A regioselective and sustainable approach for the synthesis of substituted thieno[2,3-b]chromen-4-ones with pendant imine groups via a base-promoted multicomponent reaction†

A simple and mild route for the synthesis of substituted thieno[2,3-b]chromen-4-one derivatives with pendant imine groups is reported via a one-pot three-component reaction using 4-hydroxythiocoumarin, salicylaldehyde/aryl aldehyde and trans-β-nitrostyrene. The reaction proceeds through the Michael addition of 4-hydroxythiocoumarin to trans-β-nitrostyrene, followed by a sequence of transformations involving intramolecular cyclization via nucleophilic attack, an unprecedented conversion of oxime to amine through a unique disproportionation reaction without requiring any additional reagents, and Schiff base formation with salicylaldehyde/aryl aldehyde, yielding the desired product. The process is highly regioselective, enabling the simultaneous formation of one C–C, one C–S, and two C–N bonds in a single step, offering an efficient and mild synthetic route to complex heterocyclic structures.