The Formation of Ketones by a Reaction Equivalent to R-+R′COCH2+→R′COCH2R

Abstract

A general method has been developed for the overall transformation of a-bromo ketones to a-alkyl or a-aryl ketones, with benzotriazole being used as a synthetic auxiliary. a-Benzotriazolyl ketones, when converted into their phenylhydrazones, reacted smoothly with alkyl and aryl Grignard reagents, which displaced benzotriazolate, to give the corresponding a-alkyl or a-aryl hydrazones. In some cases, these hydrolysed directly to the a-alkyl or a-aryl ketones. In each case, the product was treated with 2,4-dinitrophenylhydrazine to isolate the target ketones as the corresponding 2,4-dinitrophenylhydrazones.

Benzotriazole-mediated 4-position derivatization of 2,6-diarylpyrylium cations by electrophiles

“…Conversions of 7a-c to the carbanion 8a-c proceed at low temperature (-78 °C) in THF with n-butyllithium. In contrast to earlier investigations [1] the reactivity of anions 8a-c is more complex than that of other fused or bridged anions of type 3, and the products of their reaction with electrophiles depend dramatically on the alkyl halide type. Alkyl and arylalkyl halides, or alkylene dihalides with four or less carbon atoms in the aliphatic chain give the normal products of substitution 12-19 in moderate to high yields (Scheme 2, Table 1).…”

“…The success of this strategy was demonstrated [1] by the preparation of a series of long chain (up to 22 carbons) alkyl-, ω-arylalkyl-, ω-halogenalkyl-, (α,ω-alkylidene)bisheteronium salts, which are of interest for synthetic, physico-organic and pharmaceutical applications [3]. Significantly, only a few short-chain 4-alkyl derivatives of simple, non-bridged pyrylium salts are known; they were synthesized in low yield by condensations of either acetaldehyde or alkyl acetates with aryl methylene ketones [4, p. 884].…”

Benzotriazole-Mediated Synthesis of Nitrogen-Containing Heterocycles

“…Due to steric hindrance, the benzotriazole fragment rearranged to its 2-yl form as revealed by NMR studies. Consecutive treatments of crude 205 with Grignard reagents and benzil gave 2H-imidazoles 206 in 15-21% yield (Scheme 73) [158]. The anion derived from isocyanide 114 on treatment with KO t Bu was added readily to Schiff bases to form imidazolines 207, which under basic conditions eliminated benzotriazole to produce 1,5-diarylimidazoles 208 (Scheme 74) [106].…”

“…The reaction of bis(triphenylphosphoranylidene) derivative 205 with PhMgBr and acetylacetone provided 1,2-dihydropyrimidine 312 in 14% yield (Scheme 116) [158].…”

New method for the synthesis of difficultly available sterically hindered tritium-labeled pyridinium derivatives

“…This, in turn, may lead to an increase in the yields of the products of phenylation of the nitrogen atom. However, at the same time, the electron-donor methyl substituents in the pyridine molecule stabilize azaarene ions and, thereby, facilitate concurrent electrophilic substitution in the heterocyclic ring [37][38][39][40][41][42].…”