Indication of Pd-C or Cu-C Intermediate in Respective Bimetallic Nanoclusters Pd/Au-PVP or Cu/Au-PVP Catalyzed Oxidations of endo -4-Oxatricyclo[5.2.1.0 2,6 ]-8-decene and Tetrahydro-γ-carbolines.

Catalytic oxidations of tricyclic endo -norbornene-fused tetrahydrofuran with bimetallic nanoclusters Cu/Au-PVP and H2 O2 or t -BuOOH as an oxidant provided C-H bond oxidation adjacent to the ether function and 4-oxa-tricyclo[5.2.1.0]-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 N 2-Boc-1,2,3,4-tetrahydro-γ-carbolines and 2,3-dihydroxybenzoic acid with 2 - 5 mol% Cu/Au-PVP and H2 O2 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.