Simple alkenes and alkynes, with 3-hexyne in particular, are found to be important pi ligands for oxidative copper-based coupling (modern Ullmann) reactions. This enabled syntheses of various alkoxydienes with removable protecting groups that are valuable substrates for Diels-Alder reactions from alcohols and vinyl boronate esters. In addition to demonstrating that 3-hexyne is a ligand for copper in both stoichiometric and catalytic reactions, the reaction atmosphere was found to play a critical role.
A novel class of reagents, thioester isocyanides, have been prepared and applied in the synthesis of peptide macrocycles. The isocyanide part of the molecule is deployed in a multicomponent macrocyclization step. This step is followed by chemoselective peptide ligation at the thioester part of the macrocycle. Our method can now be used for rapid assembly and evaluation of cycle-tail peptides.
Copper(II) acetate catalyzes the coupling of pinacol vinylboronates with silanols producing enol silyl ethers. This represents a novel enol silyl ether synthesis via formation of the C-O bond instead of the conventional Si-O bond. This also constitutes the first transition-metal-catalyzed oxidative cross-coupling with silanols.
Deceptively simple as the structure may appear, there is no single general method by which to synthesize the vinyl (enol) ether functionality. However, there exists a diverse array of complementary methods by which this functionality has been achieved. This review presents the scope and limitations of these methods according to reaction type, specifically via ether modifications, elimination reactions, carbonyl olefinations, alcohol additions and carbon-oxygen coupling reactions.
A "click and activate" strategy was designed and executed in a four-component, stepwise condensation that led to a trisubstituted triazolyl-pyridazinone library. This one-pot process included regioselective azide substitution at 2-substituted-4,5-dichloropyridazinones, followed by a Cu(I) catalyzed triazole formation which triggered subsequent nucleophilic substitution at the neighboring position to achieve three points of diversity.
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