one can choose a large number of organometallic reagents which can be reacted with dienealdehydes 3a and 3b (Scheme 6), we have treated them only with phenylmagnesium bromide to highlight the 1 ,5-carbonyl transposition protocol. Thus both 3a and 3b underwent a facile 1 ,2-addition with C6H5MgBr to afford the corresponding carbinol thioacetals l2a and l2b (Scheme 6) in nearly quantitative yields. These carbinols without further purification were directly treated with BF3.Et20 in refluxing methanol to afford the corresponding dieneesters 13a and 13b in 90% and 85% yields respectively. Both 13a and 13b were earlier reported in the literaturelO and their mp, mmp, IR and lH NMR spectra were found to be identical with the reported data. On the basis of IH NMR data 2E,4E

ASOKAN et al.: AN EFFICIENT POLYENE SYNTHESIS 941

1,7-Carbonyl Transposition

OH SMe H 0 CsHsMgBr J.. � � A BF3·Et20

7a-b Et20 � CsHs A "" "" T -SMe MeOH/l" ��,� Jl CsHs "'" "'" � 'OMe R

14aa, R = H ilb,R= Me

R

15a8, R = H (80%) ab, R = Me (87%)

Scheme VIII

1,9-Carbonyl Transposition

8a-d

Scheme IX

configuration was assigned to both dieneesters 13a and 13b.

1,7-Carbonyl transposition from 7,7-bis(methylthio)-2,4,6-heptatriene-1-ones (Scheme VII)

The newly prepared trienones 5 were reduced with sodium borohydride to afford the carbinol thioacetals 14 in nearly quantitative yields (Scheme VII). These carbinol thioacetals without further purification were subjected to BF3.Et20 assisted methanolysis to afford the corresponding tetraeneesters 15 in 80-90% overall yields. However the carbinol acetal 14fa and 14tb from furyl ketone failed to yield the corresponding ene esters and only intractable product mixtures were obtained.

1,7-Carbonyl Transposition from 7,7-bis(methylthio)-2,4,6-heptatrienals 7a-b (Scheme VIII)

The heptatrienal 7a was similarly reacted with C6HsMgBr to afford the corresponding carbinol thioacetal 14aa in quantitative yield (Scheme VIII) which was subjected to BF3.Et20 assisted methanolysis as described earlier to afford the corresponding trienoate 15aa in 80% yield. The compound 15aa was fully characterized and found to be identical with that reported in the literaturelO with 2E,4E,6E double bond configuration. The trieneester 15ab was similarly prepared in 87% yield starting· from 7b which was found to be identical with that reported in the literaturelO•

1,9-Carbonyl transposition from 9,9-bis(methylthio) -2,4,6,8-nonatetraenones 8 (Scheme IX)

The bis(methylthio)tetraenones 8 (Scheme IV) were examined for 1 ,9-carbonyl transpOSition protocol. Thus 8aa was reduced with sodium borohydride to afford the corresponding carbinol thioacetal 16aa in quantitative yield which was subjected to BF3.EhO assisted methanolysis as described earlier to afford the corresponding tetraenoate 17aa in 70% yield (Scheme IX). On the basis of the earlier trends and I H NMR data 2E,4E,6E,8E configuration was assigned for the double bonds in 17aa. The other tetraenoates 17 (Scheme 9) were similarly prepared in 70-80% overall yields and were assigned E configuration around all four double bonds. The carbinol 16ab could also be obtained by addition of phenyl Grignard reagent to tetraenal lOb (Scheme IX).

I,ll-Carbonyl transposition from l l,ll-bis(methylthio )-2,4,6,8,1 O-undecapenten-1-ones 11 (Scheme X)

We have selected only two examples of undecapentaenones (llab, llhb) to demonstrate the 1 , I I -carbonyl transposition protocol. Thus enone l lab was reduced with NaB� as described before to afford the carbinol thioacetal 18ab in quantitative yield which was in situ subjected to BF3.EhO assisted methanolysis as described earlier to afford the

942 INDIAN J CHEM, SEC. B, OCTOBER 2001

1,11- Carbonyl Tranposltlon

o

OMe

Me 20hb (80%)

Scheme X

corresponding methyl undecapentaenoate 19ab in 85% yield. The analytical and spectral data of 19ab are in full agreement with the structure and we have assigned tentatively 2E,4E,6E,8E,1 0E configuration for all double bonds in line with lH NMR spectral data for lower homologues. The pentaenoate 20hb was similarly prepared as described in Scheme X in 80% yield which was tentatively assigned all trans configuration. In conclusion we have clearly demonstrated the versatile chemistry of a-oxoketene dithioacetals as basic precursors for 1 ,5- to 1 , 1 1 -carbonyl transpositions which w e hope, will provide a convenient synthetic route for polyene esters starting from simple carbonyl compounds.

Experimental Section Melting points were determined on Thomas Hoover

apparatus (capillary method) and are uncorrected. IR Spectra were obtained on Perkin-Elmer 1 37 and 983 spectrometers. lH NMR spectra were recorded on Varian A-60D (60 MHz) and EM-390 (90MHz) spectrometers using TMS as internal standard. Mass spectra were obtained on Hitachi RMU-6E and Jeol D-300 spectrometers. Elemental analyses were carried out on a Heraeus CHN-O rapid analyzer. All th� known ketene dithioacetals1 1 . 12 were prepared according to the reported procedures.

