2.2- Dimethylcyclopentanone

The yields ranged from 55% for the mixture of enamines formed from morpholine and methylisopropyl ketone to 94% for the enamine formed from dimethylamine and methyl t-butyl ketone. The hindered ketone 2,5-dimethylcyclopentanone could be converted to an enamine, but the more hindered ketone, 2,6-di-t-butylcyclohexanone, was inert. White and Weingarten 43) attribute the effectiveness of titanium tetrachloride in this reaction to its ability to scavenge water and to polarize the carbonyl bond. 

Hydrocarboxyladon of olefins [I. 721-722, after citation of ref. 8]. Nickel carbonyl reacts with 1,5-dienes in the presence of dilute acid to form cyclic ketones rather than the expected mono- and dicarboxylic acids. Thus hexadiene-1,5 is converted in 70% yield into a mixture of 2,5-dimethylcyclopentanone and 2-methyl-cyclohexanone.83... 

The hydroboration of 1,3-dimethylcycloalkenes occurs cis to produce with exceptionally high stereospecificity [4], affording ds-2, co-dimethylcycloalkyl-9-BBN. These intermediates on treatment with alkaline hydrogen peroxide, followed by chromic acid oxidation [5] afford the corresponding cis-2-o)-di-methylcycloalkanones, which otherwise are difficult to prepare in pure form. Consequently, ds-2,5-dimethylcyclopentanone and ds-2,6-dimethylcyclohexa-none are prepared with excellent high isomeric purities and in essentially quantitative yields (Chart 7.4) [4]. 

Thus, Klemchuk [699] obtained from diallyl a mixture consisting of 2,4-dimethyl-cyclopentene-3-one and 2,5-dimethylcyclopentanone. 

Houk and co-workers examined the role of torsional effects in the stereoselectivity of enolate alkylation in five-membered rings, and their interpretation can explain the preference for C(5) alkylation syn to the 2-methyl group in trans-2,3-dimethylcyclopentanone.59... 

Fig. 1.4. Transition structures for syn and anti attack on the kinetic enolate of trans-2,3-dimethylcyclopentanone showing the staggered versus eclipsed nature of the newly forming bond. Reproduced from J. Am. Chem. Soc., 121, 5334 (1999), by permission of the American Chemical Society. 

Dimethylcyclopentanones have been prepared by acid-catalysed ring expansion of isopropenylcyclobutanols (Scheme 18).33... 

The integrity of the rhodium catalyst over the course of the reaction was confirmed by the observation that the optical yield was not a function of the percent conversion. Hydrolysis and chiral G.C. analysis of one mL aliquots taken at one minute intervals from a CH2CI2 solution of 2,2-dimethylcyclopentanone, diphenylsilane and the [(S-Binap)Rh(MDPP)2]+ catalyst revealed that the e.e. is invariant over the course of the reaction. Thus, at 26% conversion the optical yield was 69% e.e., the same as that obtained at 68% conversion, 100% conversion (30 minutes) and after stirring overnight. Further studies involved the addition of a second ketone and stoichiometric silane to the precatalyst to generate an active catalyst species followed by addition of the ketone of interest. Under the standard conditions (vide supra), acetophenone (1.0 mmol) was added to the catalyst followed by 1.0 mmol of diphenylsilane. The reaction mixture was stirred for 10 minutes after which time 2,2-dimethylcyclopentanone (100 mmol) and... 

Sodium hydride (18.42 mmol) was suspended in 50 ml THF cooled to 0°C, then treated with triethylphosphonoacetate (19.30 mmol), and stirred 15 minutes. The mixture was further treated with fran -3,4-dimethylcyclopentanone (17.54 mmol) dissolved in 10 ml 1M tetrabutylammonium fluoride in THF, then stirred 2 hours at ambient temperature. The solution was then partitioned between 200 ml diethyl ether and 150 ml water and the organic phase separated and washed with brine. The solution was then dried with MgS04 and concentrated. The residue was purified by flash chromatography with silica gel using EtOAc/heptane, 1 9, and the product isolated in 94% yield as a colorless oil. 

The nopol derivative (5) has advantages in some cases but the most striking advance has been the introduction of commercially available chloroborane (6). Compound (6) is a stronger Lewis acid than (4) or (5) and also less subject to steric hindrance. It readily reduces acetophenone (98% ee), 2,2-dimethylcyclopentanone (98% ee) and pinacolone (95% ee). ... 

A tandem aldol condensation-radical cyclization sequence has been developed for the preparation of functionalized bicyclo[3.3.0]octane systems [116]. Conjugate addition of Me2AlSePh to dimethylcyclopentanone (118) followed by trapping of the resulting enolate with aldehyde gave predominantly the trans, erythro aldol 119 this then underwent radical cyclization with BusSnH and catalytic AIBN yielding the bicyclic ketol 120 stereospecifically (Sch. 80). 

The results of the Bucherer-Bergs and Read reactions on cyclopentanones such as cis-bicyclo[3.3.0]octan-3-one and cis-3,4-dimethylcyclopentanone show a stereochemical course related to the preferred conformation of the cyclopentane rings.67 The stereochemical preferences of biased cyclopentanones are much less pronounced than those of biased cyclohexanones, but Edward s rule indicates trends. 

In 2000, Tanimori and coworkers also reported a method for synthesizing the spirosuccinimide moiety of asperparaline A (123) [95], as shown in Fig. (30). 2,2-Dimethylcyclopentanone (135) was treated with malononitrile in the presence of piperidine and benzoic acid to... 

The synthesis of triticonazole is only described in patents as a one-pot sequence [57] Knoevenagel condensation of 4-chlorobenzaldehyde on 2,2-dimethylcyclopentanone gives the a,) -unsaturated ketone, which enters a Corey-Chaykovsky epoxidation reaction to afford the epoxide which in turn is opened with the potassium salt of 1,2,4-triazole (Scheme 17.10). 

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