! Modern Organic Chemistry exam 09-04-2015 time: 3 hours Every answer sheet must be provided with your name, study and student number (The maximum number of points for every question is indicated)
!
Modern Organic Chemistry
exam
09-04-2015
time: 3 hours
Every answer sheet must be provided with yourname, study and student number
(The maximum number of points for every question isindicated)
Question 1. (16 points)The group of Danishefsky presented a route of synthesisto mamanuthaquinone, part of which is presented in thescheme below.
a) Provide the structure of product 2 and the mechanismof the corresponding reaction.b) Provide the structure of product 3 and the mechanismof the corresponding reaction.c) Provide the structure of product 4 and the mechanismof the corresponding reaction.d) Provide the mechanism of the conversion of 4 ~S.Explain the stereochemistry of the reaction.
Question 2. (16 points)In the synthesis to capnellene by the group of Shibasakithe following transformations were executed.
---------------------.o :Bz="t,~i
r V:I--------------------~
(C4HgbSnH
NC1-N=N-fCN
Zn/Cu
8
1 NaOH
9
1 a) Give the reaction conditions and the structures of the -corresponding intermediates, which can be used toconvert 6 into 7.b) Give the structure of compound 8 and the mechanismof the corresponding reaction. Explain thestereochemistry of the reaction .
..c) Give the structure of compound 9 and the mechanismof the corresponding reaction .
. d) Provide the mechanism of the conversion of 9 -+ 10.
Question 3. (14 points)A new structure of the fungal metabolite, mycosporulonehas been proposed on the basis of a tota I synthesis.
H+,toluene,refluxremoval H20.. 15
o
The first step of the synthesis comprised thecondensation of ethyl 4-oxo-2-pentenoate 11 andpropionaldehyde 12 employing pyrrolidine 13 as anorganocatalyst to give 14. Crude 14 was subjected tostandard Dean-Stark dehydration conditions to afford 15as a mixture of diastereomers.a) Provide the structure of compound 14 and themechanism of the corresponding reaction.
Q b) Provide the structure of compound 15 and themechanism of the corresponding reaction.c) Provide the mechanism of the conversion of 15 -+16.
Question 4. (28 points)Ecklonialactone A is an oxylipinalgae Ecklonia stolonifera.
~ 0
isolated from the brown
NaH and then o-0-,S-CI1 eq - 11
o .19
~II lIl/OH
BnO/ 17 OH
OBn20
AeO OAe"
~
1-OAeI '0
·'1'1 .#'I/OTBS
22 0OH • 23 ---- •.•. 24 -----... 25
a) Give the structure of 18, including thestereochemistry and the mechanism of the conversion of17 -+ 18.b) Give the structure of 19, including thestereochemistry and the mechanism of the conversion of18 -+ 19.
• c) Give the structure, including the stereochemistry of20 and the mechanism of the conversion of 19 -+20.d) Give the mechanism of the conversion of 20 -+21.e) Give the structure of 23 and the mechanism of theconversion of 22 -+23.f) Give the structure of 24 and the mechanism of theconversion of 23 -+24.
11 g) Give the structure of 25 and the mechanism of theconversion of 24 -+ 25
Question 5. (16 points)The following reactions are used in the total synthesis ofFD-891 and mesembrane, respectively.
HOHO
HÖ 26
OBn
+ ,o~aBn
I 27
HO
I, ".'<,\\\"
Zn CH3~CH3
---- .•.~ 31___ --...~ 30
osn C2H50H reflux
o + ------~. 34
H
( a) Compound 28 is prepared in two steps from 26 and27. Describe the corresponding mechanisms, includingthe stereochem istry.
"\b) Give the structure of compound 30 and themechanism of 29 ~ 30.
're) Give the structure of compound 31 and themechanism of 30 ~ 31.
I d) Give the structure of compound 34 and themechanism of the conversion 32+33 ~ 34.
Question 6. (10 points)The scheme below shows two well-known reactions.
-\-035 Li
IN
(CH3bSi /" <,Si(Meb------ ..•~ 37
+/
THF/C}=O\
40
a) Provide the structure of compound 37 and themechanism of the corresponding reaction.b) Provide the structure of compound 40 and themechanism of the corresponding reaction. Explain thestereoehem istry of the reaction.