Advances Towards Regioselective Synthesis of Secondary Alkylboranes and 1,2-cis Glycosides

Abstract

The development of regioselective and diastereoselective processes provides chemists with versatile synthetic tools to access new synthetic pathways. This thesis focuses on two specific areas of regio- and diastereocontrol: hydroboration of olefins and intramolecular aglycone deliveries. The first chapter provides background literature containing existing reported strategies for regiocontrol using copper catalysts in hydroboration of olefins. This chapter lays the groundwork and motivation for investigation into the hydroboration of olefins. Subsequently, the second chapter discusses the development of a versatile procedure for the copper-catalyzed hydroboration of terminal olefins leading to the synthesis of secondary alkylboranes. This procedure provides the reversed regioselectivity compared with widely used hydroboration procedures. The newly synthesized secondary alkylboranes can be transformed to the corresponding trifluoroborate salts and used in photocatalytic cross-couplings to synthesize new carbon-carbon bonds. Furthermore, advances in the regioselective hydroboration of 1,1-disubstituted and 1,2-disubstituted alkenes are described, with efforts in the former of these areas providing the most promising outcomes for future applications. The third chapter begins with a discussion of literature methods for intramolecular aglycone delivery in the synthesis of 1,2-cis glycosides. Within this context, an overview of activating thioglycosides and latent-activation of glycosides for intermolecular glycosylation reactions is provided. The fourth chapter the describes the preparation of sugar silanes containing an o-(p-methoxyphenylethynyl)phenyl group and their utilization in intramolecular aglycone delivery strategies. Beginning with the new silanes prepared, dehydrogenative silylation with menthol was accomplished with tris(pentafluorophenyl) borane catalyst, effectively tethering the aglycone. The tethered assemblies were then examined in intramolecular aglycone delivery strategies. High levels of diastereocontrol were observed, and future work will focus on optimization of the glycosylation yields.