2- cyclopentanone

Ibuki has found unsaturated hydrocarbons and CO, as well as traces of saturated hydrocarbons and H2 among the products of the reaction between 530 and 550 °C. Johnson and Walters have detected H2, CO, C2H4 and C4H8 besides other saturated and unsaturated hydrocarbons in the range 488-543 °C. In addition, the formation of 2-cyclopenten-l-one was also observed. On the basis of the analytical results the following overall processes were postulated 

The decomposition is homogeneous. The rate of disappearance of cyclopentanone shows an induction period and cannot be described by a definite reaction order. The shapes of the concentration-time curves indicate acceleration by the products, most probably the olefinic ones. 

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A solution of 0.21 mol of butyllithium in about 140 ml of hexane (note 1) was cooled below -40°C and 90 ml of dry THF ivere run in. Subsequently a cold (< -20 C) solution of 0.25 nol of propyne in 20 ml of dry THF was added with cooling below -20°C and a white precipitate was formed. A solution of 0.10 mol of anhydrous (note 2) lithium bromide in 30 ml of THF was added, followed by 0.20 mol of freshly distilled cyclopentanone or cyclohexanone, all at -30°C. The precipitate had disappeared almost completely after 20 min. The cooling bath was then removed and when the temperature had reached 0°C, the mixture was hydrolyzed by addition of 100 ml of a solution of 20 g of NHi,Cl in water. After shaking and separation of the layers four extractions with diethyl ether were carried out. The extracts were dried over magnesium sulfate and the solvents removed by evaporation in a water--pump vacuum. Careful distillation of the remaining liquids afforded the following... 

Within the cubane synthesis the initially produced cyclobutadiene moiety (see p. 329) is only stable as an iron(O) complex (M. Avram, 1964 G.F. Emerson, 1965 M.P. Cava, 1967). When this complex is destroyed by oxidation with cerium(lV) in the presence of a dienophilic quinone derivative, the cycloaddition takes place immediately. Irradiation leads to a further cyclobutane ring closure. The cubane synthesis also exemplifies another general approach to cyclobutane derivatives. This starts with cyclopentanone or cyclohexane-dione derivatives which are brominated and treated with strong base. A Favorskii rearrangement then leads to ring contraction (J.C. Barborak, 1966). 

Cydopentane reagents used in synthesis are usually derived from cyclopentanone (R.A. Ellison, 1973). Classically they are made by base-catalyzed intramolecular aldol or ester condensations (see also p. 55). An important example is 2-methylcydopentane-l,3-dione. It is synthesized by intramolecular acylation of diethyl propionylsucdnate dianion followed by saponification and decarboxylation. This cyclization only worked with potassium t-butoxide in boiling xylene (R. Bucourt, 1965). Faster routes to this diketone start with succinic acid or its anhydride. A Friedel-Crafts acylation with 2-acetoxy-2-butene in nitrobenzene or with pro-pionyl chloride in nitromethane leads to acylated adducts, which are deacylated in aqueous acids (V.J. Grenda, 1967 L.E. Schick, 1969). A new promising route to substituted cyclopent-2-enones makes use of intermediate 5-nitro-l,3-diones (D. Seebach, 1977). 

Some straightforward, efficient cyclopentanellation procedures were developed recently. Addition of a malonic ester anion to a cyclopropane-1,1-dicarboxylic ester followed by a Dieckmann condensation (S. Danishefsky, 1974) or addition of iJ-ketoester anions to a (l-phenylthiocyclopropyl)phosphonium cation followed by intramolecular Wittig reaction (J.P, Marino. 1975) produced cyclopentanones. Another procedure starts with a (2 + 21-cycloaddition of dichloroketene to alkenes followed by regioselective ring expansion with diazomethane. The resulting 2,2-dichlorocyclopentanones can be converted to a large variety of cyclopentane derivatives (A.E. Greene. 1979 J.-P. Deprds, 1980). 

Keto acids are obtained by acylation of cyclopentanone enamines (see p. I3f.) with acid chlorides and subsequent base-catalyzed mro-aldol cleavage (S. Hdnig, 1960). 

Chlorophyll a (L.P. Vernon, 1966) contains an unsymmetrical porphyrin chromophore with two special features the double bond between C-17 and C-18 is hydrogenated and carhon atoms 13 and 15 hear a carboxylated, isocyclic cyclopentanone ting E. 

A conceptually surprising and new route to prostaglandins was found and evaluated by C.R. Johnson in 1988. It involves the simple idea to add alkenylcopper reagents stereo-selectively to a protected chiral 4,5-dihydroxy-2-cyclopenten-l-one and to complete the synthesis of the trisubstituted cyclopentanone by stereoselective allylation of the resulting enolate. 

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]... 

The prochiral meso form of 2-cyclopenlen-1,4-diol (101) reacts with the (Z)-alkenyl iodide 102 to give the 3-substituted cyclopentanone 103 with nearly complete diastereoselectivity (98 2)[92], The reaction is used for the synthesis of prostaglandin. The alkenyl iodide 102 must be in the Z form in order to obtain the high diastereoselectivity. The selectivity is low when the corresponding (Z)-alkenyl iodide is used[93]. 

The Pd(0)-catalyzed rearrangement of the iV-allylenamine 800 in CF3CO2H affords the (5, -unsaturated imine 801, which is hydrolyzed to give the 7, 8-unsaturated aldehyde 802[498]. The vinyloxaspirohexane 803 undergoes rearrangement-ring expansion to give the cyclopentanone 804 in the presence of 1 equiv. of p-nitrophenol[499]. 

Asymmetric dimerization with cyclopentanone-2-carboxylate using BPPM as a chiral ligand gave the telomer in 41% eefSS]. 

Repeat the preceding problem for cyclopentanone instead of propanal... 

Only the a hydrogens are replaced by deuterium m this reaction The key intermediate IS the enolate ion formed by proton abstraction from the a carbon atom of cyclopen tanone Transfer of deuterium from the solvent D2O to the enolate gives cyclopentanone containing a deuterium atom m place of one of the hydrogens at the a carbon... 

Show how you could prepare each of the following compounds from cyclopentanone D2O and any necessary organic or inorganic reagents... 

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