Rhodium(III)‐Catalysed Carbenoid C(sp²)–H Functionalisation of Aniline Substrates with α‐Diazo Esters: Formation of Oxindoles and Characterisation/Utility of an Intermediate‐Like Rhodacycle

Abstract

An efficient RhIII‐catalysed reaction of 2‐anilinopyridines with sulfonylated α‐diazo esters under mild conditions gave oxindole derivatives, while an analogous reaction of anilinopyrimidine precursors using α‐diazo esters led to the ortho‐alkylation products. The carbenoid coupling reaction was successfully extended to 6‐anilinopurine/purine nucleosides, and the ortho‐alkylated 6‐anilinopurines could be obtained in excellent yields. Proof of the involvement of an Rh–C‐bonded species comes from the characterisation of an intermediate‐like rhodacycle (which is also an active catalyst) by single‐crystal X‐ray crystallography.

Diazo Compounds: Versatile Synthons for the Synthesis of Nitrogen Heterocycles via Transition Metal‐Catalyzed Cascade C–H Activation/Carbene Insertion/Annulation Reactions

“…Almost at the same time, Swamy and co‐workers also reported the Rh(III)‐catalyzed coupling of 2‐anilinopyridines 11 with sulfonylated α‐diazo esters for the synthesis of oxindoles 12 (Scheme ) . Surprisingly, the analogous coupling reactions of anilinopyrimidines, and 6‐anilinopurine/purine under the standard conditions gave only the corresponding alkylated derivatives.…”

Co(III), Rh(III) & Ir(III)‐Catalyzed Direct C−H Alkylation/Alkenylation/Arylation with Carbene Precursors

“…In addition, to prove the catalyst‘s involvement, they synthesized corresponding cyclometallated Rh(III) complex intermediate and utilized for the reaction, which gave the comparable yield of oxindole derivative. And the cyclometallated Rh(III) complex characterized by single‐crystal X‐ray crystallography [19] …”

Recent Progress in the Transition Metal Catalyzed Synthesis of Indoles

“…The envisaged mechanism is very similar to that depicted in Scheme 52, Equation (1). Iridium catalyst was also able to perform the In Section 6 (Schemes 52 and 53) [96][97][98] the use of 2-pyrimidyl and 2-pyridyl directing group in the rhodium catalyzed C-H activation was described. In addition, iridium(III) complexes allowed the indolization of 2-pyrimidyl and 2-pyridylanilines and α-diazoesters (Scheme 72, Equation (1)) [139].…”

“…While methyl 2-diazo-2-(phenylsulfonyl)acetate only alkylated N-pyrimidylanilines, 2anilinopyridine and sulfonyl diazoesters led to the formation of oxindole derivatives (Scheme 53) [98]. 1-Aminoindoles are an important class of indoles in medicinal chemistry.…”