1,3-Heterocumulene-to-alkyne

Area of Science:

• Computational chemistry
• Organic reaction mechanisms
• Quantum chemistry

Background:

• 1,3-heterocumulenes are versatile building blocks in organic synthesis.
• Cycloaddition reactions are fundamental for forming cyclic compounds.
• Understanding reaction energetics is crucial for predicting reactivity and outcomes.

Purpose of the Study:

• To computationally investigate the transition structures and energy barriers of cycloaddition reactions involving 1,3-heterocumulenes and unsaturated systems.
• To explore the influence of heteroatoms on the energetics of these cycloaddition reactions.
• To compare theoretical predictions with experimental findings for validation.

Main Methods:

• Ab initio quantum chemical methods (G2(MP2) and CBS-Q) were employed for calculations.
• Density functional theory (DFT) and hybrid ONIOM methods were utilized for mechanistic studies.
• Experimental studies corroborated the computational results.

Main Results:

• Activation energies for homoheteroatomic cumulenes decrease in the order O > S > Se and NH > PH.
• Reaction energies follow the order O > S ≈ Se and PH > NH.
• Cycloaddition of carbon diselenide to cyclooctyne is faster than with carbon disulfide; 1:3 adducts form with isothiocyanates under specific conditions.

Conclusions:

• Computational methods accurately predict the relative reactivity and energetics of 1,3-heterocumulene cycloadditions.
• The nature of the heteroatom significantly impacts reaction barriers and energy profiles.
• Experimental validation confirms the theoretical models and provides insights into product formation pathways.