Retention Baeyer-Villiger oxidations

The stereochemistry of the C(3) hydroxy was established in Step D. The Baeyer-Villiger oxidation proceeds with retention of configuration of the migrating group (see Section 12.5.2), so the correct stereochemistry is established for the C—O bond. The final stereocenter for which configuration must be established is the methyl group at C(6) that was introduced by an enolate alkylation in Step E, but this reaction was not very stereoselective. However, since this center is adjacent to the lactone carbonyl, it can be epimerized through the enolate. The enolate was formed and quenched with acid. The kinetically preferred protonation from the axial direction provides the correct stereochemistry at C(6). 

The stereochemistry of the C-3 hydroxyl is established in step E. The Baeyer-Villiger oxidation proceeds with retention of configuration of the migrating group (see Section... 

Propoxyphene has chiral centers at both C-2 and C-3, with the latter equivalent to that of isomethadone. Pohland and others(86) showed the C-3 centers of (+)-propoxyphene and (-)-isomethadone to be identical (3R) by a sequence that rests upon retention of configuration during a Baeyer-Villiger oxidation step (Scheme 9.12). In subsequent work, this assumption was justified by a correlation that did not involve the C-3 center and employed a Mannich base intermediate.(87) The C-2 configuration of (+) propoxyphene was established by a lengthy sequence that required degradation of the compound to (+)-2,3-diphenylpropane of known (S) configuration. 

Jeffrey pine in America. Figure 4.49 summarizes our frontalin synthesis, which successfully provided over 10g of (LS ,5ft)-9889 The first and important step in our synthesis was the asymmetric reduction of p-kclo ester A with baker s yeast to give hydroxy ester B of 97.7% ee. Methylation of the dianion derived from B gave C diastereoselectively, which was oxidized to give D, Baeyer-Villiger oxidation of D afforded E with retention of configuration. Subsequent conversion of E to 98 proceeded smoothly to give 10 g of the sample in an overall yield of 7.8% based on A (10 steps). 

Knochel and co-workers58 reported Baeyer-Villiger oxidation of a-trisubstituted aldehydes 116 in the preparation of tertiary chiral alcohols 117. The fact that the reaction proceeds with retention of configuration of the migrating group permits the utility of this reaction. Several optically enriched, tertiary alcohols were prepared using this simple 3-step method from optically-enriched allylic tetrafluoroborates 115. 

The Baeyer-Villiger oxidation of delfone (2-pentylcyclopentan-l-one) to 5-decalactone (6-pentyloxan-2-one) finds applications in flavour and fragrance markets. The reaction is known to proceed with retention of configuration with peracetic acid, while producing acetic acid as a byproduct. An environmentally friendly alternative has been reported using Sn-Beta catalyst. The 8-decalactone was obtained in 86% yield when the... 

Ketones may be oxidized to esters by peracids or hydrogen peroxide, a process known as the Baeyer-Villiger oxidation. Unsymmetric ketones are oxidized selectively at the more substituted a carbon and that carbon migrates to oxygen with retention of configuration. Trifluoroperacetic acid generated in situ gave the double example in Equation 6.9 [14]. Cyclic ketones afford lactones (Eq. 6.10) [15]. 

The Baeyer-Villiger reaction occurs with retention of stereochemistry at die migrating center. This stereoselectivity has been utilized in a practical method for the preparation of isotopically chiral metiiyl acetic acid (5) ftom [2- H]cyclohexanone (4) prepared by enzyme-catalyzed stereoselective exchange of the pro-R a -proton and enantioconvergent exchange of the a-proton with deuterium (Scheme 2). As a cautionary note, prior epimerization of an acyl group prior to oxidation has been observed. ... 

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