2-Cyclopentenyl ketone

Coupling. Allylic carbonylation and coupling with boronic acids transform 2,3-diaza-bicyclo[2.2.1]hept-5-enes into 5-hydrazinyl-2-cyclopentenyl ketones. ... 

Cyclopentenyl ketones can undergo photoarylation when irradiated in the presence of a Lewis acid catalyst (3.25) 340). 

A one-step method for the preparation of 2/7-l-pyrindin-2-one derivatives involves a novel modification of the well-known amine-catalyzed condensation of acrylonitrile and ketones. In this procedure the reactants are treated with aqueous ammonium hydroxide solutions.92 95 97,114 117 133 134 Similarly, heating crude 2-diethylamino-ethyl 1-cyclopentenyl ketone (199) with 36% aqueous methylamine or 25% ammonium hydroxide in dioxane gives 1-methylperhydro-4-... 

The intramolecular chemical titration is conceptually and experimentally simple and convenient, but it requires that a particular dioxetane must be made that chemi-energizes the photochemically active carbonyl product K. This is usually a formidable and challenging synthetic problem. Representative intramolecularly chemienergized photochemical transformations include Norrish Type I cleavage (Eq. 44), Norrish Type II (Eq. 45a, b, c) cleavages, cyclohexadienone rearrangement (Eq. 46), and cyclopentenyl ketone rearrangement (Eq. 47). 

The further reactions of the Y(C6 0)D0 radical are more complex and result in several important products through several paths. One of these paths include the ring opening and the unzipping of the non cyclic radical to the formation of two acetylenes, CO and HC =0. The other paths result in the formation of a cyclopentenyl ketone formaldehyde radical, and to the cyclopentadienyl radical + CO2 channel. Kinetic parameters for important product channels are reported and a reduced mechanism is proposed. 

The thermal isomerization of 5-acetyl-5-methylbicyclo[2,l,0]pentane (494) has been the subject of a detailed kinetic study. Rates and activation parameters have been determined for all the processes. The exo-endo interconversion and the rearrangement to the cyclopentene (495) evidently do not involve a common intermediate. The activation parameters for the rearrangement to cyclopentenyl ketone, AH = 22.2 kcal mol and AS = - 33.0 cal K mol are indicative of a highly ordered transition state and suggest that the cyclopropyl-allylic rearrangement is an electrocyclic process. 

Nickel-catalyzed [3+2] annulation of cyclopropyl ketones with alkynes in the presence of Mc2AlCl gave cyclopentenyl ketones (Scheme 2.83) [137]. 

The reaction of alkenyl iodides or triflates, alkenylstannanes, and CO affords divinyl ketones[397,398]. Thus the capnellene skeleton 538 has been synthesized by the carbonylation of the cyclopentenyl triflate 536 with the alkenyltin 537[392], The macrocyclic divinyl ketone 540 has been prepared in a moderate yield by the carbonylative cyclization of 539[399]. 

Upon treatment of a divinyl ketone 1 with a protic acid or a Lewis acid, an electrocyclic ring closure can take place to yield a cyclopentenone 3. This reaction is called the Nazarov cyclization Protonation at the carbonyl oxygen of the divinyl ketone 1 leads to formation of a hydroxypentadienyl cation 2, which can undergo a thermally allowed, conrotatory electrocyclic ring closure reaction to give a cyclopentenyl cation 4. Through subsequent loss of a proton a mixture of isomeric cyclopentenones 5 and 6 is obtained ... 

Prins reaction, heteropolyacid catalysis, 41 156 Probe molecules, 42 119 acidic dissociation constant, 38 210 NMR solid acidity studies, 42 139-140 acylium ions, 42 139, 160 aldehydes, 42 162-163 alkyl carbenium ions, 42 154-157 allyl cation, 42 143-144 ammonia, 42 172-174 arenium ions, 42 150-154 carbonium ions, 42 157-160 chalcogenenonium ions, 42 161-162 cyclopentenyl cations, 42 140-143 indanyl cations, 42 144-147 ketones, 42 162,163-165 nitrogen-containing compounds, 42 165-170... 

