Tetrazoles alkylation

The generation of ion pairs from NH-unsubstituted tetrazoles has also been performed using sodium salts and sodium hydroxide. Tetrazole alkylation with benzyl chloromethyl ether in tetrahydrofuran (THF) in the presence of sodium hexamethyldisilazane (NaHMDS) has been reported < 1995J(P 1) 1747, 1998SL528>. Regioisomers 240 and 241 formed under these conditions in comparable amounts (Scheme 24) <1998SL528>. 

Tetrazoles alkylate and acylate on N-l(4) and/or N-2(3), the regioselectivity depending, in part, on the substituent at C-5. The fonnation of mixtures is the usual outcome for alkylation and this is a significant problem in medicinal chemistry. Although a range of specifically N-1-substituted tetrazoles are available by ring synthesis, the direct synthesis of N-2-substituted compounds is more problematic. 

Noting the similarity of tetrazole pK values to those of carboxylic acids, tetra-zoles have often been used as bioisosteric replacements for CO2H in pharmacologically active compounds. Tetrazoles alkylate and acylate on N-1 or N-2 depending on substituents at C-5, however selective 1-alkylations by quatemisation of 2-tri-w-butylstannyl derivatives have been reported. ... 

A comprehensive review of reactions of isocyanates and 1,3-dipolar compounds has been previously pubhshed (51). The example shown illustrates the reaction of azides and isocyanates to yield tetrazoles (14,R = alkyl or aryl, R = aryl or sulfonyl) (52,53). 

Similar ambiguities arise in the reactions of azole anions. At least as regards alkylation reactions in the 1,2,3-triazole series (79), the product appears to depend on the reagent used. In the 1,2,4-triazole series (80) a single product is formed, whereas tetrazole (81) gives mixtures. 

For both azole and benzazole rings the introduction of further heteroatoms into the ring affects the ease of quaternization. In series with the same number and orientation of heteroatoms, rate constants increase in the order X = 0requires stronger reagents and conditions methyl fluorosulfonate is sometimes used (78AHC(22)71). The 1-or 2-substituted 1,2,3-triazoles are difficult to alkylate, but methyl fluorosulfonate succeeds (7IACS2087). 

Alkylation of tetrazoles as the anions gives mixtures of 1- and 2-alkyl isomers. In general, electron-donating substituents in the 5-position slightly favor alkylation of the 1-position and electron-withdrawing 5-substituents slightly favor the 2-position. 

Alkyl groups and halogen atoms in tetrazoles are not highly activated unless the ring is quaternized. 

Tetrazolate, 5-(3-chlorobenzyldimethylammonium)-structures, 5, 796 Tetrazolate, 5-cyclopropyl-rearrangement, 5, 810 Tetrazolate, 5-(p-substituted)phenyl-alkylation, 5, 818 Tetrazolates anions... 

Tetrazole, 5-phenoxy-l -phenyl-mass spectra, 5, 801 photolysis, 5, 811 Tetrazole, 1-phenyl-deuterium-hydrogen exchange, 5, 806 mercuration, 5, 59 NMR, 5, 798 tautomerism, 5, 804 UV spectra, 5, 798 Tetrazole, 2-phenyl-NMR, 5, 798 tautomerism, 5, 804 UV spectra, 5, 798 Tetrazole, 5-phenyl-alkylation, 5, 818 anti-inflammatory activity, 5, 835 blowing agent, 1, 410 reactions... 

In general, tetrazolium salts are prepared by (a) oxidation of formazans and (b) alkylation of tetrazoles. Therefore, synthetic methods for formazans and tetrazoles are discussed first, followed by some direct and miscellaneous methods. 

Nitrilium salts, e.g., 66, prepared from the alkylation of nitriles, react with sodium azide to yield 1,5-disubstituted tetrazoles, e.g., 67 (Scheme 7).121 The Schmidt reaction,122 a versatile method for the preparation of 1,5-disubstituted tetrazoles from ketones and hydrazoic acid, can now be regarded as a special case of azide addition to nitrilium salts.123... 

Nitrous acid or alkyl nitrites react with a number of nitrogen compounds to yield tetrazoles. For example, hydrazidines (87), which can be prepared in situ from the corresponding iminoesters, react with nitrous acid or its derivatives to give 1-substituted tetrazoles (88).150-152 This reaction (Eq. 17), is one of the most extensively used methods for the synthesis of... 

Benson et al. 177 first reported the synthesis of tetrazolium salts by the alkylation of disubstituted tetrazoles. While selectivity is a major problem, alkylation can still be considered a viable method for the preparation of 1,3,5- and 1,4,5-trisubstituted as well as 1,5 and 2,5-disubstituted tetrazolium salts. 

Electronic effects of substituent, as well as reaction conditions (temperature, solvent) influence the ratio of isomers. The alkylation of l-alkyl-5-aryl tetrazoles with dimethyl sulfate at room temperature proceeds at the... 

Another important click reaction is the cycloaddition of azides. The addition of sodium azide to nitriles to give l//-tetrazoles is shown to proceed readily in water with zinc salts as catalysts (Eq. 11.71).122 The scope of the reaction is quite broad a variety of aromatic nitriles, activated and nonactivated alkyl nitriles, substituted vinyl nitriles, thiocyanates, and cyanamides have all been shown to be viable substrates for this reaction. The reaction of an arylacetylene with an azide in hot water gave 1,4-disubstituted 1,2,3-triazoles in high yields,123 while a similar reaction between a terminal aliphatic alkyne and an azide (except 111 - nitroazidobenzcnc) afforded a mixture of regioisomers with... 

Methyl and other alkyl esters were prepared in THF, also in high yields.[130] b) Arachidonic acid was converted via its tetrazolide with the aid of oxalyldi(l,2,3,4-tetrazole), prepared in situ, into the methyl ester.[1113... 

The 1 1 complexes arising from interaction of the hydride (as a complex with ether or trimethylamine) and various tetrazole derivatives are explosive. Tetrazoles mentioned are 2-methyl-, 2-ethyl-, 5-ethyl-, 2-methyl-5-vinyl-, 5-amino-2-ethyl-, l-alkyl-5-amino-, and 5-cyano-2-methyl-tetrazole. 

Pyridine A-oxides were converted to tetrazolo[l,5-a]pyridines 172 by heating in the presence sulfonyl or phosphoryl azides and pyridine in the absence of solvent <06JOC9540>. 3-R-5-Trinitromethyltetrazolo[l,5-a]-l,3,5-triazin-7-ones 173 have been prepared from the alkylation of 5-trinitromethyltetrazolo[l,5-a]-l,3,5-triazin-7-one silver salt with different alkylation agents <06CHE417>. The use of 2-fluorophenylisocyanide in the combinatorial Ugi-tetrazole reaction followed by a nucleophilic aromatic substitution afforded tricylic tetrazolo[l,5-a]quinoxaline 174 in good yields and with high diversity <06TL2041>. 

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