Reactions of 2-Acyl-1,3-indandiones with Nitrogen Nucleophiles

Reactions of 2-acyl-1,3-indandiones with nitrogen nucleophiles were studied rarely. The question, if they react with carbonyl carbon of acyl group or indandione skeleton, has not been answered unambiguously. To make clear the question which carbonyl carbon of 2-acyl-1,3-indandiones enters the reaction with nitrogen nucleophiles we carried out the reactions with 2-acetyl- (Ia), 2-propionyl- (Ib), 2-pivaloyl- (Ic), and 2-benzoyl-1,3-indandione (Id). We used different 2-acyl-1,3-indandiones with the aim to find out if the character of acyl group affects the course of reaction. We used ethoxyamine, primary amines, phenylhydrazine, hydrazine and methylhydrazine as nucleophile reactants. The reactions were carried out in methanol at reflux at 10% excess of nitrogen base. The reactions with phenylhydrazine, hydrazine and methylhydrazine were performed with twofold excess of nitrogen base. The separation of reaction products was carried out by chromatography on silica gel. We found that 2-acyl-1,3-indandiones I react with ethoxyamine both at the acylcarbonyl carbon to produce 2-(1-ethoxyiminoalkyl)-1,3-indandiones II and the carbonyl carbon of indandione skeleton to give rise 3-(ethoxyimino)-2-acyl-1-indanones III. In all cases, the carbonyl carbon of acyl group was preferred (the observed ratio of products II to III was 6 - 8 : 1). From the reaction of 2-acyl-1,3-indandiones with primary amines only the products IV of reaction with the acylcarbonyl carbon were isolated. The hydrazines used reacted with 2-acyl-1,3-indandiones also at carbonyl carbon of acyl group in the first step to produce hydrazones. However, the products isolated in most cases were formed by the attack of hydrazone nitrogen at carbonyl carbon of indandione skeleton giving rise to derivatives of indeno[2,3-d]pyrazole-4-one V. It is interesting that 2-acetyl-1,3-indandione and 2-propionyl-1,3-indandione, reacting with phenylhydrazine and hydrazine, yielded only corresponding hydrazones VI.