An efficient chemo-enzymatic approach towards variably functionalized benzotropolones

An efficient three-step synthesis for benzotropolones via three catalytic steps is presented. Pyrogallol phenones are formed in the first step starting from pyrogallol, which is acylated by proton-catalysis. Catalytic hydrogenation of the phenones yields the corresponding alkylated pyrogallyl dervatives. In the final enzyme-catalyzed step the pyrogallol derivatives are annulated to form the benzotropolone cores. An alternative pathway via the Pechmann reaction is also presented. The combination of the three catalytic steps gives access to a wide range of benzotropolone congeners.