Conformational analysis of 9,10-dihydroanthracenes. Molecular mechanics calculations and carbon-13 NMR

Rabideau, Peter W.; Mooney, Jennifer L.; Lipkowitz, Kenny B.

doi:10.1021/ja00286a002

Cited by 23 publications

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“…13 C{ 1 H} NMR (125 MHz, CDCl 3 ): δ 140.5, 136.1, 128.1, 127.7, 126.0, 125.9, 48.9, 35.3, 30.6, 12.1 ppm. The physical and spectral data were identical to those previously reported for this compound …”

Section: Experimental Sectionsupporting

confidence: 77%

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Birch Reduction of Aromatic Compounds by Inorganic Electride [Ca₂N]^+•e^– in an Alcoholic Solvent: An Analogue of Solvated Electrons

et al. 2018

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Birch reduction of aromatic systems by solvated electrons in alkali metal-ammonia solutions is widely recognized as a key reaction that functionalizes highly stable π-conjugated organic systems. In spite of recent advances in Birch reduction with regard to reducing agent and reaction conditions, there remains an ongoing challenge to develop a simple and efficient Birch reaction under mild conditions. Here, we demonstrate that the inorganic electride [Ca 2 N] +• e − promotes the Birch reduction of polycyclic aromatic hydrocarbons (PAHs) and naphthalene under alcoholic solvent in the vicinity of room temperature as a solid-type analogy to solvated electrons in alkali metal ammonia solutions. The anionic electrons from electride [Ca 2 N] +• e − are transferred to PAHs and naphthalene via alcoholysis in a polar cosolvent medium. It is noteworthy that a high conversion yield to the hydrogenated products is ascribed to the extremely high electron transfer efficiency of 98%. This simple protocol utilizing an inorganic electride offers a direct and practical strategy for the reduction of aromatic compounds and provides an outstanding reducing agent for synthetic chemistry.

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Section: Experimental Sectionsupporting

confidence: 77%

“…The physical and spectral data were identical to those previously reported for this compound. 42 9,10-Diphenyl-9,10-dihydroanthracene (2f′). According to the revised general procedure of GP-1 with 2f (0.05 mmol) and [Ca 2 N] +• e − (235 mg, 2.5 mmol, 5.0 equiv), compound 2f′ (83 mg, 50%) was obtained.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

Birch Reduction of Aromatic Compounds by Inorganic Electride [Ca₂N]^+•e^– in an Alcoholic Solvent: An Analogue of Solvated Electrons

et al. 2018

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“…Triphenylphosphine was purified by dissolving in hexane and running through a silica gel column. 9,10-Dihydroanthracene (DHA) was purified by a published procedure, and d 4 -DHA was also synthesized by a published procedure …”

Section: Experimental Sectionmentioning

confidence: 99%

“…Triphenylphosphine was purified by dissolving in hexane and running through a silica gel column. 9,10-Dihydroanthracene (DHA) was purified by a published procedure, 44 and d 4 -DHA was also synthesized by a published procedure. 45 All moisture-and oxygen-sensitive compounds were prepared using standard high-vacuum-line, Schlenk, or cannula techniques.…”

Section: ■ Introductionmentioning

confidence: 99%

Oxoiron(IV) Tetramethylcyclam Complexes with Axial Carboxylate Ligands: Effect of Tethering the Carboxylate on Reactivity

et al. 2017

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Oxoiron(IV) species are implicated as reactive intermediates in nonheme monoiron oxygenases, often acting as the agent for hydrogen-atom transfer from substrate. A histidine is the most likely ligand trans to the oxo unit in most enzymes characterized thus far but is replaced by a carboxylate in the case of isopenicillin N synthase. As the effect of a trans carboxylate ligand on the properties of the oxoiron(IV) unit has not been systematically studied, we have synthesized and characterized four oxoiron(IV) complexes supported by the tetramethylcyclam (TMC) macrocycle and having a carboxylate ligand trans to the oxo unit. Two complexes have acetate or propionate axial ligands, while the other two have the carboxylate functionality tethered to the macrocyclic ligand framework by one or two methylene units. Interestingly, these four complexes exhibit substrate oxidation rates that differ by more than 100-fold, despite having E values for the reduction of the Fe═O unit that span a range of only 130 mV. Eyring parameters for 1,4-cyclohexadiene oxidation show that reactivity differences originate from differences in activation enthalpy between complexes with tethered carboxylates and those with untethered carboxylates, in agreement with computational results. As noted previously for the initial subset of four complexes, the logarithms of the oxygen atom transfer rates of 11 complexes of the Fe(O)TMC(X) series increase linearly with the observed E values, reflecting the electrophilicity of the Fe═O unit. In contrast, no correlation with E values is observed for the corresponding hydrogen atom transfer (HAT) reaction rates; instead, the HAT rates increase as the computed triplet-quintet spin state gap narrows, consistent with Shaik's two-state-reactivity model. In fact, the two complexes with untethered carboxylates are among the most reactive HAT agents in this series, demonstrating that the axial ligand can play a key role in tuning the HAT reactivity in a nonheme iron enzyme active site.

