With mCPBA

Oxygenation takes place with peracids. The cyclopalladated benzylamine complex 466 is converted into the salicylaldamine complex 504 by the treatment with MCPBA[456] or /-BuO H[457]. Similarly, azobenzene is oxidized with MCPBA at the ortho position[458]. 

Three preparations of 1-azetine iV-oxides have been reported. Oxidation of the 2-aryl-l-azetine (222) with MCPBA gives the nitrone (223) (79CB3914>. However, similar treatment of 2-alkoxy-l-azetines fails to give the corresponding iV-oxides but yields products derived from oxaziridines (cf. Section 5.09.4.2.3). 

This group is stable to TEA and morpholine in pyridine at 20°. It is cleaved by oxidation with MCPBA followed by elimination with TEA in Pyr, 10 min, 20°." The rate of cleavage is proportional to the strength of the electron-withdrawing group on the phenyl ring. ... 

Tlie reaction of 5,6-dithiabicyclo[2.1.1]hexaiie 11a with OXONE led to the corresponding dithiirane 12a, which was, however, stable only in solution (Amax at 442 nm in CH2CI2). Treatment of the reaction mixture containing 12a with MCPBA gave the dithiirane 1-oxide 13a (8%) (95TL1867). Tire introduction of electron-withdrawing substituents on the benzene rings provided the dithiirane oxide 13b in a better yield (21%). 

Tlie isolable dithiiranes (4 and 7) are fairly stable under acidic conditions but quickly lose a sulfur atom to give the corresponding thioketones under basic conditions (97BCJ509). Tliey are quite sensitive toward amines and phosphines. Oxidation with MCPBA gave the corresponding dithiirane 1-oxides in high yields. 

Oxidation of the dithiete 175 with MCPBA (1 equiv.) yielded the dithiete 1-oxide 202 which, when heated in refluxing toluene, formed a mixture of the ring-opened product sulflne 203 (blue, A ax 576 nm) and 202 in the ratio 7 1 (95TL8583). Further oxidation of 202 or oxidation of 175 with... 

The action of aqueous potassium hydroxide on chloronitrile 14 in DMSO at 25-30°C accomplishes the hydrolysis of the chloronitrile moiety and furnishes ketone 13 in a yield of 80%. Treatment of a solution of ketone 13 in CH2CI2 with mCPBA and sodium bicarbonate results in a selective Baeyer-Villiger oxidation to give bicyclic lactone 12 in >95% yield. It is noteworthy that the Baeyer-Villiger oxidation is completely regioselective and that the... 

The enol ether double bond contained within the ds-fused dioxa-bicyclo[3.2.0]heptene photoadducts can also be oxidized, in a completely diastereoselective fashion, with mCPBA. Treatment of intermediate XXII, derived in one step from a Patemo-Buchi reaction between 3,4-dimethylfuran and benzaldehyde, with mCPBA results in the formation of intermediate XXIII. Once again, consecutive photocycloaddition and oxidation reactions furnish a highly oxygenated system that possesses five contiguous stereocenters, one of which is quaternary. Intermediate XXIII is particularly interesting because its constitution and its relative stereochemical relationships bear close homology to a portion of a natural product known as asteltoxin. 

It should be noted that epoxidation of a dienone with mCPBA or other electrophilic epoxidation reagents proceeds with complementary regioselectivity, yielding y,8-epoxy enones instead of the ot,P-epoxy ketones discussed above. This feature has been utilized in several natural product syntheses Scheme 9.8 demonstrates... 

Vinylsilanes (Chapter 3) can be readily converted into a/3-epoxysilanes, normally by treatment with mcpba (/). Alternatively, a-chloro-a-lithio-a-trimethylsilanes react efficiently with aldehydes and ketones in a manner reminiscent of the Darzens reaction (2). 

Oxidation of a thiiraneradialene with equimolar amounts of MCPBA in CH2C12 at about 0°C gave the corresponding thiiraneradialene S-oxide 26 in a quantitative yield47 (equation 11). 5-Membered heterocyclic sulphoxides such as 1,3-benzoxathiolane sulphoxide 27, 1,3-benzdithiolane sulphoxide 28 and 1,3-dithiolane sulphoxide 29 were readily obtained from their sulphide precursors by oxidation with MCPBA in dich-loromethane solution48. 

Compounds lb and 2b were the Urst fluorinated ligands tested in Mn-catalyzed alkene epoxidation [5,6]. The biphasic Uquid system perfluorooc-tane/dichloromethane led to excellent activity and enantioselectivity (90% ee) in the epoxidation of indene with oxygen and pivalaldehyde (Scheme 1, Table 1). In addition, the fluorous solution of the catalyst was reused once and showed the same activity and selectivity. This represents a considerable improvement over the behavior in the homogeneous phase, where the used catalyst was bleached and reuse was impossible. Unfortunately, indene was the only suitable substrate for this system, which failed to epoxidize other alkenes (such as styrene or 1,2-dihydronaphthalene) with high enantioselectivity. The system was also strongly dependent on the oxidant and only 71% ee was obtained in the epoxidation of indene with mCPBA at - 50 °C. 

The reductive elimination of a variety of )3-substituted sulfones for the preparation of di-and tri-substituted olefins (e.g. 75 to 76) and the use of allyl sulfones as synthetic equivalents of the allyl dianion CH=CH—CHj , has prompted considerable interest in the [1,3]rearrangements of allylic sulfones ". Kocienski has thus reported that while epoxidation of allylic sulfone 74 with MCPBA in CH2CI2 at room temperature afforded the expected product 75, epoxidation in the presence of two equivalents of NaHCOj afforded the isomeric j ,y-epoxysulfone 77. Similar results were obtained with other a-mono- or di-substituted sulfones. On the other hand, the reaction of y-substituted allylic sulfones results in the isomerization of the double bond, only. The following addition-elimination free radical chain mechanism has been suggested (equations 45, 46). In a closely related and simultaneously published investigation, Whitham and coworkers reported the 1,3-rearrangement of a number of acyclic and cyclic allylic p-tolyl sulfones on treatment with either benzoyl peroxide in CCI4 under reflux or with... 

Next, option B was examined. Oxidation of 14 with mCPBA proceeded well, leading to epoxide 22. However, cyclizahon of the enolate of epoxide 22 did not provide the desired five-membered product 23. The only isolated product was a tetrahydrofuran derivative 24, which resulted from the O-attack of the enolate to the epoxide instead of the desired C-attack. Therefore, development of this route was also terminated. 

With this encouraging result from the model system, a gram quantity of the racemic sulfoxide 40 was prepared by oxidation of benzoxathiin 16 with mCPBA and a small amount of chiral sulfoxide (A)-40 with 94% ee was isolated by subsequent chiral HPLC separation (Scheme 5.12). When chiral sulfoxide (S)-40 was treated with borane-dimethylsulfide, a clean reduction of the olefin and the sulfoxide was observed. More surprisingly, only the desired cis-diaryl dihydrobenzoxathiin 12 was observed in high yield and unchanged 94% ee. No trans-isomer or 16 was observed. With this proof of concept in hand, an efficient... 

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