Synthesis of Functionalized 2,3-Indoline-Fused Cyclobutanes

Significance

The synthesis of 2,3-indoline-fused cyclobutanes from indole-3-acetates under Au(I) catalysis is reported. The reaction, proposed to involve Au activation by acetylene complexation and in situ allenylic ester formation (isolated and characterized by ¹H NMR), and finally formal [2+2] cycloaddition, proceeds in good to excellent yields for several substrates. The overall reaction involves the formation of two new C-C bonds and incorporates reactive lactone and olefinic functionality in the final products.