A chiral squaramide has been supported onto a polystyrene (PS) resin through a copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction and used as a very active, easily recoverable and highly reusable organocatalyst for the asymmetric Michael addition of 1,3-dicarbonyl compounds to b-nitrostyrenes. The PS-supported squaramide could be recycled up to 10 times.
Cross-coupling reactions of Grignard reagents with functionalized aryl, heteroaryl, and sterically hindered aryl chlorides are reported. A protocol disclosing the coupling of a wide range of substrates using complexes of the type [Pd(μ-Cl)(Cl)(NHC)]2 (NHC = N-heterocyclic carbene) as precatalysts (at low catalyst loading) under mild conditions is presented. The system allows for the synthesis of highly sterically hindered products, including tri- and tetra-ortho-substituted biaryls.
[Pd(NHC)(PR(3))] complexes were shown to be active catalysts in the dehydrogenation of ammonia borane and the subsequent hydrogenation of unsaturated compounds at very low catalyst loadings (0.05 mol% for some substrates).
The synthesis of (+/-)-methoxyfumimycin, a potential new bacterial peptide deformylase (PDF) inhibitor, is reported. To generate the stereogenic fully substituted carbon, the key step is a 1,2-addition of a methyl Grignard reagent to a ketimine. The overall synthetic strategy involves a Dakin oxidation of a vanillin derivative, Friedel-Crafts acylation, Claisen rearrangement, lactonization, and rhodium-catalyzed olefin isomerization.
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