General procedure for the synthesis of carbinols 2a-b, 9b, 14, 16 and 18 by sodium borohydride reduction of the enals and enones. To a solution of a-oxoketene dithioacetal (O.Olmole) in absolute ethanol (25mL), excess sodium borohydride (0.02mole) was added slowly and the reaction mixture was then refluxed for 1 .5 hr. The mixture was cooled and poured over saturated ammonium chloride solution (200 mL). This was extracted with ether (2x50mL), washed with water, dried (Na2S04) and evaporated to give the carbinols in near quantitative

yields which were used as such for the next step without further purification.

General procedure for the synthesis of carbinols 6a-b, 9b, 12a-b, and 14 by addition of alkyVaryl Grignard reagent to enals and enones. To a wellcooled and stirred solution of alkyVaryl magnesium iodide (0.01 5mole) in dry ether (30mL), appropriate enone/enal from 3a-b, 7a-b and lOb (O.Olmole) in dry ether (20mL) was added dropwise (5min) under nitrogen atmosphere, followed by stirring for 1 .5 hr. The reaction mixture was poured into a cold saturated solution of ammonium chloride (50mL), extracted with ether (3x50mL), washed with water, dried (Na2S04) and evaporated to give the crude carbinols in quantitative yields which were used as such for further transformation' .

General procedure for the synthesis of enals 3ab, 7a-b, lOb by Vilsmeier-Haack reaction. The carbinol dithioacetals (O.Olmole) in DMF (5 mL) was added slowly to a well-cooled (O°C) stirred Vilsmeier reagent (prepared by adding phosphorus oxychloride (0.025mole) to N, N-dimethyl formamide (O.25mole) with stirring and cooling and further stirring for 30 min at room temperature). The reaction mixture was stirred for 10 to 1 5 hr for completion of reaction after which it was poured over crushed ice followed by slow addition of cold saturated potassium carbonate solution ( 100mL) to liberate aldehyde. The reaction mixture was then extracted with ether (4x100 mL) and combined ether extracts were washed with water, dried (Na2S04) and evaporated to give crude enals which were further purified by column chromatography over silica gel using EtOAc : Hexane ( 1 :20) as eluent.

General procedure for the 1,3-, 1,5-, 1,7-, 1,9-and I,ll-carbonyl transposition from carbinols 2a-b, 12a-b, 14 and 16 and 18. The carbinol (0.01 mole) was dissolved in absolute methanol

ASOKAN et at.: AN EFFICIENT POLYENE SYNTHESIS 943

(50mL) and BF3.Et20 (2mL) was added with stirring. The reaction mixture was then refluxed for 16 hr. It was then cooled to room temperature, poured into saturated solution of sodium bicarbonate ( 100mL) and extracted with CHCh (2x50mL). The chloroform extracts were washed with water (2x50mL), dried (Na2S04) and evaporated to give the crude eneester 2c-d, 13a-b, 15aa-15ib, 16, 17aa-17hb, 19ab, and 20hb which were purified by passing through a silica gel column using hexane as eluent.

5,5-Bis(methylthio)-2,4-pentadienal 3a: Orange viscous liquid, Yield 59%; IR (neat): 1670, 1 592 em-I ; IH NMR (CCI4): � 2.40 (s, 3H, SCH3), 2.41 (s, 3H, SCH3), 5 .98 (dd, J=1 6Hz, 8Hz, I H, H-2), C2-C3 E configuration, 6.30 (d, I H, J=12Hz, H-4 ), 7 .47 ( 1 H, dd, J= 16Hz, 12Hz, H-3), 9.52 (d, I H, J = 8Hz, CHO), The coupling constant for H2 and H3 confirm the 2E geometry. Anal. Calcd for C7H70S2 ( 1 74.3): C 48.24; H 5.78. Found: C 48.39; H 5.55%.

5, 5-Bis(methylthio)-4-methyl-2,4-pentadienaI 3b: Orange viscous liquid; yield: 70%; IR (neat): 1 660, 1590 em-I; IH NMR (CC4): � 2. 1 1 (s, 3H, CH3), 2.33 (s, 3H, SCH3), 2.42 (s, 3H, SCH3), 6. 1 1 (dd, I H, J=16Hz, 8Hz, H-2), 8 .06 (d, I H, J=1 6Hz, H-3) ( C2-C3 E configuration), 9.58 (d, I H, J=8Hz, CHO); Anal. Calcd for CSHI20S2 ( 1 88.3): C 5 1 .02; H 6.43. Found: C, 5 1 .30; H, 6.34%. rnIz 1 88 (M+, 5%); 14 1 (M+- 47, 100%.)

7,7 -Bis(methylthio )-I-phenyl-2, 4, 6-heptatrieneI-one 5aa: Deep red crystals; yields 95%; m.p. 62°C; IR (KBr): 1643, 1590, 1 586 em-I; IH NMR (CDCh, 300 MHz): � 2.39 (s , 3H, SCH3); 2.40 (s, 3H, SCH3), 6.36 (d, I H, J=I 1 .4Hz, H-6), 6.45 (dd, I H, J=15Hz, 1 1 .4Hz, H-5), 6.96 (d, I H, J=15Hz H-2), 7 .26 (dd, I H, J=15Hz, 1 1 . 1 Hz, H-5), 7.40-7.60 (m, 4H, ArH, olefinic H), 7.92-7.94 (m, 2H, ArH). Anal. Calcd for CIsHI60S2 (276.4): C 65. 17; H 5.83. Found: C, 65.30; H, 5.97%. rnIz 276(M+, 10%); 261 (M+- 15 . 16%).

