Cyclopentene Annulation Research Articles

New Cationic Olefin Cyclization—Pinacol Reactions. Ring‐Expanding Cyclopentane Annulations that Directly Install Useful Functionality in the Cyclopentane Ring.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Stereoselective Synthesis of Carbocyclic Ring Systems by Pinacol‐Terminated Prins Cyclizations.

AbstractFor Abstract see ChemInform Abstract in Full Text.

An efficient method for cyclopentene annulation onto alpha,beta-unsaturated ketones: W(CO)(5)(L)-catalyzed 5-endo-dig cyclization of 6-siloxy-5-en-1-ynes.

[reaction: see text] A highly efficient method for the cyclopentene annulation onto alpha,beta-unsaturated ketones is described. Indium-mediated 1,4-propargylation onto alpha,beta-unsaturated ketones in the presence of tert-butyldimethylsilyl triflate and dimethyl sulfide gives the 6-siloxy-5-en-1-yne derivatives, which undergo W(CO)(5)(L)-catalyzed 5-endo-dig cyclization to give the corresponding cyclopentene derivatives in good yield.

New cationic olefin cyclization-pinacol reactions. Ring-expanding cyclopentane annulations that directly install useful functionality in the cyclopentane ring.

Two new tandem cationic olefin cyclization-pinacol reactions that provide cyclopentane-fused cycloalkanone products are described. Treatment of cis-1-[2-alkenyl-2-(triethylsiloxy)cycloalkyl]but-3-en-2-ol derivatives 21-24 with triflic anhydride at -78 degrees C affords cycloalkanones 31-34 in 54-90% yields with diastereoselectivities of typically >20:1. In this unusual transformation, the starting cycloalkanone is ring-expanded and fused to a 2-alkenylcyclopentane fragment. Reaction of cis-(2-siloxy-2-alkenylcycloalkyl)pyrrolidin-1-ylethanones 15-17 with triflic anhydride and 2,6-di-tert-butyl-4-methylpyridine (DTBMP) at -20 to +65 degrees C followed by hydrolysis of the intermediate iminium salts 64 with aqueous KHCO(3) affords cycloalkanediones 46-48 in moderate yield and high diastereoselectivity (>20:1). These are the first examples of ring-expanding cyclopentane annulations that directly introduce a carbon side chain or carbonyl functionality at the cyclopentane C2 position. The high diastereoselectivities observed in these reactions are believed to arise from reaction through highly organized cyclic transition states.

Stereoselective synthesis of carbocyclic ring systems by pinacol-terminated Prins cyclizations

Studies that expand the scope of the Prins-pinacol synthesis of carbocyclic ring systems are described. The construction of cyclopentacyclooctanones by ring-enlarging cyclopentane annulations of cycloheptanone precursors is broadly examined as is the synthesis of related bicyclic ketones containing larger rings. Prins-pinacol reactions of acyclic alkenyl acetals were examined to gain insight into intrinsic stereochemical control elements in ring-enlarging cyclopentane annulations. The outcome of the carbocyclic constructions described in this report are rationalized by the mechanistic analysis we developed recently to describe Prins-pinacol constructions of tetrahydrofurans.

Formal total synthesis of the trinorguaiane sesquiterpenes (+/−)-clavukerin A and (+/−)-isoclavukerin

A formal total synthesis of racemic (+/−)-clavukerin A and (+/−)-isoclavukerin from 4-methylcyclohept-2-en-1-one is presented. The key step involved a Danheiser (trimethylsilyl)cyclopentene annulation.

Intramolecular C-H insertion reactions of (eta(5)-cyclopentadienyl)dicarbonyliron carbene complexes: scope of the reactions and application to the synthesis of (+/-)-sterpurene and (+/-)-pentalenene.

(eta(5)-Cyclopentadienyl)dicarbonyliron carbene complexes, [(eta(5)-C(5)H(5))(CO)(2)Fe=CHR](+)BF(4)(-), are generated as reactive intermediates from thioether derivatives, (eta(5)-C(5)H(5))(CO)(2)FeCH(R)SPh, by S-alkylation with trimethyloxonium tetrafluoroborate and loss of thioanisole. The carbene complexes undergo intramolecular C-H insertion into appropriately situated side chains to form cyclopentane derivatives. The reaction has been developed into a general procedure employing cycloalkanones as scaffolds bearing the iron carbene moieties and the side chains at C(2) and C(3), respectively. The products of the intramolecular insertion reactions are substituted bicyclo[n.3.0]alkanones. The scope and limitations of the reaction are described. The reaction is applied to a total synthesis of sterpurene and to a formal synthesis of pentalenene. Overall, this approach to cyclopentane annulation complements the related metal-catalyzed insertion reactions of diazocarbonyl compounds, which are also believed to occur via metal carbene complexes.

