Applications of Allenylsilanes in Organic Synthesis

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

• References

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