Copper-Catalyzed Cascade Annulation of <i>o</i>-Hydroxyphenyl Propargylamines with Pyrazolin-5-ones to Access Pyrano[2,3-<i>c</i>]pyrazoles

Abstract

An efficient copper-catalyzed cascade annulation of o-hydroxyphenyl propargylamines and pyrazolin-5-ones is described. This methodology leads to the rapid assembly of a series of valuable pyrano[2,3-c]pyrazoles with good yields across a wide range of substrates in a simple fashion. This novel reaction involves the formation of alkynyl ortho-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.

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