Organocatalytic Reactions Enabled by N-Heterocyclic Carbenes.

The chemistry of transition metals with three-membered ring heterocycles.

Financial support of the Spanish Ministry of Science and
Innovation (CTQ2012-38543-C03) and Generalitat Valenciana
(PROMETEO/2012/020) is acknowledged. V.M.-C. thanks the
Spanish Ministry of Science and Education for a predoctoral
fellowship (FPU AP2007-02562) and Generalitat Valenciana for
a VALi+d postdoctoral fellowship (APOSTD/2013/041).
M.D.P. thanks the Spanish Ministry of Education for a
postdoctoral fellowship and UGC India for a Startup Grant.

Macrocyclization Reactions: The Importance of Conformational, Configurational, and Template-Induced Preorganization

First reported less than a decade ago, the α,β-unsaturated acyl azolium has emerged as a central reactive intermediate for reaction discovery using N-heterocyclic carbene catalysis. In this Perspective, an introduction to the four main reactivity patterns accessible from this intermediate is provided. The Perspective is handled in a largely chronological fashion, with an emphasis on alternate approaches to the key intermediate and first-in-class reaction cascades. Finally, a brief discussion of emerging trends in this field of catalysis is presented. Although not exhaustive, the Perspective provides an overview of this active area of research and serves as a guide for future investigations.

N-Heterocyclic Carbene Catalysis via the α,β-Unsaturated Acyl Azolium

Metal carbenes usually possess versatile reactivities that are controlled by the presence of both the metals and the ligands. Diazo compounds are commonly used for the generation of such species through elimination of nitrogen. However, they are often unstable, explosive, and toxic, which limits their applications in large-scale syntheses. Thus, identifying sustainable and safe surrogates for the generation of metal carbenes has attracted great attention. In this Review, we summarize some of the most important breakthroughs in the generation, catalytic reactions, and selectivity control of metal carbenes from non-diazo starting compounds.

New Approaches to the Synthesis of Metal Carbenes

One-step synthesis of nitrogen-containing medium-sized rings via α-imino diazo intermediates.

N-Heterocyclic carbene-catalyzed annulation of α-cyano-1,4-diketones with ynals.

An unusual palladium hydride complex has been shown to be a competent catalyst in the isomerization of a variety of terminal and internal epoxides. The reaction displayed broad scope and synthetic utility. Experimental and theoretical evidence are provided for an unprecedented hydride mechanism characterized by two distinct enantio-determining steps. These results hold promise for the development of an enantioselective variant of the reaction.

Isomerization of terminal epoxides by a [Pd-H] catalyst: a combined experimental and theoretical mechanistic study

https://www.rsc.org/suppdata/cc/c4/c4cc05260a/c4cc05260a1.pdf

An air-stable cationic iridium hydride as a highly active and general catalyst for the isomerization of terminal epoxides

Densely functionalized polyether macrocycles can be prepared in one pot in yields up to 60% by the rhodium(II)-catalyzed decomposition of methyl diazoacetoacetate in the presence of a variety of substituted or unsaturated 5- and 6-membered ring cyclic ethers. A comprehensive analysis of the solid state conformations of the macrocyclic geometries is detailed as well as novel mechanistic insights about the multi-component condensation reaction.

Céline Besnard

Papers

One-step synthesis of nitrogen-containing medium-sized rings via α-imino diazo intermediates.

N-Heterocyclic carbene-catalyzed annulation of α-cyano-1,4-diketones with ynals.

Isomerization of terminal epoxides by a [Pd-H] catalyst: a combined experimental and theoretical mechanistic study

An air-stable cationic iridium hydride as a highly active and general catalyst for the isomerization of terminal epoxides

One‐Pot Multi‐Component Synthesis and Solid State Structures of Functionally Rich Polyether Macrocycles