The Knoevenagel reactions of aldehydes with carboxy compounds. I. Reactions of p-nitrobenzaldehyde with active methine compounds.

概要

論文の詳細を見る
The Knoevenagel reactions of p-nitrobenzaldehyde (1) with β-keto acids, methylmalonic (2a) and α-methylacetoacetic acids (2b) were carried out in the presence of a tertiary amine such as pyridine. We have isolated the corresponding β-hydroxy intermediate (3a) by the reaction of 2a which positively suggested the reaction proceeded by the Hann and Lapworth mechanism. A kinetic study using 1H NMR revealed the existence of the reversibility between the starting materials and the β-hydroxy intermediate and that the rate determining step was decarboxylattion. But, when using the secondary amine, both the β-hydroxy acid and the corresponding condensation product were obtained via this reaction. These findings led to the conclusion that the reaction proceeded according to the two competing mechanisms, i.e., the Hann and Lapworth and Knoevenagel mechanisms. It was further clarified that either the decarboxylation step or the formation of the bis(dialkylamino) derivative was the rate determining step. The stereoselectivity of the β-hydroxy saturated compound has been closely related to the fact that the conformation of the intermediate possesses an intramolecular hydrogen bond to a hydroxyl group.
公益社団法人日本化学会の論文