Divergent Synthesis of Chelating Aziridines and Cyclic(Alkyl)(Amino)Carbenes (CAACs) from Pyridyl‐Tethered Robust Azomethine Ylides

Abstract

Azomethine ylides are typically in situ generated synthons for making N‐heterocycles through cycloaddition reactions. But an offbeat aspect about them is the isomeric nature of aldiminium‐based azomethine ylides and (alkyl/aryl)(amino)carbenes, interconvertible by a formal 1,3‐H+ transfer. Herein, two thermally robust azomethine ylides with a N‐appended picolyl sidearm are isolated, which cyclize to pyaziridines at 80 0C but unprecedentedly result N‐picoCAAC‐CuCl (CAAC = cyclic(alkyl)(amino)carbene) complexes when heated with CuCl at merely 60 0C. The pendant Npy, as revealed by computational analysis, plays a crucial role in this unusual 1,3‐H+ shift using a deprotonation‐protonation sequence, as well as in placing the CuCl at the carbenic site in tandem. The softer nature of Cu(I) is also critical. Chelating CAACs are rare and one with a N‐tethered additional donor is priorly unknown. Both N‐picoCAAC and pyaziridine are bidentate chelators giving highly active cationic Rh(I) catalysts for hydrosilylating unactivated olefins by Et3SiH. Notably, the pyaziridine‐Rh(I) is superior than the N‐picoCAAC‐Rh(I) catalyst.

Cyclic (amino)(barrelene)carbene Ru-complexes: synthesis and reactivity in olefin metathesis

“…Based on these reports, we decided to examine a new type of CAAC-5 ligand, namely cyclic (amino)(barrelene)carbene or CABC, recently reported in 2022. 10…”

“…Readily accessible through an intramolecular [4 + 2] cycloaddition between an alkyne and an anthracene derivative, this ligand features a barrelene skeleton, which provides a unique steric environment. 10 Herein, we report the synthesis of related CABC–ruthenium complexes ( Ru-4 ) and their catalytic performances in various olefin metathesis transformations (Fig. 1B).…”