Migration of methylethynyl group in a long-lived carbocation

Area of Science:

• Organic Chemistry
• Carbocation Chemistry

Background:

• Carbocations are reactive intermediates crucial in organic synthesis.
• Understanding carbocation rearrangements provides insights into reaction mechanisms.

Purpose of the Study:

• To investigate the reactivity of long-lived phenanthrenium ions.
• To characterize the migration of ethynyl groups in carbocations.

Main Methods:

• Synthesis of a 9,10-dimethyl-9-methylethynyl-phenanthrenium ion precursor.
• Nuclear Magnetic Resonance (NMR) spectroscopy for structural elucidation and detection of the carbocation.

Main Results:

• Detection of a degenerate 1,2-shift of the methylethynyl group.
• Observation of a stable carbocation intermediate facilitating ethynyl migration.

Conclusions:

• The study provides the first evidence of ethynyl migration in a long-lived carbocation.
• This finding expands the known scope of carbocation rearrangements.