Homocyclic aromatic compounds (HAC) represent the second most abundant class of natural and anthropogenic products. Their biodegradation is central to the global carbon cycle and the bioremediation of aromatic pollutants. A key step in this process is enzymatic dearomatization, historically attributed exclusively to oxygen-dependent mono- or dioxygenases. However, over the past three decades, a growing diversity of oxygen-independent dearomatizing reductases has been identified. These enzymes act either on partially activated di- or trihydroxybenzenes and trihydroxynaphthalenes with meta-oriented hydroxyl groups, or on coenzyme A (CoA) thioesters of carboxylated HAC, converting aromatic substrates into cyclic dienes. Class I and II benzoyl-CoA reductases catalyze Birch-like reductions via radical intermediates at metal cofactors, with low-potential electrons supplied either through ATP-dependent electron transfer (class I) or flavin-based electron bifurcation (class II), whereas 2-naphthoyl-CoA reductase appears independent of an electron-activation system..
