Ethoxy vinyl ether

The most comprehensive examination of the Rokita kinetic procedure from a synthetic standpoint was carried out by Barrero and coworkers.6 They examined the effects of various leaving groups, solvents, nucleophiles, and their equivalents on subsequent [4 + 2] cycloadditions. Avast excess of the intended nucleophile (50-100 equiv) must be employed, because the fluoride triggered (3-elimination proves nearly instantaneous at room temperature resulting in a high concentration of a species that is prone to undergo dimerization and other undesired side reactions that are irreversible at these low temperatures (Fig. 4.7). Use of fewer equivalents of the intended nucleophile led to a rapid drop off in yield. For example, 5-10 equivalents of ethoxy vinyl ether (EVE) affords only a 5-10% yield of the desired benzopyran... 

In connection with mechanistic studies on the Wacker reaction, the transmetallation of ri-ethoxy- and /3-hydroxyethylmercury(II) chloride with PdCB has been carried out, giving ethyl vinyl ether and acetaldehyde[366]. The reaction proceeds by the formation of ri-ethoxy- and /3-hydroxyethylpalladium chlorides (401), which decompose as soon as they are formed. 

A quantitative comparison of metals in the hydrogenation of vinyl ethers has been made, The extent of hydrogenolysis in hydrogenation of l-ethoxy-3-methylcyclohexene decreased in the order Pt Os > Rh Ir > Pd > Ru U24e)-, in the case of ethyl 4-methyl-1-cyclohexenyl ether, the order was Pt Ir > Rh > Os Ru Pd (124d). In ethanol, ketal formation is a... 

As for cyclopropanation of alkenes with aryldiazomethanes, there seems to be only one report of a successful reaction with a group 9 transition metal catalyst Rh2(OAc)4 promotes phenylcyclopropane formation with phenyldiazomethane, but satisfactory yields are obtained only with vinyl ethers 4S) (Scheme 2). Cis- and trans-stilbene as well as benzalazine represent by-products of these reactions, and Rh2(OAc)4 has to be used in an unusually high concentration because the azine inhibits its catalytic activity. With most monosubstituted alkenes of Scheme 2, a preference for the Z-cyclopropane is observed similarly, -selectivity in cyclopropanation of cyclopentene is found. These selectivities are the exact opposite to those obtained in reactions of ethyl diazoacetate with the same olefins 45). Furthermore, they are temperature-dependent for example, the cisjtrcms ratio for l-ethoxy-2-phenylcyclopropane increases with decreasing temperature. 

However, most asymmetric 1,3-dipolar cycloaddition reactions of nitrile oxides with alkenes are carried out without Lewis acids as catalysts using either chiral alkenes or chiral auxiliary compounds (with achiral alkenes). Diverse chiral alkenes are in use, such as camphor-derived chiral N-acryloylhydrazide (195), C2-symmetric l,3-diacryloyl-2,2-dimethyl-4,5-diphenylimidazolidine, chiral 3-acryloyl-2,2-dimethyl-4-phenyloxazolidine (196, 197), sugar-based ethenyl ethers (198), acrylic esters (199, 200), C-bonded vinyl-substituted sugar (201), chirally modified vinylboronic ester derived from D-( + )-mannitol (202), (l/ )-menthyl vinyl ether (203), chiral derivatives of vinylacetic acid (204), ( )-l-ethoxy-3-fluoroalkyl-3-hydroxy-4-(4-methylphenylsulfinyl)but-1 -enes (205), enantiopure Y-oxygenated-a,P-unsaturated phenyl sulfones (206), chiral (a-oxyallyl)silanes (207), and (S )-but-3-ene-1,2-diol derivatives (208). As a chiral auxiliary, diisopropyl (i ,i )-tartrate (209, 210) has been very popular. 

Ethoxy-2-propyne, 1909 f Ethyl isopropyl ether, 2012 f Ethyl propenyl ether, 1956 f Ethyl vinyl ether, 1610... 

Metalated vinyl ethers are configurational stable up to —20°C in tetrahydrofuran. H-NMR measurements of 1-ethoxy-1-lithioethene TMEDA did not show any coalescence of the signals for the vinyl protons until the onset of decomposition. Thus, there is no evidence of inversion in this case . Similar configurational stability is displayed by a-lithiated thioethers in tetrahydrofuran no inversion occurs up to 0°C. On the contrary, deprotonated vinyl sulfoxides and sulfones are configurationally less stable . ... 

Enhanced acidity also characterizes the sp -carbon bonded hydrogen compared to the sp one. As a consequence, alkyl vinyl ethers are more acidic than dialkyl ether and thus can be deprotonated more easily. 1-Ethoxy-1-lithioethene 54252-254 gener-... 

The range of applications of lithiated vinyl ethers like 54 and 56 is distinctly enhanced by transmetalation. Thus, cuprate 178 derived of 1-ethoxy-1-lithioethene 54 undergoes... 

