Lewis Acid-Catalyzed Stereoselection on Carbohydrate Templates

Abstract

The chirality and the complexing abilities of carbohydrates are utilized for chemical stereoselection in different reactions. In this sense, the carbohydrates are investigated as the chiral auxiliaries in alkylation reactions and in Michael additions of ester enolates. Furthermore, carbohydrates are demonstrated to be efficient chiral matrices in Lewis acid-catalyzed Diels-Alder reactions. They also effect stereoselection in a new synthesis of β-branched carboxylic acid derivatives. O-Acylated glycosylamines are shown to be potent chiral templates in the Strecker synthesis and in the Ugi four-component condensation to give α-amino acid derivatives in high yield and diastereoselectivity. In particular, the O-pivaloylated galactosylamine was used as the auxiliary in efficient diastereoselective aza-Diels-Alder reactions, Mannich reactions and syntheses of enantiomerically pure alkaloids, e.g. the tobacco alkaloid (S)-anabasin.