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We herein disclose a dual synthetic approach involving electrochemical and mechanochemical strategies for diversely functionalized 3-nitro-2-aryl-immidazo[1,2- a ]pyridines. Both methods offer a practical and straightforward alternative route for accessing this important class of biologically promising nitrogen-containing heterocycles. Significant advantages of the newly developed methods include mild and energy-efficient reaction conditions, avoidance of transition metal catalysts, external heating and additional oxidants, shorter reaction times, good to excellent yields, broad substrate scope, gram-scale applicability, operational simplicity, and eco-friendliness. Furthermore, a synthetic application was extended by successfully reducing synthesized 3-nitro-2-aryl-immidazo[1,2- a ]pyridines to their corresponding amino derivatives.

We herein report the exploration of an electrosynthetic strategy as a highly efficient and straightforward alternative protocol for accessing diversely substituted and biologically promising alkyl 2-hydroxy-3-oxo-2,3-dihydrobenzofuran-2-carboxylates through an electrorearranged difunctionalization of 4-hydroxycoumarins, involving the singlet oxygen insertion from molecular oxygen, at ambient temperature. The present method is notably more advantageous than the previously reported photochemical conversion regarding yields and reaction times, substrate scope and functional group tolerability, operational simplicity, and scalability.

A straightforward and efficient electrochemical method for regioselective C( sp 2 )-H selenylation and sulfenylation of substituted 2-amino-1,4-naphthoquinones has been unearthed. This oxidative cross -coupling reaction avoids using transition metal catalysts, oxidants, and high temperatures. The other notable advantages of this protocol are the tolerance of diverse functional groups, mild reaction conditions at ambient temperature, energy efficiency, good to excellent yields, short reaction times (in minutes), gram-scale applicability, and eco-friendliness.

A photochemical method for the synthesis of functionalized dihydrofuro[3,2- c ]chromenones via intramolecular C sp 3 -H cross -dehydrogenative oxygenation within a warfarin framework has been unearthed. Advantages of this protocol include abundant sunlight or low-energy visible light as the energy source, mild reaction conditions, and avoidance of metal catalysts.

A visible light (white light-emitting diode/direct sunlight)-driven photochemical synthesis of a new series of biologically interesting 3-(alkyl/benzylthio)-4-hydroxy-2 H -chromen-2-ones has been achieved through a cross-dehydrogenative C 3 -H sulfenylation of 4-hydroxycoumarins with thiols at ambient temperature in the presence of rose bengal in acetonitrile under an oxygen atmosphere. The notable features of this newly developed method are mild reaction conditions, energy efficiency, metal-free synthesis, good to excellent yields, use of low-cost materials, and eco-friendliness.

Development of a visible light-induced and singlet oxygen-mediated green protocol has been accomplished for the first time for the photochemical transformation of 4-hydroxy-α-benzopyrones to a new series of biorelevant 2-hydroxy-3-oxo-2,3-dihydrobenzofuran-2-carboxamides and 2-hydroxy-3-oxo-2,3-dihydrobenzofuran-2-carboxylates using rose bengal as a triplet photosensitizer at ambient temperature. Metal-free one-pot synthesis, broader substrate scope, good-to-excellent yields, use of cost-effective and eco-friendly starting materials and photosensitizer, and energy efficiency are the salient features of this newly developed method.

A water-mediated and catalyst-free practical method for the synthesis of a new series of pharmaceutically interesting functionalized 5-(2-arylimidazo[1,2- a ]pyridin-3-yl)pyrimidine-2,4(1 H ,3 H )-diones has been accomplished based on a one-pot multicomponent reaction between arylglyoxal monohydrates, 2-aminopyridines/2-aminopyrimidine, and barbituric/ N , N -dimethylbarbituric acids under reflux conditions. The salient features of this protocol are avoidance of any additive/catalyst and toxic organic solvents, use of water as reaction medium, clean reaction profiles, operational simplicity, ease of product isolation/purification without the aid of tedious column chromatography, good to excellent yields, and high atom-economy and low E -factor.