Cyathane diterpenes

The metal-catalyzed [5 + 2]-cycloaddition of tethered VCPs and 7r-systems has been applied to the total syntheses of (-l-)-dictamnol,52 (+)-aphanomol l,53 and tremulenolide A.54 The tricyclic core of cyathane diterpenes such as (-l-)-allocyathin B25S and the tricyclic carbon skeleton of polyhydroazulenes such as dolatriol56 were also synthesized... 

The [5 + 2] cycloaddition was used in a synthesis of core stmcture of the cyathane diterpenes 11.146, tricyclic compounds that promote nerve growth factor (Scheme 11.50). The synthetic strategy revolved around using the cycloaddition of vinyl cyclopropane 11.147 to create the six- and seven-membered rings in a single step. 

The stmctural complexity and biological activity of the cyathane family of diterpenes has stimulated considerable interest from synthetic chemists, as reflected in the number and diversity of approaches reported thus far [42]. Our own strategy for cyathane synthesis is based on a rhodium-catalyzed [5+2] cycloaddition. The precursor for this reaction was fashioned ultimately from commercially available and inexpensive (S)-(-)-limonene. Treatment of the ketone 139 with 5 mol% [RhCl(CO)2]2 in 1,2-dichloro-ethane gave cycloadduct 140 (Scheme 13.14) in 90% yield and in analytically pure form after simple filtration through a plug of neutral alumina [43]. 

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