Isopropenyl methyl ether

With aldehydes, primary alcohols readily form acetals, RCH(OR )2. Acetone also forms acetals (often called ketals), (CH2)2C(OR)2, in an exothermic reaction, but the equiUbrium concentration is small at ambient temperature. However, the methyl acetal of acetone, 2,2-dimethoxypropane [77-76-9] was once made commercially by reaction with methanol at low temperature for use as a gasoline additive (5). Isopropenyl methyl ether [116-11-OJ, useful as a hydroxyl blocking agent in urethane and epoxy polymer chemistry (6), is obtained in good yield by thermal pyrolysis of 2,2-dimethoxypropane. With other primary, secondary, and tertiary alcohols, the equiUbrium is progressively less favorable to the formation of ketals, in that order. However, acetals of acetone with other primary and secondary alcohols, and of other ketones, can be made from 2,2-dimethoxypropane by transacetalation procedures (7,8). Because they hydroly2e extensively, ketals of primary and especially secondary alcohols are effective water scavengers. 

Isopropanolamines, 20 795, 812 2-Isopropanol-water system, evolving separation strategies for, 22 322-325. See also Water- IPA-hexane system Isopropenyl acetate, 7 148 74 596 m-Isopropenyl-a,a-dimethylbenzyl isocyanate (TMI), 25 463 Isopropenyl methyl ether, production from acetone, 7 163... 

When D-gulono-1,4-lactone was treated with isopropenyl methyl ether and a catalytic amount of p-toluenes ulfonic acid in N,N-dimethyl-formamide, 5,6-0-isopropylidene-D-gulono-1,4-lactone (51) was formed in 95% yield.176 Previously, this compound was available in only low yield as a mixture of products. In addition, 51 was converted into 2,3-di-O -acetyl-5,6-0 -isopropylidene-D-gulono-1,4-lactone by treatment with acetic anhydride. 

Industrial synthesis of nerolidol starts with linalool, which is converted into ger-anylacetone by using diketene, ethyl acetoacetate, or isopropenyl methyl ether, analogous to the synthesis of 6-methyl-5-hepten-2-one from 2-methyl-3-buten-2-ol. Addition of acetylene and partial hydrogenation of the resultant dehydroner-olidol produces a mixture of cis- and trans-nerolidol racemates. 

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. 

Isopropenyl methyl ether, m96 Isopropylacetylene, ml71 Isopropylacrylic acid, m349 Isopropyl alcohol, p203 Isopropyl chloride, c211 Isopropyl cyanide, i76 Isopropyl ether, d417 Isopropylethylene, ml 60 Isopropylidone acetone, m3 50 Isopropyl iodide, i49... 

Palladium was about half as active as rhodium, and platinum and ruthenium were almost inactive for the hydrogenation of isopropenyl methyl ether. Since these metals showed the same order of activity for the hydrogenolysis of acetone diisopropyl acetal, it has been suggested that the dissociation of the acetal to unsaturated ether and alcohol to form an equilibrium mixture (eq. 13.2) constitutes the first step in the hydrogenolysis of acetals. Hydrogenation then removes the unsaturated ether and allows further conversion of the acetal to the unsaturated ether. 

In recalcitrant cases, e.g., in the formation of trans-fused dioxolanes, 2-methoxy-propene (isopropenyl methyl ether, bp 34 °C) or 2-(trimethylsilyloxy)propene (bp 93 °C)3S can be used [Scheme 3.24J.36 The latter reaction benefits from the formation of hexamethyldisiloxane [(Me Si O] to drive the reaction to comple-tion. One of the prime advantages of using 2-methoxypropene for the formation of isopropylidene derivatives is that the conditions are very mild the reaction is fast even with weak add catalysts such as pyridinium p-toluenesulfonate [Scheme 3.25].37... 

Isopropenyl acetate is converted into the dimethylketal of acetone (2,2-dimethoxy-propane) by treatment with mercuric acetate and boron trifluoride etherate.2 Elimination of the elements of methanol by reaction with acetic anhydride and pyridine give isopropenyl methyl ether. 

Synthesis of fi-ketoallenes and a,fi-unsaturated ketones.1 Isopropenyl methyl ether, under acid catalysis (p-toluenesulfonic acid or phosphoric acid particularly), reacts with a tertiary acetylenic carbinol to give a/3-ketoallene in high yield, as exemplified by the reaction with 3 methylbutyne-l-ol-3 (1). The /3-ketoallene (2) is... 

Isopropenyl acetate, 191, 230, 309, 325 3-IsopropenylcycIohexanone, 92 Isopropenyllithium, 456 Isopropenylmagnesium bromide, 92 Isopropenyl methyl ether, 230-231 Isopropylamine, 44, 414 rw-4- 1 sopropylcyclohexane-1 -carboxylic acid, 412, 413... 

Synthesis of y,8-unsaturated ketones.3 Isopropenyl methyl ether reacts with tertiary vinylcarbinols to give y,S-unsaturated ketones. Phosphoric acid is used as... 

In order to increase the steric bulk even further, enol ethers with an additional substituent at the double bond were used. Examples are isopropenyl methyl ether 71 and 2-methyldihydrofuran 74. In these transformations the cycloadduct with a cis orientation of the N-phthaloyl and OR group would be formed via an endo-E-syn and the corresponding trans-products via an exo-E-anti transition structure [46]. 

Methyl-4,5-heptadien-2-one 9 2-Methyl-3-butyn-2-ol (172 g), light petroleum (b.p. 60 to 90° 800 ml), hydroquinone (0.4 g), and isopropenyl methyl ether (432 g) are treated with p-toluenesulfonic acid (0.2 g). There is an exothermic reaction, after which the mixture is... 

By reaction of the Cg-hydroxyketone (3R)-58 with isopropenyl methyl ether, the acetonide 59 was obtained. Subsequent reaction with but-3-yn-2-ol (60), acetylation and dehydration gave the diacetate 61 which was reduced with sodium bis-(2-methoxyethoxy)aluminium hydride (SMEAH) to (3/ )-3-hydroxy-p-ionol (62) Scheme 15). 

The hydroxyketone, protected with isopropenyl methyl ether, (73) is coupled to the protected C6-lithium acetylenide 80. The Cj -triol 87 is formed after removal of the protecting groups. Acid-catalysed dehydration of 87 leads to the Ci5-diol 88, which is partially produced in the (9Z)-form. The (9 )-compound must be isolated by crystallization from the ( 7Z)-mixture of the acetylenic Cis-phosphonium chloride 89 prepared in the conventional manner. Successive partial hydrogenation of (E)-89, palladium-catalysed isomerization, and crystallization, give 86 in an overall yield of 43% based on 73. 

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