Oxidation with wCPBA

Ticolubant (310) is a leukotriene receptor antagonist that exhibits anti-inflammatory activities. The Wittig reaction with 3-hydroxy-6-methylpicolinaldehyde followed by a Mitsunobu reaction with 2-phenylethanol gave phenyl ether 308. Oxidation with wCPBA converted the pyridine ring into the corresponding A-oxide, which then underwent the Boekelheide reaction with TFAA to afford the methyl alcohol 309. Reaction with thionyl chloride and then 2,5-dichlorothiophenol followed by saponification gave 310. ° ... 

A biomimetic oxidation with perfluorinated porphyrin complexes [(F20TPP) FeCl] showed high catalytic activity with secondary alcohols with over 97% yield in all cases [144]. Furthermore, this catalyst is able to oxidize a broad range of alcohols under mild conditions with wCPBA as terminal oxidant. Here, an a-hydroxyalkyl radical species is proposed as central intermediate. 

Similar manganese porphyrin dimers linked by different spacer molecules had catalase activity [196]. The activity was highest when the Mn-Mn separation was ca 4 A, in agreement with the Mn-Mn separation in the hypothetical Mn -O-O-Mn complex [196]. The high-valent Mn porphyrin dimer has been prepared by the oxidation of the Mn dimer with wCPBA. The Mn dimer thus formed was stable for hours at temperatures ranging from —78 to -20 °C and it was detected by ESI MS (electrospray ionization mass spectroscopy) [197]. Cyclooctene was oxidized by mCPBA (1.1 equivalent for each Mn ion) with the Mn dimer to... 

Oxidative bromination of arenes can be achieved by the reaction with a source of bromide anion and an appropriate oxidant, possibly via intermediate formation of electrophilic bromoiodanes. In particular, an efficient and regioselective monobromination of electron-rich aromatic compounds has been developed, in which iodobenzene is used as the catalyst in combination with wCPBA as the terminal oxidant. The bromination of arenes 35 with lithium bromide is fast in THF at room temperature, providing regioselective monobrominated products 36 in good yields (Scheme 4.18) [46]. 

Phenolic oxidations are pivotal steps frequently involved in the biosynthesis of natural products, which possess a variety of important biological activities. Therefore, a continuing interest exists in such transformations, in particular in asymmetric oxidative protocols. Kita et al. performed asymmetric dearomatization of naphthols 43 mediated by chiral hypervalent iodine(III) reagents, 33 and 45 having a rigid spirobiindane backbone (Scheme 20) [66, 67]. A series of other ortho-functionalized spirobiindane reagents of type 46 were synthesized. Intramolecular oxidative substitution of 43 afforded five-membered spirolactone 44 with good levels of enantioselectivity (up to 92% ee). Conformationally flexible iodoarenes employed in this study produced almost racemic products. Catalytic use of these chiral catalysts with wCPBA as cooxidant afforded the chiral spirolactones without detrimental effects on the ee values. 

Methods for indirect oxidation have also been developed. The combination of KF/ wCPBA in acetonitrile and water has been used to generate KOF CH3CN reagent, a mild and selective oxidant that reacts at 0 °C with no overoxidation [78]. This reagent functions by providing a fluorosulfonium ion intermediate, which is hydrolyzed in the presence of water to the desired sulfoxides. As a result of the indirect oxidation method, the typical stereoselectivity of mCPBA-type oxidations is not observed here. The KOFCH3CN oxidant is similar in scope and mechanism to 1-fluoropyridinium triflates, Selectfluor [302] and the more classical t-butyl hypochlorite [288]. 

Oxidation of Alkenes to Oxirans by Peroxy-acids. An improved procedure for epoxidation using aromatic peroxy-acids has been reported. After a normal epoxidation with 3-chloroperoxybenzoic acid (mCPBA) in CH2CI2, activated KF is added to the crude mixture, and this results in the precipitation of both wCPBA and the aromatic acid by-product, leaving an acid-free reaction mixture for normal work-up. As an alternative, the insoluble mCPBA-KF complex itself may be used for the epoxidation of alkenes overnight at room temperature. After filtration and treatment of the CH2CI2 solution with more KF (to ensure removal of any residual peroxy-acid), normal work-up leads to yields in excess of 95% for cyclohexene and styrene oxides. 

A major advance was accomplished with the introduction of hydrazine derivatives by Che, in particular, M-amino phthalimide [38]. Although initial work had relied on PhI(OAc)2 as the oxidant, the same group later discovered that a tricomponent system consisting of 2-iodoanisole (49), wCPBA, and the A -amino phthalimide could be employed for an in situ preparation of the required imino-iodane [39]. It is important to note that the final iminoiodane contains a 2-methoxyphenyl substituent, which is in line with the observation from Zhdankin on enhanced solubility of derivatives of the type 42. Under these conditions, a series of styrenes 48 could be submitted to intermolecular aziridination and provided products 50 under mild conditions and in good to excellent yields. 

Menthone transforms into a polymerizable monomer by Bayer-Villiger oxidation to the seven-membered lactone menthide (oxidant w-chloroperbenzoic acid, wCPBA). Controlled ROP of menthide can be achieved using a zinc alkoxide catalyst (see Scheme 8) (toluene, room temperature) to yield aliphatic polyesters with predictable MWs up to 91 kg/mol and narrow MW distributions (PDl 1.1) [96]. 

Jeong et al. also reported on allene synthesis via addition-elimination sequence as a key reaction, starting from 3,3-bis(phenylthio)-l,l,l,2,2-pentafluorobutane 64 (Scheme 26.59). Thus, treatment of 64 with an excess amount of aryllithium reagents in Et20 at low to room temperature for 1-6 hours gives 2-aryl-1,1,1-trilluoro-3-phenylthio-2-butene 65 in 80-96% yields. Bromination of 65 with NBS in MeCN at reflux temperature for 1-7 hours, followed by wCPBA oxidation in CH2CI2 at the reflux temperature for 1-12 hours, results in the formation of 1-aryl-l-trifluoro-methylallenes 66 in 74-96% yields. 

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