Preparation of Potassium Acyltrifluoroborates (KATs) from Carboxylic Acids by Copper‐Catalyzed Borylation of Mixed Anhydrides**

Abstract

We report the preparation of potassium acyltrifluoroborates (KATs) from widely available carboxylic acids. Mixed anhydrides of carboxylic acids were prepared using isobutyl chloroformate and transformed to the corresponding KATs using a commercial copper catalyst, B 2 (pin) 2 , and aqueous KHF 2 . This method allows for the facile preparation of aliphatic, aromatic, and amino acid-derived KATs and is compatible with a variety of functional groups including alkenes, esters, halides, nitriles, and protected amines.

One-Step Synthesis of Acylborons from Acyl Chlorides through Copper-Catalyzed Borylation with Polystyrene-Supported PPh3 Ligand

“…Borylation with benzoyl bromide afforded 2k in 41% yield, which is comparable to the yield (39%) with chloride. 2k did not form with benzoyl fluoride or isobutyl mixed anhydride reported by Bode under the optimized conditions . As for the aliphatic acyl chlorides, KATs 2aa – ee were formed in 8–35% yields.…”

“…Acylborons, particularly potassium acyltrifluoroborates (KATs), have recently received much attention owing to their unique reactivity and applications such as amide-forming ligation with azides, hydroxylamines, or N -chloroamines, , formation of trifluoroborate-iminiums with amines, modification of proteins, polymers, and fluorophores . Various synthetic methods for acylborons from aldehydes, , acetals, aryl/alkenyl boronic acids, aryl/alkyl halides, , acyl halides, alkynes, and carboxylic anhydrides have been developed to date. For the facile preparation of acylborons, one-step synthesis from readily available carboxylic acid derivatives and boron sources is attractive.…”

“…They proposed a reaction mechanism in which an acyl iodide/bromide generated as an intermediate is converted to an acylboron through Cu-catalyzed borylation even in the presence of an alkoxide. Inspired by this result, Bode, Mankad, and co-workers studied Cu-catalyzed borylation of activated carboxylic acid derivatives and succeeded in developing borylation of mixed anhydrides, prepared from carboxylic acids, using B 2 pin 2 , a Cu catalyst with a NHC ligand, and an alkoxide (Scheme c) . They also described attempting the borylation of acyl chlorides with high availability, instead of the acyl iodide/bromide intermediates in the carbonylative borylation, but did not successfully obtain acylborons.…”

“…KHF 2 at rt for 2 h and the yields of 2a , 3a , and 4a were determined by 1 H NMR using an internal standard. With NHC ligands IPr, IMes, ICy, and SIPr (entries 1–4), ,, the desired acylboron 2a was obtained in 17–25% yields. However, a greater amount of ester 3a through alcoholysis was also formed in 28–42% yields.…”

Copper‐Catalyzed Borylation of Acyl Chlorides with an Alkoxy Diboron Reagent: A Facile Route to Acylboron Compounds

“…In contrast, our method employs easy to handle B 2 pin 2 , which is commercially available in bulk quantities at low cost. During the preparation of our manuscript, Bode and Mankad reported the synthesis of acylboron compounds from mixed anhydrides, [25] representing a significant advance. However, their method is not compatible with acyl chlorides and requires high catalyst loading.…”