Cyclopentene derivatives 1-substituted

In the same way as arylcarbene complexes, alkenylcarbene complexes typically react with alkynes to provide [3C+2S+1C0] Dotz cycloadducts (see Chap. ccChromium-Templated Benzannulation Reactions , p. 123 in this book). However, some isolated examples involving the formation of five-membered rings through [3C+2S] cycloaddition processes have been reported [71]. In this context, de Meijere et al. found that /J-donor-substituted alkenylcarbene complexes react with alkynes to give cyclopentene derivatives [71a]. This topic is also discussed in detail in Chap.ccThe Multifaceted Chemistry of Variously Substituted a,/J-Unsaturated Fischer Metalcarbenes , p. 21 of this book. 

Sect. 2.1.1) and [3C+2S] cyclopentene derivatives. The product distribution can be controlled by choosing the appropriate reaction conditions [72]. Moreover, the cyclopentene derivatives are the exclusive products from the coupling of fi-pyrrolyl-substituted carbene complexes [72b,c] (Scheme 25). The crucial intermediate chromacyclobutane is formed in an initial step by a [2+2] cycloaddition. This chromacyclobutane rearranges to give the rf-complex when non-coordinating solvents are used. Finally, a reductive elimination leads to the formal [3C+2S] cyclopentene derivatives. 

Coupling of alkenylcarbene complexes and siloxy-substituted 1,3-dienes affords vinylcyclopentene derivatives through a formal [3C+2S] cycloaddition process. This unusual reaction is explained by an initial [4C+2S] cycloaddition of the electron-poor chromadiene system as the 471 component and the terminal double bond of the siloxydiene as the dienophile. The chromacyclohexene intermediate evolves by a reductive elimination of the metal fragment to generate the [3C+2S] cyclopentene derivatives [73] (Scheme 26). 

Fischer alkenylcarbene complexes undergo cyclopentannulation to alkenyl AT,AT-dimethylhydrazones (1-amino-1-azadienes) to furnish [3C+2S] substituted cyclopentenes in a regio- and diastereoselective way along with minor amounts of [4S+1C] pyrrole derivatives. Enantiopure carbene complexes derived from (-)-8-(2-naphthyl)menthol afford mixtures of trans,trans-cycloipentenes and ds,ds-cyclopentenes with excellent face selectivity [75]. The mechanism proposed for the formation of these cyclopentene derivatives is outlined in Scheme 28. The process is initiated by nucleophilic 1,2-attack of the carbon... 

The carbene obtained by heating compound 68 with DMAD at first gave a cyclopropene derivative, which underwent further transformations (z/rro-substitution and cyclization) to afford tricyclic product 69 in 40% yield <1999TL1483>. The thermolysis carried out in the presence of ArCH=C(CN)2 and DMAD used in excess led to the formation of highly functionalized cyclopentene derivatives 70 <2003TL5029, 2005TL201>. 

A regioselective [3 + 2]-cycloaddition approach to substituted 5-membered carbo-cycles was made available by the use of allenylsilanes [188]. The reaction involves regioselective attack of an unsaturated ketone by (trimethylsilyl)allene at the 3-position. The resulting vinyl cation undergoes a 1,2-silyl migration. The isomeric vinyl cation is intercepted intramolecularly by the titanium enolate to produce a highly substituted (trimethylsilyl)cyclopentene derivative. 

Donor-acceptor-substituted vinylcyclopropanes such as (203) have been shown to undergo thermal ring enlargement to functionalized cyclopentene derivatives (204) at... 

Buchert, M., Reissig, H. U. Rearrangement of donor-acceptor-substituted vinylcyclopropanes to functionalized cyclopentene derivatives. Evidence for zwitterionic intermediates. Liebigs Ann. Chem. 1996, 2007-2013. 

Danhelser has modified his stereocontrolled [4+1] annulation approach to cyclopentene derivatives, to accommodate carbon rather than oxygen substitution at C-3 (Scheme 19). The key step in the sequence is the carbanlon-accelerated vinylcyclopropane-cyclopentene rearrangement which appears quite efficient. Unfortunately the rather poor yields in the initial steps of the sequence and the lengthy nature of the overall procedure detract somewhat from its appeal. Posner has developed a convenient one-pot, three-component construction of cyclohexenes which involves... 

Ushakov NV, Pritula NA (1992) Synthesis of asymmetrically substituted 1-sUacyclobutane and l-sila-3-cyclopentene derivatives. Zhurnal Obshchei Khimii 62 1318-1324... 

In their preliminary studies, Grieco et al. [8] demonstrated that the Diels-Alder adducts formed with cyclopentadiene and C-acyl iminium ions can be used in the construction of substituted cyclopentene derivatives. Diels-Alder adducts 24 and 25 (see section 2.2.3) are readily converted into cyclopentene derivative 82 in 76% yield upon exposure to zinc in glacial acetic acid. Cyclopentene derivatives such as 82 can serve as precursors to carbo-cyclic analogs of purine ribo- and deoxyribonucleosides [29] ... 

The first models for asymmetric induction in [2 + 2] cycloadditions are ketimines derived from precursors such as (25), which react with both cyclic and acyclic alkenes to give adducts with high enantiomeric excesses. Full details have been reported on the regio- and stereo-specificity of the addition of dichloroketene to 1-substituted cyclohexenes. Methyl (phenylthiomethyl)-ketene (26) provides a further example of a ketene which, after cycloaddition to cyclopentadiene, undergoes facile opening of the cyclobutane that is thus formed to provide vicinally substituted cyclopentene derivatives. ... 

Figure 8. Synthesis of a) allyl, b) acetylene, and c) cyclopentene derivatives of d-valerolactone by substitution a to the carbonyl group.

The formed fully substituted cyclopentene derivatives were obtained as single diastereomers in moderate to good yields and excellent enantioselectivities of up to 99% ee (Scheme 37.5). 

Write structural formulas or build molecular models and give the lUPAC names of all the monochloro substituted derivatives of cyclopentene... 

Castagnino, E., Corsano, S., and Strappavecchia, G.P., The preparation of a novel oxo-cyclopenten-2-phosphonate derivative, useful intermediate for 2-alkyl-substituted cyclopentenones synthesis, Tetrahedron Lett., 93, 1985. 

Novel thermal and metal-catalyzed di-tert-butylsilylene 161 transfer reactions have been reported by Woerpel < / /.308-312 The transfer reactions required the inital preparation of cyclohexene-derived silacyclopropanes 169-171, which has been achieved by trapping of di-fert-butylsilylenoid, generated from /-Bu2SiCl2 and lithium, with cyclohexenes (Scheme 26).305 It is noteworthy that these reactions occur with remarkably high diastereoselectivities when 2-substituted cyclohexenes are used. The silacyclopropanation of 169 with functionalized cyclopentenes under thermal conditions (115°C) has provided /razy-silacyclopropanes, such as 172, with diastereoselectivities up to 96 4, whereas no silacyclopropanes were obtained from the direct reaction of the same cyclopentenes with /-Bu2SiCl2 in the presence of lithium (Scheme 26).308... 

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