Unsubstituted bicyclo[1.1.0]but-2-ylcarbinyl cations

Area of Science:

• Organic Chemistry
• Reaction Mechanisms
• Computational Chemistry

Background:

• Bicyclo[1.1.0]butane derivatives are strained systems with unique reactivity.
• Understanding the solvolysis of bicyclo[1.1.0]but-2-ylcarbinyl systems is crucial for predicting reaction outcomes.
• Previous studies on substituted derivatives showed puzzling product and rate data.

Purpose of the Study:

• To develop a synthesis for unsubstituted bicyclo[1.1.0]but-2-ylmethanols.
• To investigate the solvolysis mechanisms of endo- and exo-sulfonates.
• To elucidate the nature of bicyclo[1.1.0]but-2-ylcarbinyl cations using computational methods.

Main Methods:

• Synthesis of bicyclo[1.1.0]but-2-ylmethanols from 1,3-butadiene.
• Solvolysis reactions of endo- and exo-sulfonates.
• Quantum chemical calculations (DFT) to probe cation structures and energies.

Main Results:

• The endo-sulfonate underwent rearrangement, while the exo-sulfonate yielded substitution with skeletal retention.
• The endo-bicyclo[1.1.0]but-2-ylcarbinyl cation is a transition state, while the exo-isomer is an energy minimum.
• Methyl substitution at C1 and C3 destabilized the exo-cation, making it a transition state.

Conclusions:

• The differing solvolysis pathways are explained by the distinct electronic structures of the endo and exo cations.
• Wagner-Meerwein rearrangement and automerization are key processes for these systems.
• Computational studies rationalize experimental observations and explain the effect of substitution.