A Comparison between the Cycloadditions of Allenyl- and Vinyl-Cyclopentanes Using Density Functional Theory and GRRM...

Area of Science:

• Organometallic Chemistry
• Computational Chemistry
• Medicinal Chemistry

Background:

• Transition metal-catalyzed cycloadditions are vital for synthesizing functionalized molecules.
• Reactivity in these reactions is influenced by the substrate's structure, particularly the presence of allenyl versus vinyl groups in cyclic systems.

Purpose of the Study:

• To investigate the differing reactivity of allenyl and vinyl groups in rhodium(I)-catalyzed cycloaddition reactions with cyclic substrates.
• To elucidate the mechanistic basis for the observed reactivity differences using computational methods.

Main Methods:

• Density Functional Theory (DFT) was employed to model reaction pathways.
• Computational models were constructed for allenylcyclopentane-alkyne and vinylcyclopentane-alkyne systems.
• Reaction energies and transition state molecular orbitals were analyzed.

Main Results:

• The allenylcyclopentane-alkyne model exhibited significantly lower reaction energy compared to the vinylcyclopentane-alkyne model.
• DFT calculations revealed distinct reaction pathways for both models.
• Analysis of transition state molecular orbitals identified key contributors to the reactivity difference.

Conclusions:

• The presence of an allenyl group facilitates cycloaddition reactions with saturated rings larger than five carbons, whereas a vinyl group does not.
• Lower reaction energy and specific molecular orbital interactions in the transition state explain the enhanced reactivity of allenyl systems.
• Computational modeling provides valuable insights into the mechanism of transition metal-catalyzed cycloadditions.