Reactions of 3‐isopropenyltropolones with bromine and N ‐bromosuccinimide: Formation of 8 H ‐cyclohepta[ b ]furan‐8‐one derivatives

3‐Isopropenyltropolones 1a‐c were treated with bromine in carbon tetrachloride to give 3‐methyl‐8 H ‐cyclohepta[ b ]furan‐8‐ones 2a‐c and their corresponding 7‐bromo‐substituted compounds 3a‐c , while reactions in acetic acid gave the bromo‐substituted compounds 3a‐c . On the other hand, bromination of 1a‐c with N ‐bromosuccinimide afforded 7‐bromo‐3‐(2‐bromo‐1‐methylethenyl)tropolones 5a‐c . The compound 2a was treated with bromine to give 2‐bromo‐3‐methyl‐8 H ‐cyclohepta[ b ]furan‐8‐one ( 4 ). The tropolones 5a‐c were heated in the presence of potassium carbonate to give the cyclized compounds 3a‐c .