Fencholic acid from fenchone

Cleavage of carbon-carbon bonds in hydrolytic reactions is relatively rare, but those reactions that occur are important. The reagent is usually a concentrated solution of an alkali, and the starting material must contain a carbonyl group the first stage is addition of a hydroxyl anion to this group, and the resulting intermediate splits to a carbon anion and a carboxylic acid  

Cleavage by hydrolysis in this way requires relatively vigorous conditions and so is not to be expected with simple aldehydes and ketones such compounds usually undergo other reactions before the fission is reached, and only those simple ketones that cannot undergo the various side reactions are amenable to hydrolysis by alkali at elevated temperatures. An example of this last type is fenchone whose carbonyl group is flanked by carbon atoms neither of which carries hydrogen with potassium hydroxide solution at 220° it yields fencholic acid in a smooth hydrolysis 155 

Only relatively mild conditions are needed for hydrolysis of a carbon-carbon bond in / -diketones and / -oxo esters. In these cases a cationic centre formed at the / -position to the carbonyl group aids fission of the carbon-carbon bond from the carbonyl group  

One molecule of acid and one of ketone is thus obtained on hydrolysis of a / -diketone in this way but unsymmetrical / -diketones may be expected often to give two different acids and two different ketones because cleavage may occur at two different places, viz.  

however, R is an aryl and R an alkyl group, then cleavage affords almost exclusively the alkyl aryl ketone by reaction (0), e.g., acetophenone from benzoylacetone  

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Fenchone (254) occurs in a number of essential oils, such as cedar leaf and lavender, and the (—)-isomer is particularly important in fennel. Synthetic material is made from pinene. Addition of carboxylic acids to a-pinene gives the corresponding esters of fenchol. These esters can be hydrolyzed to fenchol, which is then oxidized to fenchone. It is used mainly in reconstitution of fennel oils. 

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