Pathways for Concerted [2 + 2] Cycloaddition to Cumulenes

Area of Science:

• Computational chemistry
• Organic reaction mechanisms
• Theoretical chemistry

Background:

• Cumulenes (X=C=Y) are reactive compounds studied for their unique bonding.
• Cycloaddition reactions are fundamental in organic synthesis.
• Ethylene is a simple alkene often used in model reaction studies.

Purpose of the Study:

• To computationally investigate the [2+2] cycloaddition of ethylene to cumulenes.
• To identify and characterize reaction pathways and intermediates.
• To explore the scope of these reactions with various X and Y elements (C, N, O, S).

Main Methods:

• Density Functional Theory (DFT) calculations were employed.
• Concerted reaction pathways were systematically searched.
• Transition states and intermediates were analyzed.

Main Results:

• Four distinct concerted pathways were identified for ethylene cycloaddition to 10 cumulenes.
• Three pathways were classified as pseudopericyclic, and one involved sp-hybridized carbon.
• Two novel three-membered ring intermediates were discovered in specific cycloadditions.
• Model reactions with formaldehyde, thioformaldehyde, and formaldimine were also simulated.

Conclusions:

• The study provides a comprehensive computational map of ethylene-cumulene cycloadditions.
• Novel reaction mechanisms and intermediates expand the known reactivity of cumulenes.
• These findings offer insights for designing new synthetic strategies involving cumulenes.