Stereomutation of conformational enantiomers of 9-isopropyl-9- formylfluorene and related acyl derivatives

Journal of Organic Chemistry

Volumn 73, Issue 16, 2008, Pages 6382-6385

  Casarini, Daniele ^a   Lunazzi, Lodovico ^b   Mazzanti, Andrea ^b  

^a UNIVERSITY OF BASILICATA   (Italy)

^b UNIVERSITY OF BOLOGNA   (Italy)

Author keywords

[No Author keywords available]

Indexed keywords

ARSENIC COMPOUNDS; CHIRALITY; CHLORINE COMPOUNDS; NUCLEAR MAGNETIC RESONANCE; NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY;

ACYL DERIVATIVES; LOW TEMPERATURES; NM R SPECTRUM; RESTRICTED ROTATIONS; STEREOMUTATION;

ENANTIOMERS;

1 (9 ISOPROPYL 9H FLUOREN 9 YL) 2,2 DIMETHYLPROPAN 1 ONE; 1 (9 ISOPROPYL 9H FLUOREN 9 YL) ETHANONE; 1 (9 ISOPROPYL 9H FLUOREN 9 YL)2,2, DIMETHYLPROPAN 1 ONE; 9 ISOPROPYL 9H FLUORENE 9 CARBALDEHYDE; ALDEHYDE DERIVATIVE; PROPANE;

ARTICLE; CHEMICAL BOND; ENANTIOMER; NUCLEAR MAGNETIC RESONANCE; STIMULATION; TEMPERATURE DEPENDENCE;

EID: 50149093265     PISSN: 00223263     EISSN: None     Source Type: Journal    
DOI: 10.1021/jo8008897     Document Type: Article

References (28)

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5. As often observed in conformational processes, the free energy of activation was found independent of temperature within the errors, indicating a negligible value of ΔS≠. See, for instance: (a) Lunazzi, L.; Mancinelli, M.; Mazzanti, A. J. Org. Chem. 2007, 72, 5391-5394, and references quoted therein.
6. 1 point group, as in Scheme 1) due to the frozen C9-CHO rotation at that temperature.
7. MMX force field, PC Model 7.5; Serena Software: Bloomington, IN.
8. i bond rotation is fast, this process would create a dynamic plane of symmetry that would render isochronous the isopropyl methyls and aromatic signals, in contrast with the experimental observations at-146°C
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16. 2)-C9-CHO dihedral angles of the lower (TS-1) and higher (TS-2) energy transition states are 0° and 121°, respectively.
17. 2 dihedral angle of 3 is 21° in the computed and 25° in the X-ray structure (Figure 4).
18. In both 2 and 3 the same barriers were obtained when monitoring the aromatic signals, as in the case of the aldehyde 1.
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23. -1, as in Table 1).
24. This is further confirmed by the unusual high field shift observed for the acetyl methyl signal of 2 (1.53 ppm) and for the tert-butyl methyl signal of 3 (0.64 ppm). These groups, in fact, experience the well-known effect of the aromatic ring currents because they lay above the fluorenyl ring; see: Jackman, L. M.; Sternhell, S. Applications of NMR Spectroscopy in Organic Chemistry, 2nd ed.; Pergamon Press: Oxford, UK, 1969; p 95.
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28. Thermodynamic corrections were also applied in standard conditions, using unsealed harmonic frequencies, and the corresponding results are reported in Tables S1-3 of the Supporting Information. However, these values cannot be meaningfully compared to the present experimental data because of the different temperatures, and to relevant errors in the computation of the entropic factor (see for instance: Ayala, P. Y.; Schlegel, H. B. J. Chem. Phys. 1998, 108, 2314-2325).