Direct Comparison of the Response of Bicyclic Sultam and Lactam Dienes to Photoexcitation. Concerning the Propensity of Differing Bond Types to Bridgehead Nitrogen for Homolytic Cleavage

A convergent strategy has allowed access to bridgehead sultam 9 and the related carboxamides 10 and
11. The synthetic routing proceeds via the coupling of a suitably constructed dienamine to either
o-iodobenzenesulfonyl choride or o-iodobenzoyl chloride to generate the amides. The application in
sequence of ring-closing metathesis and an intramolecular Heck reaction gave rise to advanced tricyclic
intermediates. The final two steps involved bromination in liquid bromine and proper 2-fold dehydrobromination. The latter maneuver was best achieved with tetrabutylammonium fluoride in DMSO at
elevated temperature. While the irradiation of 9 led principally via SO2−N bond homolysis and [1,5]
sigmatropic rearrangement to generate 37, 10 proceeded via disrotatory cyclization to the exo cyclobutene
39, and 11 resisted photoisomerization. The inertness of 11 may stem from its distorted structural features
which force its conjugated diene double bonds to be rigidly oriented 32° out-of-plane. The unique ability
of the sulfonamide linkage to excited-state homolysis holds comparative interest.