Abstract
An efficient process for the Friedel–Crafts acylation of 3-methylindole with acid anhydrides in the presence of sulfated zirconia was developed. This catalyst shows excellent catalytic activity with good conversion and selectivity towards formation of the products of 2-acylation (3-methyl-1H-indol-2-yl)ketones. Other advantages related to this process are the simple work-up procedure and smaller production of chemical waste. The catalyst was easily recycled and reused with a minimal loss in activity through three reaction cycles. The catalyst was characterized by FT-IR spectroscopy, X-Ray diffraction and superficial acidity.
Highlights
We have studied the synthesis of different compounds through the use of homogeneous or heterogeneous acid catalysts
The solids were characterized by FT-IR spectroscopy, X-Ray diffraction (XRD) and superficial acidity
The properties of sulfated zirconia were examined by powder XRD, FT-IR spectroscopy and superficial acidity in catalysts calcined at 550 °C, without use and after being used
Summary
Indole derivatives present wide biological importance in a variety of therapeutic areas such as anti-inflammatory, anticonvulsant, cardiovascular, antitumor, antibacterial, antiparkinsonian, antiviral and antidiabetics agents, among others [1]. There are different methods in the synthesis of acylindoles, among them the Friedel–Crafts reactions [4,5,6,7], Vilsmeier–Haack reaction [8] and the use of Grignard reactions [9] Some of these methods present advantages and shortcomings that limit their scope and performance. We have studied the synthesis of different compounds through the use of homogeneous or heterogeneous acid catalysts. Yields increased when heterogeneous catalysts were used, with simplicity in the purification process and a smaller amount of polluting waste Among those mentioned sulfated zirconia has attracted much attention in recent years because of its good catalytic activity, super-acidity, non-toxicity and several advantages such as short reaction times, high selectivity and the easiness of work-up procedure. In relation to obtaining mono acylated products, these may be substituted at the C-2 position (2), at the N-position (3) and other carbon atoms in the benzene ring (4) (Scheme 1)
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