Gold-catalyzed tandem reactions of amide-aldehyde-alkyne coupling and cyclization-synthesis of 2,4,5-trisubstituted oxazoles.

We report the first cationic gold(i)-catalyzed one-pot reaction of amide, alkyne and aldehyde followed by cyclization, to successfully access highly substituted oxazoles derivatives in good yields. A single catalyst allows the occurring of this multi-step reaction atom- and step-economically, with water as the only theoretical side product.

Aniline carbamates: a versatile and removable motif for palladium-catalyzed directed C-H activation.

The aniline carbamate is introduced as a new removable directing group for C-H activation. Its versatility and ability as a directing group are demonstrated by its use in the ortho-arylation of a wide variety of aniline derivatives under palladium(II) catalysis, with symmetric diaryliodonium salts as aryl donors. The reaction differs from previously reported arylations in its selectivity and its mechanism, as elucidated by kinetic and isotopic experiments. The directing group can also be easily removed under a variety of conditions.

Combined A3 Coupling and Click Chemistry Approach for the Synthesis of Dendrimer-Based Biological Tools.

We report a versatile approach in which two highly efficient chemical reactions, multicomponent A3 coupling and alkyne-azide click chemistry, are combined to construct dendrimer-based tools for applications in biology. Using a convergent approach, dendrons with desired architecture and an alkyne at the focal point are first assembled and then stitched together via multicomponent A3 coupling reaction. The desired functional groups, including a stealth agent, imaging dye, and drug molecules, could be easily covalently linked to the surfaces of these hyperbranched macromolecules using alkyne-azide click chemistry. These A3-click dendrimers are noncytotoxic at concentrations as high as 1 µM and in fact reduce the toxicity of the drug. The dye-coated dendrimers specifically target and localize in lipid droplets. This unison methodology represents an attractive chemical strategy in exploiting the untapped potential of A3 coupling and facilitating the development of nanodevices for imaging and drug delivery.

Site-specific modification of amino acids and peptides by aldehyde-alkyne-amine coupling under ambient aqueous conditions.

A highly efficient method for the direct, site-specific functionalization of amino acids and peptides, under ambient conditions, is described. In aqueous, nearly solvent-free conditions, copper(I) chloride catalyzed the aldehyde-alkyne-amine (A(3)) coupling of amino acids to form dipropargylated products in moderate to excellent yields. The propargylamine functionality provides a convenient handle for further structural modifications, demonstrated by a subsequent one-pot deprotection and "click" reaction and a solution-phase peptide coupling.