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

Area of Science:

• Catalysis
• Nanomaterials Science
• Organic Synthesis

Background:

• Small metal nanoparticles exhibit unique surface structures enabling catalytic activity comparable to homogeneous mononuclear metal catalysts.
• Transferring homogeneous catalytic reactions to heterogeneous systems offers advantages in separation and reusability.

Purpose of the Study:

• To investigate the heterogeneous catalytic performance of gold nanoparticles over titanium dioxide (Au NPs/TiO2) for tandem reactions.
• To adapt two specific tandem reactions, cyclisation/reduction and cyclisation/hydroalkoxylation, to heterogeneous conditions.

Main Methods:

• Utilized gold nanoparticles supported on titanium dioxide (Au NPs/TiO2) as heterogeneous catalysts.
• Employed Hantzsch ester for tandem cyclisation/reduction and various alcohols for tandem cyclisation/hydroalkoxylation of ortho-alkynyl benzaldehyde derivatives.

Main Results:

• Achieved 45-98% yields (average 70.4%) for 15 examples of tandem cyclisation/reduction reactions.
• Obtained 62-96% yields (average 84.9%) for 17 examples of tandem cyclisation/hydroalkoxylation reactions.
• Demonstrated application potential through total synthesis of a bioactive isochromene derivative and successful scale-up in a continuous flow reactor.

Conclusions:

• Gold nanoparticles on TiO2 effectively catalyze tandem cyclisation/reduction and cyclisation/hydroalkoxylation reactions under heterogeneous conditions.
• The developed catalytic system is versatile, applicable in total synthesis, and amenable to continuous flow processing with maintained efficiency.