Chelation control in carbonyl reductions and TADDOL catalyzed Diels-Alder reactions

Chelation-controlled reduction of {dollar}beta{dollar}-hydroxy ketones to syn 1,3-diols. A simple general reduction protocol for the conversion of {dollar}beta{dollar}-hydroxy ketones to syn 1,3-diols has been developed using commercially available BCl{dollar}sb3{dollar} as a chelating and organizing agent. Yields range from 65-95% with diastereomeric excesses between 62-98%. Variable temperature NMR experiments and vacuum transfer techniques are used to characterize the highly reactive boron chelate intermediate, leading to the development of a mechanistic explanation implicating A{dollar}sp{lcub}(1,3){rcub}{dollar}-like interactions and product-development control as the main stereodifferentiating features.(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI); Probing the electronic effects of the dienophile in the Ti-TADDOLate catalyzed Diels-Alder reaction: The influence of adduct population on enantioselectivity. A series of bidentate dienophiles have been synthesized to probe the electronic and steric forces that influence adduct formation. There are five possible adducts (A-E) which may be formed upon dienophile complexation to the Ti-TADDOLate catalyst. Variable temperature NMR is used to monitor adduct formation, and NOE data is used to assist in characterization of the adducts. The Diels-Alder reaction enantioselectivity is obtained for each dienophile, and role of each adduct in determining enantioselectivity will be discussed.(DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI)...