Catalytic Intramolecular Cycloaddition Reactions by Using a Discrete Molecular Architecture

Area of Science:

• Supramolecular Chemistry
• Coordination Chemistry
• Organic Synthesis

Background:

• Coordination-driven self-assembly is a powerful method for constructing complex supramolecular architectures.
• Developing efficient and selective synthetic methodologies for complex organic molecules remains a key challenge in chemistry.

Purpose of the Study:

• To synthesize a discrete tetragonal tube-shaped palladium(II) complex (MT-1) using coordination-driven self-assembly.
• To investigate the utility of the synthesized complex as a molecular vessel for performing intramolecular cycloaddition reactions.
• To evaluate the regio- and stereoselectivity and efficiency of the catalytic reactions within the confined nanospace of the coordination cage.

Main Methods:

• Synthesis of a carbazole-based tetraimidazole donor (L) and a palladium(II) acceptor ([cis-(dppf)Pd(OTf)2]).
• Coordination-driven self-assembly to form the tetragonal tube-shaped complex MT-1.
• Characterization of MT-1 using multinuclear NMR, ESI-MS, and single-crystal X-ray diffraction analysis (SCXRD).
• Utilisation of MT-1 as a molecular vessel for intramolecular [4+2] cycloaddition reactions of O-allylated benzylidinebarbituric acid derivatives.

Main Results:

• Successful synthesis and characterization of the symmetrical, tetrafacial, tube-shaped complex MT-1 with a large cavity.
• Demonstration of MT-1's efficacy as a molecular vessel for intramolecular cycloaddition reactions.
• Achieved regio- and stereoselective synthesis of penta/tetracyclouracil derivatives in good yields under mild conditions.
• MT-1 catalysis offers advantages over high-temperature reflux or solid-state melt reactions (SSMRs) reported in the literature.

Conclusions:

• The synthesized palladium(II) complex MT-1 serves as an effective molecular vessel for confined reactions.
• The MT-1-catalyzed intramolecular cycloaddition provides a mild, efficient, and selective route to valuable uracil derivatives.
• This approach offers a promising alternative to existing synthetic methods for similar compounds.