Phosphorylated imidazo[1,2‐a]pyridines

Abstract

The reaction of phosphorus(III) halides with imidazo [l,2-a]pyridines i n the presence of bases leads to the formation of 3-phosphorylated imidazo[l,2alpyridines. The reaction proceeds i n high yield and requires no catalysts. In the compounds obtained, in contrast to phosphorylated indolizines, the phosphorus-heterocycle bond is stable and not cleaved by dry hydrogen c h bride, alcohols, or water, Imidazo[l,2-a]pyridines with the phosphinic and phosphinous groups can be alkylated both at the phosphorus and at the nitrogen atom of the heterocycle, the alkylation direction being dependent on the strength of the alkylation reagent used. 0 1995 John Wiley & Sons, Inc. 1042-7 163/95/0504 19-14 Phosphorylated Irnidazo[l,2-a]pyridines 423 M e M e 29c, 33c M e 1 * Q J $ PCNEt5,>3 , Q f J M e Ie PRh II PRk 44, 45 se 46, 47 M e M e PCNEt5,>3 , 29c, 33c M e 1 * Q J $ M e PRh II PR; -44, 45 se

Synthesis, structure and reactivity of 4-phosphanylated 1,3-dialkyl-imidazole-2-thiones

“…22 The obtained yields were increased in comparison to those reported in the literature, where the imidazole-2-thiones have been prepared using different bases 19,20,25 or different methodologies. 6,26 Commonly used synthetic routes to the phosphorylated heterocycles 28,29 in pyridine-triethylamine mixtures proved to be unsuitable in the case of imidazole-2-thiones. Therefore another synthetic methodology to the imidazole-2-thione was followed by reacting 2a-f with n-butyl lithium and then subsequently with diphenylchlorophosphane to yield the 4-phosphanylated imidazole-2-thiones 3a-f (Scheme 1).…”

Phosphorylation of 1-alkylmidazoles and 1-alkylbenzimidazoles with phosphorus(III) halides in the presence of bases

“…Compounds 3 and 7 (Scheme 5), which are simi-lar to phosphorylated imidazo[1,2-a]pyridines [5], can undergo alkylation either at the nitrogen atom in the heterocycle or at the exocyclic phosphorus center, depending on the alkylating agent. The first route is realized with hard alkylating agents such as Meerwein's salts or dimethyl sulfate and leads to products 17.…”

“…Recently, the direct C-2-phosphoryl-ation of 1-alkyl substituted imidazoles and benzimidazoles was performed with phosphorus(V) chlorides in the presence of bases [3]. However, a much more promising route to the compounds that we extensively studied in recent years proved to be the phosphorylation with phosphorus(III) halides in pyridine-triethylamine medium [4,5]. The extension of the procedure to 1-alkylimidazoles and 1-alkylbenzimidazoles introduces a new way to synthesize the corresponding key halogeno-and dihalogenophosphines, the valuable precursors to various three-and four-coordinated phosphorus compounds.…”

Phosphorylation of imidazo[2,1‐b]thiazoles with phosphorus(III) halides in the presence of bases

“…Phosphines 4,8-10, like phosphorylated imidazo[1,2-a]pyridines [3] and imidazoles [1], can be selectively alkylated at the phosphorus or heterocyclic nitrogen atom, depending on the alkylating agent. The first route is realized on alkylation with methyl iodide and the molar ratio of the reagents of 1:1 to give phosphonium salts 19.…”

“…The high regioselectivity was also observed on phosphorylation of imidazoles fused to six-membered heterocycles, e.g. 2-substituted imidazo[1,2-a]pyridines, with phosphorus(III) halides [3]. Now we report on the extension of the reaction to imidazoles fused to five-membered rings, i.e., 6-substituted imidazo [2,1-b]thiazoles, the phosphorylated derivatives of which are unknown.…”