Cyclopentene Rearrangement Research Articles

Enantioselective Iminium Catalysis-Mediated Vinylcyclopropane–Cyclopentene Rearrangement

Key words vinylcyclopropane rearrangement - iminium catalysis - cyclopentenes - DYKAT

Functionalized Cyclopentenes via the Formal [4+1] Cycloaddition of Photogenerated Siloxycarbenes from Acyl Silanes.

This work describes the first formal cycloaddition reaction of photogenerated nucleophilic carbenes derived from acylsilanes with electrophilic dienes. The resulting transient donor-acceptor cyclopropane rearranges to its stable and highly functionalized cyclopentene isomer in an unprecedented metal-free process. The cyclopropanation-vinyl cyclopropane rearrangement sequence was corroborated by computational calculations. The cyclopropane formation corresponds to a higher energetic barrier, and the vinylcyclopropane-cyclopentene rearrangement proceeds through different mechanisms, although of comparable energies, depending on the stereochemistry of the cyclopropane.

ChemInform Abstract: A Facile and Efficient Synthesis of 3‐Spirocyclopentene‐2‐oxindoles via Palladium Mediated Vinylcyclopropane—Cyclopentene Rearrangement of Oxindole Derived Vinylcyclopropanes.

Palladium catalyzed synthesis of a number of novel 3-spirocyclopentene-2-oxindoles in good yields has been accomplished from geometrically strained 3-vinylcyclopropane-2-oxindole via vinylcyclopropane–cyclopentene rearrangement.

A facile and efficient synthesis of 3-spirocyclopentene-2-oxindoles via palladium mediated vinylcyclopropane–cyclopentene rearrangement of oxindole derived vinylcyclopropanes

Palladium catalyzed synthesis of a number of novel 3-spirocyclopentene-2-oxindoles in good yields has been accomplished from geometrically strained 3-vinylcyclopropane-2-oxindole via vinylcyclopropane–cyclopentene rearrangement.

ChemInform Abstract: From Discovery to Application: 50 Years of the Vinylcyclopropane—Cyclopentene Rearrangement and Its Impact on the Synthesis of Natural Products

AbstractReview: 121 refs.

From Discovery to Application: 50 Years of the Vinylcyclopropane–Cyclopentene Rearrangement and Its Impact on the Synthesis of Natural Products

A classic that hasn't lost its charm: The historical origins and current status of the vinylcyclopropane–cyclopentene rearrangement and the corresponding transformations of heteroatom-containing analogues (see scheme) are described in the context of methodology development and natural products synthesis. Several important events that greatly influenced the author's own research program some 30 to 40 years ago are recounted as personal recollections.

6‐(Diazomethyl)‐1,3‐bis(methoxymethyl)uracil, Synthesis and Transformation into Annulated Pyrimidinediones

Abstract6‐(Diazomethyl)‐1,3‐bis(methoxymethyl)uracil (5) was prepared from the known aldehyde 3 by hydrazone formation and oxidation. Thermolysis of 5 and deprotection gave the pyrazolo[4,3‐d]pyrimidine‐5,7‐diones 7a and 7b. Rh2(OAc)4 catalyzed the transformation of 5 into to a 2 : 1 (Z)/(E) mixture of 1,2‐diuracilylethenes 9 (67%). Heating (Z)‐9 in 12n HCl at 95° led to electrocyclisation, oxidation, and deprotection to afford 73% of the pyrimido[5,4‐f]quinazolinetetraone 12. The Rh2(OAc)4‐catalyzed reaction of 5 with 3,4‐dihydro‐2H‐pyran and 2,3‐dihydrofuran gave endo/exo‐mixtures of the 2‐oxabicyclo[4.1.0]heptane 13 (78%) and the 2‐oxabicyclo[3.1.0]hexane 15 (86%), Their treatment with AlCl3 or Me2AlCl promoted a vinylcyclopropane–cyclopentene rearrangement, leading to the pyrano‐ and furanocyclopenta[1,2‐d]pyrimidinediones 14 (88%) and 16 (51%), respectively. Similarly, the addition product of 5 to 2‐methoxypropene was transformed into the 5‐methylcyclopenta‐pyrimidinedione 18 (55%). The Rh2(OAc)4‐catalyzed reaction of 5 with thiophene gave the exo‐configured 2‐thiabicyclo[3.1.0]hexane 19 (69%). The analoguous reaction with furan led to 8‐oxabicyclo[3.2.1]oct‐2‐ene 20 (73%), and the reaction with (E)‐2‐styrylfuran yielded a diastereoisomeric mixture of hepta‐1,4,6‐trien‐3‐ones 21 (75%) that was transformed into the (1E,4E,6E)‐configured hepta‐1,4,6‐trien‐3‐one 21 (60%) at ambient temperature.

