Utilization of Dissociation Constant (pKa) Value Perspective of -CH Acid in Electrochemical Synthesis of 4H-Chromene and its Derivatives

Activation of acidic-H in C-H chemistry through imposition of proper electrode potential is a matterof concern among synthetic research community. In this study, our main aim is to get deeper insightinto the dissociation constant (pKa) value perspective of -CH acid and its utilization in electro-catalytictransformation. Herein, a platinum cathode was being used to attract a covalently bonded electronsthat exist between C and active-H of CH-acid (dimedone) toward itself i.e. cathodic part to formacidic-H and thus, form in-situ tautomeric enol form that acts as electro-generated base. Utilization ofthis notability has been accomplished by electrochemical synthesis of 4H-chromene and its derivativesby performing cathodic reduction. Due to acidic property of dimedone, cathodic platinum electrodedraw the potential switched to lower side that is being recorded through the potential-cum-galvanostatwhich facilitates the faster transfer of electrons from -CH acid to form enolate ion of dimedone thatact as electro-generated base for the reaction media which simultaneously undergoes cascade reaction(Michael addition/cyclization) on activated alkene (α-cyanocinnamonitrile derivatives). This approachoffers several advantages such as good yield, mild reaction condition, easy accessible, simple work-upprocedure and controlled potential selectivity at cathode. Use of no base is pivotal section of thismethodology. Electro-generated base is used instead of chemical toxic bases, so the present protocolis green as electrons that acts as intrinsically sole reagent for the reaction media which is renewable,hence sustainable for the safe future.