Cyclization of hydrazones of .alpha.,.beta.-unsaturated carbonyl compounds. Biscarbamyl- and bisthiocarbamylhydrazones of malondialdehyde

Abstract

The symmetrical bissemicarbazone of malonaldehyde 1 readily cyclized during its preparation to form the isomeric semicarbazido-substituted carbamylpyrazoline 2. The cyclization proceeded by nucleophilic addition of the acidic hydrazine nitrogen in one semicarbazone group to the polarized azomethine (imine) double bond (-N _s=+iC<) in the adjacent group. The thiosemicarbazone of malonaldehyde la reacted similarly to form a thiosemicarbazido-substituted thiocarbamylpyrazoline 2a. In a suspension of water at 20°, increasing hydrogen ion concentrations catalyzed elimination of the semicarbazido or thiosemicarbazido substituents with the formation of pyrazole-l-carboxamide (3) or pyrazole-1-thiocarboxamide (3a).

Amine‐malonaldehyde condensation products and their relative color contribution in the thiobarbituric acid test

“…The experimental details for obtaining melting points, NMR and mass spectra were described previously (10). Measurements in the visible and UV regions were made with a Beckman DB-G spectrophotometer.…”

“…The dried material was extracted with 30 ml hot ethylacetate from which fine needles or plates crystallized mp 132-133 C. 1H NMR (CDC13, 30 C) from TMS, M-Bis-bisulfite sodium sait was prepared from M and sodium metabisulfite (9). The pyrazoline and pyrazole compounds (10) and the open chain mono-addition products glycine-and methionine-M (11,12), and the diglycine-_M (13) diaddition products were prepared as reported previously. Cysteine-M (12), 2-amino-and 2-oxopyrimidine (7) were synthesized according to previously published procedures.…”

Measuring Oxidative Stability of Beef Muscles Obtained from Animals Supplemented with Vitamin E Using Conventional and Derivative Spectrophotometry

“…It is now widely accepted that the TBA test is intrinsically nonspecific for MDA. Nonlipid-derived materials, as well as fatty peroxide-derived peroxidation products other than MDA, are TBA-positive (Janero 1990) and can yield a TBA-test product which is spectrophotometrically, chromatographically, and structurally indistinguishable from genuine 1:2 MDA-TBA adduct (Buttkus andBose 1971, Kosugi andothers 1987).…”

Coordination Chemistry of a Pyrazoline Derived from 2,4-Pentanedione bis(4-Methylthiosemicarbazone). Crystal Structure of the Pyrazoline and Evidence for Metal-Mediated Ring Opening

“…3,4 The synthesis of 1,3-bisthiosemicarbazones is complicated by the fact that 1,3-diketones such as 2,4-pentanedione undergo competing cyclisation reactions with one or two equivalents of thiosemicarbazide such that the isolated product is usually the isomeric pyrazoline, 5 which can itself undergo further reaction in the presence of acid to give the corresponding 1-substituted pyrazole (Scheme 1). 6 To avoid this problem, O'Callaghan and Twomey described an indirect synthesis of 2,4-pentanedione bis(4-methylthiosemicarbazone) via 2,3-dihydro-5,7-dimethyl-6H-1,4-diazepine. 7 Recently, the identity of the product of this synthesis has also been questioned.…”