Hinged bis-porphyrin scaffolds I. The synthesis of a new porphyrin diene and its role in constructing hinged porphyrin dyads and cavity systems
Norbornene building BLOCKs formed by the reaction of porphyrin 1,3-dienes with norbornadiene or dimethyl tricyclo[188.8.131.52(2,5)]nona-2,7-diene-3,4-dicarboxylate were coupled with an ester-activated cyclobutene epoxide BLOCK to afford the first examples of hinged porphyrin-spacer-acceptor dyads. Similar dual coupling with a bis-(cyclobutene epoxide) formed doubly hinged POR-spacer-POR scaffolds separated by up to 16 sigma-bonds. The ability of the doubly hinged ZnPOR-16 sigma-ZnPOR scaffold to adopt cavity-shaped conformations was indicated by semiempirical AM1 calculations of these conformationally flexible bis-porphyrin scaffolds. (C) 2008 Elsevier Ltd. All rights reserved.