5 Sulfur Fluoride Exchange (SuFEx)

Sulfur Fluoride Exchange (SuFEx) click chemistry is a new generation technology for creating stable molecular connections with absolute reliability under metal-free conditions. SuFEx builds upon the fundamental principles of click chemistry by exploiting a unique blend of stability and latent reactivity of high oxidation state sulfur fluoride [e.g., S(VI)] functionalities to forge stable covalent linkages at connective SuFEx hubs. In this review, we focus mainly on the SuFEx hubs, sulfuryl fluoride (SO2F2), thionyl tetrafluoride (SOF4), ethenesulfonyl fluoride (ESF), 1-bromoethene-1-sulfonyl fluoride (BESF) and, 2-substituted alkyne-1-sulfonyl fluorides (SASFs). We describe each connector’s unique reactivity and their application to SuFEx click chemistry.

Facile Synthesis of Saikosaponins

Saikosaponin A (SSa) and D (SSd) are typical oleanane-type saponins featuring a unique 13,28-epoxy-ether moiety at D ring of the aglycones, which exhibit a wide range of biological and pharmacological activities. Herein, we report the first synthesis of saikosaponin A/D (1–2) and their natural congeners, including prosaikosaponin F (3), G (4), saikosaponin Y (5), prosaikogenin (6), and clinoposaponin I (7). The present synthesis features ready preparation of the aglycones of high oxidation state from oleanolic acid, regioselective glycosylation to construct the β-(1→3)-linked disaccharide fragment, and efficient gold(I)-catalyzed glycosylation to install the glycans on to the aglycones.