Catalytic Enantioselective Synthesis of Secondary Organoboronates and Progress Towards the Total Synthesis of Sarcodictyins

Abstract

This dissertation will present three main projects focusing on the transition metal-catalyzed enantioselective synthesis of secondary organoboronic esters and progress towards the total synthesis of sarcodictyins. In the first project, a palladium-catalyzed enantioselective conjunctive cross-coupling reaction with propargylic electrophiles will be described. The tetra-substituted allenes are isolated with good yield and enantioselectivity and the beneficial effects of alcohol additives are investigated. The second project describes the enantioselective synthesis of ɑ-boryl zinc reagents by a nickel-catalyzed carbozincation reaction. The in situ generated ɑ-boryl zinc intermediate can be trapped by copper-mediated allylations, palladium-catalyzed Negishi cross-couplings, and cerium-mediated halogenation reactions to construct various chiral organoboranes. The synthetic utility of this methodology is showcased by the synthesis of natural products, including bruguierol A, (-)-aphanorphine, and (-)-enterolactone. The mechanism is studied with the assistance of EPR and deuterium-labeling experiments and a catalytic cycle through a Ni(I) intermediate is proposed. The third project depicts a synthetic route to essential precursors in the progress of the total synthesis of sarcodictyins. Various attempts to construct the ten-membered ring core of sarcodictyin have been made, including Sonogashira reaction, Dieckmann condensation, and lithium—halogen exchange process.