Rh(III)-Catalyzed Regioselective Synthesis of Pyridines from Alkenes and α,β-Unsaturated Oxime Esters

Abstract

α,β-Unsaturated O-pivaloyl oximes are coupled to alkenes by Rh(III) catalysis to afford substituted pyridines. The reaction with activated alkenes is exceptionally regioselective and high yielding. Mechanistic studies suggest that heterocycle formation proceeds via reversible C-H activation, alkene insertion and a C-N bond formation/N-O bond cleavage process.

Transition Metal‐Catalyzed Reactions Involving Oximes

“…In 2013, Rovis et al. reported a Rh(III)‐catalytic coupling reaction of α,β‐unsaturated oxime esters with alkenes to synthesize substituted pyridines (Scheme ) . In the absence of β‐substitution oxime esters led to fairly good yields ( 61 and 62 ), however, the yields were low in reactions involving vinyl oxime esters ( 63 ).…”

Rh(III)-Catalyzed Decarboxylative Coupling of Acrylic Acids with Unsaturated Oxime Esters: Carboxylic Acids Serve as Traceless Activators

“…9 During the course of this study, we discovered that selectivity depends crucially on the nature of the alkene substrate. Namely, activated alkenes react with exquisite regioselectivity (eq 1) while unactivated alkenes incorporate to give mixtures of regioisomeric products (eq 2).…”

Metallkatalysierte Anellierungen durch Aktivierung und Spaltung von C‐H‐Bindungen

“…Andere Autoren entwickelten verschiedene Varianten, einschließlich der Verwendung von Benzylimin‐ oder Alkenyliminderivaten und entweder externen oder internen Oxidationsmitteln, wobei die letztgenannte Version auf vorhandenen N‐O‐ oder N‐N‐Bindungen beruht . Diesbezüglich beschrieben Rovis und Neely eine interessante Methode zum Aufbau substituierter Pyridine aus O ‐Pivaloyloximen und aktivierten Alkenen, wie Acrylaten . Die Reaktion erfolgt bei 85 °C unter Verwendung eines leichten Überschusses an Alken in Gegenwart von [Cp*RhCl 2 ] 2 und AgOAc (Schema ).…”