Reaction of heterocyclic enamines with nitrile oxide and nitrilimine precursors

Alkylidenepyrrolidines 1, 21, 24 and 26 undergo reactions with nitrile oxides and nitrilimines or their precursors to give a range of novel heterocyclic compounds. With alkylidenepyrrolidine ester 1, nitrolic acids give products in which the liberated nitrous acid reacts with the alkylidenepyrrolidine, followed by two cycloadditions to give adducts 3. In contrast, hydroximoyl chlorides give isoxazoles 10, presumably by cycloaddition/elimination. With hydrazonyl chlorides, simple acylation of the alkylidenepyrrolidine occurs to give compounds 17. With sulfonyl alkylidenepyrrolidines 24 and 26, cycloaddition onto the imine tautomer is the preferred pathway, with a stereoselective reaction taking place in the latter case.