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Alkyl boronic acids and esters are versatile synthetic intermediates that generally require several steps to synthesize. Three-component alkene arylboration reactions allow for the rapid synthesis of alkyl boronic esters. Herein, we report the base-free aerobic Pd-catalyzed three-component alkene arylboration, which allows direct access, in a single step, to alkyl boronic esters from readily available precursors: aryl boronic acids, alkenes, and bis(pinacol)diboron. This approach allows for the formal insertion of an alkene into an Ar–B bond, and thus, generates an alkyl boronic ester from an aryl boronic acid. The reaction proceeds with both electron-rich and electron-deficient aryl boronic acids as well as strained cyclic, internal, and terminal olefins. The reactions are regioselective: 1,2-arylboration products are formed with strained cyclic alkenes and b-alkyl-styrenes while 1,1-arylboration products are generated from terminal alkenes. Forty-five examples are presented with isolated yields of the resulting alkyl boronic esters ranging from 20-74%, along with several examples demonstrating the synthetic utility of the products. Mechanistic investigations support that the catalytic cycle occurs through direct arylboration of the alkene. Further, p-benzyl intermediates form when possible, and the rate of borylation is increased with electron-rich arenes relative to electron-poor. Finally, we demonstrate that aryl boroxines, generated in situ, are essential for the transformation as they rapidly undergo base-free transmetalation with the proposed palladium peroxo intermediate.
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Platinum‐Catalyzed Regio‐ and Enantioselective Diboration of Unactivated Alkenes with (pin)B−B(dan)
Abstract Asymmetric diboration of terminal alkenes is well established, and subsequent selective functionalization of the less hindered primary boronic ester is commonly achieved. Conversely, selective functionalization of the sterically less accessible secondary boronic ester remains challenging. An alternative way to control chemoselective functionalization of bis(boron) compounds is by engendering different Lewis acidity to the two boryl moieties, since reactivity would then be dictated by Lewis acidity instead of sterics. We report herein the regio‐ and enantioselective Pt‐catalyzed diboration of unactivated alkenes with (pin)B−B(dan). A broad range of terminal and cyclic alkenes undergo diboration to furnish the differentiable 1,2‐bis(boron) compounds with high levels of regio‐ and enantiocontrol, giving access to a wide variety of novel building blocks from a common intermediate. The reaction places the less Lewis acidic B(dan) group at the less hindered position and the resulting 1,2‐bisboryl alkanes undergo selective transformations of the B(pin) group located at the more hindered position. The regioselectivity of the diboration has been studied by DFT calculations and is believed to originate from thetransinfluence, which lowers the activation barrier for formation of the regioisomer that places the weaker electron donor [B(pin) vs B(dan)] opposite the strong electron donor (alkyl group) in the platinum complex.
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- Award ID(s):
- 2400056
- PAR ID:
- 10566667
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 64
- Issue:
- 1
- ISSN:
- 1433-7851
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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