2 research outputs found
Higher-Order Cyclopropenimine Superbases: Direct Neutral Brønsted Base Catalyzed Michael Reactions with α‑Aryl Esters
The
synthesis and characterization of six new classes of higher-order
superbases, including five that incorporate cyclopropenimine functionality,
has been achieved. We propose a nomenclature that designates these
as the CG<sub>2</sub>, GC<sub>2</sub>, PC<sub>3</sub>, PC<sub>1</sub>, C<sub>3</sub>, and GP<sub>2</sub> classes of superbases. The p<i>K</i><sub>BH+</sub> values were measured to be between 29.0
and 35.6 in acetonitrile. Linear correlations of ten superbase basicities
vs that of their substituents demonstrated the insulating effect of
the cyclopropenimine core. The molecular structures of several of
these materials were obtained by single-crystal X-ray analysis, revealing
interesting aspects of conformational bias and noncovalent organization.
The types of superbasic cores and substituents were each reliably
shown to affect selectivity for deprotonation over alkylation. Higher-order
cyclopropenimine and guanidine superbase stability to hydrolysis was
found to correlate to basicity. Finally, a GC<sub>2</sub> base was
found to catalyze conjugate additions of α-aryl ester pronucleophiles,
representing the first report of a neutral Brønsted base to catalyze
such reactions
Higher-Order Cyclopropenimine Superbases: Direct Neutral Brønsted Base Catalyzed Michael Reactions with α‑Aryl Esters
The
synthesis and characterization of six new classes of higher-order
superbases, including five that incorporate cyclopropenimine functionality,
has been achieved. We propose a nomenclature that designates these
as the CG<sub>2</sub>, GC<sub>2</sub>, PC<sub>3</sub>, PC<sub>1</sub>, C<sub>3</sub>, and GP<sub>2</sub> classes of superbases. The p<i>K</i><sub>BH+</sub> values were measured to be between 29.0
and 35.6 in acetonitrile. Linear correlations of ten superbase basicities
vs that of their substituents demonstrated the insulating effect of
the cyclopropenimine core. The molecular structures of several of
these materials were obtained by single-crystal X-ray analysis, revealing
interesting aspects of conformational bias and noncovalent organization.
The types of superbasic cores and substituents were each reliably
shown to affect selectivity for deprotonation over alkylation. Higher-order
cyclopropenimine and guanidine superbase stability to hydrolysis was
found to correlate to basicity. Finally, a GC<sub>2</sub> base was
found to catalyze conjugate additions of α-aryl ester pronucleophiles,
representing the first report of a neutral Brønsted base to catalyze
such reactions