Nitrogen compounds Lewis acid catalysis

Recently, scandium triflate [Sc(OTf)3] was found to be stable in water and successful Lewis acid catalysis was carried out in both water and organic solvents [6-8]. Sc(OTf)3 coordinates to Lewis bases under equilibrium conditions, and thus activation of carbonyl compounds using a catalytic amount of the acid has been achieved [6,7]. In addition, effective activation of nitrogen-containing compounds such as imines, amino aldehydes, etc. has been performed successfully [8]. Encouraged by the characteristics and the usefulness of Sc(OTf)3 as a Lewis acid catalyst, a polymer-supported scandium catalyst was prepared. 

The Lewis acid mechanism of catalysis is shown in Figure 6.2.8. In this mechanism, the tin compound functions as a classic Lewis acid, coordinating to the isocyanate either through the carbonyl oxygen or nitrogen in the initial step to polarize the carbonyl. This increases the electrophilicity of the isocyanate carbon toward nucleophilic attack by alcohol. It has been shown by cryoscopy that there is a strong association of isocyanate with di-n-butyltin dicarboxylates. ... 

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