Enantioselective aza-Friedel–Crafts reaction of furan with α-ketimino esters induced by a conjugated double hydrogen bond network of chiral bis(phosphoric acid) catalysts

Abstract

Chiral C2- and C1-symmetric BINOL-derived bis(phosphoric acid) catalysts facilitated the enantioselective aza-Friedel–Crafts reaction of 2-methoxyfuran with α-ketimino esters.

Direct Asymmetric Arylation of Imines

“…Next, the reaction of aryl α-ketimino esters with furans induced by a conjugated double hydrogen bond network of chiral bis(phosphoric acid) catalysts led to the products in high yields (83-98%) and ee's (82-96%) (Scheme 52). [66]…”

“…Chiral BINOL‐derived bis(phosphoric acid) catalysts were examined in the reaction of 2‐OMe‐furan with β,γ‐alkynyl‐α‐imino esters in the presence of chiral Brønsted acid catalysts (5 mol%) in dichloromethane at −78 °C (Scheme ) . The best catalyst in this reaction was found to be ( R )‐ 30 a , providing addition products with a yield of 88% and ee =76%.…”

Organocatalytic Enantioselective Synthesis of Tetrasubstituted α‐Amino Allenoates by Dearomative γ‐Addition of 2,3‐Disubstituted Indoles to β,γ‐Alkynyl‐α‐imino Esters

“…Meanwhile, Ishihara and co‐workers developed a regio‐ and diastereoselective C‐alkyl addition to chiral β,γ‐alkynyl α‐imino esters using a Grignard reagent (RMgX) derived zinc(II)ate to construct optically active α‐quaternary alkynyl amino acid derivatives (Scheme , path b) . More recently, the same group accomplished an enantioselective aza‐Friedel–Crafts reaction of 2‐methoxyfuran with β,γ‐alkynyl‐α‐imino esters through the use of a chiral Brønsted acid catalyst, albeit with only one successful example . Nevertheless, a direct γ‐addition of a nucleophile to β,γ‐alkynyl‐α‐imino esters to form α‐quaternary amino allenoates has never been disclosed (Scheme , path c).…”

Construction of chiral α-tert-amine scaffolds via amine-catalyzed asymmetric Mannich reactions of alkyl-substituted ketimines

“…Some alkynyl-substituted ketimines have been used for asymmetric reactions 12 including Mannich reactions, although the applicable ketimines are limited to those activated by an electron-withdrawing perfluoroalkyl or ester group ( Scheme 1b ). 8 To the best of our knowledge, examples of catalytic asymmetric reactions of alkynyl-substituted ketimines that bear an electron-donating alkyl group on the imine carbon have not yet been reported.…”