Cyclohexanone asymmetric Baeyer-Villiger oxidation

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. 

We were interested in applications of the high level of stereocontrol associated with the asymmetric Birch reduction-alkylation to problems in acyclic and heterocyclic synthesis. The pivotal disconnection of the six-membered ring is accomplished by utilization of the Baeyer-Villiger oxidation (Scheme 7). Treatment of cyclohexanones 25a and 25b with MCPBA gave caprolactone amides 26a and 26b with complete regiocon-trol. Acid-catalyzed transacylation gave the butyrolactone carboxylic acid 27 from 26a and the bis-lactone 28 from 26b cyclohexanones 31a and 31b afforded the diastereomeric lactones 29 and 30. ... 

In Baeyer-Villiger oxidations catalyzed by (achiral) copper or nickel salts substituted cyclohexanones like 4 (Eq. 3) had been shown to be reactive substrates for the conversion to the corresponding (racemic) lactones in the presence of aldehyde and molecular oxygen [22]. The next step was to develop a chiral catalyst in order to make this reaction proceed in an enantioselective manner, giving optically active oxepanones. Various copper complexes were screened in a search for asymmetric induction in the aerobic Baeyer-Villiger oxidation. The most active and selective catalyst that was eventually found was the copper complex... 

The Baeyer-Villiger (B V) oxidation reaction is a very old chemical transformation that converts ketones into the corresponding esters or lactones hy inserting an oxygen atom from the oxidant between the carbonyl carbon and the one next to it The first report on the asymmetric BV oxidation appeared about fifteen years ago thanks to the pioneering work of Bolm and Strukul. These authors independently demonstrated, with two different catalysts and oxidant combinations, that a certain degree of stereocontrol of the process was possible, with ee up to 92% on chiral cyclobu-tanones and 58% in the kinetic resolution of chiral-substituted cyclohexanones, respectively. After these seminal contributions, a series of different catalysts have been proposed. 

---