Rh-Catalyzed Synthesis of 3-Alkylideneoxindoles from 2-Alkynylisocyanates and Arylboronic Acids

Significance

Reported is a stereoselective rhodium-catalyzed reaction of 2-alkynylaryl isocyanates with aryl and alkenyl boronic acids which leads to 3-alkylideneoxindoles. The reaction proceeds via rhodium/boron transmetallation to generate organorhodium(I) species D followed by carborhodation of alkynes and isocyanates to give E. The method represents a new regioselective transfer of aryl and heteroaryl entities from boron to the alkyne moiety in an overall two C-C bond-forming process. In the proposed mechanism, three possible intermediates (F, G and H) are proposed for the transformation of E to I.