Crotonaldehyde Doebner reaction with

The yields of Skraup/Doebner-von Miller reaction can be dramatically improved by running the reaction as a two-phase mixture. Reaction of crotonaldehyde with 30 in acidic ethanol provides only 10% of quinoline 31. However, when a toluene solution of crotonaldehyde is reacted with 30 (starting as the acetanilide) in 6M HCI at 100 °C for 2 h, quinoline 31 is isolated in 80% yield on 5kg scale. 

Sorbic acid is prepared by the condensation of crotonaldehyde with malonic acid in the presence of pyridine at 100° (Doebner reaction) ... 

The Skraup synthesis consists of the reaction with acrolein which is formed in situ from glycerine/H2S04. The Doebner-Miller synthesis was originally limited to the reaction with crotonaldehyde to give quinaldines, but is increasingly used as a generic term for this reaction. 

A second similar synthesis, due to Doebner and Miller, leads to the formation of substituted quinolines. The simplest example is the production of quinaldine from aniline and paraldehyde by heating with concentrated hydrochloric acid. The course of the reaction is closely related to that of the Skraup synthesis by route II. There the aniline reacts with acrolein, here with crotonaldehyde, which is easily formed under the conditions which prevail ... 

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