Reagent hydride

Lithium aluminum hydride (LiAlH4) is the most powerful of the hydride reagents. It reduces acid chlorides, esters, lactones, acids, anhydrides, aldehydes, ketones and epoxides to alcohols amides, nitriles, imines and oximes to amines primary and secondary alkyl halides and toluenesulfonates to 

Substitution of alkoxy groups for the hydrogens in NaBH4 produces stronger reducing species this effect is attributed to resonance 

Recently reductions by a new hydride reagent, sodium bis(2-methoxy-ethoxy)aluminum hydride, have been investigated. This compound is similar to LiAlH4 in its reducing properties but because it is soluble in aromatic hydrocarbons and more stable in air than LiAlH4, it may be more convenient to use. 

Carbon-carbon double and triple bonds are generally unaffected with hydride reagents except when they are a,p- to a polar group such as the carbonyl group. Reduction of 

If the R group in a, p -unsaturated ketones is small or R=H, i.e. in a,P-unsaturated aldehydes, then 1,2-addition predominates. 

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These polar functional groups are mostly reduced to the corresponding alcohols with hydride reagents (A. Hajos, 1966, 1979). The general selectivities are indicated in table 1 (p. 97f.) and a few specific examples will be given here. 

Table 6. Behavior of Various Functional Groups Toward Hydride Reagents ...

Hydride reagents Aldehyde Ketone Acid chloride Ester Carboxyhc acid Carboxyhc salt Amide... 

The reduction of (aLkylarnino)haloboranes using hydride reagents can provide a convenient route to (aLkylamino)boranes for example, LiAlH has been utilized to prepare bis (dimethyl amino)borane [23884-11-9] from chi orobis (dimethyl amino)borane [6562-41-0] (68). When this same strategy is appHed to (bis(trimethylsi1y1)amino)ch1oro((trimethylsi1y1)amino)borane [10078-93-0] the expected compound is obtained along with the formation of two... 

Reductive cleavage to alcohols by catalytic hydrogenation (64HC(19-1)188) has largely given way to reduction with hydride reagents (Section 5.05.3.4.3(t)u)). 

BH3, toluene converts the p-AOM ether into a methyl ether. For a comparison of the stability of this group with MTM, SEM, BOM, and EOM to various hydride reagents, see the section on SEM ethers. ... 

So-called hydride reducing agents can transform carbonyl groups into alcohols, but their reducing ability depends on the nature of the hydride reagent. 

Compare atomic charges for sodium borohydride and lithium aluminum hydride. Which ion contains the most electron-rich hydride The least electron-rich hydride Based on these results alone, which hydride reagent should be the better reducing agent Explain. Obtain atomic charges for free borohydride and aluminum hydride anions. What changes, if any, does the counterion produce ... 

A second example exploits the fact that the mixed hydride reagent is capable of hydrogenolysis of certain carbon-oxygen bonds. Thus, treatment of cyclohexanone ketal (Chapter 7, Section IX) with lithium aluminum hydride-aluminum chloride results in the rupture of a C-O bond to give the oxyethanol derivative. 

The reduction of carbonyl compounds by reaction with hydride reagents (H -) and the Grignard addition by reaction with organomagnesium halides (R - +MgBr) are examples of nucleophilic carbonyl addition reactions. What analogous product do you think might result from reaction of cyanide ion with a ketone ... 

Formation of an Alcohol The simplest reaction of a tetrahedral alkoxide intermediate is protonation to yield an alcohol. We ve already seen two examples of this kind of process during reduction of aldehydes and ketones with hydride reagents such as NaBH4 and LiAlH4 (Section 17.4) and during Grignard reactions (Section 17.5). During a reduction, the nucleophile that adds to the carbonyl... 

Nucleophilic Addition of Grignard and Hydride Reagents Alcohol Formation... 

Reduction to sulphides with nucleophilic hydride reagents. ... 

D. C. Wigeield, Stereochemistry and Mechanism of Ketone Reductions by Hydride Reagents, Tetrahedron 35,449 (1979). 

In certain cases, metallic hydride reagents may also reduce double bonds in conjugation with C=0 bonds, as well as reducing the C=0 bonds, for example, ... 

By an alternative approach, the enantioselective reduction of 1,2-diketimines was achieved by using hydride reagents in the presence of stoichiometric amounts or an excess of enantiopure carboxylic acids. An... 

So far, we have seen two sources of nucleophilic H (LAH and NaBHr). There are many, many other hydride reagents that have been prepared (some that are even more reactive than LAH, and others that are even milder than NaBHr), for example ... 

Reduction to sulphides with electrophilic hydride reagents. 940... 

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