Asymmetric Synthesis Of 13 Diols And Chiral Sulfoxides

Chapter 1 Review on Asymmetric Synthesis of 1,3-Diols and Chiral Sulfoxides 1.1. Importance and applications of chiral 1,3-diols Optically active 1,3-diols are very important compounds in asymmetric synthesis, since they represent chiral building blocks for many polyketide-derived natural products, and have frequently been used as valuable intermediates in the synthesis of drugs and natural products with important biological activity. Such diols have shown promise as chiral derivatising agents and less frequently as chiral ligands. 1.1.1. As chiral ligands Unlike 1,2 and 1,4 diols, 1,3-diols are less frequently encountered as chiral ligand. A few C2-symmetric chiral 1,3-diols are known in the literature, none have proved to be very good sources of chirality. It is important that the diol is conformationally rigid for it to be an effective chiral auxiliary / ligand. Chiral 1,3-diols 20 21 were obtained from the yeast-reduction products of 2-oxocyclopentane-and 2-oxocyclohexane carboxylates and excess MeLi, BuLi or PhLi. These ligands form titanium complexes 22 with TiCl(i-Pr0)3 which are effective catalysts for enantioselective nucleophilic addition of MeMgCl to benzaldehyde and 1-naphthaldehyde yielding 1-phenyl ethanol and 1-naphthyl ethanol respectively in good enantioselectivities. Recently Matsuo and coworkers have reported effective use of a chiral 1,3-diol ligand for brà ¸nsted acid catalyzed asymmetric reduction of ketones and acyl silanes. 1.1.2. As chiral