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“…More recently, molecular mechanics calculations have suggested a fairly wide range of conformations for DHAs, including a boat-shaped central ring for monosubstituted and cis-disubstituted derivatives, and an essentially planar geometry for (symmetrical) trans-disubstituted cases.' [8][9][10][11][12][13][14][15][16][17][18][19][20] However, in almost every case, calculations suggest a parabolic potential well * Author to whom correspondence should be addressed. (which may be displaced from 180") and do not include double minima expected for a boat-to-boat interconversion.…”

Section: I'mentioning

confidence: 99%

Unusual behavior of isopropyl substituients in 9,10‐dihydroanthracenes: An NMR and molecular mechanics study

Rabideau

Smith

Ray

1989

Magnetic Reson in Chemistry

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A collection of cis-and trans-9-isopropyl-lO-R-9,lO-dihydroanthracenes were investigated. The cis compounds show large H-9-isopropyl methine coupling constants in the series R = Me, Et, i-Pr, t-Bu (8.8-9.9 Hz) due to a preferred orientation of the isopropyl group(s), caused by a transannular steric effect, wherein the H-!l-isopropyl methine dihedral angle is close to 180". These preferred conformations are predicted by molecular mechanics calculations (MM2 and MMP2) and data for the optimized geometries are presented. The trans compounds show considerably smaller coupling constants ( J = 2.6, 5.0 and 7.8 Hz for R = t-Bu, i-Pr and Et, respectively) and these numbers are easily rationalized from the calculated geometries. However, the compound with R = Me shows an unusually high value (9.6 Hz), and calculations suggested the presence of a structure with unusually large puckering of the dihydroanthracene central ring. This was confirmed by nuclear Overhauser enhancements and by proton and carbon relaxation measurements. KEY WORDS Hindered rotation 'H and 3C relaxation measurements Molecular mechanics calculations NOE experimentsA considerable amount of effort including x-ray crystallograph y,'-' ' NMR'Z-'6 and theoretical calculations'7-z0 have been directed towards an understanding of the conformational properties of 9,lO-dihydroanthracene (DHA) (1) and its derivatives. In the solid state, DHA adopts a boat conformation with a folding angle of 145" (i.e. the angle between the two planes containing the benzene rings).'.'' In solution, however, separate signals for the pseudo-axial and pseudo-equatorial protons at C-9 and C-10 were not observed by NMR, even at low temperatures, and so rapid boat-to-boat interconversion was suggested (i.e. 1 * 1 y 1 R 9 1 I I'This concept was extended to include derivatives with the expectation that the equilibrium should be shifted to allow for the pseudo-axial preference of substituent groups." More recently, molecular mechanics calculations have suggested a fairly wide range of conformations for DHAs, including a boat-shaped central ring for monosubstituted and cis-disubstituted derivatives, and an essentially planar geometry for (symmetrical) trans-disubstituted cases.' 8-20 However, in almost every case, calculations suggest a parabolic potential well * Author to whom correspondence should be addressed. (which may be displaced from 180") and do not include double minima expected for a boat-to-boat interconversion.The unusual behavior of isopropyl substituents in 9,lO-dihydroanthracenes was first noted in 1969 by Zieger et a1.,z2 who investigated the proton NMR spectrum of cis-9,lO-diisopropyl-DHA (2). They observed a large coupling constant (9.5 Hz) between isopropyl methine hydrogen(s) and H-9 (H-lo), and attributed this to restricted movement of the isopropyl groups owing to the transannular steric interaction. Hence, the preferred geometry has the isopropyl methyls bisected by H-9 (H-10) (as illustrated for 2-4). A subsequent investigationz3 of the related 1,Cdimethyl and 1,4-...

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Conformational analysis of 9,10-dihydroanthracenes. Molecular mechanics calculations and carbon-13 NMR

Cited by 23 publications

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Birch Reduction of Aromatic Compounds by Inorganic Electride [Ca₂N]^+•e^– in an Alcoholic Solvent: An Analogue of Solvated Electrons

Birch Reduction of Aromatic Compounds by Inorganic Electride [Ca₂N]^+•e^– in an Alcoholic Solvent: An Analogue of Solvated Electrons

Oxoiron(IV) Tetramethylcyclam Complexes with Axial Carboxylate Ligands: Effect of Tethering the Carboxylate on Reactivity

Unusual behavior of isopropyl substituients in 9,10‐dihydroanthracenes: An NMR and molecular mechanics study

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Conformational analysis of 9,10-dihydroanthracenes. Molecular mechanics calculations and carbon-13 NMR

Cited by 23 publications

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Birch Reduction of Aromatic Compounds by Inorganic Electride [Ca2N]+•e– in an Alcoholic Solvent: An Analogue of Solvated Electrons

Birch Reduction of Aromatic Compounds by Inorganic Electride [Ca2N]+•e– in an Alcoholic Solvent: An Analogue of Solvated Electrons

Oxoiron(IV) Tetramethylcyclam Complexes with Axial Carboxylate Ligands: Effect of Tethering the Carboxylate on Reactivity

Unusual behavior of isopropyl substituients in 9,10‐dihydroanthracenes: An NMR and molecular mechanics study

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Birch Reduction of Aromatic Compounds by Inorganic Electride [Ca₂N]^+•e^– in an Alcoholic Solvent: An Analogue of Solvated Electrons

Birch Reduction of Aromatic Compounds by Inorganic Electride [Ca₂N]^+•e^– in an Alcoholic Solvent: An Analogue of Solvated Electrons