Intramolecular Photocycloaddition of Unsaturated Isoquinuclidines. Synthesis of 2-Azatetracyclo[4.0.0.(4,9)0(7,10)]decanes and 3-Azatetracyclo[6.1.1.0.(2,7)0(5,9)]decanes.

2-Azabicyclo[2.2.2]oct-5-enes bearing an endo alkenyl substituent were synthesized by Diels-Alder addition of methyl vinyl ketone to a 1,6-dihydropyridine derived from methyl nicotinate. Although 1,5-dienes with this skeleton were unreactive under thermal conditions, they were photochemically reactive. Irradiation of these dienes through a Corex filter resulted in intramolecular [2 + 2] cycloaddition to give "parallel" and "crossed" photoadducts along with small amounts of a hexahydroisoquinoline. The latter is thought to represent leakage of a diradical intermediate responsible for the parallel photoadduct. The new 2-azatetracyclo[4.4.0.0.(4,9)0(7,10)]decane and 3-azatetracyclo[6.1.1.0.(2,7)0(5,9)]decane structures formed in the photochemical reactions are thermally stable.