The Diels-Alder reaction of 2-methoxy-5-methoxycarbonylbenzoquinone (6) with various 1-substituted isoprenes (5a-d) was studied and the 8β-substituted cis-tetrahydronapthoquinone-8αα-carboxylates (19a-d) were obtained and characterized. Some of the latter compounds are important intermediates for synthesis of the A and B rings of siccanin (3), an antifungal antibiotic.
