Acids meta-chloroperoxybenzoic

Further studies were conducted to improve this scheme to the A-ring unit, particularly, with respect to cost and scale-up practicality. Replacement of expensive meta-chloroperoxybenzoic acid by 30-40% peroxyacetic acid in acetic acid (four equivalents at 0°C) gave a 94% yield of epoxides 3a,b in a 9 1 ratio. 

A solution of 14.79 g of crude commercial meta-chloroperoxybenzoic acid (Aldrich Chemical Company, Inc., or Janssen Chimica, approximately 70%) in 150 mL of dichloromethane is dried over magnesium sulfate (MgSC>4), filtered, and the MgSC>4 is washed twice with 10 mL of dichloromethane. 

The second step of the procedure reported here is the usual epoxidation by meta-chloroperoxybenzoic acid. We have obtained the cis-epoxides (4) with different perfluoroalkyl (Rp) and aryl or alkyl (R) substituents 4... 

An epoxide can also be formed by peroxidation of an alkene. This reaction typically employs MCPBA (meta-chloroperoxybenzoic acid — now you see why we abbreviated it) however, CF3COO2H also works. Figure 3-32 illustrates one example and Figure 3-33 presents a generic mechanism. 

At that period of time, this rather primitive transition structure for the peracid epoxidation of ethylene was sufficiently novel to warrant publication as a communication Today, calculating transition structures for epoxidation of a variety of complex alkenes with the actual peracid used experimentally, such as meta-chloroperoxybenzoic acid m-CPBA), is commonplace . ... 

A nitrogen oxide 112 [113] is formed in the reaction of the corresponding azirenoimidazole with meta-chloroperoxybenzoic acid. Compound 112 can be easily reduced by sodium borohydride to the corresponding A-hydroxy derivative 113 which can be oxidized by tert-butylhypochlorite to regenerate the A-oxide group (Scheme 1.32). 

Peroxyacids (sometimes calledperacids) are used to convert alkenes to epoxides. If the reaction takes place in aqueous acid, the epoxide opens to a glycol. Therefore, to make an epoxide, we avoid strong acids. Because of its desirable solubility properties, meta-chloroperoxybenzoic acid (MCPBA) is often used for these epoxidations. MCPBA is a weakly acidic peroxyacid that is soluble in aprotic solvents such as CH2C12. 

Scheme VIII/9. a) meta-Chloroperoxybenzoic acid b) Formation of trans-diol followed by mcta-chloroperoxybenzoic acid.

Meta-chloroperoxybenzoic acid or osmiumtetroxide/sodium periodate chromic acid anhydride in acetic acid or acetic anhydride give good results with the benzofurans, but was unsatisfactory in the naphthofuran (VIII/172, R-R, CH= CH-CH=CH-) series. Ozonolysis, however, was very effective with both types of compounds (yields 63-86%). 

The preparation of a number of medium ring benzoic acid lactones was achieved by treatment of compounds such as VIII/176 with an excess of meta-chloroperoxybenzoic acid in dichloromethane, Scheme VIII/33 [103]. However, this oxidation reaction is not general for the synthesis of aromatic lactones. If the same reaction conditions are used as in the conversion of VIII/176 to VIII/177, the methoxy derivative VIII/178 is not transformed into the corresponding lactone. Instead the cyclic carbonate VIII/183 was isolated in a yield of 50 %. The proposed mechanism of this abnormal reaction is shown in Scheme VIII/33. From model compounds, the methoxyl group in the para-position to the center of oxidation seems to be important for the formation of VIII/183 [103]. The carbonate VIII/183 is unstable in aqueous alkaline medium and decomposes to the spiro compound, VIII/185, Scheme VIII/33 [103]. For an analogous reaction, see ref. [104]. 

Certain vinylstannanes will undergo cyclopropanation with diiodomethane and samarium amalgam.69 71 Epoxidation of the double bond can be carried out with meta-chloroperoxybenzoic acid,71,72 and the kinetic resolution of a 3-stannylallyl alcohol has been achieved under Sharpless conditions (equation 8-38)73... 

RC03H, such as meta-chloroperoxybenzoic acid (m-CPBA). RCO3H and then ring-opening of the epoxide with H07H20 or H7H20 to give stereoselective anti- dihydroxylation. H2/Pd/C. 

In the dehydration of aldehydes to form nitriles, Ley and colleagues used a polymer-supported hydrazine (Scheme 6.3). The immobilized hydrazine was reacted with aldehydes to give a hydrazone. Subsequent oxidation with mCPBA (meta-chloroperoxybenzoic acid) rendered the corresponding N-oxide, which spontaneously eliminated to form the desired nitrile [10]. Polyvinylpyridine was used as a scavenger for excess mCPBA. 

Lithium 2,2,6,6-tetramethylpiperidide Methylaluminum bw-(4-bromo-2,6-di-terr-butylphenoxide) bw-(2,6-di-fert-butyl-4-methylphenoxy)methyl aluminum meta-Chloroperoxybenzoic acid... 

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