Sulphur extrusion reactions applied to the synthesis of corroles and related systems

Abstract

The preparation of 21,24-dioxacorroles by condensation of dipyrromethane-5,5′-dicarboxylic acids with 5,5′-diformyl-2,2′-bifuryl or bis-(5-formyl-2-furyl) sulphide is described. It is suggested that the latter reaction involves a non-aromatic meso-thia-macrocyclic intermediate which loses sulphur by a disrotatory cyclisation to a thiiran intermediate followed by cheletropic loss of sulphur. Some evidence for this proposal is provided by the preparation of meso-thiaphlorins and a study of their thermolyses to give corroles. Further examples of sulphur extrusion from a meso-dithiaphlorin, to give a meso-thiacorrole, are given and rate enhancements, in the sulphur extrusion process, which are observed in metal complexes are discussed. Some electrophilic deuteriation studies on the 21,24-dioxa-corroles are reported.