The reaction of 2-hydroxyglycal esters with alcohols in the presence of N-iodosuccinimide, stereoselective synthesis of α anomers of alkyl 3-deoxyhex-2-enopyranosides and 3,4-dideoxyhex-3-enopyranosid-2-uloses

Abstract

Reaction of 2,3,4,6-tetra- O-acetyl-1,5-anhydro- d- arabino-hex-1-enitol ( 1; 2-hydroxyglucal tetraacetate) with 1.0–1.5 mol of primary secondary, or tertiary alcohols, in the presence of 0.1–1.0 mol of N-iodosuccinimide (NIS) in acetonitrile as solvent, afforded the α anomers of alkyl 3-deoxyhex-2-enopyranosides in very good yields. The reaction proceeded more slowly, and with poorer yields, in the case of the tetrabenzoate corresponding to 1. When 1 was treated with higher concentrations of 2-propanol, increasing proportions of a reaction by-product, 2-propyl 6- O-acetyl-3,4-dideoxy-α- d- glycero-hex-3-enopyranosid-2-ulose ( 10), were produced. Such sugar enones as 10 were more readily formed when the starting 2-hydroxyglycal acetate had the lyxo configuration. Thus, two cholesteryl α-hex-3-enopyranosid-2-ulose derivatives were each prepared in one step and with good yields. Remarkable stereoselectivity for the formation of the α anomers was observed in all of these reactions.