Photoreactivity of 2- and 3-Substituted Benzothiophene 1-Oxides in Solution

Article abstract of DOI:10.1021/jo00334a030

The photochemical behavior of various benzothiophene sulfoxides (3-methyl, 3-phenyl, 2-methyl, 2-phenyl, 2,3-dimethyl, 2-chloro, 2-bromo, 3-chloro, 3-bromo) has been studied in benzene as solvent.The bromo and chloro derivatives gave no identifiable products.The 3-methyl and 3-phenyl compounds gave three head to head anti photodimers which differ only by the stereochemistry of the S-O bond.The kinetics of the photodimerization of 3-MeBTO was studied as a function of the concentration of substrate, triplet quencher, and triplet sensitizer.A monomeric excited triplet is the proposed precursor of the hth dimer.The 2-methyl derivative led to a photoreduction giving the corresponding sulfide probably through an excited triplet.The 2-phenyl derivative gave a mixture of the photodimer hth and the corresponding sulfide.The behavior of the sulfoxides in these series is different from that of the corresponding sulfones which lead to a mixture of hth and htt dimers for the 2-substituted compounds and to the hth dimer for the 3-substituted ones.