Photochemical cyclization of thioformanilides by chloranil. Steady-state and time-resolved studies

JUAN E. ARGÜELLO; VALENTINA, REY; GABRIELA OKSDATH-MANSILLA; LUCIANA C. SCHMIDT; ALICIA B. PEÑÉÑORY

Conferencia; 12a Conferencia Latinoamericana de Físico-Química Orgánica; 2013

The photochemical behavior of a number of thioformanilides, sensitized by triplet chloranil (CA), was investigated by nanosecond laser flash photolysis and steady-state irradiation in toluene, CH2Cl2 and MeCN. The nature of the transients detected upon 355-nm laser excitation was independent of the molecular structure of the thiocarbonyl compound but strongly affected by the solvent polarity. In particular, in CH2Cl2 the quenching process of triplet CA by N-phenylthiobenzamide was accompanied by H-transfer, with formation of the semiquinone CAH• radical. In contrast, a charge transfer process with formation of the radical anion CA•-, occurred in MeCN. In meta substituted N-phenylthiobenzamide and N-1 and 2-naphthylthiobenzamide the regiochemistry of the cyclization was studied and the radical addition of the thiil radical to the aromatic ring explored by DFT quantum chemical calculations (eqns. 2 and 3).