Research

Design of new catalysts

The design of new methodologies for the synthesis of complex scaffolds often requires the development of new catalyst that fulfills some of the limitations of the existent catalysts. In our research group, we have the aim to design new catalysts or catalytic systems that lead to improved reaction consitions, stereoselectivities or new reactivities.

In 2009 we developed a catalytic system consisting in the addition of a thiourea co-catalyst to a proline catalyzed Aldol reaction. We determined that the addition of thiourea allow to a faster and easier formation of the enamine in apolar solvents probably though the Hydrogen bond interactions between the thiourea co-catalyst and the carboxylate of proline. Proline is insoluble in apolar solvents like toluene. However, the use of thioureas as co-catalyst solubilizes the proline making a most powerful catalyst (Figure 1; right vial).[1]

Figure 1 : effect of the addition of thiourea cocatalyst in the solubility of proline in toluene/acetone 5:1: first vial thiourea, second vial proline, third vial proline + thiourea (all is soluble)

 
We tested this new catalytic system in the desymmetrization of 4-substituted-cyclohexanones by an aldol reaction, affording the final compounds in excellent yields and stereoselectivities.[2]

 

Figure 2 : Aldol desymmetrization reaction

 

Related Publications:

1         “Substrate-dependent nonlinear effects in proline-thiourea catalyzed aldol reactions. Unraveling the role of the thiourea co-catalyst”. N. El-Hamdouni, X. Companyó, R. Rios*, A. Moyano*. Chem. Eur. J. 2010, 16, 1142-1148.

2          “Highly Enantio- and Diastereoselective Organocatalytic Desymmetrization of Prochiral Cyclohexanones by Simple Direct Aldol Reaction Catalyzed by Proline”. X. Companyó, G. Valero, L. Crovetto, A. Moyano, R. Rios. Chem. Eur. J. 2009, 15, 6556-6558.