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Novel synthesis of 2,4-bis(2-pyridyl)-5-(pyridyl)imidazoles and formation of N-(3-(pyridyl)imidazo[1,5-a]pyridine)picolinamidines: nitrogen-rich ligands
Vijendra Kumar Fulwa, Rojalin Sahu, Himanshu Sekhar Jena, Vadivelu Manivannan *Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781 039, India
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Heating a neat 1:2 mixture of 2-picolylamine and 2-cyanopyridine followed by treatment of the resultant red gummy substance with aqueous KOH resulted in the isolation of 2,4,5-tris(2-pyridyl)imidazole (1a) as the major product andN-(3-(2-pyridyl)imidazo[1,5-a]pyridine)picolinamidine (2a) in small amounts. Similarly, by using 3-picolylamine, 2,4,-bis(2-pyridyl)-5-(3-pyridyl)imidazole (1b) and N-(3-(3-pyridyl)imidazo[1,5-a]pyridine)picolinamidine (2b) were isolated, and by using 4-picolylamine, 2,4,-bis(2pyridyl)-5-(4-pyridyl)imidazole (1c) and N-(3-(4-pyridyl)imidazo[1,5-a]pyridine)picolinamidine (2c) were isolated. The plausible mechanism of the formationof 1a–c and 2a–c is delineated. Ó 2009 Elsevier Ltd. All rights reserved.
Article history: Received 7 August 2009 Revised 27 August 2009 Accepted 1 September 2009 Available online 4 September 2009 Keywords: Imidazole Imidazo[1,5-a]pyridine Ligand Amidine
The imidazole ring system is an important function in biology, chemistry as well as in pharmaceutical, veterinary, and agrochemicalproducts.1–4 They are useful ligands in coordination chemistry and the synthesis of the compounds containing the imidazole ring is an important area of scientiﬁc investigation.1–3 Multicomponent reaction (MCR) methods involving the isocyanides as one of the components for the synthesis of imidazole derivatives have been reviewed.5 The synthesis of the 1,2,4-trisubstituted imidazole by palladium-catalyzedcyclization of O-pentaﬂuorobenzoylamidoximes is reported.6 Addition reaction of imidazolium ylides to electron-deﬁcient imines is a useful method for the synthesis of 2(a-substituted-amidoalkyl)imidazoles.7 An efﬁcient, mild one-pot method for preparing polysubstituted imidazoles from aryl-substituted tosylmethyl isocyanide (TosMIC) reagents and in situ generated imines8 as well as a newsynthetic approach for the synthesis of chiral imidazoles using thio-Ugi reaction9 have been reported. The synthesis of the annulated terpene-imidazole,10 a microwave assisted organic synthesis (MAOS) method for the synthesis of 2,4,5-triaryl-imidazole11a as well as the synthesis, and p38 MAP kinase inhibitor property11b have been described. We recently described the Cu(NO3)2Á3H2O-mediated conversion ofthe Schiff base N-(2-pyridylmethyl)pyridine-2-methylketimine to 40 -(2-pyridyl)-2,20 :60 ,200 -terpyridine and have continuing interest in the synthesis of nitrogen-rich ligands.12 In this Letter we report a facile formation of 2,4-bis(2-pyridyl)-5-(pyridyl)imidazoles (1a–c) using a simple two-component method. In addition the details of the other minor product, N-(3-(pyridyl)imidazo[1,5-a]pyrid*Corresponding author. Tel.: +91 361 258 2306; fax: +91 361 258 2349. E-mail address: email@example.com (V. Manivannan). 0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.tetlet.2009.09.002
ine)picolinamidines (2a–c) formed in this reaction are described. The synthesis of compounds containing the imidazo[1,5-a]pyridine ring is another general area ofresearch.13,14 Formation of the varying amounts of 2,4,5-trisubstituted imidazole and imidazo[1,5-a]pyridine ring systems from 2,20 -pyridil, aromatic aldehyde, ammonium acetate, and acetic acid is relevant to mention.13 Heating a neat 1:2 mixture of 2-picolylamine and 2-cyanopyridine at 100 °C, followed by the treatment of the resultant red gummy substance with alkali resulted in the formation of...