Development of Redox-Switchable Organocatalysts

Redox-switchable catalysis is an emerging research field that seeks to regulate chemical reactions by the simple reduction-oxidation manipulation. The modulation of electron density of redox-responsible ligands in the transition metal catalyzed reactions by changing oxidation state was usually used to control catalytic activity. Meanwhile, we have developed the cation pool method which involves generation and accumulation of organic cations in relatively high concentration.For example, the accumulation of an organo-dication 2 has been accomplished by the electrochemical oxidative C-C bond cleavage of compound 1 at low temperature (Scheme 1).¹⁾ The carbocations having two electron deficient carbon centers are expected to serve as effective Lewis acids, and we revealed that several reactions such as Mukaiyama-Aldol reaction,²⁾ Diels-Alder reaction, and Nazarov cyclization, were significantly promoted by a catalytic amount of the organo-dications in a highly efficient manner (Scheme 2). We are highly motivated to investigate the utility of the dications as redox-switchable catalysts, and revealed the possibility to modulate Mukaiyama-Aldol reaction by using the reaction system (Scheme 3).

1) Okajima, M.; Suga, S.; Itami, K. Yoshida, J. J. Am. Chem. Soc. 2005, 127, 6930-6931.

2) Mukaiyama, T.; Kobayashi, S.; Murakami, M. Chem. Lett. 1984, 1759-1762.