Insights for diastereoselectivity in synthesis of 2,3-dihydropyrroles by photochemical ring contraction of 1,4-dihydropyridines

Strategies by introducing chiral auxiliaries into the photoreactive substrate 1,4-dihydropyridines, an interesting diastereoselectivity of 2,3-dihydropyrroles in the process of photochemical ring contraction was observed. The diastereoselectivity of (2 R,3 R ) and (2 S,3 S )-2,3-dihydropyrroles was related to the phenyl group and the chirality of C-4 in 1,4-dihydropyridines and similar to that of 1,4-dihydropyridines. The yields and diastereomeric excess of all obtained products supporting the experimental data were compared and discussed in theoretical calculations. A concise theoretical study was used to explain the diastereoselectivity observed in the photochemical ring contraction of 1,4-dihydropyridines to 2,3-dihydropyrroles.