Biradical intermediate in the [2 + 2] photocycloaddition of dienes and alkenes to [60]fullerene

The photocycloaddition of vinylcyclopropanes to C60 yields stereospecifically a five-membered [60]fullerene adduct. These results suggest a biradical intermediate of the [2 + 2] photocycloaddition between dienes or arylalkenes and C60. An electron transfer between the triplet excited state of C60 and the unsaturated substrates precedes the formation of the intermediate.     

NMR analyses of two isomeric cyclobutanes from a [2 + 2] photocycloaddition

Complete ¹H and ¹³C NMR assignments are reported for two isomeric cyclobutanes generated from the photochemical [2 + 2] cycloaddition of N‐methylisocarbostyril and 4‐methoxy‐3‐buten‐2‐one. The reaction is 100% regioselective and demonstrates the potential synthetic utility of de Mayo type reactions using an isocarbostyril and a stable β‐dicarbonyl enol derivative. Copyright © 2002 John Wiley & Sons, Ltd.     

Transition state analysis on regioselectivity in [2+2] photocycloaddition reactions of substituted 2-cyclohexenone with cycloalkenecarboxylates

The experimental results of the triplet [2+2] photocycloaddition reactions of substituted 2-cyclohexenone 1 with cycloalkenylesters 2, 3, 4 have showed remarkable change in the regioselectivity of the products. The ht/hh product ratio increases with increment of the cycle-size. The FMO investigations in addition to the transition state analysis were used to rationalize such regioselectivity. The FMO method with their orbital coefficients and energies could not explain the reaction selectivity since these values of 2-4 showed tendency to form the hh adduct mainly. PM3, PM5, CIS/6-31G, and B3LYP/6-31G methods were used to locate the hh and ht transition states of the three reactions. As the potential energy barriers (TS1) on the first TS surface for the major products were lower than that for the minor products in most of the cases, the real ratio can be explained in terms of TS analysis. The recently improved PM5 and the B3LYP methods were more successful in this debate as partitioning the activation energy at the potential energy barriers into reactant deformation and the interaction (or repulsion) energies is easy and effective. The changes in the ht/hh ratio with the enlargement of the alkene ring size may be due to the increment of the repulsion energy and large changes in the deformation energy of the reactants. In the transition state structures the stabilities of the major products are thought to be due to the existence of some repulsion between the enone carbonyl and esters in the alkenylesters, and some hydrogen bonding between the reactants. The FMO and second transition state (TS2) energy on the biradical intermediates are also thought to play some role in controlling the product selectivity by lowering the closure energy of the biradicals according to the possibility of their overlapping.     

[2 + 3]-Cycloadditions to C60 fullerene. Synthesis of pyrrolidinofullerenes

Pyrrolidinofullerenes were synthesized by reaction of C₆₀ fullerene with N-methylglycine and substituted aromatic aldehydes.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 10, 2004, pp. 1695–1697.Original Russian Text Copyright © 2004 by Loginova, Gunkin.This revised version was published online in April 2005 with a corrected cover date.     

Photoactivated [3+2] addition of 6,7-seco-angustilobine B to fullerene [C60

A synthesis of a new alkaloid-fullerene conjugate (1) is reported. The reaction was carried out by photoinduced [3+2] cycloaddition of the Alstonia indole alkaloid, 6,7-seco-angustilobine B (2), to fullerene[C60] (3) under aerobic conditions. The major monoaddition photoadduct (1) was characterized unambiguously by UV, IR, MALDI-TOFMS and NMR experiments. A mechanism highlighted by sequential photoinduced electron transfer andradical recombination pathways is also proposed. No significant enhancement in inhibition against M. tuberculosis H37Rv was observed for 1 compared with its parent compounds 2 and 3.     

[60]富勒烯[2＋3]环加成反应的研究进展

对[60]富勒烯[2＋3]环加成反应的研究进展进行了综述，并介绍了在环加成反应中使用的主要试剂及反应机理.     

Investigating the arenyl-diene double [3 + 2] photocycloaddition reaction

The double [3 + 2] photocycloaddition reaction involving arenyl-dienes has been used to assemble seven separate [5.5.5.5] fenestrane structures that include ether and aza variants. The primary photolysis step was a meta photocycloaddition reaction, while a secondary photocycloaddition step formed the fenestrane structure. Investigations involving the insertion of an additional methylene group into the basic arenyl-diene skeleton failed to afford the desired [5.5.5.6] fenestrane structure. The presence of an oxime moiety in the aromatic photosubstrate allowed the primary photolysis step to take place; however, an attempted secondary photocycloaddition reaction involving the oxime did not provide the intended polyheterocyclic fenestrane. An alternative strategy to form various "criss-cross" double meta photocycloadducts was investigated and led to the discovery of a Paterno-Büchi cycloaddition reaction between acetone and an angular meta photocycloadduct. Other novel thermally and photochemically mediated skeletal rearrangement reactions were also recorded.     

Pressure effects in a [2+2] photocycloaddition and -reversion

Evidence is presented to support the conclusion that the [2+2] photocycloaddition of acrylonitrile to naphthalene has a late transition state similar in volume to those in concerted thermal cycloadditions.     

