Synthesis of Multi‐Substituted 2‐Iminopyridine by Conjugate Addition of Ethyl Cyanoacetate Derivatives to Alkynyl Imines

Abstract

The synthesis of multi‐substituted 2‐iminopyridines by conjugate addition of ethyl cyanoacetate derivatives to alkynyl imines has been developed. The reaction of ethyl cyanoacetate derivatives with alkynyl imines provided multi‐substituted 2‐iminopyridines in good yields. Also described is the transformation of 2‐iminopyridines into 2‐aminopyridines by deprotection of the substituent on the nitrogen under acidic conditions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Synthesis, Coordination Chemistry and Bonding of Strong N‐Donor Ligands Incorporating the 1H‐Pyridin‐(2E)‐Ylidene (PYE) Motif

“…(12) [53] and (13). [53] For all structures only protonation at N(1) is observed, which is clear from the charge balance between the number of anion equivalents in the structure and the planarity of the heterocyclic rings.…”

“…[1] The compounds that are the focus of this work are based on the 1H-pyridin-(2E)-ylidene (PYE, A in Scheme 1) motif. Although PYE-type compounds have been known for over 80 years [2] and their organic and biological [3][4][5][6][7][8][9][10][11][12][13] chemistry and spectroscopy [14][15][16][17][18] has been studied, their coordination chemistry is essentially unknown. [19] A motivation for exploring the coordination chemistry of 1H-pyridin-(2E)-ylidenes as ligands is that straightforward modification of the pyridine and imine N substituents should be possible, which will allow access to a range of substitution patterns including chelating and chiral derivatives.…”

“…In contrast to the structures of neutral compound 7 and pyridinium salt 12, the nitrogen atoms N(1) and N(3) that are coordinated to the nickel atom exhibit distinct pyramidal geometry. For example, the angles about N(1) are C(1)-N(1)-C(7) = 115.53 (16), C(1)-N(1)-Ni(1) = 119.12 (13) and C(7)-N(1)-Ni(1) = 107.96(12)8, and similarly, for N(3) the sum of the angles is approximately 3438. Comparison of the bond lengths in the PYE groups of 7, 12 [53] and 16 (Table 2) in which, for example, the C(1)ÀN(1) imine bond lengths are 1.2294(3), 1.334(4) and 1.332(3) , respectively, indicates that the PYE ring distances are closer to protonated ligand 12 than free ligand 7.…”

“…The 13 C NMR spectroscopy data for 11-13 showed the most significant chemical shift changes at C 3 and C 4 and surprisingly little change at C 1 . Representative 1 H and 13 C NMR spectroscopy data of compound 11 are given in Table 1. DFT studies were performed on compounds 1 and 11 to gain a greater insight into the structural and electronic changes that occur in PYE compounds upon protonation and that influence the subsequent coordination of metal fragments. The geometries of 1 and 11 were optimised at the PBE0/TZVPP level by using TURBOMOLE (using the updated def2-TZVPP basis set), and the stationary points were confirmed as minima by vibrational frequency analyses.…”

Recent advances in synthesis of 2-pyridones: a key heterocycle is revisited

“…Hachiya et al [27][28][29][30][31] reported a novel route to the synthesis of 2-pyridone by means of conjugated addition of malonic esters or b-keto esters and alkynyl imines. The reaction was performed using base in THF or 1,4-Dioxane solution under reflux (Scheme 13).…”