Synthesis of optically active bridged cyclopropane derivatives

Treatment of the cyclobutene 3 with sodium methoxide leads to the cyclopropane esters 4 and 5. Experiments with deuterated compounds supply information about the course of this reaction. The optically active epoxyoxepine (+)-2a is the starting material for the synthesis of (+)-3, (−)-4 and (+)-5. The syntheses of the functionalized cyclopropanes (+)-10a, (−)-10b and (+)-12 are also described.