Microwave promoted improved regioselective synthesis of 1H,3H,6H[2]benzopyrano[4,3-d]pyrimidine-2,4-diones by radical cyclisation
作者:Pradipta Kumar Basu、Amrita Ghosh
DOI:10.1007/s13738-012-0171-7
日期:2013.2
new effective methodologies have been adopted for the preparation of 5-(2′-bromobenzyloxy)pyrimidine-2,4-diones 6(a–k). In the first methodology, 5-hydroxy uracils 4(a–f) were alkylated with 2-bromobenzyl bromide 5a or 2-bromo-5-methoxy benzyl bromide 5b under phase transfer catalysis condition using lithium hydroxide/tetrabutyl ammonium bromide in N,N-dimethylformamide at 45 °C, and in the second method
在这项工作中,采用了两种新的有效方法来制备5-(2'-溴苄氧基)嘧啶-2,4-二酮6(ak)。在第一种方法中,在相转移催化条件下,使用氢氧化锂/四丁基溴化铵在N,N中,使用2-溴苄基溴5a或2-溴-5-甲氧基苄基溴5b将5-羟基尿嘧啶4(a – f)烷基化。-二甲基甲酰胺在45°C,在第二种方法中,通过将5-羟基尿嘧啶4(a-f)与30%过量的2-溴苄基溴5a或2-溴- 5-甲氧基苄基溴5b。加入催化量的TBAB和碳酸钾,并在敞口的锥形瓶中于微波炉中辐照3–12分钟。氢化三丁基锡介导的6(ak)的自由基环化在MWI下进行,以生成1 H,3 H,6 H [2]苯并吡喃并[4,3 - d ]嘧啶-2,4-二酮7(a -k)的收率为80-89%,与以前报道的常规自由基环化方法相比,反应时间缩短了。