AUyl acetates substituted

Pd-catalyzed reactions of allylic esters such as aUyl acetates, carbonates, and phosphates with soft carbon nucleophiles such as malonate esters are useful for carbon-carbon bond formation (Sects. V.2.1.1-V.2.1.5). hi this section, Pd-catalyzed substitution reactions of nitrogen-containing allylic derivatives such as allylic amines, ammonium salts, tosylim-ides, and nitro compounds are described (Scheme 1). The allylic derivatives of other group 15 atoms have never been used as allyl unit source in Pd-catalyzed alkylation reactions so far. 

Starting from oxygen-linked 1,3-dicarbonyl compounds (malonates or acetoacetates), Tietze and co-workers have demonstrated an allylic substitution at the a-position of varions snbstrates (aUyl acetates, carbonates, and chlorides). Under the conditions employed, bisalkylation was observed in all cases. Since the acetoacetates could be alkylated by hard electrophiles at the y-position, a broad spectrum of compounds might be obtained. The cleavage from the resin was performed using DIBAL-H to obtain the corresponding diols (Scheme 24). 

Many alkenes will react with PdCl2, forming a itt-allyl complex and one mole of HCl. A base is normally added to react with the HCl produced. Solvents that have proven useful include acetic acid, chloroform, methanol, and DMF. Where isomeric itt-allyl palladium complexes can be formed, one often obtains a mixture of products. This is particularly true for reactions run in acetic acid. The addition of CUCI2 causes an increase in regioselectivity, resulting in abstraction of the allylic C-H bond that leads to the more-substituted Tr-aUyl complex (equation 53). 

Unfortunately, attempts to perform this substitution reaction on cyclohexenol and geraniol led to the exclusive formation of the corresponding silyl ethers. It thus would seem that one requirement for effective carbon-carbon bond formation is that allylic alcohols be secondary and have possess y,y-disubstitution. Pearson, however, discovered a method with less restriction on the natiue of the substrate he used allylic acetates with y-mono-substitution or primary alcohols [96]. Not only ketene silyl acetals but also a diverse set of nucleophiles including aUyl silane, indoles, MOM vinyl ether, trimethylsilyl azide, trimethylsilyl cyanide, and propargyl silane participate in the substitution of y-aryl allylic alcohol 90 to give allylated 91 (Sch. 45). Further experimental evidence suggests that these reactions proceed via ionization to allylic carboca-tions—alcohols 90 and 92 both afforded the identical product 93. 

METHYLPROPYLAMINE (13952-84-6) Forms explosive mixture with air (flash point 15°F/—9°C). An organic base. Violent reaction with strong oxidizers, acids. Incompatible with organic anhydrides, acrylates, alcohols, aldehydes, alkylene oxides, substituted aUyls, cellulose nitrate, cresols, caprolactam solution, epichlorohydrin, ethylene dichloride, isocyanates, ketones, glycols, maleic anhydride, nitrates, phenols, vinyl acetate. Attacks some metals. May accumulate static electrical charges, and may cause ignition of its vapors. 

Ireland noted in an early report that the rate of the rearrangement increased significantly with alkyl substitution at Cl, C4 or C6 (Scheme4.7) [1]. This is consistent with extensive computational and experimental studies of the parent aUyl vinyl ether [6], although the corresponding calculations of 2-OR-ketene acetals have not been reported. 

Inanaga et al. reported the first example of a nucleophileotalyzed Ireland-Claisen rearrangement (Scheme 4.11) [12]. Conjugate addition of tricyclohexyl-phosphine to aUyl acrylates generated intermediate phosphonium allyl sUyl ketene acetals, which underwent rearrangement to yield a-substituted acrylates after elimination of the phosphine. 

Allylic Halides AUyl chlorides are among the most reactive allylic substrates. As such, they should not be prone to epimerization at the state of the jT-allyl-Pd complexes, and chemoselective substitutions are possible with allylic halides/acetates [70], If halogenated dienes such as 73 are used, the protocol gives access to substituted aUenes 74 [71] (Scheme 12.37). 

The Heck reaction may also proceed in an intramolecular fashion if the aryl hahde is covalently boimd to the aUyl substrate. In this case the sequential allyhc substitution-Heck-cycIization with Pd acetate as a catalyst takes place very smoothly as an imimolecular process and furnishes the polycon-densed pyrroHdones 91 in excellent yields (Scheme 29). 

Notes and discussion. This reaction can be utilized for the preparation of a-aUyl, ethyl, phenyl and substituted aryl thioglycosides of sialic acid. NMR and NMR spectra of the crude reaction mixtures have confirmed that complete anomeric inversion occurs under the PTC condition. Adoption of tetrabutylammoniumhydro-gen sulfide as a PTC is critical for mild reaction conditions, otherwise, if triethylbenzylammonium chloride is employed, more harsh conditions are required. The use of ethyl acetate is advantageous over dichloromethane owing to the production of PhSCH2Cl and (PhS)2CH2 resulting from nucleophilic displacement of one or two chlorides of dichloromethane with thiophenol in the model experiment. 

Potassium acetate is used as the source of acetate anion in a range of addition and substitution reactions of activated cyclopropanes, epoxides, alkyl, aUyl, and benzyl electrophiles. 

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