Cyclopent-l-en-3-one

Cyclopent-2-en-l-one, 2-hydroxy-3-methyl-synthesis, 3, 693 Cyclopentenone, 4-methoxy-formation, 1, 423 Cyclopenthiazide as diuretic, 1, 174 Cyclopent[2,3-d]isoxazol-4-one structure, 6, 975 Cyclophane conformation, 2, 115 photoelectron spectroscopy, 2, 140 [2,2]Cyclophane conformation, 2, 115 Cyclophanes nomenclature, 1, 27 Cyclophosphamide as pharmaceutical, 1, 157 reviews, 1, 496 Cyclopiloselloidin synthesis, 3, 743 Cyclopolymerization heterocycle-forming, 1, 292-293 6H-Cyclopropa[5a,6a]pyrazolo[l,5-a]pyrimidine pyrazoles from, 5, 285 Cydopropabenzopyran synthesis, 3, 700 Cyclopropachromenes synthesis, 3, 671 Cyclopropa[c]dnnolines synthesis, 7, 597 Cyclopropanation by carbenes... 

A hitherto unknown type of rearrangement of l-(l-alkynyl)cyclopropanols (321) to cyclopent-2-en-l-ones (322) mediated by octacarbonyldicobalt" and hexacarbonyldicobalt" complexes has been described. A possible pathway for the transformation is outlined in Scheme 101. A -proton transfer accompanied by a metal-mediated Stevens rearrangement, which converts a coordinated dimethylsulfane... 

Ruthenium amido complexes (137) effected asymmetric Michael addition of /S-keto esters (134) to cyclopent-2-en-l-one (135) to give quantitatively the corresponding Michael adducts (136) with excellent enantioselectivity (<97% ee), although with a 1 1 diastereoisomer ratio (Scheme 8). The stereochemical outcome of the reaction was significantly influenced by the structure of the catalysts (137) and /S-keto esters.170... 

Vuagnoux-d Augustin M, KeMi S, Alexakis A (2007) Enantioselective copper-catalyzed conjugate addition to 2- or 3-substituted cyclopent-2-en-l-ones construction of stereogenic quaternary carbon centers. Synlett 2057-2060... 

In the case of benzophenone, the cycloaddition competes with the isomerization of 103 to cycloheptatriene. Exclusive isomerization was observed with acetophenone and acetone. Carbonyl compounds with triplet energies lower than 69kcal/mol prefer the cycloaddition path. Cyclopent-2-en-l-one is an exception to this rule in spite of its triplet energy of 74 kcal/mol, 2 + 2 cycloadducts were formed rather efficiently. 

Kinetic resolution is operative in the reaction with 4-substituted cyclopent-2-en-l-ones. For instance, when 2 equiv. of racemic 4-(l-methyl-l-phenylethoxy)-2-cyclopentenone (79) is reacted with the carb-anion (78), (5)-(79) reacts to yield predominantly the product derived by approach of the carbanion from the si face of (79). The formation of the cis adduct probably results from the chelation of lithium counterion with the C-4 oxygen (equation 22). Kinetically selective resolution of a bicyclic enone (80) is also effected. On treatment of the carbanion of (/ )-(78) with racemic (80) (2 equiv.), an enantiomer of (82) and (5)-(80) are obtained in 80% and 45% yields respectively. Addition of the lithio derivative (2 equiv.) of... 

In Figure 6 a hypothetical pathway leading to 2-hydroxy-3-methyl-cyclopent-2-en-l-one (HMC) by a retro-Aldol condensation of 2 molecules of 2-oxopropanol or its tautomer, 2-hydroxypropanal, respectively, is shown. To prove that two carbon-3... 

D.82) 2-Cyclopenten-l-one, 2,3-dihydroxy-, 2,3-dihydroxy-cyclopent-2-en-l-one, reductic acid [80-72-8]... 

