Camphor oxidative cleavage

It was clear that 1 would be derived from a Diels-Alder adduct. There has been a great deal of work in recent years around the development of enantioselective catalysts for the Diels-Alder reaction, but the catalysts that have been developed to date only work with activated dienophile-diene combinations. For less reactive dienes, it is still necessary to use chiral auxiliary control. One of the more effective of those was the known camphor-derived tertiary alcohol, so that was used in this project. Diels-Alder cycloaddition of the diene 4 with the enantiomerically-pure enone 5 led to the adduct 6 with high diastereocontrol. Oxidative cleavage led to the acid 7, which was carried on to the bis-enone I. 

Use For the synthesis of camphor and insecticides, as solvents for waxes, and as softeners for plastics. Oxidative cleavage of the double bond in a-R leads to optically active cyclobutane derivatives that can be us as starting materials in the synthesis of cyclobutanoid natural products. 

More recently, Oppolzer has proposed the use of enantiomeric aryl sultams 1.135 (R=Me), each being easily obtained from saccharin [468], In general, these chiral auxiliaries can be applied in the same types of reactions as the camphor sul-tam [469, 470], However, the low selectivity observed in nitrile oxide cycloadditions led to the design and synthesis of a more bulky auxiliary 1.135 (R = rert-Bu), winch is correspondingly more stereoselective [471]. Nevertheless, the cleavage of the chiral auxiliary necessitates the use ofLil BH, and generates alcohols as the final products. 

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.). 

---