REGIOCONTROL IN THE 1,3-DIPOLAR CYCLOADDITION REACTIONS OF MESOIONIC COMPOUNDS WITH ACETYLENIC DIPOLAROPHILES

The regioselectivity of 1,3-dipolar cycloaddition reactions between me soionic compounds with singly-tethered substituents is examined. The r esults with propiolate dipolarophiles are compared with other singly a nd doubly-tethered examples according to a model using an asynchronous , concerted transition state. The isolation and reaction of a novel, n on-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 a nd alkyl propiolates. (C) 1997 Elsevier Science Ltd.