Preparation and reactions of cyclic α-monocarbonyl azo-compounds: 1-pyrazolin-3-one derivatives

Abstract

1-Pyrazolin-3-one (Ia) and its 5,5-dimethyl derivative (Ib) were prepared in good yield by oxidation of the corresponding pyrazolidin-3-one derivatives (Va) and (Vb) with lead tetra-acetate at low temperature. Reactions of (Ia and b) with various nucleophiles were examined. Hydroxide, alkoxides, alcohols, and amines attack initially at the carbonyl carbon atom; ring cleavage then gives intermediate carbanions (III), which are either protonated to yield propionic and isovaleric acid derivatives (VII)–(XII), or react with unchanged (Ia or b) to yield 1- and 2-substituted pyrazolidin-3-one derivatives, (XIII)–(XX). In the case of (Ia), considerable amounts of polymeric products are formed. Compound (Ia) is isomerised quantitatively by triethylamine to 2-pyrazolin-5-one (VI) even at low temperature. Carbanions from reagents such as ethylmagnesium bromide, and the enolate derived from 6-methoxy-1-tetralone, seem to attack (Ia and b) at various positions, giving complex mixtures of products; the 1-ethylpyrazolidin-3-ones (XXIIIa and b), and 2-(3-hydroxy-5,5-dimethyl-1-pyrazolin-3-yl)-6-methoxy-1-tetralone (XXVII), were isolated in considerable yields. With boron trifluoride–ether complex, (Ia and b) were converted into pyrazolidin-3-one derivatives (XL) and (XLII) in good yield.