2- methylcyclopentanone, and

The addition of 2-nitropropene to the chiral imlne derived from 2-methylcyclopentanone and fS -Tphenylethylamine gives the adduct in high regio- and stereoselectivity fEq 471 The product is converted to a chiral 1,4-diketone via the Nef reaction... 

The two established Hnls, those from L. usitatissimum and P. amygdalus, have found biocatalytic applications for the production of (i )-cyanohydrins. The former of these Hnls is the least widely applied, the natural substrates being acetone cyanohydrin or (i )-2-butanone cyanohydrin (Table 1) [28]. Although an improved procedure for the purification of this enzyme has been reported [27] it is still only available in limited quantities (from 100 g of seedlings approximately 350 U of enzyme are obtained). It was found that this enzyme transforms a range of aliphatic aldehyde and ketone substrates [27], the latter of which included five-membered cyclic (e.g. 2-methylcyclopentanone) and chlorinated ketone substrates. In contrast, attempts to transform substituted cyclohexanones and 3-methylcyclopentanone failed and it was even found that benzaldehyde deactivated the enzyme. 

A soln. of 5-bromo-2-carbethoxy-2-methylcyclopentanone and epichlorhydrin as HBr-scavenger stirred 7 hrs. at 70° in dimethyl sulfoxide, which is then removed under reduced pressure 5-carbethoxy-2-hydroxy-5-methylcyclopent-2-en-l-one. Y 58.5%. K. Sato, Y. Kojima, and H. Sato, J. Org. Chem. 35, 2374 (1970). 

In general, these rhenium compounds are more active for the oxidation of cyclic (four-, five-, and six-membered rings) than acyclic ketones, consistent with the common lower reactivity of the latter ketones. The Re(III) tris(pyrazol-l-yl)methane compound [ReCl3 HC(pz)3 ] (11) is the most active one for 2-methylcyclopentanone and cyclohexanone or pinacolone BV oxidations, whereas the most effective oxidations are observed for cyclobutanone with [ReCl2 N2C(0)Ph (Hpz)2(PPh3)] (26) (54% yield, 99% conversion, TON of 537) (Table 22.3) [9]. 

Addition of chiral imine (202), derived from 2-methylcyclopentanone and (N)-l-phenylethylamine, to 2-nitropropene (203) furnished the expected Michael adducts... 

Write the structures of the isomeric enols of 2-methylcyclopentanone and rank them in order of relative stability. 

Identify the thermodynamie enolate for each system shown above (2-pentanone enolate A and B 2-methylcyclopentanone enolate A and B decalinone enolate A and B). Also, compare eleetrostatic potential maps for eaeh pair of enolates. What struetural and/or electronic features, if any, appear to dictate which enolate is favored ... 

In the Clemmensen reduction of 1,4-cyclohexanedione, all the products isolated from the reduction of 2,5-hexanedione were found in addition to 2,5-hexanedione (20%) and 2-methylcyclopentanone (6%). The presence of the two latter compounds reveals the mechanism of the reduction. In the first stage the carbon-carbon bond between carbons 2 and 3 ruptured, and the product of the cleavage, 2,5-hexanedione, partly underwent aldol condensation, partly its own further reduction [927], The cleavage of the carbon-carbon bond in 1,4-diketones was noticed during the treatment of 1,2-diben-zoylcyclobutane which afforded, on short refluxing with zinc dust and zinc chloride in ethanol, an 80% yield of 1,6-diphenyl-1,6-hexanedione [75<5]. 

In work which remains unpublished, Wenkert has succeeded in cleverly transforming 2-methylcyclopentanone into isocomene The key elements of his strategy (Scheme LXXXIII) are the acid-catalyzed ring expansion of methoxycyclopropane 747 to 748 and the regiospecific homologation of the cyclobutanone to 749. Unfortunately, the Wolff-Kishner reduction of this penultimate intermediate affords both 731 and its epimer. 

The regioselectivity of the enolization can be controlled in a similar way for cyclic ketones. Typical examples are the enolization of 2-methylcyclopentanone (6)5 and 2-methylcyclohex-anone (7)9, u. 

Reaction of 3,3-disubstituted-l,4-pentadiene 92 with a primary amine under cyclohydrocarbonylation conditions yielded cyclopenta[. ]pyrrole 96 as the predominant product accompanied by a small amount of cyclopentanone 95 (Scheme 15). This unique reaction is proposed to proceed through a cascade hydrocarbonylation-carbonylation process. The first hydrocarbonylation of 92 and the subsequent carbocyclization formed cyclopentanoylmethyl-Rh complex 93. If 93 immediately reacts with molecular hydrogen, 2-methylcyclopentanone 95 is formed. However, if CO insertion takes place faster than the hydrogenolysis, cyclopentanoylacetyl-Rh complex 94 is generated, which undergoes the Paal-Knorr condensation with a primary amine to yield cyclopenta[. ]pyrrole 96. ... 

