Control by Pyridine Nitrogen of the Dual-Channeled Triplet-State Di-?-methane Photorearrangement of 5,8-Dihydro-5,8-methanoquinoline Systems

Article abstract of DOI:10.1021/jo00391a013

A series of five 5,8-dihydro-5,8-methanoquinolines has been synthesized and the triplet-state photoisomerization of these compounds investigated.In the case of the parent heterocycle, a 60:40 distribution of the two possible photoisomers was observed, with the major product arising by migration of the carbon atom ortho to nitrogen.Adoption of this pathway is notably enhanced (to the 83percent level) when a chlorine is positioned at C-2 and becomes exclusive in the 2-methoxy example.The presence of a 4-chloro group reverses this trend (33:67), and the effect persists in the 4-methoxy example (25:75).The various regioselectivities are shown to conform to expectations which have their basis in molecular orbital theory.