Figure 2 - available via license: Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International
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Lewis-acidity scale (in Lewis acid units, LAU) for: B(C6F5)3, B(2,4,6-C6F3H2)3, AlCl3, In(OTf)3, Sc(OTf)3, and, Zn(OTf)2 in varying polar solvents.
Source publication
Over the years, various multiparameter methods have been developed to measure the strength of a Lewis acid. However, a major challenge for these measurements lies in the complexity that arises from variables such as solvent and other fundamental interactions, as well as perturbations of Lewis acids as their reaction environment changes. Herein, we...
Similar publications
Various methods have been developed to measure the strength of a Lewis acid. A major challenge for these measurements lies in the complexity that arises from variable solvent interactions and perturbations of Lewis acids as their reaction environment changes. Herein, we investigate the impact of solvent effects on Lewis acids for the first time as...
Citations
... 36,37 A multivariate design allowed us to evaluate all combinations between Lewis acid identity and solvent to account for possible interaction effects. 38 For N-aryl imine 1a, catalysis at room temperature forms both the desired aza-BCH 3a and the corresponding cyclobutenyl methanamine 4a (Figure 2a). The 3a to 4a ratio depends mainly on solvent, with THF giving 2-to-10-fold less 4a than DCM and toluene. ...
The development of two divergent and complementary Lewis acid catalyzed additions of bicyclobutanes to imines is described. Microscale high-throughput experimentation was integral to the discovery and optimization of both reactions. N-arylimines undergo formal (3+2) cycloaddition with bicyclobutanes to yield azabicyclo[2.1.1]hexanes in a single step; in contrast, N-alkylimines undergo an addition/elimination sequence to generate cyclobutenyl methanamine products with high diastereoselectivity. These new products contain a variety of synthetic handles for further elaboration, including many functional groups relevant to pharmaceutical synthesis. The divergent reactivity observed is attributed to differences in basicity and nucleophilicity of the nitrogen atom in a common carbocation intermediate, leading to either nucleophilic attack (N-aryl) or E1 elimination (N-alkyl).
