A one-pot assembly of 4-allyl-3-pyridinecarboxaldehyde. A new synthesis of 1-methyl-1,2,3,3a,4,8b-hexahydropyrrolo[3,2-f]pyrindine, an annulated nicotine analogue

This paper describes a two-step synthesis of 1-methyl-1,2,3,3a,4,8b-hexahydropyrrolo[3,2-f]pyrindine, a conformationally constrained nicotine analogue. The target molecule was effectively assembled by an intramolecular azomethine ylide-alkene [3+2] cycloaddition. The cyclization precursor, 4-allyl-3-pyridinecarboxaldehyde, was formed efficaciously in a single step from 3-pyridinecarboxaldehyde via sequential in situ protection, ortho lithiation, cuprate formation, allylation, and deprotection. The cuprate formation plays a vital role in minimizing/eliminating the extent of multiple alkylation.