The Preparation of Cyclopentanone

Introduction. The reduction of the carboxyl group (COOH) to the carbonyl group (CO) can be brought about by the simultaneous oxidation of another carboxyl group to carbon dioxide. This reaction takes place when the barium or calcium salt of acids is subjected to distillation  

A mixture of calcium acetate and formate gives an aldehyde  

The yields in the laboratory are not very good, but it is possible to obtain good yields by passing the vapors of acids over catalysts at 250-300 . 

The distillation of the calcium or barium salt of a dicarboxylic acid gives a cyclic ketone  

Adipic acid may be obtained from cyclohexanol by oxidation with hot nitric acid. Cyclohexanol is prepared from phenol by hydrogenation. Thus the entire series of reactions represents (a) the change of an aromatic six-carbon compound to an alicyclic one (6) the opening of a six-carbon ring to an open chain compound (c) the cyclization of an open chain compound. The object of the present experiment is to illustrate this last step through the preparation of cyclopentanone from adipic acid. 

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The C — C bond formation of 5-bromouracil derivatives with carbanions gave a new possibility for the preparation of cyclopentanone-fused pyrimi-... 

It is interesting to note in passing that azulene was in fact prepared in 1893 as a by-product in the preparation of cyclopentanone by distillation of calcium adipate [10]. In a more recent investigation dzulene was shown to be formed in small amounts when adipic acid was heated in the presence of various catalysts [11]. 

In 2011, the Carreira group developed the Rh-catalyzed asymmetric intramolecular hydroacylation reactions of pent-4-enals 17 for the preparation of cyclopentanones 18 (Scheme 8.7). In this study, the biindane-derived phos-phoramidite/olefin ligand (R)-Ll was found to be highly efficient to promote... 

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... 

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. 

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. 

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... 

The ring expansion of cyclobutane derivatives to other carbocycles remains to be one of the most powerful tool in synthetic organic chemistry. Cyclobutanones are exceptionally facile starting materials for the preparations of y-lactones as well as cyclopentanones. 

The reaction between trialkylboranes and enones has found some interesting synthetic applications. An example is the preparation of prostaglandin precursors from exo-methylene cyclopentanone, generated in situ from a Mannich base. After dehydrogenation, a second conjugate addition of tri-octylborane was used to introduce the w-chain (Scheme 25) [70]. 

Intramolecular carbene C-H insertion frequently leads to the formation of five-membered rings [967,990,1021,1113-1128], In particular l-diazo-2-alkanones tend to yield cyclopentanones exclusively when treated with rhodium(ll) carboxylates. The use of enantiomerically pure catalysts for diazodecomposition enables the preparation of non-racemic cyclopentane derivatives [1005,1052,1074,1092,1129]. Intramolecular 1,5-C-H insertion can efficiently compete with 1,2-C-H insertion... 

The preparation of 2-benzylcyclopentanone from 2-benzyl-2-carbomethoxycyclopentanone has not been previously reported. Starting with the ethyl ester, however, the compound has been prepared by heating the ester for many hours with concentrated hydrochloric acid. - The direct alkylation of cyclopentanone with benzyl chloride in the presence of sodium amide in liquid ammonia goes only in a poor yield. ... 

Oxaspiropentanes 15 and 18, prepared by the reaction of cyclopentanone and 4-tm-butylcyclo-hexanone, respectively, with diphenylsulfonium 2-methylcyclopropanide, rearranged regiose-lectively with preferential migration of the higher substituted carbon atom. Within the stereoisomeric spiro[3.5]nonan-l-ones 19 formed, a pronounced cis selectivity was observed.62... 

A variation of this route was applied to the preparation of a-methylenecyclo-pentane 179, an intermediate that was employed for the synthesis of prostaglandin PGF2o, (180) (Scheme 6.82). The acetonide-protected oxime-diol 175 [derived from propanal (174)] was treated with sodium hypochlorite without the addition of base. This led to the tricyclic adduct 176 with high stereoselectivity. One of the side chains was subsequently elaborated and the fully protected cyclopentano-isoxazo-line (177), when exposed to Raney Ni/boron trichloride, gave the 2-hydroxymethyl-cyclopentanone (178). This compound was dehydrated using mesyl chloride/ pyridine to furnish enone (179) (324). In another related synthesis of PGF2q, the p-side-chain (3-hydroxyoctenyl) was introduced prior to the cycloaddition (325). 

Bicyclic keto esters can easily be prepared by a process called a,a -annulation.29 Thus, treatment of the enamine of cyclopentanone (64) with ethyl a-(bromomethyl)acrylate (98) affords, after work-up, the bicyclic keto ester (99) in 80% yield (equation IS).2911 The mechanism probably involves an initial Michael addition and elimination (or a simple Sn2 or Sn2 alkylation) followed by an intramolecular Michael addition of the less-substituted enamine on the acrylate unit. The use of the enamine of 4,4-bis(ethoxycarbonyl)cyclohexanone (100 equation 26) with (98) gives a 45% yield of the adaman-tanedione diester (101) (yield based on 100 70% when based on 98) via a,a -annulation followed by Dieckmann condensation.29 Enamines of heterocyclic ketones can also serve as the initial nucleophiles, e.g. (102) and (103) give (105) via (104), formed in situ, in 70% yield (Scheme 11 ).29>... 

Many methods have been mentioned in the literature for the preparation of glutaric acid. Of these, the only methods of preparative interest are the hydrolysis of trimethylene cyanide with acids or alkalies,1 the hydrolysis of methylene dimalonic ester2 or methylene dicyanoacetic ester,3 and the oxidation of cyclopentanone with nitric acid.4 In this country the cheapness of trimethylene glycol makes it the best source for glutaric acid. The method described in the procedure is a modification of that originally described by Reboul.5... 

Recent studies on radical-induced cyclisation reactions have led to a simple, one step method for the preparation of hydroazulenes from appropriately substituted cyclopentanone precursors. Treatment of 1, for example, with triphenyltin hydride and AH3N in refluxing toluene gave 2 in 79% yield. 

Chiral imines have proved to be useful reagents in the synthesis of cyclic systems. For example, imines derived from (S)-( — )- and (R)-( + )-l-phenylethylamine 412 have been used in the preparation of optically pure polysubstituted cyclopentanone derivatives 414 (equation 87)252 and in enantioselective steroid synthesis (equation 88)253. 

An interesting preparation of 128 involves the cycloaddition of carbon suboxide to the anil of cyclopentanone (129).87 Compound 129 also reacts with monosubstituted malonyl chlorides to give iV-aryl-2-oxo-3-alkyl-4-hydroxy-6,7-dihydro-5ff-1 -pyrindines (131) in fair yields.88 Similarly, the oxime ether of cyclopentanone (132) reacts to give the cyclic hydroxamic acid derivative (133),89 and benzylmalonyl chloride reacts with the A,A-dimethylhydrazone of cyclopentanone (134a) to give 134b in 90% yield.90... 

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