meso-Tetraaryl-7,8-diol-21,23-dithiachlorins and their pyrrole-modified derivatives: a spectroscopic comparison to their aza-analogues

Osmium tetraoxide-mediated dihydroxylation of meso-tetraaryl-21,23-dithiaporphyrins generates the corresponding meso-tetraaryl-7,8-dihydroxy-21,23-dithiachlorins and meso-tetraaryl-7,8,17,18-tetrahydroxy-21,23-dithiabacteriochlorins. Oxidative diol cleavage reactions of the meso-tetraaryldithia-7,8-dihydroxychlorin generate, depending on the conditions chosen, the corresponding meso-tetraaryldithia-7-oxa-8-oxo-21,23-dithiaporphyrin (dithiaporpholactone) or meso-tetraaryl-7,8-ethoxy-7a-oxa-7a-homo-21,23-dithiaporphyrin (morpholinodithiachlorin), respectively. The UV–vis spectra of the heterochlorins and pyrrole-modified dithiaporphyrins are compared to those of the corresponding all-aza homologues. In general, the trends which distinguish the spectra of dithiaporphyrins from those of all-azaporphyrins are preserved. Thus, the spectra of the dioldithiachlorins tetraoldithiabacteriochlorins are chlorin- and bacteriochlorin-like and bathochromically shifted as compared to the all-azaanalogues, respectively. Also, the dithiaporpholactone spectrum is porphyrin-like. However, the UV–vis spectrum of the morpholinodithiachlorin is uncharacteristic for a morpholinochlorin spectrum. The derivatives described are the first examples of heterochlorins and pyrrole-modified dithiaporphyrins.