α-Sulfenylation between 4-Hydroxydithiocoumarin and 1,3-Dicarbonyl Compounds: A Key Precursor for the Synthesis of New Pyrazole Derivatives

Abstract

AbstractAn efficient synthetic protocol for the α-sulfenylation of 1,3-dicarbonyl compounds is reported through a cross dehydrogenative coupling reaction with 4-hydroxydithiocoumarins in the presence of 10 mol% KI and 1 equiv. TBHP in toluene under reflux conditions. Some of the products are utilized for the synthesis of substituted new pyrazole derivatives on reaction with phenylhydrazine in ethanol at room temperature. In addition, α-benzylation is also achieved on treatment with benzyl bromide using K2CO3/CH3CN under mild conditions. The salient features of the present protocol are good yields, mild reaction conditions, shorter reaction time, no byproducts were formed (sulfoxide/sulfone), and no deacylation occurs during the process. In the present protocol, 4-hydroxydithiocoumarin is converted into a suitable electrophile through a radical substitution pathway, which undergoes ultimately C–S bond formation with 1,3-dicarbonyl compounds by a nucleophilic substitution reaction.