Epoxidation with t-BuOOH

Oxidation Catalysis Olefinic alcohol epoxidation with t-BuOOH VO(OiPr)3... 

Chiral olefinic alcohol epoxidation with t-BuOOH Ti[OCH(CH3)2]4... 

Racemic epoxy sulfone derivatives are easily prepared from al-lyl ethers by reaction with sodium p-toluenesulfinate in the presence of iodine followed by treatment with triethylamine, separation of E- and Z-isomers, and epoxidation with t-BuOOH and n-BuLi in THE (eq 3). ... 

Phenylacetaldehyde was readily converted into allylic alcohol 81 by a standard olefination and reduction protocol. Epoxidation with t-BuOOH and catalytic Ti(OPr-i)4 in the presence of catalytic (-)-DIPT gave (2R, 3R)-3-benzylglycidol 82 in >99% e.e. Addition of diphenyl-methanamine and Ti(OPr-i)4 in refluxing 1,2-dichloroethane led to aminodiol 83, from which aminoepoxide (S,S)-84 was obtained by hydrogenolysis and /V-protection followed by an intramolecular Mitsunobu reaction [76]. 

Reaction of alkenes with tert-butyl hydroperoxide (t-BuOOH) in the presence of a transition metal catalyst, for example, a vanadium(V), molybdenum(VI) or titanium(IV) complex, provides an excellent method for the preparation of epoxides. The molybdenum catalysts are most effective for the epoxidation of isolated double bonds, and the vanadium or titanium catalysts are most effective for aUylic alcohols. Even terminal alkenes can be epoxidized readily. For example, 1-decene was converted into its epoxide with t-BuOOH and Mo(CO)6 on heating in 1,2-dichloroethane. 

Synthesis of 31 by Method I (107,108) and its conversion to the related anti and syn diol epoxide derivatives (32,33) has been reported (108). The isomeric trans-1,lOb-dihydrodiot 37) and the corresponding anti and syn diol epoxide isomers (38,39) have also been prepared (108) (Figure 19). Synthesis of 37 from 2,3-dihydro-fluoranthene (109) could not be accomplished by Prevost oxidation. An alternative route involving conversion of 2,3-dihydrofluoranthene to the i8-tetrahydrodiol (3-J) with OsO followed by dehydration, silylation, and oxidation with peracid gave the Ot-hydroxyketone 35. The trimethylsilyl ether derivative of the latter underwent stereoselective phenylselenylation to yield 36. Reduction of 3 with LiAlH, followed by oxidative elimination of the selenide function afforded 3J. Epoxidation of 37 with t-BuOOH/VO(acac) and de-silylation gave 38, while epoxidation of the acetate of JJ and deacetylation furnished 39. 

The kinetics of the catalytic oxidation of cyclopentene to glutaraldehyde by aqueous hydrogen peroxide and tungstic acid have been studied and a compatible mechanism was proposed, which proceeds via cyclopentene oxide and /3-hydroxycyclopentenyl hydroperoxide. " Monosubstituted heteropolytungstate-catalysed oxidation of alkenes by t-butyl hydroperoxide, iodosobenzene, and dioxygen have been studied a radical mechanism was proved for the reaction of alkenes with t-BuOOH and O2, but alkene epoxidation by iodosobenzene proceeds via oxidant coordination to the catalyst and has a heterolytic mechanism. ... 

Allylic and cis-homoallylic alcohols are epoxidized readily, but frans-homoallylic and bishomoallylic alcohols react slowly, if at all. The stereoselectivity in the epoxidation of acyclic allylic alcohols is the same as and is comparable to that observed with r-BuOOH/VO(acac)2. The stereoselectivity in epoxidation of acyclic homoallylic alcohols is also the same but lower than that obtained with t-BuOOH/ VO(acac)2. Epoxidation of cyclic allylic alcohols proceeds more slowly and in lower yield than that of acyclic allylic alcohols. 

Epoxidation of tu-hydroxy allylsilanes 162 with t-BuOOH in the presence of a catalytic amount of VO(acac)2 in toluene gives the corresponding epoxide 163 with high erythro-... 

As a catalytic test reaction, the epoxidation of cyclooctene with t-BuOOH was studied. Although the complex leaches from an Al-containing MCM-41,... 

