Epoxidation addition reactions

Tetrafluoroethylene undergoes addition reactions typical of an olefin. It bums in air to form carbon tetrafluoride, carbonyl fluoride, and carbon dioxide (24). Under controlled conditions, oxygenation produces an epoxide (25) or an explosive polymeric peroxide (24). Trifluorovinyl ethers,... 

The trans isomer is more reactive than the cis isomer ia 1,2-addition reactions (5). The cis and trans isomers also undergo ben2yne, C H, cycloaddition (6). The isomers dimerize to tetrachlorobutene ia the presence of organic peroxides. Photolysis of each isomer produces a different excited state (7,8). Oxidation of 1,2-dichloroethylene ia the presence of a free-radical iaitiator or concentrated sulfuric acid produces the corresponding epoxide [60336-63-2] which then rearranges to form chloroacetyl chloride [79-04-9] (9). 

The addition—reaction product of bisphenol A [80-05-07] and glycidyl methacrylate [106-91-2] is a compromise between epoxy and methacrylate resins (245). This BSI—GMA resin polymerizes through a free-radical induced covalent bonding of methacrylate rather than the epoxide reaction of epoxy resins (246). Mineral fillers coated with a silane coupling agent, which bond the powdered inorganic fillers chemically to the resin matrix, are incorporated into BSI—GMA monomer diluted with other methacrylate monomers to make it less viscous (245). A second monomer commonly used to make composites is urethane dimethacrylate [69766-88-7]. 

The most common method of epoxidation is the reaction of olefins with per-acids. For over twenty years, perbenzoic acid and monoperphthalic acid have been the most frequently used reagents. Recently, m-chloroperbenzoic acid has proved to be an equally efficient reagent which is commercially available (Aldrich Chemicals). The general electrophilic addition mechanism of the peracid-olefin reaction is currently believed to involve either an intra-molecularly bonded spiro species (1) or a 1,3-dipolar adduct of a carbonyl oxide, cf. (2). The electrophilic addition reaction is sensitive to steric effects. 

Addition Reactions of Metal Enolates of Non-stabilized Esters, Amides, and Ketones to Epoxides... 

In spite of their intrinsic synthetic potential, addition reactions of metal enolates of non-stabilized esters, amides, and ketones to epoxides are not widely used in the synthesis of complex molecules. Following the seminal work of Danishefsky [64], who introduced the use of Et2AlCl as an efficient catalyst for the reaction, Taylor obtained valuable spiro lactones through the addition reaction of the lithium eno-late of tert-butyl acetate to spiro-epoxides, upon treatment of the corresponding y-... 

Scheme 8.36 Addition reaction of a metalated ketone-DMH to an epoxide.

A synthetically useful diastereoselectivity (90% dc) was observed with the addition of methyl-magnesium bromide to a-epoxy aldehyde 25 in the presence of titanium(IV) chloride60. After treatment of the crude product with sodium hydride, the yy -epoxy alcohol 26 was obtained in 40% yield. The yyn-product corresponds to a chelation-controlled attack of 25 by the nucleophile. Isolation of compound 28, however, reveals that the addition reaction proceeds via a regioselective ring-opening of the epoxide, which affords the titanium-complexed chloro-hydrin 27. Chelation-controlled attack of 27 by the nucleophile leads to the -syn-diastereomer 28, which is converted to the epoxy alcohol 26 by treatment with sodium hydride. 

The initial rates in the 2" mns decreased in the following order Co-OTs > Co-OAc > Co-Cl > Co-1 (see Table 43.2), which is consistent with the idea of deactivation by counterion addition to epoxide. As reported by Nielsen et al. (7), the rate of counterion addition to epoxide determines the kinetics of HKR. We suspect that the iodide and chloride counterions undergo such rapid addition to epoxide that most of the HKR reaction in the 2" mn occurred with the much less active Co-OH catalyst formed in situ. In contrast, the weakly nucleophilic tosylate counterion reacted more slowly with the epoxide and was therefore more stable. 

Dimethylsulfonium methylide is both more reactive and less stable than dimethylsulfoxonium methylide, so it is generated and used at a lower temperature. A sharp distinction between the two ylides emerges in their reactions with a, ( -unsaturated carbonyl compounds. Dimethylsulfonium methylide yields epoxides, whereas dimethylsulfoxonium methylide reacts by conjugate addition and gives cyclopropanes (compare Entries 5 and 6 in Scheme 2.21). It appears that the reason for the difference lies in the relative rates of the two reactions available to the betaine intermediate (a) reversal to starting materials, or (b) intramolecular nucleophilic displacement.284 Presumably both reagents react most rapidly at the carbonyl group. In the case of dimethylsulfonium methylide the intramolecular displacement step is faster than the reverse of the addition, and epoxide formation takes place. 

Z-vinyl iodide was obtained by hydroboration and protonolysis of an iodoalkyne. The two major fragments were coupled by a Suzuki reaction at Steps H-l and H-2 between a vinylborane and vinyl iodide to form the C(ll)-C(12) bond. The macrocyclization was done by an aldol addition reaction at Step H-4. The enolate of the C(2) acetate adds to the C(3) aldehyde, creating the C(2)-C(3) bond and also establishing the configuration at C(3). The final steps involve selective deprotonation and oxidation at C(5), deprotection at C(3) and C(7), and epoxidation. 

Among other addition reactions dienes undergo catalytic hydrogeneration (1,2- and 1,4-), epoxidation (1,2- only, and more slowly than the corresponding simple alkenes), but they seldom undergo hydration. 

Annual Volume 71 contains 30 checked and edited experimental procedures that illustrate important new synthetic methods or describe the preparation of particularly useful chemicals. This compilation begins with procedures exemplifying three important methods for preparing enantiomerically pure substances by asymmetric catalysis. The preparation of (R)-(-)-METHYL 3-HYDROXYBUTANOATE details the convenient preparation of a BINAP-ruthenium catalyst that is broadly useful for the asymmetric reduction of p-ketoesters. Catalysis of the carbonyl ene reaction by a chiral Lewis acid, in this case a binapthol-derived titanium catalyst, is illustrated in the preparation of METHYL (2R)-2-HYDROXY-4-PHENYL-4-PENTENOATE. The enantiomerically pure diamines, (1 R,2R)-(+)- AND (1S,2S)-(-)-1,2-DIPHENYL-1,2-ETHYLENEDIAMINE, are useful for a variety of asymmetric transformations hydrogenations, Michael additions, osmylations, epoxidations, allylations, aldol condensations and Diels-Alder reactions. Promotion of the Diels-Alder reaction with a diaminoalane derived from the (S,S)-diamine is demonstrated in the synthesis of (1S,endo)-3-(BICYCLO[2.2.1]HEPT-5-EN-2-YLCARBONYL)-2-OXAZOLIDINONE. 

Alkylperoxyl radicals produced by addition reactions can be destructively isomerized with the formation of epoxides [13,139,154,155] ... 

With an operating catalytic cycle for the reductive opening of epoxides at hand, we decided to investigate the preparatively more important formation of carbon—carbon bonds. Inter-molecular addition reactions to a,(3-unsaturated carbonyl compounds have been described for the stoichiometric process of Nugent and RajanBabu [5], The general concept behind the catalytic conditions is outlined in Scheme 12.16. 

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