Synthesis of 4,7‐Dihydroxyperhydroisobenzofuran‐1‐one and Comparison with Zwergal's Structure of “garlicin”

The Diels‐Alder reaction of 2‐(benzoyloxy)furan (2) with maleic anhydride leads to the adduct 3 which, on hydrogenation, affords the exo anhydride 4a (71%) and endo anhydride 4b (2.4%). The regioselective reduction of 4a and 4b with NaBH₄ leads to the lactones 5a and 5b, respectively. Base‐catalyzed cleavage of 5a gives the keto lactone 6 or dimethyl acetal 7, depending on the reaction conditions. Catalytic hydrogenation of keto lactone 6 results in the diastereoselective formation of the title compound 8a which has been converted into the acetate 8b and trifluoroacetate 8c. The structure and properties of the dihydroxylactone 8a are discussed in comparison with garlic compound “garlicin”.