2065-43-2Relevant academic research and scientific papers
Origins of selectivity for the [2+2] cycloaddition of α,β- unsaturated ketones within a porous self-assembled organic framework
Yang, Jun,Dewal, Mahender B.,Profeta Jr., Salvatore,Smith, Mark D.,Li, Youyong,Shimizu, Linda S.
, p. 612 - 621 (2008)
This article studies the origins of selectivity for the [2+2] cycloadditions of α,β-unsaturated ketones within a porous crystalline host. The host, formed by the self-assembly of a bis-urea macrocycle, contains accessible channels of ～6 A diameter and forms stable inclusion complexes with a variety of cyclic and acyclic α,β-unsaturated ketone derivatives. Host 1 crystals provide a robust confined reaction environment for the highly selective [2+2] cycloaddition of 3-methyl-2-cyclopentenone, 2-cyclohexenone, and 2-methyl-2-cyclopentenone, forming their respective exo head-to-tail dimers in high conversion. The products are readily extracted from the self-assembled host and the crystalline host can be efficiently recovered and reused. Molecular modeling studies indicate that the origin of the observed selectivity is due to the excellent match between the size and shape of these guests to dimensions of the host channel and to the preorganization of neighboring enones into favorable reaction geometries. Small substrates, such as acrylic acid and methylvinylketone, were bound by the host and were protected from photoreactions. Larger substrates, such as 4,4-dimethyl-2-cyclohexenone and mesityl oxide, do not undergo selective [2+2] cycloaddition reactions. In an effort to understand these differences in reactivity, we examined these host-guest complexes by thermogravimetric analysis (TGA), NMR, powder X-ray diffraction (PXRD) and molecular modeling.
Effect of Cu(I) on Cyclic Enone Photodimerizations
Fox, Marye Anne,Cardona, Raul,Ranade, Arvind C.
, p. 5016 - 5018 (1985)
Cu(I) can complex with either a nonbonded electron pair on oxygen or with the C=C ? bond in enones and might act as a template to arrange the 2:1 enone-copper complex into the preferred head-to-head regiochemistry.Upon excitation of either the n,?* or ?,?* band of the resulting metal complexes of cyclopentenone or of isophorone, however, the proportion of head-to-tail regioisomer observed inthe dimeric products increases.This shift in isomer distribution is caused by metal quenching of the preferentially formed head-to-head 2:1 enone-metal complex
Influences of Lewis Acids on the Photochemical Cyclodimerization of Cyclopentenone
Ogawa, Takuji,Masui, Yoshiyuki,Ojima, Shoshi,Suzuki, Hitomi
, p. 423 - 425 (1987)
In the presence of tin(IV) chloride, photochemical dimerization of cyclopentenone gave a cis-transoid-cis head-to-head dimer as predominant product.Other Lewis acids such as zinc(II) bromide, boron trifluoride etherate, tin(II) chloride, and silver(I) trifluoromethylsulfonate, however showed little influence.Tris(2,2,6,6-tetramethyl-3,5-heptanedionato)lanthanum(III) affected regiochemistry of the reaction in a way to favor a head-to-tail dimer.
Photoinduced cycloaddition of biomass derivatives to obtain high-performance spiro-fuel
Xie, Junjian,Pan, Lun,Nie, Genkuo,Xie, Jiawei,Liu, Yakun,Ma, Chi,Zhang, Xiangwen,Zou, Ji-Jun
, p. 5886 - 5895 (2019/11/11)
The photoinduced conversion of biomass-derived chemicals to high value chemicals and advanced fuels is of great significance but still challenging. Herein, a green and efficient self-sensitized [2 + 2] cycloaddition process is developed to convert biomass-derived β-pinene and isophorone to spirocyclic molecules, which cannot be achieved by thermal catalytic conversion. The photoreaction can take place with isophorone as the self-sensitizer, with high selectivity and a yield of up to 91.1%. A triplet sensitization mechanism is disclosed by a combination of triplet quenching, phosphorescence quenching, Stern-Volmer kinetic analysis, DFT calculations and photochemical kinetic studies. When combined with hydrodeoxygenation, spiro-fuel is obtained with an overall yield of 85.0% showing a high density of 0.911 g mL-1 which is 16.8% higher than that of conventional aviation kerosene (ca. 0.78 g mL-1), along with excellent cryogenic properties. Notably the self-sensitized cycloaddition strategy can be extended to a wide range of biomass derived α,β-unsaturated ketones and alkenes. Thus, this work provides a promising ring-increasing route to upgrade low-density bio-derived feedstocks to high-density hydrocarbons.