7,7 -Bis(methylthio )-6-methyl-l-phenyl-2,4,6-heptatriene-l-one 5ab: Reddish brown crystalline solid; yield 90%; m.p 7 1 °C; IR (KBr): 1 640, 1 590cm-l ; IH NMR (CCI4): � 2 . 16 (s ,3H, CH3); 2.27 (s, 3H, SCH3), 2.34 (s ,3H, SCH3), 6.47 (dd, I H, J=15Hz, 1 1Hz, H-4), 6.96 (d, I H, J = 15 Hz, H-2), 7 .33-8.00 (m, 7H, ArH + olefinic H). Anal. Calcd for CI6HISOS2 (290.4): C, 66. 16; H, 6.24. Found: C, 66.26; H, 6.35;. M/z 290 (M+, 5%); 275 (M+- 15, 17%).

7,7 -Bis(methylthio )-1-( 4-methylphenyl)-2,4,6-heptatriene-l-one 5ba: Reddish brown crystalline solid; yield 92%; m.p.68-70°c; IR (KBr): 1640, 1600, 1575cml; IH NMR (CCI4): � 2.3 1 (s, 3H, CH3), 2.32

(s, 3H, SCH3), 2.33 (s, 3H, CH3), 6.3 1 (d, I H, J=1 1Hz, H-6), 6.33 (dd, I H, J=15Hz, 1 1Hz, H-4), 6.82 (d, I H, J = 15Hz, H-2); 7.00-7.9 1 (m, 6H, ArH + olefinic H). Anal. Calcd for CI�HISOS2 (290.4): C, 66. 16; H, 6.25. Found: C, 66.30; H, 6.40%.

7,7 -Bis(methylthio )-6-methyl-( 4-methylphenyl)-2,4,6-heptatriene-l-one 5bb: Reddish brown semisolid, Yield 88%; IR (neat): 1680, 1 650, 1605 em-I ; IH NMR (CC4): � 2 . 1 5 (s, 3H, CH3), 2.3 1 (s, 3H, ArCH3), 2.41 (s, 3H, SCH3), 2.43 (s, 3H, SCH3), 6.50 (dd, I H, J=1 5Hz, 1 1Hz, H-4); 6.89-7.95 (m, 7H, ArH + olefinic H). Anal. Calcd for C17H200S2 (304.4): C, 67.07; H, 6.62. Found: C, 67.27; H, 6.5 1 %.

7,7 -Bis(methylthio )-1-( 4-methoxyphenyl)-2, 4, 6-heptatriene-l-one Sea: Reddish brown semi-solid; Yield 90%; IR (neat): 1 638,1598 em-I ; IH NMR (CCI4): � 2.33 (s, 3H, SCH3), 2.34 (s, 3H, SCH3), 3.82 (s, 3H, OCH3), 6.32 (d, I H, J=I IHz, H-6); 6.34 (dd, I H, J=1 5Hz, 1 1Hz, H-4), 6.83 (d, I H, J =1 5Hz, H-2), 7 .00-8.0 1 (m, 6H, ArH + olefinic H). Anal. Calcd for CI6HIS02S2 (306.4): C, 62.7 1 ; H, 5 .92. Found: C, 62.80; H, 5.8 1 %.

7, 7 -Bis(methylthio )-6-methyl-l-( 4-methoxylphenyl)-2,4,6-heptatriene-l-one 5cb: Reddish brown semi-solid; yield 92%; IR (KBr): 1675, 1 600 em-I ; IH NMR (CC4): � 2.20 (s, 3H, CH3), 2.3 1 (s, 3H, SCH3), 2.38 (s, 3H, SCH3), 3.85 (s, 3H, OCH3), 6.56 (dd, IH, J=15Hz, 1 1Hz, H-4), 6.75-8.01 (m, 7H, ArH + olefinic H); MS rnIz (%) 320(M+, 2%); 305(M+- 1 5, 4%); Anal. Calcd for C17H:lO02S2 (320.4): C, 63.7 1 ; H, 6.29. Found: C, 63.80; H, 6.3 1 %.

7,7 -Bis(methylthio )-1-( 4-chlorophenyl)-2,4,6-heptatriene-l-one 5da: Reddish brown semi-solid; yield 94%; IR (neat): 1 640, 1 600 em-I ; IH NMR (CC4): � 2.32 (s, 6H, SCH3), 6.23 (d, I H, J=I IHz, H-6), 6.24 (dd, I H, J=1 6Hz, 1 1Hz, H-4), 6.8 1 (d, I H, J=16Hz, H-2), 7.22 (dd, I H, J = 1 6Hz, 1 1Hz, H-5), 7.25-7.95 (m, 5H, ArH+ olefinic H);. Anal. Calcd for CisHIsCIOS2 (3 10.8): C, 57.77; H, 5 . 17 . Found: C, 57.9 1 ; H, 5.30%.

7,7 -Bis(metbylthio )-6-methyl-l-( 4-chlorophenyl)-2,4,6-heptatriene-l-one 5db: Reddish brown semisolid; yield 90%; IR (neat): 1658, 1591 em-I ; IH NMR (CCI4): � 2.20 (s, 3H, CH3), 2.3 1 (s, 3H, SCH3), 2.33 (s, 3H, SCH3), 6.5 1 (dd, I H, J=1 5Hz, 1 1Hz, H-4);, 6.90 (d, I H, J=15Hz, H-2), 7.26-8.09 (m, 6H, ArH + olefinic H);. Anal. Calcd for CI6H17CIOS2 (324.8): C, 59. 15 ; H, 5.09. Found: C, 59.26; H 5.2 1 %.

