Epoxides, functionalization

Regioselectivity in opening of a-functionalized epoxides by treatment with trimethylamine dihydrofluoride has been observed. Thus, cw-isophorol epoxide gives exclusively 3-fluoro-l,2-diol, whereas from the trans isomer, 2-fluoro-l,3-diol is obtained as the main product together with 3-methylenecyclohexane-l,2-diol. This behavior has been discussed m terms of the influence of a-substituents on the transition state conformations [7 J] (equations 11 and 12). 

This procedure was extended to a method for asymmetric synthesis of optically active epoxides starting from optically active sulfoxides. As the oxiranyUithium 131 reacts with the acidic hydrogen of the n-butyl aryl sulfoxide, the introduction of electrophiles to the reaction mixture was problematic. Therefore, the reaction was performed by addition of 1 equivalent of f-C4H9Li at — 100°C to 130 and the sulfoxide-lithium exchange reaction was found to be extremely rapid (within a few seconds at this temperature). Moreover, as f-butyl aryl sulfoxide 138 has now no more acidic hydrogen, the addition of several electrophiles leads to functionalized epoxides 139 (equation 48). ... 

Terashima et al. 231) reported an asymmetric halolactonization reaction. This highly stereoselective reaction permits the synthesis of intermediates for the preparation of chiral a,a-disubstituted a-hydroxycarboxylic acids (227)231c), a-hydroxyketones (228) 231c), functionalized epoxides (229) 231d,e) and natural products 231h,j). Only amino acids have so far been used as a source of the chiral information in the asymmetric halolactonization reaction. Again, the best results have been obtained by using cyclic imino acid enantiomers, namely proline. 

Glycidol is an epoxide used as a chemical intermediate in the production of functional epoxides, glycidyl urethanes, pharmaceuticals and other products. It is also used as a reactive diluent in epoxy resin systems and as a sterilant. Occupational exposure may occur during its production and use. No data were available on environmental exposure to glycidol. 

CPO has been used occasionally in complex syntheses. An important application of CPO as an enantioselective epoxidation catalyst is the efficient synthesis of (R)-2-mevalonolactone (Scheme 2.26a) [270]. A survey of the literature revealed that the previous methods required many steps to produce the lactone, in low overall yield, with moderate ee, in addition to expensive starting materials. Meanwhile, a retro-synthetic analysis starting with an appropriately functionalized epoxide provided confidence that CPO could rescue the situation if used in the key stereogenic step. Another completed synthesis is depicted in Scheme 2.26b. Again, the epoxide is generated in high yield with conversion to (R)-dimethyl-2-methylaziridine-l,2-dicarboxylate, which may serve as a synthon for P-methylamino acids [283],... 

A considerable amount of work was required to optimize the leaving group and avoid racem-ization through a Payne rearrangement mechanism.12 Of course, the Sharpless epoxidation of allyl alcohols is well-known to access these 3-functionalized epoxides. 

Among the more unusual modes of epoxide reactivity is a technique for reductive deoxygenation using a system of triphenylphosphine and iodine in dimethylformamide (DMF). Under these conditions, the functionalized epoxide 98 was quantitatively converted to the diallyl ether 99. Similar conditions were found to convert epoxides to the interestingly substituted (5-bromoformate derivatives (e.g. 101) <02T7037>. 

The principle of miniemulsion polymerization to polyadditions of epoxyresins was successfully transferred to mixtures of different epoxides with varying diamines, dithiols, or diols which were heated to 60°C to form the respective polymers [125]. The requirement for the formulation of miniemulsions is that both components of the polyaddition reaction show a relatively low water solubility, at least one of them even below 10 5 g l1. The diepoxide bisphenol-A-diglycidylether was successfully used as epoxy component. In order to vary the obtained polymeric structure, tri- and tetra-functionalized epoxides were also used. As amino components a NH2 terminated poly(propylene oxide) with Mw=2032 g mol1, 4,4 -diaminobibenzyl, 1,12-diaminododecane, and 4,4 -di-aminodicyclohexylmethane were applied. As other addition components beside amine, 1,6-hexanedithiol and Bisphenol A were used. The hydrophobic compo-... 

