Unexpected formation of 2-methyl-1H-naphtho [2, 3-d] imidazole via decarboxylation governed mechanistic pathway

Present work is the outcome of the synthetic strategy for the naphthalene analogue of benzimidazole dimer, 2-methyl-1H-naphtho [2, 3-d] imidazole. It was found that 1H-naphtho [2, 3-d] imidazol-2-yl) methane (2b') was formed instead of respective dimer. Herein, we have reported two synthetic ways for 2b', first conventional refluxing method with 70 % yield and second by using synthesis reactor with 75 % yield. Both the way of synthesis involves the reaction of 2,3- diamino naphthalene and diethyl malonate in acidic medium. This example belongs to C-2(sp2)-C-1(sp3) type decarboxylation. To the best of our knowledge, it is the first-time synthesis of the 2b' has been reported via decarboxylation pathway along with crystal structure and DFT studies. Most probable mechanisms for both the compounds have been proposed based on the energy profile diagram and thermodynamic data obtained by DFT calculations [B3LYP/6-311++G (d,p)] in gas phase. Absorption responses showed potential of the naphthaimidazole based molecule 2b' as a pH and metal ion sensor of various hazardous metals such as As3+, Cr3+, Hg2+,Cd2+, Pb2+.