Cyclopentanone—continued

It is often said that the property of acidity is manifest only in the presence of a base, and NMR studies of probe molecules became common following studies of amines by Ellis [4] and Maciel [5, 6] and phosphines by Lunsford [7] in the early to mid 80s. More recently, the maturation of variable temperature MAS NMR has permitted the study of reactive probe molecules which are revealing not only in themselves but also in the intermediates and products that they form on the solid acid. We carried out detailed studies of aldol reactions in zeolites beginning with the early 1993 report of the synthesis of crotonaldehyde from acetaldehyde in HZSM-5 [8] and continuing through investigations of acetone, cyclopentanone [9] and propanal [10], The formation of mesityl oxide 1, from dimerization and dehydration of... 

Continuing with the diastereomerically pure tricycle 56, an 11-step sequence consisting of redox and protective group chemistry was necessary to generate a / -hydroxy keton (58) suitable for a retro-aldol addition via an intermediate alkoxide to the highly substituted cyclopentanone 52 (Scheme 6). 

However, palladium and nickel catalyzed versions promise, at the moment, an even wider range of possibilities. The need to maintain the catalytic cycle by continuous regeneration of the zerovalent metal catalyst limits, nevertheless, the functionalizability of the metallated center in the cyclized intermediate. For the same reason, the readily accessible starting materials may contain various functional groups which are compatible with the reaction conditions and which may be of value for the syntheses of complex heterocycles such as alkaloids. Carbon monoxide insertion reactions of the cyclized a-metal intermediates were shown to afford monocyclic methyl carboxylates and/or annulated cyclopentanones (cyclopentenones) with concomitant stereocontrolled formation of up to four carbon-carbm bonds. 

X -.".e third case, cyclopentanone has self-condensed and ignored the enone to which it was to add in a conjugate fashion and continue with a Robinson annelation (p. 761). The liiis - - again is to use a specific enolate such as an enamine though the simplest here is a keto-ester can be easily prepared by intramolecular Claisen ester condensation (p. 727). 

B) Preparation of Cyclopentanone (M.). Arrange a 250-ml distilling flask for downward distillation. The thermometer is so placed that it nearly touches the bottom of the distilling flask. Place in the flask 25 g of finely pulverized adipic acid and 3 g of finely ground barium hydroxide. Shake the flask so as to mix the contents, then insert the thermometer, and connect the flask with an air condenser. By means of a free flame heat the flask to 285-290°. The burner is moved to and fro so that the heat is directed at all sides of the flask. When the mixture has melted, adjust the flame so that the temperature remains at about 290°. If the temperature is allowed to rise above 295°, adipic acid distills over and the condenser becomes clogged. Continue the distillation until only a small residue remains in the flask. Transfer the distillate into a separatory funnel and add 10 ml of saturated salt solution and 10 ml of 5 per cent sodium bicarbonate solution. Shake cautiously and remove the ketone layer. Dry with 2-3 g of calcium chloride and distill. The yield is 14-18 g. 

Oscillating chemical reactions continue to be investigated in sulphate media. Addition of a-monobromo-ketone, one of the products of the BrO 3-Ce v-cyclohexanone and Br03 -Ce -cyclopentanone systems has been shown to decrease and, in some instances, suppress the initial induction period. The inhibitory effects of Cl ions have also been described. In the gallic acid-bromate reaction catalysed by [Fe(phen)3]+/ + the enol is the reactive form of the organic substrate. The mechanism proposed is essentially that of... 

The photochemical cycloaddition of azirine 35 with cyclopentanone has been found to depend on the experimental conditions. When 35 is irradiated and cyclopentanone is slowly added, the expected s/ /ro-S-oxazoline 53 is the main productHowever, when the cyclopentanone is irradiated first and the irradiation is continued in the presence of azirine 35, the sole product is 3-oxazoline 54. Under the latter conditions, cyclopentanone reacts first by a Norrish type I cleavage and hydrogen transfer to yield 4-pentenal. This aldehyde reacts faster with the nitrile ylide than does the cyclic ketone still present, so that only 54 is formed. Norcamphor and camphor also react with azirine 35 under photolytic conditions via the Norrish type I reaction route to give 3-oxazolines 55 and 56. 

When the halogen is axial in a-halocyclohexanones or a-cyclopentanones the formation of the zwitterion is favored. This process is apparently very sensitive to solvation and to ring strain. This interpretation is in agreement with the behavior of several a-haloketone derivatives in the bicyclo[3.1.1]heptane, bicyclo[3.2.1]octane, and bicyclo[4.1.1]octane series under basic conditions where the ring strain can be continuously varied. ... 

Cyclic compounds continue to find use as chain extenders. 5-Methylcyclo-hexane-l,3-dione has been used for the synthesis of 3-methyl- and 3,6-di-methyl-tridecanoic ester, and the enamine synthesis, usually utilizing cyclopentanone or cyclohexanone, has been extended to the use of cyclo-decanone and cyclododecanone. Reaction occurs through a cyclobutanone... 

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