Indian Joual of Chemistry Vol. 41B, August 22, pp. 1 666- 1 669 Synthesis of novel chiral auxiliaries S Narasimhan*, S Swamalakshmi, R Balakumar & S Velmathi Centre for Natural Products, SPIC Science Foundation, Chennai <0 032, India and Department of Chemistry, Guru Nanak College, Chennai <0 $2, India Received 25 November 1999; accepted (revised) 29 December 21 A simple and easy route for the preparation of the higher homologue of oxazaborolidine namely dihydrꝏxazaborin has been reported. Also, the preparations of new bicyclic oxazarolidines are rerted. Nature has provided us with a number of naturally occurring chiral compounds, which can be suitably modified to get potential chiral auxiliaries. Amino acids, which are naturally occurring chiral compounds, have been extensively used by scientists over the past several decades in preparing various chiral auxiliaries. Oxazaboroldines, developed by Itsuno l and explored in detail by Corey 2 are one such chiral auxiliary which are occupying a prominent place in the field of asymmetric synthesis. The amino acid proline was used for the preparation of the oxazaborolidines. Proline was subjected to an organometallic reaction to get an amino alcohol, which was then treated, with borane to yield the oxazaborolidines with a five membered ring containing a nitrogen, boron and oxygen in it. Now in this paper we report the synthesis of the higher homologue of these oxazaborolidines with a nitrogen, boron and oxygen in a six membered ring. Also, in the reported oxazaborolidines the acid end of the amino acid has been used up for the construction of the oxazaborolidine ring. In our present approach we wished to maintain the acid end of the amino acid intact and constructed the oxazaborin ring. The existing oxazaborolidine along with the modification we desired is represented in Figure 1 Retrosynthetic analysis (Figure 2) showed two possibilities for the consuction of the oxazaboroli- dine ring and we chose salicylaldehyde, as it is expected to offer more rigidity to the chiral auxiliary and also could participate in the stacking effect during the course of the asymmetric reductions. The compounds are easily prepared through simple reactions and in good yields. The amino acids valine, leucine, iso-leucine and phenyl alanine have been used for the preparation of these chiral auxiliaries. The reaction sequence is present in Scheme I. Salicyl- aldehyde and the amino acid ester were reacted in benzene solvent to obtain the imine ester 1. The imine R' H - / R :- (," " "R HN, 0 B/ H Itsuno Corey Mification Fire 1 fH2CHO + H2NyHCOOR CH20H R r r / C NH H CHCOOR C NHCHCOOR OH � Fire 2 � CHO I + OH