Synthesis and Photophysical Properties of β-Alkenyl-Substituted BODIPY Dyes by Indium(III)-Catalyzed Intermolecular Alkyne Hydroarylation

Abstract

A new atom-economical synthesis of β-alkenyl-substituted BODIPYs via indium(III)-catalyzed intermolecular alkyne hydroarylation with meso-substituted BODIPYs is described. While catalysis with InI₃ allows the double β-functionalization of BODIPY, resulting in regioselectively branched β,β'-disubstituted alkenyl BODIPYs, catalytic InCl₃ enables the formation of linear β-substituted alkenyl BODIPYs. Subsequent In(III)-catalyzed intermolecular alkyne hydroarylation allows the synthesis of unsymmetrical push-pull BODIPY derivatives. Therefore, indium catalysis offers complementary regioselectivity in good chemical yields and functional group tolerance. The resulting BODIPY dyes displayed bathochromically shifted absorption and emission according to the electron-nature of the substituents in the alkenyl moiety with high molar extinction coefficients (ε up to 88,200 M^-1 cm^-1) and quantum yields (0.14-0.96).

Scheme 1. Synthetic Approaches to Obtain β-Alkenyl BODIPYs

Scheme 2. Synthesis of Branched 2,6-Dialkenyl BODIPY Dyes through π-acid Catalysis

Reactions were carried out using 1a–1d (1 mmol, ∼ 0.1 M) and 14 equiv of arylacetylene. Monohydroarylated product was also obtained in 32% yield.

Scheme 3. Synthesis of Linear 2-Alkenyl BODIPY Dyes through σ-Catalysis

Reactions were carried out using 1a–1b (1 mmol, ∼ 0.1 M) and 14 equiv of alkyne. InI₃ (20 mol %) was used. In parentheses, yield of the 2,6-dialkenyl products.

Scheme 4. Synthesis of push–pull 2,6-Dialkenyl BODIPY Dyes

Figure 1

Normalized (a) absorbance and (b) emission spectra of BODIPY dyes 1a–8a, 8b, and 10a in CHCl₃ (7.5 × 10^–7 M, excited at the respective under λ_max). (c) Absorbance and (d) emission spectra of BODIPY dyes 2a–d in CHCl₃ (7.5 × 10^–7 M, excited at the respective under λ_max). (e) Photograph of the BODIPYs 2a–10a and 7b–8b under UV irradiation (λ = 365 nm).