Rh(II)/Ag(I)-Cocatalyzed Three-Component Reaction via S_N1/S_N1′-Type Trapping of Oxonium Ylide with the Nicholas Intermediate

A Rh(II)/Ag(I)-cocatalyzed three-component reaction of propargylic alcohol-Co2(CO)6 complexes with diazo compounds and benzyl alcohols is described, which represents the first trapping process of oxonium ylides with carbocations via the SN1/SN1′-type pathway. This transformation provides an efficient approach for construction of dicobalt hexacarbonyl-complexed 3,3-disubstituted oxindoles. Further derivatization of the product, initiated by the deprivation of the dicobalt species, gives the 3,3-disubstituted oxindoles with the ene alkynyl group and the privileged spirooxindole-vinyldihydropyran structure.