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.
Conformationally locked heterocycles. Structure of a doubly bridged pyrimido[1,2-a]pyrimidine from the hantzsch synthesis with 4-(2-hydroxyphenyl)but-3-en-2-one
1D and 2D nmr spectroscopy was used to assign the structure to the minor product from cyclocondensation of 4-(2-hydroxyphenyl)but-3-en-2-one with cyanamide, which was identified as (6R*, 9R*, 15R*, 17R*)-6,9-dimethyl-6,17:9,15-dimemano-6H,15H,17H-[1,3,5]benzoxadiazocino[4,5-d][1,3,5]benzoxadiazocine-7(9H)-carbonitrile, a doubly oxygen-bridged pyrimido[1,2-a]pyrimidine derivative. The observed stereose lectivity and reaction mechanisms are discussed with the help of molecular mechanics and semi-empirical PM3 calculations.