A tandem approach was developed for the efficient synthesis of substituted chromeno[4,3-b]quinolines from arylamines and O-cinnamyloxy salicylaldehydes under metal-catalyst and photosensitizer-free reaction conditions. Our protocol is based on an inexpensive I2/DMSO system in which molecular iodine first acts as a Lewis acid to promote the formation of the corresponding imine bearing the alkene moiety, then, this species fulfills a second role by catalyzing the intramolecular aza-Diels-Alder cycloaddition to generate the respective tetrahydro-chromenoquinolines as an intermediates. Finally, the dual behaviour of DMSO as an oxidant and as a solvent resulted crucial at this stage, allowing the regeneration of I2 and promoting the aromatization of the tetrahydro-chromenoquinoline intermediates to yield the desired 7-aryl-6H-chromeno[4,3-b]quinolines. This protocol features by being mild, easy to perform, high step-economy (tandem process) and for providing a new access to biologically important nitrogen and oxygen containing heterocyclic molecules.
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