Vinylcyclopentene derivative

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). 

The proposed mechanism of the above cycloisomerizations are depicted in Scheme 11.30. The oxidative coupling of a metal to an enyne yields a bicyclic metaUacyclopentene, which is a common intermediate. The reductive elimination and subsequent retro-[2+2] cycloaddition gave vinylcyclopentene derivatives, while the two patterns of P-elimination and subsequent reductive eUmination gave cychc 1,3- and 1,4-dienes, respectively. The existence of a carbene complex intermediate might explain the isomerization of the olefinic moiety. 

Dienylcyclopropanes (218) activated by two electron-withdrawing groups easily rearrange to vinylcyclopentene derivatives (219) in the presence of a catalytic amount of Pd(0) at 25-60°C (equation 145) ... 

Sol 3. (i) l,l-Divinyl-2-phenylcyclopropane derivative (I) on heating undergoes a vinylcyclopropane rearrangement to give vinylcyclopentene derivative (II). In this reaction one of the vinyl groups of I participates in the reaction and the other is a substituent. The major spirolactam (ID) is formed by a reversible aromatic Cope rearrangement followed by an irreversible ene reaction. In this... 

The dimeric azaphospholines derived from (/ )-myrtenal and (J )-l-phenylethylamine are also active ligands in the nickel catalyzed hydrovinylation of cyclopentadiene with ethylene to give exclusively 3-vinylcyclopentene (7) with 100% chemo- and regioselectivity and up to 76% ee5 (according to recent reports even higher inductions are obtainable53). No isomerization and dimerization of the products is observed. Previously, with other catalytic systems the same... 

Feldman and coworkers have generated radicals from vinylcyclopropanes in the presence of thiyl radicals and studied their reaction with alkynes to give vinylcyclopentenes. A general [3+2] annulation strategy considers vinylcyclopropanes 39 as the three atom components and alkynes 40 as the two atom counterparts (Scheme 14). The vinylcyclopentene products have been obtained as mixtures of syn- and a /-substituted stereoisomers the authors considered that product stereochemistry is set during the cyclization of the 5-hexadienyl radical 41 and derives from the two conformations (chair- or boat-like) in the transition state. 

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