Thermal isomerisation of 1-chloro-1-fluoro-2-vinylcyclopropanes: competition between the vinylcyclopropane–cyclopentene rearrangement and cyclopropyl–allyl transformation

The gas-phase pyrolysis of 1-chloro-1-fluoro-2-vinylcyclopropane and 1-chloro-1-fluoro-2-methyl-2-vinylcyclopropane at 305–360 °C afforded 4-chloro-4-fluorocyclopentenes and chlorofluorobutadienes as a result of competitive vinylcyclopropane–cyclopentene rearrangement and cyclopropyl–allyl isomerisation.

Dynamics of the biradical mediating vinylcyclopropane–cyclopentene rearrangement

A previous direct dynamics trajectory study of the thermal vinylcyclopropane–cyclopentene rearrangement [C. Doubleday, J. Phys. Chem. A, 2001, 105, 6333], based on an AM1-SRP potential energy surface (PES), is extended to study details of the intramolecular and unimolecular dynamics in the biradical region of the PES. The branching ratio of the 4 diastereomeric products and the time dependence of their formation depend on the transition state at which the trajectories are initialized and its vibrational temperature or mode specific excitation. For the small amount of reaction occurring after ∼600 fs, there is considerable stereorandomness in the product yield, which contrasts with the short-time nonstatistical and mode specific reaction. Varying the initial amount of energy in reaction coordinate translation has only a minor effect on the biradical lifetime, but may have an appreciable effect on the relative product yield. Changing the rotational temperature has a negligible effect on the reaction dynamics. This study illustrates the utility of the quasiclassical trajectory method for studying short-time unimolecular dynamics and the importance of including zero-point energy motion in the trajectory initial conditions.

Easy Access to (n+3)-Dimethylamino-1-ethenylbicyclo[n.1.0]alkanes and their Facile Conversion to Ring-annelated Cyclopentadienes

Aminocyclopropanation of 1-ethenylcycloalkenes 2a-d with N,N-dibenzyl- and N,N-dimethylformamide, respectively, by treatment with cyclohexylmagnesium bromide in the presence of methyltitanium triisopropoxide yielded the exo-(n+3)-N,N-dime­thylamino-1-ethenylbicyclo[n.1.0]alkanes 3a-d (58-72%). Compounds 7b-d could be transformed by thermal vinylcyclopropane to cyclopentene rearrangement to the corresponding exo-4-dimethyl­aminobicyclo[n.3.0]alk-1-enes 7b-d (84-90%). Elimination of the dimethylamino group led to the cyclopentadienes 11b-d and 12b-d (72-82%). The 5-dimethylamino-1-ethenylbicyclo[2.1.0]pentane did not undergo the typical vinylcyclopropane rearrangement, but ring-opening at the bridgehead-bridgehead bond to form 1-ethenyl-2-dimethylaminocyclopentene 8.

Mechanism of the Vinylcyclopropane−Cyclopentene Rearrangement Studied by Quasiclassical Direct Dynamics

The stereochemical course of the thermal rearrangement of vinylcyclopropane to cyclopentene is computed using quasiclassical trajectories run on a modified AM1 potential parametrized to fit ab init...

Thermal Stereomutations and Vinylcyclopropane-to- Cyclopentene Rearrangement of 2-Methylene-3-spiro- cyclopropanebicyclo[2.2.1]heptane

Thermal Stereomutations and Vinylcyclopropane-to- Cyclopentene Rearrangement of 2-Methylene-3-spiro- cyclopropanebicyclo[2.2.1]heptane

Substituent Effects on the Vinylcyclopropane–Cyclopentene Rearrangement – A Theoretical Study by Restricted and Unrestricted Density Functional Theory

The effect of donor substitution by the hydroxy group and of acceptor substitution by the cyano group on the activation energies of the vinylcyclopropane–cyclopentene rearrangement was calculated by the spin-restricted RB3LYP/6-31G* method for reactant structures and by the spin-unrestricted UB3LYP/6-31G* method for transition structures. The activation energies of the rearrangement of hydroxy- and cyano-substituted vinylcyclopropanes are very similar for substitution in the same position. In agreement with earlier findings the substituent effects on the activation energies are closely connected with the radical stabilizing properties of the substituents. As indicated by singlet/triplet splitting energies, the transition structures are essentially biradicaloid. In spite of spin pairing in the transition structure the substituent effects on bond lengths and on stabilization energies are very similar to those of the free radicals corresponding to the two radical substructures. Thus, the transition structures may be considered, in good approximation, as structures consisting of two weakly interacting radicals.

