Directed regioselective arylation of imidazo[1,2-a]pyridine-3-carboxamides using Rh(III) catalysis

In contrast to previously reported free-radical pathways to functionalize imidazo[1,2-a]pyridines at the C-5 centre, directing group approaches are rare. Herein, we demonstrate a rhodium(III) catalyzed efficient and regioselective strategy for directed C-5 functionalization of imidazo[1,2-a]pyridines using N-methoxyamide as a directing group. This methodology facilitates directed arylation without the necessity for pre-functionalization. It also allows for gram-scale synthesis and post-functionalization.

Zinc-Catalyzed Cyclization of Alkynyl Derivatives: Substrate Scope and Mechanistic Insights

Novel alkyl zinc complexes supported by acetamidate/thioacetamidate heteroscorpionate ligands have been successfully synthesized and characterized. These complexes exhibited different coordination modes depending on the electronic and steric effects of the acetamidate/thioacetamidate moiety. Their catalytic activity has been tested toward the hydroelementation reactions of alkynyl alcohol/acid substrates, affording the corresponding enol ether/unsaturated lactone products under mild reaction conditions. Kinetic studies have been performed and confirmed that reactions are first-order in [catalyst] and zero-order in [alkynyl substrate]. DFT calculations supported a reaction mechanism through the formation of the catalytically active species, an alkoxide-zinc intermediate, by a protonolysis reaction of the Zn-alkyl bond with the alcohol group of the substrate. Based on the experimental and theoretical results, a catalytic cycle has been proposed.

Rhodium(I)-Catalyzed Ring-Closing Reaction of Allene-Alkene-Alkynes: One-Step Construction of Tricyclo[6.4.0.02,6 ] and Bicyclo[6.3.0] Skeletons from Linear Carbon Chains

Treatment of dodecatrienyne derivatives with [RhCl(CO)₂ ]₂ in refluxing toluene effected the cycloisomerization to produce tricyclo[6.4.0.0^2,6 ]dodecadienes. The one-carbon shortened undecatrienyne derivatives, however, afforded bicyclo[6.3.0]undecatriene derivatives instead of tricyclic compounds, the latter of which are well known as a basic skeleton of naturally occurring octanoids. On the basis of two experiments with deuterated substrates, a plausible reaction mechanism for the construction of these products was proposed.