Palladium-catalysed cross-coupling reaction of ultra-stabilised 2-aryl-1,3-dihydro-1H-benzo[d]1,3,2-diazaborole compounds with aryl bromides: A direct protocol for the preparation of unsymmetrical biaryls.

Siphamandla Sithebe,Ross S Robinson

doi:10.3762/bjoc.10.109

Siphamandla Sithebe, Ross S Robinson

Open Access

https://doi.org/10.3762/bjoc.10.109

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Journal: Beilstein journal of organic chemistry	Publication Date: May 13, 2014
Citations: 6	License type: CC BY 2.0

Abstract

There has been a significant interest in organoboron compounds such as arylboronic acids, arylboronate esters and potassium aryltrifluoroborate salts because they are versatile coupling partners in metal-catalysed cross-coupling reactions. On the other hand, their nitrogen analogues, namely, 1,3,2-benzodiazaborole-type compounds have been studied extensively for their intriguing absorption and fluorescence characteristics. Here we describe the first palladium-catalysed Suzuki–Miyaura cross-coupling reaction of easily accessible and ultra-stabilised 2-aryl-1,3-dihydro-1H-benzo[d]1,3,2-diazaborole derivatives with various aryl bromides. Aryl bromides bearing electron-withdrawing, electron-neutral and electron-donating substituents are reacted under the catalytic system furnishing unsymmetrical biaryl products in isolated yields of up to 96% in only 10 minutes.

Highlights

Arylboronic acids 1, arylboronate esters 2 and potassium aryltrifluoroborate salts 3 (Figure 1) have received considerable attention and have found a special place as mild and versatile nucleophilic coupling partners for carbon–carbon bond-forming cross-coupling reactions [1,2,3,4,5]
The use of organoboron compounds 1, 2 and 3 (Figure 1) as nucleophilic coupling partners in the Suzuki–Miyaura cross-coupling reaction is attractive due to the non-toxicity of the byproducts, the ease with which they are transmetalated and their high stability towards air and moisture, which are the key features for coupling reactions [7]
Unlike bromobenzene and 4-bromoanisole, the cross-coupling reaction of electron-deficient electrophiles (4-bromoacetophenone (13d) and 4-bromonitrobenzene (13c)) furnished the desired coupled products in excellent yields ranging from 85 to 96% (Table 3) [6,21]. These observations are consistent with the literature and aReaction conditions: boronate 9–12 (1.1 eqiuv), 13c–e (1.0 equiv), Pd(OAc)2 (4.0 mol %), PCy3, (8.0 mol %), K2PO4·H2O (3.0 equiv), toluene (0.50 mL) and H2O (0.10 mL), 80 W of microwave energy, 100 °C, 100 psi, 10 minutes. bYields of isolated products after a flash column chromatography

Summary

Introduction

Arylboronic acids 1, arylboronate esters 2 and potassium aryltrifluoroborate salts 3 (Figure 1) have received considerable attention and have found a special place as mild and versatile nucleophilic coupling partners for carbon–carbon bond-forming cross-coupling reactions [1,2,3,4,5]. Attempted cross-coupling reaction of compound 9 with bromobenzene (13a), in the absence of both the ligand and a base, gave, as expected, zero conversion of the starting materials (Table 1, entry 1). The addition of PPh3 as a ligand and K3PO4 as a base failed to afford the desired coupled product in any substantive yield (Table 1, entry 2).

Results

Conclusion