Stereochemistry of the Thermal Isomerization of 1-Ethenyl-7-exo-Phenylbicyclo[4.1.0]heptane to 7-Phenylbicyclo[4.3.0]non-1(9)-ene: The Conformational Course of an Antarafacial,Retention Vinylcyclopropane−Cyclopentene Rearrangement

The thermal vinylcyclopropane−cyclopentene rearrangement of 1-ethenyl-7-exo-phenylbicyclo[4.1.0]heptane at 220 °C gives mostly migration with retention to form 7-exo-phenylbicyclo[4.3.0]non-1(9)-ene. 1-(E-d-Ethenyl)- and 1-(Z-d-ethenyl)-7-exo-phenylbicyclo[4.1.0]heptanes give both 8-exo and 8-endo deuterium-labeled products. The suprafacial,retention and antarafacial,retention paths for this rearrangement are used in 85:15 proportions. The antarafacial process may involve passage through a “semicircular” diradical conformation; it cannot occur through rotation in the opposite sense, passing through an “extended” diradical geometry.

ChemInform Abstract: The Cation Radical Vinylcyclopropane → Cyclopentene Rearrangement: Reaction Mechanism and Periselectivity.

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Epimerization of Cyclic Vinylphosphirane Complexes: The Intermediacy of Biradicals

The phosphinidene complex Ph−P−W(CO)5 reacts with cyclopentadiene, 1,3-cyclohexadiene, 1,3-cycloheptadiene, and 1,3-cyclooctadiene to give in each case isomeric mixtures of syn- and anti-vinylphosphiranes. With longer reaction times and/or higher reaction temperatures, the anti adducts isomerize to the syn adducts. These epimerizations are likely to proceed via biradical intermediates. Only the syn-vinylphosphirane of 1,3-cyclohexadiene undergoes a [1,3]-sigmatropic shift to yield a syn-phopholene. The dichotomy of biradical and concerted mechanisms is discussed in relationship with the analogous mechanism for the vinylcyclopropane → cyclopentene rearrangement.

The cation radical vinylcyclopropane→cyclopentene rearrangement: reaction mechanism and periselectivity

The vinylcyclopropane→cyclopentene rearrangement catalyzed by one-electron oxidation has been shown to be most consistent with a stepwise, cation radical mechanism. It was also discovered that the formal rearrangement periselectivity of vinylcyclopropanes with cis-alkyl substituents can be changed by one-electron oxidation.

Syntheses of Two Stereoselectively Trideuterated Vinylcyclopropanes

An experimental determination of the stereochemistry of the thermal vinylcyclopropane to cyclopentene rearrangement is of some importance. Therefore, the authors have synthesized multigram quantities of methyl 2-cyclopropene-1-carboxylate have been converted in five steps to the syn-E and syn-Z isomers of 2,3,2{prime}-d{sub 3}-vinylcyclopropane with high levels of deuterium incorporation and steroselectivity. 2 figs.

Zur Bildung von Vinylcyclopropan‐ und Cyclopentenderivaten aus alkenylsubstituierten Chromcarben‐Komplexen: Konkurrenz von formalen [2 + 1]‐ und [3 + 2]‐Cycloadditionen

Formation of Vinylcyclopropane and Cyclopentene Derivatives from Alkenyl‐Substituted Chromium Carbene Complexes: Competition between Formal [2 + 1] and [3 + 2] Cycloadditions.The alkenyl‐substituted chromium carbene complexes 1 – 4 were synthesized following the method of Aumann which starts from the corresponding aldehydes. At 80°C the styryl‐substituted complex 1 and electron‐deficient olefins smoothly provide vinylcyclopropane derivatives 6,8, 10, and 12 in good yields. On the other hand, methyl acrylate and the anisyl‐ and furyl‐substituted vinylcarbene complexes 2 and 3 give mixtures of the expected vinylcyclopropanes and of cyclopentene derivatives. The pyrrolyl‐substituted complex 4 and methyl acrylate exclusively afford the cyclopentenes 24a/b which are the result of a hitherto unprecedented formal [3 + 2] cycloaddition of the vinylcarbene complex to the olefin. However, there are strong arguments suggesting the corresponding vinylcyclopropanes as intermediates. The very smooth vinylcyclopropane→cyclopentene rearrangement probably occurs via zwitterionic intermediates that are wellstabilized by donor and acceptor substituents. Hydrolysis of 24a/b to the cyclopentanone derivatives 25a/b demonstrates that this new route to five‐membered carbocycles should have synthetic potential.

Evidence for thermal 3,5-sigmatropy of 7-vinylnorcaradienes

7-Phenyl-7-vinylcycloheptatrienes rearrange via their endo-norcaradiene valence tautomers (1; a–d) to give the dihydroindenes (2; a–d) and the Cope products (3; a–c); dihydroindene formation is stereospecific, and strongly inhibited in the benzonorcaradienes (7; b–d) in agreement with 3,5-sigmatropy rather than vinylcyclopropane–cyclopentene rearrangement.