Enantiospecific Synthesis of Alkylboronate Esters Enabled by Carbopalladation of C─C σ-Bond and Novel Tsuji–Trost-Type Allylations
Final Report Abstract
Organoboron compounds are some of the highly valuable building blocks in organic synthesis, especially chiral boron compounds, because they can be easily transformed into other functional groups with high levels of enantioselectivity due to the unique reactivity of the C−B bonds. Our initial plan was to investigate and design more versatile, less strained substrates to accomplish the catalytic ‘conjunctive’ crosscouplings and synthesize different racemic α-halo allyl boronic esters to achieve the Tsuji-Trost reactions with different nucleophiles, which provided the new opportunities for synthesis of chiral alkyl-boronic esters. Unfortunately, the designed cyclobutyl boronate complex could not provide the sufficient driving force for 1,2-migration due to the low strain energy; in addition, the reactivity and regio-selectivity of Tsuji-Trost reactions could not also be optimized, making the reactions of both strategies failed. After that, we started looking for other ways to achieve the same goal. We found that the Giese-type reaction of 1,2-bis-boronic esters through radical 1,2-boron shifts reported by our group could offer great opportunities for the synthesis of valuable organoboron compounds. Therefore, we set out to develop new methods to synthesize the boronic esters through radical 1,2-boron shifts. To our surprise, the monodeboronative arylation of 1,2-bis-boronic esters could be achieved via 1,2-boron shift in two different reaction systems, affording the secondary/tertiary functionalized arylated products, albeit not in a chiral manner. Finally, we have demonstrated the deboronative (hetero)arylation reactions driven by the photochemical activity of electron donor−acceptor (EDA) complexes and dual nickel/photoredox-catalysis. The reactions allow easy access to secondary/tertiary-coupled arylated products with good regioselectivity via 1,2-boron shifts, highlighting their complementary selectivity to Pd-catalyzed cross-coupling reactions. Given that the works represent the first example of the site-selective arylation via the radical process from alkylboronates and provide valuable products retaining primary boronic esters, we believe that this study will promote the development of organoboron chemistry.
Publications
- Stereospecific 1,2‐Migrations of Boronate Complexes Induced by Electrophiles. Angew. Chem. Int. Ed. 2020, 59, 16859-16872
H. Wang, C. Jing, A. Noble, V. K. Aggarwal
(See online at https://doi.org/10.1002/anie.202008096) - Selective Coupling of 1,2-Bis- Boronic Esters at the more Substituted Site through Visible-Light Activation of Electron Donor-Acceptor Complexes. Angew. Chem. Int. Ed. 2022, 61
H. Wang, J. Wu, A. Noble, V. K. Aggarwal
(See online at https://doi.org/10.1002/anie.202202061)
