3.5- Dimethyl-4-carbethoxy-2-cycloHEXENE-l-ONE

Dimethyl-4-carbethoxy-2-cyclohexen-l-one and 3,5-di-methyl-2-cyclohexen-l-one have always been prepared from acetaldehyde and acetoacetic ester through the Knoevenagel condensation.2 The keto ester has previously been obtained by selective saponification and decarboxylation methods which have involved heating the crude condensation product with water at 140° 2 3 or with sodium ethoxide in alcohol.3 The ketone has been obtained from the same condensation product by prolonged refluxing in 20% sulfuric acid.2-4 6... 

A. 3,5-Dimethyl-4-carbethoxy-2-cyclohexen-l-one. In each of three 500-ml. Erlenmeyer flasks (Note 1) is placed 210 ml. (210 g., 1.61 mole) of ethyl acetoacetate (Note 2). The flasks are placed in an ice-salt bath and chilled to 0° to each flask there is then added 45 ml. (35.2 g., 0.78 mole) of acetaldehyde. When the contents of the flasks have cooled to —5° to 0° there is added to each flask, with shaking, a solution of 2 ml. of piperidine in 5 ml. of absolute alcohol. The flasks, the contents of which become cloudy in a short time because of the separation of water, are kept in an icc-salt bath for 6 hours. The reaction mixtures are then combined in a 1-1. flask and placed in an icebox. 

B. 3,5-Ditnclhyl-2-cyclohexen-l-one. The ether solution of crude 3,5-dimethyl-4-carbethoxy-2-cyclohexen-l-one obtained as described above is transferred to a 3-1. round-bottomed flask. 

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