Dioxane dibromide mediated bromination of substituted coumarins under solvent-free conditions

• Subrata Kumar Chaudhuri,
• Sanchita Roy and
• Sanjay Bhar

Beilstein J. Org. Chem. 2012, 8, 323–329, doi:10.3762/bjoc.8.35

• of the substituents on the outcome of the reaction have been rationalized with a proposed mechanism. Keywords: coumarins; solvent-free reaction; substituents; vinylic bromination; Introduction Brominated coumarins have immense synthetic, biological and industrial importance due to their occurance

• , representing two ortho protons, which were bound to be due to aromatic hydrogens at C6 and C5, respectively. Obviously C8 carried the second bromine atom in 2bb. In 1d, with an alkyl substituent at C4, vinylic bromination occurred at C3 (Table 1, entry 5). This was supported from 1H NMR data in which the

• in 1e and 1f, vinylic bromination occurred regioselectively to furnish 2e and 2f in high yield without further bromination at C6 and C8, when a stoichiometric amount of DD was used (Table 1, entries 6 and 7). Interestingly, 7-(allyloxy)coumarin (1g) underwent chemoselective addition of bromine across