Cyclopentanecarboxaldehyde cyclohexene

Cyclopentanecarboxaldehyde has been prepared by the procedure described above 2 3 by the reaction of aqueous nitric acid and mercuric nitrate with cyclohexene 6 by the action of magnesium bromide etherate 6 or thoria 7 on cyclohexene oxide by the dehydration of frarei-l, 2-cyclohexanediol over alumina mixed with glass helices 8 by the dehydration of divinyl glycol over alumina followed by reduction 9 by the reaction of cyclopentene with a solution of [HFe(CO)4] under a carbon monoxide atmosphere 10 and by the reaction of cyclopentadiene with dicobalt octacarbonyl under a hydrogen and carbon monoxide atmosphere.11... 

A suspension of thallium (III) nitrate in pentane at room temperature can react with alkenes to give vtc-dinitrate esters. Cyclohexene reacts with this reagent to give 1,2-cyclohexanediol dinitrate (85 %) (as a mixture of isomers) and 15 % cyclopentanecarboxaldehyde (hydride shift in the dethallation step). Some alkenes react extremely slowly with this reagent e.g. isomeric 5-decenes. 

Oxidation of cyclohexene by peroxydisulfate in the presence of copper(II) salts results in the formation of cyclopentanecarboxaldehyde as the main product in an aqueous acetonitrile solution (equation 261), and 2-cyclohexenyl acetate in an acetic acid solution (equation 262).588,589 Reaction (261) has been interpreted as the formation of a radical cation (186) by oxidation of cyclohexene with S2Og, followed by hydrolysis of (186) to the /3-hydroxy alkyl radical (187), which is oxidized by copper(II) salts to the rearranged aldehydic product (188 equation 263).589... 

Cyclohexene is oxidized to cyclopentanecarboxaldehyde in 85% yield in fact this TTN-induced ring contraction is probably the method of choice for preparation of this aldehyde. This reaction was used by Corey and Ravindranathan- as one step in a synthesis of 11-desoxyprostaglandins for the conversion of (1) into (2). However, in this case, the use of the original conditions led to complex mixtures containing only a... 

In the second procedure, T1(III)(N03)3 3H2O (4.4g, lOmmol, TTN [13453-38-8]) is dissolved in MeOH (50ml), cyclohexene (lOmmol) is added, and the mixture is stirred at room temperature or heated until a starch-iodide paper indicates complete reduction of Tl(III) to T1(I) (usually within a few minutes). The mixture is filtered, and an alcoholic solution containing lOmmol of 2,4-dinitrophenylhydrazine is added. This is evaporated to 1/3 its volume and after addition of H2O (10ml) the mixture is heated on a steam bath for 10 minutes. On cooling to 0°, the 2,4-dinitrophenylhydrazone [20956-07-4] crystallises out and is recrystallised from EtOH to m 195.5-196° (85% yield). Hydrolysis of the hydrazone in the usual way provides the free aldehyde. On a preparative scale the precipitated T1(I)(N03) salt is filtered off, the filtrate is evaporated to a small volume, the mixture of aldehyde and its methyl acetal formed is heated on a steam bath with excess of 5% H2SO4 for 30 minutes, and cyclopentanecarboxaldehyde is isolated by ether extraction followed by distillation as in the first preparation above. [Taylor et al. J Am Chem Soc 95 3635 1 973] It should be stabilised with 0.1% of hydroquinone as before. 

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