Intramolecular Photocycloaddition of 2-Pyridines Tethered by a Three-Carbon Chain: Studies on the Formation of Cycloadducts and Control of Stereogenesis. 3

Article abstract of DOI:10.1021/jo00080a015

Irradiation of a pair of 2-pyridones tethered at the 3- and 6'-positions by a three-carbon chain initiates an efficient <4 + 4> cycloaddition to produce a densely functionalized, fused 5-8 carbocyclic ring system with the trans isomer predominant.An asymmetric center on the tether influences stereogenesis at the four new tetrahedral centers.This effect was probed with an alcohol substituent and its silyl ether as a function of solvent.A combination of inter- and intramolecular hydrogen-bonding can account for the observed levels of selectivity.Some of the cis products are unstable and undergo Cope rearrangement, yielding cyclobutane isomers.