Triple role of boronic acid as a catalyst in the alkylation of quinoline to functionalized tetrahydroquinoline

The triple role of arylboronic acid as a catalyst in the alkylation of quinoline to <i>N</i>-substituted tetrahydroquinoline with a diaryl motif at the C6-position has been developed. This reaction involves the tandem reduction of quinoline to tetrahydroquinoline, followed by reductive <i>N</i>-alkylation with aldehyde to form <i>N</i>-alkylated tetrahydroquinoline and subsequent regioselective alkylation at the C6-position using <i>para</i>-quinone methides (<i>p</i>-QMs) in a one-pot operation. The methodology is compatible with a wide variety of functional groups and is also useful in the late-stage functionalization of pharmaceuticals. The mechanistic study demonstrates the existence of organoboron catalysts as both Lewis acids and hydrogen-bond donors.