N-bis(methylthio)methylene derivatives. 5. New synthesis of 2-aminoindolizine and related compounds via a formal [3 + 3] cycloaddition reaction using N-bis(ethoxycarbonylmethylthio)methylenephenylsulfonamides†

Reaction of pyridinium N-ylide 5a with N-bis(ethoxycarbonyl)methylthio)(p-substituted-phenyl)sulfon-amides 2a,c in the presence of triethylamine as a base in ethanol gave diethyl 2-(p-substituted-phenylsulfonyl)aminoindolizine-1,3-dicarboxylates 9a,b via a new formal [3 + 3] cycloaddition reaction. In a similar manner, 2-sulfonylaminopyrrolo[2,1-a]isoquinoline derivatives 11a-e were also obtained by the reaction of 2a-c and 4a,b with the corresponding isoquinoline N-ylides 10a.b with good results.