Further examples of photocycloadditions of 1,3-diketonatoboron difluorides to olefins: a description of the reaction pattern and mechanism

1997 ◽  
Vol 75 (6) ◽  
pp. 720-726 ◽  
Author(s):  
Yuan L. Chow ◽  
Xianen Cheng ◽  
Shi S. Wang ◽  
Susan P. Wu
Keyword(s):  
Excited State ◽  
Double Bond ◽  
Phenyl Group ◽  
Adduct Formation ◽  
Reaction Pattern ◽  
Methyl Substituent ◽  
Cyclic Olefins ◽  
Dibenzoylmethanatoboron Difluoride

The photocycloaddition of dibenzoylmethanatoboron difluoride (DBMBF2) with conjugated nitriles, ketones, and esters occurs more slowly than that with simple olefins and with fair regioselectivity. For these electron-deficient olefins, the cyclic analogues react more slowly than the acyclic ones and the cyano analogues react more slowly than all others; also a β-methyl substituent reverses the regioselectivity in adduct formation. Benzoylacetonatoboron difluoride (BABF2) photocycloadds to simple cyclic olefins from the excited state isomer in which the double bond is conjugated with the phenyl group, and occurs more slowly than that of the corresponding reaction of DBMBF2. The efficiency and regiochemistry of these cycloadditions have been explained with respect to the exciplex as the immediate intermediate. Keywords: photocycloaddition, dibenzoylmethanatoboron difluoride, benzoylacetonatoboron difluoride, exciplex.

The photocycloaddition of dibenzoylmethanatoboron difluoride (DBMBF2) with conjugated enones and en-esters

1993 ◽  
Vol 71 (6) ◽  
pp. 846-854 ◽  
Author(s):  
Yuan L. Chow ◽  
Shi-Sen Wang ◽  
Xian-En Cheng
Keyword(s):  
Excited State ◽  
Charge Transfer ◽  
Ring Opening ◽  
Electron Donors ◽  
Head Orientation ◽  
Singlet Excited State ◽  
Methyl Substitution ◽  
Unsaturated Ketones ◽  
Dibenzoylmethanatoboron Difluoride

Dibenzoylmethanatoboron difluoride (DBMBF2), the BF2 complex of dibenzoylmethane, reacted from its singlet excited state with α,β-unsaturated ketones and esters to give 1,5-diketones by a [2+2] cycloaddition and ring-opening sequence in an analogous pathway to that observed in the photocycloaddition to olefins and dienes. The present photoreaction is unexpected since conjugated enones and en-esters are poor electron donors to comply with the previously proposed charge transfer requirement in DBMBF2 photoreactions. The photocycloaddition to these substrates was highly regioselective and stereoselective, giving the head-to-head orientation, which could be enhanced by α-methyl substitution; β-methyl substitution increased the alternate head-to-tail orientation. The photolysis of a mixture of DBMBF2 and a cyclic enone also caused the latter to dimerize to give head-to-head and head-to-tail dimers in significant yields. These photodimerizations were apparently caused by DBMBF2 sensitization. The mechanism of the sensitization is discussed.

Réactions avec le diazométhane d'esters cinnamylidène maloniques ou cyanacétiques méthylés ou phénylés en γ des groupements fonctionnels et des malononitriles correspondants. Thermolyse des pyrazolines obtenues

1977 ◽  
Vol 55 (22) ◽  
pp. 3942-3950 ◽  
Author(s):  
J. Martelli ◽  
R. Carrié
Keyword(s):  
Double Bond ◽  
Phenyl Group

The syntheses of cinnamylidene malonic or cyanacetic esters, bearing a methyl or a phenyl group in the position γ to the withdrawing groups, were achieved. The configurations of the various isomers were established and the conformations are discussed. Diazomethane adds exclusively to the α,β double bond of these dipolarophiles in only one orientation. The thermolysis of the resulting 1-pyrazoline was studied.

scholarly journals N-Arylphenothiazines as strong donors for photoredox catalysis – pushing the frontiers of nucleophilic addition of alcohols to alkenes

2019 ◽  
Vol 15 ◽  
pp. 52-59 ◽  
Author(s):  
Fabienne Speck ◽  
David Rombach ◽  
Hans-Achim Wagenknecht
Keyword(s):  
Excited State ◽  
Nucleophilic Addition ◽  
Reduction Potential ◽  
Phenyl Group ◽  
Addition Product ◽  
Electrochemical Characteristics ◽  
Photoredox Catalysis ◽  
Reaction Conditions ◽  
State Reduction ◽  
Reducing Properties

