Regiocontrol in the 1,3-dipolar cycloaddition reactions of mesoionic compounds with acetylenic dipolarophiles.

The regioselectivity of 1,3-dipolar cycloaddition reactions between mesoionic compounds with singly-tethered substituents is examined. The results with propiolate dipolarophiles are compared with other singly and doubly-tethered examples according to a model using an asynchronous, concerted transition state. The isolation and reaction of a novel, non-aryl substituted mesoionic compound 7 is reported. A regiodirected synthesis starting with N-(2-thiazolinyl)proline gives a complementary dihydropyrroline compared with the reaction between N-formylproline and alkyl propiolates. (C) 1997 Elsevier Science Ltd.