Introduction
Allenylsilanes 2 are versatile reagents widely used in organic synthesis.[1] Generally, allenylsilanes react as propargyl anion equivalents in Lewis acid mediated[2] or thermal[3] nucleophilic addition to electrophiles such as carbonyls, imines, Selectfluor, and
N-bromosuccinimide, etc.[1]
[4]
[5] The regiospecific addition of allenylsilanes provides a β-vinyl cation, which is
stabilized by a C–Si bond, which is called β effect. The C–Si bond in allenylsilanes
is oriented cis-coplanar to the p-orbital of the carbocation and provides direct stabilization.[5] Allenylsilanes undergo [3+2] annulations with α,β-unsaturated carbonyls, carbonyl
compounds, imines, and nitrosyl cations to form cyclo-pentenones, dihydrofurans, dihydropyrroles,
and isoxazoles, respectively.[1]
[4]
[5]
The efficient methods for the synthesis of allenylsilanes 2 are copper-mediated 1,3-substitution reactions of carbon nucleophiles to propargylic
substrates 1 having a leaving group at the propargylic position.[6]
[7]
Scheme 1 Synthesis of allenylsilanes