Allyl halides reduction

Allyl Halides. Reduction of a polyfunctional allyl chloride occurs without rearrangement and without reduction of the tosylate using Ph2SiH2/ZnCl2/... 

Allyl halides, reduction reactions, 31 Aluminum chloride reagent/catalyst alkyl halide reduction, 30-31 secondary alkyl alcohol reduction, 14-15... 

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. ... 

One of the most gentle methods for the generation of reactive allylmetallic reagents was introduced in 1977 by Hiyama and Nozaki1,2,3,33. By the action of two equivalents of chromi-um(II) chloride on allylic halides in tetrahydrofuran at 0°C in the presence of a carbonyl compound, reductive coupling with the formation of a homoallylic alcohol takes place. 

Benzylic, allylic and propargylic positions enhance the cathodic cleavage rate of C— heteroatom bonds as, for example, in the reduction of benzylic and allylic halides or alcohols56. Similar activated sulphones, due to their acidity, are in a class apart. Figure 8 shows the similitude between the cathodic behaviour of an allylic sulphone and its isomer, i.e., the corresponding vinylic sulphone when the electrolyses are run in an aprotic solvent. However, in the presence of an excess of proton donor, discrepancies appear. 

Similar kinetics are exhibited by the reduction of vicinal dihalides by Cr(II) , which proceeds 10-40 times faster than that of the allylic halides. Such activation by a second halogen atom suggests a neighbouring group effect, viz. 

The reductive coupling of allyl halides to 1,5-hexadiene at glassy C electrodes was catalyzed by tris(2, 2,-bipyridyl)cobalt(II) and tris(4,4 -dimethyl-2, 2/-bipyridyl)cobalt(II) in aqueous solutions of 0.1 M sodium dodecylsulfate (SDS) or 0.1 M cetyltrimethylammonium bromide (CTAB).48 An organocobalt(I) intermediate was observed by its separate voltammetric reduction peak in each system studied. This intermediate undergoes an internal redox reaction to form 1,5-hexadiene... 

There are few reports of oxidative addition to zerovalent transition metals under mild conditions three reports involving group 10 elements have appeared. Fischer and Burger reported the preparation of aTT -allylpalladium complex by the reaction of palladium sponge with allyl bromide(63). The Grignard-type addition of allyl halides to aldehydes has been carried out by reacting allylic halides with cobalt or nickel metal prepared by reduction of cobalt or nickel halides with manganese/iron alloy-thiourea(64). 

Alkyl Halides. Commonly, reductions with liquid silanes and liquid alkyl halides do not require the use of a solvent.186 When the alkyl halide is a solid, either pentane186 or dichloromethane may be used as solvent.192 No significant difference in reactivities is observed between alkyl chloride and bromide substrates,186 but allyl halides are more reactive than 2-halopropanes, which, in turn, are more reactive than 1-halopropanes.190,146... 

Alkyl halides and triflates, alkane reduction, 27-32 alkyl halides, 28-31 a-halocarbonyl compounds, 31 vinyl and aryl halides and triflates, 32 Alkynes, alkane reduction, 45-46 Allyl acetates, reduction of, 51 Allyl alcohols ... 

Stille coupling (12, 56).1 The key step in a synthesis of (E)-neomanoalide (4) involves palladium-catalyzed coupling of an allyl halide with an a-stannylfuran. Thus 1 and 2 couple in the presence of Pd(dba)2 and P(C6H5), to form 3 as a 1 1 mixture of (E)- and (Z)-isomers in 66% yield. Conversion of 3 to 4 involves reduction (DIBAH) and selective singlet oxygen oxidation of a 2-silylfuran to a butenolide. 

The reaction of methylenesulphones with allyl halides in the presence of quaternary ammonium salts produces the 1-allyl derivatives [52], unlike the corresponding reaction in the absence of the catalyst in which the SN- product is formed (Scheme 6.5). In contrast, alkylation of resonance stabilized anions derived from allyl sulphones produces complex mixtures [51] (Scheme 6.6). Encumbered allyl sulphones (e.g. 2-methylprop-2-enyl sulphones) tend to give the normal monoalkyl-ated products. Methylene groups, which are activated by two benzenesulphonyl substituents, are readily monoalkylated hydride reduction leads to the dithioacetal and subsequent hydrolysis affords the aldehyde [61]. 

