摘要:
                                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.