Analysis of Interconversion between Atropisomers of Chiral Substituted 9,9'-Bicarbazole

Interconversion of atropisomers of chiral 3,3'-di-tert-butyl-9,9'-bicarbazole linked by a single N-N bond was analyzed by DFT calculations and experiments. The calculations revealed that the trans transition state has a lower energy for the interconversion than the cis transition state. The lowest transition state of interconversion between natural dixiamycins A and B containing a 9,9'-bicarbazole structure was found to be the trans transition state. The calculations also indicated that degradation through N-N bond cleavage was faster than racemization. Atropisomeric enantiomers of 3,3'-di-tert-butyl-9,9'-bicarbazole were resolved by chiral HPLC for the first time, and then racemization and N-N bond cleavage were investigated by heating experiments, showing that racemization did not take place below the degradation temperature.

Automated summary

The interconversion of atropisomers of chiral 3,3'-di-tert-butyl-9,9'-bicarbazole linked by a single N-N bond was analyzed through DFT calculations and experiments, revealing that the trans transition state has a lower energy. The study also found that N-N bond cleavage in degradation occurred faster than racemization.