New Strategies for Stereoselective Preparation of Densely Functionalized Cyclobutanes

Abstract

This dissertation describes the utility of 1,2-azaborine motif as a 4C+1B+1N synthon in organic synthesis, especially for the preparation of densely functionalized cyclobutanes based on the framework of the 1,2-azaborine photoisomerization. The substitution of a CC unit with a BN unit in benzenes significantly modifies the properties of classic benzenoid compounds, leading to new reactivities and functionalities. In this vein, Chapter 1 discloses photoisomerization of 1,2-azaborines to selectively form BN-analogues of the Dewar benzene. Three applications of the Dewar photoisomers are described herein: 1) a rhodium-catalyzed ring-opening reaction to form 1,2-azaborines; 2) furnishing cis aminoborylated cyclobutanes with the boron unit as a further functionalization handle; 3) a stereospecific ring-opening reaction to afford diene which can engage in Diels-Alder reaction. Chapter 2 elaborates on a modular and stereoselective strategy to access a variety of cyclobutane β-amino alcohols. Discussed herein are regioselective functionalizations and di-functionalizations of the 1,2-azaborine core and a tandem photoisomerization-hydrogenation-oxidation protocol to translate the functionalized azaborine core to cyclobutane amino alcohols. Also examined herein are the scope of azaborine photoisomerization and Dewar hydrogenation.