Base 20 has also been applied in the deprotonation of functionalized epoxides. Thus (15,4f ,55 )-12 could be obtained in 94% ee using 2 equiv. of 20 (Scheme 16)27. 

Besides the most important area of surface coatings, the use of photopolymers as photoresists in the manufacture of printed circuits is well established. Photoimaging with aryldiazonium salt photoinitiators and multifunctional cresol-novolac epoxides was first described by Schlesinger Crivello has mentioned several new photoresists based on the photopolymerization of epoxides with onium initiators Meier and Zweifel have shown that iron arene salts in combination with multifunctional cresol-novolac epoxides yield photoresists with high resolution and contrast. Dual functional epoxides (cf. Sect. 5) containing chalcone groups as light-sensitive units have been described as suitable photoresists especially... 

Functionalized epoxides are regioselectively opened by use of trimethylsilyl azide-Al(OPr )3 giving 2-trimethylsiloxy azides by attack on the less substituted carbon (Sch. 15) this provides a promising way for the preparation of /3-amino aleohols [35]. The functional groups acetoxy, methoxy, phenoxy, tert-butoxy, p-toluenesulfonyloxy, phthalimido, chloro, and bromo were unaffected in this reaction. 

Carbox> I terminated polybuladicnc polymers require curing in order to form a tridimensional network. Poly functional epoxides and aziridines arc used for cross-linking. 

The reaction of a wide variety of functionalized epoxides containing esters, amides and acetals with chlorotitanium triphenoxide and allylmagnesium chloride provides exclusive reaction at the more substituted carbon <05T6726>. The use of protected chiral epoxides, 54 and 56, with the same reagent system provides a facile route into chiral quaternary centers, 55 and 57. 

Nucleophilic substitutions proceeding via Sn2 pathways can be activated by pressure, as has been demonstrated in many examples. In particular, the ring opening of epoxides can be initiated by pressure, and also by Lewis acid catalysis. Consequently, combining these two activation modes might lead to an even more effective way to functionalize epoxides, and indeed, this strategy has been successfully applied. 

Figure 3. HNMR spectrum of a mixture of hydrosilane-functional epoxides.

Copolymerization of caprolactone with epoxides opens a wide range of various functionalities that can be accessed. These functional epoxides can be based on substituted epichlorohydrin [63] or on other molecules. In our laboratory, we recently presented an epoxide system based on 2-methyl-4-pentenoic acid, which is esterified in a first step with a desired functional moiety and then epoxidized to obtain a functional epoxide that is compatible with caprolactone copolymerization [44,62], This toolbox approach allows for the functionalization with different functional moieties on demand. One advantage of these statistical copolymers is that the copolymer composition can be controlled by the reactivity of the monomers, and therefore, defined copolymers can be obtained (Figure 9.7). 

FIGURE 9.7 Functionalization via statistical copolymerization with functional epoxides [62],... 

More recently, Simpkins has described a route to functionalized epoxides by diastereoselective reduction of racemic cychc P-ketosulfoxides (Scheme 4.7) [10]. Exclusive formation of (12a), (R = Bu, Pr DIBAL), or (12b) (R = Me, Et, Bu, Pr, Ph ZnCl2/DIBAL), could be realised by appropriate selection of reaction conditions. Preference for (12a) was rationalized by intramolecular hydride delivery from... 

Interestingly, functionalized epoxides were readily obtained through functional group interconversion (Scheme 4.8). Although it was initially performed on a... 

Subsequent technology consists of preparation of difunctional silicon-containing monomers by monohydrosyldation of an a,co-difunctional Si-H-terminated siloxane with a vinyl-functional epoxide or oxetane. This is followed by the dehydrodimerization of the resulting Si—H—functional intermediate. The method uses simple, readily available starting materials and it... 

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