Increasing the Reactivity of Nitrogen Catalysts

Abstract

This review article presents how nitrogen-centred Lewis bases were modified in order to increase their reactivity in catalytic processes. As examples, we focus on alcohol acylation and Morita-Baylis-Hilman reactions in order to showcase the fundamental parameters at play in transformations initiated by catalysts bearing respectively an active sp(2) or sp(3) nitrogen atoms. These two aspects are epitomised by two leading compounds, the Steglich base 4-dimethylaminopyridine (DMAP), and 1,4-diazabicyclo[2.2.2]octane (DABCO). Throughout this review, we stress the role played and the information brought by physical organic chemistry. Comprehension of these complex transformations relies on the fundamental knowledge of parameters, such as, nucleophilicity, nucleofugality, Lewis basicity, and crucially also the knowledge of their divergent impacts on each elementary step of the catalytic cycle.

Rapid assembly of complex cyclopentanes employing chiral, α,β-unsaturated acylammonium intermediates

“…Use of more weakly coordinating counterions such as sodium and potassium led to drastically lower yields (entries 7, 8), while magnesium afforded a comparable yield (entry 9). A brief screening of nucleophiles, 37 including 9-azajulolidine, revealed that 4-pyrrolidinopyridine (4-PPY) and LiHMDS was an optimal combination for the NCMAL process (entries 10, 11). As evidence for the requirement of the nucleophile, a control reaction without 4-PPY did not afford any β-lactone (entry 12).…”

Cation affinity numbers of Lewis bases

“…Cation affinity values are important guidelines for the reactivity of Lewis and Brønstedt bases [1–3]. While proton affinity numbers (either as gas phase proton affinities or as solution phase p K a values) have been used for a long time in quantitative approaches to describe base-induced or base-catalyzed processes, affinity data towards carbon electrophiles have only recently been adopted as tools for the assessment of Lewis base reactivity [4].…”

Chiral Bicyclic Imidazole Nucleophilic Catalysts: Design, Synthesis, and Application to the Kinetic Resolution of Arylalkylcarbinols

“…Introducing an electron-donating group onto the imidazole ring, as evidenced by the increased activity of 4-pyrrolidinylpyridine (abbreviated as PPY) compared to pyridine, seems to be a reasonable method to improve the catalytic activity ( Figure 1). [10] However, to the best of our knowledge, there are no reports concerning aminoimidazole catalysts. [10,11] In our continuing work on chiral imidazole nucleophilic catalysts, we have developed a simple and adjustable chiral bicyclic imidazole (6,7- Figure 1), which does not require H-bonding assistance.…”

“…[10] However, to the best of our knowledge, there are no reports concerning aminoimidazole catalysts. [10,11] In our continuing work on chiral imidazole nucleophilic catalysts, we have developed a simple and adjustable chiral bicyclic imidazole (6,7- Figure 1), which does not require H-bonding assistance. This catalyst, which was readily prepared, has been applied to several different reactions, such as the asymmetric Steglich rearrangement, Black rearrangement and phosphorylation reactions.…”