Photoreactions of various dithioacetals and ketals using tris(p-chlorophenyl)pyrylium perchlorate as a sensitizer were studied. Irradiation (λ&>360 nm) of dichloromethane solutions containing dithioacetals or ketals and pyryliumsalt afforded the corresponding carbonyl compounds in good to excellent yields in the presence of molecular oxygen.
Methyltriphenylphosphoniumtribromide acts as an efficient mild dethioketalization reagent with high selectivity for 2-phenyl and 2-vinyl 1,3-dithiannes versus 2-alkyl 1,3-dithiannes and without any secondary brominationreaction of the investigated substrates. The reaction was also successful with trimethylphenylammonium tribromide.
The reaction of dithioacetals with 30% hydrogen peroxide in the presence of catalytic amounts of tantalum(V) and iodide ion effectively produced carbonyl compounds in high yields. Dithioacetals also can be deprotected using the niobium(V) catalyzed oxidation of iodide ion by hydrogen peroxide under mild conditions.
The reaction of dithioacetals with 30% hydrogen peroxide in the presence of catalytic amounts of iron(III) acetylacetonate and sodium iodide efficiently produced the corresponding carbonyl compounds in high yields. (C) 2013 Elsevier Ltd. All rights reserved.