Cyclopentanone, preparation

The enolate of cyclopentanone, prepared by sonication of the ketone in the presence of sodium hydride, reacts with diethyl trithiopyrocarbonate, to give 2-ethoxythiocarbonyl cyclopentanone (Eq. 17). ... 

Show how you could prepare each of the following compounds from cyclopentanone D2O and any necessary organic or inorganic reagents... 

Diketones are readily transformed to cycHc derivatives, such as cyclopentanones and furans. In this manner, the fragrance dihydrojasmone (3-meth5l-2-pentyl-2-cyclopenten-l-one) is prepared by the base-catalyzed aldol condensation of 2,5-undecanedione. 2,5-Undecanedione is itself prepared from heptanal and methyl vinyl ketone in the presence of thiazoHum salts (329). i7j -Jasmone can be similarly prepared (330,331). 

A variety of esters can be prepared from the corresponding ketones usiag peracids ia a process usually referred to as the Baeyer-Villiger reaction (95) ie, cyclopentanone is converted to 5-valerolactone upon treatment of the ketone with peroxytrifluoroacetic acid ... 

Glutaric acid is easily and cheaply prepared by oxidation of cyclopentanone cf. Adipic Acid, Coll. Vol. i, 18. The oxidation needs careful control—if it gets out of hand succinic acid results. 

The secondary amines used in the preparation of enamines have been primarily simple dialkylamines or cyclic amines of five- or higher-membered rings. Azetidine (4) yields a stable enamine with cyclopentanone (28). No simple enamines formed by condensation of ethylenimine (5) or a substituted ethylenimine with an aldehyde or ketone have been reported. 

The preparation of long-chain fatty acids has been carried out in this way because cleavage of 115 with strong sodium hydroxide gives the ketoacid (116), which is easily reduced by the Wolf-Kishner method to the saturated acid. A similar sequence of reactions can be carried out starting with the cyclopentanone enamine, and this method allows lengthening the chain... 

In addition, the cyclopentylidene ketal has been prepared from dimethoxy-cyclopentane, TsOH, CH3CN, or cyclopentanone (PTSA, CUSO4 >70% yield) and can be cleaved with 2 1 ACOH/H2O, rt, 2 h. Certain epoxides can be converted directly to cyclopentylidene derivatives as illustrated in the following reaction ... 

Although chemically related to the above cycloalkylamines, pentethylcyclanone (71) is stated to have antitussive activity. The compound is prepared rather simply by alkylation of the anion (70a) of the self-condensation product of cyclopentanone (70) with N-(2-chloroethyl)-morpholine. ... 

Following the procedure given above, cyclopropylidenecyclopentane is prepared in 85% yield from 34.4 g (0.09 mole) of the phosphonium salt, 3.83 g (0.097 mole) of sodium amide (used instead of phenyllithium), and 8.4 g (0.1 mole) of cyclopentanone in ether as solvent (350 ml). The product has bp 69-70770 mm. 

Choice of catalyst and solvent allowed considerable flexibility in hydrogenation of 8. With calcium carbonate in ethanol-pyridine, the sole product was the trans isomer 9, but with barium sulfate in pure pyridine the reaction came to a virtual halt after absorption of 2 equiv of hydrogen and traws-2-[6-cyanohex-2(Z)-enyl]-3-(methoxycarbonyl)cyclopentanone (7) was obtained in 90% yield together with 10% of the dihydro compound. When palladium-on-carbon was used in ethyl acetate, a 1 1 mixture of cis and trans 9 was obtained on exhaustive hydrogenation (S6). It is noteworthy that in preparation of 7 debenzylation took precedence over double-bond saturation. 

How mighl you use a conjugate addition reaction to prepare 2-methyl-3-propyl-cyclopentanone ... 

The cyclic /3-keto ester produced in a Dieckmann cyclization can be further alkylated and decarboxylated by a series of reactions analogous to those used in the acetoacetic ester synthesis (Section 22.7). For example, alkylation and subsequent decarboxylation of ethyl 2-oxocyclohexanecarboxylate yields a 2-alkylcvclohexanone. The overall sequence of (1) Dieckmann cyclization, (2) /3-keto ester alkylation, and (3) decarboxylation is a powerful method for preparing 2-substituted cyclohexanones and cyclopentanones. 

This methodology has been extended to the preparation of 3,3-disubstituted cyclopentanones. The yields and the enantiomeric excess of the final product is heavily dependent on the nature of alkyl groups and the organocopper reagent14. 

Commercial food grade water-soluble Cu-chlorophyllin is the most notable among these preparations. Copper chlorophyllins are produced from crude natural chlorophyll extracts followed by the hydrolysis of the phytyl and methyl esters, cleavage of the cyclopentanone (E) ring in dilute alkali, and the replacement of magnesium by copper. ... 

Originally, 1 was prepared by medicinal chemists from three key components, namely, a cyclopentanone moiety 2, a pyrazole moiety 3, and commercially available D-valine, as depicted in Scheme 2.1 [1], These synthetic disconnections provided an applicable and convergent route to 1, and consequently, were utilized in our strategy to develop an efficient and scalable synthesis of 1. 

Since preparation of pyrazole 3 was deemed straightforward (vide infra.) and D-valine tert-butyl ester was commercially available, our efforts focused on developing a synthesis of tbe more challenging cyclopentanone 2 [3], The original synthetic method for 2 by medicinal chemists is depicted in Scheme 2.2. 

The major issue for the large scale preparation of our target 1 was the preparation of the cyclopentanone 2. With the exception of 2, we felt the original Medicinal route was suitable for the large scale preparation with standard development optimization. Thus, the outline of this section is ... 

Although cyclopentanone 2 is a rather simple looking small molecule, the 3,4-trans-substituted architecture in a cyclopentanone ring provides significant complexity to this molecule. We devised two alternative routes for the preparation of 2. 

Fernandez-Matess recently demonstrated that nitriles constitute excellent radical traps in titanocene-mediated epoxide openings, even though these cyclizations are considered as being quite slow. As shown in Scheme 31 cy-clobutanones, cyclopentanones, and cyclohexanones can be prepared in high yields [122]. 

A variety of enzymes (such as acetylcholine esterase, Porcine pancreatic lipase, Pseudomonas cepacia lipase, and Candida antarcita lipase) have been found useful in the preparation of enantiomerically pure cyclopentenol (+)-2 from 1. The enantiomeric (—)-2 has been prepared from diol 4 by enzymatic acetylation catalyzed by VP-345 with isopropenyl acetate in an organic medium. The key intermediate cyclopentanones (+)-6, (—)-6, 7, and 8, which are useful in the preparation of many bioactive molecules, can be obtained from 3 and 5 via routine chemical transformations.7... 

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