Concise Synthesis of (±)-Rhinacanthin A, Dehydro α-Lapachone, and β-Lapachone, and Pyranonaphthoquinone Derivatives

A concise synthesis of (+/-)-rhinacanthin A is achieved in two steps by epoxidation of dehydro-alpha-lapachone, followed by chemo- and regioselective reduction. Dehydro-alpha-lapachone was also synthesized in two steps starting from 4-methoxy-1-naphthol by ethylenediamine diaetate (EDDA)-catalyzed benzopyran formation and a CAN-mediated oxidation reaction. beta-Lapachone was synthesized in three steps from 4-methoxy-1-naphthol by benzopyran formation, catalytic hydrogenation, and Jones oxidation. As additional reactions, synthesis of pyranonaphthoquinone derivatives with the pyranokunthone B skeleton has been achieved in a single step from readily available 2-hydroxy-6-methoxy1,4-naphthoquinone and 2-hydroxy-7-methoxy-1,4-naphthoquinone.