Sulfamic Acid: A Mild, Efficient, and Cost-Effective Catalyst for Synthesis of Indoloquinoxalines at Ambient Temperature

Abstract

A simple, cost-effective method for synthesis of indoloquinoxalines from isatin and o-phenylenediamine employing a catalytic amount of sulfamic acid at ambient temperature is reported. Moreover, the method is applicable for a variety of isatins, ninhydrin, 4-hydroxynaphthaquinone, and 1,2-diketones. The key features of the protocol include rapid reactions with good yields, simple workup procedure, and easy isolation of products.

GRAPHICAL ABSTRACT

Keywords:

• Cost-effective
• 1,2-diaminobenzene
• indoloquinoxalines
• isatins
• sulfamic acid

Notes

^a Isolated yields.

^b As catalyst is insoluble in water, extraction of reaction mixture with ethyl acetate is carried out for isolation of product.

Notes. Reaction conditions: Isatin/acenaphthoquinone/2-hydroxynaphthoquinone/ninhydrin (1 mmol), o-phenylene diamine (1 mmol), sulfamic acid (20 mol%), ethanol 10 mL; temp. = RT.

^a Isolated yields.