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 insequence of ring-closing metathesis and an intramolecular Heck reaction gave rise to advanced tricyclicintermediates. 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 atelevated temperature. While the irradiation of
9 led principally via SO
2-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 featureswhich force its conjugated diene double bonds to be rigidly oriented 32
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out-of-plane. The unique abilityof the sulfonamide linkage to excited-state homolysis holds comparative interest.