1.2.3- Triazole 2-alkyl

H-1,2,3-Triazoles, l-alkyl-4,5-dihydro-, 153 1/f-1,2,4-Triazoles, l-farylsulfonyl)- nucleotide condensation with, 218 2H-1,2,3-Triazoles, 2-alkyl- synth., 151-152 2 2-Tribromoethoxycarbonyl (Tbeoc) protected alcohols and amines, 157-158, 163 2,2,2-Trichloroethoxycarbonyl (Tceoc) protected alcohols and amines, 157-158,162-163 2,2 -Trichloroethyl (Tee) protected phosphates, 166-167, 216, 218... 

In peptide syntheses, where partial racemization of the chiral a-carbon centers is a serious problem, the application of 1-hydroxy-1 H-benzotriazole ( HBT") and DCC has been very successful in increasing yields and decreasing racemization (W. Kdnig, 1970 G.C. Windridge, 1971 H.R. Bosshard, 1973), l-(Acyloxy)-lif-benzotriazoles or l-acyl-17f-benzo-triazole 3-oxides are formed as reactive intermediates. If carboxylic or phosphoric esters are to be formed from the acids and alcohols using DCC, 4-(pyrrolidin-l -yl)pyridine ( PPY A. Hassner, 1978 K.M. Patel, 1979) and HBT are efficient catalysts even with tert-alkyl, choles-teryl, aryl, and other unreactive alcohols as well as with highly bulky or labile acids. 

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). 

Thiadiazoles are quaternized to give 3- or mixtures of 2- and 3-alkyl quaternary salts. In 5-amino-1,2,4-thiadiazole, quaternization takes place at the 4-position (90) (64AHC(3il). 1-Substituted 1,2,4-triazoles are quaternized in the 4-position (91), and 4-substituted 1.2,4-triazoles are quaternized in the 1- or the 2-position (92) 64AHC(3)l). 

Thiadiazole with MeaO BF gives the diquaternary salt (95) diquaternary salts are also known in the 1,2,4-triazole series. 1,3-Disubstituted 1,2,4-triazolium salts can be further alkylated to diquaternary derivatives. 

N-Unsubstituted 1,2,3-triazoles are methylated mainly in the 1-position with methyl iodide and silver or thallium salts, but mainly in the 2-position by diazomethane. There is also some steric control. For example, 4-phenyl-l,2,3-triazole with dimethyl sulfate gives the 2-methyl-4-phenyl (38%) and l-methyl-4-phenyl isomers (62%), but none of the more hindered 1-methyl-5-phenyltriazole (74AHC(16)33). JV-Unsubstituted 1,2,4-triazoles are generally alkylated at N-1. 

H- Pyrro lo[l,2-c][l,2,4]triazol-3-ones synthesis, 6, 991 Pyrroloyl azides Curtius rearrangement, 4, 288 Pyrrolyl anions acylation, 4, 232 alkylation, 4, 235 solvent effects, 4, 236 C-alkylation... 

The latter compound is not the 7-alkyl derivative, and the salt is believed to be 136 by analogy with the quaternization behavior of 1,2,4-triazoles. ... 

The mesomeric effect of the C=S linkage is very pronounced and is responsible for the facile quaternization of heterocyclic N-alkylated thiones (159) this effect is operative even when such a shift does not increase the aromaticity of the ring. Thione derivatives of pyridazine, benzothiazole, quinazoline, 1,3-thiazine, triazole,and isoindole are examples of compounds which readily form quaternary salts. 

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