Preparation of Chiral and Achiral Triazolium Salts: Carbene Precursors with Demonstrated Synthetic Utility

Abstract

4,4a,9,9a‐Tetrahydro‐1‐oxa‐4‐azafluoren‐3‐one (1 R , 2 S )‐(+)‐ cis ‐!‐Amino‐indol 2‐Pentafluorophenyl‐6,10b‐dihydro‐4 H ,5a H ‐5‐oxa‐3,10c‐diaza‐2azoniacyclopenta[ c ]fluorene;tetraborate Trimethyloxonium tetrafluoroborate Pentafluorophenyhydrazine

Asymmetric Synthesis of anti-β-Amino-α-Hydroxy Esters via Dynamic Kinetic Resolution of β-Amino-α-Keto Esters

“…This umpolung reactivity has precedent, 13 but it has not been demonstrated using glyoxylate as the nucleophile. Starting from readily accessed amido-sulfones 1 14 and using the triazolium carbene derived from 2 , 15 we observed Mannich addition of ethyl glyoxylate into in situ formed imines (Scheme 2). The requisite carbamates 3a and 3b were obtained in low and variable yields.…”

ChemInform Abstract: Asymmetric N‐Heterocyclic Carbene (NHC) Catalyzed Acyl Anion Reactions

“…We quickly identified amino indanol as the optimal chiral amino alcohol in the morpholine series, which could be coupled with a variety of structurally and electronically diverse hydrazines to furnish bench stable triazolium salts (Chart 2). 19 In the pyrrolidine series, a variety of sidechains (ultimately derived from amino acids such as phenyl alanine and valine) were identified as efficient chiral scaffolds which could also incorporate a variety of hydrazines to furnish bench stable triazolium salts (Chart 2). …”

A Late-Stage Strategy for the Functionalization of Triazolium-Based NHC Catalysts

“…These catalysts are often formed from the condensation of an amide, hydrazine, and an orthoformate, each of which may be tuned in an effort to achieve improved utility. 6 …”