Cerorubenic acid-III

In the total synthesis of cerorubenic acid-III methyl ester (105), diene 102 was converted to enantiopure tricyclic ketone 103 through an anionic oxy-Cope rearrangement (equation 56)82. Conversion of 102 to 103 afforded the entire ABC substructure of 104 and 105, most notably the double bond occupying a bridgehead site. 

Paquette, L. A. Poupart, M.-A. Studies directed toward the total synthesis of cerorubenic acid-III. 1. Expedient construction of the tetracyclic core by oxyanionic sigmatropy. J. Org. Chem. 1993, 58, 4245-4253. 

Studies Toward the Total Synthesis of a Cerorubenic Acid-III... 

Paquette has reported an intramolecular oxidative coupling using ferric chloride to prepare the intermediate 30 for the synthesis of cerorubenic acid-III. Addition of the dienolate of 28 to FeCls in dmf at —78°C produced the cyclopropane intermediate 29 in 54% yield (equation 16). Although the mechanism of this oxidative cyclization is not discussed in the paper, it is likely that a one-electron transfer pathway is involved. Copper(n) salts have also been utilized for intramolecular enolate coupling, but they proved to be somewhat less effective in the present context. 

The tetracyclic precursor 9 of cerorubenic acid III (a principal component of secretions produced by the scale insect Ceroplastes rubens Maskell, which plays an important role in communication between these wasps) is prepared by stereospecilic addition of vinylmagnesium bromide to ketone 6 to give 7 and anionic oxy-Cope rearrangement by heating 7 with excess potassium hexamethyldisilazanideI093. 

A useful reaction of ketone enolates is their oxidative coupling, e.g. in the formation of a tricyclic intermediate towards the synthesis of the diterpene cerorubenic acid-III (eq 12). ... 

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