Pyrrole‐Modified Subporphyrins Bearing a Sulfur‐Containing Heterocyclic Unit

Abstract

As new pyrrole‐modified subporphyrins (PMSubPs) bearing a sulfur‐containing heterocyclic unit, dithiazolosubporphyrin 5, dithiazinosubchlorin 6, and oxodithiazinosubchlorin 7 were synthesized from α‐fluorosubchlorophin 2 via α’‐selective nitration with Cu(NO3)2 followed by double SN2 reaction with methyl 3‐mercaptopropionate as a key step. Oxidation of 5 with H2O2 in the presence of a tungsten catalyst afforded S,S‐dioxodithiazolosubporphyrin 8 and nitration of 5 with Cu(NO3)2·3H2O gave β‐nitrodithiazolosubporphyrin 9 or β,β‐dinitrodithiazolosubporphyrins 10a and 10b depending on reaction conditions. In the solid‐states, the dithiazole units in 8 and 9 are almost planar but the dithiazine unit in 6 and the 2‐oxodithiazine unit in 7 are non‐planar. Compared to subchlorophin 1, dithiazolosubporphyrin 5 possesses a significantly reduced diatropic ring current and a greatly perturbed absorption spectrum showing largely split Q‐like bands at 501 and 660 nm. These perturbed electronic and optical properties of 5 are considerably attenuated in 6 and 7 and completely vanished in 8, suggesting the importance of disulfide bond for the large perturbation.