Rhodium catalyzed direct C H functionalizations of sulfoximines and copper catalyzed enantioselective synthesis of dihydropyrazoles

The carbon-hydrogen bonds (abbreviated as C-H bonds) are fundamental and most common chemical bonds in a variety of organic compounds. Owing to the high bond dissociation energy, transformations of inert C H bonds into C-C bonds or C-X bonds (X= S, O, N, Cl, Br, etc.) are still great challenges nowadays. In general, traditional approaches for the transformations of C-H bonds rely on prefunctionalized starting materials for both reactivity and selectivity or require costly chemical steps. Thus, the development of a cheap and alternative method is still desirable to address the above issues. Transition metal catalyzed direct functionalization of inert C H bonds has attracted great attention and gradually emerged as a powerful method in organic synthesis. In the first chapter, a new combination of rhodium(III) and Fe(OAc)2 have been utilized for the functionalization of the NH-sulfoximines through direct C-H activation pathway, including annulation reaction with alkynes and addition reaction with hetero bicycle alkenes. Mechanistically, the transformations involved a dual C-H/N-H activation, which was substantiated by KIE studies and the isolation of a reactive rhodacycle intermediate. Then the useful applications of the yielded products have been demonstrated by the oxidative cleavage of the 1,2-benzothiazines or I2-mediated phosphorylation or acid-assisted dehydration of the addition products. In the second chapter, we focus on the [4+1] cycloaddition reactions between hydrazones and sulfur ylides. Previouslu, numerous examples have been reported for the synthesis of dihydropyrazole. Most of the reported protocols utilize asymmetric 1,3-dipolar cycloaddition (1,3-DC) reactions for the preparations of the five-membered compounds, and this methodology dominate the field today. 1,3-Dipoles such as diazomethanes, azomethine imines and nitrile imines have been frequently utilized as the coupling partners ever since the first example from Fischer and Knövenagel.[45] In this chapter, we will introduce some transition metal-catalyzed [3+2] cycloaddition reactions towards pyrazoles or pyrazolines. The initiative work applied easily accessible copper salt as the catalyst for the asymmetric formal [4+1] cycloaddition reaction of in situ-generated azoalkenes with sulfur ylides. It provided an efficient, enantioselective access to a variety of optically active dihydropyrazoles