Potassium vinyl ethers

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). 

Vinyl chloride reacts with sulfides, thiols, alcohols, and oximes in basic media. Reaction with hydrated sodium sulfide [1313-82-2] in a mixture of dimethyl sulfoxide [67-68-5] (DMSO) and potassium hydroxide [1310-58-3], KOH, yields divinyl sulfide [627-51-0] and sulfur-containing heterocycles (27). Various vinyl sulfides can be obtained by reacting vinyl chloride with thiols in the presence of base (28). Vinyl ethers are produced in similar fashion, from the reaction of vinyl chloride with alcohols in the presence of a strong base (29,30). A variety of pyrroles and indoles have also been prepared by reacting vinyl chloride with different ketoximes or oximes in a mixture of DMSO and KOH (31). 

Ethyl Vinyl Ether. The addition of ethanol to acetylene gives ethyl vinyl ether [104-92-2] (351—355). The vapor-phase reaction is generally mn at 1.38—2.07 MPa (13.6—20.4 atm) and temperatures of 160—180°C with alkaline catalysts such as potassium hydroxide and potassium ethoxide. High molecular weight polymers of ethyl vinyl ether are used for pressure-sensitive adhesives, viscosity-index improvers, coatings and films lower molecular weight polymers are plasticizers and resin modifiers. 

The vinyl ether may be further purified by dissolving it in 15 ml of dry ether and adding a solution of 0.25 g of lithium aluminum hydride in 10 ml of dry ether. The mixture is refluxed for 30 minutes, and excess hydride is destroyed by addition of ethyl acetate (1 ml). Ice-cold dilute (0.5 N) sulfuric acid (25 ml) is gradually added to the cooled mixture, the ethereal layer is rapidly separated, the aqueous layer is extracted once with 10 ml of ether, and the combined ethereal solution is washed once with water and dried over potassium carbonate. Removal of the solvent, followed by distillation of the residue affords about 85% recovery of the pure vinyl ether, bp 102-10376 mm, 1.5045. 

The reaction mixture comprising 2,2,2-trifluoroethyl vinyl ether, 2,2,2-trifluoroethanol and potassium 2,2,2-trifluoroethylate was fractionally distilled, whereupon crude 2,2,2-trifluoroethyl vinyl ether was obtained which boiled at 42° to 45°C at 760 mm. More 2,2,2-trifluoroethyl vinyl ether was obtained when the distillation residue was returned to the bomb and reacted with acetylene in the same manner as hereinabove described. 

Otera and coworkers have published several reaction sequences160-163 that effect eliminations of phenylsulphonyl groups under basic conditions. In one sequence160, a-methoxy phenyl sulphones are treated with potassium t-butoxide in THF to give fairly good yields of vinyl ethers, by the elimination of phenylsulphinate anion, as shown in equation (67). 

Some chemicals are susceptible to peroxide formation in the presence of air [10, 56]. Table 2.15 shows a list of structures that can form peroxides. The peroxide formation is normally a slow process. However, highly unstable peroxide products can be formed which can cause an explosion. Some of the chemicals whose structures are shown form explosive peroxides even without a significant concentration (e.g., isopropyl ether, divinyl acetylene, vinylidene chloride, potassium metal, sodium amide). Other substances form a hazardous peroxide on concentration, such as diethyl ether, tetrahydrofuran, and vinyl ethers, or on initiation of a polymerization (e.g., methyl acrylate and styrene) [66]. 

Asymmetric hydrogenation of vinyl ether alcohols proceeded in better selectivity than the ester counterparts, but acid sensitivity was observed for 66a-d, and a stoichiometric equivalent of potassium carbonate relative to the substrate was... 

Vinyl ethers were reductively cleaved by lithium, sodium or potassium in liquid ammonia especially in the absence of alcohols (except terf-butyl alcohol) A mixture of l-methoxy-1,3- and l-methoxy-l,4-cyclohexadiene gave in this way first methoxycyclohexene and, on further reduction, cyclohexene Reductive cleavage of a-alkoxytetrahydrofurans and pyrans will be discussed in the chapter on acetals (p. 104). 

This article reports on the synthesis of photosensitive polymers with pendant cinnamic ester moieties and suitable photosensitizer groups by cationic copolymerizations of 2-(cinnamoyloxy)ethyl vinyl ether (CEVE) (12) with other vinyl ethers containing photosensitizer groups, and by cationic polymerization of 2-chloroethyl vinyl ether (CVE) followed by substitution reactions of the resulting poly (2-chloroethyl vinyl ether) (PCVE) with salts of photosensitizer compounds and potassium cinnamate using a phase transfer catalyst in an aprotic polar solvent. The photochemical reactivity of the obtained polymers was also investigated. 

