Synthesis, Structure, and Acidity Constants of Ligated α‐Boryl Acetic Acids

Abstract

Basic hydrolyses of various ligated α-boryl acetic acid esters provided the first ligated derivatives of the unknown compound boroacetic acid (BH CH CO H). Four monoacids (L-BH CH CO H) and one diacid (L-BH(CH CO H) ) were prepared with N-heterocyclic carbene, amine, and pyridine ligands (L). The stable acids were characterized by X-ray crystallography and acidity constant (pK ) measurements. They rank among the least acidic of all known carboxylic acids. In turn, their conjugate bases are among the strongest of all carboxylates.

Substituent Effects of Tetracoordinate Boron in Organic Synthesis

“…The examples selected for this review indicate that these tetracoordinate boryl groups can be roughly [a] Taken from Ref. [38].…”

“…[37c-g] In 2018, Weber and Curran elucidated the acidity of α-boryl acetic acids ligated by Lewis bases. [38] The targeting α-boryl acetic acids 98 are available by basic hydrolysis of the corresponding α-boryl esters 97 that are prepared by iodinecatalyzed reactions between ethyl diazoacetate and ligated boranes. Hydrolysis of 97 is rather slow, indicating that these ethyl esters are less electrophilic due to effects by electron-rich α-boryl groups.…”

“…In 2018, Weber and Curran elucidated the acidity of α‐boryl acetic acids ligated by Lewis bases [38] . The targeting α‐boryl acetic acids 98 are available by basic hydrolysis of the corresponding α‐boryl esters 97 that are prepared by iodine‐catalyzed reactions between ethyl diazoacetate and ligated boranes.…”