Cyclopentanecarboxylic acid cyclohexanone

Wiberg and Koch 167) also disagreed with Littler s results, and found that the major product (75%) obtained on treatment of cyclohexanone with aqueous thallium(III) perchlorate was cyclopentanecarboxylic acid (XL). 2-Hydroxycyclohexanone was isolated in only 3 % yield unchanged starting material accounted for the remainder of the product. Wiberg and Koch were unable to detect any cyclohexane-1,2-dione in the product mixture, but did prove that 2-hydroxycyclohexanone did not function as the precursor to the ring-contracted acid. From the results obtained from a study of the oxidation of 2,2,6,6-[Pg.196]

Another useful route to cyclopentanes is the ring contraction of 2-bromo-cyclohexanones by a Favorskii rearrangement to give cyclopentanecarboxylic acids. If a,fi-dibromoketones are used, ring opening of the intermediate cyclopropanone leads selectively to /J,y-unsaturated carboxylic acids (S.A. Achmad, 1963, 1965 J. Wolinsky, 1965). 

Oxidation of cyclohexanone. Oxidation of cyclohexanone with TTN in acetic acid at room temperature proceeds rapidly to give adipoin (5) in 84% yield. If the oxidation is performed at first at room temperature, the thallium(I) nitrate removed hy filtration, and then the filtrate heated to about 40° for a few minutes, the product is cyclopentanecarboxylic acid (4), obtained in 84% yield. McKillop et al. propose that both products are derived from a common precursor, an epoxy enol (3). 

Problem 20.13 How could you distinguish between cyclopentanecarboxylic acid and 4-hydroxy-cyclohexanone by H and I3C NMR spectroscopy (See Problem 20.12.)... 

Mechanism 1 is closely related to that of the benzilic acid rearrangement. In this case, the chlorine-bearing carbon atom of the 2-chloro-l-cyclohexanone I becomes exclusively the Qt-carbon atom of the cyclopentanecarboxylic acid II. In Mechanism 2, which proceeds via... 

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