Fluorine Effects on Group Migration via a Rhodium(V) Nitrenoid Intermediate

Abstract

An unprecedented rhodium(III)-catalyzed hydroarylation of α,α-difluoromethylene alkynes with N-pivaloxyl aroylamides through sequential C-H activation and aryl migration is detailed herein. A large array of α,α-difluoromethylene alkynes and N-pivaloxyl aryl amides were amenable to this transformation, thus providing a novel synthetic protocol for the construction of difluorinated 2-alkenyl aniline derivatives in high yields and with excellent regioselectivity. Notably, unique fluorine effects were found to underlie the thus unconventional reaction manifold.

Efficient Synthesis of Spirooxindole Pyrrolones by a Rhodium(III)‐Catalyzed C−H Activation/Carbene Insertion/Lossen Rearrangement Sequence

“…To determine the order of the Lossen rearrangement and the carbene migratory insertion, 1 na was subjected to the standard reaction condition with several nucleophiles such as methanol and aniline instead of 2 a , which, however, resulted in no Lossen rearrangement/nucleophilic addition product, but only in recovery of the starting materials (Scheme E). This result indicated that pathway B might be more favorable, and is also consistent with previous reports by the groups of Feng and Tanaka …”

Formal Lossen Rearrangement/[3+2] Annulation Cascade Catalyzed by a Modified Cyclopentadienyl RhIII Complex

“…Addition of MeOH furnishes rhodacycle D , and subsequent reductive elimination affords 4 aa and the Cp A Rh I complex, which is oxidized by air to regenerate the Cp A Rh III complex. DFT calculation supports the formal Lossen rearrangement via a nitrene intermediate as shown in the Supporting Information (Scheme S1) . Alternatively, the pathway via rhodacycles E and F is also capable of affording 4 aa .…”

Formal Lossen Rearrangement/Alkenylation or Annulation Cascade of Heterole Carboxamides with Alkynes Catalyzed by CpRhIII Complexes with Pendant Amides

“…The Xu and Liu groups reported that in the intramolecular reactions of anilides with alkynes, reductive elimination proceeds to give an annulation product when using an electron‐rich alkyne, but protonation proceeds to give an alkenylation product when using an electron‐deficient alkyne (Scheme b) . The groups of Loh and Feng reported that in the [4+2] annulation of N ‐acyloxybenzamides with internal alkynes, not reductive elimination but β‐fluorine elimination or protonation proceeds to give [4+1] annulation or alkenylation products when using difluorinated internal alkynes (Scheme c). In these Cp*Rh III ‐catalyzed C−H bond‐functionalization reactions, substrate structures deter direct reductive elimination from rhodacycle intermediates.…”