The synthesis of hetero-bridged [5](3,6)oxepinophanes

Abstract

The [5](3,6)oxepinophanes (8) are the oxepines with the shortest bridge reported so far. They were obtained starting from diethyl furan-3,4-dicarboxylate (3) which, with lithium aluminium hydride, afforded the diol (4); this was converted into the seven-membered siloxanes (5a and b) by reaction with dichlorodimethylsilane or dichlorodimesitylsilane, respectively. By the Prinzbach–Tochtermann sequence, compounds (5) were converted into the oxepinophanes (8) in three steps: Diels–Alder reaction of (5) with dimethyl acetylenedicarboxylate to give the fused 7-oxanobornadienes (6), photochemical transformations of compounds (6) to the fused 7-oxaquadricyclanes (7), and thermal isomerization of compounds (7) to (8). Attempted conversion of (8a) into (11a), a derivative of [5]paracyclophane, was unsuccessful.