Morita-Baylis-Hillman reaction of masked 5-alkylidene-2-cyclopentenones: general entry to 5-alkylidene-2-(hydroxyalkyl)- 2-cyclopentenones

The reaction of masked 5-alkylidene-2-cyclopentenones with aldehydes catalyzed by tributylphosphine in the presence of phenol provided the corresponding Morita-Baylis-Hillman adducts, which were subjected to flash vacuum pyrolysis to afford 5-alkylidene-2-(hydroxyalkyl)-2-cyclopentenones.     

Intramolecular acylation of α-sulfinyl carbanion a new general route to 5-methylene-2-cyclopentenones

A convenient synthesis of 5-methylene-2-cyclopentenones including Methylenomycin B involving the intramolecular acylation of α-sulfinyl carbanion followed by methylation and pyrolysis is described.     

Unusual endoperoxide isomerizations: a convenient entry into 2-vinyl-2-cyclopentenones from saturated fulvene endoperoxides

An unusual peroxide base-promoted isomerization is uncovered. Saturated endoperoxides derived from fulvenes give rise to 2-vinyl-2-cyclopentenones upon treatment with DBU in CH₂Cl₂ in a one-pot reaction. This methodology is applied to a convenient synthesis of dihydrojasmone. Moreover, functional groups placed on the side chain at C-6 participate in the base-catalyzed isomerizations via conjugate attack at the enone moiety to give 2-cyclopentenones carrying oxygen heterocycles at C-2.     

Coupling of cyclopropylcarbene-chromium complex with ferrocenyl alkynes: synthesis of 5-ferrocenyl-5-hydroxy-2-cyclopentenones and 4-ferrocenyl-4-cyclopentene-1,3-diones

The coupling of ferrocenyl alkynes with cyclopropylcarbene-chromium complex leads to ferrocenyl-substituted 2-cyclopentenones with or without a hydroxy substituent, namely 4-cyclopentene-1,3-diones, 2-cyclobutenones, and α,β-unsaturated aldehydes in varying amounts. The reaction initially produces a cyclopentadienone intermediate, then to the double bond of which, bearing a ferrocenyl group, addition of water occurs to afford hydroxy-substituted 2-cyclopentenones. In all the products, the hydroxy group ends up α to the ferrocenyl moiety. In contrast, where no addition of water occurs, the alkenic bond is reduced to give 2-cyclopentenones. A secondary reaction product, namely 4-cyclopentene-1,3-dione, is formed by hydrolysis of the cyclopentadienone intermediates.     

Intramolecular acylation of α-sulfinyl carbanions with masked α,β-unsaturated esters: a general strategy to 5-alkylidene-2-cyclopentenones

A general method for the preparation of 5-alkylidene-2-cyclopentenones and their 2-phenylsulfanyl substituted derivatives, involving the intramolecular acylation of α-sulfinyl carbanions with cyclopentadiene-α,β-unsaturated esters as the key reaction followed by flash vacuum pyrolysis, is described. The reactions start from readily available Diels-Alder adducts, synthons of α-carbanions of α,β-unsaturated esters.     

Cyclopentanones—XVI : Prostaglandin synthesis involving catalytic hydrogenation of 2,3-dialkyl-4-hydroxy-2-cyclopentenones

2,3-Dialkyl-4-hydroxy-2-cyclopentenones with differently functionalised side chains yield predominantly all-cis 2,3-dialkyl-1-4,-dihydroxycyclopentanes on catalytic hydrogenation. Epimerisation at C-12 (PG numbering) leads to prostaglandin synthons. Influence of the side-chain functions on these reactions is described.     

The acylation of acetylenes with β, γ-unsaturated acid chlorides: a new sysnthesis of 5,5-disubstituted 2-cyclopentenones

The acylation of acetylenes with α,α-disubstituted, β,γ-unsaturated acid chlorides was found to lead to 5,5-disubstituted 2-cyclopentenones bya novel intramolecular cyclization-rearrangement process.     

Prostanoids. LXXVIII. New sp2-Functionalized 4-Hydroxy-2-cyclopentenones from 6,7-Dichloro-1,4-dioxaspiro[4.4]non-6-en-8-one

Readily accessible 6,7-dichloro-1,4-dioxaspiro[4.4]non-6-en-8-one was converted into 2,3-dichloro-, 2-ethylthio-, and 3-chloro-2-ethylthio-4-hydroxy-2-cyclopentenones.     

