Table of Contents
Organic Chemistry International
Volume 2011 (2011), Article ID 394619, 6 pages
http://dx.doi.org/10.1155/2011/394619
Research Article

Microwave-Assisted Improved Regioselective Synthesis of 12H-Benzopyrano[3,2-c][1]benzopyran-5-ones by Radical Cyclisation

Department of Chemistry, Hooghly Mohsin College, P.O. Chinsurah, Dist. Hooghly, West Bengal 712101, India

Received 25 April 2011; Revised 15 July 2011; Accepted 16 July 2011

Academic Editor: Ashraf Aly Shehata

Copyright © 2011 Pradipta Kumar Basu and Amrita Ghosh. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Two new effective methodologies have been adopted for the preparation of 4-(2-bromobenzyloxy)benzopyran-7-ones 3(a–h). In the first methodology, 4-hydroxy[1]benzopyran-2-ones 1(a–d) was alkylated with 2-bromobenzyl bromide 2a or 2-bromo-5-methoxy benzyl bromide 2b under phase transfer catalysis condition using lithium hydroxide/tetrabutyl ammonium bromide in N,N-dimethylformamide at 40–50°C and in the second method the microwave irradiation protocol has been exploited by simply mixing of 4-hydroxy[1]benzopyran-2-ones 1(a–d) with 25% excess of 2-bromobenzyl bromide 2a or 2-bromo-5-methoxy benzyl bromide 2b. A catalytic amount of TBAB and potassium carbonate were added and irradiated in an open Erlenmeyer flask in a microwave oven for 4–10 min. The tributyltin-hydride-mediated radical cyclisation of 3(a–h) was carried out under microwave irradiation to generate 12H-benzopyrano[3,2-c][1]benzopyran-5-ones 4(a–h) in 78–88% yield and in this technique yields were significantly improved and reaction time was shortened compared to the previously reported conventional radical cyclisation method.