Epoxides with hydrogen peroxide

Maltol. Otsuka Chemical Co. in Japan has operated several electroorganic processes on a small commercial scale. It has used plate and frame and aimular cells at currents in the range of 4500—6000 A (133). The process for the synthesis of maltol [118-71 -8], a food additive and flavor enhancer, starts from furfural [98-01-1] (see Food additives Flavors and spices). The electrochemical step is the oxidation of a-methylfurfural to give a cycHc acetal. The remaining reaction sequence is acid-catalyzed ring expansion, epoxidation with hydrogen peroxide, and then acid-catalyzed rearrangement to yield maltol, ie ... 

The presence of 9a-fluorme in the molecule of a 1 iP-hydroxy-8 -3-keto steroid causes completely stereospeafic alkalme epoxidation with hydrogen peroxide m a much slower reacuon (4 days vs 4 h) compared with the nonfluonnated analogue [21]... 

Epoxidation with hydrogen peroxide has also been tried. The epoxidation reaction is catalyzed with compounds of As, Mo, and B, which are claimed to produce propylene oxide in high yield ... 

As a, (3-unsaturated ketones are electron-poor alkenes, they do not generally give epoxides when treated with peracids. They can be epoxidized with hydrogen peroxide which involves nucleophilic attack by HOO- to give the epoxy ketone (Figure 4.1). 

In some cases, the pyrrolo[l,2-f]oxazoles were epoxidized with hydrogen peroxide in dichloromethane affording the epoxide with control of stereoselectivity (Equation 52) <1997TA2421, 2000T2437, 2004TA1239>. 

As a third example for an organocatalytic reaction, based on multiple hydrogen bonding and mechanistically investigated by DFT, we selected olefin epoxidation with hydrogen peroxide in fluorinated alcohol solvents, such as 1,1,1,3,3,3-hex-afluoro-2-propanol (HFIP) (Scheme 8). Here we encounter a new type of catalytic hydrogen bond the cooperative hydrogen bond. 

Niobia-supported MTO has been prepared either by the deposition of sublimed MTO onto the support, or by the impregnation of the support by a solution of MTO, and has been well characterised [54]. A large variety of oxidation reactions were efficiently performed with niobia-supported MTO, such as olefin metathesis catalysis [53,54], reactions of ethyl diazoacetate, heteroatom oxidation (amine and phosphine oxidations) and olefin epoxidation with hydrogen peroxide [55] (Scheme 13). 

Asymmetric epoxidation with hydrogen peroxide as the oxidizer promoted by chiral phase-transfer catalysts (chiral PTCs, Figure 6.7) can be performed under mild... 

The presence of a 9x-fluorine in a 11/l-hydroxy-A4-3-oxo steroid 10 results in completely stereospecific alkaline epoxidation with hydrogen peroxide to give 11 in a much slower reaction (4 d vs 4h) than that of the nonfluorinated analog.19 The nonfluorinated C = C bond in 3-perfluoroalkylated prop-1-ene 12 is epoxidized, with difficulty, in 7 days by 3-chloroperoxy-benzoic acid to give 13.20... 

A number of oxidation reactions of mono- and difluorosteroid compounds has been reported. In some reactions, the specific influence of a fluoro substituent on the reactivity has been observed the presence of a 9a-fluorine in a 11 /i-hydroxy-A4-3-oxo steroid causes completely stcreospecific alkaline epoxidation with hydrogen peroxide in a much slower reaction (4d vs 4 h) in comparison with the nonfluorinated analog.322 Most oxidations are accomplished by the highest selective biochemical (that is, by bacterial enzymatic) transformations. As the biochemical oxidation systems are not discussed in this section, only a list of selected transformations of steroids is presented in Table 21. For additional information see ref 323. 

Conjugated propylene epoxidation with hydrogen peroxide is the main reaction proceeding in the temperature range of 500-580 °C under optimal conditions the average propylene oxide yield reaches 50%. 

It is common knowledge that the rate of epoxidation by alkylperoxy radicals is defined by their structure. The simplest representative and the parent radical of this class is the HO radical. In the case of propylene epoxidation with hydrogen peroxide in the gas phase at 500-580 °C and contact time r = 4.4 s, the epoxidating particle is, probably, the HO radical whose activity in the absence of catalysts is higher than the RO activity. 

Epoxidation with hydrogen peroxide, Ruff hydrocarbon degradation, a-degradation of hydroxy acids and other reactions. 

Effective kinetic and thermodynamic parameters of propylene epoxidation with hydrogen peroxide on biomimic (perFTPhPFe(III)0H/Al203)... 

Figure 2.30 Possible mechanism of epoxidation with hydrogen peroxide in the presence of Strukel catalysts.

Berkessel A, Adrio JA (2004) Kinetic studies of olefin epoxidation with hydrogen peroxide in l,l,l,3,3,3-hexafluoro-2-propanol reveal a crucial catalytic role for solvent clusters. Adv Synth Catal 346 275-280 Berkessel A, Adrio JA (2006) Dramatic acceleration of olefin epoxidation in fluorinated alcohols activation of hydrogen peroxide by multiple H-bond networks. J Am Chem Soc 128 13412-13420 Berkessel A, Adrio JA, Huttenhain D, Neudorfl JM (2006a) Unveiling the booster effect of fluorinated alcohol solvents aggregation-induced conformational changes, and cooperatively enhanced H-bonding. J Am Chem Soc 128 8421-8426... 

Berkessel A, Andreae MRM (2001) Efficient catalytic methods for the Baeyer-Villiger oxidation and epoxidation with hydrogen peroxide. Tetrahedron Lett 42 2293-2295... 

Initially, /-menthyl 2-cyano-3-methyI-2-pentenoate, and /-menthyl and r/-bornyl cy-clopentylidenecyanoacetateswere epoxidized with hydrogen peroxide in the presence of sodium tungstate. Some asymmetric induction was achieved, but the degree of diastereoselectivity was not estimated26. In the final step of the synthesis of the antibiotic phosphonomycin, (Z)-propenylphosphonic acid was epoxidized under Weitz-Scheffer conditions and 92% optically pure phosphonomycin (+ )-x-phenethylammonium-c -epoxypropylphosphonate crystallized from the reaction mixture. It is unclear whether an asymmetric induction occurs during the epoxidation step and to what extent27. 

Hydroxynaphthalenones 7 were epoxidized with hydrogen peroxide in the presence of sodium carbonate in aqueous ethanol/acetone (96 4) to give epoxides 8 in 90% yield as the sole product78. 

Griseofulvin (20a) and its analogs 20b,c were epoxidized with hydrogen peroxide/potassium hydroxide and/or benzoyl peroxide in the presence of sodium methoxide yielding epoxides 21 a-e, respectively, as single diastereomers in moderate yield83. 

Asymmetric epoxidation, synthetic aspects of 85MI10 87YGK90. Epoxidation with hydrogen peroxide catalyzed by heteropoly acids 89YGK889. 

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