7,7-Bis(methylthio)-I-(2-thienyl)-2, 4, 6-heptatriene-I-one 5ea: Reddish brown semi-solid; yield 90%; IR (KBr): 1 640, 1578cm- l ; IH NMR (CC4): � 2.33 (s,

944 INDIAN J CHEM, SEC. B, OCTOBER 2001

6H, SCH3), 6.32 (d, I H, J= 15Hz, H-2), 6.33 (dd, I H, J =15 Hz, 11 Hz, H-4), 6.79(d, I H, J=11Hz, H-6), 7.05-7.8(m, 5H, thienyl + olefinic H); MS mlz (%) 282 (M+,9%); 267 (M+-15 15%). Anal. Calcd for C13HI40S3 (282.4): C 55.28; H 5 .00. Found: C, 55.35; H 5.2 1 %.

7,7-Bis(methylthio)-6-methyl-l-(2-thienyl)-2,4,6-heptatriene-l-one Seb: Reddish brown crystalline solid, yield 95%; m.p. 105-106°C; IR (KBr): 1659, 1629, 1569cm-I; IH NMR (CC4) 8: 2.18 (s, 3H, CH3), 2.29 (s, 3H, SCH3), 2.41 (s, 3H, SCH3), 6.51 (dd, I H, J = 15Hz, H-4), 6.89 (d, I H, J = 15Hz, H-2), 6.9 1 -7.87 (m, 5H, thienyl + olefinic H); MS mlz(%) 296 (M+,4%); 28 1 (M+- 1 5 48%). Anal. Calcd for CI4HI60S2 (296.7): C, 56.67; H 5 .43. Found: C, 56.71; H, 5.52%.

7,7-Bis(methylthio)-I-(2-furyl)-2, 4, 6-heptatriene-I-one Sfa: Reddish brown semi-solid; yield 94%; JR (neat): 1 645 , 1580 cm-I; IH NMR (CCI4): 8 2.33 (s, 6H, SCH3), 6.3 1 (d, IH, J = l 1Hz, H-2), 6.32 (dd, I H, J = 1 5Hz, 1 1Hz, H-4), 6.79 (d, I H, J =15Hz, H-6), 7.03-7.7 1 (m, 5H, fury I + olefinic H). MS (mlz, %): 266 (M+ 13%); 251(M+- 1 5, 19%); Anal. Calcd for C13HI402S2 (266.4): C, 58 .62; H, 5 .30. Found: C, 58.7 1 ; H, 5.45%.

7,7-Bis(methylthio)-6-methyl-l-(2-furyl)-2, 4, 6-heptatriene-l-one Sib: Reddish brown solid; yield 92%; m.p. 148-149°C; IR (KBr): 1 640, 1 590 cm-I; IH NMR (CCI4. 300 MHz): 8 2.13 (s, 3H, CH3), 2.30 (s, 3H, SCH3), 2.40 (s, 3H, SCH3), 6.54 (dd, I H, J = 15Hz, 1 1 Hz, H-4), 6.94 (d, I H, J = 15Hz, H-2), 7.15 (dd, J = 4Hz, 5Hz, I H, Furyl), 7.59-7.77 (m, 4H, furyl + olefinic H). MS (mlz, %): 280 (M+ 32%); 265 (M+-1 5, 98%). Anal. Calcd for CI4HI602S2 (280.4): C, 59.97; H, 5 .75%. Found: C, 59.8 1 ; H, 5.61 %.

2-[ (1,1-Bis(methylthio )-I,3-(pentadienylidiene)]I-tetralone Sga: Reddish brown semi-solid; yield 94%; IR (KBr): 1640, 1595 cmI; IH NMR (CCI4): 8 2. 1 8 (s, 3H, CH3), 2.22 (s, 3H, CH3), 2.3 1 (s, 3H, SCH3), 2.72-2.89 (m, 4H, -CH2), 6.30-6.81 (m, 3H, ArH + olefinic H), 7.38 (d, I H, J = 12Hz, H-5), 7.65 (d, I H, J =15Hz, H-3), 7.92 (d, I H, J = 7.5Hz, I H, ArH). Anal. Calcd for CI9H2202S2 (346.5): C, 65.86; H, 6.40. Found: C, 65.91; H, 6.50%.

2-(I,I-Bis(methylthio)-2-methyl-l,3-pentadienylidiene) -1-tetralone 5gb: Orange crystalline solid; yield 92%; m.p. 1 02°C; IR(KBr): 1648, 1599 cm-I; IH NMR (CCI4): 8 2.32 (s, 6H, SCH3), 2.86 (s, 4H, CH2), 6.36 (d, I H, J = 1 1 Hz, H-2), 6.48 (dd, H, J = 1 1 Hz, 15Hz, H-4), 7.00-8.21 (m, 6H, ArH + olefin). Anal.

Calcd for C17HISOS2 (302.5): C, 67.50; H, 6.00. Found: C, 67.61; H, 6.09%.