Cyclopent-2-en-l-ones. A mixture of 2.3 g. 5-(5-nitro-2-furyl)-2-methyl-4-ethyl-2-cw-4-tran5-pentadienal, 0.5 N HCl, and tetrahydrofuran heated 2 hrs. on a water bath -> 1.2 g. 2-(5-nitro-2-furyl)-3-ethyl-5-methylcyclopent-2-en-l-one. F. e. s. H. Saikadii, H. Ogawa, and K. Sato, Chem. Pharm. Bull. 77,1757 (1969). 

A -Heterocyclic carbenes (NHCs) 115 have proved to be efficient catalysts for the aza-MBH reaction of cyclopent-2-en-l-one or cyclohex-2-en-l-one with various A -tosylarylimines to give the aza-MBH adduct in high yields (Scheme 2.55). Crossover experiments show the NHC can add to At-tosylarylimines in a reversible manner, which allows the addition of NHC to cyclic enones and thus catalyzes the aza-MBH reaction. ... 

When we extended the activated olefins to cyclohept-2-en-l-one and cyclooct-2-en-l-one we found that the reaction is very complicated, because the Lewis bases, solvents and the ring-size of the cyclic enone can all significantly affect the MBH reaction rate and even the reaction product. The reaction of cyclohept-2-en-l-one with A-arylidene-4-methylbenzenesulfonamides afforded the usual MBH adducts 203 along with abnormal adducts 204, whereas the corresponding reaction of cyclooct-2-en-l-one provided different aldol products (205-207) depending upon the Lewis base employed (no MBH adduct was formed in any of the cases) (Scheme 2.104). Moreover, the formation of aldol products 209 along with the usual MBH adducts 208 has been observed in the reaction between cyclopent-2-en-l-one and aromatic aldehydes in the presence of BU3P (Scheme 2.105). 

In the MBH type reaction of chiral non-racemic A-sulfinimines 210 with cyclopent-2-en-l-one we found that, in the presence of a catalytic amount of dimethylphenylphosphine (PhPMc2), a diastereoselective reaction could be achieved in toluene at room temperature to give the normal MBH adducts 211 in good yields with high diastereoselectivities (Scheme 2.106). ... 

Fu et al modified Ikegami s procedure by converting air-sensitive trialkylphosphines into air-stable phosphonium salts, via protonation on phosphorus, which serve as an alternative catalyst to the corresponding phosphines (simple deprotonation under the reaction conditions by a Bronsted base liberates the trialkylphosphine) to perform the MBH reaction of cyclopent-2-en-l-one with 3-phenyl-l-propanal. The desired product was obtained with an isolated yield that is comparable to that furnished by Ikegami s procedure (Scheme 2.204). 

As stated before, the enantioselective MBH reaction of cyclopent-2-en-l-one with 3-phenyl-1-propanal resulted in low enantioselectivities (<10%) when using (i )-BINOL and tributylphosphine. However, better results have been achieved using calcium chiral catalyst 379 along with BU3P, with the desired adduct provided in 56% enantiomeric purity (Scheme 2.215). ... 

Cyclopent-2-en-l-ones. A suspension of 2-n-amyl-3-methylcyclopentan-2-ol-l-one propylene ketal in 25%-H2S04 refluxed 2 hrs. with stirring, then steam-distilled dihydrojasmone. Y 84%. J. L. E. Erickson and F. E. Gollins, Jr., J. Org. Ghem. 30, 1050 (1965). 

Draw the structures of cyclopent-2-en-l-one, cyclohex-2-en-l-one, cyclohex-3-en-l-one, 1-cyclohexene-l-carboxaldehyde, and 3-cyclohexene- 1-carboxaldehyde. 

Heating cyclopentene with LiAlH4 gives no reduction but heating it with cyclopent-2-en-l-one leads to reduction of both the C=C unit and the C=0 unit and formation of cyclopentanol as a major product. Explain this experimental fact. 

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