Regioselectivity of [3+2] Cycloadditions of Heteroaryl Azides and Ethyl-Vinyl Ether

摘要

The reaction of ethyl vinyl ether with some heteroaryl azides in the presence of MnSO4 affords some unexpected products. In the case of 2-azido-1,3-thiazole an imidate is formed, while 2-azidobenzothiophene gives an unprecedented 3,3a-dihydro-2H-8-thia-1-aza-cyclopenta[a]indene system, with loss of the aromaticity of the benzotiophene ring. DFT calculations are performed to justify these structures. Selenophene -derived acyl azides on the contrary, afford in two cases N-heteroaryl carbamates, probably due to the reaction of an intermediate isocyanate and cleavage of the ether linkage.