The same process was used to obtain 4 from 2 and methyl acrylate, and to obtain 5 and 6 from the imine of 2-methylcyclopentanone. 

Unsymmetrical ketones can yield two different enolates, and in some cases the one that is the less stable thermodynamically is formed faster.148 Scheme 24 illustrates the example of 2-methylcyclopentanone. When this ketone is added slowly to excess f-butyllithium, the proton is removed preferentially from the less substituted carbon. If excess ketone is added, it can serve as a proton donor to allow equilibrium to be established, and nearly all the enolate is then the more highly substituted one.149 It may be possible in some cases to take advantage of such a selective formation of one of two possible enolates in synthesis. A more general procedure is to use a compound in which the desired position is activated... 

In addition to acyclic ketones, dolichoderine ants in the genus Azteca generate an alarm signal with 2-methylcyclopentanone (xxxi),cis-l-acetyl-2-methylcyclopentane (XXXII), and 2-acetyl-3-methylcyclopentene (XXXIII) (128). That some ant species utilize aromatic compounds as alarm pheromones is demonstrated by the identification of methyl 6-methyl salicylate (XXXIV) in the... 

The rates for the methylation of cyclopentanone and for the proton abstraction from 2-methylcyclopentanone were significantly increased by a factor of 7500 and 5, respectively, when six equivalents of HMPA were added to the reaction. Using 31P, 7Li and 13C NMR spectroscopy, Suzuki and Noyori found that the tetrasolvated Dy dimer was exclusively generated from the tetrameric (T0,4) and dimeric (D0,4) tetrasolvated lithium amine-free enolate of cyclopentanone (0.16 M in THF, —100 °C, ratio 2/3)275. Kinetic analysis gave a first-order reaction in dimer and HMPA for the reaction with a modulation for free HMPA33, and a first-order reaction in dimer for deprotonation, independent of HMPA. Possible transition state structures for alkylation and proton abstraction are drawn in Scheme 85. 

Considerable information about the course of aldehyde decarbonylations has been gleaned from the decarbonylations of alk-4-enals. Pent-4-enals form cyclopentanones in high yield in decarbonylations catalyzed by [RhCl(PPh3)3], The major product from the decarbonylation of hex-4-enal is 2-methylcyclopentanone. As shown in Scheme 5, the cyclization reaction requires a vacant site on rhodium. The other products result from decarbonylation of the unsaturated acyl before cyclization can take place. In these cases, there is competition between addition of deuterium to C-1 of the alkenyl ligand or its addition to the alkene bond and the formation of an unstable metallocycle. ... 

TABLE 5. Regio- and enantioselective alkylation of 2-methylcyclopentanone (31a) and 2-methylcyclohexanone (31b) with an optically active Lewis acid... 

How would the compounds in each pair differ in their IR spectra (a) CH3(CH2)4CHO and CH3(CH2)3COCH3 (b) C6H5CH2COCH and C6H5COCH2CH3 (c) cyclohexanone and 2-methylcyclopentanone ... 

Several biochemical oxidations can be applied to the conversions of secondary alcohols into ketones. In a complex system containing horse liver alcohol dehydrogenase, ( )-trans-3-methylcyclohexanol and ( )-cis-2-methylcyclopentanol are dehydrogenated to (-)-(5)-3-methylcyclohex-anone (yield 50% ee 100%) and to (+ )-(5)-2-methylcyclopentanone (yield 55% ee 96%), respectively [1036]. 

Scheme 2 shows the results of two studies on the methylation of the lithium enolate of cyclopentanone (10), which was prepared by deprotonation of the ketone with trityllithium in DME or by cleavage of the 1-trimethylsiloxycyclopentene with methyllithium in THF. A signiEcant quantity of over-alkylation occurred when the enolate was treated with methyl iodide, particularly when DME was employed as the solvent at room temperature. Also, as indicated in Scheme 2, Noyori and coworkers showed that by adding 3 equiv. of HMPA to the enolate (10) and reducing the temperature at which the reaction was conducted, the yield of 2-methylcyclopentanone was greatly improved.

The highest enantiomeric excess of 58% was achieved with 2-( -pentyl)cy-clopentanone (11) as substrate and BINAP/2-vaniUin platinum complex 12 as catalyst (Eq. 5). As a comparison with the reaction of 2-methylcyclopentanone revealed, a shorter side chain in the substrate led to a sHghtly faster reaction but significantly decreased the enantioselectivity at the same time. Also, a six-mem-bered cyclic ketone, 2-methylcyclohexanone, was converted under identical conditions to the corresponding (S)-lactone with 45% ee. 

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