Ketones Baeyer-Villiger rearrangement

Oxidation of Ketones to Esters (Baeyer-Villiger rearrangement)... 

RB3LYP calculations indicate that the s-cis conformer of peroxy acids is more stable than the s-trans conformer. Calculations on the reaction of prop-2-enol with some peroxy acids showed that trans-transition states collapse to the epoxide via a 1,2-shift, whereas a 1,4-shift is operable for cis-transition states.195 Quantum mechanical calculations have been performed on the migration step of the Baeyer-Villiger rearrangements of some substituted acetophenones with m-chloroperbenzoic acid (m-CPBA). The energy barriers, charge distributions and frontier molecular orbitals, determined for the aryl migration step, have been used to explain the effects of substituents on the reactivity of the ketones.196... 

The reason for this becomes plain when you see that the new 1,6-diCO relationship does allow a very interesting reconnection. Adjustment of the oxidation state allows a reconnection to a lactone 61 that should be the product of a Baeyer-Villiger rearrangement on the ketone 62. 

Fig. 14.34. Regioselective and stereoselective Baeyer-Villiger rearrangement of an unsymmetrical ketone with magnesium monoperox-ophthalate hexahydrate (in the drawing, Mg is omitted for clarity).

Fig. 14.35. Chemoselective oxidations of an unsaturated ketone the imido peracid A epoxidizes the C=C double bond, while the peracid B reacts with the C=0 double bond causing a Baeyer-Villiger rearrangement...

Fig. 14.36. Regioselective Baeyer-Villiger rearrangement of an unsymmetrical ketone with HCPBA (meta-chloro-peroxybenzoic acid). The aryl group is [l,2]-shifted in all cases and irrespective of whether the acetophenone is electron-rich or electron-poor.

Fig. 14.39. Baeyer-Villiger rearrangement of a strained ketone with alkaline tert-BuOOH.

Similar migrations to electron-deficient oxygen also occur. In the Baeyer-Villiger rearrangement a ketone is reacted with a peracid. The product is an ester in which one of the alkyl groups of the ketone has migrated to oxygen ... 

The Baeyer-Villiger rearrangement often is called Baeyer-Villiger oxidation (see the last subsection of Section 14.3.2, Oxidative Cleavage of Ketones). In the Baeyer-Villiger rearrangement a carbonyl compound (ketones are almost always used) and an... 

Cyclobutanones are the only ketones that undergo Baeyer-Villiger rearrangements not only with peracids but even with alkaline H202 or alkaline ferf-BuOOH (Figure 11.35). In this case, the driving forces of two crucial reaction steps are higher than... 

One of the most important methods for lactone preparation, and hence of the corresponding hydroxy acids (or halogeno acids, Section 5.14.1 above) is the Baeyer- Villiger rearrangment of cyclic ketones by the action of peracids. A wide variety of peracids have been used in this reaction but currently the reagents of choice are pertrifluoroacetic acid, m-chloroperbenzoic acid, and permaleic acid. The mechanism is formulated below for the conversion of an acyclic ketone into an ester. 

Scheme 11/24 gives the proposed mechanism [133]. The central intermediate, 11/195, is tetrahedral. From studies of a series of unsymmetrical substituted ketones, the relative ease of migration of various groups has been found to be tert-alkyl (best) > cyclohexyl, sec-alkyl, benzyl, phenyl > prim-alkyl > methyl [134]. To illustrate this method, some examples of the Baeyer-Villiger rearrangement are given in Scheme II/2512). 

The oxidation of the bicyclic amino-ketone shown in the margin demonstrates how useful this effect can be. This is the Baeyer-Villiger rearrangement, which you will meet in Chapter 37. The mechanism is not important here all you need to know is that it inserts an oxygen atom on one side or the other of the ketone C=0 group. The question is—which side ... 

Tetroxans ( dimeric ketone or aldehyde peroxides ) (7) are readily obtainable from carbonyl compounds and Caro s acid or hydrogen peroxide and sulfuric acid by the method described by Baeyer and Villiger.28,20 However, aromatic ketones undergo a Baeyer-Villiger rearrangement under these conditions to form esters of carboxylic acids.30... 

The Baeyer-Villiger rearrangement of cyclohexanone and acetophenone with TS-I/H2O2 proved to be poorly selective [117]. Notably, Ti-P and Sn-P have different chemoselectivities in the oxidation of unsaturated ketones, leading selectively to corresponding epoxides and lactones, respectively [118]. The different oxidation pathways were attributed to the preferential adsorption of hydrogen peroxide on Ti-sites and of the carbonyl group on Sn-sites. 

When a ketone (i) is treated with a peroxy acid it appears to be converted reversibly into a complex (2) this may undergo Baeyer-Villiger rearrangement with migration of an alkyl group from carbon to oxygen to give an ester or lactone... 

The oxygen nucleophile may be that of a peroxy acid such as perbenzoic acid. In this case a rearrangement may occur under acidic conditions. This takes place with the expulsion of benzoate and the insertion of an oxygen adjacent to the carbonyl group. The reaction, known as the Baeyer-Villiger rearrangement leads to the conversion of a ketone to an ester (Scheme 3.43) or a cyclic ketone to a lactone (cyclic ester). 

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