Stereoselective Synthesis of Indoline-Fused Cyclobutanes via Dual Functionalization of Alkynyl Diazo Carboxylates.

We report stereoselective synthesis of indoline-fused cyclobutanes through dual functionalization of alkynyl diazoacetates. The development proceeds through Rh-catalyzed insertion of alkynyl carbenes into 2-alkenyl anilines, followed by a base-promoted alkynoate-allenoate isomerization and cycloaddition cascade. The protocol expands the synthetic utility of alkynyl diazoacetates and provides a broad range of indoline-fused cyclobutanes with excellent yields and stereoselectivity (up to 97% yield and >20:1 dr). The synthetic applications of densely functionalized indoline scaffolds are shown toward obtaining useful motifs.