SYNTHESIS OF MEDIUM AND LARGE RINGS .36. SYNTHESIS OF A BRIDGED BICYCLO[2.1.0]PENTANE DERIVATIVE WITH INSIDE CONFIGURATION

Dihydrocyclobutafurans 4 (H instead of Br) are reactive intermediates in the photochemical rearrangement of 3,6-hexanooxepine-4,5-dicarboxyl ic esters. The synthesis of the bromo derivative 4 was achieved by irr adiation of the epoxyoxepine 1 followed by a regio- and stereoselectiv e NBS bromination of 2 and deoxygenation of 3 with tungsten hexachlori de/n-butyllithium. Treatment of the allylic bromide 4 with sodium meth oxide gave surprisingly the title compound 5. The structure of 5 was e stablished by thorough NMR analysis.