Alcohols => epoxides

The hydrogenolyaia of cyclopropane rings (C—C bond cleavage) has been described on p, 105. In syntheses of complex molecules reductive cleavage of alcohols, epoxides, and enol ethers of 5-keto esters are the most important examples, and some selectivity rules will be given. Primary alcohols are converted into tosylates much faster than secondary alcohols. The tosylate group is substituted by hydrogen upon treatment with LiAlH (W. Zorbach, 1961). Epoxides are also easily opened by LiAlH. The hydride ion attacks the less hindered carbon atom of the epoxide (H.B. Henhest, 1956). The reduction of sterically hindered enol ethers of 9-keto esters with lithium in ammonia leads to the a,/S-unsaturated ester and subsequently to the saturated ester in reasonable yields (R.M. Coates, 1970). Tributyltin hydride reduces halides to hydrocarbons stereoselectively in a free-radical chain reaction (L.W. Menapace, 1964) and reacts only slowly with C 0 and C—C double bonds (W.T. Brady, 1970 H.G. Kuivila, 1968). 

C—O single bonds (alcohols, epoxides, ethers, acetates, etc.). 

Additives. Because of their versatility, imparted via chemical modification, the appHcations of ethyleneimine encompass the entire additive sector. The addition of PEI to PVC plastisols increases the adhesion of the coatings by selective adsorption at the substrate surface (410). PEI derivatives are also used as adhesion promoters in paper coating (411). The adducts formed from fatty alcohol epoxides and PEI are used as dispersants and emulsifiers (412). They are able to control the viscosity of dispersions, and thus faciHtate transport in pipe systems (413). Eatty acid derivatives of PEI are even able to control the viscosity of pigment dispersions (414). The high nitrogen content of PEIs has a flame-retardant effect. This property is used, in combination with phosphoms compounds, for providing wood panels (415), ceUulose (416), or polymer blends (417,418) with a flame-retardant finish. 

Me3SiI, CH2CI2, 25°, 15 min, 85-95% yield.Under these cleavage conditions i,3-dithiolanes, alkyl and trimethylsilyl enol ethers, and enol acetates are stable. 1,3-Dioxolanes give complex mixtures. Alcohols, epoxides, trityl, r-butyl, and benzyl ethers and esters are reactive. Most other ethers and esters, amines, amides, ketones, olefins, acetylenes, and halides are expected to be stable. 

The AE reactions on 2,5,5-trisubstituted allyl alcohols have received little attention, due in part the limited utility of the product epoxides. Selective ring opening of tetrasubstituted epoxides are difficult to achieve. Epoxide 39 was prepared using stoichiometric AE conditions and were subsequently elaborated to Darvon alcohol. Epoxides 40 and 41 were both prepared in good selectivity and subsequently utilized in the preparation of (-)-cuparene and the polyfunctoinal carotenoid peridinin, respectively. Scheme 1.6.12... 

The reaction is carried out using a titanium silicalite-1 (TS-1) zeolite catalyst [30, 122]. This type of catalyst is known to accelerate the selective oxidation of alcohols, epoxidation of alkenes and hydroxylation of aromatics. These reactions have importance for fine-chemical production. 

In acyclic secondary -allylic alcohols, epoxidation by the vanadium system shows opposite stereospecificity to that of peracid and molybdenum carbonyl-mediated epoxidation (see Scheme 6)22 The predominance of the erythro isomer in the former process is rationalized22 in terms of the energetically more favorable transition state (6, cf. 5) and in this context the mechanism has analogy in the epoxidation behavior of medium-ring cyclic allylic alcohols.23... 

The enantioseiective hydrogenation of a-amino ketones has been applied extensively to the synthesis of chiral drugs such as the / -agonist SR 58611 (Sanofi Cie). m-Chlorstyreneoxide was obtained via carbene-induced ring closure of the amino alcohol. Epoxide-opening by a chiral amine obtained via a ruthenium-catalyzed hydrogenation of an enamide has led to the desired compound where... 

Figure 5.1 Allylic alcohol epoxidation using a chiral titanium(IV) complex.

Key words Olefin epoxidation, allylic alcohol epoxidation, insertion, direct oxygen... 

An extensive set of experimental data on regioselectivity, face selectivity [106-109] and kinetics [110] of allylic alcohol epoxidation by the MTO system is available. On the basis of these results experimentalists have suggested a variety of transition structures (Figure 10) [28, 108, 110]. 

The metal-alcoholate mechanism is well established for allylic alcohol epoxidation in the presence of Ti and V catalysts. [41, 51, 52, 111-113], In principle, it can provide a viable pathway also for catalysis by a Re complex. In fact, allylic alcohols may add, at least formally, to either an oxo-Re or peroxo-Re moiety (e.g. of 5a or 5b) in a process which is referred to as metal-alcoholate binding this mechanism gives rise to metal-alcoholate intermediates. We identified four intermediates of alcohol addition to di(peroxo) complexes two resulting transition states, S-8 and S-9b, are shown in Figure 11. All metal-alcoholate intermediates he significantly higher in energy (by 10-22 kcal/mol) than 5b + propenol, except the... 

The presence of the stereogenic centre at C(l) introduces an additional factor in the asymmetric epoxidation now, besides the enantiofacial selectivity, the diastereoselectivity must also be considered, and it is helpful to examine epoxidation of each enantiomer of the allylic alcohol separately. As shown in Fig. 10.2, epoxidation of an enantiomer proceeds normally (fast) and produces an erythro epoxy alcohol. Epoxidation of the other enantiomer proceeds at a reduced rate (slow) because the steric effects between the C(l) substituent and the catalyst. The rates of epoxidation are sufficiently significative to achieve the kinetic resolution and either the epoxy alcohol or the recovered allylic alcohol can be obtained with high enantiomeric purity [9]. 

The peroxotungstate [W203(02)4(H20)2], immobilized on dihydroimidazolium-based ionic liquid-modifed Si02 has been employed for alkene and allylic alcohol epoxidation... 

Adam and coworkers have carried out several studies aimed at elucidating the geometry of the transition-state structure for the allylic alcohol epoxidation using chiral substrates as stereochemical probe (equation 38). The threo.erythro diasteroselec-tivities for the epoxidation of a set of methyl-substituted chiral allylic alcohols with A ... 

Chiral metal complexes, aUylic alcohol epoxidation catalysis, 394-401 Chiral naphthalene derivatives, singlet oxygen cycloaddition, 271... 

Diisopropyl tartrate (DIPT), aUyhc alcohol epoxidation, 395... 

Table 3 Allylic alcohol epoxidation with TBHP/dioxomolybdenum Mo02(acac)(L ) catalysts, where the catalysts were homogeneous or zeolite-Y-supported... 

In their stereorational synthesis of (+)-[10.10] 61b, they reacted the epoxide 107 with a 1 1 3-butenylmagnesium bromide-cuprous iodide complex in dimethyl-sulfide-THF at low temperature. The predominant SN2 pathway gave the (+)-( )-allyl alcohol 108 whose Sharpless asymmetric epoxidation in dichloromethane at —23 °C for 10 min provided the corresponding epoxy alcohol and recovered (+)-(R)-allyl alcohol 108 (78 % yield and 95 % optical purity). The (R)-configuration was assigned following the Sharpless model61 for allylic alcohol epoxidation. 

Alkyl halides, alcohols, epoxides, carboxylic acid and its derivatives, and benzene and its derivatives. 

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