A new range of N-phenylphenothiazine derivatives was synthesized as potential photoredox catalysts to broaden the substrate scope for the nucleophilic addition of methanol to styrenes through photoredox catalysis. These N-phenylphenothiazines differ by their electron-donating and electron-withdrawing substituents at the phenyl group, covering both, σ and π-type groups, in order to modulate their absorbance and electrochemical characteristics. Among the synthesized compounds, alkylaminylated N-phenylphenothiazines were identified to be highly suitable for photoredox catalysis. The dialkylamino substituents of these N-phenylphenothiazines shift the estimated excited state reduction potential up to −3.0 V (vs SCE). These highly reducing properties allow the addition of methanol to α-methylstyrene as less-activated substrate for this type of reaction. Without the help of an additive, the reaction conditions were optimized to achieve a quantitative yield for the Markovnivkov-type addition product after 20 h of irradiation.

scholarly journals Bridge effect of the C=C, C=N and N=N bonds on the long distance electronic charge transfer ofpara‒substituted stilbenoid compounds

2000 ◽  
Vol 14 (4) ◽  
pp. 259-267 ◽  
Author(s):  
Manuel A. Leiva ◽  
Raul G. E. Morales
Keyword(s):  
Charge Transfer ◽  
Double Bond ◽  
Molecular System ◽  
Chemical Shifts ◽  
Phenyl Group ◽  
Point Of View ◽  
Electronic Charge ◽  
Orbital Theory ◽  
Long Distance ◽  
C Nmr

By means of13C‒NMR spectroscopy and ab initio molecular orbital theory calculations, we have analyzed the bridge effect of the C=C, C=N and N=N bonds on the long distance charge transfer of4‒dimethylamino‒4'‒nitrostilbenoid compounds in the ground electronic state.After a complete spectral assignment of the13C‒NMR signals in these molecular compounds, we have characterized the effect of the nitrogen centres on the molecular bridge by means of the chemical shifts of the carbon centres, the theoretical charge densities and the dipolar moments.From an electronic molecular point of view, our results describe two main properties of the double bond bridge. The first is related to the local charge accumulation capacity given by the type of the atomic centres and the structural orientation of the double bond bridge, and the second property is related to the modulation of the electronic charge distribution through the molecular system by the electrical polarization of the bridge.Other complementary experimental evidences have permit us to establish new local molecular domains of the bridge effect in these stilbenoid compounds by means of linear correlations between13C‒NMR chemical shifts of the aromatic carbon centres of the acceptor‒phenyl group and the molecular polarity of the species under study.

The influence of phenylethynyl linkers on the photo-physical properties of metal-free porphyrins

2000 ◽  
Vol 04 (07) ◽  
pp. 669-683 ◽  
Author(s):  
GARY A. BAKER ◽  
FRANK V. BRIGHT ◽  
MICHAEL R. DETTY ◽  
SIDDHARTH PANDEY ◽  
COREY E. STILTS ◽  
...  
Keyword(s):  
Excited State ◽  
Radiative Decay ◽  
Phenyl Group ◽  
Quantum Yields ◽  
Fluorescence Lifetimes ◽  
Strongly Coupled ◽  
Metal Free ◽  
Fluorescence Quantum Yields ◽  
Porphyrin Core ◽  
Absorbance Spectra

Series of 5,10,15,20-tetraarylporphyrins 1 and 5,10,15,20-tetrakis[4-(arylethynyl)phenyl]porphyrins 2 were prepared via condensation of pyrrole with the appropriate benzaldehyde or 4-(arylethynyl)benzaldehyde derivative (3). Condensation of meso-phenyldipyrromethane with mixtures of benzaldehyde and 4-(trimethylsilyl-ethynyl)benzaldehyde gave a separable mixture of mono- (6), bis- (both cis-7 and trans-8) and tris[4-(trimethylsilylethynyl)phenyl]porphyrin (9). Following removal of the trimethylsilyl groups of 6–9, the 4-ethynylphenyl groups of 11–14 were coupled to 1-iodo-3,5-di(trifluoromethyl)benzene with Pd ( OAc )2 to give 15–18 bearing one, two (both cis- and trans-) and three 4-[bis-3,5-(trifluoromethyl)phenylethynyl]phenyl groups respectively. Coupling of 11 and 1-iodo-4-nitrobenzene with Pd ( OAc )2 gave porphyrin 19 with one 4-(4-nitrophenylethynyl)phenyl group. Porphyrin 24 with a p-quinone linked to the porphyrin core via a phenylethynyl group was prepared via similar chemistry. The absorbance spectra, emission maxima, excited-state fluorescence lifetimes, quantum yields of fluorescence, rates of fluorescence and rates of non-radiative decay were measured for each of the porphyrins. Absorbance spectra and emission maxima were nearly identical for all the porphyrins of this study, which suggests that the aryl groups and 4-(arylethynyl)phenyl groups are not strongly coupled to the porphyrin core in these metal-free compounds. Fluorescence quantum yields and rates of radiative decay were larger for porphyrins bearing 4-(arylethynyl)phenyl groups, while excited-state fluorescence lifetimes were somewhat shorter. These effects were additive for each additional 4-(arylethynyl)phenyl group.

