Oxirane reactions with amines

The epoxy group (oxirane ring) can react with both nucleophilic and electrophilic reagents. The most typical example of a step-growth polymerization of epoxy monomers is the reaction with amines, which are the most commonly curing agents/hardeners used to build up epoxy networks. The reactions shown in Scheme 28.1 take place in this case. 

Step polymerization reactions, where little molecules such as epoxies (oxiranes) react with amines, or isocyanates react with polyols with functionality greater than two to form short, branched chains, eventually condensing it into epoxies or polyurethanes, respectively. Schematically... 

Vinyl-functional alkylene carbonates can also be prepared from the corresponding epoxides in a manner similar to the commercial manufacture of ethylene and PCs via CO2 insertion. The most notable examples of this technology are the syntheses of 4-vinyl-1,3-dioxolan-2-one (vinyl ethylene carbonate, VEC) (5, Scheme 24) from 3,4-epoxy-1-butene or 4-phenyl-5-vinyl-l,3-dioxolan-2-one (6, Scheme 24) from analogous aromatic derivative l-phenyl-2-vinyl oxirane. Although the homopolymerization of both vinyl monomers produced polymers in relatively low yield, copolymerizations effectively provided cyclic carbonate-containing copolymers. It was found that VEC can be copolymerized with readily available vinyl monomers, such as styrene, alkyl acrylates and methacrylates, and vinyl esters.With the exception of styrene, the authors found that VEC will undergo free-radical solution or emulsion copolymerization to produce polymeric species with a pendant five-membered alkylene carbonate functionality that can be further cross-linked by reaction with amines. Polymerizations of 4-phenyl-5-vinyl-l,3-dioxolan-2-one also provided cyclic carbonate-containing copolymers. 

Some examples of ring opening reactions with carbanions leading to five-membered heterocyclic ring formation are shown in Scheme 85. Pyrrole syntheses from functionally substituted oxiranes and amines are often described and typical examples are shown in Scheme 86. 

The commonest of these for oxirane opening are amines and azide ion [amide ions promote isomerization to allylic alcohols (Section 5.05.3.2.2)]. Reaction with azide can be used in a sequence for converting oxiranes into aziridines (Scheme 49) and this has been employed in the synthesis of the heteroannulenes (57) and (58) (80CB3127, 79AG(E)962). 

When ketones are reacted with dichlorocarbene in the presence of secondary amines, a-aminoacetamides are obtained via the ring opening of the intermediate oxiranes by the amine [19]. Similar products are obtained from the corresponding reactions with aniline and also with aldehydes (see Section 7.4). 

A related amination/rearrangement/cyclization tandem sequence had been introduced by Cossy [49]. Starting from cyclic epoxyketones 224 the reaction with propargylamines 225 caused an oxirane-opening condensation process to generate the enaminoketones 226. Upon heating in toluene to reflux, aza-Claisen rearrangement delivered the intermediate allenyl imines 227, which... 

In a second step, the gel is fimctionahzed for NA attachment. Common methods for polyacrylamide gel fimctionahzation are based on the treatment of the polymerized support with reagents such as hydrazine or ethylenedi-amine. These treatments generate amine groups in the gel that can react with amine-modified ONDs via glutaraldehyde coupling, or directly with oxidized DNA probes (Fig. 15). Alternatively, the fimctional groups may be introduced by copolymerization reactions (e.g. co-polymerization with N-hydroxysuccinimide acryhc or oxirane acryhc derivatives) [59]. 

Few solid-phase syntheses of oxazoles have been reported (Table 15.17). The most general strategy is the dehydration of a-(acylamino) ketones (Entry 2, Table 15.17) or 2-(acylamino)phenols (Entry 1, Table 15.17). Oxazolidin-2-ones have been prepared by intramolecular nucleophilic cleavage of carbamates from insoluble supports (Entries 5 and 6, Table 15.17). Resin-bound 2-aminoethanols, which are accessible by nucleophilic ring-opening of oxiranes with amines, undergo cyclocondensation with aldehydes to yield oxazolidines [220,221]. These compounds are unstable towards acids, and can be released from the support only under neutral or basic reaction conditions. 

With oxiranes suitably functionalized, cyclic carbamates can be obtained. Accordingly, when chloromethyl oxirane was used as the epoxydic substrate, its reaction with primary aliphatic amines and C02 (333 K, IMPa, 10-15h) gave 3-alkyl-5-hydroxyoxazin-2-ones, albeit in a low yield of 2.5-10% (Scheme 6.15) [79],... 

Catalytic amounts of tin(II) chloride have been found to give good yields (72-86%) of the trans-amino alcohols when oxiranes have been treated with aromatic amines in acetonitrile at room temperature.27 Only the reaction with styrene oxide was regiospe-ciflc with the amine adding to the benzylic carbon of the epoxide ring. 

The isomerization of ethynyl-oxiranes 223 leads to furans 224, as illustrated in Scheme 128 <1969JCC12>. A similar reaction of ethynyl-oxiranes with amines gives pyrroles (see Scheme 86 in Section 4.2.3.3.1). Aziridine 225 reacts with bis(trimethylsilyl)acetylene upon heating to provide pyrrole 226 (Scheme 129) <1999JOC1630>. 

Barton oxidation was the key to form the 1,2-diketone 341 in surprisingly high yield, in order to close the five-membered ring (Scheme 38). The conditions chosen for the deprotection of the aldehyde, mercuric oxide and boron trifluoride etherate, at room temperature, immediately led to aldol 342. After protection of the newly formed secondary alcohol as a benzoate, the diketone was fragmented quantitatively with excess sodium hypochlorite. Cyclization of the generated diacid 343 to the desired dilactone 344 proved very difficult. After a variety of methods failed, the use of lead tetraacetate (203), precedented by work performed within the stmcmre determination of picrotoxinin (1), was spectacularly successful (204). In 99% yield, the simultaneous formation of both lactones was achieved. EIcb reaction with an excess of tertiary amine removed the benzoate of 344 and the double bond formed was epoxidized with peracid affording p-oxirane 104 stereoselectively. Treatment of... 

Oxiranes may also be prepared by the cooxidation of aldehydes and olefins. There are two assumptions as regards the mechanism the oxidation occurs via either an acylperoxy radical or a peracid. The peracid oxidation is stereospecific. Experiments carried out with a view to assessing the radical versus nonradical mechanism indicate that the extent of the radical epoxidation depends on the structure of the olefin and the olefin/aldehyde ratio. Cooxidation in the presence of oxygen was achieved by irradiating the aldehyde and carrying out the reaction with the alkene after a suitable quantity of peracid had been obtained. Enantioselective epoxidation has been described in the reaction of (1-phenyl-alkylidene)malonitriles 63 catalyzed by optically active tertiary amines. ... 

Oxiranes can be opened stereo- and regiospecifically under mild conditions with alcohols, thiols, amines, and acetic acid, with simultaneous activation of the nucleophilic and electrophilic centers on an alumina surface.Diols have been obtained on silica gel in the presence of water " and adsorbed FeCls. On an ion-exchange resin, the opening of oxirane isomers to diols and the separation of the latter, ethanolysis, the reaction with phenol,and catalytic ammonolysis have been described. Hydrolysis and methanolysis catalyzed by Nafion-H, a perfluorinated resinsulfonic acid have been reported. ... 

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