Revision of the stereochemistry of the reductive Heck cyclisation of 1-(2-iodobenzoyl)-4-substituted-1.4-dihydro-pyridine-3-carbaldehyde aminals

The stereochemistry of reductive and non reductive Heck cyclisations of 4-substituted-1.4-dihydropyridines is reexamined. The both reactions occur mainly via an anti (from the C4 substituent) 5-exo process without any epimerisation of the C4-H.