CONTROL OF MOLECULAR CONFORMATION BY CRYSTALLIZATION AND THE APPLICATION TO SUSTAINABLE CHEMISTRY

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Organic crystals provide specific environment where the molecular arrangement and the conformation are strongly influenced by crystal packing. Therefore, the organic crystals were widely utilized to product- and stereo-selective reactions. In this research project, we studied sustainable chemistry in the crystalline environment involving asymmetric synthesis and stereo-selective reactions.(Result 1) Several aromatic amides derived from L-proline, which exist as a mixture of several diastereomers in solution, converged to single diastereomer by crystallization. And the conformational transformation was controlled after the crystals were dissolved in the solvent at low temperature, where the frozen conformation was retained long enough for subsequent asymmetric reaction.(Result 2) Anew methodology using the molecular homochirality in the crystal as a source of homochirality in solution was explored. The chirality can be effectively transferred to optically active products by asymmetric reactions involving a nucleophilic reaction, an intermolecular 4+4 photochemical cycloaddition reaction, a SNAr reaction, a 2+2 photochemical cyclobutane formation with almost quantitative enantiomeric yields.(Result 3) The molecular homochirality generated by crystallization was utilized to kinetic resolution of sec-BuLi and cyclic amines with moderate enantiomeric yields.(Result 4) We found that several axially chiral N-arylpyrimidinones and pyrimidinethiones gave conglomerate crystals, and crystallization at high temperature lead to chiral breaking of symmetry to give optically active materials up to 90% ee without any outside chiral source.