Hydrogen epoxidation with

Besides hydrogenations, epoxidations with hydrogen-bonded catalysts were reported [51, 52]. Copper(I) pyrazolborates (Fig. 14) were immobilized on sil-icagel by dissolving the complexes in dichloro methane and subsequent stirring forseveral hours and filtration. 

Several cortisone derivatives with glucocorticoid effects are most active, if they contain fluorine in the 9or-position together with an Il(9-OH group. Both substituents are introduced by the cleavage of a 9,11 -epoxide with hydrogen fluoride. The regio- and stereoselective formation of the -epoxide is achieved by bromohydrination of a 9,11-double bond and subsequent alkali treatment (J. Fried, 1954). 

The reaction of perfluoroalkenes with alkaline hydrogen peroxide is a good general method for the preparation of the corresponding epoxides with the exception of the most reactive of the series, TFEO (eq. 6). 

Hydrogen Sulfide andMercaptans. Hydrogen sulfide and propylene oxide react to produce l-mercapto-2-propanol and bis(2-hydroxypropyl) sulfide (69,70). Reaction of the epoxide with mercaptans yields 1-aLkylthio- or l-arylthio-2-propanol when basic catalysis is used (71). Acid catalysts produce a mixture of primary and secondary hydroxy products, but ia low yield (72). Suitable catalysts iaclude sodium hydroxide, sodium salts of the mercaptan, tetraaLkylammonium hydroxide, acidic 2eohtes, and sodium salts of an alkoxylated alcohol or mercaptan (26,69,70,73,74). 

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 ... 

The monomer (laurolactam) could he produced from 1,5,9-cyclododeca-triene, a trimer of hutadiene (Chapter 9). The trimer is epoxidized with peracetic acid or acetaldehyde peracetate and then hydrogenated. The saturated epoxide is rearranged to the ketone with Mgl2 at 100°C. is then changed to the oxime and rearranged to laurolactam. 

The second major discovery regarding the use of MTO as an epoxidation catalyst came in 1996, when Sharpless and coworkers reported on the use of substoichio-metric amounts of pyridine as a co-catalyst in the system [103]. A change of solvent from tert-butanol to dichloromethane and the introduction of 12 mol% of pyridine even allowed the synthesis of very sensitive epoxides with aqueous hydrogen peroxide as the terminal oxidant. A significant rate acceleration was also observed for the epoxidation reaction performed in the presence of pyridine. This discovery was the first example of an efficient MTO-based system for epoxidation under neutral to basic conditions. Under these conditions the detrimental acid-induced decomposition of the epoxide is effectively avoided. With this novel system, a variety of... 

Begue and coworkers recently achieved an improvement in this method by performing the epoxidation reaction in hexafluoro-2-propanol [120]. They found that the activity of hydrogen peroxide was significantly increased in this fluorous alcohol, in relation to trifluoroethanol, which allowed for the use of 30% aqueous H202. Interestingly, the nature of the substrate and the choice of additive turned out to have important consequences for the lifetime of the catalyst. Cyclic dis-ubstituted olefins were efficiently epoxidized with 0.1 mol% of MTO and 10 mol%... 

Asymmetric epoxidation of olefins with ruthenium catalysts based either on chiral porphyrins or on pyridine-2,6-bisoxazoline (pybox) ligands has been reported (Scheme 6.21). Berkessel et al. reported that catalysts 27 and 28 were efficient catalysts for the enantioselective epoxidation of aryl-substituted olefins (Table 6.10) [139]. Enantioselectivities of up to 83% were obtained in the epoxidation of 1,2-dihydronaphthalene with catalyst 28 and 2,6-DCPNO. Simple olefins such as oct-l-ene reacted poorly and gave epoxides with low enantioselectivity. The use of pybox ligands in ruthenium-catalyzed asymmetric epoxidations was first reported by Nishiyama et al., who used catalyst 30 in combination with iodosyl benzene, bisacetoxyiodo benzene [PhI(OAc)2], or TBHP for the oxidation of trons-stilbene [140], In their best result, with PhI(OAc)2 as oxidant, they obtained trons-stilbene oxide in 80% yield and with 63% ee. More recently, Beller and coworkers have reexamined this catalytic system, finding that asymmetric epoxidations could be perfonned with ruthenium catalysts 29 and 30 and 30% aqueous hydrogen peroxide (Table 6.11) [141]. Development of the pybox ligand provided ruthenium complex 31, which turned out to be the most efficient catalyst for asymmetric... 

The Payne epoxidation with benzonitrile/ hydrogen peroxide is also an efficient epoxidation process. It is often the method of choice for industrial batch-type applications, but on a small scale the need for continuous pH control is inconvenient. 

Cleavage of epoxides with hydrogen halides Addition of hypohalous acids to alkenes... 

The preparation of Pans-1,2-cyclohexanediol by oxidation of cyclohexene with peroxyformic acid and subsequent hydrolysis of the diol monoformate has been described, and other methods for the preparation of both cis- and trans-l,2-cyclohexanediols were cited. Subsequently the trans diol has been prepared by oxidation of cyclohexene with various peroxy acids, with hydrogen peroxide and selenium dioxide, and with iodine and silver acetate by the Prevost reaction. Alternative methods for preparing the trans isomer are hydroboration of various enol derivatives of cyclohexanone and reduction of Pans-2-cyclohexen-l-ol epoxide with lithium aluminum hydride. cis-1,2-Cyclohexanediol has been prepared by cis hydroxylation of cyclohexene with various reagents or catalysts derived from osmium tetroxide, by solvolysis of Pans-2-halocyclohexanol esters in a manner similar to the Woodward-Prevost reaction, by reduction of cis-2-cyclohexen-l-ol epoxide with lithium aluminum hydride, and by oxymercuration of 2-cyclohexen-l-ol with mercury(II) trifluoro-acetate in the presence of ehloral and subsequent reduction. ... 

In the same spirit DFT studies on peroxo-complexes in titanosilicalite-1 catalyst were performed [3]. This topic was selected since Ti-containing porous silicates exhibited excellent catalytic activities in the oxidation of various organic compounds in the presence of hydrogen peroxide under mild conditions. Catalytic reactions include epoxidation of alkenes, oxidation of alkanes, alcohols, amines, hydroxylation of aromatics, and ammoximation of ketones. The studies comprised detailed analysis of the activated adsorption of hydrogen peroxide with... 

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>. 

---