Synthese mittlerer und großer Ringe, XXXVI. Synthese eines überbrückten, in‐konfigurierten Bicyclo[2.1.0]pentan‐Derivates

Synthesis of Medium and Large Rings, XXXVI. — 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‐dicarboxylic esters. The synthesis of the bromo derivative 4 was achieved by irradiation of the epoxyoxepine 1 followed by a regio‐ and stereoselective NBS bromination of 2 and deoxygenation of 3 with tungsten hexachloride/n‐butyllithium. Treatment of the allylic bromide 4 with sodium methoxide gave surprisingly the title compound 5. The structure of 5 was established by thorough NMR analysis.