1.2.3- Triazole 5-lithio-1-phenyl

Substituted 1,2,4-triazoles have received less attention than their isomeric counterparts, but those results that are available indicate that their lithio derivatives are less stable than their 1-substituted isomers. Thus, in addition to undergoing the expected a-lithiation and reaction at the 5-position, 3-phenyl-4-benzyl-1.2.4-triazole also gave products resulting from ring-opening, even at -78°C (Scheme 65) (86JHC1257). 

The halogen metal exchange reaction between 7-bromo or 7-iodo-3-phenyltriazolopyrimidine 165 and butyllithium in iV,N,N, N -tetra-methylethylenediamine afforded the 7-lithio compound 166, whereas a similar reaction with the 7-chloro derivative 165 (R = H) gave the ring-fission product, 5-amino-l-phenyl-l//-l,2,3-triazole-4-carbonitrile 169 (91 CPB2793). Reaction of 166 with electrophiles such as benzaldehyde and ketones gave 170 and 167 respectively, together with 7,7 -bis[3-phenyl-3//-1,2,3-triazolo[4,5-d]pyrimidine] 168 (Scheme 34). 

Dibromo-l-methoxymethyl-l,2,3-triazole forms the 5-lithio compound with n-butyllithium at-80 °C and 4,5-dibromo-2-methoxymethyl-l,2,3-triazole undergoes a comparable exchange. l-Phenyl-1,2,3-triazoles participate in Diels-Alder cycloadditions with dimethyl acetylenedicarboxylate using aluminium chloride catalysis, producing l-phenylpyrazoles. " ... 

C-Lithiations can be easily effected on A -1-protected 1,2,4-triazoles, the resulting 5-lithio derivatives being much more stable than C-hthiated 1,2,3-triazoles 5-Silylation can even be achieved using triethyl-amine with trimethylsilyl bromide - deprotonation of an iV -trimethylsilyl triazolium cation is presumably involved Exactly comparable silylations can be achieved with 2-aryl-l,3,4-oxa- and -thia-diazoles application of this regime to 1-phenyltetrazole produced phenyl trimethylsilyl carbodiimide in 90% yield ... 

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