Cyclopentenes vinylcyclopentenes

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 presence of additional unsaturation in vinylcyclopropane (56) was invoked as an explanation for its facile nickel(0)-catalyzed rearrangement to vinylcyclopentene (57) in excellent yield (Scheme 12). The geometry of the diene in (56) turned out not to be important as the ring opening led to the equilibration of ( )- and (Z)-isomers prior to the final clostire. The reaction was therefore stereoselective, but cyclopentene (57) suffered, in some cases, isomerization to (58) under the reaction conditions. 

HDC 3-Butyl-4-vinylcyclopentene 3-(l-hexenyl)cyclopentene 6-(l-butenyl)-cyclohepta-1,4-diene 6-butylcyclo-l,4-heptadiene 1,3,5-undecatriene 2,4,6-undecatriene heptadecane 5-octadecene eicosa-5,8,ll,14-tetramethylenoate eicosa-5,8,11,14,17-pentamethylenoate [55]. 

HDC 4-[(l )-Hexenyl]-cyclopentene 6-[(l )-butenyl]-cyclohepta-l,4-diene c/s-3-butyl-4-vinylcyclopentene trans-1 - [(1 Z)-hexenyl] -2-vinylcyclopropane... 

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