Of epoxides to alcohols

By studying the NMR spectra of the products, Jensen and co-workers were able to establish that the alkylation of (the presumed) [Co (DMG)2py] in methanol by cyclohexene oxide and by various substituted cyclohexyl bromides and tosylates occurred primarily with inversion of configuration at carbon i.e., by an 8 2 mechanism. A small amount of a second isomer, which must have been formed by another minor pathway, was observed in one case (95). Both the alkylation of [Co (DMG)2py] by asymmetric epoxides 129, 142) and the reduction of epoxides to alcohols by cobalt cyanide complexes 105, 103) show preferential formation of one isomer. In addition, the ratio of ketone to alcohol obtained in the reaction of epoxides with [Co(CN)5H] increases with pH and this has been ascribed to differing reactions with the hydride (reduction to alcohol) and Co(I) (isomerization to ketone) 103) (see also Section VII,C). 

More frequent than the deoxygenation of epoxides to alkenes is reduction of epoxides to alcohols. Its regiospecificity and stereospecificity depend on the reducing agents. 

Hydrogenolysis of epoxides to alcohols by catalytic hydrogenation over platinum requires acid catalysis. 1-Methylcyclohexene oxide was reduced to a mixture of cis- and /ranj-2-methylcyclohexanol [652]. Steroidal epoxides usually gave axial alcohols stereospecifically 4,5-epoxycoprostan-3a-ol afforded cholestan-3a,4/J-diol [652 ]. 

Reagents of choice for reduction of epoxides to alcohols are hydrides and complex hydrides. A general rule of regioselectivity is that the nucleophilic complex hydrides such as lithium aluminum hydride approach the oxide from the less hindered side [511, 653], thus giving more substituted alcohols. In contrast, hydrides of electrophilic nature such as alanes (prepared in situ from lithium aluminum hydride and aluminum halides) [653, 654, 655] or boranes, especially in the presence of boron trifluoride, open the ring in the opposite direction and give predominantly less substituted alcohols [656, 657,658]. As far as stereoselectivity is concerned, lithium aluminum hydride yields trans products [511] whereas electrophilic hydrides predominantly cis products... 

Arene(tricarbonyl)chromium complexes, 19 Nickel boride, 197 to trans-alkenes Chromium(II) sulfate, 84 of anhydrides to lactones Tetrachlorotris[bis(l,4-diphenyl-phosphine)butane]diruthenium, 288 of aromatic rings Palladium catalysts, 230 Raney nickel, 265 Sodium borohydride-1,3-Dicyano-benzene, 279 of aryl halides to arenes Palladium on carbon, 230 of benzyl ethers to alcohols Palladium catalysts, 230 of carboxylic acids to aldehydes Vilsmeier reagent, 341 of epoxides to alcohols Samarium(II) iodide, 270 Sodium hydride-Sodium /-amyloxide-Nickel(II) chloride, 281 Sodium hydride-Sodium /-amyloxide-Zinc chloride, 281 of esters to alcohols Sodium borohydride, 278 of imines and related compounds Arene(tricarbonyl)chromium complexes, 19... 

The reduction of epoxides to alcohols has been accomplished by a variety of reducing agents. The reduction of unsymmetrical epoxides with lithium aluminium hydride in general occurs by attack of the hydride at the least-hindered side of the epoxide to form the more highly substituted alcohol. 

Although electrochemical reduction and enzymic reduction of epoxides to alcohols have been reported, little information is available about their characteristic features. 

Enantioselective ring opening of epoxides to alcohols 02EJO393. 

The borate (1) is a new reagent for the reductive opening of epoxides to alcohols, with reduction occurring at the least substituted carbon of aliphatic epoxides, and at the most substituted carbon when an aryl substituent is present (Scheme 2). This provides a pattern of regioselectivity which contrasts with other methods. 

Polymerization to Polyether Polyols. The addition polymerization of propylene oxide to form polyether polyols is very important commercially. Polyols are made by addition of epoxides to initiators, ie, compounds that contain an active hydrogen, such as alcohols or amines. The polymerization occurs with either anionic (base) or cationic (acidic) catalysis. The base catalysis is preferred commercially (25,27). 

Lithium aluminum hydride (LiAlH4) is the most powerful of the hydride reagents. It reduces acid chlorides, esters, lactones, acids, anhydrides, aldehydes, ketones and epoxides to alcohols amides, nitriles, imines and oximes to amines primary and secondary alkyl halides and toluenesulfonates to... 

The (3-elimination of epoxides to allylic alcohols on treatment with strong base is a well studied reaction [la]. Metalated epoxides can also rearrange to allylic alcohols via (3-C-H insertion, but this is not a synthetically useful process since it is usually accompanied by competing a-C-H insertion, resulting in ketone enolates. In contrast, aziridine 277 gave allylic amine 279 on treatment with s-BuLi/(-)-spar-teine (Scheme 5.71) [97]. By analogy with what is known about reactions of epoxides with organolithiums, this presumably proceeds via the a-metalated aziridine 278 [101]. 

Isomerization has been observed with many a,j3-unsaturated carboxylic acids such as w-cinnamic 10), angelic, maleic, and itaconic acids (94). The possibility of catalyzing the interconversion of, for example, 2-ethyl-butadiene and 3-methylpenta-l,3-diene has not apparently been explored. The cobalt cyanide hydride will also catalyze the isomerization of epoxides to ketones (even terminal epoxides give ketones, not aldehydes) as well as their reduction to alcohols. Since the yield of ketone increases with pH, it was suggested that reduction involved reaction with the hydride [Co" (CN)jH] and isomerization reaction with [Co (CN)j] 103). A related reaction is the decomposition of 2-bromoethanol to acetaldehyde... 

