Synthesis of Benzo[1,4]thiazines via Ring Expansion of 2-Aminobenzothiazoles with Terminal Alkynes Under Metal–Organic Framework Catalysis

Abstract

Copper–organic framework Cu–MOF-74 was synthesized, and consequently utilized as a heterogeneous catalyst for the synthesis of benzo[1,4]thiazines via ring expansion of 2-aminobenzothiazoles with terminal alkynes. Different from previous works, the reaction proceeded readily in the presence of lower catalyst concentration, at lower temperature, and under ligand-free conditions. The combination of 5 mol% framework catalyst, 20 mol% Cs2CO3, and 3 equivalents of di-tert-butyl peroxide led to high yields of benzo[1,4]thiazines. This copper-based framework demonstrated higher catalytic efficiency than a series of MOF-based heterogeneous catalysts and traditional homogeneous catalysts. In this system, the donation of soluble active copper species to the formation of benzo[1,4]thiazines was trivial. The copper–organic framework was reutilized without a remarkable decline in catalytic efficiency. To our best knowledge, this ring expansion reaction was not previously performed with a recyclable catalyst.