8- vinyl ether

Vinyl ethers undergo many cycloaddition reactions similar to those which take place with enamines. In general, however, these cycloaddition reactions with vinyl ethers take place less readily than those with enamines. These reactions include cycloaddition of vinyl ethers with ketene (200-205), phenyl isocyanate (206), sulfene (207,208), methyl acrylate (209), diethyl acetylenedicarboxylate (210), and diphenylnitrilimine (183). 

Huisgen, R. Groshey, and J. Sauer, The Chemistry of Alkenes (S. Patai, ed.), Wiley-lntersdence, New York, 1964, p. 739. 

Muller and J. Hamer, 1,2-Cycloaddition Reactions, Wiley-Interscience, New York, 1967. 

Hamer (ed.), 1,4-Cycloaddition Reactions, Academic Press, New York, 1957. 

Christol, D. Lafont, and F. Plenat, Bull. Soc. Chim. France, 1966, 1176. 

Vinyl ethers, also known as enol ethers, are generally prepared from acetals by acid-catalyzed elimination of an alcohol. The acetals can also be cleaved at -20°C to room temperature using trimethylsilyl trifluorometh-anesulfonate and V, V-diisopropylethylamine, affording the vinyl ethers in 89-98% yields along with the alkyl trimethylsilyl ether [60], 

An ester can be treated with a 1,1-dibromoalkane to give mostly the Z-vinyl ether in yields ranging from 52 to 96% depending on the substitution of the reactants, which also affects the 7/E ratio. An example is shown in Equation 6.36 [61]. 

Vinyl ethers are readily formed by the iridium catalyzed addition of alcohols to vinyl esters (Eq. 6.37) [62]. The catalyst, di-yw-chloro-fcw (l,5-cyclooctadiene)diiridium(I), [Ir(cod)Cl]2, is commercially available. A number of additional procedures for the synthesis of vinyl ethers are described in the literature [62]. 

Silyl enol ethers are usually prepared by treating a ketone with trimethylsilyl chloride and triethylamine in refluxing DMF. In unsymmet-rical ketones, this gives the more substituted double bond (Eq. 6.38) [63]. When the less substituted product is desired, it is made from the less 

These enol derivatives are used for formation of carbon-carbon bonds at the a position (Section 7.1.2). They also make the enol double bond available for oxidative cleavage or use in Diels-Alder reactions (Section 8.6). 

The vinyl ether transfer agents, like other vinyl ethers, can show marked acid sensitivity. They are not suited for use with acid monomers. Even traces of acidic impurities in the monomer or the polymerization medium can catalyze decomposition of the transfer agent. 

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They are colourless liquids with characteristic odours, and are prepared by the condensation of ketones with alkyl orthoformates in the presence of alcohols, or by the reaction of acetylenes with alcohols in presence of HgO and BF3. In some cases trichloroethanoic acid is used as the catalyst. They lose alcohol when heated and form vinyl ethers. Exchange of alcohol groups occurs when the ketals of the lower alcohols are boiled with alcohols of greater molecular weight. See acetals. 

Claisen Rearrangements - allyl vinyl ether to an y,5-unsaturated carbonyl... 

Apparatus 250-ml round-bottomed flask for the cleavage of THF 500 ml flask (see Fig. 1) for the coupling with ethyl vinyl ether 1-1 flask (see Fig. 1) for the reaction with allenyl1ithiurn 500-ml round-bottomed flask for the deprotection. 

Hate 1. This excess was used to be absolutely sure that all a-chloroether would have reacted. Traces of this compound, if still present in the reaction mixture, will hydrolyse during the aqueous work up. The acid that is liberated can cause hydrolysis of the product to H2C=CH-C(=0)CH(CH3)0C2H5. HoLp. A. Prepared by introducing 0.30 mol of dry gaseous HCl (weight increase) into 45 ml of freshly distilled ethyl vinyl ether (excess) at -30°C. 

F.N. Tebbe (1978 [footnote 20]) and R.R. Schrock (1976) have shown that electrophilic titanium or tantalum ylides can alkylidenate the carbonyl group of esters. Vinyl ethers are obtained in high yields with Tebbe s reagent, p-chlorobis(ri -2,4-cyclopentadien-l-ylXdime-thylaluminum)- 4-methylenetitanium (S.H. Pine, 1980 A.G.M. Barrett, 1989). 

Conjugate addition of vinyllithium or a vinyl Grignard reagent to enones and subsequent oxidation afford the 1.4-diketone 16[25]. 4-Oxopentanals are synthesized from allylic alcohols by [3,3]sigmatropic rearrangement of their vinyl ethers and subsequent oxidation of the terminal double bond. Dihydrojasmone (18) was synthesized from allyl 2-octenyl ether (17) based on Claisen rearrangement and oxidation[25] (page 26). 

Oxidation of ethylene in alcohol with PdCl2 in the presence of a base gives an acetal and vinyl ether[106,107], The reaction of alkenes with alcohols mediated by PdCl2 affords acetals 64 as major products and vinyl ethers 65 as minor products. No deuterium incorporation was observed in the acetal formed from ethylene and MeOD, indicating that hydride shift takes place and the acetal is not formed by the addition of methanol to methyl vinyl etherjlOS], The reaction can be carried out catalytically using CuClj under oxygen[28]. 

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. 

Under certain conditions, the /(-substitution products are obtained as major products[66]. Methyl vinyl ether reacts with bromonitrobenzene to give the f-methoxystyiene 64 in good yield in toluene at 120 "C by using Pd on carbon as... 

Butyl vinyl ether reacts with aroyl chlorides using Pd(OAc)2 without a ligand to give the unsaturated ketone 839, which is a precursor of a 1-aryl-1,3-dicarbonyl compound. The reaction is regioselective /3-attack. Addition of PhjP inhibits the reaction[718]. 

The cyclohexadiene derivative 130 was obtained by the co-cyclization of DMAD with strained alkenes such as norbornene catalyzed by 75[63], However, the linear 2 1 adduct 131 of an alkene and DMAD was obtained selectively using bis(maleic anhydride)(norbornene)palladium (124)[64] as a cat-alyst[65], A similar reaction of allyl alcohol with DMAD is catalyzed by the catalyst 123 to give the linear adducts 132 and 133[66], Reaction of a vinyl ether with DMAD gives the cyclopentene derivatives 134 and 135 as 2 I adducts, and a cyclooctadiene derivative, although the selectivity is not high[67]. 

Addition of nucleophiles to both activated and unactivated alkenes is catalyzed by Pd(II). Addition of alcohols or AcOH to alkenes bearing EWGs is catalyzed by PdCl2(PhCN)2 to give the corresponding ethers and esters. The addition of an alcohol to the cyclic acetal of acrolein 82 to give the ether 83 is also possible with the same catalyst[64]. Amines add to the vinylic ether 84 to give 85, but not to simple alkenes[65]. 

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