Synthesis Of Cyclopropane Via 1,3-Migration Of Acyloxy Group Triggered By Formation Of α-Imino Rhodium Carbene

The metal carbene intermediates,synthesized from various metals(such as Rh,Au,Cu and Pd)and diazo compounds,can participate in various selective reactions.As a result,metal carbene is used to synthesize many valuable molecules.In recent years,a lot of related reactions have been reported.It is well known that intramolecular 1,n-migration(or 1,n-insertion)is a common reaction mode in carbene chemistry.The 1,2-migration of hydrides,alkyls and heteroatoms can produce various substituted alkenes;1,4-,1,5-and 1,6-H migration are convenient methods for the preparation of four-,five-and six-membered rings,respectively.However,1,3-migration of carbene,which affords cyclopropane,was rare.Because of the unique structure and widely existence in various bioactive molecules,the synthesis of cyclopropane is a long-term hot topic.In this research,the success of 1,3-acyloxy migration of α-rhodium carbene generated by rhodium-catalyzed transformation of 1-sulfonyl-1,2,3-triazole,and the application of this method in cyclopropane synthesis were achieved.The optimized reaction conditions were established as follows:under the protection of nitrogen atmosphere,with Rh2(piv)4(3 mol%)as catalyst,heated in DCE at 60℃ for 40 min,1-sulfonyl-1,2,3-triazole could be converted to cyclopropane in up to 99%yield.The substrate scope was quite broad,and the chemoselectivity was excellent,tolerating various functional groups,especially those that were sensitive to carbene.The desired cyclopropane could be further transformed to some other useful molecules by ring opening,reduction and hydrolysis,illustrating the potential of the protocol.Primary investigation of mechanism was conducted by several control experiments.