SYNTHESIS OF MEDIUM AND LARGE RINGS .33. OPTICALLY-ACTIVE 3A,6-METHANOHYDROAZULENES VIA CHIRAL INDUCTION OF THE SOLID-STATE PHOTOCHEMICAL-REARRANGEMENT OF BIS(1,2-5,6-DI-O-ISOPROPYLIDENE-ALPHA-D-GLUCOFURANOS-3-O-YL) AND BIS(1,2-5,6-DI-O-ISOPROPYLIDENE-ALPHA-L-GLUCOFURANOS-3-O-YL) 3,6-HEXANOOXEPINE-4,5-DICARBOXYLATE

Irradiation of an aqueous suspension of the crystalline 3,6-hexanooxepine-4,5-dicarboxylic esters 2a and 2b affords the (3aS,6R,8aR)- and (3aR,6S,8aS)-methanohydroazulenes 3a and 4b in 54 - 58% yield with 92 - 93% de. Irradiation of an ethereal solution of 2a-2d on the other hand proceeds with low diastereoselectivity. The absolute configurations were established by X-ray structural analysis of the dimenthyl ester (+)-3d, comparison of CD spectra and chemical transformations. The origin of the high diastereoselectivity of the rearrangements 2a --> 3a and 2b --> 4b in the solid state is discussed on the basis of the X-ray structural analysis of the 3,6-heptanooxepine (-)-5a. Procedures for the removal of the chiral auxiliaries are described. Di-O-isopropylidene-alpha-L-glucofuranose is recycled in 95% yield.