Cyclopentyl methyl ketone

Cyclopentyl methyl ketone has been prepared from 1 4 dibro... 

Saponification followed by decarboxylation gives cyclopentyl methyl ketone. 

Predict the products of the following reactions. (a) cyclopentyl methyl ketone + excess CI2 + excess NaOH (b) 1-cyclopentylethanol + excess I2 + excess NaOH (c) propiophenone + excess Br2 + excess NaOH ... 

PROBLEM 21.9 Cyclopentyl methyl ketone has been prepared from 1,4-dibro-mobutane and ethyl acetoacetate. Outline the steps in this synthesis by writing a series of equations showing starting materials, reagents, and isolated intermediates. 

The whole family of carotenoids with one or two k end groups is preferably synthesized via aldol condensation of a cyclopentyl methyl ketone of the type 43-47 [97-103]. Again these keto building blocks were all used in large excess, even in cases where the keto derivative is more difficult to synthesize than the aldehyde compound, as, for example, in the case of the optically active (3i5,5/ ,3 5,5 / )-capsorubin (413), (3 iS,5 / )-cryptocapsin (303) and 3R,yS, 5 / )-capsanthin (335). These few examples illustrate selected cases where the aldol condensation is the reaction of choice for synthesizing a given carotenoid. However, the superior versatility of the enol ether and especially the Wittig condensations clearly show the limited scope of the aldol condensation. 

Cyclopentyl methyl ketone added all at once at 80° under Ng to K-hexacyano-ferrate(III) and water, then degassed coned, ammonium hydroxide added dropwise at 80-85° during 0.5 hr. heated 10-15 hrs. longer at the same temp., and the soln. of the resulting crude a-aminoketone in 6%-HCl basified with NaOH product. Y 57%. F. e. s. D. G. Farnum and G.R. Carlson, Synthesis 1972, 191. 

If the reaction is carried out with excess alkane, a second hydride transfer occurs, resulting in reduction of the enone to the corresponding saturated alkyl methyl ketone. For example, stirring AcCl/AlCls in excess cyclohexane (30-35 °C, 2.5 h) affords 2-methyl-l-acetylcyclopentane in 50% yield (unpurified based on AcCl) and stirring AcCl/AlBr3 in excess cyclopentane (20 °C, 1 h) affords cyclopentyl methyl ketone in 60% yield (based on AcCl eq 7). ... 

Similarly, the [3-1-4] annulation of the E- and Z-isomers of /3-hetero-substituted acryloylsilanes 52 with lithium enolates of a,-unsaturated methyl ketones 54 gave stereospecifically the c -6,7-cyclopentyl-5-trimethylsilyl-3-cycloheptenone 55 (equation 20). The stereospecificity in the annulation was explained by an anionic oxy-Cope isomerization of the 1,2-divinylcyclopropanediol intermediate 56, which was generated through the Brook isomerization of the initial 1,2-adduct (equation 20). 

The first examples of a Michael-Stork enamine addition to allenyl esters and ketones R1CH=C=C(R2)COX (X = alkyl, alkoxyl) has been reported. Mechanistic investigation revealed that 2 equiv. of enamine are required for optimum yields. In the case of an allenyl methyl ketone, cyclopentyl enamine addition afforded 8-oxobicyclo[3.2.1]octane, providing evidence for the in situ formation of an enamine intermediate following the initial Michael-Stork reaction.187... 

Methyl-l -phenylpropan-1 -one Cyclopentyl phenyl ketone Cyclobutyl phenyl ketone Cyclopropyl phenyl ketone 4-Benzhydrylbenzophenone 9-Acetylfluorene... 

Kl=acetophenone, K7=l-tetralone, K8=l-acetylnaphthalene, K9=2-acetylnaphthalene, K16= 1-cyclohexenyl methyl ketone, K23=4-BrPhCOCH3, K24=PhCOEt, K25= -PrCOEt,K26=EtCO-cyclopentyl... 

