Phyllocladene synthesis

A total synthesis of ( )-royleanone from 5,7,8-trimethoxy-l-tetralone (123) has been described.129 The tetralone was converted into the tricyclic ketone (124), which was in turn converted into 11,12,14-trimethoxypodocarpatriene (125). Demethyla-tion and oxidation afforded the quinone (126 R = H) which was alkylated to give royleanone (126 R = Pr ). Synthetic studies in the resin acid series have led130 to the preparation of the dicarboxylic acid (127) with a cis a/b ring junction. The preparation of some tetracyclic ketones as intermediates for gibberellin synthesis has been described.131 132 The key reaction involves photolysis of a diazoketone (128) to afford the tetracyclic system (129). In a synthesis of phyllocladene from abietic acid... 

The Chemistry of the Tetracyclic Diterpenoids.—The reaction of cnt-kaur-16-ene with thallium(lli) nitrate affords cnt-kaur-16-en-15j8-ol nitrate which undergoes a ready [3,3] sigmatropic rearrangement to cnt-kaur-15-en-17-ol nitrate. The reactions of phyllocladene and of labda-8(17)-en-13-ol with sodium azide and iodine chloride have been examined. ° The synthesis of 13-hydroxylated cnt-kaur-16-ene derivatives such as steviol using an acyloin-like cyclization of keto-esters has been developed. A detailed analysis was made of the products arising from the use of sodium in liquid ammonia in this reaction. 

However, reductions of aromatic ketones over Rh or Ru in appropriate solvent and under elevated pressure afford saturated carbinols with maintenance of benzyl oxygen, as in the synthesis of natural products such as d-phyllocladene ... 

In 1961, two experiments which provided the basis for deducing the skeleton of enmein were carried out by Kanatomo (75, 16). In the first he obtained l-ethyl-4(3,3-dimethylcyclohexyl)-benzene (II) whose structure was proved by synthesis (75). In the second he isolated retene (III) by selenium dehydrogenation of the material obtained by LiAlH4 reduction of enmein (16). Thus enmein was proved to be a diterpene and a phyllocladene (IV) skeleton was proposed for it (16). Kubota and coworkers (77) deduced the presence of a hemiacetal ring (V) and partial structure (VI), with the lactone function part of a six-membered ring, on the basis of chemical evidence and spectral data of various derivatives, and advanced four formulas including (VII) as possible structures for enmein. 

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