Small gold nanoparticles for tandem cyclization/reduction and cyclization/hydroalkoxylation reactions

With peculiar structural features present at the surface of small metal nanoparticles, catalytic behavior similar to that observed with mononuclear metal catalysts in solution can be displayed by some discrete sites. The transfer of two catalytic tandem reactions from homogeneous to heterogeneous conditions has been studied. Tandem cyclisation/reduction of ortho-alkynyl benzaldehyde derivatives was successfully achieved using Au nanoparticles supported on TiO₂ (Au NPs/TiO₂) in the presence of Hantzsch ester, with yields ranging from 45 to 98% for 15 examples (average yield: 70.4%). Similarly, tandem cyclisation/hydroalkoxylation of ortho-alkynyl benzaldehyde derivatives was successfully carried out with Au NPs/TiO₂ in methanol or other alcohols, yielding 62 to 96% for 17 examples (average yield: 84.9%). The application potential of this catalytic system was demonstrated by the total synthesis of a bioactive isochromene derivative, where one of the developed reactions was employed as the key step, and by the implementation of the tandem cyclisation/hydroalkoxylation in a continuous flow reactor, with the reaction being scaled up by a factor of 10 without loss of efficiency.

• Plevová, K
• Michelet, V
• Antoniotti, S

• Université Côte d'Azur, CNRS. Institut de Chimie de Nice, Nice cedex 2, France

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