Practical Synthesis of Allyl, Allenyl, and Benzyl Boronates through S_N1′-Type Borylation under Heterogeneous Gold Catalysis

Abstract

Efficient borylation of sp3 C–O bonds by supported Au catalysts is described. Au nanoparticles supported on TiO2 showed high activity under mild conditions employing low catalyst loading conditions without the aid of any additives, such as phosphine and bases. A variety of allyl, propargyl, and benzyl substrates participated in the heterogeneously catalyzed reactions to furnish the corresponding allyl, allenyl, and benzyl boronates in high yields. Besides, Au/TiO2 was also effective for the direct borylation of allylic and benzylic alcohols. A mechanistic investigation based on a Hammett study and control experiments revealed that sp3 C–O bond borylation over supported Au catalysts proceeded through SN1′-type mechanism involving the formation of a carbocationic intermediate. The high activity, reusability, and environmental compatibility of the supported Au catalysts as well as the scalability of the reaction system enable the practical synthesis of valuable organoboron compounds.

Gold-catalyzed thioetherification of allyl, benzyl, and propargyl phosphates

“…We previously reported that Au/TiO 2 catalyst showed high activity for the borylation of propargyl carbonates to give allenyl boronates. 40 In contrast, the present thioetherification took place exclusively at C–O bonds, and no allenyl sulfides were formed.…”

“…38 In the course of our studies on the catalytic effects of Au NPs toward carbon–heteroatom bond formation, 39 we developed an efficient borylation of C(sp 3 )–O bonds of allyl, benzyl and propargyl esters in the presence of supported Au catalysts. 40 This result inspired us to develop further applications of Au NP catalysts to the nucleophilic substitution of carbon electrophiles. Herein, we report the thioetherification of C(sp 3 )–O bonds by supported Au catalysts.…”

Silver-catalysed [3 + 2] annulation reaction of aryldiazonium salts with allenes enabled by boronate direction

“…Subsequently, the scope of allenylboronates 1 was probed with aryl diazonium salt 2a under the optimal reaction conditions (Scheme 3). 14 α,α-Disubstituted allenylboronates participated in the annulation reaction smoothly and gave the 3-alkyl- N 1 -aryl-pyrazoles 3ba and 3ca in practical yields with exclusive regioselectivity. More significantly, a series of 3,5-disubstituted- N 1 -aryl-pyrazoles 3da–3ja were readily obtained from the corresponding trisubstituted allenylboronates and diazonium salt 2a under the standard conditions.…”

Highly dispersed nano‐copper catalyst on porous polyvinyl chloride for highly regioselective borylation of alkynes

“…On the other hand, a heterogeneous catalytic system based on supported metal nanoparticles (NPs) [ 12 ] has been researched and applied extensively because of their high stability, reusability, and reducing metal contamination in products, which makes heterogeneous catalytic system possible to synthesize highly valuable chemicals in scaled synthesis via a green and convenient manner. Usually, the heterogeneous catalysts could be prepared via the deposition of metal particles to the organic or inorganic supports.…”