Trimethylcyclopentanone

Submitted by George D. Ryerson, Richard L. Wasson, and Herbert O. House.1 

The preparation of isophorone oxide was described in an earlier volume of this series.5 

A practical grade of boron trifluoride etherate, purchased from Eastman Kodak Company, was redistilled before use. The pure etherate boils at 126°. 

If the organic layer is dried over magnesium sulfate and 

The specified period of shaking is sufficient to ensure complete deformylation of the intermediate /3-keto aldehyde. Ordinarily, no difficulty is experienced with emulsification provided that the recommended quantity (or more) of ether is added to the reaction mixture. 

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At this point about 150-200 ml. of liquid remains in the still pot. If the distillation is continued, the peppermint-like odor of the product, 2,4,4-trimethylcyclopentanone, can be detected in the distillate. 

If an appreciable quantity of higher-boiling material (consisting of 2-formyl-2,4,4-trimethylcyclopentanone see Note 4) remains after the product has been collected, the residue should be dissolved in ether and shaken with aqueous sodium hydroxide as described in the procedure. After the ethereal extract has been dried over magnesium sulfate, distillation will permit the isolation of an additional quantity of 2,4,4-trimethylcyclopen-tanone. 

Trimethylcyclopentanone has been prepared by the oxidation of 1-hydroxy-2,4,4-trimethylcyclopentanecarboxylic acid with lead dioxide in sulfuric acid,3 by the hydrogenation of 2,4,4-trimethyl-2-cyc.lopentenone, 4 5 by the Clemmensen reduction of dimethyldihydroresorcinol,6 7 by the distillation of powdered 2,4,4-trimethyladipic acid with sodium hydroxide,8 and by the saponification and decarboxylation of ethyl 2-keto-l,4,4-tri-mcthylcylopentanecarboxylate.9 10 The rearrangement of iso-phorone oxide 11 appears to represent the optimum combination of favorable yield and convenient procedure. 

In the case of derivatives carrying two carbonyl functions stereochemically close to each other, Clem-mensen reduction affords an interesting product distribution, passing through characteristic intermediates. o In the case of 1,3-diketones, a cyclopropanediol is involved, similar to the cyclopropanes formed from conjugated carbonyl systems. For instance, 5,5-dimethylcyclohexane-l,3-dione (16) is converted into 2,4,4-trimethylcyclopentanone (17) as the major product (equation 10). ... 

If the organic layer is dried over magnesium sulfate and fractionally distilled at this point, both 2,4,4-trimethylcyclo-pentanone and 2-formyl-2,4,4-trimethylcyclopentanone, b.p. 49-50° (2 mm.), By 1.4495, may be isolated. The pot residue from this distillation contains a small amount of the enol form of 3,5,5-trimethyl-l,2-cyclohexanedione which crystallizes from petroleum ether as white needles, m.p. 92-93°. 

The water-washed organic layer is shaken for 1-2 min. with alkali to eliminate formaldehyde and give 2,4,4-trimethylcyclopentanone. 

Trimethyl-1,3-cyclopentanedicarboxylic acid, (1R, 3S) 2,2,4-Trimethylcyclopentanone 2,4,4-Trimethylcyclopentanone 1,1,2-Trimethylcyclopropane... 

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