Enantioselective Synthesis of 2‐Substituted Indoles Bearing Trifluoromethyl Moiety by the Friedel‐Crafts Alkylation Reaction of 4,7‐Dihydroindole with
<i>N</i>
−H Trifluoromethyl Ketimines
The Friedel‐Crafts alkylation reaction of 4,7‐dihydroindole with N‐unprotected trifluoromethyl ketimines by means of chiral phosphoric acid and the subsequent oxidation with DDQ afforded chiral 2‐indolylmethylamines bearing a trifluoromethyl moiety in good to high yields with excellent enantioselectivities under one‐pot conditions. The adduct was transformed without loss of enantioselectivity and the
N-unprotected ketimines is realized for the first time by employing chiral BIBOP-type ligands with a Rh loading as low as 1 mol %. A range of chiral α-trifluoromethyl-α,α-diaryl α-tertiary amines or 3-amino-3-aryloxindoles were formed with excellent ee values and yields by employing either WingPhos or PFBO-BIBOP as the ligand. The method has enabled an efficient enantioselective synthesis of cipargamin