Pyridinyl Amide Ion Pairs as Lewis Base Organocatalysts

Abstract

Pyridinyl amide ion pairs carrying various electron-withdrawing substituents were synthesized with selected ammonium or phosphonium counterions. Compared to neutral pyridine-based organocatalysts, these new ion pair Lewis bases display superior catalytic reactivity in the reaction of isocyanates with alcohols and the aza-Morita−Baylis−Hillman reaction of hindered electrophiles. The high catalytic activity of ion pair catalysts appears to be due to their high Lewis basicities toward neutral electrophiles as quantified through quantum chemically calculated affinity data.

Versatile New Reagent for Nitrosation under Mild Conditions

“…Geometries for the NO-1a, NO-1a (sp 3 ), and NO-1b reagent were all calculated using the B3LYP/6-311+G(2p, d) model chemistry with the PCM(acetonitrile) solvent model. [1,3,4] Additionally, vibrational frequency analysis was performed to confirm that all geometries were true minima. [2] Once the ground state geometries were confirmed the Nitrogen-Nitrogen bond dihedral angle was scanned/rotated using a scan job in gaussian, changing the dihedral angle by ten degrees all the way until three-hundred sixty degrees is reached, calculating a ground state energy.…”

“…Reagents and solvents were purchased and used without purification. Yields refer to homogenous material that is purified by silica-gel chromatography and spectroscopically pure (>95%) by 1 H NMR and 13C NMR. Yields in the Supporting Information describe the result of a single experiment, whereas the yields reported in Schemes 1-3 are an average of two or more experiments.…”

Cycloaddition of CO2 to epoxides by highly nucleophilic 4-aminopyridines: establishing a relationship between carbon basicity and catalytic performance by experimental and DFT investigations

“…Overall, this work demonstrates that highly nucleophilic aminopyridines hold significant potential as new, efficient halogen-free organocatalysts for the cycloaddition of CO2 to epoxides and we expect that this work will inspire the design of new homogeneous and heterogeneous halogen-free organocatalysts. In this context, the application of even more nucleophilic, 73,74 recently developed aminopyridines appears highly promising and is currently under investigation.…”

“…72 Whereas all the above-mentioned halogen-free organocatalysts contain nucleophilic and basic nitrogen atoms to assist in the activation and coordination of CO2, there has been scarce attention at systematically exploring the effect of nitrogen nucleophilicity within a series of comparable compounds with well-known and parameterized nucleophilicity. In this context, 4-aminopyridines are a class of N-nucleophilic catalysts whose nucleophilicity can be strongly enhanced by structural modifications [73][74][75] and conformational fixation. 76,77 Their nucleophilicity can be parameterized by using theoretically calculated and experimental descriptors.…”

Annelated Pyridine Bases for the Selective Acylation of 1,2‐Diols

“…[28] From the time dependence of the mole fraction of monoester 17 shown in Figure 4a we see that the effective rate constant k 3 for acylation of the primary hydroxyl group in 16 is largest for DMAP (1) and smallest for 3,4-diaminopyridine catalyst 4 m. It is particularly surprising that catalyst 1 is more reactive here than TCAP (3), which is in contrast to most other reactivity studies with these two Lewis bases. [6,12,29] Quantitative analysis in the framework of the mechanistic model shown in Scheme 3 yields the values shown in Table 1 and thus an approx. 10-fold reactivity difference between the fastest and slowest catalysts.…”