Template Synthesis of Decaphyrin without Meso-Bridges: Cyclo[10]pyrrole

An acenaphthylene-fused cyclo[10]pyrrole 1b was selectively synthesized via an oxidative coupling reaction of the corresponding 2,2′-bipyrrole with the appropriate dianion template, croconate anion. The structure of 1b as the isolated largest cyclo[n]pyrrole was elucidated by X-ray crystallographic analysis. The absorption spectrum exhibited a markedly red-shifted, intensified L band at 1982 nm, which was interpreted by application of Michl’s perimeter and Gouterman’s 4-orbital models, supported by magnetic circular dichroism (MCD) data and theoretical calculations.