(Ss)-5-ethoxy-3-p-tolylsulfinylfuran-2(5H)-ones as chiral dipolarophiles: First asymmetric cycloaddition of diazomethane to vinyl sulfoxides

Abstract

Cycloadditions of diazomethane to (Ss)-5-ethoxy-3-p-tolylsulfinylfuran-2(5H)-ones 1a–b and their corresponding 4-methyl derivatives 3a–b, proceeds in quantitative yields, to give enantiomerically pure 3H,6H,3a,6a-dihydrofuro[3,4-c]pyrazol-4-ones 2a–b and 4a–b, respectively. The sulfinyl group at C-3 strongly increases both the reactivity and the π-facial selectivity. The dipole approach mode is determined by the configuration at the sulfinyl group. Pyrolysis of pyrazolines 2a or 2b gives the methyl derivatives 3a or 3b in excellent yield.