Snehlata Yadav

Visible light induced, catalyst free, convenient synthesis of chromene nucleus and its derivatives using water–ethanol mixture as a solvent

A highly efficient, green, eco-friendly, one pot protocol has been demonstrated for the synthesis of 2-imino-2H-chromene-3-carbonitrile (3), 2-aminochromene (4) and chromeno(2,3-b)pyridines (5). The synthesis of the chromene nucleus has been carried out under visible light irradiation in a water–ethanol mixture at room temperature using salicylaldehyde and malononitrile in different proportions. The adopted method shows significant advantages such as mild and clean reaction conditions, eco-friendly procedures, absence of catalysts and a short reaction time. This protocol involves the use of CFL as the visible light source and shows high selectivity in the presence of a mixture of ethanol and water. The reaction proceeds with good to excellent yield.

Visible light triggered, catalyst free approach for the synthesis of thiazoles and imidazo[2,1-b]thiazoles in EtOH : H2O green medium

The development of a visible light promoted, mild and greener approach for the synthesis of highly functionalized thiazoles and imidazo[2,1-b]thiazoles under photochemical activation in EtOH : H2O green medium is demonstrated. The characteristic feature of the present protocol is the utilization of visible light (an omnipresent, nontoxic, environmentally benign and inexpensive reagent) to form C–S and C–N bonds and circumvent the use of catalysts or photosensitizers. The reported protocol is the first example of visible light promoted synthesis of thiazoles and imidazo[2,1-b]thiazoles with various attractive features like being catalyst free, eco-efficient and possessing cost effectiveness, short reaction time, excellent yields and sustainability to fulfill the parameters of green chemistry.

Oxidative organophotoredox catalysis: a regioselective synthesis of 2-nitro substituted imidazopyridines and 3-substituted indoles, initiated by visible light

We have established a mild, metal-free, one pot, visible light-catalyzed procedure for a highly regioselective synthesis of 2-nitro-3-arylimidazo [1,2-a] pyridines via nitroalkene and 2-aminopyridine under an open atmosphere involving a photoredox catalyst, Eosin Y, which is an inexpensive organic dye that has been employed as a photo sensitizer in the conversion. This protocol serves as an example of green chemistry, due to the fact that molecular oxygen and visible light have been utilized effectively for the transformation. The procedure involves intramolecular C–N heterocyclization, followed by aerobic oxidation and C–C bond formation at room temperature. This green protocol has also been successfully extended to the regioselective synthesis of 3-substituted indoles via indole and nitroalkene by a free radical pathway.

β-Cyclodextrin: A Biomimetic Catalyst used for the Synthesis of 4H-chromene-3-carbonitrile and Tetrahydro-1H-xanthen-1-one Derivatives

An efficient and facile protocol has been documented for the synthesis of 4H-chromene and xanthen-1-one derivatives via a three component one pot reaction of salicyladehyde, malononitrile/dimedone and indole utilizing biomimetic catalyst. Affiliation between biomimetic and organocatalyst exhibits a versatile and high catalytic activity emerging to be a sustainable alternative to other catalysts. The significant features of this protocol are compatibility with various types of indole and active-methylene compound, accomplishment of high yields, cleaner reaction condition and avoidance of the use of costly catalysts. Recyclability of β-cyclodextrin a “biomimetic catalyst” is a significant feature of this protocol.Graphical Abstract

A green and clean pathway: one pot, multicomponent, and visible light assisted synthesis of pyrano[2,3-c]pyrazoles under catalyst-free and solvent-free conditions

A mild, eco-efficient and metal-free synthetic protocol for the production of biologically significant scaffold dihydropyrano[2,3-c]pyrazoles via reaction between ethylacetoacetate (1), hydrazine hydrate (2), aromatic aldehydes (3) and malononitrile (4) as reactants and exploiting visible light as a reaction promoter has been developed. Cost effectiveness, nontoxicity, being catalyst-free and solvent-free, the easy-availability of reactants and non-involvement of specific glasswares and a photo-reactor system are some of the significant traits of the present protocol. The scope of the current methodology is further extended by using diethyl acetylene dicarboxylate (6) as a reactant in place of ethylacetoacetate.

A Peerless Aproach: Organophotoredox/Cu(I) Catalyzed, Regioselective, Visible Light Facilitated, Click Synthesis of 1,2,3-Triazoles via Azide–Alkyne [3 + 2] Cycloaddition

A visible light initiated, mild, one pot, multicomponent copper catalyzed azide alkyne [3 + 2] cycloaddition in the presence of organo photoredox catalyst Eosin Y using EtOH:H2O as reaction medium for the synthesis of substituted 1,2,3-triazoles is reported. A facile regioselective ring opening of epoxides followed by 1, 3 dipolar cycloaddition with alkynes under CFL (Compact fluorescent light) irradiation as a source of visible light resulting in the formation of C–N bonds, is the characteristic feature of the present strategy. Scope of the present protocol is further extended by using benzyl chloride in place of epoxide.Graphical Abstract

A visible light-initiated, one-pot, multi-component synthesis of 2-amino-4-(5-hydroxy-3-methyl-1 H -pyrazol-4-yl)-4 H- chromene-3-carbonitrile derivatives under solvent- and catalyst-free conditions

The reported work allows an accessible construction of 4-substituted 2-amino-4H-chromenes starting from ethylacetoacetate (1), hydrazine hydrate (2), salicylaldehyde (3) and malononitrile (4) in the presence of visible light. The salient features of the proposed route is being a solvent-free and catalyst-free, one-pot, multi-component reaction with high to excellent yield. Visible light mediation makes the reaction mechanistically interesting and adds to the green credentials of the reaction.Graphical Abstract