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Vinylcyclopropanes rearrangements, thermal

Siloxy-l-vinylcyclopropanes rearrange thermally to give 1-siloxycyclopentene derivatives or may be hydrolyzed to cyclobutanones by acids (J.M. Conia, 1975 B.M. Trost, 1973 G.C. Girard, 1974). The cyclopropane ring may also be opened by base-catalyzed hydrolysis of the silyl ethers to form ethyl ketones. [Pg.77]

The thermal rearrangement of vinylcyclopropanes 1 to yield cyclopentenes 2 is called the vinylcyclopropane rearrangement. [Pg.282]

In practice, it was found that whereas the synthesis of hirsutene according to the dual strategy met with success under thermal conditions, but at temperatures as high as 580 °C, under photochemical conditions it afforded the unnatural cis, syn, cis configuration of some intermediates which then need further elaboration. Although the transformations 44 — 43a and 45. — 43a by a [2 + 2] -cycloaddition and a vinylcyclopropane rearrangement, respectively, may involve intermediates with a more or less biradical character, they are not typical radical reactions such as the ones we are considering here. [Pg.202]

In order to sec the influence that a trifluoromethyl substituent has on cyclopropane reactivity, l-(trifluoromethyl)-2-vinylcyclopropane (18) was prepared and its thermal reactions studied.13 Both the cisitrans isomerization and the vinylcyclopropane rearrangement were slower than those of any 2-substituted vinylcyclopropane previously reported. When m-18 is heated at 275 C, a clean and reversible cisitrans isomerization takes place (Kequi, = 5.33). At 332-364 C, 18 undergoes normal vinylcyclopropane rearrangement to 4- and 3-(tri-fluoromethyl)cyclopentenc (19) and (20). respectively. [Pg.243]

The Cope rearrangement of c/j-di vinylcyclopropanes is thermally allowed and offers an attractive stereoselective approach to cycloheptadienes. Cyclopropanation reactions can be used to prepare divi-nylcyclopropanes, as shown in Scheme 23.120 Reaction of ethyl diazopyruvate with butadiene generated... [Pg.1048]

Further studies on the scope and stereochemical course of the oxyanion-accelerated vinylcyclopropane reairangement were reported in 1981. This paper introduced a general [4+1] annulation strategy for the synthesis of cyclopentene derivatives in which the anion-accelerated VCP rearrangement functions as the key step. In this report, the accelerated version of the vinylcyclopropane rearrangement was also shown to proceed with remarkably high stereoselectivity, in further contrast to the thermal process. [Pg.1008]

Dinnocenzo and Conlon have described the remarkable effect of one-electron oxidation on the rate of certain vinylcyclopropane rearrangements. Exposure of several l-p-anisyl-2-vinylcyclopropane derivatives to a catalytic amount of tris(4-bromophenyl)aminium hexafluoroantimonate in acetonitrile at room temperature was found to induce ring expansion to form cyclopentenes (equation 25) temperatures in excess of 200 °C are required for the conventional thermal rearrangement cf these systems. At this time it is uncertain whether these reactions follow concerted mechanisms, or are stepwise processes involving trimethylene cation radical intermediates. [Pg.1014]

The photochemical counterpart of the thermal vinylcyclopropane rearrangement has been described ". ... [Pg.857]

Vinylcyclopropane-cyclopentene rearrangement Thermal or photochemical rearrangement of substituted vinylcyclopropanes to substituted cyclopentenes. 470... [Pg.512]

Andrews, G. D., Baldwin, J. E. Thermal isomerization of (+)-(1S,2S)-trans,trans-2-methyl-1-propenylcyclopropane quantification of four stereochemical paths in a vinylcyclopropane rearrangement. J. Am. Chem. Soc. 1976, 98, 6705-6706. [Pg.701]

Treatment of a vinylcyclopropane substituted with two geminal electron-withdrawing groups on the three-membered ring with catalytic amounts of a palladium(O) complex gives a zwitte-rionic 7r-allyl complex, which reacts regioselectively but not stereoselectively to form a vinyl-cyclopen tene 5 13. This method represents a mild alternative to the thermal vinylcyclopropane rearrangement. [Pg.171]

The vinylcyclopropane rearrangement is an important part of Trost s seco-alkylation sequence (see sec. 8.8.B.ii). In this protocol, trimethylsilyloxyvinylcyclopropanes such as 524 are generated by reaction with diphenylcyclopropyl sulfide and subsequent reaction with lithium diisopropyl amide (LDA), to open the oxaspiro-pentane) and trapping the resulting alkoxide anion with chlorotrimethylsilane. Thermal... [Pg.1013]

