Angucyclinones Related to Ochromycinone. IV* The Structures and Reactions of Unusual Diels-Alder Adducts Formed from Maleic Anhydride and Racemic 5,5-Dimethyl-3-vinylcyclohex-2-en-1-ol

The Diels–Alder reaction between maleic anhydride and racemic 5,5-dimethyl-3-vinylcyclohex-2-en-1-ol gives two racemic diastereomers, the major product (2a,S,3R,8aS,8bR)-7,7-dimethyl-2-oxo-2a,3,4,6,7,8,8a,8b-octahydro-2H-benzo[cd]isobenzofuran-3-carboxylic acid (63% yield), and the minor product (2aR,3S,8aS,8bS)-7,7-dimethyl-2-oxo-2a,3,4,6,7,8,8a,8b-octahydro-2H-benzo[cd]isobenzofuran-3-carboxylic acid (9%). Epoxidation of the major product gives racemic (1aS,3R,3aS,5aR,8aS,8bR)-7,7-dimethyl-4 oxoperhydro-benzo[cd]oxireno[2,3-e]isobenzofuran-3-carboxylic acid in 81% yield, while opening of the epoxide ring gave the trans diol (2aS,3R,5S,5aR,8aR,8bR)-5,5a-dihydroxy-7,7-dimethyl-2-oxoperhydrobenzo[cd]isobenzofuran-3-carboxylic acid in 58% yield. Treatment of the major Diels–Alder product with osmium tetraoxide gave the cis diol (2aS,3R,5S,5aR,8aS,8bR)-5,5a-dihydroxy-7,7-dimethyl-2-oxoperhydrobenzo[cd]isobenzofuran-3-carboxylic acid in 86% yield. The structures of four products were confirmed by X-ray and n.m.r. methods. None of the products exhibit anticancer activity.