3,4,5-Triphenylpyrazoles

Ab Initio Study of 2,4-Substituted Azolidines. II. Amino−Imino Tautomerism of 2-Aminothiazolidine-4-one and 4-Aminothiazolidine-2-one in Water Solution

“…Experimental studies on the amino-imino tautomerism of 2-aminothiazolidine-4-one have been reported in several papers. [2][3][4][5][6][7][8][9][10][11][12][13][14] However, the opinions of the authors are contradictory. Amirthalingam and Muralidharan 7 have confirmed by X-ray the existence of the imino form of pseudothiohydantoin.…”

“…Twenty-two years later Steel and Guard 14 have redetermined the crystal structure of pseudothiohydantoin at 128 K and have shown that the compound exists in the amino form. Using UVvis spectral data, Comrie 3 and Akerblom 4 have reported that in water solution both tautomeric forms exist with domination of the imino tautomer. By means of IR spectroscopy, Khovratovich and Chizhevskaya 5 have shown that in chloroform solution the amino form exists.…”

Photochemistry of N-heterocycles. Part 1. Synthesis and photochemistry of some 2(4),5-dihydro-1,2,4-triazines. X-Ray molecular structure of 1-(4-methyl-3,5,6-triphenyl-1,4,5,6-tetrahydro-1,2,4-triazin-6-yl)ethanol

“…The mixture was kept overnight and poured onto a 1:l mixture of ice and hydrochloric acid (100 ml). The aqueous layer was discarded; the thick oily product was taken up in EtOAc (30 ml), and the solution was washed with water, dried (MgSO,), and diluted with Et,O (200 ml) to precipitate compound( IS) ( (19).-PC1, (2.1 g, 1 0 mmol) was added to a solution of compound (18) (4.8 g, 10 mmol) in dry CHCI, (30 ml) under argon. The mixture was refluxed until a homogeneous solution was formed.…”

Heterocyclic tautomerism. VI. A redetermination and reassignment of the structure of 2-aminothiazol-4(5H)-one (pseudothiohydantoin)

“…the presence of a carbonyl absorption and the absence of an hydroxyl absorption, thereby eliminating three of the possible tautomers, (3)-(5). Early studies of the tautomerism of this compound in the solid state concluded that it exists as the imino tautomer (2) (Comrie, 1964;Khovratovich & Chizhevskaya, 1967). In 1972 this was apparently confirmed by two X-ray crystal structure determinations (Amirthalingam & Muralidharan, 1972;Ananthamurthy, Udupa & Murthy, 1972).…”