Stereoelective Conversion of Ethyl Pipecolinate into (±)-α- and (±)-β-Conhydrins

Abstract

Reaction of ethyl N-benzhydrylpipecolinate with ethylmagnesium bromide in the presence of catalytic amount of titanium(IV) isopropoxide furnished in a high yield the corresponding hydroxypropyl-substituted piperidine that by treating with alcoholic alkali was quantitatively converted into 1-benzhydryl-2-propionylpiperidine. The reduction in the latter of carbonyl group with lithium aluminum hydride or sodium borohydride in methanol gave rise prevailingly to threo-aminoalcohol. With sodium borohydride in the presence of cerium chloride an erythro-aminoalcohol was the main product. Deprotection of the nitrogen atom from the benzhydryl group of the aminoalcohols obtained provided racemic α- and β-conhydrines.