2-[ (1,I-Bis(methylthio )-2-methyl-l,3-pentadienylidiene)]-6-methoxy-l-tetralone Sha: Reddish brown crystalline solid; yield 94%; m.p. 89-90°C; IR (KEr): 1647, 1599 cm-I; IH NMR (CCI4, 300 MHz): 8 2.22 (s, 3H, CH3), 2.30 (s, 3H, SCH3), 2.40 (s, 3H, CH3), 2.92-2.93 (m, 4H, CH2), 6.65 (dd, I H, J =15Hz, 1 2Hz, H4), 7.25 (d, I H, J = 7.5Hz, ArH), 7.34 (t, I H, J =7.5Hz, ArH), 7.46 (t, I H, J =7.5Hz, ArH), 7.56 (d, I H, J = 12Hz, H-5), 7.77 (d, I H, J = 1 5Hz, H-3), 8. 10 (d, J = 7.5Hz, I H, ArH); MS (mlz, %): 316 (M+ 5% ), 301 (M+-15 43%); Anal. Calcd for CIsH200S2 (316.5): C, 68.31; H, 6.37. Found: C, 68.40; H, 6.21%.

2-(1,1-Bis(methylthio )-1,3-pentadienylidiene )-6-methoxy-l-tetralone Shb: Orange crystalline solid, yield: 93%; m.p. 1 36°C; IR (KEr): 1647, 1 603, 1 57 1 cm-I; IH NMR (CC4, 300MHz): 8 2.38 (s, 3H, SCH3),

. 2.31(s, 3H, SCH3), 2.85-2.95 (m, 4H, -CH2-), 3 .82 (s, 3H, OCH3), 6.42 (d, I H, J = 11Hz, H-2), 6.56 (dd, I H, J = 16Hz, 1 2Hz, H-4) 6.70-6.87 (m, 2H, ArH), 7 .27 (dd, I H, J =15Hz, 11Hz, H-3), 7 .46 (d, IH, J = 12Hz, H-5), 8.07 (d, J = 8Hz, I H, ArH); MS (mlz, %): 332 (M+, 13%); 317(M+-15, 24%). Anal. Calcd for CIsH2002S2 (332.5): C, 65.02; H, 6.06. Found: C, 65 . 1 5 ; H, 6.21 %

8,8-Bis(methylthio )-7 -methyl-3,S, 7 -octatatriene-2-one Sib: Reddish brown semisolid; yield 85%; IR (KEr): 1658, 1600, 1 580 cm-I; IH NMR (CCI4): 8 2.09 (s, 3H, CH3), 2.11 (s, 3H, CH3), 2.25 (s, 3H, SCH3), 2.35 (s, 3H, SCH3), 6.09 (d, I H, J =15Hz, H-3), 6.31 (dd, I H, J = 11Hz, 15Hz, H-5), 7.19 (dd, IH, J = 11Hz, 15Hz, H-4); 7.57(d, I H, J =15Hz, H-6); MS (mlz, %): 228 (M+,9%), 2 1 3 (M+-15, 29%); Found: C, 57.90; H, 7.21%. Anal. Calcd for CIIHI60S2 (228.4): C, 57.83; H, 7.06%.

7,7-Bis(methylthio)-2,4,6-heptatrienal 7a: Reddish brown liquid; yield 70%; IR (neat) 1 675, 1612, 1 585 cm-I; IH NMR (CCI4): 8 2.1 1 (s, 3H, CH3), 2.25 (s, 3H, SCH3), 2.34 (s, 3H, SCH3), 5 .98 (dd, I H, J =15Hz, J =8Hz, H-3), 6.23-7.21 (m, 3H, olefinic H), 7 .42 (d, I H, J = 15Hz, H-7); 9.49 (d, 1H, J =8Hz, -CHO); MS(mlz, %): 240 (M+, lOO%). Anal. Calcd for CI2HI60S2 (240.4): C, 59.96; H, 6.71. Found: C, 60.01; H, 6.80%.

7,7 -Bis(methylthio )-6-methyl-2,4,6-heptatrienal 7b: Reddish brown semisolid; yield 70%; IR (neat) 1658, 1612, 1585 cm-I ; IH NMR (CCI4): 8 2.11 (s, 3H, CH3), 2.25 (s, 3H, SCH3), 2 .34 (s, 3H, SCH3), 5 .98 (dd, I H, J = 1 5Hz, J = 8Hz, H-3), 6.23-7.21 (m,

ASOKAN et al.: AN EFFICIENT POLYENE SYNTHESIS 945

4H, olefinic H), 7.42 (d, IH, J = 1 5Hz, H-7); 9.49 (d, I H, J = 8Hz, -CHO); MS (mlz, %): 240 (M+, 1 00%). Anal. Ca1cd for C12HI60S2 (240.4): C, 59.96; H, 6.7 1 . Found: C, 60.0 1 ; H, 6.80%.

9,9-Bis(methylthio)-1-phenyl-2, 4, 6,8-nonatetraene-I-one 8aa: Reddish brown semi-solid; yield 92%; IR(neat): 1 652, 1 598cm·l ; IH NMR (CCI4) : 8 2.33 (s, 3H, SCH3), 2.34 (s, 3H, SCH3), 6.29 (d, J = 1 1Hz, H-8), 6.50-7. 1 8 (m, 5H, olefinic H), 7 .23-8 .01 (m, I H, ArH). Anal. Ca1cd for C17H1SOS2 (302.4) : C, 67.5 1 ; H, 6.00. Found: C, 67.60; H, 6.2 1 %.

