Henri Viols

Carbon-nitrogen bond formation in cyclisations by deoxygenation, thermolysis, or photolysis of phenylimidazo[1,2-a]pyridine systems: access to pyrido[1′,2′ : 1,2]imidazo[4,5-b]indoles

Reductive cyclisation of 2-(2-nitrophenyl)imidazo[1,2-a]pyridine with triethyl phosphite gives the indolic structures (5) and (6). The latter are of interest because of preferential C insertion rather than reaction of the nitrene at N-1 of the imidazole ring. 2D N.m.r. confirms structure (5). Both thermolysis or photolysis of the representative 2-(2-azidophenyl)imidazo[1,2-a]pyridines (7) and (8) are also reported and shown to produce novel indole, cinnoline, and benzofuran structures in an extremely facile fashion.

Aza-indolizine with bridgehead nitrogen. Metalation, halogen-metal exchange and directed ortho-lithiation in the imidazo[1,2-a]pyrazine series

Abstract The n-BuLi and lithium 2,2,6,6-tetramethylpiperidine (LTMP) metalation of imidazo[1,2-a]pyrazine heterocycles and subsequent quenching with electrophiles is described. Bromine atoms exhibit different behaviours towards lithiation depending on their positions (3 or 6) on the imidazo[1,2-a]pyrazine heterocycle. Halogen-metal exchange occurs readily with the bromine on position 3. On the contrary, bromine on position 6 only leads to C-5 substituted derivatives further to an ortho-directing effect.

REACTIVITY OF METHYLLITHIUM TOWARDS BRIDGEHEAD NITROGEN HETEROCYCLES

Reactivity of methyllithium towards some bridgehead nitrogen heterocycles was investigated. In a previous communication we have reported the reactivity of phenyllithium on some polyazaindenes (1). The results obtained prompted us to investigate other bases. Among alkyllithium derivatives, methyllithium was attractive because the reactivity of this reagent toward bridgehead nitrogen heterocycles seemed uninvestigated. Methyllithium adds to pyridine or quinoline to give 4-methyl-l,4-dihydropyridine or quinoline (2) while Peake and coworkers, obtained 2-methylquinoline by the action of methyllithium and iodine for aromatization (3) . Recently Shiotani and coworkers (4), using methyllithium-lithium bromide complex at -78°C, reported the ring opening of furan cycle in 3-bromofuropyridines to give ethynylpyridinol and unsubstituted heterocycle. In this work, we report the reaction of methyllithium on imidazo[l,2a]pyridine (A), imidazo[l,2-a]pyrimidine (B) , imidazo[l,2-a]pyrazine (C) , imidazo[1,2-c]quinazoline (D), and imidazo[1,2-a][1,8]naphthyridine (E) in ether at 20°C. A X = CH, Y=CH Β X = N, Y = CH C X=CH, Y = N οσ