Dynamic Covalent Metathesis in the C═C/C═N Exchange between Knoevenagel Compounds and Imines

Abstract

Fast and reversible dynamic covalent C═C/C═N exchange takes place without catalyst in nonpolar solvents between barbiturate-derived Knoevenagel (Kn) compounds and imines. A detailed study of the reaction indicates that it proceeds by an associative organo-metathesis mechanism involving the formation of a four-membered ring azetidine intermediate by addition of the imine C═N group to the C═C bond of the Kn compound. This intermediate could be generated cleanly and stabilized at low temperature by condensation of the o,p-dinitrophenyl Kn derivative with the cyclic imine 1-azacyclohexene. It was characterized by extensive NMR and mass spectrometric studies. The process described represents a genuine dynamic covalent organo-metathesis through a four-membered ring adduct as intermediate. It paves the way for the exploration of a wide set of dynamic systems involving (strongly) polarized C═C bonds and various imines, extending also into covalent dynamic polymers and polymolecular assemblies.

Lewis Base Promoted Delayed Copper Catalysis: Borylative α-C-H Allylation of Alicyclic Amines

“…bearing contiguous quaternary and tertiary stereocentres. Gratifyingly, this method could be extended to other alicyclic amine frameworks such as piperidine (15,16), piperazine (17), pyrrolidine (18) and azepine (19), obtaining in all cases the product in good yield with perfect regio-and diastereoselectivity. Of note is the reaction with 4methylpiperidin-1-yl benzoate which afforded 16 bearing three new stereocentres which were generated with total stereocontrol.…”

“…However, alicyclic imines are unstable, and they tend to undergo trimerization, resulting in non-reactive compounds. 16,17 Recently, Seidel and co-workers reported a method for the in-situ generation of alicyclic imines based on the reduction of a sacrificial ketone hydride acceptor by the corresponding N-lithiated amine. 18,19 The cyclic imine can then be trapped by an organolithium compound 18 or a Grignard reagent using Lewis acid activation, 19 thus resulting in a net α-C-H functionalization ( Figure 1B).…”

Using Visible Light to Tune Boronic Acid–ester Equilibria

“…178.80 (11) C9 C10 C11 C12 0.30 (19) F19 C6 C5 C4 178.18 (11) C14 C9 C10 C11 0.38 (18) N8 N7 C1 C2 -172.67 (10) C14 C13 C12 C11 -0.35 (19) N8 N7 C1 C6 6.46(18) C1 C2 C3 C4 -0.2 (2) N8 C9 C14 C13 179.08 (9) C1 C6 C5 C4 -1. 10(19) N8 C9 C14 B15 -2.43 (17) C2 C1 C6 F19…”

“…177.51 (11) C9 N8 N7 C1 178.75 (9) C13 C14 B15 O17 -3.07 (17) C9 C14 C13 C12 0.98 (17) C13 C14 B15 O16…”

Reductive cleavage of CC bonds as a new strategy for turn-on dual fluorescence in effective sensing of H2S

“…As we all know, C C bonds are fundamental structures of alkenes, where the C C π bond is localized above and below the C–C σ bond wherein π electrons are relatively far away from the nuclei and are loosely bound, so that they can be easily attacked to construct a new bond. 1 , 2 Indeed, addition reactions are one of the common reactions of C C bonds, such as reactions with HX (X = Cl, Br, I, OH, SH, RS, etc. ) as described in Scheme 1a .…”