A novel reaction between benzothiazoles and diaroylacetylenes in the presence of Meldrum’s acid: ring expansion of benzothiazoles to functionalized 1,4-benzothiazines
A novel and efficient ringexpansion of benzothiazoles to functionalized 1,4-benzothiazines is described. The reactive 1:1 zwitterionic intermediates formed by addition of benzothiazoles to diaroylacetylenes were trapped with Meldrum’s acid under mild reaction conditions to produce 2-[2-hydroxy-2-aryl-2H-1,4-benzothiazin-3(4H)-yliden]-1-aryl-1-ethanones in excellent yields.
描述了新颖且有效的苯并噻唑环扩环为官能化的1,4-苯并噻嗪。在温和的反应条件下,将由苯并噻唑加成到二芳酰基乙炔中形成的反应性1:1两性离子中间体用Meldrum酸捕获,生成2- [2-羟基-2-芳基-2 H -1,4-苯并噻嗪-3(4 H) -yliden] -1-芳基-1-乙炔具有极好的收率。