Cyclohexene, see Cyclohexene Cyclohexyl alcohol, see Cyclohexanol Cyclohexyl ketone, see Cyclohexanone Cyclohexylmethane, see Methylcyclohexane Cyclopenta-1,3-diene, see Cyclopentadiene 1,3-Cyclopentadiene, see Cyclopentadiene Cyclopentamethylene, see Cyclopentane Cyclopenta[(/,e]naphthalene. see Acenaphthylene Cyclopenten, see Cyclopentene Cyclopentenyl, see Cyclopentene... 

Acylation with cyclopentenyl- or cyclohexenylacetyl chloride gave three-membered ring systems.113 114 An interesting example is the reaction of ethylene with acid chlorides complexed with excess A1C13 to give the 17 p.y-unsaturated ketones 115... 

Coordination to the ketone makes it more of a carbocation, and hence the conjugated system more of a pentadienyl cation 4.90. The cyclization takes place to give the cyclopentenyl cation 4.91, which loses the silyl group and picks up a proton to give the ketone 4.92. The relative stereochemistry at C-l and C-5 has the two hydrogen atoms trans, proving that the cyclization has... 

Cycloalkenyllithiums.3 Alkenyllithiums are usually prepared by reductive lithiation of trisylhydrazones of ketones with butyllithium, but this method fails with the hydrazones of cyclic ketones. However, the cycloalkenyl sulfides, prepared by reaction of cyclic ketones with thiophenol, can be reductively lithiated with LDBB at -78°. This lithiation fails in the case of cyclopentenyl sulfides, but is useful in the case of the vinyl sulfides obtained from 6-, 7-, and 8-membered cycloalkanones. 

The ketone IR absorption of 3-methyl-2-cyclohexenone occurs near 1690 cm-1 because the double bond is next to the ketone group. The ketone IR absorption of 3-cyclopentenyl methyl ketone occurs near 1715 cm-1, the usual position for ketone absorption. 

As shown for the transformations of the cyclopentenyl methyl ketones (3a-d) to mixtures of (4a-d) and (5a-d) (Scheme 1), the ODPM rearrangement occurs from the lowest electronically excited p,y-enone triplet state. - The ir. ir configuration has been assigned to this state on the basis of CNDO-MO calculations, phosphorescence studies at 77 and mechanistic examinations. The phosphorescence data together with sensitization experiments have revealed a Ti energy range of 289-310 kJ mol (4.18 kJ = 1.0 kcal) for (3a-c) and a much lower Ti of 253 kJ mol for (3d). ... 

Beyond the disrotatory or conrotatory stereochemical imperative which must accompany all Nazarov cyclizations there exists a secondary stereochemical feature. This feature arises because of the duality of allowed electrocyclization pathways. When the divinyl ketone is chiral the two pathways lead to dia-stereomers. The nature of the relationship between the newly created centers and preexisting centers depends upon the location of the cyclopentenone double bond. The placement of this double bond is established after the electrocyclization by proton loss from the cyclopentenyl cation (equation 5). Loss of H, H or in this instance generates three tautomeric products. The lack of control in this event is a drawback of the classical cyclization. Normally, the double bond occupies the most substituted position corresponding to a Saytzeff process. The issue of stereoselection with chiral divinyl ketones is iUustrated in Scheme 7. The sense of rotation is defined by clockwise (R) or counterclockwise (5) viewing down the C—O bond. Thus, depending on the placement of the double bond, the newly created center may be proximal or distal to the preexisting center. If = H the double bond must reside in a less substituted environment to establish stereoselectivity. 

Note that (5) can also be obtained in 35% yield by irradiation for 125 min. of l-cyclopentenyl isobutyl ketone (6). ... 

Cyclopentanecarboxaldehyde, 493 Cyclopentanecarboxylic add, 494,495 Cydopentanone, 139, 214,445, 551 Cydopentene, 319 Cydopentene epoxide, 404 2-Cyclopentenone, 158, 227, 262, 511 2-Cyclopentenones, 218 Cyclopentenone thioketals, 218 1-Cyclopentenyl isobutyl ketone, 512 Cyclopentyne, 209 Cyclopropanation, 153 Cyclopropanecarboxaldehyde, 43,44, 520-521... 

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