ChemInform Abstract: Functionalized Allylsilanes from Silylcopper Reagents and Allene. A Useful Strategy for Cyclopentane Annulations.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Functionalised Allylsilanes from Silylcopper Reagents and Allene. A Useful Strategy for Cyclopentane Annulations

Silylcupration of allene using phenyldimethylsilylcopper or t-butyldiphenylsilylcopper followed by reaction with α,β-unsaturated acyl chlorides, aldehydes or ketones affords allylsilane-containing divinyl ketones and oxoallylsilanes, respectively. They undergo highly stereocontrolled silicon-assisted intramolecular cyclizations when treated with protic or Lewis acid leading to cyclopentane ring-formation.

ChemInform Abstract: Iridoids from Carbohydrates via Pauson—Khand Cyclopentane Annulation Mediated Strategies: Preliminary Studies.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Iridoids from Carbohydrates via Pauson–Khand Cyclopentane Annulation Mediated Strategies: Preliminary Studies

The Pauson–Khand reaction on suitable carbohydrate derivatives obtained from L-arabinose gives annulated pyranosides that can be transformed into advanced synthetic intermediates for the synthesis of iridoid aglycones. Preliminary studies towards this end are described.

ChemInform Abstract: A Simple Route to Cyclopentane Annulation.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

A simple route to cyclopentane annulation

We have developed a simple method for cyclopentane annulation using inexpensive reagents which is useful for the synthesis of polyquinane systems.

New Aspects of Vinylsulfide Chemistry.

By utilizing the characteristic features of vinylsulfides, 2- (alkylthio) allyl silyl ethers were designed as efficient ene substrates, and their use led to exploration of general carbonyl and imine ene reactions. By using 3- (alkylthio) -2-siloxyallyl acetates, a useful [3 + 2] cyclopentane annulation methodology was developed. Further, a tandem C-C bond formation/cleavage methodology was also designed.

ChemInform Abstract: A Novel Cyclopentane Annulation by (3 + 2) Cycloaddition of Substituted Methylenecyclopropyl Ketones with Allyltrimethylsilane.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

A novel cyclopentane annulation by [3+2] cycloaddition of substituted methylenecyclopropyl ketones with allyltrimethylsilane

Reaction of subtituted methylenecyclopropyl ketones with allyltrimethylsilane affords functionalized methylene or alkylidenecyclopentanes in good yield via a TiCl 4 mediated cleavage of the carbocycle followed by a [3+2] cycloaddition of the resultant 1,3-zwitterion with allyltrimethylsilane which acts as the 1,2-partner.

Stereochemical course of the allylsilane based cyclopentane annulation

Allylsilanes function as three-carbon components in a highly stereoselective [3+2] annulation strategy for the synthesis of tri- and tetrasubstituted five-membered carbocycles.

Conjugate addition reactions of chiral (E)-crotylsilanes: application to an asymmetric [3 + 2] cyclopentane annulation

Functionalized (E)-crotysilanes 1 undergo Lewis acid promoted conjugate addition reactions with α-substituted enals and methyl vinyl ketone 2 to produce tetrasubstituted cyclopentanes 3 with high levels of diastereoselection. The reaction is believed to proceed by an initial 1,4-addition which is followed by a 1,2-silyl migration and a final cyclization step involving the derived boron enolate resulting in the construction of the cyclopentanoid product

Ring enlargement–cyclopentane annulation via thermal oxy-Cope rearrangement

Thermal oxy-Cope rearrangement of 1,2-divinylcycloalkanols led to ring expansion–cyclopentane annulation; the effect of ring size on the reaction has been studied.

Ring-enlarging cyclopentene annulations

Ethynylation of 2-[(2,2-dialkoxy)ethyl]cycloalkanones followed by Lewis acid-promoted rearrangement occasions cyclopentene annulation with concomitant one-carbon ring expansion of the starting cycloalkanone.