Accessing elusive σ-type cyclopropenium cation equivalents through redox gold catalysis

Area of Science:

• Organic Chemistry
• Organometallic Chemistry

Background:

• Cyclopropenes are the smallest unsaturated carbocycles.
• Aromatic π-type cyclopropenium cations (CPCs) are well-studied, but σ-type CPCs remain unexplored due to instability.

Purpose of the Study:

• To develop stable electrophilic cyclopropenyl-gold(III) species as synthetic equivalents of unexplored σ-type CPCs.
• To establish a mild and efficient method for synthesizing highly functionalized alkynyl- or alkenyl-cyclopropenes.

Main Methods:

• Utilized electrophilic cyclopropenyl-gold(III) species.
• Employed cyclopropenyl benziodoxoles (CpBXs) for gold(I) to gold(III) oxidation and cyclopropenyl group transfer.
• Reacted with terminal alkynes and vinylboronic acids.

Main Results:

• Achieved synthesis of functionalized alkynyl- and alkenyl-cyclopropenes under mild conditions with low catalyst loadings (2 mol%).
• Demonstrated generality and functional group tolerance of the protocol.
• Successfully applied the method for late-stage modification of complex molecules.

Conclusions:

• Introduced a novel approach to access σ-type cyclopropenium cation chemistry.
• Developed a versatile and efficient synthetic route to functionalized cyclopropenes.
• Highlighted the potential of this methodology in drug discovery and natural product synthesis.