Microwave promoted improved regioselective synthesis of 1H,3H,6H[2]benzopyrano[4,3-d]pyrimidine-2,4-diones by radical cyclisation

作者：Basu Pradipta Kumar^*; Ghosh Amrita

来源：Journal of the Iranian Chemical Society, 2013, 10(1): 55-62.

DOI：10.1007/s13738-012-0171-7

• Microwave assisted
• Radical cyclisation
• 2-Bromobenzyl bromide
• Azobisisobutyronitrile
• Tri-n-butyltin hydride

In this work, two 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 degrees C, and in the second method, the microwave irradiation (MWI) protocol has been exploited by mixing 5-hydroxy uracils 4(a-f) with 30 % excess of 2-bromobenzyl bromide 5a or 2-bromo-5-methoxy benzyl bromide 5b. A catalytic amount of TBAB and potassium carbonate was added and irradiated in an open Erlenmeyer flask in a microwave oven for 3-12 min. The tributyltin hydride-mediated radical cyclisation of 6(a-k) was carried out under MWI to generate 1H,3H,6H[2]benzopyrano[4,3-d]pyrimidine-2,4-diones 7(a-k) in 80-89 % yield, and the reaction time was shortened compared to the previously reported conventional radical cyclisation method.

• 出版日期2013-2