Study on the synthesis of new chiral derivatives of squaric acid and their application in asymmetric catalytic borane reduction of prochiral aryl ketones

Abstract

Eleven new chiral squaric acid amidoalcohols bave been synthesized by reaction of alkyl amines or thiols with 3 - butoxy - [(1'S, 2'R) - (2' - hydroxy - 1', 2' - diphenylethyl) amino] - 3 - cyclobutene - 1, 2 - dione,which is prepared by the reaction of (1R, 2S) - 2 - amino - 1, 2 - diphenylalcohol with dibutyl squrate, The in situ formed chiral oxazaborolidines have been used in the enantioselective borane reduction of prochiral ketones to afford the alcohol products in a range 88% similar to 98% yield and 42% similar to 81% enantiomeric excesses, respectively. All of the new compounds are confirmed by IR, H-1 NMR, MS and element analysis, in which compound 4b is also confirmed by X - ray analysis.