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Constructive Organic Chemistry

  • Yoshio Ito, Associate Professor
Physical organic chemistry of photochromism and synthetic organic chemistry are the main research fields in this laboratory.
Photochromism is the reversible process of absorption in some chemical substances. We are studying crystalline photochromism of N-salicylideneaniline derivatives. Recently, we developed organic solid solution method to observe other photochromic behaviors.
Asymmetric catalysis is useful for preparation of enantiomerically pure compounds where the stereochemistry plays an important role in the biological activities. Recently we have been focusing on development of environmentally benign organocatalysts.

Physical organic chemistry of photochromism

Photochromism is the phenomenon that changes the color reversibly by irradiating a chemical material. N-Salicylideneanilines are well-known photochromic compounds, which show crystalline photochromism. This phenomenon is observable as the result of photo-isomerizations between different forms, which show different absorption spectra.

Figure 1

Although some N-salicylideneaniline derivatives do not exhibit crystalline photochromism, we have developed three practical methods to obtain photochromic crystals of N-salicylideneanilines. (1) By introduction of tert-butyl group. (2) By construction of clathrate crystals with deoxycholic acid. (3) By use of 2,6-dialkylanilines. Recently, we have developed an organic solid solution method as a conventional way to observe photochromism.

Catalytic asymmetric reaction

For efficient syntheses of enantiomerically pure compounds, various types of asymmetric catalysts have been developed. Among them, chiral organic compounds (i.e. asymmetric organocatalysts) have been paid much attention as environmentally benign catalysts.

Figure 2

α,α-Diphenylprolinols are representative asymmetric organocatalysts but has been reported as disadvantageous compared to transition metal complex catalyzed reactions because of lower catalytic reactivity. In order to overcome the problem, we prepared new prolinol derivatives having Lewis base group such as pyridyl group.