Oxathiaborolium-catalyzed enantioselective [2 + 2] cycloadditions

Area of Science:

• Organic Chemistry
• Catalysis
• Synthetic Methodology

Background:

• Lewis acids are crucial catalysts in organic synthesis.
• Developing efficient and selective catalysts for cycloaddition reactions remains a key challenge.
• Quaternary stereogenic centers are important structural motifs in complex molecules.

Purpose of the Study:

• To develop a novel Lewis acid catalyst for enantioselective [2+2] cycloadditions.
• To synthesize ring-fused cyclobutanes bearing quaternary stereogenic centers.
• To establish an efficient and atom-economical synthetic route.

Main Methods:

• Generation of sulfur-stabilized borenium cations using SnCl4.
• Formation of oxathiaborolium pentachlorostannate as the active Lewis acid catalyst.
• Catalysis of [2+2] cycloadditions between N-substituted maleimides and silyl enol ethers.

Main Results:

• Successful synthesis of cycloadducts with excellent enantioselectivities (up to 96% ee).
• Demonstration of the methodology with 17 different examples.
• Formation of ring-fused cyclobutanes with quaternary stereogenic centers.

Conclusions:

• Oxathiaborolium pentachlorostannate is a highly effective Lewis acid catalyst.
• The developed methodology offers a viable and efficient route to complex organic molecules.
• The approach combines pot, atom, and step economy for sustainable synthesis.