We previously reported the atropisomeric properties of 2′-
t-butyl-6′-iodo-substituted
N-benzoyl-3-bromocarbazole,
i.e., the steric or electronic effects of the substituents restricted the rotation about the N–C7′ and C7′–C1′ bonds to separate four stereoisomers (
cis/
trans for the N–C7′ axis, a
R/a
S for the C7′–C1′ axis). Furthermore, the 2′-
t-butyl-6′-iodo-substituted
N-benzoyl 3-bromocarbazole was confirmed to be a gear molecule, in which the rotation about the C7′–C1′ bond was in perfect concert with that about the N–C7′ bond. Herein, we report a unique crystallization-induced diastereomeric transformation found in this molecule. In the isolation process, where the product is recrystallized from the diastereoisomeric mixture,
in situ isomerization and selective crystallization could lead to a diastereomeric transformation, and a mixture of diastereomers (
trans/
cis=54 : 46) was converted to
trans-isomer-enriched crystals (
trans/
cis>96 : 4) in 95% yield. Conformational analysis clarified the preference for the
trans versus cis isomer.
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