R)-[(2/ ,6S )-6-Ethoxy-5,6-dihydro-2//-pyran-2-yl]phenylmethanol [Representative Example of a Tandem Catalytic Enantioselective [4-1-2] Cyclo-addition/Allylboration]. A mixture of 3-boronoacrolein pinacolate (364 mg, 2.00 mmol) and ethyl vinyl ether (1.90 mL, 20.0 mmol) was placed in an oven-dried 10-mL round-bottom flask with a stir bar. To this solution was added the Jacobsen tridentate chromium(Ill) catalyst 88 (9.60 mg, 0.020 mmol) and powdered BaO (400 mg). After the mixture had been stirred for 1 hour at room... 

Meyers and Shimano discovered the unusual deprotonation behavior of ethoxy-vinyllithium-HMPA complex (EVL-HMPA) for the deprotonation of the trans-oxazoline 366 and the cw-oxazoline 367. The EVL-HMPA complex is prepared by deprotonation of ethyl vinyl ether with ferf-butyllithium in THE followed by addition of HMPA. Reaction of the frani-oxazoline 366 with both the EVL-HMPA complex and conventional alkyllithium reagents (RLi) resulted in deprotonation at the benzylic 5-position. In contrast, deprotonation of 367 occurred at the 4-position with an alkyllithium reagent RLi, whereas benzylic deprotonation predominated with the EVL-HMPA complex (Scheme 8.117). ° The authors proposed that EVL-HMPA complexes with the 5-phenyl substituent prior to deprotonation. 

The mechanism Favorskii envisioned involved the initial attack of the ethoxy anion on the triple bond to form a vinyl ether. The now accepted carbanionic mechanism assumes the formation of resonance-stabilized anions, allowing the stepwise interconversion of 1- and 2-alkynes, and allenes143 147 (Scheme 4.9). 

A peroxy acid mediated oxidative rearrangement of 2-alkoxy-3,4-dihydro-2//- pyrans affords 5-alkoxytetrahydrofuran-2-carbaldehydes (79JCS(Pi)847>. This reaction pathway was used in developing a method for the synthesis of optically active monoalkylfurans. (S)-2-Ethoxy-5-s-butyl-3,4-dihydro-2//-pyran (319), obtained through a cycloaddition reaction of (S)-2-s-butylacrolein to ethyl vinyl ether, was converted to (S)-2-s-butyl-5-ethoxytetrahydrofuran-2-carbaldehyde (320) (Scheme 85). 

The synthesis of epoxy ethers by peroxy acid treatment of suitable vinylic ethers, on the other hand, is complicated by the acid sensitivity of epoxy ethers. For example, Bergmann and Mk>keley1Ss claimed in 1921 to have prepared 1 -ethoxy-1 (2 -epoxyethane by the oxidation of ethyl vinyl ether with perbenzoic aoid, bat B years later modified their structure to a dioxone type of dimer.186 In 1 B0 Mous-seron and co-wcrkere1168-1184 reported the preparation of an epoxy ether from 1 -ethoxy-1 -eydohexene, but 4 years later Stevens and Taznma164 showed the compound obtained in this oxidation, not to have the structure initially assigned to it. 

Ethyl vinyl ether Ether, ethyl vinyl (8) Ethene, ethoxy- (9) (109-92-2)... 

The y8-silyl effects are much greater for the purely aliphatic systems than the vinyl ether or phenylacetylene, indicating that the stabilization in these latter systems is attenuated by the carbocation-stabilizing ability of the ethoxy and phenyl groups, respectively. 

Kresge and Tobin80 investigated the /1-silicon effect on the hydrolysis of vinyl ethers (equation 29) and found a rate acceleration on the hydrolysis of 175 compared with 176, and hence a stabilizing effect of the /1-silyl group on the intermediate -ethoxy carbocation 177 compared with 178. The acceleration is small the rate factor (175) (176) of 129 is equivalent to a free energy of activation difference AAG of 2.9 kcalmol-1,... 

A new alcohol and phenol protective group, the l-[(2-trimethylsilyl)ethoxy]ethyl moiety, readily introduced using 2-(trimethylsilyl)ethyl vinyl ether and catalytic pyridinium p-toluenesulfonate (PPTS), has been described76. Cleavage is achieved under near-neutral conditions using TBAF monohydrate (equation 16). 

Hydrosilylation of divinyl ether has been applied for the synthesis of silacyclopentane 12 using Speier s catalyst (Scheme l)13. One of the two carbon-carbon double bonds was hydrosilylated first with a dialkyl(ethoxy)silane, giving silylethyl vinyl ether 10 in 53-59% yield, which was reduced with LiAlELr to hydrosilane 11. The intramolecular hydrosilylation of 11 affords silacyclopentane 12 in moderate yields (Scheme 1). The reaction with HSiEt2(OEt) gives 12a exclusively in 45% yield, while silacyclohexane 13b is formed as the minor product when HSiMe2(OEt) is used as the hydrosilane (12b/13b = 2.3/1 50% total yield)13. Other intramolecular hydrosilylation reactions useful in organic syntheses will be discussed in the section n.C. (vide infra). 

---