Gold-Catalyzed Reaction of Propargyl Esters and Alkynylsilanes: Synthesis of Vinylallene Derivatives through a Twofold 1,2-Rearrangement

Abstract

The reaction of propargyl esters with alkynylsilanes under gold catalysis provides vinylallene derivatives through consecutive [1,2]-acyloxy/[1,2]-silyl rearrangements. Good yields, full atom-economy, broad substrate scope, easy scale-up and low catalyst loadings are salient features of this novel transformation. Density Functional Theory (DFT) calculations suggest a reaction mechanism involving initial [1,2]-acyloxy rearrangement to generate a gold vinylcarbene intermediate which upon regioselective attack of the alkynylsilane affords a vinyl cation which undergoes a type II-dyotropic rearrangement involving the silyl group and the metal fragment. Preliminary results on the enantioselective version of this transformation are also disclosed.

Keywords: alkynylsilanes; allenes; carbenes; gold; rearrangements.

Scheme 1

Intermolecular trapping of gold carbene intermediates arising from propargyl esters with alkynes.

Scheme 2

Gold‐catalyzed reaction of propargyl ester 1 a and alkynylsilane 1 b: initial finding.

Scheme 3

Proposed reaction mechanism for the gold(I)‐catalyzed reaction of propargylic esters 1 and alkynylsilanes 2.

Figure 1

Computed reaction profile for the gold‐catalyzed reaction of propargyl ester 1 a and alkynylsilane 2 a. Relative free energies (ΔG, at 298 K) and bond distances are given in kcal mol⁻¹ and angstroms, respectively. All data have been computed at the PCM‐B3LYP‐D3/def2‐TZVPP//PCM‐B3LYP‐D3/def2‐SVP level.

Scheme 4

A) Gram‐Scale Reaction. B) Product derivatization. C) Implementation to alkynylgermanes.