Synlett 2020; 31(01): 13-20
DOI: 10.1055/s-0039-1690215
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© Georg Thieme Verlag Stuttgart · New York

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

Reto M. Witzig
,
We gratefully acknowledge the Swiss National Science Foundation (Grant Numbers BSSGI0-155902/1 and 175746), the University of Basel, and the NCCR Molecular Systems Engineering for financial support.
Further Information

Publication History

Received: 12 September 2019

Accepted after revision: 07 October 2019

Publication Date:
22 October 2019 (online)


Abstract

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