During the preparative investigation of π-expanded porphyrinoids based on the retro-Diels-Alder reaction of bicyclo[2.2.2]octadiene(BCOD)-fused precursors for benzo- and benzo[k]fluorantho[9,10]-[b]porphyrins by the [3+1] porphyrin synthesis using tripyrrane-1,14-dicarbaldehyde and BCOD-fused pyrroles, serendipitous formation of the corresponding corroles was observed. After elucidation of the reaction conditions, the [3+1] reaction afforded 21,31-dihydro-21,31-ethanobenzo[k]fluorantho[9,10-b]corrole in 23% yield as well as a trace amount of the corresponding porphyrin. In the sapphyrin synthesis by the [3+2] approach using the tripyrrane-1,14-dicarbaldehyde and a bipyrrole, the similar reaction conditions resulted in the formation of 5-pyrrolylcorrole in a 38% yield as well as isosmaragdyrin and the originally targeted sapphyrin.
