meso-Tetraaryl-7,8-dihydroxydithiachlorins: first examples of heterochlorins

Osmium tetraoxide-mediated dihydroxylation of meso-tetraaryldithiaporphyrins generates the corresponding meso-tetraaryldithia-7,8-dihydroxychlorins and meso-tetraaryldithia-7,8,17,18-tetrahydroxybacteriochlorins. The products are spectroscopically characterized and the substitution positions were unequivocally determined. The UV–vis of the heterochlorins and heterobacteriochlorins are chlorin- and bacteriochlorin-like, respectively. However, the chlorin spectra are surprisingly hypsochromically shifted as compared to the corresponding all-aza chlorins, whereas the bacteriochlorin is bathochromically shifted. meso-Tetraaryldithia-7,8-dihydroxychlorins are susceptible to oxidative ring-opening reactions to form the corresponding meso-tetraaryldithia-7-oxo-8-oxa-dithiaporphyrin (dithiaporpholactone). These derivatives are the first examples of heterochlorins and β-modified dithiaporphyrins.