A Boron Activating Effect Enables Cobalt-Catalyzed Asymmetric Hydrogenation of Sterically Hindered Alkenes.
J Am Chem Soc
; 142(8): 3923-3930, 2020 02 26.
Article
en En
| MEDLINE
| ID: mdl-32009399
Unsymmetric 1,1-diboryl alkenes bearing one -[BPin] (BPin = pinacolatoboryl) and one -[BDan] (BDan = 1,8-diaminonaphthalatoboryl) substituent each were hydrogenated in high yield and enantioselectivity using C1-symmetric pyridine(diimine) (PDI) cobalt complexes. High activities and stereoselectivities were observed with an array of 2-alkyl-, 2-aryl-, and 2-boryl-substituted 1,1-diboryl alkenes, giving rise to enantioenriched diborylalkane building blocks. Systematic study of substrate substituent effects identified competing steric and electronic demands in the key activating role of the boron substituents, whereby sterically unencumbered boronates such as -[BDan], -[BCat] (BCat = catecholatoboryl), and -[Beg] (Beg = ethylene glycolatoboryl) promote the hydrogenation of trisubstituted alkenes by enabling irreversible α-boron-directed insertion pathways to achieve otherwise challenging hydrogenations of trisubstituted alkenes. Deuterium-labeling studies with 1,1-diboryl alkenes support an insertion pathway generating a chiral intermediate with two different boron substituents and cobalt bound to the same carbon.
Texto completo:
1
Colección:
01-internacional
Base de datos:
MEDLINE
Idioma:
En
Revista:
J Am Chem Soc
Año:
2020
Tipo del documento:
Article
País de afiliación:
Estados Unidos
Pais de publicación:
Estados Unidos