Regioselective alkylation of indoles with α-pinene by BF3.Et2O catalyst

Monoterpenes are renewable resources that are widely used in the pharmaceutical, perfume, cosmetic and food industries.1 Among them, α-pinene is a readily available and inexpensive raw material usually obtained from the pine gum. It is present to the extent of 85% in turpentine oil of pine. Several transformations of α-pinene, such as acetoxylation, hydration, isomerization and oxidation can be applied to produce a wide variety of added value products.2,3Indole is the core structure of many pharmacological agents and natural products. Therefore, the synthesis and selective functionalization of indoles have been the focus of active research over the years.4 Herein, we report the synthesis of 3-alkylated indoles by means of α-pinene as a starting material, which was separated from turpentine oil by distillation method. The indole derivatives undergo alkylation with α-pinene in the presence of BF3.Et2O (30 mol %) in dichloromethane at room temperature to produce the corresponding 3-alkylated indoles in good yields with high trans-selectivity (Fig. 1). The products were obtained as oil and the structures were characterized on the basis of their mass spectrum, 1H and 13C NMR, and IR spectroscopic data.

کلیدواژه ها:

One-pot reaction ، Monoterpenes ، Turpentine oil ، α-Pinene ، Indoles