1- cyclo- cyclopentanone

Oxidative rearrangement takes place in the oxidation of the 1-vinyl-l-cyclo-butanol 31, yielding the cyclopentenone derivative 32[84], Ring contraction to cyclopropyl methyl ketone (34) is observed by the oxidation of 1-methylcyclo-butene (33)[85], and ring expansion to cyclopentanone takes place by the reaction of the methylenecyclobutane 35. [86,87]... 

Irradiations of Testosterone Acetate (114), —In t-Butanol. 1.25 g of (114) in 250 ml t-butanol is irradiated for 32 hr at 30° under nitrogen with a Hanau Q81 high-pressure mercury lamp placed in a central water-cooled Pyrex immersion well with acetone filter. The solvent is evaporated in vacuo and the residue chromatographed on 125 g silica gel with benzene-ethyl acetate (4 1) to yield 0.29 g 17 -hydroxy-la,5 -cyclo-10a-androstan-2-one acetate [(118) 23%] mp 164-165°, after crystallization from acetone-hexane [a]i3 37 (CHCI3) 0.14 g cyclopentanone (120) (11%) mp 106-107° [aJo 38° (CHCI3) and 0.58 g starting material [(114) 46%]. Ratio (118) (120) - 2 1. 

Scheme 33 illustrates the difference in reactivity between triazolines obtained from cyclohexanone and cyclo-pentanone enamines. Thus, the reactions of azidophosphonates 239 with cyclohexanone enamines produce unstable aminotriazolines 240 that cannot be isolated due to their spontaneous elimination of amines to provide triazoles 241. Contrary to that, triazolines 242, derived from cyclopentanone enamines, are isolated in good yield (76-88%) and cannot be converted to the corresponding triazoles even by thermolysis <1995H(40)543>. Probably, introduction of a double bond between two five-membered rings would involve too much molecular strain. 

Photoisomerization of the unsaturated lactone (200) to the 1,5-cyclo-lactone (201) provides the first example of a Type A rearrangement in an j8-unsaturated lactone. An X-ray structure analysis has confirmed the photoisomerization of the /3-y-unsaturated ketone (202) to the cyclopentanone (203) by a 1,3-acyl shift. A similar rearrangement of the 3-oxo-A "° " -compound (204) to the cyclo-butanone (205) is in contrast with earlier reports of the oxo-di- r-methane rearrangement of 3-oxo-A " Lcompounds on direct irradiation. Benzophenone-... 

Hydrocarbonylation of 1,4-dienes.3 Hydrocarbonylation of 1,4-pentadiene catalyzed by Co2(CO)8 results in 2-methylcyclopentanone as the only cyclic product. As expected, a gem-dimethyl group at C3 enhances the tendency to form cyclo-pentanones. Thus hydrocarbonylation of the 1,4-diene 1 leads to the tetramethyl-cyclopentanone 2 with a marked preference for the cw-isomer. The reaction has... 

The construction of cyclopentanones can take several avenues based upon the concepts evolving from use of small ring conjunctive reagents. A very simple one is a-cuparenone (183) which can be thought to derive by a ring expansion of a cyclo-butyl carbinyl system as in 184 (Scheme 8) 110,1 U). If X- is an anion stabilizing... 

The kinetics of the potassium hexacyanoferrate(III)-catalysed oxidation of glucose with ammonium peroxodisulfate have been studied.82 The kinetics and mechanism of oxidation of some cycloalkanols by alkaline Fe(CN) have been reported.83 The same group has also studied the oxidation of cycloalkanones under comparable conditions and determined the order of reactivity as cyclohexanone > cyclopentanone > cyclo-octanone > cycloheptanone.84 Palladium(II) has been found to catalyse the oxidation of formaldehyde, thiourea, and thioacetamide by alkaline Fe(CN)g, whereas no effect is observed in the oxidation of acetaldehyde.85 The orders of reaction have been determined and a mechanism was proposed. 

The alicyclic ketones have been identified as being important flavor precursors by Flament et al. (15) and more recently by MacLeod and Ames (44), who identified a similar compound (3-methyl-cyclo-pentanone) in heated ground beef. Flament et al. (15) singled out the importance of these compounds, particularly in the presence of alhylpyrazines. Nishimura et al. (41) produced a meaty odor by heating 2-hydroxy-3-methylcyclopent-2-enone with cyclotene and HaS. Two volatile compounds described as having meaty odor were 2-methyl-cyclopentanone and 3-methylcyclopentanone. Thus, cyclotene appears to be a key precursor of "roast beef" flavor. 

