Asymmetric Synthesis with Sugar Derivatives. I. The Conjugate Additions of Grignard Reagents to α, β-Unsaturated Esters of Sugar Derivatives

Abstract

Abstract Partial asymmetric syntheses were carried out in the reaction of Grignard reagents with crotonic and cinnamic esters of 1,2:5,6-di-O-cyclohexylidene-d-glucose, 1,2:5,6-di-O-isopropylidene-d-glucose, 1,2-O-isopropylidene-5-deoxy-d-xylose and (−)-menthol. The reaction of 3-O-crotonyl-1,2:5,6-di-O-cyclohexylidene-d-glucose (Ic) with phenylmagnesium bromide, followed by the hydrolysis of the resulting ester, gave (−)-3-phenylbutyric acid (III) in 33% optical and 12% synthetic yields, while in the presence of cuprous chloride as a catalyst, III was obtained in 74% and 58% yields respectively. The reaction of 3-O-crotonyl-1,2-O-isopropylidene-5-deoxy-d-xylose (Ie) with phenylmagnesium bromide gave (+)-acid (III) without cuprous chloride in 16% optical and 32% synthetic yields and (−)-acid (III) with cuprous chloride, in 58% and 61% yields respectively. The reaction of 3-O-cinnamoyl-1,2:5,6-di-O-cyclohexylidene-d-glucose (IVc) with benzylmagnesium chloride, followed by the saponification of the resulting ester, gave (−)-3,4-diphenylbutyric acid (VI) in 18% optical and 62% synthetic yields without cuprous chloride, and in 17% and 58% yields with cuprous chloride. In the formation of acid (VI), cuprous chloride seemed to have no effect on optical and synthetic yields nor on the change in the sign of optical rotation. The steric courses of these reaction are discussed.