First asymmetric cycloaddition of carbonyl ylides to vinyl sulfoxides and furan-2(5H)-ones

The Rh2(OAc)4-catalyzed reactions of o-(methoxycarbonyl)-alpha-diazoacetophenone with enantiomerically pure 5-ethoxy-3-p-tolylsulfinylfuran-2(5H)-ones 1a and 1b afford 4,10-epoxybenzo[4,5]cyclohepta[1,2-c]furan-3,9-diones 6a and 6b, in good or moderate yields and in a completely regioselective way. The pi-facial selectivity is complete for 1a, which only yields anti-6a adducts, and very high for 1b. The endo stereoisomers are favored with respect to the exo ones in both reactions. The sulfinyl group significantly increases the reactivity of the dipolarophile as it has been demonstrated by studying the behavior of 5-methoxyfuran-2(5H)-one (3).