Conjugation has a great influence on the structure of aliphatic and alicyclic compounds. Thus, the existence of an amino form has been established (in addition to the extreme case of aromatic amines17) for all compounds where the double bond is conjugated with a carbonyl group (or its equivalent),12 with esters12,18 and nitriles of a,/8-un-saturated /8-amino acids,519,20 and with /8-amino-ketones. The /3-keto-esters ethyl 2-cyclopentanone- 1-carboxylate and ethyl 2-cyclo-hexanone-l-carboxylate exist as mixtures containing 95% of the keto... 

Jasmonoids, important raw materials in the perfume industry, are among the best known and most often synthetized members of the cyclopentanoid class, because these simple compounds incorporate the 2,3-dialkylated cyclopentanone and cyclo-... 

From four-membered rings An acid-catalyzed transformation has been observed in the conversion of l-[l-methylsulfinyl-l-(methylthio)alkyl]cyclo-butanol to 3-methyl-2-(methylthio)cyclopentanone [9]. - Rearrangement of a /3-lactone to a y-lactone derivative in the presence of magnesiumdibromide [10]. - A borontrifluoride catalyzed cyclobutene to cyclopentene rearrangement [11]. - Ring expansion of a [2+2] photoadduct to a five-membered ring [12]-... 

It can be seen from model observations that this hairpin conformation is only then optimally attained, if both side chains are bonded to a cyclopentane, cyclo-pentene, cyclopentanone or cyclopentenone. Therefore the chances to obtain a final molecule showing good biological activity seemed to be optimal, when the prostanoid ring system is kept intact, while the ring substitution is varied. 

FIGURE 4. Energy diagrams for (a) cyclo-butanone and (b) cyclopentanone. 

From a comparison of the spectroscopy of cyclo-butanone to that of cyclopentanone, we see apparently similar absorption and emission predissociative behavior for cyclobutanone when Xex > 313 nm, while no such effect is found for cyclopentanone. If we suggest that three competing pathways account for the predissociative behavior, we have done little more than to offer a detailed but uninformative representation of the observations. Furthermore, we would be forced into adding more primary acts when interpreting the [1,3]-shifts and aldehydeforming reactions discussed above. 

Interestingly, /3,7-unsaturated a-diazoketones are also sources of cyclo-butanones when they are exposed to protic acid. For example, compound XI furnished XII in high yield upon contact with concentrated sulfuric acid (see Scheme 42.3). In a conceptually analogous reaction, /S.y-unsaturated a-diazoketones proved to be useful in the constmction of cyclopentanones XIV" in a polyolefinic cationic cyclization process reminiscent of the mechanism by which plants in nature build their polycyclic triterpenoid metabolites from squalene, that is, XV - XVI. 

Sequential reaction at both positions a to a carbonyl group (as its enamine derivative) with a bifunctional electrophile provides for ring formation, as illustrated in equation (24) by the preparation of a bi-cyclo[3.2.1]octane bridged system from a cyclopentanone. Alternatively, spiro systems can also be formed, as in equation (25). A comprehensive study with a variety of bifunctional electrophiles has been reported recently. ... 

Cyclohexanones can be dehydrogenated to enones by treatment of the corresponding enol silanes with DDQ in the presence of a catalytic amount of the bis-silyl derivative of acetamide. However, the yields fall off drastically when the reaction is applied to cyclopentanones and cyclo-heptanones. Another new method for dehydrogenation of carbonyl compounds consists of conversion to their pyridine-2-sulfIde derivatives, followed by oxidation (MCPBA), and by mild heat. ... 

A method for extraction of 2-cyclopentyl-cyclopentanone from polyamide 6.6 by MAE was developed to quantitate the amount of 2-cyclopentyl-cyclo-pentanone in the polyamide 6.6 samples [66] and to validate a MHS-SPME method for extraction of 2-cyclopentyl-cyclopentanone [67]. The method was optimized with respect to the type of solvent, extraction temperature, extraction time and sample-to-solvent ratio. Chloroform and methanol were evaluated as extracting solvents. After extraction at 90 °C for 30 min the highest recovery was achieved using methanol as a solvent. This is attributed to the better compatibility between polar polyamide 6.6 and polar methanol, which gives good swelHng of the polyamide 6.6 matrix and more effective extraction of analyte. The effect of extraction time on the recovery of 2-cyclopentyl-cyclopentanone was studied by extracting 1.0 g of... 

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