PHOTOCHEMICAL CYCLIZATION OF THIOFORMANILIDES BY CHLORANIL. STEADY-STATE AND TIME-RESOLVED STUDIES

ARGUELLO, JUAN E; REY, VALENTINA; GABRIELA OKSDATH MANSILLA; SCHMIDT, L. C.;; ALICIA B. PEÑÉÑORY

Foz Iguazú

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 (eqn. 1 and Figure 1). Transient absorption spectra obtained upon LFP (λ = 355 nm) of CA (1 mM), under argon: in the absence of quencher (▲) and in the presence of: 1 m M of 1 in 1,2-dichloroethane (■) and MeCN (●),Spectra recorded 2.5 μs after the laser pulse. 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).