Enamines can be obtained from cyclopropyl, cyclopentyl, methyl, and ethyl ketones [the latter affording the (jE)-isomer stereoselectively] but the reaction of amines with dicyclopropyl and cyclopropyl phenyl or a-thienyl ketones results in homoallylic rearrangement to 1-substituted 1,4-diaminobut-l-enes. ... 

The first preparative use of intramolecular C—H insertion in organic synthesis was based on the observation that on flash vacuum pyrolysis, a conjugated alkynyl ketone such as 1-(1-methyl-cyclopentyl)-2-propynonc is smoothly converted to a mixture of the cyclizcd enones 1 and 223. This elegant reaction apparently proceeds via isomerization of the alkyne to the corresponding alkylidene carbcne, followed by subsequent intramolecular C-H insertion. It should be noted that despite a 3 2 statistical predominance of primary C-H bonds over secondary C—H bonds, a marked preference for insertion into the latter (methylene) is observed. 

However, the oxidation of 1-methyl-1-cyclohexene, having a substituent in position 1 (entry 8), proceeds much less selectively, providing only 44% of a cyclic ketone in the reaction products. The reaction is accompanied by a significant cleavage of double bonds leading to 1-cyclopentyl-ethanone and 6-hepten-l-one. An aldehyde (C7H120) is also found in the reaction products ( 2-3%). 

Methyl-3-[N-(l-phenyl-ethyl)-hydroxyamino]- -methylester E16a, 127 (R-NH-OH + En) Pyridin 3-(Dimethoxy-methyl)-4-(fnmy-3-hydroxy-cyclopentyl)-E7b/2, 483 C-[CH(OR)2]-1,2,4-triazin + 3-OH —1-(CO — CH3) — cyclopentan Pyridin-l-oxid 4-Ethoxy-2-(l-hydroxy-cyclohexyl)- E19d. 605 (H - Li/ -(- Keton) Pymolo l,2-a azepin 6-Ethenyl-5-methoxycarbonyl-3-oxo-(5R, 6S, 9aR )-octa-hy dro-E21b, 1974 l-[CH(OH) —... 

Intramolecular reaction of an allylsilane and an aldehyde was performed to prepare cyclic compounds as illustrated in Eq. (90) [233], which shows a high diastereoselec-tivity. The cyclization of optically active allylsilane proceeds stereoselectively in a manner consistent with the antiS l mechanism (Eq. 91) [234]. Development of a new reagent with a bis-allylsilane moiety effected tandem inter- and intramolecular cyclizations to give cyclic compounds as exemplified in Eqs (92) [235] and (93) [236-238]. In Eq. (92), the double addition product initially formed underwent a pinacol-type rearrangement under the influence of TiCU to give, eventually, the methyl cyclopentyl ketone. Further examples of intramolecular cyclization of allylsilanes are summarized in Table 8. 

Probkm 28.28 Using 9-BBN plus any alkenes and unhalogenated acids or ketones, outline all steps in the synthesis of (a) 2-heptanone (b) 4-methylpentanoic acid (c) 4-methyl-2-hexanone (d) l-cyclohexyl-2-propanone (e) ethyl (trans Z-methylcyclopentyl)acetate (f) l>phenyl-4-methyM-pentanone (g) i-cyclopentyl-33 dimethyl-2-butaBone. 

A more complex sequence, such as that suggested in Scheme 2, must be invoked to explain the formation of the ring-contracted methyl cyclopentyl ketone from cyclohexanecarbaldehyde. ... 

The synthetic potential of the bicyclo[3.1.0]hexan-6-ols has been realized in the stereoselective synthesis of methyl cyclopentyl ketones, as exemplified for the selective synthesis of trans-l- 3-methylcyclopentyl)ethanone (16) from bicyclohexanol 14 by alkaline hydrolysis and subsequent pyrolysis. ... 

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