Reactions of Nitro Sugars. XXXI. Formation of 2,3- and 3,4-Unsaturated Derivatives in the 6-Deoxyhexose Series

Abstract

The methyl 3,6-dideoxy-3-nitrohexopyranosides having the α-L-galacto (1), α-L-manno (2), α-L-galacto (3), and α-L-talo (4) configurations and their 2,4-diacetates (6, 11, 16, and 18, respectively) served as starting materials for the preparation of 2,3- and 3,4-unsaturated derivatives. The reactions employed included dehydroacetylation of diacetates and of some monoacetates (5, 7, and 12) that had been obtained by partial acetylation or partial acid-catalyzed de-O-acetylation, and also dehydrations occurring under conditions of acetylation. The following nitroolefins were obtained: methyl 3,4,6-trideoxy-3-nitro-α-L-erythro-hex-3-enopyranoside (8) and its 2-acetate (9), the corresponding α-L-threo isomer (13) and its 2-acetate (10) and 2-O-methyl derivative (20), and methyl 2,3,6-trideoxy-3-nitro-α-L-erythro-hex-2-enopyranoside (14) and its 4-acetate (15) as well as the 4-acetate (17) of the corresponding α-L-threo isomer. In addition, 1,4-di-O-acetyl-2,3,6-trideoxy-3-nitro-α-L-threo-hex-2-enose (19) was obtained by acetolysis of 17. Factors assumed to be responsible for a pronounced regioselectivity in some of the reactions are discussed.