ELECTROPHILIC CARBOCYCLISATIONS, INCLUDING TANDEM PROCESSES, USING NOVEL COBALOXIME PI-CATION INTERMEDIATES

Intramolecular cyclisations of substituted gamma- and delta-unsaturate d cobaloxime pi-cations (detived from 1 --> 4) are shown to occur from the 5-exo, 5-endo and 6-endo orientated double bonds but not from the corresponding 6-exo orientation, 2. An unprecedented tandem cyclisati on from the pyrrole substituted unsaturated hydroxy cobaloxime 19 in t he presence of pTSA leads to the tricycle 21 by way of the novel cobal t pi-cation intermediate 20.