The photochemistry of ketones derived from carbohydrates. Part 5. Photochemical cross-pinacolisation of acetalised pyranos-3-ulose derivatives with methanol; a route to branched-chain sugar derivatives

Abstract

U.v. irradiation of methanolic solutions of the 4,6-O-ethylidene-1,2-O-isopropylidene derivative (1) and the 4,6-O-benzylidene-1,2-O-propylidene derivative (2) of ribo-hexos-3-ulose gave in each case the corresponding 1,2:4,6-substituted 3-C-hydroxymethyl-glucopyranose and -allopyranose derivatives, (3) and (4) and (11) and (12), from a cross-pinacolisation reaction, in combined yields of 42 and 55%, respectively. The gluco-[(3) and (11)] and allo-[(4) and (12)] structures were determined by ¹H and ¹³C n.m.r. spectroscopy. In addition a little 1,2:4,6-diacetalised glucose and allose were produced by photoreduction, and significant amounts of 4,6-O-ethylidene-allono-δ-lactone (17) were formed from (1).