Regiochemical aspects of intramolecular cycloadditions of nitrones derived from N-(2-alkenyl)-2-pyrrolecarbaldehydes. Competitive entries to pyrrolizidine and indolizidine derivatives

Intramolecular cycloadditions of unsaturated nitrones derived from a series of N-(2-alkenyl)-2-pyrrolecarbaldehydes (2) have been systematically studied. A pronounced substituent effect has been observed as far as the competitive formation of fused- and bridged-ring regioisomers are concerned. Further elaboration of the two kinds of cycloadducts has given pyrrolizidine and indolizidine derivatives, respectively.