Naturally occurring quinones. Part XI. The tanshinones

Abstract

The structures of the pigments tanshinone I, tanshinone IIA, and cryptotanshinone, from the root of Salvia miltiorrhiza, have been established by synthesis. The key step is the conversion of a 2-hydroxy-1,4-quinone into a dihydrofurano-o-quinone by reaction with a β-chloropropionyl peroxide. 8-Methyl-3-phenanthrol was converted into 3-hydroxy-8-methyl-1,4-phenanthraquinone which gave 2,3,4,5-tetrahydro-3,9-dimethylphenanthra[1,2-b]-furan-4,5-dione by reaction with β-chloro-α-methylpropionyl peroxide. Subsequent dehydrogenation with dichlorodicyanobenzoquinone yielded tanshinone l (4,5-dihydro-3,9-dimethylphenanthra[1,2-b]furan-4,5-dione). By the same route 5,6,7,8-tetrahydro-8,8-dimethyl-3-phenanthrol was converted into racemic cryptotanshinone (2,3,4,5,6,7,8,9-octahydro-3,9,9-trimethylphenanthra[1,2-b]furan-4,5-dione) which gave tanshinone IIA on dehydrogenation. It is deduced from spectroscopic data that tanshinone IIB is 4,5,6,7,8,9-hexahydro-9-hydroxymethyl-3,9-dimethylphenanthra[1,2-b]furan-4,5-dione.