Synthesis of 4-alkylidene-3, 5, 5-trimethylcyclohex-2-enones 7 has been achieved utilising 1, 4-conjugate dehydrobromination of allylic bromides 5 as a key step. This chemical transformation is applied to the synthesis of degradation products of carotenoids: megastigmatrienones 7e/1–4, 4-methylene-3, 5, 5-trimethylcyclo