Pulegone ketone chiral auxiliaries from

An asymmetric synthesis of mevalolactone in over 87% e.e. employs a 1,3-oxathiane as the chiral auxiliary (81TL2859). The reagent (818), easily prepared from (+)-pulegone (81TL2855), was metallated with u-butyllithium and the anion reacted with acetaldehyde. Oxidation of the diastereomeric mixture of alcohols to the ketone (819) and reaction of... 

The cyclic monoterpenes are also very useful. Menthol 79 is very cheap and the ketones pulegone 81 and carvone 82 are moderately cheap. All are available as the other enantiomer, e.g. 80. An important application is as a chiral auxiliary, the favourite being 8-phenylmenthol 83 made from pulegone,23 see chapter 30. 

Pulegone has also been used to make the chiral auxiliary 86 that acts as an asymmetric d1 reagent. Conjugate addition of the thiol PhCH2SH gives a diastereomeric mixture of ketones 84 from which the single compound 85, having all substituents equatorial, can be made by reduction. 

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