Pyridines in Photoelectrocyclization Reactions: The Effect of Substitution and Reaction Conditions on Pyridine Photoelectrocyclizations

Outlined here are photoelectrocyclization reactions of substituted phenylpyridylcyclohexenones leading to the synthesis of dihydrobenzoquinolines, where the substituents are important in the diastereoselectivity of the products from the reactions. For those substrates that provided mixtures of products, the incorporation of the triplet quenchers 2,3-dimethylbutadiene or Zn(OAc)₂ demonstrated that the mixtures resulted from triplet excited states or mixtures of singlet and triplet excited states. Also demonstrated is that the reductive dearomatization of the dihydrobenzoquinolines gives the corresponding dehydropiperidine scaffold, as are present in members of the ergot alkaloid class of natural products.