Oxazoline epoxides

In turn the oxazoline-containing polymer may then react very rapidly (e.g. at 240°C) with such groups as carboxyls, amines, phenols, anhydrides or epoxides, which may be present in other polymers. This reaction will link the two polymers by a rearrangement reaction similar to that involved in a rearrangement polymerisation without the evolution of water or any gaseous condensation products (Figure 7.14). 

Variations and Improvements on Alkylations of Chiral OxazoUnes Metalated chiral oxazolines can be trapped with a variety of different electrophiles including alkyl halides, aldehydes,and epoxides to afford useful products. For example, treatment of oxazoline 20 with -BuLi followed by addition of ethylene oxide and chlorotrimethylsilane yields silyl ether 21. A second metalation/alkylation followed by acidic hydrolysis provides chiral lactone 22 in 54% yield and 86% ee. A similar... 

Oxazolines can be obtained by the Lewis acid catalyzed epoxide ring opening of glycidic esters or amides (e.g., 118) with acetonitrile . Oxazolidines are available from the palladium-catalyzed cycloaddition of vinyl epoxides with imines <00H885> or the samarium-promoted reaction of ketimines (e.g., 120) with unfunctionalized... 

The sequential addition method also allows the synthesis of many different block copolymers in which the two monomers have different functional groups, such as epoxide with lactone, lactide or cyclic anhydride, cyclic ether with 2-methyl-2-oxazoline, imine or episul-Hde, lactone with lactide or cyclic carbonate, cycloalkene with acetylene, and ferrocenophane with cyclosiloxane [Aida et al., 1985 Barakat et al., 2001 Dreyfuss and Dreyfuss, 1989 Farren et al., 1989 Inoue and Aida, 1989 Keul et al., 1988 Kobayashi et al., 1990a,b,c Massey et al., 1998 Yasuda et al., 1984]. 

Epoxytrichloroacetimidates 153 also undergo oxazoline ring formation in the presence of a catalytic amount of Lewis acids.Diethylaluminum chloride was found to be superior to boron trifluoride, which tends to further hydrolyze the oxazoline 154 to the trichloroacetamide. Generally, formation of the six-membered ring oxazine 155 is not favored, but it can be a serious side reaction if the epoxide contains substituents that stabilize the incipient cation generated prior to ring closure. Examples from this study are summarized in Table 8 19 (Fig 8 8 Scheme 8.45). 

Epoxides also participate in the Ritter reaction with nitriles. An investigation of the ring opening of several alkyl-substituted glycidic esters and amides 181 showed that this transformation occurs with inversion and is completely regiospecific. ° Esters appeared to be somewhat more reactive than amides. However, phenyl-substituted glycidic esters and amides 184 are almost totally nonstereoselective. In addition, the oxazolines 186 are isolated in low yield due to the propensity of intermediate 185 to generate an aldehyde byproduct 187 (Scheme 8.53). 

Epoxides also undergo the Ritter reaction in good yields with retention of configuration via a episulfonium intermediate 190a (double-inversion process). For monosubstituted epoxides, the yields of oxazolines are lower due to nondis-criminatory attack of the nitrile on both the primary and the secondary carbon atom of the episulfonium intermediate. Complete retention of configuration is still observed despite the lower yield (Scheme 8.54). 

Allyl amides (enamides), for example, 225, 228, and 230 cyclize to oxazolines, for example, 226, 229, and 231 when the double bond is activated by an electrophile. The double bond can also be conjugated to a ketone, or present as an allylic epoxide. Reagents commonly used to promote the cyclization include acids,iodine,selenium reagents,and trimethylsilyl triflate (Scheme 8.63). ... 

During an investigatior of the utihty of epoxide 240 as an intermediate in the synthesis of the HIV protease inhibitor Indinavir 241, it was found that the amino alcohol 237 must first be protected prior to iodination. Without protection, the iodination of the unsaturated amide 237 gave the unstable oxazoline 239 in 83% yield (Scheme 8.65). 

The transformation of optically active epoxides with acetonitrile into optically active oxazolines (167,168) can be induced by various superacids714 [Eq. (5.264)]. The reaction proceeds with inversion of the asymmetric center with high stereospecificity with anhydrous HF and A1C13, whereas partial racemization is observed in triflic acid (Table 5.39). 

II-Hydroxy isocyanides p-amino alcohols The reagent reacts with epoxides in ihe presence of zinc iodide to give -hydroxy isocyanides in contrast to the usual ji-hydroxy nitriles (5, 720). The products are useful intermediates to oxazolines and [S-mnino alcohols. The reaction is highly regio- and stereoselective (equation I). 

One recent publication from the group of Abu-Omar reports on a condensation reaction involving glycerol and furfural, both renewables, to produce dioxolanes, formally a dehydration reaction. Here, a cationic oxorhenium(V) oxazoline species is used as the catalyst for the formation of various 1,3-dioxalanes from furfural with diols or epoxides under mild conditions (Scheme 21). Especially interesting is the reaction of furfural with glycerol to obtain a 70 30 mixture of the corresponding 1,3-dioxolane and 1,3-dioxane in solvent-free conditions [125]. 

Again, since mixtures of 2-oxazolines are obtained from nitriles and unsymmetrical epoxides,15 it does not seem likely in this case that a purely carbonium ion mechanism is involved, for this would require the formation of primary carbonium ions. An alternate possibility is that the nitrile nucleophilically attacks the oxonium salt (27) of the epoxide to give the nitrilium salts 28 and 29, which then cyclize, thus ... 

The epoxide/cyanate compositions contain catalysts of cyanate cyclotrimerization and oxazoline ring formation. Curing agents for epoxide resin are mentioned in... 

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