Electrochemically modified Corey-Fuchs reaction for the synthesis of arylalkynes. The case of 2-(2,2-dibromovinyl)naphthalene

Abstract

The electrochemical reduction of 2-(2,2-dibromovinyl)naphthalene in a DMF solution (Pt cathode) yields selectively 2-ethynylnaphthalene or 2-(bromoethynyl)naphthalene in high yields, depending on the electrolysis conditions. In particular, by simply changing the working potential and the supporting electrolyte, the reaction can be directed towards the synthesis of the terminal alkyne (Et₄NBF₄) or the bromoalkyne (NaClO₄). This study allowed to establish that 2-(bromoethynyl)naphthalene can be converted into 2-ethynylnaphthalene by cathodic reduction.

Keywords: 2-(2,2-dibromovinyl)naphthalene; Corey–Fuchs reaction; arylalkyne; carbon–bromine bond cleavage; cathodic reduction.

Scheme 1

The Corey–Fuchs reaction.

Scheme 2

Electrochemical reduction of a carbon–halogen bond.

Scheme 3

Electrochemical synthesis of vinyl bromides [25].

Scheme 4

Scope of this work.

Figure 1

Voltammetric curves of 1a 0.020 mol dm⁻³; Pt, glassy carbon (GC) or Ag cathode. ν = 0.2 V s⁻¹, T = 25 °C; solvent left: DMF/Et₄NBF₄ 0.1 mol dm⁻³; right: ACN/Et₄NBF₄ 0.1 mol dm⁻³.

Scheme 5

Possible products from the electrolysis of 2-(2,2-dibromovinyl)naphthalene (1a).

Figure 2

Variation of the amounts of 1a, 2a, and 3a with the number of Faradays of 1a.

Scheme 6

Mechanistic hypothesis for the synthesis of alkyne 2a and bromoalkyne 3a from 2-(2,2-dibromovinyl)naphthalene (1a). Alkene configurations are not defined.

Scheme 7

Possible reaction using NaClO₄ as supporting electrolyte.

Scheme 8

Electrochemical synthesis of 9-ethyl-3-ethynyl-9H-carbazole (2b).

Scheme 9

Electrochemical synthesis of 1-ethynyl-4-methoxybenzene (2c).