4,5-Dihydro-3-methyl-5-(4-methylphenyl)-1H-pyrazole-1-carboxamidinium acetate acetone hemisolvate.
The X-ray structure analysis of the unexpected product of the reaction between 4-(4-methylphenyl)but-3-en-2-one and aminoguanidine revealed the title compound, C(12)H(17)N(4)(+) x -C(2)H(3)O(2)(-) x 0.5C(3)H(6)O, consisting of a protonated amidine moiety joined to a substituted pyrazoline ring at the N1 atom. The amidine group is protonated and the positive charge is delocalized over the three C[bond]N bonds in a similar manner to that found in guanidinium salts. The amidinium moiety of the cation is linked to the acetate anions through four N[bond]H...O hydrogen bonds, with N...O distances of 2.749 (4), 2.848 (4), 2.904 (4) and 2.911 (4) A. The pyrazoline ring adopts a flattened envelope conformation and the substituted phenyl ring is oriented perpendicular to the attached heterocycle. The acetone solvate molecule lies across a twofold rotation axis.
ChemInform Abstract: Unexpected Ring Closure Reaction of α,β-Unsaturated Ketones with Aminoguanidine. Entry into 1,3,5-Trisubstituted Pyrazoles.
Cyclizations of α,β-unsaturated ketones with aminoguanidine under neutral conditions were examined. In contrast to literature reports of 1,2,4-triazines as reaction products, formation of 5-aryl-4,5-dihy-dro-3-methyl-1H-pyrazole-1-carboximidamides and carboxamides was observed. An explanation based on the Hard-Soft Acid-Base principle is presented and the probable causes of divergent reaction pathways are discussed.
The Hantzsch synthesis with salicylaldehyde revised. On the formation of bridged tetrahydropyridine derivatives
The Hantzsch condensation of salicylaldehyde with ethyl acetoacetate and ammonia has been re-examined. The reaction leads primarily to a 1,4-dihydropyridine intermediate which, after isomerization, undergoes a ring closure to give a bridged 1,4,5,6-tetrahydropyridine product, or is oxidized to 4-methyl-2-(2-oxo-2H-1-benzopyran-3-yl)[1]benzopyrano[3,4-c]pyridin-5-one. Bridged tetrahydropyridines with the 8-oxa-10-azatricyclo[7.3.1.02,7]trideca-2,4,6,11-tetraene skeleton were found in the Hantzsch-type condensation of salicylaldehyde with malononitrile, ammonium acetate, and acetone or butan-2-one. A mechanism for these reactions is discussed.