Synthesis of Enantioenriched Tetra- ortho -3,3′-substituted Biaryls by Small-Molecule-Catalyzed Noncanonical Polyketide Cyclizations.

The arene-forming aldol condensation is a fundamental reaction in the biosynthesis of aromatic polyketides. Precisely controlled by the polyketide synthases, the highly reactive poly-β-carbonyl substrates are diverged into numerous aromatic natural products by selective cyclization reactions; a fascinating biosynthetic strategy that sparked our interest to investigate atroposelective aldol condensations. In this Account, we contextualize and highlight the ability of small-molecule catalysts to selectively convert noncanonical hexacarbonyl substrates in a double arene-forming aldol condensation resulting in the atroposelective synthesis of tetra- ortho -3,3′-substituted biaryls. The hexacarbonyl substrates were obtained by a fourfold ozonolysis enabling a late-stage introduction of all carbonyl functions in one step. Secondary amine catalysts capable of forming an extended hydrogen-bonding network triggered the noncanonical polyketide cyclization in order to form valuable biaryls in high yields and with stereocontrol of up to 98:2 er. 1 Biosynthesis of Aromatic Polyketides 2 Rotationally Restricted Aromatic Polyketides 3 3,3′-Substituted Binaphthalenes in Catalysis 4 Stereoselective Synthesis of Atropisomers 5 Synthesis of Enantioenriched Tetra- ortho -3,3′-Substituted Biaryls by the Atroposelective Arene-Forming Aldol Condensation 6 Conclusion [ABSTRACT FROM AUTHOR]