In an unpublished work, Doering and Roth examined the thermal equilibration of 6,6-d2- and 4,4-d2-bicyclo[3.1.0]hexene (Scheme 7.29). This reaction is a vinylcyclopropane rearrangement involving the bridgehead bond. Since the reaction is constrained to a six-membered ring it cannot proceed via an allowed si or ar pathway. [Pg.103]

Some particularly striking examples of Cope rearrangements can be found in the rearrangement reactions of cw-divinylcyclopropanes. But before we go into these, let us examine vinylcyclopropane itself, which is known to rearrange thermally to cyclopentene ... [Pg.446]

Sol 1. (b) The thermal expansion of a vinylcyclopropane to a cyclopentene ring involves a [1,3] sigmatropic migration of carbon. The reaction is known as a vinylcyclopropane rearrangement. The reaction involves the formation of a strained four-membered transition state and usually occurs at a temperature higher than 300 °C. [Pg.94]

Irradiation of the diazocyclohexadienone (108) in the presence of isoprene affords the spiro-adduct (109), whereas the thermally induced reaction gives only (110), which is probably formed via (109) by a vinylcyclopropane rearrangement cf. p. 111). Photolysis if diazomethyltrimethylsilane with frans-but-2-ene gives the trans-cyclopropane (111) (23%) and olefin (112) (61%), consistent with singlet carbene formation. With ethylene, only 17% of cyclopropyl trimethylsilane was obtained, along with 30% of (112). The steric hindrance in tetramethylethylene completely prevented cyclopropane formation, as did electronic effects in fluoro-olefins. No... [Pg.29]

Thermal Reactions.— Vinylcyclopropanes and Related Compounds. The trimethyl-silyl enol ether-vinylcyclopropane rearrangement has been extended to bicyclo-[n,l,0]alkane systems (n = 3—5). With the silyl enol ether at the 1-position... [Pg.60]

When carbene 21 is generated from the diazo precursor photochemically in solution, it reacts with added alcohols by 0,H insertion (equation 55), in contrast to the gas-phase copyrolysis where the silene intermediate is trapped . Similarly, photolysis of 20 in the presence of 2,3-dimethylbutadiene gives mainly vinylcyclopropane 184, while after copyrolysis of 20 and the same diene one finds that most of the vinylcyclopropane rearranged to the cyclopentene, together with the [4-1-2] cycloaddition product of diene and silene 22 °. Furthermore carbene 21, generated photochemically or thermally (at 117-148 °C) in solution, undergoes [1 4-2] cycloaddition to alkynes to give cyclopropenes 185. [Pg.750]

The methods for attachment of the third and fourth rings in these two syntheses diverge and will be considered separately. Scheme 11.21 uses an annulation sequence which had been developed and shown to be a reasonably general way of constructing a cyclopentanone ring onto an existing carbonyl system. The C-8 C-11 bond is established by a thermally-induced vinylcyclopropane rearrangement. [Pg.591]

Adducts derived from cyclopropyl-TMM reactions are versatile synthetic intermediates. Alkylidenecyclopropanes have been proven useful in further Pd-cata-lyzed transformations [4], On the other hand, vinylcyclopropanes can undergo smooth thermal ring-expansion to cyclopentenes. Thus, a total synthesis of 11-hy-droxyjasionone (27) was achieved with the cyclopropyl-TMM cycloaddition as the crucial step, and the thermal rearrangement of the initial adduct (28) as an entry to the bicyclo[6.3.0]undecyl compound (29), a key intermediate in the synthetic sequence (Scheme 2.9) [19]. [Pg.64]


See other pages where Vinylcyclopropanes rearrangements, thermal is mentioned: [Pg.77]    [Pg.77]    [Pg.51]    [Pg.1443]    [Pg.1323]    [Pg.49]    [Pg.57]    [Pg.45]    [Pg.479]    [Pg.1006]    [Pg.1007]    [Pg.854]    [Pg.470]    [Pg.515]    [Pg.701]    [Pg.2590]    [Pg.1006]    [Pg.1007]    [Pg.619]    [Pg.591]    [Pg.231]    [Pg.243]   


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Rearrangement thermal

Vinylcyclopropanation

Vinylcyclopropane

Vinylcyclopropane rearrangement

Vinylcyclopropane thermal rearrangement

Vinylcyclopropane- cyclopentene rearrangement mechanism, thermal

Vinylcyclopropane-cyclopentene rearrangement thermal

Vinylcyclopropanes, rearrangement

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