Alkanes allyl halides

Selective reduction of halides.1 Thecomplexl reduces tertiary halides to alkanes without attack on primary or secondary halides. It is more selective than organotin hydrides. Benzylic and allyl halides are also reduced easily. The reagent reduces a mixture of the halides 2 mainly to trims-3 thus, a partial inversion oftonfiguration is... 

Methods reported this year for the reduction of alkyl halides to alkanes include the potassium-dicyclohexyl-18-crown-6 reduction of alkyl fluorides, sodium borohydride reduction of alkyl chlorides, bromides, and iodides (or sulphonate esters) under liquid-liquid phase-transfer conditions, and the selective reduction of tertiary alkyl, benzyl, and allyl halides with the borate (61). Continuing... 

Simple alkyl halides can be prepared by radical halogenation of alkanes, but mixtures of products usually result. The reactivity order of alkanes toward halogenation is identical to the stability order of radicals R3C- > R2CH- > RCH2-. Alkyl halides can also be prepared from alkenes by reaction with /V-bromo-succinimide (NBS) to give the product of allylic bromination. The NBS bromi-nation of alkenes takes place through an intermediate allylic radical, which is stabilized by resonance. 

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 ... 

Aryl aldehydes, alkane reduction, 71-72 Aryldiazonium salts, reduction of, 104 Aryl halides and triflates, reduction reaction, 32 Aryl ketone, allylation,... 

C-Alkylations have been performed with both support-bound carbon nucleophiles and support-bound carbon electrophiles. Benzyl, allyl, and aryl halides or triflates have generally been used as the carbon electrophiles. Suitable carbon nucleophiles are boranes, organozinc and organomagnesium compounds. C-Alkylations have also been accomplished by the addition of radicals to alkenes. Polystyrene can also be alkylated under harsh conditions, e.g. by Friedel-Crafts alkylation [11-16] in the presence of strong acids. This type of reaction is incompatible with most linkers and is generally only suitable for the preparation of functionalized supports. Few examples have been reported of the preparation of alkanes by C-C bond formation on solid phase, and general methodologies for such preparations are still scarce. 

The allylmagnesium halide in ether is slowly added to a suspension or solution of the metal halide at 0°C or lower. Addition at low T improves yields and is essential for the synthesis of thermally unstable, homoleptic allyl complexes. The complexes are isolated by evaporation of the reaction mixture and extraction into an aromatic or alkane solvent. Purification is effected by crystallization or sublimation. When stable allyl compounds are prepared, an aqueous wash of the reaction mixture can be used to remove Mg salts and xs RMgX or -Li reagent the crude products can then be isolated from the resultant organic layer. 

This chapter surveys the reduction of saturated alkyl halides to alkanes. Reductive -eliminations of vicinal dihalides to alkenes are also described briefly. Reduction of vinyl and aryl halides is covered in this volume. Chapter 4.5 hydrogenolysis of allyl and benzyl halides is covered in this volume. Chapter 4.7, and reduction of a-halo-substituted carbonyl compounds CX—CO to carbonyl compounds CH—CO is covered in this volume. Chapter 4.8. 

HALIDES, ALLYLIC alkanes + halo-succinimides 14-03 from aldehydes or ketones 16-24... 

Deoxygenation. Alkanes are obtained from alcohols by reaction with PdClj-EtjSiH (by adding an alkyl halide such as Mel to the reaction medium the halides are produced). Secondary allylic alcohols and acetates are reduced to the hydrocarbons with EtjSiH-LiClO. The facile removal of the oxygen atom from aryl ketones by TiCl -mediated reaction with Et,SiH makes the synthesis of a-amino acids containing carbon chains of different length and a terminal aryl group much easier. A synthesis of CHIRAPHOS via the phosphine oxides calls for deoxygenation with HSiCl -EtaN." ... 

Secondary and tertiary alkyl halides give olefins on occasions,223 and / -un-saturated alkyl halides give products of allylic rearrangement.224 -Dibromo-alkanes give bisphosphonium salts in satisfactory to high yield.225 Unlike di-bromomethane, tribromomethane reacts with triphenylphosphine only to the monoquaternary salt stage, the reaction being radical jin nature.226... 

Typical alkyl halides are monochloro. bromo, or iodo derivatives of simple alkanes or cycloalkanes. Allylic and benzylic halides, a-haloke-tones, etc., are excluded, as are cycloalkyl halides with cycloalkyl ring sizes less than live. Cyclopropyl halides, in particular, are treated separately. 

Primary or secondary alkyl halides RX are completely transformed into alkane RH after reflux for several hours in 0.1 M THF solution of Sml (one equivalent). There is no reaction at room temperature. As predicted from redox potentials the reactivity decreases in the following direction RI > RBr > RCl. Phenyl or vinyl halides are unreactive, apart from 1-io-do naphthalene which was reduced to naphthalene (21), presumably because of the decrease in redox potential by the naphthalene ring. Allylic and benzylic halides are very reactive and give a coupling reaction in a few minutes at room temperature (eq. 9]). 

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