FeF3-mediated tandem annulation: a highly efficient one-pot synthesis of functionalized N-methyl-3-nitro-4H-pyrimido [2, 1-b] [1,3] benzothiazole-2-amine derivatives under neat conditions

A straight forward and highly efficient one-pot annulation of 2-aminobenzothiazole, (E)-N-methyl-1-(methylthio)-2-nitroethenamine, and aldehydes in the presence of FeF3 is described. Diverse functionalized N-methyl-3-nitro-4H-pyrimido [2, 1-b] [1, 3] benzothiazole-2-amine derivatives were obtained with excellent yields under neat conditions. The one-pot annulation was shown to be valid for the synthesis of highly functionalized derivatives of N-methyl-3-nitro-4H-pyrimido [2, 1-b] [1, 3] benzothiazole-2-amine from readily accessible substrates. The catalyst FeF3 can be easily recovered and reused for the next reaction without any effects on the yields of the products. This green protocol provides structurally complex, biologically important N-methyl-3-nitro-4H-pyrimido [2, 1-b] [1, 3] benzothiazole-2-amine in a one-pot operation.