Isopropenyl ether

Apparatue 500-ml three-necked round-bottomed flask, with a dropping funnel, a mechanical stirrer and a thermometer, combined with a vent, for the addition to the isopropenyl ether for the further reaction the dropping funnel was replaced with a thermometer and the combination of thermometer and vent with a reflux condenser. 

In the flask were placed 1.50 mol of the isopropenyl ether (conmercially available) and 0.10 mol of the (dry) acetylenic alcohol (also commercially available), and in the dropping funnel 0.4 mol of the latter compound. The mixture was cooled to 0°C and 100 mg of anhydrous p-toluenesulfonic acid were added with stirring. 

Reaction conditions depend on the reactants and usually involve acid or base catalysis. Examples of X include sulfate, acid sulfate, alkane- or arenesulfonate, chloride, bromide, hydroxyl, alkoxide, perchlorate, etc. RX can also be an alkyl orthoformate or alkyl carboxylate. The reaction of cycHc alkylating agents, eg, epoxides and a2iridines, with sodium or potassium salts of alkyl hydroperoxides also promotes formation of dialkyl peroxides (44,66). Olefinic alkylating agents include acycHc and cycHc olefinic hydrocarbons, vinyl and isopropenyl ethers, enamines, A[-vinylamides, vinyl sulfonates, divinyl sulfone, and a, P-unsaturated compounds, eg, methyl acrylate, mesityl oxide, acrylamide, and acrylonitrile (44,66). 

Linalool can be converted to geranyl acetone (63) by the CarroU reaction (34). By transesterification with ethyl acetoacetate, the intermediate ester thermally rearranges with loss of carbon dioxide. Linalool can also be converted to geranyl acetone by reaction with methyl isopropenyl ether. The linalyl isopropenyl ether rearranges to give the geranyl acetone. 

The rather unusual conversion of an acetonide to an isopropenyl ether was developed to differentiate a terminal acetonide from several internal ones. The isopropenyl ether was in turn converted to the 1-methylcyclopropyl ether, which was later cleaved with NBS or DDQ. ... 

Diels-Alder reaction, of acrolein with B-butyl cyclohexenyl ether, n-butyl vinyl ether, and ethyl isopropenyl ether, 34, 30... 

Figure 10. Preparation of chiral glycerol derivatives and D- and L-glycerol acetonide. a 1. Hj/Pd-C 2. methyl isopropenyl ether/pyridinium p-toluensulfonate 3. K2C03/Me0H...

Using a similar approach, Chechik and Crooks (73), modified the PAMAM dendrimer-encapsulated palladium nanoparticles with perfluoropolyether tails utilizing non-covalent ion-pair interactions. The catalytic hydrogenation of six substrates under biphasic conditions (toluene/ perfluoro-2-butyltetrahydrofuran FC-75) was investigated. Allyl alcohol, methyl acrylate, vinyl isopropenyl ether, and... 

Under comparable conditions the submitters found that the corresponding dihydropyran derivatives were similarly obtained by the condensation of acrolein with methyl vinyl ether in 80-81% yield, with ethyl vinyl ether (77-85% yield), with w-butyl vinyl ether (82% yield), with ethyl isopropenyl ether (50% yield), and with w-butyl cyclohexenyl ether (40% yield). Other <, /3-un-saturated carbonyl compounds that have thus been condensed with ethyl vinyl ether are crotonaldehyde (87% yield), meth-acrolein (40% yield), a-ethyh/3-n-propylacrolein (54% yield), cinnamaldehyde (60% yield), /3-furylacrolein (85% yield), methyl vinyl ketone (50% yield), benzalacetone (75% yield), and benzal-acetophenone (74% yield). 

The kinetic-acetonation procedure previously reported,107 employing alkyl isopropenyl ethers in N,N-dimethylformamide, and applied to the common pentoses and hexoses, has been extended to various hexuloses, oligosaccharides, and other sugar systems.108 Maltose gave the 4, 6 -monoacetal, isolated as the crystalline hexaacetate, on treatment with isopropenyl methyl ether inN,N-dimethylformamide in the presence of p-toluenesulfonic acid. 

J. Gelas and D. Horton, Acetonation of D-ribose and D-arabinose with alkyl isopropenyl ethers, Carbohydr. Res. 45 181 (197S). 

A result that is of interest in the planning of synthetic strategy W as obtained by Gajewski and co-workcrs in the rate comparison of isopropenyl ethers 58-61.6 At 80 C the 4,4-dialkyl derivative 61 reacts roughly twice as fast as the 4-alkyl-4-(trifluoromethyl) compound 60, 20 times faster than the monoalkyl derivative 59, and 550 times faster than the parent compound 58. 

The transformation could also be performed using a chiral enantiopure enol ether as dienophile. The best results were achieved with the isopropenyl ether 182b derived from cheap and commercially available (—)-(lR,2S,5R)-menthol. The cycloadduct was obtained with an endo/exo-selectivity of 4.1 1 and an induced dia-stereoselectivity of 88 12. Treatment of 178b with trifluoroacetic acid/water 19 1 provided (S)-warfarin 175 in an overall yield of 61% referred to 4-hydroxy coumarin 55 and an enantiomeric excess of 76% (HPLC), which could be increased to 95% ee by recrystallization using the purified endo-product 178b as substrate for the hydrolysis. In the same manner (S)-coumachlor 176 and (S)-acenocoumarol 177 were obtained with 56% overall yield and 93% ee and 59% overall yield and 95% ee, respectively. 

Dimethoxy propane Methyl isopropenyl ether + methanol... 

Saucy, G., Marbet, R. Reaction of tertiary vinylcarbinols with isopropenyl ether. New method for the preparation of Y,S-unsaturated ketones. Helv. Chim. Acta 1967, 50, 2091-2094. 

Deprotonation. Exposure of 1-alkenes to the strong base and then a chlorosilane gives (Z)-2-alkenylsilanes. Alkenoic acids are similarly converted to 4-silyl-2-alkenoic acids. The preparation of an acetone enolate equivalent is by lithiation of methyl isopropenyl ether at low temperature. ... 

Esters -> vinyl ethers. The original publication (8, 83-84) mentioned that ethyl acetate reacts with 1 to give ethyl isopropenyl ether. More recent work1 has shown that this conversion of esters to vinyl ethers is general and proceeds in high yields. The reaclion rate is dramatically increased by the presence of donor ligands (THF, C,11SN). The solvent is benzene or toluene. Ketone methylenation is possible, and actually Ihc rate is lour times that of ester methylenation. Isolated yields are cited in the examples. 

The allyl vinyl ethers are usually prepared in situ, but it is also possible to isolate the primarily formed mixed acetals or allyl vinyl ethers155-1 57. With low-boiling vinyl ethers the reaction is carried out in a sealed tube with an excess of the vinyl ether. For a tandem Claisen-rearrangc-ment-ene cyclization involving the Saucy-Marbet reaction cf. ref 158. The generation of isopropenyl ethers from esters is described in ref 159. For a related Claisen rearrangement by the reaction of 2-methoxybutadiene with ends and phenols see ref 160. 

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