Bases Sodium hydride

Cycl[3.2.2]azines may also be obtained by the cycloaddition of a bifunctional three-carbon unit to a 3//-pyrrolizine. Vinamidinium salts have been used for this purpose <1984CB1649>, although the reactions require the use of a strong base (sodium hydride) and extended reaction times. They appear to proceed via a stepwise mechanism, since intermediates (the conjugated enamines 354 and 355) have been isolated in certain cases (Scheme 94). 

Conversely, treatment of the anion with the very strong base sodium hydride abstracts a sccund proton ... 

The ethyl ester of l-cyclopropyl-7-(2,6-dimethyl-4-pyridyl)-5,6,8-trifluoro-4-oxo-1,4-di-hydroquinoline-3-carboxylic acid26 and of the closely related (7>)-10-(2,6-dimethyl-4-pyridyl)-8,9-difluoro-3-methyl-7-oxo-2.3-dihydro-7//-pyrido[1,2,3-tfe]-l,4-bcnzoxazine-6-carboxylic acid 427 can be thiolated in tetrahydrofuran at low temperature, using the strong base sodium hydride. 

Nitrile-stabilized anions are so nucleophilic that they will react with alkyl halides rather well even when a crowded quaternary centre (a carbon bearing no H atoms) is being formed. In this example the strong base, sodium hydride, was used to deprotonate the branched nitrile completely and benzyl chloride was the electrophile. The greater reactivity of benzylic electrophiles compensates for the poorer leaving group. In DMF, the anion is particularly reactive because it is not solvated (DMF solvates only the Na+ cation). 

Various electron-withdrawing groups can be used in almost any combination with good results. In this example an ester and a nitrile cooperate to stabilize an anion. Nitriles are not quite as anion-stabilizing as carbonyl groups so this enolate requires a stronger base (sodium hydride) in an aprotic solvent (DMF) for success. The primary alkyl tosylate serves as the electrophile. 

Note Deprotonation of the palladium coordinated amine is difficult and dependant upon the choice of base. Sodium hydride is a strong base and upon abstraction of a proton produces molecular hydrogen, which evolves from the reaction without reacting with the palladium centre. 

Two compounds which illustrate further the general effectiveness of stereochemical control are the i4a,i7j8-diol 17-tosylate (19) and i4yS,i7a diol 17-tosylate (22). The former compound permitted oxetane formation by the action of the very powerful base sodium hydride in boiling tetrahydrofuran (weaker bases were ineffective), although the i4a,i7a-oxide (20) was too unstable to be isolated. Its transient formation... 

Benzodiazepine 7a undergoes a thermal rearrangement with ring contraction to give the quin-azoline 8a in 32- 37% yield.Benzodiazepine 7b is transformed to quinazoline 8b by either base (sodium hydride in dimethylformamide or potassium hydroxide in ethanol) or acid (hydrogen chloride in ethanol)." ... 

Acylation of ketones. Noting that on alkylation of malononitrile in ethanol or benzene with sodium ethoxide as base the yield is only 70% and formation of imide esters is an important side reaction, Bloomfleld was led to try the non-nucleophilic base sodium hydride in dimethyl sulfoxide, a relatively non-nucleophilic solvent capable of dissolving intermediate salts. With this combination he obtained dimethyl-malononitrile in 60% yield. He then studied the acylation of the ketone (1) with the... 

The lithium-free experiments of Table 11 tell a consistent story, one that has changed little compared to the overview presented in 1970 (1). Typical nonstabilized ylides of the Ph3P=CHR family are > 90% selective for the formation of (Z)-alkenes at room temperature. The (Z)-alkene selectivity increases to > 95% as the reaction temperature is lowered (Table 11, entries 10-18) and is highest for tertiary aldehydes (entries 78-87). Relatively few -branched ylides have been studied, but the more recent entries appear to follow the usual pattern of (Z)-alkene selectivity (entries 88,95,96). Somewhat lower Z E selectivities appear in one study of the cyclopropylcarbinyl member of the -branched ylide family (entries 90-92) (73), but these experiments involve benzaldehyde as the substrate and employ the relatively inefficient base sodium hydride for ylide generation. These factors may increase the risk of catalyzed equilibration of intermediates. A more recent study reports a typical Z E ratio of 9 1 in the case of a 2,3-diphenyl-cyclopropylcarbinyl ylide (salt-free conditions 2,3-diphenylcyclopropane-carboxaldehyde substrate) (77). 

Monoalkylation of a., -unsaturated ketones see also 4, 300). Alkylation of enamines of enones usually gives low yields of C-alkylated products because of competing N-alkylation. An expedient is to convert the N,N-dimethylhydrazone of the enone into the metalloenamine by a strong base (sodium hydride or LDA... 

Bicarbonate may be new to you, but you might reasonably guess that it has basicity similar to a carboxylate anion. The base sodium hydride, and the p/C, of its conjugate acid, appears on p. 237 of the textbook. 

There are a few other examples of the Sn reactiOTis in the series of unactivated arenes, such as nucleophilic methylation of anthracene and phenanthrene by action of dimethyl sulfoxide (DMSO) in the presence of a strong base (sodium hydride or potassium t-butoxide) [11, 95, 96]. However, it is clear that the addition of nucleophiles to such aromatic systems is a very unfavorable process, due to the... 

When bromo-alcohol A is reacted with the base sodium hydride (NaH), the... 

Triphenyl- -acetylvinylphosphonium halides (X = Cl, Br) react with TUD (in DMSO) in the presence of base (sodium hydride) to give the imidazolylphosphonium salts in high yield (eq 4). These imidazolyl hahdes can he readily converted to multifunctional imidazoles with quantitative recovery of PPhs for example, 4-methyl-(5-methylimidazolyl)triphenylphosphonium halide, on... 

Imidazolium salts are precursors (preligands) of carbene ligands. In several cases, they can be directly submitted to the formation of metal complexes. Various approaches for the synthesis of imidazolium salts of types 1 and 2 are reported in the literature (Scheme 2.151) [23]. The most common synthesis of 1 is based on the Af-alkylation of l//-imidazole with alkyl halides in the presence of bases (sodium hydride, sodium or potassium hydroxide, or potassium tert-butoxide, route A). 1-Substituted imidazoles, usually Al-methylimidazol, are convenient starting materials to generate nonsymmetric imidazolium salts of type 1 by treatment with a second equivalent of alkyl or aryl halide [25]. 

The intramolecular cycUzation takes place smoothly in the 6-endo-trig fashion on treatment with a base (sodium hydride or triethylamine) of N-[ortho-0, i-difluoroaUyl)phenyl] substituted p-toluenesulfonamides 55. As a result 2-fluoro-quinolines 56 are formed in high yields (Scheme 21) [32],... 

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