Vinylcyclopropane- cyclopentene 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 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. 

Because of the discovery of a growing number of naturally occurring substances of biological importance that contain the five-membered ring moiety 178), the synthesis of cyclopentanoid compounds is a subject of present interest. Indeed, among the various approaches recently investigated, the thermal vinylcyclopropane-cyclopentene rearrangement of readily available 1-siloxy-l-vinylcyclopropanes (vide supra, Sect. 4.1.5) constitutes an efficient three-carbon annelation process 179). 

Doubleday, C. Nendel, M. Houk, K. N. Thweatt, D. Page, M. Direct dynamics quasiclassical trajectory study of the stereochemistry of the vinylcyclopropane-cyclopentene rearrangement, J. Am. Chem. Soc. 1999,121,4720-4721. 

The conversation of free and Cr(CO)s-complexed 2-vinylphosphirane into 2,5-dihydro-17/-phosphole via 1,3-sigmatropic shifts was studied with DFT and compared with the corresponding vinylcyclopropane-cyclopentene rearrangement (Equation 2) <2002JA13903>. 2-Vinylphosphirane has smaller barriers as in the case of vinylcyclo-propane and the complexed species has still smaller one. The rearrangement of syn- and /F2-vinylphosphirane is a... 

The substituent effects have been quantitatively addressed in the context of specific transformations, for example the vinylcyclopropane-cyclopentene rearrangement, and will be discussed in the appropriate sections. The donor/acceptor principles have been applied to thermal, heterolytic and transition metal catalyzed rearrangements and have been reviewed. These principles take into account the possible intermediate structures listed in Table 1 and are used to explain the reactivity of a particular cyclopropane system. In the discussion that follows emphasis will be given to the processes that are uniformly selective with regard to regio-, stereo- and enantio-chemical integrity of the products. 

Table 3 Substituent Effects in the Vinylcyclopropane-Cyclopentene Rearrangement...

With the exception of vinylcyclopropane-cyclopentene rearrangements (cf. Section VII) radical reactions have so far rather rarely been used synthetically. This is also true for pericyclic modes of cyclopropane cleavage which are mainly restricted to divinylcyclopropane-cycloheptadiene type expansions. Cycloadditions, whether concerted or stepwise, occur only with very specific compounds. ... 

Photochemical vinylcyclopropane-cyclopentene rearrangements open an alternative to prepare racemic grandisol from (optically active) A -carene (equation 184). On the other hand, irradiation of tricyclic enones has resulted in two different product types as shown in equation 185, depending on the nature of substituent R both classes of compounds should be of synthetic value . ... 

The reactivity of these promising building blocks has very recently been reviewed by de Meijere S therefore only a few principles will be discussed in this text. Treatment with n-butyllithium as outlined in equation 187 will give certain functionalized alkynylcyclopro-panes , which can serve as active components in cycloadditions or reactions with olefins in the presence of Co2(CO)g. The latter [2 + 2 + l]-addition provides cyclopropyl cyclopentenones capable of undergoing vinylcyclopropane-cyclopentene rearrangement. 

The thermal vinylcyclopropane-cyclopentene rearrangement discovered by Neureiter in 1959 has been the subject of many mechanistic and theoretical studies (equation 121)206... 

Usually the activation free energy required for the thermal vinylcyclopropane-cyclopentene rearrangement ranges from 48 to 53kcal mor A quantitative treatment of the substituent effect has been conducted It appears that the trimethyl-... 

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