Rearrangement of Vinylcyclopropane to Cyclopentene

MD trajectories have been computed for the 8 9 using an AMl-SRP PES fit to the MRCI/cc-pVDZ//CASSCF(4,4)/cc-pVDZ critical point energies. ° Trajectories at 573 K were initiated at three TSs TS(si), TS(90,0), and TS(0,0). The product distribution from these trajectories is listed in Table 8.1. The product distribution is dependent on which TS is the origin of the trajectory. Trajectories started at TS(si) preferentially produce the Woodward-Hoffmann allowed products, while the ai product is the major one produced from the TS(0,0) trajectories. Trajectories from TS(90,0) give nearly equal distribution of the four possible products. This mode selectivity strongly discounts the presence of a diradical intermediate that has some appreciable lifetime. Such a diradical would undergo intramolecular vibrational energy redistribution, and the trajectories from the three different TSs would result in identical product distributions. 

The product distribution is also time dependent. Listed in Table 8.2 is the time dependence of the s/a and Ur ratios for the trajectories initiated at the three TSs. Trajectories from TS(si) show strong preference for s over a in the short trajectories. These are trajectories that essentially directly travel a least-motion rotation of the vinyl gronp to the product. Over longer times, the TSfi O trajectories lose specificity. 

TABLE 8.1 Percent Yields from TVajectories Begun at Three TSs  

The trajectories from TS(90,0) show strong preference for i over r at short times. This also reflects a least-motion pathway. The overall s/a ratio time dependence is dominated by the results of the TS(y/) trajectories. 

Recent reviews by Baldwin summarize the experimental and theoretical approaches to the vinylcyclopropane and vinylcyclobutane rearrangements. It is 

---

The thermal rearrangement of vinylcyclopropane to cyclopentene was uncovered in I96090 91. That vinylcyclopropanes, like other cyclopropanes, may undergo cis, trans iso-merizations was inferred in 1964 when trans-l-vinyl-2-methylcyclopropane was thermally converted to mostly (4Z)-1,4-hexadiene, a product formed at much lower temperatures from cw-1-vinyl-2-methylcyclopropane92. The reversible interconversion of the cis and trans isomers of l-vinyl-2-d-cyclopropane (equation 2) was reported soon thereafter, in 196793"96. Additional examples, including cases showing both geometrical isomerization and enantiomerization processes, soon followed. 

The rearrangement of vinylcyclopropane to cyclopentene was first observed by Neureiter in 1959. The mechanism of this transformation has been studied extensively and the rearrangement has enjoyed numerous applications in methodology development and total synthesis. The topic has been the subject of many recent reviews. It is generally accepted that the transformation of a vinylcyclopropane to a cyclopentene proceeds through diradical intermedi-... 

Some rearrangements of vinylcyclopropanes to cyclopentenes take place under conditions of charge acceleration and may be difficult to classify into any of the categories listed in this section. A review of such rearrangements has been compiled. ... 

The thermal rearrangements of vinylcyclopropanes to form cyclopentenes as well as 1,4-hexadienes by homodienyl [l,5]-shift are well-known16,49-51 and even described in textbooks (see, e.g., Chapter 18 in Reference 4). However, the heteroanalogous transformations are less known. 

Table 6. Transition structure geometries, activation energies, and reaction energies for transition structures of vinylcyclopropane to cyclopentene rearrangement [62]... 

Hudlicky, T. Reed, J.W. in Comprehensive Organic Synthesis, Trost, B.M. Fleming, I., Eds. Pergamon Oxford, 1991 Vol. 5, p899. (Review of vinylcyclopropane to cyclopentene rearrangement and its heterocyclic variants, i.e. cyclo-propylimines and ketones, vinylaziridines and oxiranes, etc.). 

Q 1. The conversion of vinylcyclopropane to cyclopentene upon heating is an example of which of the following sigmatropic rearrangements ... 

The thermal rearrangement of vinylcyclopropanes 1 to yield cyclopentenes 2 is called the vinylcyclopropane rearrangement. 

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],... 

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%). 

Vinylcyclopropane - cyclopentene.2 This one-electron oxidant permits rapid rearrangement of some vinylcyclopropanes to cyclopentenes in CH3CN at ambient temperatures. 

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

The use of Ni as a catalyst for the rearrangement of vinylcyclopropanes (VCPs) to cyclopentenes was first reported in 1979 [1,2]. In combination with a phosphine ligand, activated VCPs could be converted to the corres-... 

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... 

A similar acceleration has most recently been observed in the rearrangement of vinylcyclopropanes of type (39 Scheme 8). This fluoride-mediated vinylcyclopropane-cyclopentene isomerization proceeds at -78 C to give (40) in 85% yield this is to date the mildest condition available. Two possible intermediates, the enolate anion (39a) or the diradical anion (39b), may be responsible for such acceleration in analogy to the enolate anion accelerated divinylcyclobutane rearrangement recently reported." The mechanism of this transformation is unclear but may involve anion acceleration similar to that observed in the rearrangement of sulfonyl anions derived from (42 Scheme 8). By comparison the thermolysis of (39) produced exclusively the endo isomer of (41) at 580... 

---