An unexpected N-heterocyclic carbene-catalyzed esterification of α,β-unsaturated aldehydes including aromatic aldehydes with reactive cinnamyl bromides in the presence of air oxygen or MnO(2) as an oxidant is described. In the presence of oxygen, halogenated and electron-deficient aldehydes react smoothly to furnish esters in good yields. Great efforts have been made on mechanistic studies to deduce a plausible mechanism, based on the experimental results and isotopic labeling experiment.
An efficient and versatile approach for the synthesis of 2-deoxy-C-aryl glycosides is reported. This strategy is based on a palladium-catalyzed decarboxylative Heck coupling reaction of benzoic acids and glycals. A wide variety of glycals and benzoic acids have been screened, and all these reactions could afford the desired C-aryl glycoside products in moderate to good yields with exclusive regio- and stereoselectivities.
A facile and general method leading to polyfunctionalized quinolines was developed. In the presence of a highly efficient combination encompassing (PPh)(3)AuCl and AgOTf, the reactions between 2-aminocarbonyls and an array of internal alkynes proceeded smoothly to afford quinoline derivatives in good to excellent yields (up to 93%).
An efficient method for a Pd(OAc)(2)-catalyzed cross-coupling reaction of glycals with activated alkenes under mild conditions has been developed. This transformation provides an expedient synthetic method to C(2)-functionalized glycals, which are common structural building blocks in natural products and other biologically active compounds. The reaction scope includes different kinds of carbohydrates, protecting groups and substituents on alkene. Moderate to excellent yields and pure E configuration selectivity were obtained.
Mild and sweet: The title reaction proceeds under mild conditions with high regio‐ and diastereoselectivity (see scheme, PG=protecting group, DiPPF=1,1′‐bis(diisopropylphosphino)ferrocene). This reaction is suitable for a wide range of glycal‐derived γ‐ketone esters and affords C‐glycosides with exclusive β‐selectivity. The method was further applied to a concise formal synthesis of aspergillide A.
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