Chiral Brønsted Acid from Chiral Phosphoric Acid Boron Complex and Water: Asymmetric Reduction of Indoles

Abstract

An ew chiral Brønsted acid, generated in situ from ac hiral phosphoric acid boron (CPAB) complex and water, was successfully applied to asymmetric indole reduction. This "designer acid catalyst", which is more acidic than TsOH as suggested by DFT calculations,allows the unprecedented direct asymmetric reduction of C2-aryl-substituted N-unprotected indoles and features good to excellent enantioselectivities with broad functional group tolerance.D FT calculations and mechanistic experiments indicates that this reaction undergoes C3-protonation and hydride-transfer processes.Besides,bulky C2-alkyl-substituted N-unprotected indoles are also suitable for this system.

Catalytic Atroposelective Catellani Reaction Enables Construction of Axially Chiral Biaryl Monophosphine Oxides

“…To validate the feasibility of our conjecture and continue our long-term interest in boron chemistry, [58][59][60][61][62][63] 1-iodonaphthalene (1a), (2-bromo-3-methylphenyl)diphenylphosphine oxide (2a), and phenylboronic acid were first chosen as model substrates for the assembly of axially chiral monophosphine oxides. First, enantiopuresubstituted NBEs were prepared according to literature procedures 50,51 ; unfortunately, after careful condition screening (see Supporting Information Table S1 for details), only n-propyl ester NBE L3 demonstrated reactivity to deliver the desired axially chiral product in 57% NMR yield (48% isolated yield) with 98% ee, due to various Suzuki reaction side products (see Supporting Information for details).…”