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Lewis acid-initiated reaction of (het)aryl-substituted donor-acceptor cyclopropanes with styrenes was studied. The initiation of the process by tin(IV) chloride caused the reaction to proceed in two alternative directions, namely, with the formation of substituted cyclopentanes ((3+2) cycloaddition products) and substituted indanes or their hetero analogs ((3+2) annulation products). The chemoselectivity of the reaction was controlled by several factors, such as the reaction conditions and the nature of reacting compounds and initiator. [ABSTRACT FROM AUTHOR]

Electron ionization (EI) mass spectra of saturated carbocyclic hydrocarbons containing a single ring with three or more members are discussed followed by the examination of their unsaturated analogs, including aromatic hydrocarbons. Mass spectrometry characteristics of heterocyclic compounds for each cycle size with one, two, three, and more hetero-atoms in a ring are considered along with their mono- and polyunsaturated analogs. An effect of the (a) size of a cycle; (b) number, nature, and location of elements in a ring; (c) position and nature of ring substituents; and (d) nature and location of unsaturation on the dissociation is revealed. Characteristic dissociation directions of these compounds and diagnostically important ions in their spectra are identified. Basic dissociation rules for alicyclic, heterocyclic, and aromatic compounds under EI are established for further use in the analysis of complex chemicals containing these structural elements. [ABSTRACT FROM AUTHOR]

Tri‐substituted cyclopentadienes and cyclopentanes, high‐value‐added compounds, are readily prepared from ethyl levulinate, a chemical platform easily obtained from biomass. Key steps involve coupling two molecules of ethyl levulinate in the presence of pyrrolidine, followed by a base‐catalyzed intramolecular aldol condensation, to provide a singly‐purified and easily derivatizable cyclopentadiene in almost 40 % isolated overall yield. Reaction conditions are mild, simple and employ green solvents such as ethanol and anisole. This method opens a new pathway to preparing complex molecules from renewable feedstocks. The synthesis of three‐substituted cyclopentadienes and cyclopentanes is achieved from renewable ethyl levulinate (EL), an important biomass platform. Using enamine chemistry, EL is promptly converted to a substituted cyclopentadiene after condensation and cyclization. Derivatization of this intermediate provided several cyclopentadienes and cyclopentanes in just one step. [ABSTRACT FROM AUTHOR]

We have recently disclosed a palladium-catalyzed Trost- Oppolzer type Alder-ene reaction of 2,4-pentadienyl acetates for the synthesis of highly substituted cyclopentadienes and cyclopentenefused aromatics. The overall transformation also represents an acid-free iso-Nazarov type cyclization. Herein, we provide the hypothesis and rationale behind this work, while highlighting the seminal contributions of Trost, Oppolzer and others towards the development of the palladium- ene reaction. [ABSTRACT FROM AUTHOR]

Herein, we report a zirconium-catalyzed enantio- and diastereoselective inter/intramolecular double carboalumination of unactivated 2-substituted 1,5-dienes, which provides efficient and direct access to chiral cyclopentanes through the generation of two stereocenters, including one all-carbon quaternary stereocenter, generally with excellent diastereo- and high enantioselectivity. This tandem carboalumination process creates two new C−C bonds as well as one C−Al bond, which can be oxidized in situ with O2 or hydrolyzed. Furthermore, the obtained chiral cyclopentanes can be readily functionalized to provide various chiral compounds. [ABSTRACT FROM AUTHOR]

A cascade reaction of donor-acceptor cyclopropanes with enynals to construct indanone-fused cyclopentanes via a sequential hydrolysis/Knoevenagel condensation/[3+2] cycloaddition is reported. The desired indanone-fused cyclopentanes were obtained in good yields. This method features mild reaction conditions and broad substrate scope, which render it very appealing to chemists for the synthesis of complex molecules containing an indanone-fused cyclopentane moiety. Moreover, the products could be further converted into compounds with different functional groups through the well-known transformations. [ABSTRACT FROM AUTHOR]

A Sc(OTf)3-catalyzed reaction of vinyl azides with donor-acceptor cyclopropanes affords highly functionalized azidocyclopentanes in a diastereoselective fashion. The resulting azidocyclopentanes could be transformed into various cyclic scaffolds. [ABSTRACT FROM AUTHOR]

We present a formal [3+2] cycloaddition based on synergistic catalysis. Vinylcyclopropanes derived from cyanoesters react with enals by dual activation using palladium(0) and secondary amines to form the corresponding cyclopentanes in good yields and stereoselectivities. [ABSTRACT FROM AUTHOR]

A double synergistic cascade reaction is reported, combining transition metal and amine catalysis. The reaction between vinyl cyclopropanes and enals renders the final cyclopentane derivatives in excellent yields and stereoselectivities. [ABSTRACT FROM AUTHOR]

A double synergistic cascade reaction is reported, combining transition metal and amine catalysis. The reaction between vinyl cyclopropanes and enals renders the final cyclopentane derivatives in excellent yields and stereoselectivities. [ABSTRACT FROM AUTHOR]

