CUMULENE PHOTOCHEMISTRY - SUBSTITUENT EFFECTS ON THE MECHANISM OF 1,2-CYCLONONADIENE PHOTOCHEMISTRY

The photoreactions of l-methyl-l,2-cyclononadiene (2) are described and contrasted with those of 1,2-cyclononadiene (1). Direct irradiation yields as primary products seven isomers. The major singlet products are best accounted for by excited-state 1,2-hydrogen migration to 3-methylcyclonon-2-enylidene (15). Independent generation of this vinylcarbene and an isomeric carbene are reported. Minor products from 2 include 3-methylcyclononyne (9) and two isomeric tricyclo[4.3.0.02,9]nonanes (7 and 8). An important conclusion is that in contrast to the apparently concerted reaction of 1, methyl derivative 2 seems to favor vinylcarbene intermediates. Triplet-sensitized reactions of 2 are similar to 1, affording isomeric tricyclononanes 7 (46%) and 8 (41%). © 1990, American Chemical Society. All rights reserved.