Asymmetric reactions using new chiral auxiliaries derived from (S)-indoline-2-carboxylic acid

Abstract

In order to control stereoselectivity in the asymmetric reduction of ketones, a series of new chiral aminoalcohols have been synthesized from (S)-indoline-2-carboxylic acid. It was possible to do stereocontrolled enantioselective reduction of ketones to (R)-form and (S)-form of secondary alcohols, respectively, using new chiral aminoalcohols with borane (up to 96\% ee). Diastereoslective reduction of chiral $\alpha$-ketoamides to the $\alpha$-hydroxy acids has been carried out by the reaction of chiral $\alpha$-ketoamides with borohydrides in the presence of lithium bromide(95:5). Sterocontrolled addition of diethylzinc to aldehydes provided chiral ethylated alcohols(up to 97\%ee). The opposite optically active secondary alcohols were successfully obtained in high optical yields from the enantioselective addition of diethyzinc to aldehydes catalyzed by aminoalcohols, respectively. The asymmetric Diels-Aler reaction between chiral acrylates and diens gave cycloaddition products with high diastereoface selectivity($>98\%$ee). The diastereoselectivities were affected by the various conditions such as Lewis acids, solvents and reaction temperatures. The asymmetric 1,3-dipolar cycloaddition of nitrile oxides to chiral $\alpha,\,\beta$-unsaturated amides gave the two isoxazolines with the high diast-ereoselectivity(96:4). The degrees of selectivity were studied under various conditions.