TY - JOUR
T1 - BITHIENOLs
T2 - Promising C2-Symmetric Biheteroaromatic Diols for Organic Transformation
AU - Gabrieli, Sara
AU - Cirilli, Roberto
AU - Benincori, Tiziana
AU - Pierini, Marco
AU - Rizzo, Simona
AU - Rossi, Sergio
PY - 2017/1/26
Y1 - 2017/1/26
N2 - 2,2′,5,5′-Tetraphenyl-3,3′-bithiophene-4,4′-diol, the first member of a new class of chiral C2-symmetric atropisomeric diols based on a biheteroaromatic scaffold, has been synthesized. Dynamic enantioselective HPLC experiments revealed a racemization barrier of 22.9 kcal/mol at 25 °C, which is high enough to permit the chromatographic collection of both enantiomers on a semi-preparative scale, but at the borders of application as a promoter in asymmetric catalysis. The ground and transition states involved in the enantiomerization process have been identified through DFT calculations, which suggest the intermediacy of a tautomeric species in which a thiophen-3-ol unit and a 2,3-dihydrothiophen-3-one ring are present. The proposed racemization mechanism is supported by the results of dynamic HPLC experiments. Calculations also suggested which substituent groups at the 2,2′-positions of the thiophene rings could lead to an increase in enantiomerization barriers sufficient to confer full configurational stability on the 3,3′-bithiophene framework.
AB - 2,2′,5,5′-Tetraphenyl-3,3′-bithiophene-4,4′-diol, the first member of a new class of chiral C2-symmetric atropisomeric diols based on a biheteroaromatic scaffold, has been synthesized. Dynamic enantioselective HPLC experiments revealed a racemization barrier of 22.9 kcal/mol at 25 °C, which is high enough to permit the chromatographic collection of both enantiomers on a semi-preparative scale, but at the borders of application as a promoter in asymmetric catalysis. The ground and transition states involved in the enantiomerization process have been identified through DFT calculations, which suggest the intermediacy of a tautomeric species in which a thiophen-3-ol unit and a 2,3-dihydrothiophen-3-one ring are present. The proposed racemization mechanism is supported by the results of dynamic HPLC experiments. Calculations also suggested which substituent groups at the 2,2′-positions of the thiophene rings could lead to an increase in enantiomerization barriers sufficient to confer full configurational stability on the 3,3′-bithiophene framework.
KW - Alcohols
KW - Atropisomerism
KW - Biaryls
KW - Chiral resolution
KW - Racemization
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U2 - 10.1002/ejoc.201601353
DO - 10.1002/ejoc.201601353
M3 - Article
AN - SCOPUS:85011634432
VL - 2017
SP - 861
EP - 870
JO - Justus Liebigs Annalen der Chemie
JF - Justus Liebigs Annalen der Chemie
SN - 0075-4617
IS - 4
ER -