Oxidative bromination of tricyclic sesquiterpenoids (1S,3S,5R,6S,9S)-5-hydroxy-6,10,10-trimethyl-tricyclo[7.2.0.0 ^1,6]udecan-2-one and clovane-2β,9α-diol with the HBr-DMSO system

Oxidation of tricyclic sesquiterpenoids of the caryophyllene type with the HBr-DMSO system afforded α,β-unsaturated a-bromoketones. Since tricyclic derivatives, unlike simple alicyclic ketones, cannot undergo aromatization, all intermediate oxidation products can be isolated, which provide evidence that oxidation proceeds according to the following scheme: ketone→α-bromoketone→α,α-dibromoketone→α, β-unsaturated α-bromoketone.