An Efficient Rhodium/Oxygen Catalytic System for Oxidative Heck Reaction of Indoles and Alkenes via CH Functionalization

Abstract

catalyzed direct selective C-2 alkenylation reaction of indoles with alkenes has been developed with molecular oxygen as the sole oxidant. The rhodium/oxygen catalytic system is applicable to a broad range of indoles and alkenes, which provides a novel access to various C-2 alkenylated indoles and pyrroles.

Ruthenium(II)‐Catalyzed CH Activation/Alkyne Annulation by Weak Coordination with O2 as the Sole Oxidant

“…[3,4] Despite these advances,all the ruthenium(II)-catalyzed alkyne annulations thus far required the use of additional oxidants,such as copper(II) or silver(I) salts,thereby leading to the formation of undesired stoichiometric metal-containing by-products.I n contrast, molecular oxygen is significantly more attractive as as acrificial oxidant, since it is inexpensive and leads to the formation of water as the only by-product. [7][8][9] In contrast, ruthenium(II)-catalyzed oxidative C À Ha lkynylations with ambient oxygen have unfortunately proven elusive.W ithin our program on sustainable CÀH activation, [10] we developed unprecedented ruthenium-catalyzed oxidative alkyne annulations with molecular oxygen as the cheapest sacrificial oxidant in the absence of any cooxidant ( Figure 1). [7][8][9] In contrast, ruthenium(II)-catalyzed oxidative C À Ha lkynylations with ambient oxygen have unfortunately proven elusive.W ithin our program on sustainable CÀH activation, [10] we developed unprecedented ruthenium-catalyzed oxidative alkyne annulations with molecular oxygen as the cheapest sacrificial oxidant in the absence of any cooxidant ( Figure 1).…”

“…Interestingly,different ruthenium(II) precursors could be employed for efficient aerobic alkyne annulations (entries [9][10][11]. Thed esired synthesis of isocoumarin 3aa also occurred under an atmosphere of ambient air, albeit with asomewhat reduced efficacy(entry 8).…”

Regioselective Direct C‐Alkenylation of Indoles

“…The utilization of the N‐ (2‐pyrimidyl) group for the selective C‐2 alkenylation of indoles is effective using Rh III complexes coupled with Cu(OAc) 2 , or molecular oxygen as terminal oxidants (Scheme ) . The yields of the prepared adducts are comparable with those previously obtained using the same metal and the N , N ‐dimethylcarbamoyl directing group.…”

Transition‐Metal‐Catalyzed Redox‐Neutral and Redox‐Green C–H Bond Functionalization

“…Inspired by the success of the rhodium‐catalyzed oxidative C–H functionalization with O 2 as the sole oxidant, a rhodium‐catalyzed C‐2 alkenylation of indoles 42 with alkenes 43 using molecular O 2 as the sole oxidant was established by our group (Scheme ) 24. A variety of C‐2 alkenylation indoles were afforded in moderate to good yields by using the combination of [Cp*Rh(OAc) 2 (H 2 O)] and HOAc as the catalytic system.…”