Copper-Catalyzed Cascade Annulation of -Hydroxyphenyl Propargylamines with Pyrazolin-5-ones to Access Pyrano[2,3-]pyrazoles.

An efficient copper-catalyzed cascade annulation of -hydroxyphenyl propargylamines and pyrazolin-5-ones is described. This methodology leads to the rapid assembly of a series of valuable pyrano[2,3-]pyrazoles with good yields across a wide range of substrates in a simple fashion. This novel reaction involves the formation of alkynyl -quinone methides, a 1,4-conjugate addition, and a subsequent 6-endo cyclization process. The mechanistic elucidation is well supported by control experiment and literature precedents.