Vinyl ether epoxides

Cyclization of vinyl ether epoxides, Epoxy dihydropyranes undergo cyclization in the presence of Lewis acids. Thus treatment of 1 with basic alumina affords 2 in almost quantitative yield. The product can be converted into the keto aldehyde 5 by treatment with a mineral acid followed by oxidation. Another useful reaction of 2 is conversion to the keto lactone 3 by singlet oxygen. 

Substituted phenethyl isocyanates undergo cyclization to lactams when treated with BF3 Et20 [65]. Vinyl ether epoxides (Eq. 37) [66], vinyl aldehydes [67], and epoxyjS-keto esters [68] all undergo cyclization with BF3 Et20. 

Dialkyl ethers Aryl ethers Vinyl ethers Epoxides u—. Acetals (ketals)... 

Polymerization Catalyst. Several types of polymerization have been promoted by trityl fluoroborate, including reactions of orthocarbonates and orthoesters, vinyl ethers, epoxides, and lactones... 

Another synthesis of the cortisol side chain from a C17-keto-steroid is shown in Figure 20. Treatment of a C3-protected steroid 3,3-ethanedyidimercapto-androst-4-ene-ll,17-dione [112743-82-5] (144) with a tnhaloacetate, 2inc, and a Lewis acid produces (145). Addition of a phenol and potassium carbonate to (145) in refluxing butanone yields the aryl vinyl ether (146). Concomitant reduction of the C20-ester and the Cll-ketone of (146) with lithium aluminum hydride forms (147). Deprotection of the C3-thioketal, followed by treatment of (148) with y /(7-chlotopetben2oic acid, produces epoxide (149). Hydrolysis of (149) under acidic conditions yields cortisol (29) (181). 

Cationic polymerization in hot melts has been applied to epoxidized polymers [38,39]. No hot melts based on vinyl ether or other cation-sensitive functionalized polymers have been described in the literature. With cationic systems, it is important that the other ingredients in the adhesive be of low basicity to avoid scavenging the initiating acid generated by the photoinitiator. 

Increasing use is being made of pyran syntheses based upon [4 + 2] cycloadditions of carbonyl compounds. The appropriate unsaturated aldehyde with ethyl vinyl ether yields 53 with peracids this affords an epoxide that undergoes ring contraction to the aldehyde 54 (Scheme 23) and rhodium catalyzed decarbonylation affords the required 3-alkylfuran with the optical center intact.116 Acetoxybutadiene derivatives add active carbonyl compounds giving pyrans that contract under the influence of acids to give... 

Cationic photopolymerizations of epoxides and vinyl ethers offer tremendous potential in the area of high-speed, solvent-free curing of films and coatings. The polymers formed exhibit excellent clarity, adhesion, abrasion, and chemical... 

The results of the olefin oxidation catalyzed by 19, 57, and 59-62 are summarized in Tables VI-VIII. Table VI shows that linear terminal olefins are selectively oxidized to 2-ketones, whereas cyclic olefins (cyclohexene and norbomene) are selectively oxidized to epoxides. Cyclopentene shows exceptional behavior, it is oxidized exclusively to cyclopentanone without any production of epoxypentane. This exception would be brought about by the more restrained and planar pen-tene ring, compared with other larger cyclic nonplanar olefins in Table VI, but the exact reason is not yet known. Linear inner olefin, 2-octene, is oxidized to both 2- and 3-octanones. 2-Methyl-2-butene is oxidized to 3-methyl-2-butanone, while ethyl vinyl ether is oxidized to acetaldehyde and ethyl alcohol. These products were identified by NMR, but could not be quantitatively determined because of the existence of overlapping small peaks in the GC chart. The last reaction corresponds to oxidative hydrolysis of ethyl vinyl ether. Those olefins having bulky (a-methylstyrene, j8-methylstyrene, and allylbenzene) or electon-withdrawing substituents (1-bromo-l-propene, 1-chloro-l-pro-pene, fumalonitrile, acrylonitrile, and methylacrylate) are not oxidized. 

The relative stability of l, 2 -epoxyvinylbital, and the great instability of its diol, can be gainfully compared with the fate of the corresponding metabolites of phenyl vinyl ether (10.69, R = H) and 4-nitrophenyl vinyl ether (10.69, R = N02), two mutagenic and tumorigenic compounds [144] [145]. Their primary metabolic route is by vinyl epoxidation to the corresponding... 

Since the starting tellurides are easily prepared (see Section 3.1.3.2) from the corresponding alkyl bromides and tellurolate ions, and -hydroxyalkyl tellurides by the opening of epoxides with the same reagents, the combined procedures furnish a method for the dehydrobromination of alkyl bromides and for the conversion of epoxides into allylic alcohols. Moreover, combining the telluroxide elimination with the methoxytelluration of olefins (see Sections 3.9.3.2 and 4.4.8.3), allylic and vinylic ethers are easily prepared. 

That ethylene oxide can react directly with oxonium ions is shown by its reaction with triethyl oxonium borofluoride but this reaction, because of its complexity, does not shed much light on the polymerization. The sole product is dioxane and the vinyl ether colors appear only after all epoxide has reacted. Initial rates suggest first order in catalyst but the first order plots of monomer disappearance are flat S-curves suggesting a rate which first falls off, then tends towards zero order. The first step in the reaction is most probably a simple bimolecular alkylation of the epoxide by oxonium salt but the subsequent steps are obscure. The simplest path would be... 

Vinyl ethers, such as EtOCH=CH2, EtOCH=CHMe, EtOCH=CHOEt, etc. (with or without an additional oxygen function), have been shown to react with a-peroxy lactones (54) to give mainly the products of stereoselective cycloaddition (55) contaminated by epoxides (56).57... 

An NMR spectrum would readily distinguish between these possibilities. For example, the vinyl ether would show a methyl singlet at about 5 3-4, the middle structure would show a 4H multiplet at 8 3-4, and the epoxide would show a methyl doublet at about 5 1.0-1.5. The presence of a band at about 1650 cm-1 in the IR spectrum (C=C stretch) would indicate that the compound is the vinyl ether (the first of the three compounds) and not the cyclic ethers. 

Optically pure 1,3-oxathiins have been used as chiral auxiliaries for the synthesis of (E)-monoaryl epoxides (95JOC3494) and (5-substituted ketones (95SL501), whilst the desulfurisation of some dihydro-1,4-oxathiins affords E-alkyl vinyl ethers (95SL1274). 

When perfluoro-2-methylpent-2-ene reacts with glycidol, the initially formed product is vinyl ether 38, whose epoxide ring opens under the action of mineral acids (8% HBr, 33% HC1). Alcohol 39 formed in the course of ring cleavage is readily cyclized into 1,3-dioxolane 40 in the presence of catalytic amounts of NEt3. 

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