A novel synthesis, including asymmetric synthesis, of 2,4,4-trisubstituted 2-cyclopentenones based on the reaction of 1-chlorovinyl p-tolyl sulfoxides with acetonitrile and its homologues

Reaction of 1-chlorovinyl p-tolyl sulfoxides, which were synthesized from chloromethyl p-tolyl sulfoxide and ketones in high overall yields, with cyanomethyllithium (lithium α-carbanion of acetonitrile) gave adducts in high to quantitative yields. The adducts were treated with LDA followed by lithium α-carbanion of the homologues of acetonitrile to give 3,5,5-trisubstituted enaminonitriles in good to high yields. Hydrolysis of the enaminonitriles under acidic conditions gave 2,4,4-trisubstituted 2-cyclopentenones in good yields. By using the optically active chloromethyl p-tolyl sulfoxide and unsymmetrical ketones, this procedure gave the optically pure 2,4,4-trisubstituted 2-cyclopentenones. The scope and limitations of this method and the mechanism of the reactions are also discussed. These procedures offer a new and effective method for the synthesis of 2,4,4-trisubstituted 2-cyclopentenones from four components, ketones, chloromethyl p-tolyl sulfoxide, acetonitrile, and its homologues.     

Cyclopentanones—XVIII : The lithium-liquid ammonia reduction of some 2,3-dialkyl-(4-hydroxy)-2-cyclopentenones. the importance of the protonation of intermediate enolate anions on the stereochemical outcome

The stereochemical outcome of the lithium-liquid ammonia reduction of 2,3-dialkyl-4-hydroxy-2-cyclopentenones and 2,3-dialkyl-2-cyclopentenones possessing bulky substituents (i-propyl and t-butyl) is investigated, using different proton donors. The relative configuration of both alkyl groups in the reduction products is interpreted on the basis of the geometry of the transition state for protonation of the intermediate enolate anions formed during the reduction     

Reactions of 2,3-Dichloro- and 2,3,5-Trichloro-4,4-ethylenedioxy-2-cyclopentenones with Some O-, S-, and N-Nucleophiles

2,3-Dichloro- and 2,3,5-trichloro-4,4-ethylenedioxy-2-cyclopentenones react with allyl and benzyl alcoholates and thiolates and benzylamine to give products resulting from Ad_NE substitution of the 3-chlorine atom, [1,3]-sigmatropic rearrangement, and cleavage of the C¹-C² bond.     

Cyclopentanones—VIII : Stereochemistry of the lithium-liquid ammonia reduction of 2,3-dialkyl-4-hydroxy-2-cyclopentenones

2,3-Dialkyl-1,4-cyclopentanediols are obtained by lithium-liquidammonia-alcohol reduction of 2,3-dialkyl-4-hydroxy-2-cyclopentenones. The configuration of the diastereoisomers formed was proved by ¹H-NMR spectroscopy and by chemical evidence. In the most abundant isomer the alkyl groups are trans and each is in trans position to the vicinal hydroxyl function. In another diastereoisomer formed in substantial amount the alkyl groups have a cis orientation and are trans to the vicinal hydroxyl function. The ¹H-NMR parameters found are more useful generally for configurational assignments to synthetic and modified prostaglandins.     

Asymmetric synthesis of 4,4-disubstituted 2-cyclopentenones from optically active 1-chlorovinyl p-tolyl sulfoxides and cyanomethyllithium with formation of a quaternary chiral center

Treatment of optically active 1-chlorovinyl p-tolyl sulfoxides having two different substituents at the 2-position, which were synthesized from unsymmetrical ketones and (R)-(−)-chloromethyl p-tolyl sulfoxide in three steps, with cyanomethyllithium gave optically active 2-amino-1-cyano-5,5-disubstituted-1,3-cyclopentadienes with very high asymmetric induction from the sulfoxide chiral center. The products were converted to the enantiomerically pure 4,4-disubstituted 2-cyclopentenones by heating with phosphoric acid in acetic acid.     

