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Studies related to the synthesis of eremopbilane sesquiterpenes

University of British Columbia

The synthesis of decalone (122) has been achieved by two alternative methods. Stereoselective conjugate addition of lithium dimethylcuprate to the ketal octalone (131) afforded the ketal decalone (129). Wolff-Kishner reduction of the latter compound, followed by acidic hydrolysis produced decalone (122) contaminated with its epimer, decalone (148). A more -efficient procedure for the preparation of (122) involved an annelation of 2.3-dimethylcyclohexanone. The key step in this process was the reaction of the enol lactone (157) with methyllithium to produce, after appropriate aldol cyclization, octalone (69a). Subsequent hydrogenation of this compound afforded decalone (122). A naturally occurring sesquiterpene, fukinone, has recently been isolated and assigned structure (16). The total synthesis of racemic fukinone, reported herein, was achieved by the following sequence. The hydroxymethylene derivative of octalone (69a) was prepared. Hydrogenation of this compound, followed by oxidation with 2,3-dichloro-5,6-dicyanobenzoquinone afforded a critical intermediate, keto aldehyde (167). Oxidation of the latter and esterification of the resulting carboxylic acid (170) produced keto ester (171), which was subsequently hydrogenated to afford keto ester (172). Reaction of this compound with methyllithium and dehydration of the resulting alcohol afforded (±)-epi-fukinone (174). Olefinic isomerization of the latter produced (±)-fukinone (16). The synthesis of (±)-fukinone reported herein, establishes a stereoselective synthetic entry into the eremophilane class of sesquiterpenes.

Text

2011-06-07

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http://hdl.handle.net/2429/35268

Chemistry

University of British Columbia

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