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Updated: May 22, 2025

Facile Preparation of 2Z,4E-Dienamides by the Olefination of Electron-deficient Alkenes with Allyl Acetate
Published on: June 21, 2017
Lewis-Base-Catalyzed Asymmetric Allylation of Isatins with Allyltrichlorosilane
Yasemin Özkaya1, Frederic Ballaschk1, Christian Wagner1
1Organic Chemistry, Bergische Universität Wuppertal, Gaußstr. 20, 42119 Wuppertal, Germany.
Abstract:
Herein we report the enantioselective synthesis of 3-allyl-3-hydroxyoxindoles, a core scaffold in a wide range of bioactive molecules, using a Lewis-base catalyst and readily abundant and inexpensive allyltrichlorosilane. This transition-metal-free protocol employs relatively low catalyst loadings of a privileged bispyrrolidine-type scaffold to achieve high yields and enantioselectivities (up to 98% yield and 98:2 er). The total syntheses of the natural products (-)-flustraminol B and (-)-chimonamidine were also successfully carried out using our newly developed method as a key step, highlighting the potential of this method for the efficient and precise synthesis of complex natural products.
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Acidity of 1-Alkynes
The acidic strength of hydrocarbons follows the order: Alkynes > Alkenes > Alkanes. The strength of an acid is commonly expressed in units of pKa — the lower the pKa, the stronger the acid. Among the hydrocarbons, terminal alkynes have lower pKa values and are, therefore, more acidic. For example, the pKa values for ethane, ethene, and acetylene are 51, 44, and 25, respectively, as shown here.

