Reactivity of the double bond in coumarins and related α-β unsaturated carbonyl compounds Part IV. Action of bromine on coumaric acids

Abstract

By the action of bromine on coumaric, 4-methylcoumaric and 5-nitrocoumaric acids in boiling glacial acetic acid solution 3:6:8-tribromocoumarin, 3:6:8-tribromo-7-methylcoumarin and 3:8-dibromo-6-nitrocoumarin have been obtained in good yield. The primary products are the dibromides of the bromo-compounds produced by the addition at the double bond, subsequent substitution in the nucleus and final ring closure. Hydrogen bromide gets slowly removed during the boiling and during the subsequent crystallisations so as to yield the above-mentioned bromocoumarins. The best method for this however is to use cold alcoholic potash. Small quantities of the lower bromination products are also produced as by-products.