Epoxidations with tert-butyl hydroperoxide

S. Bhor, M. K. Tse, M. Klawonn, C. Dbbler, W. Magerlein, M. Beller, Ruthenium-catalyzed asymmetric alkene epoxidation with tert-butyl hydroperoxide as oxidant, Adv. Synth. Catal. 346 (2004) 263. 

Allylic alcohols, for example geraniol, 2-methylallyl alcohol, 3,3-dimethylallyl alcohol, 3-buten-2-ol, l-octen-3-ol, and l-hexen-3-ol, are epoxidized with tert-butyl hydroperoxide in the presence of a vanadyl salen oxo-transfer catalyst in supercritical CO2. The metal catalyst was prepared in a simple two-step, Schiff base-type reaction to form the salen ligand, followed by complexation to the vanadyl group. The use of non-toxic supercritical CO2 in the presence of the new epoxidation vanadium catalyst led to yields and diastereoselectivities that were comparable to those resulting from the use of environmentally hazardous solvents such as CH2CI2 [59]. 

The epoxidation of the dienone 92 proceeded to give the epoxide 93 using the cinchonidinium catalyst 9 (R=H, X=C1) with tert-butyl hydroperoxide.1701... 

Natural compounds are also applied as chiral ligands in enantioselective homogeneous metallo-catalysts. A classical example is the Sharpless epoxidation of primary allylic alcohols with tert-butyl hydroperoxide [37]. Here the diethyl ester of natural (R,R)-(+)-tartaric acid (a by-product of wine manufacture) is used as bi-dentate ligand of the Ti(iv) center. The enantiomeric excess is >90%. The addition of zeolite KA or NaA is essential [38], bringing about adsorption of traces of water and - by cation exchange - some ionization of the hydroperoxide. 

In the context of asymmetric catalysis, titanium silsesquioxanes containing the chiral ligand (lR,2S,5R)-(-)-menthoxo ligand (MentO) (figure 14.3) have been synthesized from the monosilanol la (R = cyclopentyl) and Ti(OPr )4 [70]. The molecular complexes were tested as asymmetric homogeneous catalysts for the epoxidation of cinammic alcohol with tert-butyl hydroperoxide and compared... 

Sharpless Asymmetric Epoxidation This is a method of converting allylic alcohols to chiral epoxy alcohols with very high enantioselectivity (i.e., with preference for one enantiomer rather than formation of racemic mixture). It involves treating the allylic alcohol with tert-butyl hydroperoxide, titanium(IV) tetra isopropoxide [Ti(0—/Pr)4] and a specific stereoisomer of tartaric ester. For example,... 

Kinetics. The kinetics of the epoxidation of olefins with tert-butyl hydroperoxide in the presence of molybdenum hexacarbonyl have been studied. The reaction rate is first order in tert-butyl hydroperoxide, in olefin, and in molybdenum hexacarbonyl. Olefins substituted near the double bond by electron-releasing alkyl groups react more rapidly than the corresponding unsubstituted olefins. The kinetic data indicate that the epoxidation reaction proceeds according to the rate law,... 

The existence of a facile epoxidation of II at a more rapid rate than that of TME is of interest in relation to a possible intermolecular pathway for formation of an epoxy alcohol from an allylic hydroperoxide during olefin oxidation. When a solution of II (0.01 mole) in TME (0.09 mole) was treated with tert-butyl hydroperoxide (0.01 mole) in the presence of... 

In the epoxidation of alkenes with tert-butyl hydroperoxide and a molybdenum oxide catalyst, addition of an aliphatic amine first accelerates the formation of the intermediate 229 and also favours the production of epoxide in favour of the alternative fragmentation to carbonyl compounds (Scheme 5)356. 

From these considerations, the synthesis of silsesquioxanes was optimised, by means of HTE, as a function of the activity of the catalysts obtained after titanium coordination to the silsesquioxane structures. Therefore, this approach aimed at producing any incompletely condensed silsesquioxane that would result in active catalysts after titanium coordination rather than a specific structure (like silsesquioxane ulhS). The epoxidation of 1-octene with tert-butyl hydroperoxide (TBHP) as the oxidant was chosen as test reaction for the activity of the catalysts [26]. 

A new parameter space for the synthesis of silsesquioxane precursors was defined by six different trichlorosilanes (R=cyclohexyl, cyclopentyl, phenyl, methyl, ethyl and tert-butyl) and three highly polar solvents [dimethyl sulfoxide (DMSO), water and formamide]. This parameter space was screened as a function of the activity in the epoxidation of 1-octene with tert-butyl hydroperoxide (TBHP) [26] displayed by the catalysts obtained after coordination of Ti(OBu)4 to the silsesquioxane structures. Fig. 9.4 shows the relative activities of the titanium silsesquioxanes together with those of the titanium silsesquioxanes obtained from silsesquioxanes synthesised in acetonitrile. The values are normalised to the activity of the complex obtained by reacting Ti(OBu)4 with the pure cyclopentyl silsesquioxane o7b3 [(c-C5H9)7Si7012Ti0C4H9]. 

Two different epoxidation reactions have been studied using chiral phase transfer catalysts. The salts 22 and 23 have been used to catalyse the nucleophilic epoxidation of enones (e.g. 24) to give either enantiomer of epoxides such as 25 (Scheme 9) [17]. Once again, the large 9-anthracenylmethyl substituent is thought to have a profound effect on the enantio selectivity of the process. A similar process has been exploited by Taylor in his approach to the Manumycin antibiotics (e.g. Manumycin C, 26) [18]. Nucleophilic epoxidation of the quinone derivative 27 with tert-butyl hydroperoxide anion, mediated by the cinchonidinium salt la, gave the tx,/ -epoxy ketone 28 in >99.5% ee (Scheme 10). 

