Research on development of efficient chirality alternation methods under thermodynamic conditions

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We have investigated isomerization properties of [14]parapyridinophane derivatives and demonstrated that crystallization-induced and adsorption-induced asymmetric transformations are efficient protocols to prefer the opposite sense of stereochemistry in planar-chiral [14]parapyridinophane derivatives, respectively. We have also found that azaspirene analog having its characteristic spiro skeleton readily undergoes racemization in neutral aqueous media and that efficient resolution was achieved by using an appropriate chiral auxiliary to resolve the analog by the following acidic hydrolysis of each diastereoisomer to afford highly enantio-enriched azaspirene analog in excellent yields without a loss of their enantiomeric excesses. The sequential transformation to enantiomerically pure analog and its recycling process to its racemic body achieved an efficient synthetic route to an optically active analog of azaspirene.