Phosphorus-containing Lewis base catalyzed highly regioselective cyclization of isatin derived electron-deficient alkenes with but-3-yn-2-one

In this paper, we reported that phosphorus-containing Lewis bases catalyzed [4+2] cyclization of N-protected isatin derived electron-deficient alkenes with but-3-yn-2-one could proceed smoothly to give the corresponding dihydropyrano[2,3-b]indoles in good to excellent yields under mild conditions. The substrate scope has been carefully examined and the plausible reaction mechanism has been also proposed.

Graphical abstractIn this paper, we reported that phosphorus-containing Lewis bases catalyzed [4+2] cyclization of N-protected isatin derived electron-deficient alkenes with but-3-yn-2-one could proceed smoothly to give the corresponding dihydropyrano[2,3-b]indoles in good to excellent yields under mild conditions. The substrate scope has been carefully examined and the plausible reaction mechanism has been also proposed.Figure optionsDownload full-size imageDownload as PowerPoint slide