Palladium-catalyzed carbonylative cyclization of unsaturated aryl iodides and dienyl triflates,iodides, and bromides to indanones and 2-cyclopentenones

Indanones and 2-cyclopentenones have been successfully prepared in good to excellent yields by the palladium-catalyzed carbonylative cyclization of unsaturated aryl iodides and dienyl triflates, iodides, and bromides, respectively. The best results are obtained by employing 10 mol % of Pd(OAc)(2), 2 equiv of pyridine, 1 equiv of n-Bu(4)NCl, 1 atm of CO, a reaction temperature of 100 degrees C, and DMF as the solvent. This carbonylative cyclization is particularly effective on substrates that contain a terminal olefin. The proposed mechanism for this annulation includes (1) Pd(OAc)(2) reduction to the active palladium(0) catalyst, (2) oxidative addition of the organic halide or triflate to Pd(0), (3) coordination and insertion of carbon monoxide to produce an acylpalladium intermediate, (4) acylpalladation of the neighboring carbon-carbon double bond, (5) reversible palladium beta-hydride elimination and re-addition to form a palladium enolate, and (6) protonation by H(2)O to produce the indanone or 2-cyclopentenone.     

A novel synthesis of 2,4,4-trisubstituted 2-cyclopentenones by consecutive reaction of 1-chlorovinyl p-tolyl sulfoxides with acetonitrile and its homologues

1-Chlorovinyl p-tolyl sulfoxides were synthesized from several kinds of ketones and chloromethyl p-tolyl sulfoxide in three steps in high overall yields. Treatment of the 1-chlorovinyl p-tolyl sulfoxides with cyanomethyllithium (lithium α-carbanion of acetonitrile) at low temperature gave the adducts in almost quantitative yields. The adducts were then treated with LDA followed by excess lithium α-carbanion of the homologues of acetonitrile to afford 3,5,5-trisubstituted cyclopentadienyl enaminonitriles, which were hydrolyzed and heated under acidic conditions to give 2,4,4-trisubstituted 2-cyclopentenones in good overall yields.     

A (π2 + π2) photocycloaddition reaction as a facile route to angularly substituted cis-hydrindanes and cis-decalanes

The photochemical addition of 1,2-bis(trimethylsiloxy) cyclobutene to, respectively, 2-cyclopentenones and 2-cyclohexenones represents a novel and facile entry into angularly substituted bicyclo[4.3.0]nona-2,5-diones and bicyclo-[4.4.0]deca-2,5-diones.     

Tricarbonylcyclohexadienyliron complexes : synthetic equivalents of aryl cations; a facile synthesis of 2-aryl-cyclopentenones and its application towards prostaglandin analogues

Tricarbonylcyclohexadienyliron cations of type 1 are converted, by alkylation with 1,2-bis(trimethylsiloxy)-1-cyclopentene, dehydration and subsequent dehydrogenation, into specifically substituted 2-aryl-2-cyclopentenones.     

Die Acylierung von Acetylenen mit β, γ-ungesättigten Säurechloriden. Eine neue Synthese von 5-Cyclopentenonen

The Acylation of Acetylenes with β,γ-Unsaturated Acid Chlorides, A New Synthesis of 5-Substituted 2-Cyclopentenones The acylation of acetylenes with α,α-disubstituted, β,γ-unsaturated acid chlorides under Friedel-Crafts-type conditions leads to 5-substituted 2-cyclopentenones. Phenols are formed with β,γ-unsaturated acid chlorides bearing at least one α-H-atom. These transformations are explained by the intramolecular cyclization of the initially formed vinyl cation, which, in the cases of α,α-disubstituted acid chlorides, is followed by ring contraction. The reaction leading to 2-cyclopentenones is applied to the synthesis of some spiro[4.4]nona- and spiro[4.5]deca-2,6-dienones.     

Notiz über die Verwendung von 3-(Arylsulfonyl)-2-cycloalkenonen als 2-Cycloalkinon-Synthese-Equivalente

Note on the Use of 3-(Arylsulfonyl)-2-cycloalkenones as Synthesis Equivalents of 2-Cycloalkynones 3-(Arylsulfonyl)-2-cyclopentenones and 3-phenylsulfonyl-2-cyclohexnone undergo Diels-Alder reactions with cyclopentadiene. Elimination of arylsulfinic acid leads to products, which would have been obtained directly from a Diels-Alder reaction of 2-cyclopentynone or 2-cyclohexynone.     

Intramolecular acylation of α-sulfinyl carbanion: A new general route to 5-substituted Δ2 cyclopentenones

A general method for the preparation of 5-substituted Δ²-cyclopentenones $\text{via}$ the intramolecular acylation of $\text{αot}$-sulfinyl carbanions has been demonstrated.