Spectroscopic analysis, thermogravimetric analysis, and crossover experiments performed on a series of imidazolium carboxylates revealed carboxylation was reversible with N-aryl substituted adducts.

[reaction: see text] A series of N-heterocyclic carbenes (NHCs) were evaluated as potential catalysts for the cyclotrimerization of isocyanates to afford isocyanurates. 1,3-Bis-(2,6-diisopropylphenyl)-4,5-dihydroimidazol-2-ylidene (SIPr) was found to be a highly efficient catalyst for the cyclotrimerization of a variety of isocyanates.

Alkenes and arenes represent two classes of feedstock compounds whose union has fundamental importance to synthetic organic chemistry. We report a new approach to alkene arylation using diaryliodonium salts and Cu catalysis. Using a range of simple alkenes, we have shown that the product outcomes differ significantly from those commonly obtained by the Heck reaction. We have used these insights to develop a number of new tandem and cascade reactions that transform readily available alkenes into complex arylated products that may have broad applications in chemical synthesis.

Substituted arenes dominate the properties of many natural products, medicines, and materials.[1] Therefore, the development of new methods for direct and selective aromatic functionalization is a persistent challenge for synthetic chemists.[2] A particularly important class of substituted aromatic compounds is the a-aryl carbonyl structure. These molecules represent broadly useful starting materials for complex molecule synthesis, and the basic structural framework is present in a wide range of medicinally relevant molecules.[3] Despite the importance of these structures, surprisingly few direct methods are available to selectively functionalize the arene nucleus in the absence of other groups: aromatic substitution reactions require directing functionality to control reactivity and selectivity; cross coupling processes need pre-installed functional groups; and while the acidity of the CÀH bonds between the arene and carbonyl groups facilitates a wealth of enolate chemistry, it precludes the use of directed ortho-lithiation reactions. [4] A potential solution to some of these limitations has recently been presented through the development of orthoselective Pd II -catalyzed C À H bond functionalization reactions. [5,6] The cyclometalation strategy employed in these transformations, however, cannot be used to facilitate metaor para-functionalization of these molecules due to restrictive geometric constraints. [7,8] The synthetic utility of the generic a-aryl acetic acid motif would be significantly expanded by a methodology that provides direct access to isomeric molecules of potentially beneficial therapeutic value (Scheme 1 A). Herein, we report a copper-catalyzed meta-selective arylation of the a-aryl carbonyl scaffold with diaryliodonium salts that is directed by a remote and versatile Weinreb amide group (Scheme 1 B). This method provides a novel synthetic route to arenes displaying diverse substitution, benzylic chirality and quaternary centers. Its potential is further enhanced through its compatibility with iterative C À H bond functionalization methods that will have broad utility in the synthesis of highly functionalized arenes.As part of our studies towards meta-selective functionalization processes, [8d] we postulated that the location of a carbonyl group plays a key role in determining the selectivity of our Cu II -catalyzed meta-arylation of pivanilides. To test this hypothesis, we speculated that the a-aryl carbonyl would also provide a similar reactivity platform because the carbonyl motif is displayed in a similar position relative to the arene nucleus. Notably, the arene nucleophilicity of the electronically neutral a-aryl carbonyl motif is drastically different to the electron-rich pivanilide.To test whether a-aryl carbonyl compounds could be functionalized at the meta-position, we prepared diethylamide 1 a and treated it with diphenyliodonium triflate and 20 mol % Cu(OTf) 2 in dichloroethane at 70 8C, conditions that are identical to those used for the arylation of pivanilides.[8d]After reacti...

A mild and general route for preparing pyridines from nitriles and diynes is described. Ni/imidazolyidene complexes were used to mediate cyclization alkynes and both aryl and alkyl nitriles at ambient temperature. In addition, the efficacy of this protocol allows for the preparation of a fused seven-membered pyridone and for intermolecular cyclizations. When an asymmetrical diyne was employed, cyclization afforded a single pyridine regioisomer.