The reaction starts with an oxidative addition of an allylic compound to palladium(O) and a Tt-allyl-palladium complex forms. Carboxylates, allyl halides, etc. can be used. In practice one often starts with divalent palladium sources, which require in situ reduction. This reduction can take place in several ways, it may involve the alkene, the nucleophile, or the phosphine ligand added. One can start from zerovalent palladium complexes, but very stable palladium(O) complexes may also require an incubation period. Good starting materials are the 7t-allyl-palladium intermediates ... 

A classic paper by Baizer and Chruma [35] describes synthetic applications based on the reduction of allyl halides. Electrolyses of 4-bromo- and 4-chloro-2-butene can be employed for the allylation of acetone and benzaldehyde [36], and the reduction of allyl halides in the presence of trimethylchlorosilane affords silylated compounds [34]. 

Cathodic substitution stands for C,C bond or C, heteroatom bond formation with cathodically generated anions. The question of regioselectivity is encountered in the reaction of such anions with allyl halides (path a) or in the reaction of allyl anions generated in an ECE process from allyl halides (path b). Cathodic reductive silylation of an allyl halide proceeds regioselectively at the less substituted position (Fig. 15) [91]. From the reduction potentials of the halides it is proposed that the reaction follows path b. 

Regioselectivity in the cathodic allyla-tion of ketones and aldehydes is greatly affected by the relative ease of the reduction of the allyl halide compared with that of the carbonyl compound. When the carbonyl compound is more easily reduced than the allyl halide, the allylation takes... 

The Barhier-type reaction of aldehydes and ketones with allyl halides (485) in the presence of Sml2, leading to homoallyl alcohols (486), has received recent interest as a one-step alternative to the Grignard reaction. However, the reactions require the use of stoichiometric amounts of the reducing Sm(III) species. Recently, the electroreductive Barhier-type allylation of carbonyl compounds in an SmH-mediated reaction has been developed [569]. The electrolysis of (485) is carried out in a DMF-SmCl3-(Mg/Ni) system in an undivided cell to give the adduct (486) in 50 85% yields (Scheme 168) [569]. Electrosynthesis of y-butyrolactones has been achieved by the reductive coupling of ethyl 3-chloropropionate with carbonyl compounds in the presence of a catalytic amount of SmCfi [570]. 

Reduction of allyl bromides and iodides at vitreous carbon in an aptotic solvent generally gives good yields of the dimer. This product arises by rapid substitution by the allyl carbanion, formed in an overall two-electron reaction, onto a second molecule of allyl halide [55, 56]. 

Reduction of a range of allyl and benzyl chlorides at a stainless steel cathode in dimethylformamide in the presence of carbonyl compounds and using a sacrificial anode of aluminium or zinc, leads to a Reformatsky-type reaction in 40-80 % yields. Allyl halide give products by reaction at both the a- and y-positions. Tetra-chioromethane and bromotrifluoromethane take part in similar reactions provided a... 

Transmetallation of allyltributyltin with organolithium species has been used for the generation of allyllithium solutions free of the coupling byproducts which often result from reduction of allylic halides with lithium metal. These solutions may then be used directly for the preparation of Gilman reagents and other reactive modifications of the parent allyllithium. 

The conjugate addition reactions probably occur by a mechanism similar to that for substitution on allylic halides. There is probably an initial complex between the cuprate and enone.44 The key intermediate for formation of the new carbon-carbon bond is an adduct formed between the enone and the organocopper reagent. The adduct is formulated as a Cu(III) species which then undergoes reductive elimination. The lithium ion also plays a key role, presumably by Lewis acid coordination at the carbonyl oxygen.45 Solvent... 

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