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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]

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]

Abstract A range of novel β-nitroacetamides with an alkenyl- or alkynyl tether were synthesized using the deprotonative or conjugate addition nitro-Mannich reaction. They were subjected to radical denitration-cyclisation with a 10 equivalent excess of tributyltin hydride, catalytic AIBN in refluxing benzene to explore the structural and electronic requirements for efficient cyclisation. Cyclisations of the β-nitroacetamides were successful in most cases, undergoing 5- exo -trig cyclisation to give the desired cyclopentyl or indanyl structures. Radical 1,4-translocation of a phenyl group was observed in several cases. Diastereoselectivity was low, with 2 or 3 of 4 possible diastereoisomers observed in most cases. Further purification by crystallisation allowed the isolation of some as single diastereoisomers. It was found that higher yields were obtained by increasing the substitution or reducing the degrees of freedom of the tether between the nitro group and the radical acceptor. Graphical abstract Image 1 [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]

Abstract: An efficient reaction protocol for the palladium-catalyzed synthesis of 2,4-diacetoxycyclopentylideneacetates by a reaction of acetic acid with 3,6-heptadienoic esters, has been developed. The process, which occurs in the presence of oxidants, represents the first example of sequential double acetoxylation–cyclization of substituted 1,4-dienes to form cyclopentane rings with oxygen functionalities at 2 and 4 carbon atoms. The use of a water/acetic acid reaction medium has also been shown to give satisfactory results. [Copyright &y& Elsevier]

An efficient and simple new stereocontrolled access route to novel disubstituted cispentacin derivatives with multiple stereogenic centers from norbornene β-lactam has been developed. The synthesis involves olefinic bond functionalization by dihydroxylation followed by oxidative ring cleavage and transformation of the dialdehyde intermediate through a Wittig reaction. [ABSTRACT FROM AUTHOR]

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]

The addition of various amines to 5-chloro-1-pentenylphosphonate 4 , prepared by zirconation or titanation of the corresponding alkynylphosphonates, has been used to produce novel substituted pyrrolidinyl-methylphosphonates 5 in 68–81% isolated yield. [ABSTRACT FROM AUTHOR]

Abstract: A combination of organotransition metal catalysis and organocatalysis allows for Tsuji–Trost 5-exo- and 6-exo-cyclizations of aldehydes. This transformation can also be accomplished as a catalytic asymmetric reaction, which affords vinylcyclopentane derivatives with up to 98%ee. [Copyright &y& Elsevier]

Highly substituted cyclopentane rings are present in a wide range of targets, and the efficient synthesis of such compounds constitutes a continuing challenge to organic synthesis. We present two complementary approaches to the regio- and diastereoselective synthesis of highly substituted cyclopentane structures. In both cases, a non-symmetrically disposed norbornene is employed as a common intermediate. One strategy relies on the Lewis acid-catalyzed ring opening of an anhydride, while the other employs production of a bicyclic lactone followed by its selective functionalization. [Copyright &y& Elsevier]

The recent results concerning the carbocyclisation reaction of zinc enolates onto an unactivated double bond are summarized, particularly on the stereochemical point of view. The implications of the observed stereochemistries on the mechanism of the reaction (O-centred zinc enolate vs C-centred zinc enolate) are discussed. Some new results leading stereoselectively to 1-amino-1-carbomethoxy-2-methyl cyclopentanes are reported, as well as the consequences of the observed stereochemistry as a strong evidence for a C-centred zinc enolate intermediate. To cite this article: E´. Sliwinski et al., C. R. Chimie 6 (2003) 000–000. [Copyright &y& Elsevier]

The new, axially chiral borates 2, 9, and 11 and boronates 3–6 and 12 are synthesized in good yields. They are representatives of three different structural types. The bicyclic borates 2 and 9 are homochiral propeller compounds; their exclusive formation is used to increase the enantiomerical purity of 1. Especially the borates are efficient Lewis acidic catalysts for stereoselective Diels–Alder reactions. The new seven-membered boron compounds 4, 5, 6, and 12 are interesting reagents for different asymmetric synthetic steps. Activated vinylboronates 31 can serve as efficient cyclophiles in [3+2] cycloaddition reactions with methylenecyclopropane 27 giving borylated methylenecyclopentanes 32. [Copyright &y& Elsevier]

An improved protocol for the preparation of cyclopentadiene monoaziridine is described (88% yield). The utility of cyclopentadiene monoaziridine is demonstrated by its use in (i) the shortest synthetic entry into 4-amino substituted cyclopentenes and (ii) the preparation of two key intermediates in a concise synthetic approach to the cyclopentane core of agelastatin A. The agelastatin A model studies make use of a lithium amide-mediated epoxide to allylic alcohol rearrangement reaction. [Copyright &y& Elsevier]

A highly diastereoselective annulation strategy for the synthesis of alicyclic ketones from diols and pentamethylacetophenone is described. This process is mediated by a commercially available iridium(III) catalyst, and provides efficient access to a wide range of cyclopentane and cyclohexane products with high levels of stereoselectivity. The origins of diastereoselectivity in the annulation reaction have been explored by a series of control experiments, which provides an explanation for how each stereocentre around the newly forged ring is controlled. Image 1 • A highly diastereoselective annulation strategy for the synthesis of alicyclic ketones from diols and pentamethylacetophenone is described. • This process provides efficient access to a wide range of cyclopentane and cyclohexane products with high levels of stereoselectivity. • The origins of diastereoselectivity in the annulation reaction have been explored by a series of control experiments, which provides an explanation for how each stereocentre around the newly forged ring is controlled. [ABSTRACT FROM AUTHOR]