Explaining Regiodivergent Vinylations with Vinylbenziodoxolones

Area of Science:

• Organic Chemistry
• Hypervalent Iodine Chemistry

Background:

• Vinylbenziodoxolones (VBX) are efficient hypervalent iodine(III) reagents for electrophilic vinylations.
• VBX reagents offer transition metal-free reaction conditions.
• Their reactivity allows for the synthesis of either internal or terminal alkenes, depending on the nucleophile class.

Purpose of the Study:

• To conduct the first mechanistic investigation of vinylbenziodoxolone (VBX) vinylations.
• To elucidate the mechanisms governing the formation of internal and terminal alkenes.
• To rationalize the observed regio- and stereochemical outcomes in VBX vinylations.

Main Methods:

• Nuclear Magnetic Resonance (NMR) studies.
• Deuterium labelling experiments.
• Computational chemistry investigations.

Main Results:

• Internal alkene formation in S-vinylation proceeds via a ligand coupling mechanism, similar to diaryliodonium salts.
• Terminal alkene formation in P-vinylations involves a phosphinous acid-coordinated VBX complex.
• A concerted deprotonation and Michael-type addition, followed by base-assisted protonation and E2 elimination, yields terminal alkenes.

Conclusions:

• The study provides a mechanistic understanding of VBX vinylations.
• Distinct pathways are responsible for internal versus terminal alkene synthesis.
• These findings enable prediction of regioselectivity for various nucleophile classes in vinylations.