9, 9-Bis(methylthio)-8-methyl-1-phenyl-2, 4, 6, 8-nonatetraene-1-one 8ab: Reddish brown semi-solid; yield 70%; IR (neat): 1 678, 1590cm'l ; IH NMR (CCI4) : 8 2. 1 0 (s, 3H, CH3), 2.2 1 (s, 3H, CH3), 2 .35 (s, 3H, SCH3), 6.22-8. l 8, (m, l lH, ArH + olefinic H ). Anal. Ca1cd for CIsH200S2 (3 1 6.4); C, 68.32; H, 6.37. Found: C, 68.5 ; H, 6.44%.

9,9-Bis(methylthio )-8-methyl-1-( 4-chlorophenyl)-2,4,6,8-nonatetraene-1-one 8db: Reddish brown crystalline solid; yield 75%; m.p. 1 20- 1 23°C; IR (KBr): 1 642, 1 597cm' l ; IH NMR (CCI4. 300MHz): 8 2. 1 7 (s, 3H, CH3); 2.29 (s, 3H, SCH3), 2.38 (s, 3H, SCH3), 6.45 (dd, 1 H, J = 15Hz, 1 1 Hz, H-6), 6.52 (dd, I H, J = 15Hz, 1 1Hz, H-4), 6.84 (dd, I H, J = 15Hz, 1 1Hz, H-5), 6.93 (d, IH, J = 1 5Hz, H-2), 7.42-7.56 (m, 4H, ArH + olefinic H), 7.87-7.90 (m, 2H. ArH). Anal. Ca1cd for CIsH I9CIOS2 (350.8): C, 6 1 .62; H, 5.46. Found: C, 6 1 .82; H, 5 .66%; MS (%) mlz 350 (M+, 24%); 35 1 (5%).

2-[ (l,l-Bis(methylthio )-1,3,5-heptatrienylidene) J-6-methoxy-1-tetralone 8hb: Reddish brown crystalline solid; yield 78%; m.p. 1 14- 1 1 5°C; IR (KBr): 1 647, 1 602,cm'l ; IH NMR (CDCI3.300MHz): 8 2. 17 (s, 3H, CH3), 2 .29 (s, 3H, SCH3), 2.38 (s, 3H, SCli3), 2.93 (s, 4H, CH2), 3.86 (s, 3H, OCH3), 6.49 (dd, I H, J = 1 5Hz, 1 1Hz, H-4), 66 1 -6.87 (m. 4H, ArH + olefinic H), 7.43 (d, IH, J = 1 5Hz, H-7), 7.47 (d, I H, J = 1 2Hz, H-3), 8.07 (d, IH, J = 8Hz, ArH). Anal. Ca1cd for C21H240S2 (3n.5): C, 67.70; H, 6.49. Found: C, 67.75; H, 6.5 1 %; MS(%) mlz 3n (M+, 49%).

9,9-Bis(methylthio)-8-methyl-2, 4, 6,8-nonatetraenal lOb: Reddish brown liquid; yield, 70%; IR (neat) : 1675, 16 1 2, 1585cm'l ; IH NMR (CCI4) : 8 2. l 1 (s, 3H, CH3); 2.25 (s, 3H, SCH3); 2 .34 (s, 3H, SCH3) ; 5.98 (dd, I H, J=1 5Hz, 8Hz); 6.23-7 .2 1 (m, 4H, olefinic H), 7.42 (d, J=1 5Hz, IH, aromatic H-7), 9.49 ( lH, d, J=8Hz,CHO); MS (%) mlz 240(M+, 100%). Anal. Ca1cd For CI2HI60S2 (240.4): C, 59.96; H, 6.7 1 . Found: C, 60.0 1 ; H, 6.80%.

1 l,1l-Bis(methylthio)-1-methyl-1-phenyl-2, 4, 6, 8, 10-undecapentene-1-one l lab: Deep red semisolid; yield 90%; IR (neat): 1 655, 1 595cm'l ; IH NMR (CCI4) : 8 2.00 (s, 3H, CH3); 2. 1 3 (s, 3H, SCH3); 2.23 (s, 3H, SCH3); 6. 1 5-8.20 (m, 1 3H, ArH+olefinic H), Anal. Ca1cd for C2oH220S2(342.5): C, 70. 1 3; H, 5 .89. Found: C, 70.25 ; H, 5.91 %.

2-[1,1-Bis(methylthio)-2-methyl-1, 3, 5,7-nonatetraenylideneJ-6-methoxy-1-tetralone llhb: Deep red semisolid; yield 95%; IR (neat): 1 650, 1 6 1 Ocm'l ; IH NMR (CCI4): 8 1 .96 (s, 3H, CH3); 2. 1 0 (s, 3H, SCH3); 2.23 (s, 3H, SCH3); 2.73 (s, 4H, CH2), 3.66 (s, 3H ,OCH3), 6. 1 0-7.50 (m, 9H, ArH + olefin), 7.93 (d, J = 8Hz, I H, ArH). Anal. Ca1cd for C23H260S2(382.6): C, n.20; H, 6.85. Found: C, n.3 1 ; H, 6.90%.

Methyl 5-phenyl-2,4-pentadienoate 13a: Colourless crystalline solid; yield 90%; m. p. 70-7 1 °C (IR and NMR data)9c.

Methyl 5-phenyl-2-methyl-2,4-pentadienoate 13b: Colourless crystalline solid; yield 85%; m.p. 86°C (IR and NMR data)9c.

