2-(Amino-κN)ethanolato-κO]diphenylboron

Abstract

[15614-89-8] C14H16BNO (MW 225.10) InChI = 1S/C14H16BNO/c1-3-7-13(8-4-1)15(16-11-12-17-15)14-9-5-2-6-10-14/h1-10H,11-12,16H2 InChIKey = QKVRQZFQCGZLDA-UHFFFAOYSA-N (reagent for derivatization of flavonoids; inhibitor of Ca2+ channels; precursor to diphenylborinic acid; precatalyst for regioselective acylation, alkylation, sulfonylation, and glycosylation reactions) Alternate Names: 2-aminoethyl diphenylborinate; 2-APB; diphenylborinic acid 2-aminoethyl ester; Natural Product Reagent A. Physical Data: white crystalline solid, mp 189–190 °C. Solubility: soluble in acetone, DMSO, DMF, methanol, and THF. Preparative Methods: condensation of diphenylborinic acid or a diphenylborinate ester with ethanolamine. Diphenylborinic acid and esters thereof are generated by addition of phenylmagnesium halides to trialkyl borates. Several variants of the protocol have been reported. The ammonia complex of diphenylborinic acid isobutyl ester may be generated by addition of phenylmagnesium bromide to B(Oi-Bu)3, followed by hydrolysis and treatment with anhydrous NH3. Treatment of this complex with ethanolamine in toluene at reflux yields the crystalline ethanolamine ester.1 Addition of phenylmagnesium bromide to trimethoxyboroxine, quenching with aqueous HCl, and complexation with ethanolamine in water generates the diphenylborinate ester in 62% yield.2 A similar procedure employing phenylboroxine in place of trimethoxyboroxine has been reported.3 Aminoethyl diphenylborinate may also be prepared by treatment of triphenylborane with ethanolamine in refluxing benzene,4 or from sodium tetraphenylborate and ethanolamine hydrochloride.5 Purification: recrystallization (e.g., from ethanol/water). Handling, Storage, and Precautions: borinic acids are frequently isolated as their ethanolamine adducts because of the resistance of the latter to oxidation under ambient conditions, as well as their ease of purification by recrystallization. Aminoethyl diphenylborinate has been reported to be stable upon storage for up to 3 years on the bench top,6 although storage at −20 °C is recommended by certain suppliers. Hydrolysis of aminoethyl diphenylborinate to diphenylborinic acid is accomplished by treatment with aqueous acid.1, 6 The kinetics of this process have been studied in detail.7 Dissociation of the complex takes place within a few minutes in aqueous phosphate buffer at pH 7.0.8