Transition from Kwon [4+2]- to [3+2]-cycloaddition enabled by AgF-assisted phosphine catalysis

Area of Science:

• Organic Chemistry
• Catalysis
• Organophosphorus Chemistry

Background:

• Phosphine catalysis typically involves carbanion-phosphonium zwitterions formed from phosphine nucleophilic addition to electrophiles.
• Modifying zwitterion structures with different electrophiles is a common method to diversify phosphine catalysis.

Purpose of the Study:

• To introduce a new strategy using silver fluoride (AgF) to expand the scope of phosphine catalysis.
• To investigate the mechanism of AgF-mediated transformation of intermediates in phosphine catalysis.

Main Methods:

• Utilizing AgF as an additive in phosphine-catalyzed reactions.
• Investigating the reaction between 2-substituted allenoates and imines.
• Employing experimental and computational studies to elucidate the catalytic mechanism.

Main Results:

• AgF converts carbanion-phosphonium zwitterions to silver enolate-fluorophosphorane intermediates, initiating a P(III)/P(V) catalytic cycle.
• The strategy successfully shifted a Kwon [4+2] cycloaddition to a [3+2] cycloaddition.
• The new [3+2] cycloaddition exhibited high diastereoselectivity, good yields, and broad substrate compatibility.

Conclusions:

• The AgF-assisted strategy provides an alternative route to expand phosphine catalysis.
• This approach facilitates the development of P(III)/P(V) catalysis, offering a powerful tool for organic synthesis.
• The findings suggest significant potential for AgF in advancing organophosphorus chemistry.