Methyl 1-phenyl-2,4,6-heptatrienoate 15aa. Pale yellow crystalline solid; yield 80%; m.p. I l l - 1 1 2°C (IR and NMR data)9c.

Methyl 2-methyl-7 -phenyl-2,4,6-heptatrienoate 15ab: Pale yellow crystalline solid; yield 87%; m.p. 1 73°C (IR and NMR data)9c.

Methyl 1-( 4-methyl phenyl)-2,4,6-heptatrienoate 15ba: Pale yellow crystalline solid; yield 78%; m.p. 1 3 1 °C (lR and NMR data)9c.

Methyl 2-methyl-7 -(4-methylphenyl)-2,4,6-heptatrienoate 15bb. Yellow crystalline solid; yield 85%; m.p. 1 0 1 - 1 02 DC; (IR and NMR data)9c.

Methyl 1-( 4-methoxyphenyl)-2,4,6-heptatrienoate 15ca: Pale yellow crystalline solid; yield 76%; m.p. 166°C (lR and NMR data)9c.

Methyl 2-methyl-7 -( 4-methoxyphenyl)-2,4,6-heptatrienoate 15cb: Yellow crystalline solid; yield 84%; m.p. 95-96 DC; (IR. and NMR data)9c.

Methyl 1-( 4-chlorophenyl)-2,4,6-heptatrienoate 15da: Pale yellow crystalline solid; yield: 75%; m.p. 1 52 °C; IR (KBr): 1 7 1 5, 1 6 10 cm'l ; IH NMR (CCI4) 8: 3.68 (s, 3H, OCH3), 5 .80 (d, I H, J = 1 5Hz. H-2), 6.30-7.40 (m, 9H, ArH+olefinic H). Anal. Calcd for CI4H13CI02 (248.7): C, 67.60; H, 5 .26. Found: C, 67.8 1 ; H, 5.31 %.

Methyl 2-methyl-7 -( 4-chlorophenyl)-2,4,6-heptatrienoate 15db: Pale yellow crystalline solid, yield 82%; m.p. 1 1 5- 1 1 7°C; IR (KBr) : 1 705, 1 600 cm'l ; IH NMR (CCI4) 8: 1 .95 (s, 3H, CH3), 3.7 1 (s, 3H,

946 INDIAN J CHEM, SEC. B, OCTOBER 2001

OCH3), 6.38-7.47 (m, 9H, ArH + olefinic H). Anal. Calcd for CI 5HI5CI02 (262.7): C, 68.58; H, 5.76. Found: C, 68.6 1 ; H, 5.9 1 %.

Methyl 7-(2-thienyl)-2,4,6-heptatrienoate ISea: Yellow semi-solid; yield 70%; IR (neat): 1 7 1 8, 1590 em- I ; 'H NMR (CCI4) 8: 3.66 (s, 3H, OCH3), 5 .79 (d, IH, J = 16Hz, H-2), 6.31 -7.50 (m, 8H, thienyl + olefinic H). Anal. Calcd for C12HI202 S (220.3): C, 65.42; H, 5.49. Found: C, 65.50; H, 5.58 %.

Methyl 2-methyl-7 -(2-thienyl)-2,4,6-heptatrienoate ISeb: Pale yellow semisolid; yield 79%; IR (KBr): 1705, 1595 em- I ; 'H NMR (CCI4) 8: 1 .98 (s, 3H, CH3), 3.68 (s, 3H, OCH3), 6.45-7.28 (m, 8H, thienyl + olefinic H). Anal. Calcd for C13HI402 S (234.3): C, 66.64; H, 6.03%. Found: C, 66.78; H, 6.2 1%. Methyl S-(3,4-dihydronapth-2-yl) -2,4-pentadienoate ISga: Pale yellow crystalline solid; yield 78%; m.p. 86-87°C; IR (KBr) : 1 7 16, 1605 em-I ; IH NMR (CCI4) : 8 2.33-3. 13 (m, 4H, CH2), 3.80 (s, 3H, OCH3), 5.86 (d, J = 16Hz, H-2) 6.31 -7.76 (m, 8H, ArH + olefinic H). Anal. Calcd for CI6HI602 (240.3): C, 79.97; H, 6.7 1 . Found: C, 80.0 1 ; H, 6.8 1 %.

Methyl S-(3,4-dihydronapth-2-yl)-2-methyl-2,4-pentadienoate 15gb: Yellow crystaliine solid; yield 78%; m.p. 82-84°C; IR (KBr): 1700, 1608 em- I ; 'H NMR (CCI4, 300MHz): 8 2.00 (s, 3H, CH3), 2.55 (t, 2H, J = 8Hz, CH2), 2.89 (t, 2H, J = 8Hz, CH2), 3.77 (s, 3H, OCH3), 6.57-7.35 (m, 8H, ArH + olefinic H). Anal. Calcd for C17HI S02 (254.3): C, 80.28; H, 7. 13. Found: C, 80.30, H, 7.2 1 %; MS (%) mJz 254 (M+, 99%).

Methyl S-(3,4-dihydro-6-methoxynaphth-2-yl)-2,4-pentadienoate ISha: Pale yellow crystalline solid; yield 76%; m.p. 108- 109°C; IR (KBr): 17 10, 1608 em- I ; 'H NMR (CCI4): 8 2.3 -3. 1 2 (m, 4H, CH2), 3.8 1 (s, 3H, OCH3), 3.82 (s, 3H, Ar-OCH3), 5.86 (d, I H, J = 16Hz, H-2), 6.20-7.60 (m, 7H, ArH + olefinic H). Anal. Calcd for C1 7HIS03 (270.3); C, 75.53; H, 6.7 1 . Found: C, 75.75; H, 6.61 %.

