Rhodium(II)-Catalyzed Regioselective Remote C–H Alkylation of Protic Indoles

Control of regioselectivity that
defies the intrinsic reactivity
of arene C–H bonds remains a formidable challenge. In this
work, dimeric Rh­(II) complexes have been applied as an efficient catalyst
for the regioselective coupling of NH indoles with diazo compounds.
Two-substituted indoles mostly reacted with C(6) selectivity. Mechanistic
studies revealed that the regioselectivity results from the hydrogen-bonding
directing effect, and the C–C bond formation proceeds via the
Friedel–Crafts-type attack of indole toward the Rh­(II) carbene
species. In contrast, the reaction of 4-methoxyindoles occurred exclusively
with the complementary C(7) selectivity.