Sodium amide hydride

The formation of the above anions ("enolate type) depend on equilibria between the carbon compounds, the base, and the solvent. To ensure a substantial concentration of the anionic synthons in solution the pA" of both the conjugated acid of the base and of the solvent must be higher than the pAT -value of the carbon compound. Alkali hydroxides in water (p/T, 16), alkoxides in the corresponding alcohols (pAT, 20), sodium amide in liquid ammonia (pATj 35), dimsyl sodium in dimethyl sulfoxide (pAT, = 35), sodium hydride, lithium amides, or lithium alkyls in ether or hydrocarbon solvents (pAT, > 40) are common combinations used in synthesis. Sometimes the bases (e.g. methoxides, amides, lithium alkyls) react as nucleophiles, in other words they do not abstract a proton, but their anion undergoes addition and substitution reactions with the carbon compound. If such is the case, sterically hindered bases are employed. A few examples are given below (H.O. House, 1972 I. Kuwajima, 1976). 

Hydrazinium salts, N2H5 X, are acids in anhydrous hydrazine, metallic hydrazides, N2H, are bases. Neutralization in this solvent system involves the hydrazinium and hydrazide ions and is the reverse of equation 7. Metal hydrazides, formally analogous to the metal amides, are prepared from anhydrous hydrazine and the metals as well as from metal amides, alkyls, or hydrides. (The term hydrazide is also used for organic compounds where the carboxyUc acid OH is substituted with a N2H2.) Sodium hydrazide [13598-47-5] is made from sodium or, more safely, from sodium amide (14) ... 

A AlI lation. 1-Substitution is favored when the indole ring is deprotonated and the reaction medium promotes the nucleophilicity of the resulting indole anion. Conditions which typically result in A/-alkylation are generation of the sodium salt by sodium amide in Hquid ammonia, use of sodium hydride or a similar strong base in /V, /V- dim ethyl form am i de or dimethyl sulfoxide, or the use of phase-transfer conditions. 

Sodium hydride, sodium amide, or other strong bases also can be used. The reagent can be generated in the presence of an appropriate carbonyl compound that reacts direcdy. 

In the case of tertiary and some of the more complex alcohols, the use of alkaU hydroxides is not feasible, and it is necessary to use reagents such as sodium hydride, sodium amide, or the alkaU metal to form the alkoxide ... 

Methylindole has been prepared from the a5-methylphenyl-hydrazone of pyruvic acid, by the action of sodium amide or sodium hydride on indole followed by methyl iodide at elevated temperatures,by treatment of indole with methyl p-toluene-sulfonatc and anhydrous sodium carbonate in boiling xylene, and by the action of inelhyl sulfate on indole previously treated... 

The most common base used for the Claisen condensation is sodium ethoxide, although for some substrates stronger bases such as sodium amide or sodium hydride may be necessary. 

Of the several syntheses available for the phenothiazine ring system, perhaps the simplest is the sulfuration reaction. This consists of treating the corresponding diphenylamine with a mixture of sulfur and iodine to afford directly the desired heterocycle. Since the proton on the nitrogen of the resultant molecule is but weakly acidic, strong bases are required to form the corresponding anion in order to carry out subsequent alkylation reactions. In practice such diverse bases as ethylmagnesium bromide, sodium amide, and sodium hydride have all been used. Alkylation with (chloroethyl)diethylamine affords diethazine (1), a compound that exhibits both antihista-minic and antiParkinsonian activity. Substitution of w-(2-chloroethyl)pyrrolidine in this sequence leads to pyrathiazine (2), an antihistamine of moderate potency. 

On treatment with a strong base such as sodium hydride or sodium amide, dimethyl sulfoxide yields a proton to form the methylsulfinyl carbanion (dimsyl ion), a strongly basic reagent. Reaction of dimsyl ion with triphenylalkylphosphonium halides provides a convenient route to ylides (see Chapter 11, Section III), and with triphenylmethane the reagent affords a high concentration of triphenylmethyl carbanion. Of immediate interest, however, is the nucleophilic reaction of dimsyl ion with aldehydes, ketones, and particularly esters (//). The reaction of dimsyl ion with nonenolizable ketones and... 

Powdered sodium amide reacts with dimethyl sulfoxide to generate the sodium salt under the same conditions, with the evolution of ammonia, and is comparable to sodium hydride in its reactivity. 