Sulphated zirconia catalysts can be acidic or superacidic depending on the method of treatment. A variety of acid-catalysed reactions, referred to earlier in this section, can be carried out with sulphated zirconia. Yadav and Nair (1999) have given a state-of-the art review on this subject. Examples of benzylation of benzene with benzyl chloride / benzyl alcohol, alkylation of o-xylene with. styrene, alkylation of diphenyl oxide with 1-dodecene, isomerization of epoxides to aldehydes, acylation of benzene / chlorobenzene with p-chloro benzoylchloride, etc. are covered in the review. 

By combining several click reactions, click chemistry allows for the rapid synthesis of useful new compounds of high complexity and combinatorial libraries. The 2-type reaction of the azide ion with a variety of epoxides to give azido alcohols has been exploited extensively in click chemistry. First of all, azido alcohols can be converted into amino alcohols upon reduction.70 On the other hand, aliphatic azides are quite stable toward a number of other standard organic synthesis conditions (orthogonality), but readily undergo 1,3-dipolar cycloaddition with alkynes. An example of the sequential reactions of... 

The combination of (EtO)3SiH/CsF (or KF) provides a convenient reagent for the reduction of esters to alcohols.76,80,83 The yields are in the 70% range. Potassium tetraethoxyhydridosilicate also reduces esters in moderate yields.288 The combination of PM HS/CpiTiCE/n-BuLi reduces esters in high yields even in the presence of an epoxide and a trisubstituted olefin (Eq. 140).289 The reagent combination can reduce a methyl ester in the presence of a tert-butyl ester (Eq. 141).290... 

Butyne-l,4-diol has been hydrogenated to the 2-butene-diol (97), mesityl oxide to methylisobutylketone (98), and epoxides to alcohols (98a). The rhodium complex and a related solvated complex, RhCl(solvent)(dppb), where dppb = l,4-bis(diphenylphosphino)butane, have been used to hydrogenate the ketone group in pyruvates to give lactates (99) [Eq. (15)], and in situ catalysts formed from rhodium(I) precursors with phosphines can also catalyze the hydrogenation of the imine bond in Schiff bases (100) (see also Section III,A,3). 

Heterogeneous catalysis is widely used in technology for gas-phase oxidation of hydrocarbons to alcohols, aldehydes, epoxides, anhydrides, etc. Homogeneous catalysis predominates in the liquid-phase oxidation technology. Nevertheless, a series of experimental studies was devoted in the 1970s to 1990s to heterogeneous catalysis. The main objects of study were metal oxides and metals as catalysts. 

BASE-INDUCED REARRANGEMENT OF EPOXIDES TO ALLYLIC ALCOHOLS trans-Pinocarveol,... 

TT-ALLYLNICKEL HALIDES METHALLYLBENZENE, 52, 115 Rearrangement of epoxides to allylic alcohols, 53, 17 Reduction, by controlled-po-tential electrolysis, 52, 22 by lithium aluminum hydride of exo-3,4-dichlorobicyclo [3.2.l]oct-2-ene to 3-chlorobicyclo[3.2.l]oct-2-ene, 51, 61... 

ARO reaction with phenols and alcohols as nucleophiles is a logical extension of HKR of epoxides to synthesize libraries of stereochemically defined ring-opened products in high optical purity. To this effect Annis and Jacobsen [69] used their polymer-supported Co(salen) complex 36 as catalyst for kinetic resolution of epoxides with phenols to give l-aiyloxy-2-alcohols in high yield, purity and ee (Scheme 17). Conducting the same reaction in the presence of tris(trifluoromethyl)methanol, a volatile, nonnucleophilic protic acid additive accelerates KR reaction with no compromise with enantioselectivity and yield. Presumably the additive helped in maintaining the Co(III) oxidation state of the catalyst. 

The overall transformation of alkenes to alcohols that is accomplished by epoxidation and reduction corresponds to alkene hydration. This reaction sequence is therefore an alternative to the methods discussed in Chapter 4 for converting alkenes to alcohols. 

Because of the mildness of the procedure, this is probably the best means of accomplishing this conversion. The selenoxide reaction has been used in a procedure for the conversion of epoxides to allylic alcohols.229... 

Enantioselective deprotonation.2 The rearrangement of epoxides to allylic alcohols by lithium dialkylamides involves removal of the proton syn to the oxygen.3 When a chiral lithium amide is used with cyclohexene oxide, the optical yield of the resulting allylic alcohol is 3-31%, the highest yield being obtained with 1. 

Isomerization of epoxides to ally lie alcohols. The isomerization of (- )-ver-nolic acid (1) to ( + )-coriolic acid (2) is best effected with this magnesium amide in toluene at 0°.1... 

Both undergo oxidation with epoxide and aldehyde formation, but the former gives an epoxidation/alcohol oxidation ratio of 3, whereas the latter gives an epoxidation/alcohol oxidation ratio of only 0.2. That this difference is due to the steric requirements inside the pores of the catalyst is demonstrated by the fact that the relative rates of epoxidation and alcohol oxidation of the same molecules on a large-pore Ti02/Si02 catalyst are almost the same (Tatsumi et al., 1993). 

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