Hydrogenation allyl halides

The ( )-vinylsilane 151 was prepared by treatment of the silylstannation product 150 with hydrogen iodide[75] and the silylzincation product with water[70]. The silylstannylation of 1-ethoxyacetylene proceeds at room temperature using Pd(OAc)i and 1,1,3,3-tetramethylbutyl isocyanide regioselec-tively and an Si group is introduced at the ethoxy-bearing carbon. Subsequent Cul- and Pd-catalyzed displacement of the stannyl group in the product 152 with allyl halide, followed by hvdrolvsis, affords the acylsilane 153[79],... 

Both resonance forms of the allylic carbocation from 1 3 cyclopentadiene are equivalent and so attack at either of the carbons that share the positive charge gives the same product 3 chlorocyclopentene This is not the case with 1 3 butadiene and so hydrogen halides add to 1 3 butadiene to give a mixture of two regioisomeric allylic halides For the case of electrophilic addition of hydrogen bromide at -80°C... 

Methylsuccinic acid has been prepared by the pyrolysis of tartaric acid from 1,2-dibromopropane or allyl halides by the action of potassium cyanide followed by hydrolysis by reduction of itaconic, citraconic, and mesaconic acids by hydrolysis of ketovalerolactonecarboxylic acid by decarboxylation of 1,1,2-propane tricarboxylic acid by oxidation of /3-methylcyclo-hexanone by fusion of gamboge with alkali by hydrog. nation and condensation of sodium lactate over nickel oxide from acetoacetic ester by successive alkylation with a methyl halide and a monohaloacetic ester by hydrolysis of oi-methyl-o -oxalosuccinic ester or a-methyl-a -acetosuccinic ester by action of hot, concentrated potassium hydroxide upon methyl-succinaldehyde dioxime from the ammonium salt of a-methyl-butyric acid by oxidation with. hydrogen peroxide from /9-methyllevulinic acid by oxidation with dilute nitric acid or hypobromite from /J-methyladipic acid and from the decomposition products of glyceric acid and pyruvic acid. The method described above is a modification of that of Higginbotham and Lapworth. ... 

Entries 3 to 6 are examples of ester enolate alkylations. These reactions show stereoselectivity consistent with cyclic TSs in which the hydrogen is eclipsed with the enolate and the larger substituent is pseudoequatorial. Entries 4 and 5 involve SN2 substitutions of allylic halides. The formation of the six- and five-membered rings, respectively, is the result of ring size preferences with 5 > 7 and 6 > 8. In Entry 4, reaction occurs through a chairlike TS with the tertiary C(5) substituent controlling the conformation. The cyclic TS results in a trans relationship between the ester and vinylic substituents. 

The base-promoted dehydrohalogenation of vinyl or allylic halides affords poor yields of allenes because of the competing side reaction leading to acetylenes [21,22], The presence of tertiary hydrogens a to the halogen also helps to... 

A general method for preparing allylic halides is by addition of hydrogen halides to conjugated dienes. This reaction usually produces a mixture of 1,2- and 1,4-addition products (see Sectioii 13-2) ... 

Amino acid synthesis (8, 389). Alkylation of the aldimine (1) from glycine ethyl ester and /j-chlorobenzaldehyde under phase-transfer conditions offers a general route to amino acids. Either liquid-liquid phase-transfer or solid-liquid phase-transfer catalytic conditions are satisfactory with active halides, but alkylation with allylic halides and less active alkyl halides is best effected under ion-pair extraction conditions (6,41), with 1 equiv. of tetra-n-butylammonium hydrogen sulfate (76-95% yields).1... 

Frimer, A. A., J. Org. Chem., 1977, 42, 3194—3196, footnote 7 A new method of preparation involves interaction of allylic halides in solvents with 98% hydrogen peroxide in presence of silver ion and base at ambient temperature under argon. The reactions must be run in the dark to prevent precipitation of metallic silver, which will catalyse decomposition of the hydroperoxide or excess hydrogen peroxide. In an experiment not run in the dark, the hydroperoxide from 3-chlorocy-clohexene ignited spontaneously after isolation and concentration. 

We had to be careful in chapter 25 when we wanted to add bromoketones 4 to enolates 3 to make the 1,4-dicarbonyl compound 5. We could not use a lithium enolate because it would be too basic. No such difficulties exist in the reaction of enolates with allylic halides such as 2. Any enol(ate) equivalent will do as there are no acidic hydrogens and allylic halides are good electrophiles for the Sn2 reaction. 

The role of the solvent in practically all of the reactions so far discussed is decisive. For example, allylic halides having electron-attracting substituents, such as methyl bromocrotonate, upon treatment with nickel carbonyl in hydroxylic solvents do not react with CO. Instead substitutive hydrogenation of the halogenated carbon atom occurs (55), while in ketonic solvents the products which might be expected from the carbonylation of normal allylic halides are obtained (50). 

Under conditions similar to those for allyl halides, 1,4-dichlorobutene reacts with nickel carbonyl to give butadiene. However, a double insertion of acetylene and carbon monoxide can be successfully carried out using 4-chloro-2-buten-l-ol and generating hydrogen halide in situ with a weak acid inorganic halide combination, e.g., NaBr-H3P04 (58). 

The elimination of hydrogen chloride from an allylic halide to cyclopropenes and is of particular value in the preparation of the parent hydrocarbon and of simple alkyl derivatives. Although yields are often low the reagents are very readily avaiable ... 

Carbon monoxide is essential for the present reaction (vide supra), and no reaction occurred at all under an argon atmosphere. The addition of base is also indispensable, and EtsN is the most effective base, which should be a hydrogen source for the products. Allylic carbonates and allylic halides did not give products in good yield. 

Allyl phenyl telluriums, prepared from allyl halides and benzenetellurolate, experience oxidative cleavage of the allyl group when treated with hydrogen peroxide, tcrr.-butyl hydroperoxide, sodium periodate, oxygen, or air The allyl group is converted to unsaturated alcohols, aldehydes, and ketones. Before elimination from the molecule the phenyltelluro group is probably oxidized to a telluroxide or a tellurinic ester ... 

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