The retarding effect of alcohols on the rate of epoxidation manifests itself in the observed autoretardation by the alcohol coproduct.428,434 446,447 The extent of autoretardation is related to the ratio of the equilibrium constants for the formation of catalyst-hydroperoxide and catalyst-alcohol complexes. This ratio will vary with the metal. In metal-catalyzed epoxidations with fe/T-butyl hydroperoxide, autoretardation by tert-butyl alcohol increased in the order W < Mo < Ti < V the rates of Mo- and W-catalyzed epoxidations were only slightly affected. Severe autoretardation by the alcohol coproduct was also observed in vanadium-catalyzed epoxidations.428 434 446 447 The formation of strong catalyst-alcohol complexes explains the better catalytic properties of vanadium compared to molybdenum for the epoxidation of allylic alcohols.429 430 452 On the other hand, molybdenum-catalyzed epoxidations of simple olefins proceed approximately 102 times faster than those catalyzed by vanadium.434 447 Thus, the facile vanadium-catalyzed epoxidation of allyl alcohol with tert-butyl hydroperoxide may involve transfer of an oxygen from coordinated hydroperoxide to the double bond of allyl alcohol which is coordinated to the same metal atom,430 namely,... 

Company was the largest producer. In that year, Oxirane brought on stream the first peroxidation process involving catalyzed epoxidation of propylene with tert-butyl hydroperoxide. In 1977, Oxirane (later Arco Chemical) commercialized a process which employed ethylbenzene hydroperoxide as the epoxidizing agent and produced PO and styrene (Fig. 10.23). 

Asymmetric epoxidation Is accomplished by reaction of an allylic alcohol with tert-butyl hydroperoxide In the presence of J)-(-) or L-(+)-dlethyl tartrate and titanium tetralsopropoxlde (Figure la). The orientation of the product can be predicted in advance (-) tartrates epoxldize from the top face of the double bond when the bond Is viewed In a horizontal plane and the carbinol group is on the right, as seen from the front of the plane. The (+) tartrates epoxldize from below the plane (Figure lb). 

Table 1. Enantioselective Epoxidation of 6 with tert-Butyl Hydroperoxide in Buffer Solution at pH = 11 in the Presence of BSA (0.05 molar equiv)...

The bulk of oxidations with tert-butyl hydroperoxide consists of epoxidations of alkenes in the presence of transition metals [147, 215, 216, 217, 218]. In this way, a,p-unsaturated aldehydes [219] and ketones [220] are selectively oxidized to epoxides without the involvement of the carbonyl function. Other applications of tert-butyl hydroperoxide such as the oxidation of lactams to imides [225], of tertiary amines to amine oxides [226, 227], of phosphites to phosphates [228], and of sulfides to sulfoxides [224] are rare. In the presence of a chiral compound, enantioselective epoxidations of alcohols are successfully accomplished with moderate to high enantiomeric excesses [221, 222, 223]. 

Molybdenum hexacarbonyl, Mo(CO)6 [328], and molybdenum ace-tylacetonate, Mo02(acac)2 [530], catalyze the stereoselective epoxidation of allylic alcohols with tert-butyl hydroperoxide. 

Next, the process chemistry for a large-scale synthesis of (+)-6a (MGS0008) is presented (see Scheme 3.2) [41], The reaction of racemic (+)-16 with TMSC1 and LHMDS, followed by dehydrosilylation with palladium acetate afforded enone ( )-2 (90% yield), which was stereoselectively epoxidized using tert-butyl hydroperoxide (TBHP) in the... 

M. Fujiwara, H. Wessel, H. Park, H. W. Roesky, Formation of titanium tert-butylperoxo intermediate from cubic silicon-titanium complex with tert-butyl hydroperoxide and its reactivity for olefin epoxidation. Tetrahedron 58 (2002) 239. 

S. Ivanov, R. Boeva, S. Tanielyan, Catalytic epoxidation of propylene with tert-butyl hydroperoxide in the presence of modified carboxy cation-exchange resin "Amberlite" IRC-50, J. Catal. 56 (1979) 150. 

The most interesting conversions of geraniol to linalool would be those introducing chirality in the linalool. This can be effected by using chiral auxiliaries during allylic epoxidation of geraniol. Allylic epoxidation of geraniol is efficiently carried out with tert-butyl hydroperoxide in presence of aluminum tri-tert-... 

Figure 4 Effect of preparation method on the reactivity of titania/silica catalysts in the epoxidation of cyclooctene with tert-butyl hydroperoxide in tert-butanol...

Figure 5 shows effect of oxidant on the reactivity of the sol-gel titania/silica catalysts in the epoxidation of cyclooctene. The conversion in the epoxidation of cyclooctene with tert-butyl hydroperoxide sharply increases with reaction time. However, when the oxidant is hydrogen peroxide, the conversion is quite low... 

Alternatively, an enantiomerically pure catalyst that is not an enzyme can be used to obtain an enantiomerically pure target molecule. For example, an enantiomerically pure epoxide of an allylic alcohol can be prepared by treating the alcohol with tert-butyl hydroperoxide, titanium isopropoxide, and enantiomerically pure diethyl tartrate (DET). The structure of the epoxide depends on the enantiomer of diethyl tartrate used. 

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