scholarly journals A Computational Study of a Prebiotic Synthesis of the Steroid Progesterone (A and B Rings)

2020 ◽  
Vol 17 ◽  
Keyword(s):  
Double Bond ◽  
Hydroxyl Radicals ◽  
Computational Study ◽  
Prebiotic Synthesis ◽  
Magnesium Ion ◽  
Methyl Substituent ◽  
Trans Conformation ◽  
Trans Orientation ◽  
Metal Site ◽  
Enthalpy Changes

The magnesium ion metalloporphyrin complex is shown to bind the ligands propyne (p) and ethyne (e) on the metal or nitrogen pyrrole sites as a two site catalyst in their copolymerization. The order of addition of the monomers is (pepeeepee). The steroid ring D (pep) is formed first from the propyne adduct bound to the metal site and the but-diene adduct bound to the N-site. The optimal orientation of these adducts determines the β-orientation of the 17-substituent. Further reaction with hydroxyl radicals allows this to be a 17 β- acetyl substituent. Further addition of three ethyne monomers forms a N-tri-ene cyclopentene derivative able to cyclise to form the steroid ring C (pee) with a trans conformation and a 13-β methyl substituent.. Further binding of propyne on the metal site together with the N-indenyl bound adduct enables the B-ring (eep) to form with a trans orientation and a 10-β-methyl substituent. Further addition of two ethyne monomers to the Mg.porphin.N-phenanthrenyl bound adduct allows cyclisation to form the A-ring (pee). The polymerization is curtailed by reaction with hydroxyl radical to form the 3-keto substituent. The cleavage of the Mg.porphin catalyst produces the double bond of pregnane-4,5-diene-3,20-dione. The reactions have been shown to be feasible from the overall enthalpy changes in the ZKE approximation at the HF and MP2 /6-31G* level, and with acceptable activation energies.

Ionic and Radical Mechanisms in Olefinic Systems, with Special Reference to Processes of Double-Bond Displacement, Vulcanization and Photogelling

1942 ◽  
Vol 15 (4) ◽  
pp. 774-779
Author(s):  
Ernest Harold Farmer
Keyword(s):  
Double Bond ◽  
Special Reference ◽  
Methyl Substituent ◽  
Benzene Nucleus ◽  
Methyl Group ◽  
Unsaturated System ◽  
Alkyl Groups ◽  
Electron Release

Abstract The α-methylenic reactions discussed in the preceding two papers recall a series of interesting observations by Baker and Nathan, which indicate that a p-methyl substituent attached to the benzene nucleus can permit electron release to the nucleus in a manner that appears only in lesser degree in higher alkyl groups, and may be absent in some (e.g., Buγ). Thus in p-methylbenzyl bromide, the suggested function of the methyl group (dotted arrows in (I) permits (see PDF for diagram) additional electron release at the C—Br bond, and so facilitates the anionization of the bromine. Baker and Nathan suggest that the electrons of the duplet constituting the C—H bond of the methyl group are less localized than those in a similarly placed C—C bond, and hence that a methyl group attached to the necessary conjugated unsaturated system is capable of electron-release by a mechanism similar to the tautomeric effect:

Triphenylpyrazine: methyl substitution to achieve deep blue AIE emitters

2019 ◽  
Vol 7 (42) ◽  
pp. 13047-13051 ◽  
Author(s):  
Haozhong Wu ◽  
Jiajie Zeng ◽  
Zeng Xu ◽  
Bing Zhang ◽  
Han Zhang ◽  
...  
Keyword(s):  
Excited State ◽  
Phenyl Group ◽  
Decay Process ◽  
Methyl Group ◽  
Methyl Substitution ◽  
State Decay ◽  
Deep Blue

Based on our deep comprehension of the unique excited state decay process of tetraphenylpyrazine derivatives, triphenylpyrazine-3-carbazole (TrPP-3C) was designed by replacing the phenyl group with a methyl group at the 3-position of pyrazine.

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