A Pd-catalyzed heterocyclization/carbonylation cascade reaction encompassing the formation of 3 new bonds, affording dihydropyrazole-esters in moderate to excellent yields and good functional group tolerance is described, comprising a new methodology for direct access to esterified heterocycles using alcohols as readily available feedstock. Optimization was carried out along with a phosphine/base parameterization study, providing important structure-reactivity insights for pyridinebases, mono-and bisphosphines.

Over the past years, Pd(II)-catalyzed oxidative couplings enabled the achievement of molecular scaffolds with high structural diversity via C−C, C-N and C-O bond-formation reactions. In contrast to the use of stoichiometric amounts of more common oxidants, such as metal salts (Cu and Ag) and benzoquinone derivatives, the use of molecular oxygen in the direct or indirect regeneration of Pd(II) species presents itself as a more viable alternative in terms of economy and sustainability. In this review, we describe recent advances on the development Pd-catalyzed oxidative cyclizations/functionalizations, where molecular oxygen plays a pivotal role as the sole stoichiometric oxidant. 1 Introduction 2 Oxidative C-C and C-Nu Coupling 2.1 Intramolecular Oxidative C-Nu Heterocyclization Reactions 2.1.1 C-H Activation 2.1.2 Wacker/aza-Wacker Type Cyclization 2.1.3 Tandem Wacker/aza-Wacker and Cyclization/Cross Coupling Reactions 2.2 Intermolecular Oxidative C-Nu Heterocoupling Reactions 2.3 Intramolecular Oxidative (C-C) Carbocyclization Reactions 2.4 Intermolecular Oxidative C-C Coupling Reactions 2.4.1 Cyclization Reactions 2.4.2 Cross-Coupling Reactions 2.4.3 Homo-Coupling Reactions 3 Aerobic Dehydrogenative Coupling/Functionalization 4 Oxidative C-H Functionalization 5 Summary

Herein, we report the synthesis of 3-carbonyl-trisubstituted furans via Pd-catalyzed oxidative cycloisomerization reactions of 2-alkenyl-1,3-dicarbonyl scaffolds, using molecular oxygen as the sole oxidant to regenerate active palladium catalytic species, featuring good functional tolerance and mild reaction conditions. Deep investigation of intermediates and transition states of the reaction mechanism were conducted via experimental and DFT studies, providing a detailed mechanistical profile. The new developed methodology presents a greener alternative to Wacker-type cycloisomerizations and avoids the use of stoichiometric amounts of oxidants and strong acid additives.

Visible light-induced Pd mediated reactions have become a novel and promising field in organic synthesis. This photocatalytic arsenal presents complementary features towards traditional Pd-chemistry, allowing the achievement of new and unique reactivities by generation of versatile Pd-radical hybrid species. These putative intermediates can be produced by direct excitation of Pd complexes, together with organic radical precursors. This review aims at describing recent advances regarding the combination of Pd-based photocatalytic manifolds and radical generation in the functionalization of important motifs in synthetic chemistry, encompassing detailed mechanism descriptions and relevant examples.