Dithionite-Mediated Tandem Nitro Reduction/Imine Formation/Intramolecular Cyclization for the Synthesis of Dihydro-benzothiadiazine-1,1-dioxides.

A one-pot, tandem reductive annulation of 2-nitrobenzenesulfonamides with aldehydes to the synthesis of substituted 3,4-dihydro-2 H -1,2,4-benzothiadiazine-1,1-dioxides in the presence of sodium dithionite (Na 2 S 2 O 4 ) is reported under mild conditions. The method involves in situ reduction of the nitro group followed by condensation with aldehydes to form an imine, which upon subsequent intramolecular cyclization forms the product under one-pot conditions. The protocol features use of inexpensive Na 2 S 2 O 4 as the exclusive reagent, appreciable functional group tolerance, broad substrate scope, high product yields, and scalability.