Cyclopentenes rearrangement

An illustrative example for the generation of cyclopentenes from vinylcyclopropanes is the formation of bicyclo[3.3.0]oct-l-ene 10 from 1,1-dicyclopropylethene 9 by two consecutive vinylcyclopropane cyclopentene rearrangements. ... 

Temperatures in parentheses refer to thermal vinylcyclopropane -> cyclopentene rearrangement. 

The photoindueed 1,7-cycloaddition of carbon monoxide across the divinyl-cyclopropane derivative 32 yields the two cyclic dienyl ketones 34, via the ferracyclononadiene intermediate 33 [18]. (Scheme 11) cyclopentene rearrangement. The dienylcyclopropane 35 is capable of forming the complex 36, followed by ring enlargement to 37 [19]. 1,1-Dicyclopropylethylene 29 is also converted to the 1-cyclopropyl-1-cyclopentene 38. The additional functionality of vinylcyclopropanes is necessary to serve as a 7t-donor... 

Upon flash vacuum pyrolysis or under silver nitrate catalysis, a variety of 2-ethenyl-sub-stituted cydopropylamines 146 cleanly undergo a vinylcyclopropane to cyclopentene rearrangement [129] and afford high yields (up to 95%) of 4-aminocyclopent-l-enes 147, some of which have unprecedented substitution patterns (Scheme 11.37) [130],... 

Scheme 11.38. Vinylcyclopropane to cyclopentene rearrangement in (n+3)-(dimethylamino)-l-ethenyl bicyclo[n.l. OJalkanes 66...

The extrapolation of the vinylcyclopropane-cyclopentene rearrangement to a vinyl-cyclobutaiie-cyclohexene synthesis begins to create new insights into the synthesis of six membered ring natural products. The eudesmane sesquiterpene (—)-P-selinene, 217 illustrates such a strategy as summarized in Scheme 14 80). A suitable cyclohexene... 

Since the pioneering work by Sarel and co-workers on the iron carbonyl promoted transformation of vinylcyclopropanes and related compounds [1], a variety of transition metal complexes have been examined to achieve effective activation of the vinylcyclopropane-cyclopentene rearrangement which usually requires pyrolytic conditions. These reactions have been applied to natural product synthesis in some cases and have already been reviewed in several excellent articles [2-4]. 

Unlike the well-known chemistry of the vinylcyclopropane-cyclopentene rearrangement, there is no general method for the rearrangement of alkynyl-cyclopropane to cyclopentene derivatives. One specific example is the pyrolysis of l-ethynyl-2-methylcyclopropane to methylenecyclopentene and other compounds [5]. At 530°C, l-ethynyl-2-methylcyclopropane (1) undergoes a [1,5]-hydrogen shift to give hexa-l,2,5-triene (2), which further isomerizes to methy-lenecyclopentenes 3 and 4 in 38 and 29% yield, respectively (Scheme 1). 

C. Doubleday, Mechanism of the Vinylcyclopropane-Cyclopentene Rearrangement Studied by Quasiclassical Direct D3mamics, J. Phys. Chem. A 2001, 105, 6333. 

One of the classical papers in this area is Neureiter s discovery of the vinyl-cyclopropane to cyclopentene rearrangement [185]. This important process was first observed on a l,l-dichloro-2-vinylcyclopropane derivative, which on heating yielded a chlorocyclopentadiene, presumably by the loss of hydrochloric acid from the initially formed 4,4-dichlorocyclopentene. 

Several photochemically induced vinylcyclopropane to cyclopentene rearrangements of nor-carene derivatives to form bicyclo[3.2.0]heptenes can be understood as ring contractions of cyclohexenes to cyclobutanes. Upon direct irradiation of norcar-2-ene (bicyclo[4.1.0]hept-2-ene) at 214 nm (pentane solution), however, complex product mixtures were obtained containing only small amounts of bicyclo[3.2.0]hept-2-ene, while toluene sensitized photolysis in 50 millimolar solution in degassed pentane at 254 nm gave mainly the cyclobutane derivative 13 in addition to EjZ-isomeric hepla-l,3,6-trienes.72... 

When one attempts to extend these empirical correlations once again, now considering rate constants for vinylcyclopropane to cyclopentene rearrangements, a fair linear correlation is obtained (Figure 4). The correlation line has an intercept of 56.7 kcal mol 1 and a slope of 0.690 (R2 = 0.99). The rate constants utilized were corrected for symmetry (a factor of 1/2 for vinylcyclopropane, and of 1/4 for 1,1-dicyclopropylethene) and the radical stabilization energies of-CH2CR=CH2 for R=Me or cyclopropyl were taken to be identical. The rate constants for vinylcyclopropane to cyclopentene rearrangements respond... 

Vinylcyclopropane to cyclopentene rearrangement 184 Dissociation of acetone radical cation 186 The wolff rearrangement 187... 

During studies on pyrethroid insecticides methyl permethrate 1 (a mixture of cis and trans isomers) was pyrolysed at 260-270°C in the expectation that a vinylcyclopropane-to-cyclopentene rearrangement would occur. The product, however, was found to be methyl o-toluate (78%). 

This reaction does not create a ring but there is an important group of sigmatropic rearrangements that make five-membered rings—the vinyl cyclopropane to cyclopentene rearrangement. 

On the other hand, Rh1 in the absence of CO leads to 12 [12] formed via a vinyl cyclopropane/cyclopentene rearrangement. Such a rearrangement without a catalyst would require temperatures between 300 and 400 °C ... 

Cooke, R.S. (1970) A photochemical vinylcyclopropane to cyclopentene rearrangement. Journal of the Chemical Society D Chemical Communications, (7), 454—455. 

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