The first nitro-group-initiated redox-neutral [3+2] cycloaddition of nitrocyclopropanes with alkenes by using visible-light-absorbing transition-metal complexes was reported. High diastereoselectivities were observed for two quaternary carbon centers on the ring and validated by DFT calculations. Spiro- or polycyclic structures can be constructed smoothly. Cyclic γ-amino acid derivatives and polysubstituted cyclic amino alcohols can be obtained easily through reduction of the nitro group. [ABSTRACT FROM AUTHOR]

Catalyzed by Rhodococcus erythropolis AJ270, a nitrile hydratase-amidase containing microbial whole-cell catalyst under mild conditions, enantioselective desymmetrizations of meso-cyclopentane-1,3-dicarbonitriles and cyclopentane-1,3-dicarboxamides were studied. Although the nitrile hydratase was found to exhibit high enzymatic activity, but low 1 R enantioselectivity toward dinitriles, a number of 2,2-unsymmetrically substituted meso-cyclopentane-1,3-dicarboxamide substrates were converted by the 1 S enantioselective amidase into quaternary carbon-bearing enantiopure (1 S,2 R,3 R)-3-carbamoylcyclopentanecarboxylic acids in yields up to 94 %. The application of the method was demonstrated by convenient and practical transformations of the resulting (1 S,2 R,3 R)-2-allyl-3-carbamoylcyclopentanecarboxylic acid derivatives into functionalized cyclopentane-fused δ-lactam and δ-lactone compounds. [ABSTRACT FROM AUTHOR]

An efficient, highly stereoselective asymmetric synthesis of fully functionalized cyclopentanes bearing an oxindole moiety and several other functional groups in one pot has been developed. Key step is an organocatalytic triple Michael domino reaction forming three CC bonds and six stereocenters, including a quaternary one. Starting from equimolar amounts of simple substrates, a high molecular complexity can be reached after a Wittig olefination in one pot. The new protocol can easily be scaled up to gram amounts. [ABSTRACT FROM AUTHOR]

A relay strategy is described that permits ring-closing metathesis and bifunctional chiral amine (thio)urea-catalyzed Michael addition reactions to proceed in a one-pot fashion. The process offers an alternative approach to the synthesis of structurally diverse chiral cyclopentanes in good yields and good enantioselectivities. [ABSTRACT FROM AUTHOR]

A simple modular tandem approach to multiply substituted cyclopentane derivatives is reported, which succeeds by joining organometallic addition, conjugate addition, radical cyclization, and oxygenation steps. The key steps enabling this tandem process are the thus far rarely used isomerization of allylic alkoxides to enolates and single-electron transfer to merge the organometallic step with the radical and oxygenation chemistry. This controlled lineup of multiple electronically contrasting reactive intermediates provides versatile access to highly functionalized cyclopentane derivatives from very simple and readily available commodity precursors. The antiviral activity of the synthesized compounds was screened and a number of compounds showed potent activity against hepatitis C and dengue viruses. [ABSTRACT FROM AUTHOR]

The requirement for new strategies for synthesizing five-membered carbocycles has driven an expansion in study of the Nazarov cyclization. This renewed interest in the reaction has led to the discovery of several interesting new methods for generating the pentadienyl cation intermediates central to the cyclization. Methods reviewed include carbon-heteroatom ionization, double bond functionalization, nucleophilic addition, or electrocyclic ring opening. Additional variations, such as iso- and imino-Nazarov cyclization, employ unconventional substrates to produce new pentacycles. Here we provide an overview of these unconventional, yet highly useful versions of the Nazarov cyclization. [ABSTRACT FROM AUTHOR]

β-Dicarbonyl compounds exist as mixtures of keto and enol tautomers. Depending on reaction conditions and nature of the groups connected to the carbon-oxygen skeleton of a β-dicarbonyl reagent, it may react via active methylene carbon or enolate oxygen atom. An acyclic vinyl sulfone-modified polyol having a leaving group reacted with a series of β-dicarbonyl and related reagents. It underwent keto-enol tautomerism to afford a series of five-membered carbocycles in a diastereoselective fashion. Only carbocycles were isolated indicating the exclusive double participation of the metheylene carbon only as the nucleophile. [ABSTRACT FROM AUTHOR]

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A method for the stereoselective synthesis of substituted 4a S*,7a S*-hexahydrocyclopenta[ c]pyran-3(1 H)-one, promising synthon of isoprostanes, has been developed based on the intramolecular dipolar [3+2] cycloaddition of silyl nitronates generated from 6-nitrohex-1-ene derivative. [ABSTRACT FROM AUTHOR]

Ruthenium catalyzed ring opening cross-metathesis of resin-bound bicyclic alkenes with terminal aryl olefins was utilized for the construction of a combinatorial library containing highly functionalized cyclopentane derivatives. The technology described herein represents a convergent method for the diastereospecific synthesis of unique cyclopentane molecular scaffolds useful for exploratory medicinal chemistry. [ABSTRACT FROM AUTHOR]

The feasibility of adopting a new approach to the preparation of chiral carbocyclic compounds has been demonstrated by experiment. Synthesis was achieved by way of intramolecular free radical C-C cyclization of carbohydrate derivatives, which produced compounds with quaternary C carbon atom having a strictly defined configuration. [ABSTRACT FROM AUTHOR]