The development and applications of unsymmetrical diboron compounds

Abstract

Organoboron compounds have shown a wide variety of applications in both organic synthesis and the pharmaceutical field in the past decades. Transition metal-catalyzed boration of unsaturated compounds has been studied extensively as an efficient method to install C-B bonds. Most of the previous examples employed symmetrical diboron reagents such as B2(pin)2 (pin = pinacolate) and B2(cat)2 (cat = catecholate). There are, however, limited examples of boration using unsymmetrical diboron reagents. This dissertation discloses two transition metal-catalyzed borations of unsaturated compounds with unsymmetrical diboron compounds.

A Cu-catalyzed �[BULLET]-boration of electrophilic allenoates with a novel sp2-sp3 hybridized diboron reagent (PDIPA) is described. This unsymmetrical diboron reagent is preactivated and allows the boration to go smoothly under mild reaction conditions. The reaction provides �[BULLET]-borylated �[BULLET],�[BULLET]-unsaturated esters with exclusive (Z)-double bond geometry. These borylated products are useful intermediates for subsequent Suzuki-Miyaura cross-coupling reaction.

In order to install two C-B bonds in one reaction, a Pt-catalyzed diboration of allenes with a differentially protected diboron reagent (PDAN) is presented. This unsymmetrical diboron reagent is prepared from the sp2-sp3 hybridized diboron compound, and it reacts with a series of 1,1-disubstituted allenes chemo- and regioselectively. Steric control ensures that both boryl moieties add to the terminal double bond, and the pinacol boronate preferentially attaches to the sp-hybridized carbon. The bis-boronyl products can be further converted to other functional groups as well as cross-coupling reactions.

A collaborative project with Department of Physics and Department of Chemical Engineering is also discussed. In this project, a series of o-nitrobenzyl ligands containing a disulfide group as the anchor to gold surfaces are synthesized. The o-nitrobenzyl group uncages an amine upon photoexcitation. Attempts to make a water soluble analog failed, however, the mixture of methanol and water as the solvent was sufficient to attach them on gold surfaces.