1,3-Difunctionalization of Propargyl Silanes with Concomitant 1,2-Silyl Shift: Synthesis of Allyl Functionalized Vinyl Silanes

Abstract

Terminal alkynes with a silyl group at the propargylic position upon activation with electrophiles such as N-bromosuccinimide undergo (E)-selective 1,2-silyl group migration. Subsequently, an allyl cation is formed that is intercepted by an external nucleophile. This approach provides allyl ethers and esters with stereochemically defined vinyl halide and silane handles for further functionalization. The scope of propargyl silanes and electrophile–nucleophile pairs are investigated, and various trisubstituted olefins are prepared in up to 78% yield. The obtained products have been demonstrated to serve as building blocks for transition-metal-catalyzed cross-couplings of vinyl halides, silicon-halogen exchange, and allyl acetate functionalization reactions.

1,2-Silyl Shift-Induced Heterocyclization of Propargyl Silanes: Synthesis of Five-Membered Heterocycles Containing a Functionalized Olefin Side Chain

“…We have previously reported such allyl cation formation, which after deprotonation provided 2-silyl-1,4-dienes (proton loss from R 1 /R 2 groups in intermediate III , Scheme ). Alternatively, if propargyl silane activation with electrophile occurs in a nucleophilic solvent, ( E )-selective 1,3-difunctionalization of the starting material takes place by the addition of the solvent, and ( E )-3-bromo-2-(trialkylsilyl)­allyl esters and ethers are obtained . Now, the design of propargyl silanes of type IV and the use of a non-nucleophilic solvent allowed us to obtain five-membered heterocycles V (pyrrolidines, tetrahydrofurans, butyrolactones, thiolanes, and isoxazolines) with geometrically defined olefin side chains (Scheme ).…”