Alkenyl acetate

With higher alkenes, three kinds of products, namely alkenyl acetates, allylic acetates and dioxygenated products are obtained[142]. The reaction of propylene gives two propenyl acetates (119 and 120) and allyl acetate (121) by the nucleophilic substitution and allylic oxidation. The chemoselective formation of allyl acetate takes place by the gas-phase reaction with the supported Pd(II) and Cu(II) catalyst. Allyl acetate (121) is produced commercially by this method[143]. Methallyl acetate (122) and 2-methylene-1,3-diacetoxypropane (123) are obtained in good yields by the gas-phase oxidation of isobutylene with the supported Pd catalyst[144]. 

Slightly more exotic carbon-centered nucleophiles can also participate in the ring-optening of epoxides. For example, the vinyl metallate 81, prepared by the treatment of the alkenyl acetal 86 with Schlosser s reagent, attacks mono-substituted epoxides 82 at the C-2 position to give the labile homoallyl alcohols 83 in fair to very good yields <96TET1433>. 

A variety of other powerful electrophiles add to the allylzirconium species 91, as shown in Scheme 3.26. Such reactions include the Lewis acid catalyzed addition of aryl, alkyl, or alkenyl acetals, derived from aldehydes, but not from ketones, and the addition of imi-nium species that lack p-hydrogens [56,58]. 

When the allyl group is part of a cyclic structure, a k-g reaction cannot take place to epimerise one of the chiral carbon atoms after having formed the k-g intermediate, the same Jt-face comes back-on to palladium. Thus, if we start from a racemic cyclic alkenyl acetate mixture, racemisation at the complex is blocked and the product will also be a racemate at 100% conversion. Kinetic resolution is still an option to obtain chiral product and starting material. Nevertheless high ee s were obtained when cyclic alkenyl acetates were used. 

The most synthetically valuable method for converting alkynes to ketones is by mercuric ion-catalyzed hydration. Terminal alkynes give methyl ketones, in accordance with the Markownikoff rule. Internal alkynes will give mixtures of ketones unless some structural feature promotes regioselectivity. Reactions with Hg(OAc)2 in other nucleophilic solvents such as acetic acid or methanol proceed to / -acetoxy- or /i-mcthoxyalk-enylmercury intermediates.116 These intermediates can be reduced to alkenyl acetates or solvolyzed to ketones. The regiochemistry is indicative of a mercurinium ion intermediate which is opened by nucleophilic attack at the more positive carbon that is, the additions follow the Markownikoff rule. Scheme 4.7 gives some examples of alkyne addition reactions. 

Oxidation of alkenes by Co(OAc)3 preferentially occurs at the allylic positions, yielding 2-alkenyl acetate. Oxidation of cyclohexene by Co(OAc)3 and TFA in AcOH results in the formation of cyclohexenyl acetate along with minor amounts of the corresponding allyl alcohol.550 The oxidation of ethylene by Co(TFA)3 in TFA affords ethylene glycol bis(trifluoroacetate).552... 

Selective ozonation of a trisubstituted double bond. l-Methyl-(lZ,5Z)-cyclo-octadiene (1) can be selectively cleaved to the aldehyde 2 by ozone. The produet was used for synthesis of sex pheromones of the (Z)-alkenyl acetate series (3). ... 

Ahiko, T.-a., Ishiyama, T., Miyaura, N. Asequence of palladium-catalyzed borylation of allyl acetates with bis(pinacolato)diboron and intramolecular allylboration for the cyclization of oxo-2-alkenyl acetates. Chem. Lett. 1997, 811-812. 

Multicarbon homologation of olefins.1 In a new general ketone synthesis, thexylborane is allowed to react with an equimolar quantity of an olefin to give a thexylmono-alkylborane (1). Addition of an w-alkenyl acetate yields a thexyldialkylborane (2). 

In addition, cyclic alkenyl acetates and carbonates react in an enantio- and di-astereoselective fashion with the carbobenzyloxytetralone to give the alkylated products in 96 and 99% ee for the five- and six-membered rings, respectively. The diasteromeric ratios were typically greater than 98 2 (Scheme 47). 

Coupled with in situ racemization of the unacetylated enantiomer by a ruthenium complex, the complete conversion of a secondary alcohol to the chiral acetate is efficient." An alternative method involves hydrogenation of alkenyl acetates in the presence of both lipase and a Ru(II) catalyst."... 

The reactions collected in Schemes 56 and 57 contain overwhelming evidence proving that the direction of the addition to alkynyl and alkenyl acetate complexes of osmium and ruthenium is determined by the electronic nature of the metallic center (Os or Ru), by the electronic properties of the ancillary ligands of the complexes, and also by the source of the electrophile. 

Although the catalytic activity of the alkenyl acetate compounds previously mentioned have not been studied, Kawano et al. have recently shown that the triphenylphosphine derivative Ru C(=CHPh)0C(0)Et Cl(C0)(PPh3)2 catalyzes the addition of propanoic acid to phenylacetylene to give (Z)-2-phenylethenyl propanoate, selectively. This complex is prepared by reaction of RuC1(k2-02CEt)(C0)(PPh3)2 with phenylacetylene [84]. 

Generation of a-Acyl Radicals. As a one-electron oxidant, Ce can promote the formation of radicals from carbonyl compounds. In the presence of interceptors such as butadiene and alkenyl acetates, the a-acyl radicals undergo addition. The carbonyl compounds may be introduced as enol silyl ethers, and the oxidative coupling of two such ethers may be accomplished. Some differences in the efficiency for oxidative cyclization of, s-, and ,f-unsaturated enol silyl ethers using CAN and other oxidants have been noted (eq 14). ... 

From higher alkenes, three kinds of products, namely alkenyl acetates, allylic acetates and dioxygenated products, are obtained. Reaction of propylene gives two propenyl acetates 77 and 78 and allyl acetate (79) by acetoxypalladation to form two intermediates 75 and 76, followed by elimination of different jS-hydrogens. 

Atyl carbo lates and alkenyl acetates were also catalytically coupled with arylboroxines using NiCl2(PCy3)2 (Scheme 14.22). It was found that water can promote this transformation. The optimal amount of water is 0.88 equivalents (based on the acetate) for the atyl carbojgrlates and 1.0 equivalents for the alkenyl acetates.However, NiCl2(PCy3)2-catalysed coupling of aryl pivalates with aryl boronic acids does not require a water additive. ... 

The first data on the effect of temperature on half-lives of pheromones in rubber septa were reported for n-alkyl and n-alkenyl acetates (14). The correlations with the Equation 6, were high,... 

Because the heat of vaporization, AH, for the n-alkyl and n-alkenyl acetates increased with molecular weight, the ratio of pheromone components in the vapor, having different molecular weights, will change with temperature. A somewhat common combination of a 2 component pheromone consists of 2 components separated by 2 carbon atoms in a homologous series such as Z9-14 Ac and Zll-16 Ac. From the half-lives (Table I) and Equation 1, a septum containing 61.2 /ig of Z9-14 Ac and 402 /xg Zll-16 Ac would produce a ratio in the vapor of 50 50 at 30 C and a modest change to 54 46 in favor of Z9-14 Ac at 20 . 

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