The mechanism of the photochemical cycloaddition reaction between 2-cyclopentenone and polar alkenes: Trapping of triplet 1,4-biradical intermediates with hydrogen selenide
Andrew, David,Hastings, David J.,Weedon, Alan C.
, p. 10870 - 10882 (2007/10/02)
The regiochemistry of the photochemical cycloaddition reaction between 2-cyclopentenone and the polar alkenes 1,1-difluoroethene and methyl acrylate has been investigated. With 1,1-difluoroethene the major cycloaddition product is a cyclobutane adduct possessing head-to-tail regiochemistry; with methyl acrylate the reaction is non-regioselective and a 46.5:53.5 ratio of head-to-head and head-to-tail cyclobutane regioisomers is obtained. These regiochemical outcomes are not those predicted by the Corey - de Mayo mechanism conventionally used to describe the enone - alkene photocycloaddition reaction. The triplet 1,4-biradicals implicated as intermediates in the photocycloaddition reaction between 2-cyclopentenone and the polar alkenes methyl acrylate and ethyl vinyl ether have been trapped quantitatively using hydrogen selenide as a hydrogen atom donor. The structures of the trapped products have been determined and hence the structures of their biradical precursors have been inferred. The yields of the trapped biradicals indicate that in both reactions the product distribution is controlled by the extent to which each of the isomeric biradical intermediates closes to products in competition with fragmentation to its ground state precursors. The product distribution does not reflect the relative rates of formation (and hence the relative amounts) of the isomeric biradical intermediates formed in each reaction. This conclusion is inconsistent with the long held idea that an oriented exciplex intermediate controls the reaction regiochemistry by favoring the formation of some biradicals over others. The structures of the biradical intermediates also reveal that both the 2-position and the 3-position of the enone are involved in forming the first bond to the alkene; with ethyl vinyl ether this bond is to the less substituted end of the alkene exclusively, while with methyl acrylate no selectivity in the site of initial bonding is observed.
Stereoselectivity in Photocycloaddition Reactions, 5.- Photoreaction of 2-Cyclopenten-1-one with Enol Ethers
Griesbeck, Axel G.,Stadtmueller, Stefan,Busse, Holger,Bringmann, Gerhard,Buddrus, Joachim
, p. 933 - 940 (2007/10/02)
The regio- and stereoselectivity of photocycloaddition reactions between 2-cyclopenten-1-one (1) and the electron-rich alkenes: ethyl, isopropyl, and phenyl vinyl ether (2-4) as well as 2,3-dihydrofuran (10) were examined.In all cases the annulated cyclobutene derivatives 5-7 and 11 were isolated in yieldsbetween 70 and 99percent.The regioisomeric HT/HH products were formed in a ratio of 3:1 to 4:1.For the determination of the product stereochemistry, INADEQUATE and 1H,1H-decoupling experiments were performed.Computer-assisted investigations on the molecular geometry and 1H,1H coupling constants were performed by using semiempirical methods (AM1, FINITE).The HT regioisomers were formed with moderate endo diastereoselectivity, whereas in the case of the HH regioisomers both diastereomers (exo/endo) were formed in equal amounts.Photoreaction with 2,3-dihydrofuran (10) led to almost exclusive formation of exo-diastereomeric HH and HT regioisomers 11.The observed stereoselectivity is rationalized by the optimal geometry of the intermediate triplet 1,4-biradicals during intersystem crossing. Key Words: Photocycloaddition / Selectivity, stereo-, regio- / 1,4-Biradicals / INADEQUATE / Calculations, AM1, FINITE
Radical clocks as probes of 1,4-biradical intermediates in the photochemical cycloaddition reactions of 2-cyclopentenone with alkenes
Rudolph, Andreas,Weedon, Alan C.
