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Digging into the mechanism of oxidative Pd(II)-catalyzed aminations

corresponding

MELANIE M. LORION1,2, FADY NAHRA1,2, VU LINH LY1,2, CARLO MEALLI3, ABDELATIF MESSAOUDI3, FRÉDÉRIC LIRON1,2, JULIE OBLE1,2, GIOVANNI POLI*1,2
*Corresponding author
1. Sorbonne Universités, Institut Parisien de Chimie Moléculaire, F-75005, Paris, France
2. CNRS, UMR 8232, Institut Parisien de Chimie Moléculaire, F-75005, Paris, France
3. Istituto di Chimica dei Composti Organometallici ICCOM-CNR, Via Madonna del Piano 10, 50019 Sesto Fiorentino, Firenze, Italy

Abstract

Although the Pd(II)-catalyzed alkene aminopalladation and allylic C-H activation have been much described in literature, the in-depth mechanism of such type of process is far from being a simple matter. This account focuses on the oxidative intramolecular Pd(II)-catalyzed amination of unsaturated N-sulfonyl carbamates and carboxamides, revealing that different mechanistic paths can be operative. In particular, after activation of the unsaturation by Pd(II) catalyst, aminopalladation can take place, affording the corresponding high-energy cyclic (5- or 6-membered) aminopalladated intermediate (AmPI). This latter can evolve along different pathways, such as: distocyclic β-H elimination, oxidation by a strong terminal oxidant, or carbopalladation. Otherwise, the cyclic AmPI can lay dormant, in equilibrium with the initial substrate. In this case, alternative reactivities may take place, such as allylic C-H activation of the olefinic substrate, [3,3]-sigmatropic rearrangement, or decomposition.


INTRODUCTION

The two interlaced Pd-catalyzed allylation paths
Pd(0)-catalyzed allylation is a powerful transformation discovered in the sixties by Tsuji.(1) In 1970, the first catalytic version of this reactivity appeared in publications or patents (2, 3) and, a few years later, Trost reported the first asymmetric version(4), confirming the synthetic potential of this method. In this transformation, a Pd(0) complex undergoes oxidative addition by an allylic system, to generate an electrophilic η3-allyl-palladium intermediate I, which is finally trapped by a nucleophile to lead to the allylated product (Scheme 1, right). During the following decades, this Pd(0)-catalyzed allylation protocol gained a huge succe