The molecular rearrangements of cyclopropyl epoxides generated from various flavonoid systems

Abstract

The fused three-ring systems, naphtho[1,2-c]pyran and 1H-pyrano[4,3-b]benzofuran, were obtained by the reaction of αβ-unsaturated ketones and cyclopropyl ketones with DMOSM and DMSM, presumably via cyclopropyl epoxides. An attempt to prepare a pyranobenzopyran by reaction of a 3-bromo-2,3-dihydrochromenone with DMOSM gave 1a,7a-dihydro-1a-phenylcyclopropa[b]chromen-7(1H)-one and a ring-contracted product, a spiro[benzofuran-2,1′-cyclopropan]-3(2H)-one; methylenation of both products gave benzofurans. The αβ-unsaturated carbonyl group of 2-phenylchromen-4-one reacted with DMOSM to give, as well as 1a,7a-dihydro-1a-phenylcyclopropa[b]-chromen-7(1H)-one, diastereoisomeric 2-(methylphenylmethylene)benzofuran-3(2H)-ones, a thiin oxide, and a 2,3-dihydro-3-methylenebenzofuran.