NAD(P)+-NAD(P)H Models. 87. Nonsteric Stereochemistry Controlled by a Carbonyl Dipole

Article abstract of DOI:10.1246/bcsj.69.1679

6,7-Dihydro-1,6,11-trimethyl-5-oxo-5H-benzo[c]pyrido[2,3-e]azepin-1-ium iodide (11-Me-MMPA⁺I^-) was synthesized, and it was confirmed that the axial chirality in the salt is stable at room temperature. Upon the reduction of 11-Me-MMPA⁺ with a pair of diastereomeric dihydropyridine derivatives, the reacting face is always that in which the carbonyl dipole in the cation is included (i.e., syn selectivity), regardless the configuration of the reducing agent. A steric hindrance, in a classical sense, and other factors contribute to the stereochemistry of the reaction only in a minor part. Plausible intermolecular arrangements at the transition state of the reaction are discussed in order to understand the mechanism of this nonsteric stereochemistry.