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Paper | Regular issue | Vol 53, No. 9, 2000, pp.1915-1938
Published online, 1st January, 1970
DOI: 10.3987/COM-00-8946
Reactions of a Stable Benzonitrile Oxide with Aminopyridines

Paolo Beltrame, Enzo Cadoni, Costantino Floris, Gioanna Gelli,* and Adolfo Lai

*Dipartimento di Scienze Chimiche, Università di Cagliari, S. P. Monserrato-Sestu km 0.700, I-09042 Monserrato, Italy

Abstract

Stable aryl nitrile oxide (1) and isomeric aminopyridines (2) undergo different reactions depending on both the isomer and the conditions. The nitrile oxide gives 1,3-cycloaddition to the 4-aminopyridine (2c) in its iminic form if acids are present to promote the formation of imine. In such a case, the stable products 3,5-dichloro-2,4,6-trimethyl-N’-(4-pyridinyloxy)benzene carboximidamide (3E) and (3Z) are observed, otherwise, 2c catalyzes the dimerization, with the loss of an oxygen atom, of 1, leading to 3,5-bis-(3,5-dichloro-2,4,6-trimethylphenyl)-1,2,4-oxadiazole (4) as the main product. A similar 1,3-cycloaddition is given by 2-aminopyridine (2a): the compounds (5R and 5S)-(±)-3-(3,5-dichloro-2,4,6-trimethylphenyl)-1-oxa-2,4,6-triazaspiro [4,5]-deca-2,7,9-triene (6) and (5R and 5S)-(±)-3-(3,5-dichloro-2,4,6-trimethylphenyl)-1-oxa-2,4,6-triazaspiro[4,5]-deca-3,7,9-triene (7) have been identified, although subsequent reactions give the stable products (NZ,N’Z)-3,5-dichloro-2,4,6-trimethyl-N-[2(1H)-pyridinylidene]-N-(2-pyridinyloxy)benzene carboximidamide (8) and (NE,N’Z)-3,5-dichloro-2,4,6-trimethyl-N-[2(1H)-pyridinylidene]-N’-(2-pyridinyloxy)benzene carboximidamide (9); these reactions proceed even in the absence of acids with no dimerization of 1, but acids (pyridinium chloride) speed them up remarkably. Addition of 1 onto the 3-aminopyridine (2b) leads to N-hydroxybenzenecarboximidamides (12), as well as to small amounts of a benzamide (13), and the effect of the pyridinium chloride is negligible.