1,3-O-Benzylidene-l-sorbose

Abstract

Abstract It has been proposed that 1,3-O-benzylidene-l-sorbose (III) exists as an equilibrium mixture of a pyranose form (IIIp), a keto-form (IIIk) and a furanose form (IIIf) in solutions. The acetylation of III in pyridine afforded the acetates of IIIf; one of them (IV) is in a keto-form (IVk) in a crystalline state, and at a low temperature, while the acetates of IIIf and IIIp at higher temperatures. When a pyridine solution of III was allowed to stand for some time before acetylation, the yield of the acetate of IIIp increased. The recrystallization of III usually gave crystals of IIIf, however, while the addition of petroleum ether to the concentrated pyridine solution of III afforded a powder which was consisted mainly of IIIp. These results suggest that III exists as IIIf in a crystalline state and as an equilibrium mixture of IIIf, IIIk, and IIIp in solution; the existence of this equilibrium was also confirmed by proton magnetic resonance spectroscopy.