Catalytic Synthesis Of Trans-Aziridines, Trans-Stilbenes And Bulky Pyridine-Based Ligands

Zhipeng Zheng, University of Pennsylvania


Chapter 1 and 2 detailed the use of organocatalysts sulfenate anion (RSO–) and selenenate anion (RSeO–) to catalyze the synthesis of trans-aziridines, trans-stilbenes, and ppv (poly(p-phenylene vinylene))-type polymers with good to excellent yields. Chapter 3 introduced a palladium-catalyzed method for synthesis of bulky pyridine-based ligands. In Chapter 1, a broadly applicable and diastereoselective synthetic method is reported for the synthesis of trans-aziridines from imines and benzylic or alkyl halides utilizing sulfenate anions (PhSO–) as the catalyst. Substrates bearing heterocyclic aromatic groups, alkyl, and electron-rich and electron-poor aryl groups were shown to be compatible with this method (33 examples), giving good yields and high diastereoselectivity (trans : cis > 20:1). Further functionalization of aziridines containing cyclopropyl or cyclobutyl groups was achieved through ring-opening reactions, with a cyclobutyl-substituted norephedrine derivative obtained through a four-step synthesis. In Chapter 2, we introduced the selenenate anion (RSeO–) as an active organocatalyst for the dehydrohalogen coupling of benzyl halides to form trans-stilbenes. It is shown that RSeO– is a more reactive catalyst than the previously reported sulfur analogues (sulfenate anion, RSO–) and selenolate anions (RSe–) in the aforementioned reaction. This catalytic system was also applied to the benzylic-chloromethyl-coupling polymerization (BCCP) of a bis-chloromethyl arene to form ppv (poly(p-phenylene vinylene))-type polymers with high yields, Mn (average molecular weight) up to 13,000 and PDI (polydispersity index) of 1.15. In Chapter 3, an efficient and convenient method is developed to synthesize bulky N,N’-bidentate ligands. Using this method, twenty bulky 2,2’-bipyridine and thirteen bulky (S)-pyridine-oxazoline ligands were obtained in yields up to 95% and over 99% ee for the chiral PyOx ligands. Key to this method is the use of a Pd(NIXANTPHOS)-based catalyst system that we have demonstrated to perform with high efficiency in the coupling of weakly acidic azaaryl methyl group with aryl bromides in the presence of silyl amide bases. The straightforward access to these ligand makes them attractive for catalyst development.