Homofarnesylic acid

The conversion of nerolidol into homofarnesylic acid, either via the corresponding bromide, its substitution by cyanide and hydrolysis, or by direct carbonyl-ation, [245] produces a mixture of (3 /2,7 )-isomers. 

Alternatively, nerolidol can be isomerised into farnesol, via a trisilylated tungstate (formally a metalla-Claisen rearrangement). The product is purified by distillation. [246] After its conversion into farnesyl chloride, this is treated with carbon dioxide and freshly precipitated barium, giving ( , )-homofarnesylic acid, which is finally reduced with lithium aluminium hydride. [247, 248]... 

Giinther Lucius succeeded in cyclising homofarnesylic acid into a mixture of sclareolide diastereomers. These could be separated by crystallisation, although the yield was only around 15%, while the mixture did not contain racemic sclareolide. [237]... 

As a consequence, a series of other Bronsted and Lewis acids were probed for their impact on the stereoselectivity of cyclisations. Thus, the sclareolide isomers were obtained from homofarnesylic acid in 91 % yield, when the reaction was carried out with stannic chloride in dichloromethane at -78 °C. [249] On the other hand, the use of boron trifluoride as catalyst produced racemic sclareolide in a yield of only 38%. [250] The company Henkel patented a procedure, in which an ( /Z)-mixture of homofarnesylic acid isomers was treated at -10 °C with methanesulfonic acid in dichloromethane, although, this yielded only a mixture of sclareolide isomers. [251]... 

Polyene cyclisations of homofarnesol and homofarnesylic acid constitute especially elegant total syntheses. 

Homogeranic acid (203) has been synthesised by conjugate addition of prenylmagnesium halide to g-isopropenyl-g-propio-lactone (204). Homofarnesylic acid has been made by a similar route. The acid (203) reacts with phenylselenyl chloride or with... 

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