Practical Solvent‐Free Microwave‐Assisted Hydroboration of Alkynes

Abstract

A simple and rapid protocol for the anti-Markovnikov hydroboration of alkynes assisted by microwave irradiation has been developed. Pinacolborane smoothly reacts with terminal alkynes to obtain (E)-alkenyl boronates in good yields and short [a] microwave irradiation gave a 25 % yield after 20 minutes (entry 6). Finally, the reaction time was optimized to 18 minutes, leading to a 79 % yield of (E)-styryl pinacolboronate in 4.5 mmol scale (entry 7). [22] Eur.

Synthesis and preliminary structure-activity relationship study of 3-methylquinazolinone derivatives as EGFR inhibitors with enhanced antiproliferative activities against tumour cells

“…980 mg; 43% yield; 1 H NMR (400 MHz, CDCl 3 ) d 7.47 À 7.42 (m, 2H), 7.28 (dd, J ¼ 8.0, 6.0 Hz, 1H), 7.24 À 7.16 (m, 2H), 7.05 (d, J ¼ 16.4 Hz, 1H), 6.94 À 6.87 (m, 4H), 3.83 (s, 3H). Spectral properties were in accordance with the literature 24 .…”

Cobalt‐Catalyzed Markovnikov‐Type Selective Hydroboration of Terminal Alkynes

“…[3] Commonly, the anti-Markovnikov products with b(E)-selectivity are usually obtained in noncatalytic hydroboration of terminal alkynes. [4] Various metal catalysts have been discovered for selective hydroboration of terminal alkynes to efficiently produce b(E)-and b(Z)-alkenyl boronates, respectively. [5,6] However, hydroboration of terminal alkynes to access a-alkenyl boronates is still challenging and less explored.…”

“…[10] Compared to the protonboration, metal-catalyzed selective hydroboration of alkynes using hydroboranes offers an atom-economic way to access a-alkenyl boronates (Scheme 1). Nevertheless, Markovnikov-type selective hydroboration of terminal alkynes with HBpin via a metal hydride strategy has not been explored due to several challenges in this system: 1) The insertion of terminal alkyne into metal hydride species usually delivers the intermediate bearing the metal at terminal carbon due to the steric and electronic effect; [11] 2) the intrinsic background reactions affording anti-Markovnikov selective hydroboration products may lower the regioselectivity; [4] and 3) in the presence of metal hydride species, the side-reactions including alkyne hydrogenation, double hydroboration, and isomerization may become dominant. [12] In recent years, cobalt hydride catalysis, which emerged as an economical and ecologically tool for sustainable synthesis, has shown its unique reactivity and selectivity on various organic transformations.…”

Palladium-Catalyzed Multicomponent Assembly of (Z)-Alkenylborons via Carbopalladation/Boronation/Retro-Diels–Alder Cascade Reaction

“…Therefore, the development of methods for the synthesis of alkenylborons in a practical and efficient manner has attracted increasing attention. ( E )-Alkenylborons can be obtained conveniently from transition metal-catalyzed, base-mediated, Lewis acid-promoted, electrochemical, tropylium-promoted, and microwave-assisted hydroboration of terminal alkynes. Conversely, methods to make the thermodynamically disfavored ( Z )-isomers are more challenging.…”