Isopropenyl - from

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. 

The industrial precursor to 2,4-pentanedione is isopropenyl acetate, produced from acetone and ketene (307,308). The diketone is formed by the high temperature isomerization of isopropenyl acetate over a metal catalyst (309—311). 

Benzo[b]furan, 2,3-dihydro-2-hydroxymethyl-4//-chromene synthesis from, 3, 764 Benzo[b]furan, 2,3-dihydro-2-isopropenyl-synthesis, 4, 678, 680... 

Grignard reagents from, 5, 106 reactions, 5, 104 6, 274, 292 reactivity, 6, 292 synthesis, 6, 297 Thiazoles, imino-reactivity, 6, 250 Thiazoles, isopropenyl-radical polymerization, 6, 278 Thiazoles, mercapto-industrial uses, 6, 330 reactions, 5, 102 synthesis, 6, 298-299 tautomerism, 6, 247, 248, 269, 289 Thiazoles, methyl-... 

A -Dien-3-ol esters e.g., acetates) have greater utility as reaction intermediates than as protecting groups. They are prepared from A" -3-ketones by reaction with the acetic anhydride"" or by exchange with isopropenyl acetate. 

Enol esterification with acetyl chloride-acetic anhydride gives the A -trien-3-acetate, but reaction with isopropenyl acetate or with hot acetic anhydride-pyridine gives A " -trien-3-acetates. " Since A"" -3-ketones react with Girard reagents, these linear dienones can be separated from A ""-3-ketones. ... 

The dimethyl acetal (94) is readily prepared from the 22-aldehyde (93) by direct reaction with methanol in the presence of hydrogen chloride. Ena-mines (95) are formed without a catalyst even with the poorly reactive piperidine and morpholine.Enol acetates (96) are prepared by refluxing with acetic anhydride-sodium acetate or by exchange with isopropenyl acetate in pyridine.Reaction with acetic anhydride catalyzed by boron trifluoride-etherate or perchloric acid gives the aldehyde diacetate. 

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. ... 

Methylisoquinolinium 2-carboxylate (230), originally prepared by Quast (70LA64), was recently identified as a defensive betaine from Photuris versicolor fireflies (99JNP378). It is a pseudo-cross-conjugated mesomeric betaine isoconjugate to the odd alternant hydrocarbon 2-isopropenyl-naphthalene anion which is an odd alternant hydrocarbon anion. This compound therefore is a member of class 13, which is very rare. The UV absorption maxima Imax (methanol) were found at 235 (4.35), 320 (shoulder, 3.97), and 326 (3.99) nm. This compound undergoes similar reactions as Homarine 19 (Scheme 75). The NMR data are presented in Table VIII. 

The stability of the heterocyclic ring toward oxidation by permanganate depends on the experimental conditions. In acid media the ring is not cleaved, and acetylisoxazoles are readily prepared from isopropenyl derivatives.2-Isoxazolines are dehydrogenated into isoxazoles (cf. 192 193). The stability of the heterocyclic ring is also observed when this oxidation is carried out in acetone solution. It is of interest that this method allows the preparation both of... 

A series of benzimidazole and benzimidazolone derivatives from the Janssen laboratories has provided an unusually large number of biologically active compounds, particularly in the area of the central nervous system. Reaction of imidazolone itself with isopropenyl acetate leads to the singly protected imidazolone derivative 51. Alkylation of this with 3-chloro-l-bromopropane affords the functionalized derivative Use of this... 

Cyclic 1,3-diacetoxy-l,3-dienes can be generated in situ from cyclic 1,3-diketones under the influence of isopropenyl acetate. The dienes then undergo Diels-Alder reactions with maleic anhydride giving as products 1-acetoxybicycloalkane dicarboxylic anhydride derivatives (10). The procedure is also successful with cyclic 1,2- and 1,4-diketones as well as cyclic a,j3-unsaturated ketones. The products, after hydrolysis to... 

In a 500-ml round-bottom flask is placed a mixture of 25 g (0.178 mole) of dimedone, 21.8 g (0,22 mole, 25 % excess) of pulverized maleic anhydride, 0.1 g of /7-toluenesulfuric acid, and 150 ml of isopropenyl acetate. The mixture is refluxed for 72 hours, then cooled, and the acetone is removed at room temperature on a rotary evaporator. The resulting solution is cooled to —20° in a Dry Ice bath, whereupon the product crystallizes. It is collected by filtration to yield the crude product in about 80% yield. Recrystallization from hexane-ethyl acetate and decolorization by Norit gives colorless crystals, mp 164-166°. 

With a secure route to pentacyclic amine 2, the completion of the total synthesis of 1 requires only a few functional group manipulations. When a solution of 2 in ethanol is exposed to Pd-C in an atmosphere of hydrogen, the isopropenyl double bond is saturated. When a small quantity of HCI is added to this mixture, the hydro-genolysis of the benzyl ether is accelerated dramatically, giving alcohol 15 in a yield of 96%. Oxidation of the primary alcohol in 15 with an excess of Jones reagent, followed by Fischer esterification, gives ( )-methyl homosecodaphniphyllate [( )-1] in an overall yield of 85 % from 2. 

In 1992, Oda et al. reported a one-pot synthesis of optically active cyanohydrin acetates from aldehydes, which were converted to the corresponding racemic cyanohydrins through transhydrocyanation with acetone cyanohydrin, catalyzed by a a strongly basic anion-exchange resin [46]. The racemic cyanohydrins were acetylated by a lipase from P. cepacia (Amano) with isopropenyl acetate as the acyl donor. The reversible nature of the base-catalyzed transhydrocyanation enabled continuous racemization of the unreacted cyanohydrins, thereby effecting a total conversion (Figure 4.21). 

Figure 8. Equatorial el,e2, e3 and axial al,a2, a3 conformations of the carvone molecule. The asymmetric (chiral) carbon is shaded light gray, the =CH2 carbon in the isopropenyl tail is shaded mid-gray and the carbonyl oxygen atom is shaded dark gray. Taken from Ref. [38].

The number average molecular weights, Mq, of the polymers obtained in Table II ranged from 1300 to 3900 as determined by vapor nressure osmometry (VPO), and they were further characterized by - -H- and C-NMR spectrometry at ambient temperature and at 90°C, as well as by IR spectroscopy. The homopolymers of isopropenylferro-cene were found to have the expected structure, P, shown below, obtained by polymerization through the isopropenyl units, as indicated by spectroscopic characterization ... 

From our cationic polymerization studies of isopropenyl organometailic monomers, it can be concluded that structural and electronic... 

Figure 23 Monitoring of isomerisation of allyl end groups of PPG to isopropenyl functionality over time by means of h NMR spectroscopy (a) 0 h, (b) 89 h and (c) 594 h. Reproduced from Ref. [56] with permission of John Wiley Sons, Inc.

With a less reactive olefin such as isopropenyl acetate, diazoketone 86 gives only a low yield of cyclopropane 90 a-acyl enol ether 92, resulting from an intramolecular rearrangement of the ketocarbenoid, becomes the favored reaction product. If 91... 

Olefins analogous to 158 and 159 were also isolated from the CuS04-catalyzed decomposition of ethyl diazoacetate in the presence of 2-isopropenyl-2-methyl-1,3-dithiane (total yield 56%, E Z — 4 1) a butadiene was absent from the reaction mixture 161). With dimethyl diazomalonate instead of ethyl diazoacetate, only the Z-olefin resulting from a [2,3]-sigmatropic rearrangement of the corresponding sulfur ylide was obtained in 36 % yield 161). When the same procedure was applied to... 

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