The tertiary amino effect in heterocyclic synthesis : mechanistic and computational study of the formation of six-membered rings

摘要: The mechanism of the ring closure [2-(1-pyrrolidinyl)phenylmethylene]-propanedinitrile (2a) to l,2,3,3a,4,5-hexahydropyrrolo[1,2-a]quinoline-4,4-dicarbonitrile (3a) has been studied by kinetic measurements using 1H-NMR spectroscopy. It could be shown that rate-determining step consists an intramolecular 1,5 hydrogen transfer, which is accompanied charge separation within the- molecule. calculated (AM1) and experimental (X-ray) molecular structure 2a are in fairly good agreement. In ground state geometry a transfer will most likely take place suprafacially. Subsequent rotation former vinyl group C-C-bond formation, leading six-membered ring, also stereochemically defined way.