Baeyer-Villiger Oxidation
The CAS oxidation of bishomocubanone gives the corresponding lactone (Scheme 12). This is obtained only as a minor product in the peroxy acid promoted Baeyer-Villiger oxidation conditions.
Scheme 12
4.1.3 Cerium(III) Chloride (CeCl 3 ยท7H 2 O)
Cerium(III) chloride is a mild Lewis acid. For some applications, it must be anhydrous. Some of the important transformations follow.
1,2-Addition Reactions
Organocerium reagents are conveniently prepared from the reactions of lithium compounds with anhydrous CeCl3 in THF. They are highly oxophilic and significantly less basic than RLi and RMgBr. Thus, 1,2-addition with enolizable ketones can be performed. Although alkyl and vinyl cerates are often employed, Cl2 CeCH2 CN, Cl2 CeCH2 CO2 R and Cl2 CeCH2 SiMe3 are known to be equally effective. Some of the examples follow:
The methylation of enolizable ketones can be accomplished in high yield (Scheme 13).
Scheme 13
a,b -Unsaturated esters can be converted into allylsilanes in high yield (Scheme 14).
Scheme 14
High levels of steric hinderance can be tolerated (Scheme 15).
Scheme 15
CeCl3 can be used as promoter to improve the addition of alkyl Grignard to give vinylogous ester (Scheme 16).
Scheme 16
In the addition of Grignard reagent to chiral a -keto amides, the stereoselectivity can be reversed using CeCl 3 (Scheme 17).
Scheme 17