We disclose a green, practical, efficient and scalable synthetic route to diverse pyrrole fused N heterocycles via an inexpensive and readily available single electron reductant. The key question is whether a one-pot, tandem chemoselective reductive cyclization could be developed expanding the scope of the use of green reductant described herein to the preparation of pyrrolo[1,2-a] quinoxalines, 5H-benzo[e]pyrrolo[1,2-a] [1,4] diazepines, and pyrrolo[1,2-a] quinoxaline-4(5H)-ones that are present in natural products and pharmaceuticals having a broad range of biological activities. The reduction of nitro group to the corresponding amino group is a vital organic transformation practised both in academia and industry for the preparation of valuable compounds that are used as, or for developing pharmaceuticals, agrochemicals etc. As nitro compounds are abundant, cheap and readily available feedstock, this reduction is widely used to prepare amines and derivatives thereof. However, the classical reduction of aromatic nitro compounds to the corresponding aromatic amines accompanied largely by metal salts in the presence of an acid is a method of choice especially in industry causing production of tremendous waste. The practical disadvantages of these reactions include sluggish reaction, expensive steam distillation, tedious work up, long reaction time, and incompatibility of the acid-sensitive functional groups. In addition, chemoselective reduction of a nitro group especially in the presence of carbonyl functionality presented a significant challenge, albeit limited to a few successful reports. Therefore, development of a practical method avoiding accompanied limitations (vide supra), mild and greener nitro group reduction is highly desirable. Owing to the disadvantages discussed we have tried to demonstrate a protocol that features an efficient one-pot, tandem reductive cyclization performed at room temperature, very short reaction time (1 h), no aqueous work up, purification by crystallization, isolated yields generally &gt;90%. The scalability of the developed protocol is further demonstrated by a gram-scale synthesis.

Sulfoxylate radical anion mediated one-pot, tandem chemoselective reductive cyclization to the synthesis of pyrrole fused N-heterocycles

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