Molybdenum trioxide (M0O3) deposited on silica was one of the first supported Mo catalysts to be prepared. In contrast to Ti/SiC>2, which is used industrially, Mo/SiC>3 did not break through commercially, mainly owing to substantial leakage of Mo under catalytic conditions. Trifiro et al. (213) showed that when M0O3 on silica is used for the epoxidation of cyclohexene with t-BuOOH in benzene at 353 K, part of the activity originates from dissolved Mo. The main reason why Mo is not entirely retained on silicas and aluminas is thought to be the formation of soluble neutral Mo-diol complexes. 

All the polymers of Table III have been applied for the epoxidation of olefins with alkyl hydroperoxides. For example, the polymers with iminodiacetic acid or diethylene triamine groups were used for the regioselective epoxidation of (E)-geraniol with t-BuOOH to the 2,3-epoxide (225), whereas the Mo anchored to the diphenylphosphinopolystyrene catalyst is used in the epoxidation of cyclohexene with t-BuOOH (228). The polymer-supported molybdenyl thioglycolate has also been used for the catalytic oxidation of thiols and phosphines with air or pyridine N-oxide as the oxidant (234). 

As shown in Table III, supported Mo catalysts may be derived not only from the traditional Mo02(acac)2, Mo naphthenate, or Mo(CO)6 precursors. A yellow Mo peroxide complex, synthesized from Mo metal and hydrogen peroxide, was immobilized on a cross-linked polystyrene functionalized with triethylenetetramine (229). This Mo-containing material was capable of catalyzing the epoxidation of various olefins with t-BuOOH as the oxidant in the temperature range of 298-333 K. For example, cyclohexene oxide was obtained in 90% yield after 5 h of reaction at 333 K in benzene. 

The sterically crowded ligand (106) forms a very rare square-planar Co complex, as shown by an X-ray crystal structure, and a spin triplet (paramagnetic) ground state was also identified in the solid state. The Co complex of (107) catalyzes the epoxidation of norbomene with t-BuOOH or Phi as terminal oxidant, catalysis driven by formation of t-BuOO radicals employing a Co redox process. 

A variation of the Sharpless asymmetric epoxidation is to employ chiral hydroperoxides. The chiral iminium salt 89 has moderate enantiocontrol for epoxidation. Quatemized cinchona alkaloids can serve as chiral catalyst and phase-transfer agents in epoxidation of enones with NaOCl. Enones are also epoxidized by oxygen in the presence of diethylzinc and A-methylpseudoephedrine, whereas IZj-enones are submitted to enantioselective epoxidation by t-BuOOH-O-PrO),Yb and the BINOL 90. 

TABLE 3.4 Epoxidation of Various Olefins by Mn(Me2EBC)Cl2 with t-BuOOH ... 

Miscellaneous reactions. BINOL-phosphate ID has also found applications in a Pd-catalyzed allylation of aldehydes by l-benzhydrylamino-2-alkenes, and epoxidation of enals with t-BuOOH ... 

Tf the OH group is not blocked at all but left free, and the epoxidation reagent is the vanadium complex VO(acac)2 combined with t-BuOOH, the syn epoxide is formed instead. The vanadyl group chelates reagent and alcohol and delivers the reactive oxygen atom to the same face of the alkene. 

Epoxidation of allylic alcohols with t-BuOOH in the presence of Ti(Oi-Pr)4 and a dialkyl tartrate as a chiral ligand affords the corresponding epoxides in good yield with high regio- and enantioselectivity (Scheme 8). The enantioselec-tivity can be anticipated by empirical rule as shown in Scheme 8 when (S,S)-(-)-dialkyl tartrate is used as the chiral auxiliary, P-epoxide 55 is obtained, while (/ ,/ )-(-l-)-dialkyl tartrate gives a-epoxide 56. 

Reaction D in Fig. 5 represents a very useful approach to a number of enantiomerically pure allylic alcohols by the Sharpless epoxidation procedure [32], In the reported example, the reaction carried out with t-BuOOH/Ti(OPr-i)4 on racemic ( )-l-cyclohexyl-2-butenol in the presence of (-l-)-diisopropyltartrate (DIPT) occurs almost exclusively on the (5)-enantiomer of the substrate, and affords a single epoxide. The unreacted (R)-alcohol can be isolated in 96% e.e. 

