ChemInform Abstract: SIGMATROPIC AND ELECTROCYCLIC REACTIONS OF BICYCLO(3.2.0)HEPTADIENYL RADICALS, 3‐QUADRICYCLANYL RADICALS, AND 7‐NORBORNADIENYL RADICAL

Abstract

The rearrangement of matrix-isolated organic radicals with bicyclo[3.2.0]heptadienyl structure (2, 5, lla,b), 3-quadricyclanyl structure (16,26,27), and of 7-norbornadienyl radical 15 is studied. Final rearrangement products are radicals with tropylium structure. 16, 26, and 27 isomerize to radicals with bicyclo[3.2.0]heptadienyl skeleton before electrocyclic ring opening to tropylium radicals takes place. 7-Norbornadienyl radical 15 is the least stable radical on the C,-hypersurface. Free radical rearrangements of bicyclic model systems under conditions of long life time have been the subject of several electron spin resonance investigations and a part of the work presented here has been published in preliminary form'-3). The purpose of studying rearrangements of matrix isolated free radicals is to demonstrate that sofar unknown radical reactions can take place with activation energies similar to reactions of comparable ionic species. Eventually this may lead to the application of such reactions in the synthesis of complex organic molecules.In solution bicyclo[3.2.0]hepta-2,6-diene (1) is converted by hydrogen abstraction of an allylic hydrogen atom with photolytically generated tert-butoxy radicals to bicyclo[3.2.0]heptadienyl radical (2). Its ESR spectrum can be interpreted in terms of four different coupling constants. Due to the molecular symmetry hy-0 VCH Verlagsgesellschaft mbH, D