Bi(OTf)₃-Catalyzed Intramolecular Amination of Triazenylaryl Allylic Alcohols: A Stereoselective, High-Yield Synthesis of (E)-3-Alkenyl 2H-indazoles

Abstract

An efficient Bi(OTf)₃-catalyzed synthesis of 3-alkenyl-2-pyrrolidine-2H-indazoles from triazenylaryl allylic alcohols via the intramolecular direct amination process is reported. Compared with the dodecyl benzenesulfonic acid (DBSA)-catalyzed method, the new method is more efficient and gives greater yields and functionality tolerance. Additionally, the 3-alkenyl-2-pyrrolidine-2H-indazoles can be transformed to a series of new products under different reaction conditions.

GRAPHICAL ABSTRACT

Keywords:

• Alkenyl 2H-indazole
• amination
• bismuth triflate
• triazenylaryl allylic alcohols

Notes

^a All reactions were carried out with 3-aryl triazenylaryl allylic alcohol 1a (0.5 mmol) and catalyst in DCM (2 mL) at room temperature for 12 h.

^b Yield of the isolated product after flash column chromatography.

^a Bi(OTf)₃-catalyzed reaction: All reactions were carried out with triazenylaryl allylic alcohol 1 (0.5 mmol), and Bi(OTf)₃ (0.025 mmol, 5 mol%) in DCM (2 mL) at room temperature for 12 h.

^b Yield of the isolated product of Bi(OTf)₃-catalyzed reaction after flash column chromatography.

^c DBSA-catalyzed reaction: All reactions were carried out with triazenylaryl allylic alcohol 1 (0.5 mmol) and DBSA (0.1 mmol, 20 mol%) in water (2 mL) at 35 °C for 24 h to 4 d.

^d Yield of the isolated product of DBSA-catalyzed reaction after flash column chromatography from Ref. 7.