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Metal-Free Synthesis of 2‑Aminobenzothiazoles via Iodine-Catalyzed and Oxygen-Promoted Cascade Reactions of Isothiocyanatobenzenes with Amines
In
this paper, a highly efficient and sustainable synthesis of
2-aminobenzothiazoles through the cascade reactions of isothiocyanatobenzenes
with primary or secondary amines by using iodine as a catalyst and
oxygen as an oxidant is presented. Mechanistically, the formation
of the title compounds involves the in situ formation of the required
benzothiourea intermediate followed by its intramolecular cross dehydrogenative
coupling of a CÂ(sp<sup>2</sup>)–H bond and a S–H bond.
To our knowledge, this should be the first example in which 2-aminobenzothiazoles
are efficiently prepared from simple and cheap isothiocyanates and
amines under metal-free conditions by using iodine as a catalyst and
molecular oxygen as an oxidant with water as the byproduct. Compared
with literature protocols, this method eliminates the use of <i>ortho</i>-halo-substituted precursors, expensive transition-metal
catalysts, and hazardous oxidants