Novel reaction pathways for 2-pyridone [4+4] photoadducts.

[Structure: see text] Transannular ring closure of a pyridone-furan [4+4] photoadduct has been evaluated in a model system. A combination of nitrogen substitution and an isopropyl group gave full control of the four new stereogenic centers. Chlorination transformed the 1,5-cyclooctadiene to a [4.2.0] ring system instead of to the expected [3.3.0] ring system. Changing an alkene to an enone suppressed this pathway and led to a new rearrangement, converting the 5-8-5 ring system to a 6-7-5 system.