Synthesis of 3-Oxa- and 3-Azabicyclo[4.1.0]heptanes by Gold-Catalyzed Cycloisomerization of Cyclopropenes

Allyl 3,3-dimethylcyclopropenylcarbinyl ethers or sulfonamides undergo gold-catalyzed cycloisomerization leading to 5-isopropylidene-3-oxa- and 3-azabicyclo[4.1.0]heptanes in excellent yields and with high diastereoselectivities. These reactions constitute the first examples of intramolecular cyclopropanation of an alkene by a gold carbene generated by electrophilic ring opening of a cyclopropene in the presence of gold(I) chloride.