DFT study on [4+2] and [2+2] cycloadditions to [60] fullerene

The functionalisation of C₆₀ fullerene with 2,3-dimethylene-1,4-dioxane (I) and 2,5-dioxabicyclo [4.2.0]octa-1(8),6-diene (II) was investigated by the use of density functional theory calculations in terms of its energetic, structural, field emission, and electronic properties. The functionalisation of C₆₀ with I was previously reported experimentally. The I and II molecules are preferentially attached to a C—C bond shared and located between two hexagons of C₆₀ via [4+2] and [2+2] cycloadditions bearing reaction energies of ?15.9 kcal mol^?1 and ?72.4 kcal mol^?1, respectively. The HOMO-LUMO energy gap and work function of C₆₀ are significantly reduced following completion of the reactions. The field electron emission current of the C₆₀ surface will increase after functionalisation of either the I or II molecule.     

Propellanes-LXXV A [2+2]photocycloaddition of an N = n bond to a C=c bond

Irradiation of an azo-propellane derivative in which an olefinic bond is proximate to the azo group forms a cage compound containing a 1,2-diazacyclobutane ring.     

Intramolecular pyridone/enyne photocycloaddition: partitioning of the [4 + 4] and [2 + 2] pathways

Intramolecular photocycloaddition (>290 nm) between a 1,3-enyne and a 2-pyridone is far more selective than the intermolecular version; a three-atom linkage both controls regiochemistry and separates the [2 + 2] and [4 + 4] pathways. All four head-to-head, head-to-tail, tail-to-head, and tail-to-tail tetherings have been investigated. Linkage via the ene of the enyne leads to [2 + 2] products regardless of alkene geometry, whereas linkage through the yne results in [4 + 4] cycloadducts. The bridged 1,2,5-cyclooctatriene products of [4 + 4] cycloaddition are unstable and undergo a subsequent [2 + 2] dimerization reaction.     

Diastereoselective transannular [2+2] photocycloaddition of ascorbic acid derivatives

Ring-closing metathesis of bis-O,O-alkenyl ascorbic acid derivatives affords cyclic ethers in good yields which can be further converted by irradiation at 254 nm into new polyoxacyclic structures according to a diastereoselective transannular [2+2] photocycloaddition.     

Synthesis and evaluation of a chiral menthol functionalized silsesquioxane: application to diastereoselective [2+2] photocycloaddition

A novel chiral menthol derivative supported on silsesquioxane was easily synthesized by hydrosilylation of the corresponding arylmenthyl olefin with commercially available silsesquioxane-type hydrosilane. We evaluated the applicability of the silsesquioxane-based compound to diastereoselective [2+2] photocycloaddition reaction. The newly synthesized silsesquioxane-based chiral menthol derivative 9 indicated similar diastereoselectivity to the corresponding p-methoxyphenyl menthol derivative.     

Progress toward the total synthesis of Bielschowskysin: a stereoselective [2+2] photocycloaddition

[STRUCTURE: SEE TEXT] The tetracyclic core of the diterpene bielschowskysin has been prepared as a single enantiomer via a stereoselective intramolecular [2+2] photocycloaddition of 5-alkylidene-2(5H)-furanone 3.     

3He NMR: from free gas to its encapsulation in fullerene

The ³He nuclear magnetic shieldings were calculated for single helium atom, its dimer, simple models of fullerene cages (He@C_n), and single wall carbon nanotubes. The performances of several levels of theory (HF, MP2, DFT‐VSXC, CCSD, CCSD(T), and CCSDT) were tested. Two sets of polarization‐consistent basis sets were used (pcS‐n and aug‐pcS‐n), and an estimate of ³He nuclear magnetic shieldings in the complete basis set limit using a two‐parameter fit was established. Theoretical ³He results reproduced accurately previously reported theoretical values for helium gas, dimer, and helium probe inside several fullerene cages. Excellent agreement with experimental values was achieved. ³He nuclear magnetic shieldings of single helium atom approaching various points of benzene ring were tested, and an impact of ³He confinement within fullerene cages of different size on the ³He chemical shift was determined. Copyright © 2013 John Wiley & Sons, Ltd.     

Photochemistry of benzotriazole: an unprecedented tautomer-selective intermolecular [2+2] photocycloaddition

[reaction: see text]. Irradiation of benzotriazole with a variety of maleimide derivatives leads to the stereo- and regioselective formation of aryl [2 + 2] photocycloaddition products. Further studies with 2-alkyl benzotriazole derivatives indicates that in the case of the parent benzotriazole this cycloaddition proceeds selectively via the 2H-tautomer.     

Catalytic [2+1]-cycloaddition of ethyl diazoacetate to fullerene [60]

Cyclopropanation of C₆₀-fullerene was performed with ethyl diazoacetate in the presence of Pd(PPh₃)₄ catalyst. A probable reaction mechanism is suggested.     

Catalytic [2+1] cycloaddition of diazo compounds to [60]fullerene

A catalytic method for the efficient synthesis of 5,6-open and 6,6-closed (2π+1π) fullerene adducts by [2+1] cycloaddition of ethyl 2-alkyl(hetaryl)-2-diazoacetates to [60]fullerene in the presence of a three-component catalyst Pd(acac)₂—PPh₃—Et₃Al have been developed.