Methyl S-(3,4-dihydro-6-methoxynaphth-2-yl)-2-methyl-2,4-pentadienoate IShb: Yellow crystalline solid; yield 76%; m.p. 99- 10 1°C; IR (KBr) : 1700, 1605 cml ; IH NMR (CCI4) : 8 1 .95 (s, 3H, CH3), 2.23-2.84 (m, 4H, CH2), 3.60 (s, 3H, OCH3), 3.64 (s, 3H, Ar-OCH3), 6.31 -7.3 1 (m, 7H, ArH + olefinic H). Anal. Calcd for CI sH2003 (284.3): C, 76.04; H, 7.09. Found: C, 76. 15 ; H, 7 . 1 8%.

Methyl 9-phenyl-2,4,6,8-nonatetraenoate 17aa: Yellow crystalline solid; yield 70%; m.p. 1 5 1 - 1 53°C;

IR (KBr): 1708, 1 6 1 8 em-I ; IH NMR (CDCI3. 300 MHz): 8 3. 1 8 (s, 3H, OCH3), 5 .89 (d, IH, J = 15Hz, H-2), 6.22-6.89 (m, 7H, ArH+olefin H), 7.02-7.25 (m, 5H, ArH + olefinic H). Anal. Calcd for CI6HI602 (240.3): C 79.97; H 6.7 1 . Found: C, 67.75; H, 6.5 1%.

Methyl 2-methyl-9-phenyl-2,4,6,8-nonatetraenoate 17ab: Yellow crystalline solid; yield 75%; m.p. 103- 104°C; IR (KBr): 1 695, 1598 em-I ; IH NMR (CCI4) : 8 1 .95 (s, 3H, CH3); 3.69 (s, 3H, OCH3); 6.25-7 .48 (m, 1 2H, ArH + olefinic H). Anal. Calcd for C17HIS02 (254.3): C, 80.28 ; H, 7. 13. Found: C, 80.40; H, 7.25 %.

Methyl 2-methyl-9-( -4-chlorophenyl)l-2,4,6,8-nonatetraenoate 17db: Yellow crystalline solid; yield 70%; m.p. 150°C; IR (KBr): 1 705, 1 608 em- I ; IH NMR (CDCh. 300 MHz): 8 1 .98 (s, 3H, CH3), 3.76 (s, 3H, OCH3), 6.4 1 -6.86 (m, 6H, olefin), 7.24-7.34 (m, 5H, ArH + olefinic H). Anal. Calcd for C1 7H17CI02 (288.8): C, 70.69; H, 5 .93. Found: C, 70.75; H, 6.0 1%; MS (%) mJz: 288(M+ 100%).

Methyl 2-methyl-7 -( -3,4,-dihydro-6-methoxynaphth-2-yl)-2,4,6-heptatrienoate 17hb: Yellow crystalline solid; yield 80%; m.p. 139- 140°C; IR (KBr) 1700, 1608 em- I ; H NMR (CDCh. 300MHz): 8 1 .97(s, 3H, CH3) , 2.48 (t, 2H, J=8.5Hz, CH2); 2.85 (t, 2H, J = 8.5Hz, CH2), 3.76 (s, 3H, OCH3), 3.79 (s, 3H, OCH3), 6.4 1 -6.70 (m, 7H, ArH + olefin), 7.01 (d, J = 9Hz, IH, ArH), 7.27 (d, J = 10Hz, IH, ArH). Anal. Calcd.for C2oH2203 (310.4): C, 77.38; H, 7. 14. Found: C, 77.59 1 ; H, 7.29%; MS (%) mJz 310 (M+, 100%).

Methyl 2-methyl-l l-phenyl-2,4,6,8,10-undecapentenoate 19ab: Yellow seniisolid; yield 85%; IR (neat): 1 705, 16 17 em- I ; 'H NMR (CDCh): 8 2.00 (s, 3H, CH3); 3.36 (s, 3H, OCH3), 6.30-7 . 10 (m, 8H, ArH + olefinic H), 7 .93 (d, J=8Hz, I H, ArH). Anal. Calcd for C23H260S2(382.6): C, 72.20; H, 6.85. Found: C, 8 1 .4 1 ; H, 7 .20%.

Methyl 2-methyl-(3,4-dihydro-6-methoxynaphth-2-yl)-2,4,6,8-nonatetraenoate 20hb: Yellow crystalline solid; yield 80%; m.p. 149- 1 5 1°C; IR (KBr): 1 705, 1600 em- I , IH NMR (CCI4): 8 1 .83 (s, 3H, CH3), 2.20-2.80 (m, 4H, CH2), 3.6 1 (s, 3H, OCH3), 6.34 (s, 3H, OCH3), 6. 1 5-7.35 (m, l lH, ArH + olefin H). Anal. Calcd for C22H2403 (336.4): C, 78.54; H, 7 . 19 . Found: C, 78.66; H, 7.33%.

Acknowledgement We thank CSIR, DAE and DST for financial support and RSIC, NEHU, Shillong for analytical facility.

ASOKAN et al. : AN EFFICIENT POLYENE SYNTHESIS 947

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