Ueber Phenyl‐fluoren

Kliegl, A.

doi:10.1002/cber.19050380156

Cited by 19 publications

(3 citation statements)

References 11 publications

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“…Recycle of 9-phenylfluorene to 9-bromo-9-phenylfluorene was accomplished by heating a mixture of 9-phenylfluorene (969 mg, 4.00 mmol) and N -bromosuccinimide (711 mg, 4.00 mmol) in CCl 4 (4 mL) at a reflux for 1 h. After cooling, the reaction was concentrated in vacuo, and the residue was successively digested with volumes of hexanes until TLC analysis showed that no UV-active material was contained in the hexanes. Concentration of the combined hexane volumes gave 9-bromo-9-phenylfluorene as a yellow solid (1.23 g, 96%): mp 98−100 °C (lit . mp 99 °C).…”

Section: Methodsmentioning

confidence: 99%

Alkyl Substituent Effects on Pipecolyl Amide Isomer Equilibrium: Efficient Methodology for Synthesizing Enantiopure 6-Alkylpipecolic Acids and Conformational Analysis of TheirN-AcetylN‘-Methylamides

1999

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Enantiopure 6-alkylpipecolic acid hydrochlorides 1a-e were synthesized in five steps and 15-59% overall yields from alpha-tert-butyl beta-methyl N-(PhF)aspartate (3) via an approach featuring selective hydride reduction to the corresponding aspartate beta-aldehyde 2, aldol condensations with the enolates of various methyl alkyl ketones, and diastereoselective intramolecular reductive aminations. The influence of the 6-position substituent on the equilibrium and the energy barrier for isomerization of the amide N-terminal to pipecolate was then explored via the synthesis of N-acetyl N'-methylpipecolinamide (16) and its (2S,6R)-6-tert-butylpipecolinamide counterpart 17, and their conformational analysis by proton NMR spectroscopy and coalescence experiments. The presence of the tert-butyl substituent augmented the population of the amide cis-isomer and lowered the barrier for pipecolyl amide isomerization in water. Compared with the results from our previous examination of N-acetyl-5-tert-butylproline N'-methylamides (Beausoleil, E.; Lubell, W. D. J. Am. Chem. Soc. 1996, 118, 12902), the consequences of the bulky 6-alkyl substituent on the acetamide geometry and isomerization barrier were less pronounced in the pipecolate series relative to the respective proline amides.

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Section: Methodsmentioning

confidence: 99%

Alkyl Substituent Effects on Pipecolyl Amide Isomer Equilibrium: Efficient Methodology for Synthesizing Enantiopure 6-Alkylpipecolic Acids and Conformational Analysis of TheirN-AcetylN‘-Methylamides

1999

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“…Ph3CH (Fluka) was recrystallized from ligroin, 9-Ph-fluorene (9-Ph-flH) was prepared from the corresponding carbinol, 19 and 9-Ph-fl-NHPh from the 9-Ph-fl-Cl and aniline. 20 Acetonitrile (MeCN), hexane, cyclohexane, ethanol, tetrachloromethane (Merck), and n-butyl chloride (Fluka) were spectroscopic grade and used as received.…”

Section: Methodsmentioning

confidence: 99%

“…The triphenylmethyl chloride (Merck) was recrystallized from hexane by adding drops of acetyl chloride. Ph 3 CH (Fluka) was recrystallized from ligroin, 9-Ph-fluorene (9-Ph-flH) was prepared from the corresponding carbinol, and 9-Ph-fl-NHPh from the 9-Ph-fl-Cl and aniline …”

Section: Methodsmentioning

confidence: 99%

Photodissociation of N-(Triphenylmethyl)anilines: A Laser Flash Photolysis, ESR, and Product Analysis Study¹

et al. 1998

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CPh 3 ), upon photolysis with 248-and 308-nm laser light, as well as by lamp irradiation with 254-nm light in acetonitrile and hexane solutions, undergo exclusively C-N bond homolysis to give the triphenylmethyl radical in a monophotonic process. Product analysis gives as main products Ph 3 CH, 9-Ph-fluorene, and PhNH 2 . The quantum yields for the formation of Ph 3 C • are high (0.6-0.8, 248-nm excitation) and independent of the solvent. This effective homolytic dissociation results from the low electronegativity difference between the carbon and nitrogen atoms constituting the bond to be broken, the low bond dissociation enthalpy of the C-N bond, the high excitation energy of the local chromophore (aniline), and probably from a favorable alignment of the C-N bond in a plane perpendicular to the anilino chromophore (due to the large steric requirements of the trityl group), thus enabling an effective hyperconjugative interaction with it. The above dissociation competes effectively with heterolytic cleavage, which is the pathway dominating, e.g., in the photolysis of Ph 3 C-Cl in MeCN under the same conditions. At high pulse intensities the trityl radicals formed above are excited by a second photon leading to either electrocyclization to 4a,4b-dihydro-9-phenylfluorenyl radical (DHPF • ), or photoionization to Ph 3 C + , the latter only in MeCN and only on 248-nm photolysis. A new intermediate (9-Ph-4aH-fluorene) on the way to the final product 9-Ph-fluorene is identified resulting from electrocyclization, supporting a mechanism proposed earlier. The optical measurements are supported by ESR studies (irradiation with 254-nm light).

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9‐Bromo‐9‐Phenylfluorene

et al. 2003

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Ueber Phenyl‐fluoren

Cited by 19 publications

References 11 publications

Alkyl Substituent Effects on Pipecolyl Amide Isomer Equilibrium: Efficient Methodology for Synthesizing Enantiopure 6-Alkylpipecolic Acids and Conformational Analysis of TheirN-AcetylN‘-Methylamides

Alkyl Substituent Effects on Pipecolyl Amide Isomer Equilibrium: Efficient Methodology for Synthesizing Enantiopure 6-Alkylpipecolic Acids and Conformational Analysis of TheirN-AcetylN‘-Methylamides

Photodissociation of N-(Triphenylmethyl)anilines: A Laser Flash Photolysis, ESR, and Product Analysis Study¹

9‐Bromo‐9‐Phenylfluorene

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Ueber Phenyl‐fluoren

Cited by 19 publications

References 11 publications

Alkyl Substituent Effects on Pipecolyl Amide Isomer Equilibrium: Efficient Methodology for Synthesizing Enantiopure 6-Alkylpipecolic Acids and Conformational Analysis of TheirN-AcetylN‘-Methylamides

Alkyl Substituent Effects on Pipecolyl Amide Isomer Equilibrium: Efficient Methodology for Synthesizing Enantiopure 6-Alkylpipecolic Acids and Conformational Analysis of TheirN-AcetylN‘-Methylamides

Photodissociation of N-(Triphenylmethyl)anilines: A Laser Flash Photolysis, ESR, and Product Analysis Study1

9‐Bromo‐9‐Phenylfluorene

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Photodissociation of N-(Triphenylmethyl)anilines: A Laser Flash Photolysis, ESR, and Product Analysis Study¹