Bioinspired Vitamin B12 Catalysis

Abstract

Vitamin B12 catalysis is inspired by the ultimate chemist Nature, as methylcobalamin and adenosylcobalamin are involved in numerous biocatalytic reactions including isomerization, methylation and dehalogenation.[1,2] This type of catalysis has been successfully translated into the laboratory and used in a small collection of reactions.[2, 3] The advantage of using vitamin B12 as a catalyst lays in the complete stability of the central cobalt ion, whereas most catalytic reactions require the addition of toxic metals plus complex ligands into a cocktail of reagents, vitamin B12in itself is a package deal. It has also been well documented that the reaction mechanism usually follows a radical pathway, bringing a new dimension to this already interesting field. Along this line, we have proposed vitamin B12 photochemical activation in bond forming and cleavage reactions.[4] Our results show that TiO2 can be utilized in a catalytic system with vitamin B12, allowing for the efficient photocatalytic reduction of Co(III) to Co(I). Under light irradiation vitamin B12 derivative unusually catalyzes a new olefinic sp2 C-H alkylation reaction, with diazo reagents as a carbene source, instead of the expected cyclopropanation. Furthermore, we also use challenging acyl radicals in C-C bond forming reactions. Light-induced vitamin B12-catalyzed methods are also suitable for C-O bond cleavage. Our studies showed that reduced cyanocobalamin catalyzes C-O bond cleavage in allyloxyarenes. These key findings emphasize the unique feature of vitamin B12as a catalyst to achieve something unachievable with other methodologies or to find a greener approach. 1. Banerjee, R. Chemistry and Biochemistry of B12, John Wiley & Sons, Inc, 1999 2. K. ó Proinsias, M. Giedyk, D. Gryko, Chem. Soc. Rev. 2013, 42, 6605-6619. 3. Giedyk, M.; Fedosov, S.; Gryko, D. Chem. Commun. 2014, 50, 4674-4676. 4. a) Shimakoshi, H.; Nishi, M.; Tanaka, A.; Chikama, K.; Hiseada, Y. Chem. Commun. 2011, 47, 6548-6550. b) K. Tahara, Y. Hisaeda, Green Chem. 2011, 13, 558-561. H. Shimakoshi, L. Li, M. Nishi, Y. Hisaeda, Chem. Commun. 2011, 47, 10921-10923. Figure 1