UC Irvine

The first chapter serves as a general introduction to the topic of stereochemistry andstereochemical determination in organic chemistry. Stereochemistry is a subject that was first conceived following Pasteur’s separation of tartaric acid enantiomers in 1848. The notion of asymmetric carbon atoms is now second nature to organic chemists, however determination of the geometrical configuration about stereogenic carbon atoms is still non-trivial. This chapter provides a general introduction for the work discussed in chapters 2–4. The second chapter details efforts towards developing a Competing Enantioselective Conversion (CEC) method to determine the absolute configuration of dienes bearing adjacent chiral centers. Chiral analogues of 1,2,4-triazoline-3,5-diones (TAD) were synthesized and used as dienophiles in enantioselective Diels–Alder reactions with dienes bearing adjacent chirality. Kinetic resolution with these new reagents displayed moderate selectivity, but the prohibitive synthesis of the reagents rendered efforts to develop a CEC method fruitless. The third chapter details an expansion of the competing enantioselective conversion (CEC) method for cyclic secondary amines. Previously, Bode’s chiral acylated hydroxamic acids were used to determine the stereochemistry of primary amines, as well as cyclic and acyclic secondary amines. The enantioselective acylation has herein been evaluated for 4-, 5-, and 6-membered cyclic secondary amines, including medicinally relevant compounds. The limitations of the method were studied through computational analysis and experimental results. Control experiments were performed to investigate the cause of degrading selectivity under the CEC reaction conditions. The present study expands the scope of the CEC method for secondary amines and provides a better understanding of the reaction profile. The fourth chapter details the crystallization of alkenes and diols as osmate ester derivatives. Organic compounds containing alkenes are often challenging to crystallize. We have found that osmium tetroxide and TMEDA form stable crystalline adducts with alkenes, allowing the determination of absolute structure by X-ray crystallography. Osmium, a heavy atom, facilitates the crystallographic analysis and the determination of absolute configuration using common Mo X-ray sources. The utility of this method for determining absolute structure and configuration was demonstrated on several unsaturated substrates. We also investigated a redoxneutral crystallization strategy of 1,2- and 1,3- diols using potassium osmate, and results are reported. The fifth chapter details the completion of the first total synthesis of (2R)- hydroxynorneomajucin. Our synthetic strategy initially hinged on utilizing a Pauson–Khand reaction of an advanced bis-lactone intermediate to construct the core of the natural product which, unfortunately, was not successful. The key features of our revised synthetic strategy include an asymmetric Tsuji–Trost allylic alkylation to set a key quaternary center, a Pauson–Khand to close the core of the molecule, and a late-stage conjugate addition to install the final quaternary center. This strategy has allowed us to complete the first total synthesis of (2R)-hydroxynorneomajucin to date in 17 steps from simple starting materials.