Cumulene Photochemistry: Photoreactions of a Strained 1,2-Cyclooctadiene

Article abstract of DOI:10.1021/jo00022a029

The singlet and triplet photoreactions of 1-tert-butyl-1,2-cyclooctadiene (1) are described.This is the first example of an isolable eight-membered ring allene and is predicted to have a bent allenic unit.Triplet reactions of 1 are phase dependent.Benzene-sensitized irradiation affords products of hydrogen abstraction at tert-butyl or ring carbons in vapor phase or solution phase, respectively.Direct irradiation of thoroughly degassed pentane solutions at 254 nm affords primarily 3-tert-butylbicyclo<3.3.0>oct-2-ene and other products that are attributed to initial excited-state 1,2-hydrogen migration to a vinylcarbene.Independent generation of this vinylcarbene gives a similar collection of products, which include an isolable bicyclo<5.1.0>oct-1(8)-ene.Irradiation of 1 in oxygenated solutions yields tert-butylcycloheptene (15), apparently through loss of carbon monoxide from an intermediate cyclopropanone.Oxidation of 1 with m-CPBA also leads efficiently to 15.