Dissolving metals benzylic compounds

Hydrogenolysis ofAllyl and Benzyl Halides and Related Compounds 4.7.4 DISSOLVING METAL REDUCTIONS... 

Metallic sodium plus alcohol constitutes the most commonly used system for chemical hydrogenolysis. One of the first reagents employed, it has found continual use ever since. The benzylated compound is dissolved in the alcohol, and small pieces of sodium are added. After the sodium has... 

One of die most popular reactions in organic chemistry is dissolving metal reductions [1-3], Two systems are frequently used - sodium dissolved in ammonia with alcohol and lithium dissolved in alkylamines [4]. Although calcium is seldom used, it has been successfully applied to the reduction of a variety of compounds and functional groups [5], including aromatic hydrocarbons, carbon-carbon double and triple bonds, benzyl ethers, allyl ethers, epoxides, esters, aliphatic nitriles, dithianes, als well as thiophenyl and sulfonyl groups. 

In addition to being more selective, dissolved calcium metal functions in a similar way to lithium and sodium metals towards organic functional groups [45]. Tab. 4.2 lists reductions giving the same products by the three dissolved metals. Among these, calcium affords the highest yields for some substrates (entries 1-3). The compounds in Tab. 4.2 include an aldehyde, indole [46], aryl ketone, enone, naphthalene [47], pyridine N-oxide [48], benzyl alcohol, styrene, and buckminster-fullerene. 

The carbon-metal bond in such compounds can range from an almost completely ionic bond to one that is predominantly covalent. Benzyl-sodium, for example, may be dissolved in ether to yield a conducting solution on the other hand, the lithium-carbon bond in the colorless ethyliithium is quite nonpolar. The chemistry of such compounds, be they ionic or covalent, is best understood by considering them as sources of the highly basic carbanions that would be formed by removal of the metal ion thus the chemistry of benzylsodium is the chemistry of the CeH CH ion, whereas the chemistry of ethyliithium is the chemistry of the ethide ion, C2H Such ions will attack acidic hydrogens to form the parent hydrocarbons, will attack the more positive end of a double bond, and can carry out a number of nucleophilic displacements these reactions are discussed in texts on organic chemistry. 

Apart from their behaviour as ligands in metal catalyst systems, studies of the reactivity of phosphites towards a wide variety of other substrates have attracted attention. New aspects and applications of the classical Michaelis-Arbuzov reaction and its variants continue to appear. Evidence of the thermal disproportionation of methyltriaryloxyphosphonium halides formed in the reactions of triarylphosphites with alkyl halides, together with the formation of P-O-P intermediates, has been reported. The Michaelis-Arbuzov reaction has been used in the synthesis of phosphonate-based styrene-divinylbenzene resins and polyphosphonated chelation therapy ligands.Treatment of electron-rich benzylic alcohols dissolved in triethylphosphite with one equivalent of iodine affords a low-temperature one-pot route to the related benzylic phosphonates, compounds which are otherwise difficult to prepare. Upper-rim chloromethylated thiacalix[4]arenes have also been shown to undergo phosphonation on treatment with a phosphite ester in chloroform at room temperature. The nickel(II)-catalysed reaction of aryl halides with phosphite esters in high boiling solvents, e.g., diphenyl ether, (the Tavs reaction), has also... 

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