Stereoselective reduction of the ketone group in α-allyl β-keto esters
摘要:
Stereoselective reduction of the ketone carbonyl group in alpha-allyl-substituted beta-keto esters with sodium tetrahydridoborate in the presence of 2 equiv of MnCl2 quantitatively afforded the corresponding syn-isomeric alcohols. The reduction of the same substrates with L-selectride [LiBH(s-Bu)(3)] in anhydrous THF was characterized by low chemoselectivity, and anti-isomeric alcohols were formed in about 50% yield. Under analogous conditions, alpha-allyl ketones smoothly reacted with L-selectride to give syn-isomeric alcohols in quantitative yield. The corresponding anti isomers were synthesized by the Mitsunobu reaction of the syn isomers with formic acid, followed by alkaline hydrolysis.