Using Epoxides

Since its introduction in carbohydrate chemistry by Hicks and Fraser-Reid in 1975 [22], applications of the opening of epoxide with carbon nucleophiles abound in the literature. Just a few seminal examples will be mentioned here, other examples will be found in combination with other branching-chain methods. 

Another example from the macrolide field is the synthesis of antimycin A3, which starts with opening of epoxide 9 [28]. Opening of this manno epoxide with butylmagnesium chloride afforded the C3 branched-derivative 10 with total regio- and stereo-selectivity. Again the Fiirst-Plattner rule applies and the introduction of the substituent at C3 was expected. The remainder of the synthesis 

SCHEME 11.3 Reagents i MejCuLi ii (i) dMSO, AcqO and (2) MeONa, MeOH. 

The clear-cut behavior in the opening of epoxides can sulfer some exceptions. Such abnormal reactions have been reported in the opening of epoxide 21 with vinylmagnesium bromide. In this case, the vinyl residue was introduced at C2 as expected but with retention of configuration this is because of preferential opening with the bromide ion followed by the displacement of the bromide atom with the carbon nucleophile [34]. 

As mentioned above, ring opening of conformationally unbiased epoxides is less regioselective and the two expected compounds can be obtained in a ratio depending on the conformational equilibrium between the C4 and chairs. Obviously the use of the 4,6-acetal ring allows opening 

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The chemical resistance of PTFE is exceptional. There are no solvents and it is attacked at room temperature only by molten alkali metals and in some cases by fluorine. Treatment with a solution of sodium metal in liquid ammonia will sufficiently alter the surface of a PTFE sample to enable it to be cemented to other materials using epoxide resin adhesives. 

From what alkene was the following 1,2-diol made, and what method was used, epoxide hydrolysis or Os04 ... 

Epoxidation by Dioxirane Derivatives. Another useful epoxidizing agent is dimethyldioxirane (DMDO),86 which is generated by in situ reaction of acetone and peroxymonosulfate in buffered aqueous solution. Distillation gives about aO.lM solution of DMDO in acetone.87... 

In a similar manner, the Gansauer group also used this domino methodology for the constructions of annulated tetrahydrofurans 3-150 using epoxides of type 3-149 [63]. In this way, a broad variety of products could be synthesized in a ds-selective fashion in good yields and high diastereoselectivity (Scheme 3.39). 

The most significant development in the etherification using epoxides is the ARO process that occurs through the catalysis of metallosalen complexes (Figure 5).270 Mechanistic studies that have been carried out on these systems by... 

In the challenge to develop more environmentally benign routes to useful epoxidized fatty derivatives, the exploitation of heterogeneous catalysts is one of the... 

The same strategy was also employed in the synthesis of the saturated analogue of protolichesterinic acid ( )-dihydroprotolichesterinic acid (4) can be synthesized using epoxide 32 as a starting material for the intramolecular radical cyclization to yield 33 as the major diastereomer (Scheme 5). Subsequent oxidation gave finally rise to ( )-4, which could be obtained in di-astereomerically pure form by fractional crystallization. 

By using epoxides as electrophiles, diols 335 were isolated and easily cyclized by treatment with boron trifluoride into the corresponding substituted tetrahydrobenzoxepines 336 (Scheme 99) l... 

What is the advantage of using epoxidized soybean oil as a stabilizer for PVC ... 

Polymerization using epoxides as monomers includes the ring opening of epoxides via C-O bond cleavage. Thus, a mode of G-O bond cleavage (Sn2 or SnI) and selectivity, that is, which C-O bond is cleaved, coupled with the symmetry of epoxides (symmetrical or unsymmetrical), cause regio- and stereochemical issues to be controlled in the epoxide polymerization. 

A recent report (J. Org. Chem. 2004, 69, 8510) by Paul G. Williard of Brown University and Ruggero Curci of University di Bara of the oxidation of 5 to 6 serves as a timely reminder that the widely-used epoxidation reagent dimethyl dioxirane is also useful for the oxidation of secondary alcohols to ketones. 

The transformation of carboxylic acids and their functional derivatives to the corresponding peroxycarboxylic acids or diacyl peroxides are generally known reactions.200-201 Among the hydroperoxy derivatives, trifluoroperacetic acid is a frequently used epoxidizing reagent in organic chemistry and is usually prepared in situ.200-201... 

Hart, H. Lavrik, P. B. Synthetically useful epoxidations with molecular oxygen. /. Org. Chem. 1974, 39, 1793-1794. 

Gansauer and coworkers studied very thoroughly titanocene chloride-catalyzed radical cyclizations using epoxides as starting materials [142-145]. More recently the applicability of 10 mol% of titanocene chloride complexes 47a-d in radical 4-exo cyclizations of 6,7-epoxy-2-heptenoate derivatives 79 was demonstrated... 

Fig. 55 Cobalt-catalyzed Fleck reactions using epoxides...

Most of the transformations carried out on catharanthine have naturally been concerned with the preparation of potential precursors of dimeric bases related to vinblastine. For example, 15-acetoxydihydrocatharanthine (configuration at C-15 unknown) is also obtained, together with the recently reported221 20-acetoxydi-hydrocatharanthine, when catharanthine is subjected to the modified Prevost reaction.139 The conversion of catharanthine (236) into the potentially useful epoxides (237a), (237b), and (239), the lactone (238), and the diol (240) (stereochemistry at C-15 and C-20 not rigorously proved) has also been described (Scheme 25).140,141... 

Sml2-mediated aldol reactions can also be carried out using epoxides and aziridines as precursors to the Sm(III) enolate. In 2000, Mukaiyama reported a method for the synthesis of unsymmetrical bis-aldols using Sml2 to... 

The author [3] developed a method for preparing cyclic trithiocarbonates, (II), using epoxides in the ionic solvent l-butyI-3-methyIimidazoIium... 

Epoxides and Imincs react with carbon dioxide to form both monomeric products as well as polymers. The conversion using epoxides, which lead to monomeric carbonates or polycarbonates has been intensively studied. 

S)-rra/if-verbenol when (+)-DIPT is used in Ae catalyst. For allylic alcohols with an exocyclic double bond, kinetic resolution gives 2-methylenecyclohexanol (78) with 80% ee and a 46% yield when (-)-DIPT is used. Epoxidation of the homochiral 4-methylene-Sa-cholestan-3P-ol (79) is reported to be much faster with catalyst derived from (-( )-DET than from (-)-DET. The variable enantioselectivities seen in these results likely stem from conformational restraints imposed by the cyclic structures which prevent the allylic alcohols from attaining an ideal conformation for the epoxidation process (see Section 3.2.6 and Figure 5 for the proposed ideal conformation). 

A review by Darensbourg outlining the use of metal-salen complexes as catalysts for the formation of polymeric materials using epoxides as starting materials was published in 2007 <2007CRV2388>. 

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