Total synthesis of four naturally occurring 2-azaanthraquinone antibiotics, 6-deoxy-8-methylbostrycoidin, 6-deoxybostrycoidin, 7-O-demethyl-6-deoxybostrycoidin and scorpinone

A total synthesis of four natural 2-azaanthraquinones, 6-deoxy-8-methylbostrycoidin, 6-deoxybostrycoidin, 7-O-demethyl-6-deoxybostrycoidin and scorpinone was accomplished using an optimized procedure for 2-azaanthraquinone synthesis, involving a [4+2]-cycloaddition protocol, of a polyoxygenated diene with a suitably functionalized benzoquinone, acetonylation with pyridinium ylids, cyclisation with ammonia and O-demethylation with boron(III) bromide. 2-Azaanthraquinones are rarely found in nature and reveal interesting physiological properties.