Substituent-Dependent Chemoselective Synthesis of Highly Functionalized­ Benzo[h]quinolines and 4-Benzylpyrans from 2-Methyl-5-nitro-benzonitrile

Abstract

A facile, efficient and atom-economic synthesis of highly substituted benzo[h]qninolines was established by reaction of 2-methyl-5-nitrobenzonitrile with suitably functionalized 2H-pyran-2-ones under basic conditions. We observed that the presence of a thiomethyl group at the C-4 position of pyran provides 6-aryl-4-(2-cyano-4-nitrobenzyl)-2-oxo-2H-pyran-3-carbonitrile exclusively without any trace of benzo[h]quinolines. Depending on the nature of the functional group at C-4 of the pyran ring, different products were achieved. To probe the mechanism, we performed control experiments and isolated 3-(1-amino-7-nitro-3-thiophen-2-yl-naphthalen-2-yl)-3-piperidin-1-yl-acrylonitrile, which, on further treatment with base, provided the benzo[h]quinolines. The structure of one the products was characterized by single-crystal X-ray diffraction.