Ring opening vinylcyclopropane-cyclopentene rearrangement

The vinylcyclopropane radical cation, generated at 77 K by X-irradiation of (139) in a Freon-113 matrix, was shown to rearrange at 105-110 K to afford two ring-opened distonic radical cationic species.300 The rearrangement reactions of the radical cations of 1,3- and 1,4-pentadiene and cyclopentene and the formation of spin adducts with 2.4.6-tri-/-butylnitrosobenzene (BNB) are discussed. The pulse radiolysis of 1,1 -binaphthyl-2,2,-diyl hydrogenphosphate (BiNPCUH) (140) in deaerated f-butanol at... 

The vinylcyclopropane to cyclopentene rearrangement is seemingly broadly applicable to solution of the five-ring annulation problem. Besides the example cited in Scheme 8, routes provided by Trost,61 Miller,62a and Conia62b are conceptually attractive. Thus, we see that reaction of a cyclopentanone with the cyclopro-pyldiphenylsulfonium ylide provides an oxaspiropentane which can be opened efficiently with an amide base (Scheme 10). The resulting silylated cyclopropanol can be... 

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. 

At higher temperatures, bicyclo[3.3.0]oct-2-ene was formed from the equilibrium mixture, and the fact that 8,8-dideuteriobicyclo[5.1.0]oct-2-ene gave 3,3-dideuter-iobicyclo[3.3.0]oct-2-ene indicates that cyclopropane ring opening occurs and results in the vinylcyclopropane to cyclopentene rearrangement (see Chapter 6, Section 2.1). 

---