Synthesis and X-ray Crystallographic Analysis of 1,4-dihydropyridine Photodimerization

Abstract

1,4-dihydropyridine undergoes a head-to-tail [2+2] photodimerization that leads to the formation of anti-dimer, syn-dimer and cage dimer in solution. Their crystal X-ray crystallographic analysis suggests that the stereoisomers in solution are restrainted by the relative position of double bonds of intramolecules, hydrogen bonds and steric hindrances, which are different in the solid state. The cage dimer is formed by the intramolecular reaction of syn-dimer, and is topochemical controlled by the nearest distance between potentially reacting double bonds, rotational angles of the building cyclobutane ring and the orientation of carbonyl ester.