Materials. CEVE and 4-nitrophenyl vinyl ether (VNP) were synthesized and purified as reported earlier (12,13), respectively. 2-(4-Nitrophenoxy)ethyl vinyl ether (NPVE) (m.p. 72-73°C) was prepared by reacting of potassium 4-nitrophenoxide (PNP) (142 g 0.8 mol) and CVE (842 g 7.9 mol) using tetra-n-butylammonium bromide (TBAB) (4.0 g 12 mmol) as a phase transfer catalyst at the boiling temperature of CVE for 12 h. The potassium chloride produced was filtered off, the filtrate washed with water, excess CVE evaporated, and then the crude product was recrystallized twice from n-hexane. (Yield 61.7%. IR (KBr) 1630 (C=C), 1520 (-N02), and 1340 cm-1 (-N02).) Elemental analysis on the product provided the following data Calculated for C10HnNO4 C, 57.40%, H, 5.30%, N, 6.69%. Found C, 57.49%, H, 5.3%, N, 6.72%. 

The isomerization of allyl ethers to 1-propenyl ethers, which is usually performed with potassium tert-butoxide in dimethyl sulfoxide, can also be carried out under milder conditions using tris(triphen-ylphosphine)rhodium chloride,208 and by an ene reaction with diethyl azodicarboxylate,209,210 which affords a vinyl ether adduct. Removal of an O-allyl group may be achieved by oxidation with selenium dioxide in acetic acid,211 and by treatment with N-bromosuccinimide, followed by an aqueous base.201,212... 

Starch can be vinylated with acetylene in the presence of potassium hydroxide in an aqueous tetrahydrofuran medium.1 1 The mechanism possibly involves the addition of the potassio derivative of starch across the carbon-carbon triple bond of acetylene, with subsequent hydrolysis of the organometallic intermediate to give the vinyl ether. Such a mechanism has been postulated for the formation of vinyl ethers from monohydric alcohols and acetylene, in the presence of an alkali metal base as catalyst.1 2 The vinylation of amylose is very similar to the vinylation of amylopectin, except for the relative ratio of mono- to di-substitution. With amylopectin, the proportion of disubstitution is greater. In both starches, the hydroxyl group on C-2 is slightly more reactive than the hydroxyl group on C-6 there is little substitution at the hydroxyl group on C-3. 

Potassium hydroxide is taken in an equimolar ratio with respect to the initial ketoxime. The yield of 0-vinyloximes (92) amounts to 65% with 52-77% conversion of ketoximes. At present, this seems to be the only suitable route to 0-vinyloximes bearing no substituent in the vinyl group. The IR and H-NMR spectra of 0-vinyloximes resemble those of vinyl ethers in the position and shape of characteristic bands and proton signals of the vinyloxy group (80KGS1299). 

Acceleration of Claisen rearrangements.2 The Claisen rearrangement of an allyl vinyl ether is markedly accelerated by a stabilized a-sulfonyl carbanion at the 2-position. Thus 1 and 2 rearrange to the y,d-unsaturated ketone 3 in the presence of potassium hydride and 18-crown-6 at moderate temperatures. Rates can be further enhanced by addition of HMPT. Substitution of methyl groups on either the allyl or vinyl units does not affect the regioselectivity but can accelerate the rate of rearrangement. 

Chiral alkoxy allenes derived from 1,3-alkylidene-L-erythritol and -D-threitol have been used in cycloaddition reactions to provide the 4-substituted /3-lactams 418 (R = Me, Ph). Intramolecular alkylation at nitrogen was achieved by the action of potassium carbonate and tetrabutylammonium bromide in dry acetonitrile. The absolute stereochemistry of the product 419 (R = Me, Ph) was assigned on the basis of the CD helicity rule (see Section 2.04.3.5) and NMR spectroscopy. The [2+2] cycloaddition of CSI to threitol vinyl ethers was found to have low stereoselectivity in contrast to the findings with erythritol derivatives <2004CH414, 2005EJ0429>. 

Terminal attack occurs with water, methyl iodide, and trimethylchlorosilane, whereas central attack was preferred with alkenyl halides, aldehydes, and ketones at low temperatures under kinetic control [Eq. (5)]. The Et3SiO group is readily removed from 6 by potassium fluoride in isopropanol to give the vinyl ether RCH2CH2COCH=CH2 (61). Some of these reactions have also been used in elegant syntheses of terpenes (99-102). 

Phenyl(propynyl)iodonium tetrafluoroborate reacts with potassium 2-phenyl-1,3-indandionate in tetrahydrofuran to give the alkynyl and spiroannulated indandiones shown in equation 265. With sodium 2-ethyl-1,3-indandionate in terf-butyl alcohol, a vinyl ether is produced (equation 266). These observations are relevant to the general comments in section II.D.7 concerning the fate of 26 and related alkylidenecarbenes in reactions of [5 + OJenolates with alkyliodonium ions containing short (< three carbons) alkyl chains. 

In many instances the reaction of an alcohol with dihydropyran (or ethyl vinyl ether or 2-methoxypropene) does not go to completion despite the addition of a large excess of the enol ether as much as 20% of the starting material will be present at equilibrium. The equilibrium, once reached, can be shifted toward product by adding excess finely powdered anhydrous potassium carbonate and stirring the reaction mixture at room temperature. As the acid concentration gradually diminishes, the reaction goes to completion. 

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