Studies Dealing with the Excited-State Behavior of Substituted 8-Oxabicyclooct-6-en-2-ones

Article abstract of DOI:10.1021/jo00003a032

A series of 8-oxabicyclo<3.2.1>oct-6-en-2-ones was prepared by the rhodium(II)-catalyzed cyclization-cycloaddition reaction of α-diazopentanedione with various alkynes.The photochemical behavior of these oxabicyclic enones was investigated.Both direct and sensitized photolysis cleanly results in a 1,3-acyl shift.A slower, secondary photoprocess involving intramolecular hydrogen atom transfer and intramolecular cycloaddition of the resulting ketene was also uncovered.The photobehavior of the closely related 9-oxabenzocycloheptene system was also examined.The initially formed 1,3-sigmatropic rearranged product was found to undergo a novel 1,4-methoxyl migration on extended photolysis.The photochemistry of the homologous 7-oxabicyclo<2.2.1>hepten-2-one was studied.The results obtained can be interpreted in terms of an initial Norrish type I cleavage.The resulting diradical either couples to give the 1,3-acyl shift product or undergoes bond fragmentation, giving products derived from a stepwise retro-Diels-Alder reaction.