Final-stage site-selective acylation for the total syntheses of multifidosides A-C
Yoshihiro Ueda1, Takumi Furuta1, Takeo Kawabata2
1Institute for Chemical Research, Kyoto University, Gokasho, Uji city, Kyoto 611-0011 (Japan).
Abstract:
The first total syntheses of multifidosides A-C have been achieved. The synthetic strategy is characterized by catalytic site-selective acylation of unprotected glycoside precursors in the final stage of the synthesis. High functional-group tolerance of the site-selective acylation, promoted by an organocatalyst, enabled the conventionally difficult molecular transformation in a predictable and reliable manner. An advantage of this strategy is to avoid the risks of undesired side reactions during the removal of the protecting groups at the final stage of the total synthesis.
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The DCC-promoted synthesis of amides begins with the protonation of DCC by carboxylic acid. The protonation makes it a better acceptor. Next, the addition of carboxylate to the protonated carbodiimide gives a reactive acylating agent.
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