Monoperoxycamphoric acid

Since Marshall s strategy55 in preparing optically active betweenanenes was asymmetric epoxidation by (-t-)-monoperoxycamphoric acid, this approach would be solely effective in [m.n]betweenanenes where the m ring is large enough to sway away, so exposing the buried unsaturated center. 

The use of chiral peracids was pioneered by Henbest1 who produced epoxides with an enantiomeric excess of 5% using ( + )-monoperoxycamphoric acid (1). The acid used was shown to be a mixture of isomers2 and later work improved enantiomeric excess in these reactions to 15% by using more highly purified epoxidizing agent. 

A chiral substituent on nitrogen can direct the predominant attack of an oxidizing agent to one dia-stereotopic face of an imine. Ratios as high as 97 3 were observed in a series of imines derived from a-methylbenzylamine (equation 43). The oxidation of achiral imines with optically active peroxy acids, most notably monoperoxycamphoric acid [(+)-MPCA], do afford optically active oxaziridines, but not generally in synthetically useful optical ratios, but ratios as high as 80 20 have been reported. ... 

Chiral peroxy acids, such as monoperoxycamphoric acid, have been used in a classical Prilezhaev reaction for the preparation of chiral epoxides [1], however, the enantiomeric excess (e.e.) of the epoxides formed was below 10%,... 

Asymmetric epoxidation of alkenes using H2O2 and the dehydrating agent (20 X = 2, Y = CO) is only marginally better than with monoperoxycamphoric acid... 

Scheme 8.1. Generalized illustration of epoxidation of a fran -alkene using a chiral peracid R = a generic chiral substituent (in early work, monoperoxycamphoric acid was often used).

Under comparatively drastic reaction conditions, camphor is oxidized with ring cleavage to give camphoric acid (69). Alternatively, bomeol may be used as starting material. Both enantiomers are commercially available. As oxidants nitric acid is most frequently used the best results are obtained when ammonium vanadate is added as a catalyst68. The ( + )-enantiomer was used for the preparation of monoperoxycamphoric acid, which is an isomeric mixture and difficult to separate69. The peracid has been applied with limited success as an enantioselective epoxidation reagent (Section D.4.5.2.). 

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