Silver‐Mediated exo‐Selective Tandem Desilylative Bromination/Oxycyclization of Silyl‐Protected Alkynes: Synthesis of 2‐Bromomethylene‐Tetrahydrofuran

Abstract

Dedicated to Professor Eun Lee on the occasion of his retirement and 65th birthdayTandem reactions are one-pot multi-step processes and are thus among the most useful synthetic methods. [1] Recently, the use of transition metals in tandem reactions has received considerable attention and has revolutionized the synthetic strategies in organic chemistry. [2] Among the transition metal-based tandem reactions, the processes that involve heterocyclization reactions of unsaturated substrates are of particular interest, [3,4] as they provide a direct method for the construction of synthetically and biologically valuable heterocycles.The intramolecular heterocyclization of g or d-hydroxyalkynes promises to be a convenient way to access the functionalized tetrahydrofurans and pyrans, which are common motifs in a variety of natural products. This cyclization can be driven by transition metal catalysts, and the regioselectivity of these reactions varies depending on the metal and the conditions employed. [5] Among the metals thus far reported for these reactions, silver and gold have been demonstrated to be the most effective and selective for the formation of exo-dig products. [6,7] These metals can promote heterocyclization of both internal and terminal alkynes. Even halogenated and silylated alkynes can be converted into the corresponding exo-dig products using these metals.

Practical Synthesis of Pachastrissamine (Jaspine B), 2-<i>epi</i>-Pachastrissamine, and the 2-<i>epi</i>-Pyrrolidine Analogue

“…9,10) Because of its novel structural features and impressive biological activity, many total syntheses of 1 have been accomplished. [3][4][5][6][7][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] The stereoisomers of 1 have also been synthesized, 5,6,[20][21][22][23][24][25][26][27][28][29][31][32][33][34][35][36][37][38][39][40] and their biological activity investigated. Interestingly, the 2-epimer 2 6,…”