CARBACHLORINS

Acid-catalyzed 3 + 1 condensation of the aliphatic bicyclic dialdehyde 8, or the related isolated alkene 7. with tripyrrane 5 gave the first examples of carbachlorins (9 and 11) after oxidation with DDQ in refl uxing toluene. These novel dihydroporphyrinoids exhibited strong Soret bands in their electronic absorption spectra at 404 nm, and a moderat ely strong band al 650 nm. The latter feature closely resembles the el ectronic spectra of true tetrapyrrolic chlorins. The H-1 NMR spectra f or 9 and 11 showed a strong diamagnetic ring current consistent with 1 8-pi-electron delocalization over the macrocycle, Addition of TFA gave rise to the related monocations 12, and these species showed slightly enhanced diatropic ring currents, shown by significant upfield and do wnfield shifts for the internal and external protons, respectively The UV/Vis spectra of 12 also had many similarities to those previously r eported fur tetrapyrrolic chlorin monocations, including the presence of a split Soret band. Carbachlorins 9 and 11, however, differed from the related tetrapyrrolic structures by resisting oxidation to porphyr in.