Synthetic and mechanistic studies on the heck reaction using CMK-supported bimetallic catalysts and ring closing enyne metathesis of acrylamides

Abstract

Heterogeneous catalysts were prepared by impregnation method using the transition metals like Pd, Ni and Cu with carbon mesoporous material. Thus, the prepared bimetallic Catalysts such as Pd-Ni and Pd-Cu impregnated Carbon Mesoporous Materials were characterized and applied for the first time for catalytic carbon-carbon coupling reactions. The catalysts exhibits a high activity and selectivity toward Heck reaction of even aryl chloride with olefins for small catalyst concentrations (≤ 0.1 mol %). Heterogeneity of the reaction was done by conducting the heck reaction using hot filtrate of Pd-Ni/CMK-3 with bromobenzene and styrene as reacting components. The catalysts can easily be separated from the reaction mixture and reused after washing without loss in activity. Ring Closing Enyne Metathesis (RCEYM) was efficiently carried out using three different alkyne substituted N-benzyl acryl amides. On the basis of experimental results, we believe that the alkyne-initiation route can explain the outcome of the RCEYM. The transition in exo/endo-mode selectivity observed in our enyne system is therefore the manifestation of the reactivity of alkene in the electron-deficient acryl amides. Furthermore, the exo-endo-mode selectivity was achieved by performing the reaction under ethylene atmosphere, which generates the triene intermediate that in turn generates selectively the endo-product. Relay Ring Closing Enyne Metathesis (RRCEYM) was also carried out as an alternative way to improve the selectivity. Enyne having carbon tether more than two gave the macrocycle instead of seven or eight membered cyclized products due to their unrestricted conformations. Thus, the alkynes linked with the electron-deficient acrylamides were efficiently used for ring closing enyne metathesis under our reaction conditions. Asymmetric synthesis of chiral alcohol, a key intermediate of Modhephene was synthesized using Organic catalyst. Quinidine was used to synthesize the organic cataly...