Copper-Mediated Oxidative Transformation of N‑Allyl Enamine Carboxylates toward Synthesis of Azaheterocycles

A method for synthesis of 3-azabicyclo[3.1.0]­hex-2-enes has been developed by intramolecular cyclopropanation of readily available N-allyl enamine carboxylates. Two complementary reaction conditions, CuBr-mediated aerobic and CuBr2-catalyzed-PhIO2-mediated systems effectively induced stepwise cyclopropanation via carbocupration of alkenes. Oxidative cyclopropane ring-opening of 5-substituted 3-azabicyclo[3.1.0]­hex-2-enes was also developed for synthesis of highly substituted pyridines. In addition, diastereoselective reduction of 3-azabicyclo[3.1.0]­hex-2-enes to 3-azabicyclo[3.1.0]­hexanes was achieved using NaBH3CN in the presence of acetic acid.