Alcohols and Epoxides

Alkenes in (alkene)dicarbonyl(T -cyclopentadienyl)iron(l+) cations react with carbon nucleophiles to form new C —C bonds (M. Rosenblum, 1974 A.J. Pearson, 1987). Tricarbon-yi(ri -cycIohexadienyI)iron(l-h) cations, prepared from the T] -l,3-cyclohexadiene complexes by hydride abstraction with tritylium cations, react similarly to give 5-substituted 1,3-cyclo-hexadienes, and neutral tricarbonyl(n -l,3-cyciohexadiene)iron complexes can be coupled with olefins by hydrogen transfer at 140°C. These reactions proceed regio- and stereospecifically in the successive cyanide addition and spirocyclization at an optically pure N-allyl-N-phenyl-1,3-cyclohexadiene-l-carboxamide iron complex (A.J. Pearson, 1989). 

Alcohols can be synthesized by the addition of carbanions to carbonyl compounds (W.C. Still, 1976) or epoxides. Both types of reactions often produce chiral centres, and stereoselectivity is an important aspect of these reactions. 

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As with i -substituted allyl alcohols, 2,i -substituted allyl alcohols are epoxidized in excellent enantioselectivity. Examples of AE reactions of this class of substrate are shown below. Epoxide 23 was utilized to prepare chiral allene oxides, which were ring opened with TBAF to provide chiral a-fluoroketones. Epoxide 24 was used to prepare 5,8-disubstituted indolizidines and epoxide 25 was utilized in the formal synthesis of macrosphelide A. Epoxide 26 represents an AE reaction on the very electron deficient 2-cyanoallylic alcohols and epoxide 27 was an intermediate in the total synthesis of (+)-varantmycin. 

The reaction of olefins,alcohols,and epoxides > with or at high temperatures over catalysts such as... 

Transesterification and Hydrolysis of Carboxylic Acid Derivatives, Alcohols, and Epoxides... 

A range of reactions of 2-chlorocyclohexyl(dichloro)phosphine (60) with alcohols and epoxides has been described, largely with a view to the synthesis of polymer intermediates and flame-retardants.50 The copolymerization of dichloro(phenyl)-phosphine with styrene and vinyl butyl ether in the presence of maleic anhydride has been studied.61... 

Acyl substituents at the 3- and/or 4-positions result in decreased hydrolytic stability compared with the alkyl and aryl derivatives described above. Despite this constraint most of the usual reactions of the carbonyl group are possible. Aldehydes <9ILA1211> and ketones are oxidized to the carboxylic acid, borohydride reduction affords the expected alcohols, and epoxides are formed on reaction with diazomethane. Oximes and arylhydrazones are formed with hydroxylamine and arylhydrazines, and the products may subsequently undergo monocyclic rearrangement involving the oxadiazole to give the corresponding isomeric furazans and 1,2,3-triazoles (Section 4.05.5.1.4). 

A nucleophile is an electron rich species that reacts with an electrophile. The term electrophile literally means electron-loving , and is an electron-deficient species that can accept an electron pair. A number of nucleophilic substitution reactions can occur with alkyl halides, alcohols and epoxides. However, it can also take place with carboxylic acid derivatives, and is called nucleophilic acyl substitution. 

Linford and coworkers have shown that the attachment of alkenes to H-terminated silicon surfaces can also be initiated by direct mechanical scribing, in a process termed chemomechanical functionalization [145-147]. The reaction of 1-alkenes (as well as 1-alkynes) leads to attachment of the molecule to the surface through two new Si—C bonds. The proposed mechanism is the mechanical cleavage of Si—H and Si—Si bonds, leading to silicon radicals that then react with the reactive liquid. Interestingly, Linford and coworkers have also extended this work to show that chemomechanical functionalization can be carried out not only on H-terminated Si, but also on sihcon covered with oxide, and have shown that the process works with a variety of halides, alcohols, and epoxides in both the liquid and gas phase [146]. 

Nucleophilic Hydroxymethylation of Aldehydes, Ketones, Organic Halides, Alcohols, and Epoxides.8... 

The direct reaction between alcohols and epoxides is very slow so alkaline catalysts are employed and are presumed to increase the rate by converting the growing chain to the more nucleophilic alkoxide ion. Polymerizations of this kind have recently been carefully investigated by Gee and coworkers (21). The reactions are still not rapid even at elevated temperatures so the molecular weights obtained in this way are normally quite low (< 10,000). The most rapid reactions of epoxides are those catalysed by acids but even they must be regarded as of the nucleophilic type with acceleration due to the increased reactivity of the protonated monomer,... 

In conclusion, six-, seven- or as here eight-membered rings as well as macrocycles can be synthesized. Stereogenic centers are not touched and the process is compatible with many other functional groups like esters, amines, alcohols and epoxides. 

Much of the work on model systems was stimulated by the observation of Udenfriend and co-workers in 19546S4a,b that a mixture of Fe(II), EDTA, ascorbic acid, and molecular oxygen could hydroxylate arenes to phenols under mild conditions. Udenfriend s reagent also hydroxylates alkanes to alcohols and epoxidizes olefins.670 6 74 The EDTA in Udenfriend s reagent probably reduces the redox potential of the Fe(II)/Fe(III) couple. The ascorbic acid functions as an electron donor, analogous to the cofactor in monooxygenases, and can be replaced by other enediols.672... 

Metalloporphyrins catalyze the autoxidation of olefins, and with cyclohexene at least, the reaction to ketone, alcohol, and epoxide products goes via a hydroperoxide intermediate (129,130). Porphyrins of Fe(II) and Co(II), the known 02 carriers, can be used, but those of Co(III) seem most effective and no induction periods are observed then (130). ESR data suggest an intermediate cation radical of cyclohexene formed via interaction of the olefin with the Co(III) porphyrin this then implies possible catalysis via olefin activation rather than 02 activation. A Mn(II) porphyrin has been shown to complex with tetracyanoethylene with charge transfer to the substrate (131), and we have shown that a Ru(II) porphyrin complexes with ethylene (8). Metalloporphyrins remain as attractive catalysts via such substrate activation, and epoxidation of squalene with no concomitant allylic oxidation has been noted and is thought to proceed via such a mechanism (130). Phthalocyanine complexes also have been used to catalyze autoxidation reactions (69). 

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