Transition Metal Catalyst Free and Single-Step Synthesis of Significant Thiosemicarbazones via Oxidative Coupling Strategy

The efficacy and selectivity of the transition metal-free catalysis have been emphasized in constructing thiosemicarbazone derivatives from the dehydrogenative coupling of alcohols and thiosemicarbazides under aerobic conditions. A broad spectrum of thiosemicarbazones was obtained in good-to-excellent yields up to 90 %, with water as the only by-product. The catalytic synthesis worked in an atom-economical fashion in the absence of any oxidant with only 1 mmol of the base loading per mmol of the substrates. Further, the impact of different temperatures, solvents, bases, and base loading of the coupling reaction has been explored. A probable pathway that involves the generation of an aldehyde intermediate to thiosemicarbazones, which releases only water has been proposed.