Chiral proton donor reagents: tin tetrachloride--coordinated optically active binaphthol derivatives

Area of Science:

• Organic Chemistry
• Asymmetric Synthesis

Background:

• Chiral Brønsted acids are crucial catalysts in asymmetric synthesis.
• Developing efficient chiral proton donors for enantioselective reactions remains a key challenge.

Purpose of the Study:

• To develop novel Lewis acid-assisted chiral Brønsted acids (LBAs) for enantioselective protonation and biomimetic polyene cyclization.
• To explore the catalytic potential of these LBAs in synthesizing complex organic molecules.

Main Methods:

• Preparation of chiral LBAs from tin tetrachloride and optically active binaphthol derivatives.
• Application of chiral LBAs for enantioselective protonation of silyl enol ethers and ketene disilyl acetals.
• Investigation of chiral LBA-induced enantioselective ene cyclization of isoprenoids.

Main Results:

• Chiral LBAs achieved high enantiomeric excess (up to 98% ee) in protonation reactions.
• A catalytic enantioselective protonation protocol was established.
• Biomimetic cyclization of isoprenoids yielded natural products like (-)-ambrox and (-)-chromazonarol with up to 90% ee.

Conclusions:

• Lewis acid-assisted chiral Brønsted acids are highly effective reagents for enantioselective synthesis.
• These LBAs offer a versatile platform for both enantioselective protonation and complex polycyclic molecule construction.
• This work represents a significant advancement in chiral Brønsted acid catalysis and biomimetic synthesis.