Synthesis of Furan-Annelated BINOL Derivatives: Acid-Catalyzed Cyclization Induces Partial Racemization.

Area of Science:

• Organic Chemistry
• Supramolecular Chemistry

Background:

• BINOL (1,1'-bi-2-naphthol) derivatives are crucial in asymmetric synthesis.
• Phosphoric acids derived from BINOL are valuable chiral catalysts.
• Synthesis of complex BINOL-based structures remains an active research area.

Purpose of the Study:

• To synthesize novel BINOL-based bis- and trisphosphoric acids.
• To investigate the formation of a unique phosphoric acid monoester motif.
• To study the stereochemical outcomes of acid-catalyzed reactions involving BINOL scaffolds.

Main Methods:

• Acid-catalyzed cyclization of 3-alkynyl-substituted BINOL precursors.
• Phosphorylation of phenolic alcohols.
• Separation and spectroscopic characterization of diastereomers.
• X-ray crystal structure analysis.
• Density Functional Theory (DFT) calculations.

Main Results:

• Successful synthesis of BINOL-based bis- and trisphosphoric acids with a phosphoric acid monoester motif.
• Formation of furan-annelated BINOL derivatives via 5-endo-dig cyclization.
• Observation of unexpected partial racemization in BINOL scaffolds during cyclization.
• Separation and characterization of resulting diastereomeric mixtures.
• DFT calculations supported experimental findings on cyclization and racemization pathways.

Conclusions:

• The study presents a novel synthetic route to BINOL-based phosphoric acids.
• Acid catalysis can induce both cyclization and racemization in BINOL systems.
• The observed racemization, though partial, is a significant stereochemical consideration for these scaffolds.