Rhodium(III)‐Catalyzed in situ Oxidizing Directing Group‐ Assisted CH Bond Activation and Olefination: A Route to 2‐Vinylanilines

Abstract

A new and efficient method for the synthesis of 2-vinylanilines from the reaction of arylhydrazine hydrochlorides with alkenes and diethyl ketone via a rhodium-catalyzed C À H activation is described. The oxidant-free olefination reaction involves the in situ generation of an À N À N=CR 1 R 2 moiety as the oxidizing directing group thus providing an easy access to 2-vinylanilines.

A comprehensive overview of directing groups applied in metal-catalysed C–H functionalisation chemistry

“…In the first one, the group of Cheng developed an alkenylation protocol in which the final products are ortho alkenylated anilines ( Scheme 62A ). 332 The actual DG is a hydrazone, since 1.2 equivalents of ketone, namely 3-pentanone, transform the hydrazine in situ to a hydrazone. Only then ortho C–H insertion by Rh took place and the olefination occurred with styrene derivatives or acrylates in quite good yields (>70%).…”

Rhodium(III)-Catalyzed Ortho-Alkenylation of Anilines Directed by a Removable Boc-Protecting Group

“…For example, treatment of 3aa with CF 3 CO 2 H at rt for 12 h gave deprotected n -butyl ( E )-2-aminocinnamate ( 3aa′ ) quantitatively (Scheme S1). Next, we examined further derivatization of thus-obtained N -unprotected 2-alkenylanilines 3′ . First, 3ha′ was treated with benzaldehyde using MgSO 4 /Na 2 SO 4 as dehydrative condensation reagents in THF at room temperature for 12 h. Without isolation, the crude aldimine intermediate was subjected to a Stetter-type reaction .…”

C–H Activation and Alkyne Annulation via Automatic or Intrinsic Directing Groups: Towards High Step Economy

“…In 2015, Cheng et al . reported a synthetic method of 2‐vinylaniline from arylhydrazines and alkenes by with 3‐pentanone as C=O source, which extended the versatility of hydrazone DG auto . In a control experiment without adding C=O source, messy side products were formed, which was also observed in our indole synthesis system, indicating C=O sources are necessary for ArNHNH 2 substrates.…”