ULTRASOUND-PROMOTED CYCLOADDITIONS IN THE SYNTHESIS OF SALVIA-MILTIORRHIZA ABIETANOID ORTHO-QUINONES

The ultrasound-promoted Diels-Alder reaction of 3-methyl-4,5-benzofurandione with appropriately substituted vinylcyclohexenes has led to the synthesis of tanshinone IIA, nortanshinone, tanshindiol B, methyl tanshinonate, and tanshinone IIB, biologically active metabolites of the Chinese traditional medicine, Dan Shen, prepared from the roots of Salvia miltiorrhiza Bunge. Methyltanshinquinone, the dihydro derivative of the natural product, methylenetanshinquinone, was similarly prepared. The effect of ultrasound in promoting the cycloadditions parallels that of high pressure and improved the regioselectivity in favor of the natural isomers. © 1990, American Chemical Society. All rights reserved.