The total syntheses of cybrodol (1), isocybrodol (2), cybrodal (3), cybrodic acid (4), and trisnorcybrodolide (5), starting from 2-bromomesitylene (6) are described. The route involves oxidation of the 5-methyl group of 6 by means of chromyl acetate, addition of the β-hydroxyethyl chain by aryllithiation and reaction with ethylene oxide, and addition of the fifth carbon substituent by aryllithiation and treatment with ethyl chloroformate to give the key intermediate, methyl 3-(2-hydroxyethyl)-6-methoxymethyl-2,4-dimethylbenzoate (18d). The latter was transformed into trisnorcybrodolide (5), and further elaborated via the corresponding aldehyde 21 into the remaining cybrodins.
The isolation and structure determination of the "cybrodins", a new group of sesquiterpenoids produced by a new strain of the bird's nest fungus Cyathus bulleri, is reported. Cybrodol (3), isocybrodol (4), cybrodal (5), trisnorcybrodolide (6), and cybrodic acid (7) may be classified as seco-illudalane sesquiterpenes. The evidence leading to the structural assignments is presented, along with chemical correlations among the cybrodins. The possible mode of biogenesis is discussed. Pterosin-C (13), a known norsesquiterpene, and 3-methyllumichrome (17) were also isolated. Small quantities of a new sesquiterpenoid, broderol, believed to possess structure 21, were obtained on two occasions.