Cycloshikonin and Its Derivatives. A Synthetic Route of Shikonin

Article abstract of DOI:10.1021/jo00384a011

Intramolecular cyclizations of 5,8-dihydroxy-2-(1,4-dihydroxy-4-methylpentyl)-1,4-naphthoquinone (4) and 2-(1-hydroxy-4-methyl-4-pentenyl)-1,4,5,8-tetramethoxynaphthalene (9) with p-toluenesulfonic acid gave 5,8-dihydroxy-2-(5,5-dimethyl-2-tetrahydrofuranyl)-1,4-naphthoquinone (2), and 2-(5,5-dimethyl-2-tetrahydrofuranyl)-1,4,5,8-tetramethoxynaphthalene (6), respectively.Demethylation of 6 with CAN and AgO-40percent HNO3 gave 2.Ring-opening of 2 in acetic anhydride with p-toluenesulfonic acid was succesful to afford 5,8-diacetoxy-2-(1,4-diacetoxy-4-methylpentyl)-1,4-naphthoquinone (12), and the following hydrolysis by alkali produced 4, which could be derived to (+/-)-shikonin.