Development of a Telescoped Process for Preparation of N,O-Chelated Diarylborinates

Abstract

A telescoped process has been developed for practical preparation of N,O-chelated four-coordinate diarylborinates via direct reaction of N,O-chelate ligands with a diarylborinate solution prepared by removal of magnesium via precipitation from a one-pot reaction of aryl bromides, magnesium, and tributylborate. Ten N,O-chelated diarylborinates of representative N,O-chelate ligands of 2-picolinic acid, quinolin-8-ol, N-dimethylglycine, and amino alcohols were readily obtained in good yields. The telescoped process not only minimizes chemical waste and circumvents tedious purification of diarylborinic acids but also eliminates handling of Grignard reagents and improves compatibility with acid-sensitive groups.

Highly Efficient Palladium‐Catalyzed Suzuki Coupling of N‐Tosyl Aryltriazenes with Diarylborons for Access to Biaryls

“…4 a gave a remarkably lower yield for 3 aa (74 %) (Table 2, entry 12). Attempts to use 0.1 mol % PdCl 2 (PPh 3 ) 2 as catalyst led to a low yield (49 %) for 3 aa, but still the highest one among the tested palladium catalysts, e. g. PdCl 2 (dppf) (41 %), PdCl 2 (dppm) (33 %), PdCl 2 (dppe) (28 %), PdCl 2 (dppb) (22 %), PdCl 2 (binap) (12 %) and Pd-PEPPSI-IPr (35 %) (Table 2, entries [13][14][15]. Again, almost no reaction was observed with PdCl 2 , Pd(OAc) 2 or Pd/C under the otherwise identical conditions (Table 2, entry 16).…”

Recent Advances in the Synthesis of Borinic Acid Derivatives

“…A recent study by Zou et al also showed the importance of the workup conditions ( Scheme 3 ) [ 15 ]. As just mentioned, they observed the selective formation of the p -tolylborinic ester 9 when using tributyl borate B(O n -Bu) 3 , instead of B(OMe) 3 or B(O i -Pr) 3 .…”

“…In general, good yields are obtained whatever the substitution pattern on the aromatic ring. Furthermore, electron-withdrawing (i.e., 12a [ 24 ], antibacterial agent 13f [ 25 ] , 13h [ 15 ] ) and -donating ( 12b [ 6 , 26 ], 12d ) [ 7 ] substituents are tolerated, as well as napththyl groups (i.e., 12g , a 1,2-diol complexing agent for absolute configuration prediction) [ 27 ]. However, the reaction is less efficient for para vinyl-substituted borinic acid 13e [ 28 ], probably because of the potential reaction of the styrenyl moiety with the Grignard reagent.…”

“…This is a main drawback of this strategy because only functional groups compatible with Grignard reagents (or organolithium) and acidic workup are allowed, which considerably narrows the scope of the reaction. However, the recent method reported by Zou et al using water instead of HCl for the hydrolysis, enables the synthesis of diketal 13c in a good 65% yield [ 15 ].…”

“…Accordingly, purification over silica gel generally results in a low isolated yield. An alternative way of purifying borinic acids is to form a chelate complex with amino alcohols, typically, ethanolamine [ 15 ]. The resulting stable aminoborinates 7 usually precipitate and can be filtered off to remove the soluble impurities (boronic acid derivatives, etc.)…”