Photochemical Synthesis. Conversion of o-Vinylthioanilides to Quinolines

Article abstract of DOI:10.1021/jo01297a001

Quinoline derivatives are formed in fair to good yields when acetonitrile solutions of o-vinylthioanilides are irradiated with Pyrex-filtered light.The transformation is a singlet reaction and involves intramolecular cycloaddition of the thioamide, yielding unstable thietanes, as the initial step.In the case of o-(1-trans-propenyl)thioacetanilide (2a) the corresponding thietane has been detected by 1H NMR spectroscopy by irradiating a toluene solution of the compound at -78 deg C.The quantum yield of quinoline formation from 2a appeared to be solvent dependent.Concomitant with quinoline formation, triplet cis-trans isomerization of the vinyl moiety takes place.In the case of 2a the quantum yield for trans -> cis isomerization is 0.506.A variable-temperature 1H NMR study of 2,3-dimethylquinoline in toluene solution has also been performed.For the 2,3-dimethylquinoline-toluene complex the enthalpy and entropy of formation are -1.03 +/- 0.10 kcal/mol and -3.7 +/- 0.2 gibbs/mol, respectively.