Synthese mittlerer und großer Ringe, XXXIII [1] . Optisch aktive 3a,6‐Methanohydroazulene durch chirale Induktion der photochemischen Festkörperumlagerung von Bis(1,2:5,6‐di‐ O ‐isopropyliden‐α‐ D ‐ und ‐α‐L‐glucofuranos‐3‐ O ‐yl)‐3,6‐hexanooxepin‐4,5‐dicarboxylat

Synthesis of Medium and Large Rings, XXXIII [1] .–Optically Active 3a,6‐Methanohydroazulenes via Chiral Induction of the Solid‐State Photochemical Rearrangement of Bis(1,2:5,6‐di‐ O ‐isopropylidene‐α‐ D ‐ and ‐α‐ 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 (3a S ,6 R ,8a R )‐ and (3a R ,6 S ,8a S )‐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‐α‐ L ‐glucofuranose is recycled in 95% yield.