TY - JOUR
T1 - Does the Threshold Enantiomerization Route of Crowded Tetraarylethenes Involve Double Bond Rotation?
AU - Maeda, Katsuhiro
AU - Okamoto, Yoshio
AU - Morlender, Natalia
AU - Haddad, Nizar
AU - Eventova, Irina
AU - Biali, Silvio E.
AU - Rappoport, Zvi
PY - 1995
Y1 - 1995
N2 - The chiral tetraarylvinyl propeller 1,2-bis(4-tert-butyl-2,6-dimethylphenyl)-1,2-dimesitylethene (4) was synthesized by irradiation of (4-tert-butyl-2,6-dimethylphenyl)mesitylketene 5. Ethene 4 exists in two diastereomeric forms (E and Z), each existing as a racemate (i.e., (+)/(—) 4Z and (+)/(-) 4E). The enantiomers were resolved by chiral HPLC and the EIZ diastereomers were separated by (achiral) supercritical fluid chromatography. The enantiomerization process which was studied in n-pentadecane has a barrier of ΔG* = 44.8 ± 0.7 kcal mol-1. A 4Z ⇌ 4E interconversion was not observed under the enantiomerization conditions. Consequently, we conclude that the threshold enantiomerization process of 4 does not involve a double bond rotation. A lower limit of 48.7 kcal mol-1 is estimated for the barrier of the latter rotation.
AB - The chiral tetraarylvinyl propeller 1,2-bis(4-tert-butyl-2,6-dimethylphenyl)-1,2-dimesitylethene (4) was synthesized by irradiation of (4-tert-butyl-2,6-dimethylphenyl)mesitylketene 5. Ethene 4 exists in two diastereomeric forms (E and Z), each existing as a racemate (i.e., (+)/(—) 4Z and (+)/(-) 4E). The enantiomers were resolved by chiral HPLC and the EIZ diastereomers were separated by (achiral) supercritical fluid chromatography. The enantiomerization process which was studied in n-pentadecane has a barrier of ΔG* = 44.8 ± 0.7 kcal mol-1. A 4Z ⇌ 4E interconversion was not observed under the enantiomerization conditions. Consequently, we conclude that the threshold enantiomerization process of 4 does not involve a double bond rotation. A lower limit of 48.7 kcal mol-1 is estimated for the barrier of the latter rotation.
UR - http://www.scopus.com/inward/record.url?scp=0000917093&partnerID=8YFLogxK
U2 - 10.1021/ja00143a010
DO - 10.1021/ja00143a010
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AN - SCOPUS:0000917093
SN - 0002-7863
VL - 117
SP - 9686
EP - 9689
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 38
ER -