Asymmetric Baeyer-Villiger oxidation reaction

Bolm et al. (130) reported the asymmetric Baeyer-Villiger reaction catalyzed by Cu(II) complexes. Aerobic oxidation of racemic cyclic ketones in the presence of pivalaldehyde effects a kinetic resolution to afford lactones in moderate enan-tioselectivity. Aryloxide oxazolines are the most effective ligands among those examined. Sterically demanding substituents ortho to the phenoxide are necessary for high yields. Several neutral bis(oxazolines) provide poor selectivities and yields in this reaction. Cycloheptanones and cyclohexanones lacking an aryl group on the a carbon do not react under these conditions. 

The use of a chiral hydroperoxide as oxidant in the asymmetric Baeyer-Villiger reaction was also described by Aoki and Seebach, who tested the asymmetric induction of their TADOOH hydroperoxide in this kind of reaction98. Besides epoxidation and sulfoxidation, for which they found high enantioselectivities with TADOOH (60), this oxidant is also able to induce high asymmetry in Baeyer-Villiger oxidations of racemic cyclobutanone derivatives in the presence of DBU as a base and LiCl as additive (Scheme 174). The yields and ee values (in parentheses) of ketones and lactones are given in Scheme 174 as... 

Katsuki successfully appHed two different metal salen complexes in asymmetric Baeyer-Villiger reactions. Cationic cobalt complex 51 catalyzes the reaction between cyclobutanone 50 and UHP as oxidant to give lactone 46 with 77% ee in 72% yield [349], In the same transformation zirconium salen complex 52 affords the product with higher enantioselectivity (87% ee) (Scheme 9.5). Over 99% ee could be achieved in the conversion of tricyclic ketone 47 [350],... 

Another method for the asymmetric version of the Baeyer-Villiger reaction was presented by Lopp and coworkers in 1996 . By employing overstoichiometric quantities of Ti(OPr-t)4/DET/TBHP (1.5 eq./1.8 eq./1.5 eq.), racemic andprochiral cyclobutanones were converted to enantiomerically enriched lactones with ee values up to 75% and moderate conversions up to 40% (Scheme 171). Bolm and Beckmann used a combination of axially chiral C2-symmetric diols of the BINOL type as ligands in the zirconium-mediated Baeyer-Villiger reaction of cyclobutanone derivatives in the presence of TBHP (or CHP) as oxidant (Scheme 172) . With the in situ formed catalysts 233a-d the regioisomeric lactones were produced with moderate asymmetric inductions (6-84%). The main drawback of this method is the need of stoichiometric amounts of zirconium catalyst. 

A Baeyer-Villiger oxidation has the potential of being asymmetric if a regioselective reaction is conducted on a meso-substrate or if a stereodifferentiated stereogenic center is already present. The oxidation can be chemical or enzymatic.213-215 216 An example of a chemical reagent in a Baeyer-Villiger reaction is provided in the synthesis of fragment A 26 from /f-carvone (27) (Scheme 9.38) as part of a synthesis of Cryptophycin A (28).217... 

Asymmetric Baeyer-Villiger oxidation reaction In 1994, Bolm et al used chiral Cu and Ni complexes (7.23) in catalytic amount with different oxidation systems. 

Alphand, V., Furstoss, R. Asymmetric Baeyer-Villiger oxidation using biocatalysis. Asymmetric Oxidation Reactions). 2001,214-227... 

Bolm, C., Luong, T. K. K., Beckmann, O. Oxidation of carbonyl compounds asymmetric Baeyer-Villiger oxidation. Asymmetric Oxidation Reactions). 2001,147-151... 

Baeyer-Villiger oxidation as indicated by Strukul and coworkers. Reaction of K2PtCl4 and 6-methoxysalicylaldehyde in the presence of 2,2 -bis(diphenylphosphino)-l,l -binaphthyl (BINAP) gives acylplatiumn complexes, which in the presence of perchloric acid catalyzes the asymmetric Baeyer-Villiger oxidation with hydrogen peroxide (equation 83). ... 

For selected reviews on the Baeyer-Villiger (BV) oxidation (a) ten Brink, G.-J., Arends, I. W. C. E., Sheldon, R. A. (2004). The Baeyer-Villiger reaction new developments toward greener procedures. Chemical Reviews, 104, 4105-4123. For selected reviews on asymmetric BV oxidation (b) Bohn, C., Beckmann, O. (1999). Baeyer-Villiger reaction. In Jacobsen, E. N., Pfaltz, A., Yamamoto, H., Comprehensive Asymmetric Catalysis. Springer, Berlin, Vol. 2, pp. 803-812. 

Urea hydrogen peroxide adduct (UHP) was employed in metal-catalysed asymmetric epoxidation [98] and Baeyer-Villiger oxidation [99,100]. Since the presence of urea does not change the course of the reaction, this will not be described here. Conversion of epoxides to halohydrins with elemental... 

Table 5. Direct catalytic asymmetric aldol reactions promoted by heteropolyme-tallic asymmetric catalyst and following Baeyer-Villiger oxidations.

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