Affiliation: College of Arts and Sciences, Department of Chemistry
[Chapter 1: Enantio- and Diastereoselective Synthesis of β-Hydroxyboronates via Cu- catalyzed Addition of gem-Diboronate Esters to Aldehydes.] The development of an enantio- and diastereoselective addition of gem-diboronate esters to aryl and alkenyl aldehydes in the presence of stoichiometric LiOt-Am is presented. The reaction proceeds in up to 92% yield, >99:1 d.r., and 96:4 e.r. Mechanistic studies reveal the formation of a lithium tert-butylborate species that stereospecifically transmetallates to a copper catalyst, which then diastereoselectively adds to the aldehyde. [Chapter 2: Ag(I)-Catalyzed Synthesis of anti-1,2-Hydroxyboronates through α-Boryl Alkyl Silver Additions to Aldehydes.] The Ag(I)-catalyzed, diastereoselective addition of various gem-diboronate esters to aryl, alkenyl, and alkyl aldehydes is discussed. The reactions proceed in the presence of either stoichiometric KOt-Bu or n-BuLi at -25 °C in thf. Mechanistic studies indicate an alpha-boryl-alkyl silver species as the active nucleophile in the reaction. The hydroxyboronates are isolated in up to 77% yield and 99:1 d.r. favoring the anti diastereomer. [Chapter 3: Enantio- and Diastereoselective Synthesis of 1-Hydroxy-2,3-Bisboronates via a Copper–Catalyzed Multicomponent Reaction] The multicomponent coupling of vinyl boronic acid pinacol ester, B2(pin)2, and various aldehydes in the presence of a copper-bis-phosphine catalyst is discussed. The reaction can be accomplished both diastereoselectively and enantioselectively. Mechanistic investigations reveal that nitrile ligands have a deleterious effect on the enantioselectivity of the reaction, manifested in the isolation of a copper(keteneimide) complex, which is potentially the first ever of its kind to be reported. The 1-hydroxy-2,3-bisboronate esters are isolable via silica gel chromatography in up to 84% yield, >99:1 d.r., and 97:3 e.r.