Rhodium(III)‐Catalyzed Asymmetric [4+1] and [5+1] Annulation of Arenes and 1,3‐Enynes: A Distinct Mechanism of Allyl Formation and Allyl Functionalization

Abstract

We report chiral RhIII cyclopentadienyl‐catalyzed enantioselective synthesis of lactams and isochromenes through oxidative [4+1] and [5+1] annulation, respectively, between arenes and 1,3‐enynes. The reaction proceeds through a C−H activation, alkenyl‐to‐allyl rearrangement, and a nucleophilic cyclization cascade. The mechanisms of the [4+1] annulations were elucidated by a combination of experimental and computational methods. DFT studies indicated that, following the C−H activation and alkyne insertion, a RhIII alkenyl intermediate undergoes δ‐hydrogen elimination of the allylic C−H via a six‐membered ring transition state to produce a RhIII enallene hydride intermediate. Subsequent hydride insertion and allyl rearrangement affords several rhodium(III) allyl intermediates, and a rare RhIII η4 ene‐allyl species with π‐agostic interaction undergoes SN2′‐type external attack by the nitrogen nucleophile, instead of C−N reductive elimination, as the stereodetermining step.

Rhodium(III)‐Catalyzed [4+1] Oxidative Annulation of Amides with 1,3‐enynes Through 1,4‐Rhodium Migration

“…This outcome supports the 1,4-Rh(III) migration. [4a] On the basis of these findings and relevant literature, [4,5] we believe that the reaction (Scheme…”

“…[4] Subsequently, Li group reported the [n + 1] asymmetric oxidative annulation of 1,3-enynes with arenes via 1,4-rhodium migration. [5] All these reactions were accomplished involving the different directing groups such as 1,3-dione, hydroxyl, amide and imide groups. However, CÀ H functionalization/ annulation via 1,4-rhodium migration assisted by Ncarboxamide or sulfonamide as the directing groups with 1,3-enynes is unexplored and expected to opens an efficient entry to varied imidazolones or sultams.…”

Enantioselective Access to C-N Axially Chiral Isoquinolones via Dynamic Kinetic Transformation of Carbene Reagents: Unique Chiral Induction Enabled by Dual Role of the Catalyst

“…Chiral ligand 69 was also applied to Ru-catalyzed nucleophilic addition between a benzaldehyde and phenyl boronic acid, affording diarylmethanol 72 in 73% ee. [99][100][101][102][103][104][105][106][107][108][109][110][111][112][113][114][115][116] are typical arene substrates that react via a C-H activation pathway through a concerted-metalation-deprotonation mechanism.…”