Triazolo pyridine lithiation

Chloroperoxidase catalysis by, 58, 302 in chlorination of pyrazoles, 57, 337 Chlorophyll, thioaldehyde synthetic intermediate to, 55, 3 Chlorosulfonyl isocyanate, reaction with 2-arylhydrazono-3-oxobutanoate, 59, 148 Chromatography, of [l,2,4]triazolo[l,5-a]-pyrimidines, 57, 106 Chrom-3-enes, see 2//-l-Benzopyrans Chromium tricarbonyl complexes of 3,5-diphenyl-l-(alkyl- or oxido-)-thiabenzenes, 59, 206, 227 indoles, lithiation of, 56, 181, 184 of pyridine, 58, 160 pyridines, lithiation of, 56, 230, 239 of 2f/-thiopyrans, 59, 227 Chromones, see l-Benzopyran-4-ones Cinnamonitrile, a-cyano-, condensations with thio-, seleno-amides, 59, 184, 186 Cinnoline, nitration, MO calculation, 59, 302... 

The ring-chain isomerisation of phosphino-substituted triazolo-pyridines was found to depend on the nature of the phosphine substituent. Conversion of the phosphines to their selenides resulted in a complete shift of the equilibrium towards electron-acceptor structure D (Scheme 10). Acenaphthene and acenaphthylene were converted to polycyclic phosphole derivatives via Ti(II)-mediated cyclization of the corresponding dialkynylated arenas. The related phosphole oxides were stable species (Scheme 11). Asymmetric lithiation of dimethyl-tert-butylphosphine sulfide and trimethylsilylation gave an intermediate that was subjected to a five-step reaction sequence including metallation, P-functionalization (in three steps) and removal of the silyl group to yield the precursor of Mini-PHOS (Scheme 12). ... 

It was not possible to brominate the [l,2,4]triazolo[l,5-a]pyridine species (137) directly with bromine or NBS, but the 5- and 8-bromo (66CPB523) and 3-chloro (66JOC265) derivatives were made from the diazonium salts. More recently regiospecific 5-lithiation of 137 has provided access to the 5-bromo derivative in 94% yield (92JOC5538). 

Further studies on l,2,3-triazolo[l,5-a]pyridine (511) showed that competitive lithiations occur at the C-4 and C-7 positions with two different rates (fast lithiation at the C-7 position and slow at the C-4 position) [83JCR(S)144],... 

Direct lithiation of l,2,3-triazolo[l,5-a]pyridines occurs with ease, at C-7, subsequent reaction with electrophiles being unexceptional, for example conversion into the 7-bromo derivative then allows nucleophiles to be introduced via displacement of bromide, thus providing, overall, a route to 2,6-disubstituted pyridines. ... 

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