Synthesis (Stuttg). 2023 Apr;55(8):1227-1240. doi: 10.1055/a-2001-6888. Epub 2020 Dec 20.
Catalytic oxidations of tricyclic endo-norbornene-fused tetrahydrofuran with bimetallic nanoclusters Cu/Au-PVP and H2O2 or t-BuOOH as an oxidant provided C-H bond oxidation adjacent to the ether function and 4-oxa-tricyclo[220.127.116.11]-8,9-exo-epoxydecane (4), however, oxidation with Pd/Au-PVP took place at the C=C function giving epoxide 4 and oxidative three-bond forming dimeric product, dodecahydro-1,4:6,9-dimethanodibenzofurano[2,3-b:7,8-b’]bisoxolane (5). Formation of the latter suggests the involvement of a reactive Pd-C intermediate. Similarly, oxidative C-C bond forming reactions were found in cycloaddition reactions of N2-Boc-1,2,3,4-tetrahydro-γ-carbolines and 2,3-dihydroxybenzoic acid with 2 – 5 mol% Cu/Au-PVP and H2O2 at 25 °C, providing two-bond-forming [4+2] cycloadducts. Under similar reaction conditions, Pd/Au-PVP did not produce the cycloadduct, indicating a need of complexation between Cu with the carboxylic acid group of 2,3-dihydroxybenzoic acid and allylic amine function of γ-carbolines in the cyclization reaction. The reported intermolecular coupling reactions using Pd/Au-PVP or Cu/Au-PVP nanocluster catalysts under oxidative conditions at 25 °C are unprecedented.
PMID:37151600 | PMC:PMC10162490 | DOI:10.1055/a-2001-6888