, p. 1590 - 1597 (2007/10/02)
The products of the photochemical reaction of 2-cyclopentenone with 1,6-heptadiene and with vinylcyclopropane have been examined.With 1,6-heptadiene the products were cyclobutanes, which arise from 2+2 photocycloaddition between the cyclopentenone carbon-carbon double bond and one of the two terminal double bonds of the heptadiene.The 1,4-biradical that is an intermediate in this reaction contains a derivative of a 1-hexenyl radical; no products derived from cyclization of this intermediate to a cyclopentenylmethyl radical were observed.With vinylcyclopropane some of the products isolated also arose from 2+2 photocycloaddition; in addition, comparable quantities of products resulting from rearrangement of the intermediate 1,4-biradical were obtained.In this case the initially produced intermediate 1,4-biradical contains a cyclopropylmethyl radical that can rearrange to a homoallylic radical; the products isolated were derived from intramolecular disproportionation in the new 1,7-biradical containing the homoallylic radical.The rate constant for the rearrangement of the cyclopropylmethyl radical to the homoallylic radical is known and was used as a clock to estimate the lifetime of the initially produced 1,4-biradical.The value estimated is of the order of 50 ns.The structures of the products indicate that the initial bonding between the excited cyclopentenone and vinylcyclopropane takes place at both the α-position and the β-position of the enone and not exclusively at the α-position as a recent report claims.
Electrophilic Opening of Photochemically Generated Bicyclopentane Derivatives - A Two-Step 3,3-Dimethylcyclopentane Anellation
Misslitz, Ulf,Primke, Hartmut,Meijere, Armin de
, p. 537 - 544 (2007/10/02)
Tricyclic compounds 7a-e with 5,5-dimethylbicyclopentane subunits were obtained - although in poor yields - by photochemically initiated cycloaddition of 3,3-dimethylcyclopropene to 2-cycloalken-1-ones 4a-e.Catalytic hydrogenation of bicyclopentanes 7a/7c proceeded regioselectively to give bicyclic compounds 17a/17c with gem-dimethyl-substituted cyclopentane units.Treatment of carbonyl-protected bicyclopentanes 16a/16c with mercury(II) acetate in THF/water or THF/methanol followed by reductive demercuration afforded - with practically quantitative diastereo-, but no recognizable regioselectivity - gem-dimethyl-substituted hydroxy- or methoxycyclopentanes 18-21, respectively.Upon warming under reflux the hydroxymercurated ketone 7c gave the regioselectively formed β-elimination product endo-7-hydroxy-8,8-dimethylbicyclonon-1(9)-en-2-one (23).Upon analogous treatment, however, hydroxymercurated 7a was recovered unchanged. - Keywords: Cycloaddition of 3,3-dimethylcyclopropene/ Ring-anellated bicyclopentanes/ Hydroxymercuration of bicyclopentanes/ 3,3-Dimethylcyclopentane anellation
STRUCTURE DETERMINATION OF PHOTOCYCLODIMERS OF 2-CYCLOALKENONES VIA ENANTIOSELECTIVE GAS CHROMATOGRAPHY AND GC/MS ANALYSIS
Anklam, Elke,Koenig, Wilfried A.,Margaretha, Paul
, p. 5851 - 5854 (2007/10/02)
Enantioselective gas chromatography combined with GC/MS analysis allows the direct assignment of constitution and configuration of the photocyclodimers of cyclic enones 1a - 1h.
