Heterocycles, acylation lithiation

Benzotriazole is the most versatile of these heterocycles,55 because it is easily introduced and easily removed. It promotes a-lithiation even at hindered tertiary centres, and the lithiation of a-benzotriazole ethers 79 gives useful acyl anion equivalents 80.56... 

A number of techniques are available for the one-pot conversions of carbonyl substrates to thiiranes. These entail the addition of a lithiated thiol derivative to the substrate, transfer of either an acyl group or heterocycle to the oxygen atom, and cyclization. A recent example is depicted in Scheme 19. ... 

Lithiation of l-aryl-17/-imidazoles followed by quenching with electrophiles provided a route to 1,2-diaryl, l-aryl-2-cycloalkyl- and l-aryl-2-heterocycle-substituted imidazoles <05H(65)2721>. Isoprene-catalyzed lithiation of imidazole provided a synthetic route to 2-(hydroxyalkyl)- and 2-(aminoalkyl)imidazoles <05X11148>. 2-Lithiobenzimidazoles were efficiently acylated with esters, lactones and lactams <05TL5081>. 

Pivaloylamino-5-methoxypyridine has been selectively acylated and alkylated in the 4-position by successive reaction with n-butyl-lithium and an electrophile. The activating effect of a A -pivaloylamino- (NHCOBu ) or a methoxy-group alone failed to give orf/to-lithiation. A new general route to nitroso-substituted heterocycles, particularly useful when direct nitrosation is inapphcable, as in the case of pyridine, is illustrated in Scheme 16. 

Bicyclo[6.3.0]undecapentaenium salts, 390 Biphenylene, 221 preparation, 222 reactions, 224 acylation, 226 with carbenes, 228 electrophilic substitution, 224 halogenation, 225 homolytic substitution, 228 lithiation, 227 mercuriation, 226 nitration, 224 with nucleophiles, 227 oxidation, 224 photolysis, 228 reduction, 224 thermolysis, 228 Biphenylenes, benzo, 230 Biphenylene dianion, 229 Biphenylene dication, 229 Biphenylenes, heterocyclic analogues, 233... 

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