Butylation of ethyl phenylacetate, /-butyl phenylacetate, and ethyl 2-phenylhexanoate has also been accomplished with M-butyl bromide and sodium hydride in refluxing monoglyme in 64%, 66%, and 56% yields, respectively.6 In contrast to the sodium amide reactions above, however, careful fractionation of the crude products was required to obtain pure products. 

Carboxylic esters can be treated with ketones to give p-diketones in a reaction that is essentially the same as 10-118. The reaction is so similar that it is sometimes also called the Claisen condensation, though this usage is unfortunate. A fairly strong base, such as sodium amide or sodium hydride, is required. Yields can be increased by the catalytic addition of crown ethers. Esters of formic acid (R H) give P-keto aldehydes. Ethyl carbonate gives P-keto esters. 

The overall sequence of three steps may be called the Wittig reaction, or only the final step. Phosphonium salts are also prepared by addition of phosphines to Michael alkenes (hke 15-8) and in other ways. The phosphonium salts are most often converted to the ylids by treatment with a strong base such as butyllithium, sodium amide, sodium hydride, or a sodium alkoxide, though weaker bases can be used if... 

In the presence of a very strong base, such as an alkyllithium, sodium or potassium hydride, sodium or potassium amide, or LDA, 1,3-dicarbonyl compounds can be converted to their dianions by two sequential deprotonations.79 For example, reaction of benzoylacetone with sodium amide leads first to the enolate generated by deprotonation at the more acidic methylene group between the two carbonyl groups. A second equivalent of base deprotonates the benzyl methylene group to give a dienediolate. 

When the carbonyl compound is added to this base, abstraction of a proton and formation of the enolate anion follow, as seen with sodinm hydride or sodium amide above. Again, this reaction is essentially irreversible because the other product is the weak base diisopropylamine (pATa 36). So far, there does not seem any particular advantage in nsing LDA rather than sodium hydride or sodium amide. 

High yields of amines have also been obtained by reduction of amides with an excess of magnesium aluminum hydride (yield 100%) [577], with lithium trimethoxyaluminohydride at 25° (yield 83%) [94] with sodium bis(2-methoxy-ethoxy)aluminum hydride at 80° (yield 84.5%) [544], with alane in tetra-hydrofuran at 0-25° (isolated yields 46-93%) [994, 1117], with sodium boro-hydride and triethoxyoxonium fluoroborates at room temperature (yields 81-94%) [1121], with sodium borohydride in the presence of acetic or trifluoroacetic acid on refluxing (yields 20-92.5%) [1118], with borane in tetrahydrofuran on refluxing (isolated yields 79-84%) [1119], with borane-dimethyl sulflde complex (5 mol) in tetrahydrofuran on refluxing (isolated yields 37-89%) [1064], and by electrolysis in dilute sulfuric acid at 5° using a lead cathode (yields 63-76%) [1120]. 

Very strong bases can be used in other reactions that are similar to the Claisen condensation. In these reactions, carbanions are formed instead of enolates. Figures 15-7, 15-8, and 15-9 show examples of various reactions employing three different strong bases sodium ethoxide, sodium amide, and sodium triphenylmethanide. Sodium hydride, NaH, is a strong base that would also work. Any of these very strong bases could be used in each of the specific reactions. 

Carbazole can be more easily converted fully and irreversibly to its N-anion by bases stronger than potassium or sodium hydroxide amide and hydride bases under anhydrous conditions have been employed. Thus, sodium amide in liquid ammonia was utilized with the appropriate halide for the preparation of 9-(prop-l-yn-3-yl)carbazole (29 R = CH2C=CH) ° and 9-methylcarbazol-l-ylcarboxylic acid the preparation of 3-dimethylamino-9-(2-hydroxyethyl)carbazole from ethylene oxide utilized sodium amide in... 

The heterocycles react directly with alkali metals or undergo exchange reactions with, for example, sodium amide and hydride, n-butyllithium and thallium ethoxide, to form the TV-heteroaryl salts. The salts of the alkali metals exist as solvent separated ion-pairs or as contact ion-pairs (71JOC3091), as do the quaternary ammonium salts, whereas the salts of the heavier metals are generally considered to have a high N—metal covalent character. These characteristics, which can be modified by a change in the polarity of the solvent, control the reactions of the heteroaryl anions. 

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