The oxidation of allylic alcohols has been studied thoroughly using a variety of catalysts. The reactivity of the vanadium-tert-butyl hydroperoxide reagents towards the double bond of allylic alcohols makes possible selecfive epoxidation. Thus, reaction of geraniol with t-BuOOH and vanadium acetylacetonate [VO(acac)2] gave the 2,3-epoxide 33 (5.44). With peroxy-acids, reaction takes place preferentially at the other double bond. 

Related polydentate ligands are the polymer-anchored bis(phosphonomethyl)amino and bls(2-hydroxyethyl) amino species, studied by Suzuki (13). These ligands have been attached to both microreticular and macroreticular polystyrene-co-divinyl benzene and coordinated to both oxo-vanadium (V) and oxo-molybdenum(VI). Using the catalytic epoxidation of (E)-geraniol as a model system (with t-BuOOH) it was found that the macroreticular oxo-vanadium(V) catalyst was the most reactive, particularly with the phosphorous ligand (Equation 3). 

Scheme 7.3 Epoxidations of ot,P-unsaturated aldehydes with t-BuOOH.

As can be seen, stepwise synthesis of robust chelating ligands allows a strong anchoring of the metal center on the silica surface. Studies on the epoxidation of different olefins with t-BuOOH as the oxygen source indicated the following reactivity... 

Chemistry-based kinetic resolution methods, which make use of the preferential reaction of one enantiomer with a chiral reagent (e.g. hydroboration of racemic alkenes with diisopinocampheylborane) or an achiral reagent in the presence of an appropriate chiral catalyst (e.g. Sharpless epoxidation of racemic allylic alcohols with t-BuOOH in the presence of (2R,3R)- or (25,35)-diisopropyl tartrate and Ti(Oi-Pr)4) have not been exploited so far for the isolation of e.p. labeled substances. In contrast, biochemical methods have been widely used, particularly for the resolution of racemic a-[ " C]amino acids and various [ C]carboxylic acids. Such methods, including ... 

Allylic alcohols can be converted to epoxy-alcohols with tert-butylhydroperoxide on molecular sieves, or with peroxy acids. Epoxidation of allylic alcohols can also be done with high enantioselectivity. In the Sharpless asymmetric epoxidation,allylic alcohols are converted to optically active epoxides in better than 90% ee, by treatment with r-BuOOH, titanium tetraisopropoxide and optically active diethyl tartrate. The Ti(OCHMe2)4 and diethyl tartrate can be present in catalytic amounts (15-lOmol %) if molecular sieves are present. Polymer-supported catalysts have also been reported. Since both (-t-) and ( —) diethyl tartrate are readily available, and the reaction is stereospecific, either enantiomer of the product can be prepared. The method has been successful for a wide range of primary allylic alcohols, where the double bond is mono-, di-, tri-, and tetrasubstituted. This procedure, in which an optically active catalyst is used to induce asymmetry, has proved to be one of the most important methods of asymmetric synthesis, and has been used to prepare a large number of optically active natural products and other compounds. The mechanism of the Sharpless epoxidation is believed to involve attack on the substrate by a compound formed from the titanium alkoxide and the diethyl tartrate to produce a complex that also contains the substrate and the r-BuOOH. ... 

Sharpless epoxidation involves treating an allylic alcohol with titanium(IV) tetraisopropoxide [Ti(0-/Pr)4], tert-butyl hydroperoxide [t-BuOOH], and a specific enantiomer of a tartrate ester. 

Typical procedure The mole ratio of alkene t-BuOOH catalyst was 10 10 0.25 and 40 mmol of the olefin serving as its own solvent. Thus, 10 mmol of TBHP (80% in di-tert-butyl peroxide) and 0.25 mmol of vanadium pentoxide were added to 50 mmol of the olefin and the reaction mixture was stirred at 60°C under a dinitrogen atmosphere. The products formed were analyzed by GC by comparison of their retention time with those of authentic samples. Good yields of epoxides were obtained only with an excess of olefin to TBHP of 5 1. That the olefin doubles up as the solvent makes for a more practical procedure. Typical results (34) are shown in Table 1 ... 

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