Magnetically Separable Nano Fe₃O₄ Catalyzed Direct Azidation of Allylic and Benzylic Alcohols Followed by Copper-Catalyzed Click Reaction

Abstract

A competent one-pot method comprising magnetically separable nano Fe₃O₄ catalyzed direct azidation of allylic and benzylic alcohols followed by the copper-catalyzed click reaction of the corresponding azides with alkynes is reported. This method gave a direct access to several 1,2,3-triazoles starting from various allylic and benzylic alcohols via their respective azides.

Key words

alcohols - azides - click reaction - cycloaddition - triazoles - magnetite

• References and Notes

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• 16 General Procedure for the Magnetic Nano Fe₃O₄ Catalyzed Direct Azidation of Allylic Alcohol 1a A mixture of alcohol 1a (0.5 mmol), trimethylsilyl azide (1.25 mmol), and magnetic nano Fe₃O₄ (particle size <50 nm, 15 mol%; the particles can be handled using a Teflon spatula) in DCE (3 mL) was stirred at 70 °C for 6 h. At this stage a magnet was externally applied to the reaction flask to attract the magnetic Fe₃O₄ nanoparticles, and the resulting clear solution was transferred to another flask using a pipette. The catalyst was washed using EtOAc (2 mL), and the residual Fe₃O₄ nanoparticles were heated in an oven at 100–110 °C overnight, and the catalyst was reused in subsequent cycles. The combined organic layers were evaporated under vacuum and purified by column chromatography to give the product 2. General Procedure for the One-Pot Magnetic Nano Fe₃O₄ Catalyzed Direct Azidation of Allylic Alcohols and Click Reaction The direct azidation of 1a (0.5 mmol) was carried out as above, the catalyst was removed using an external magnet, and the solvent was evaporated. Then to the residue THF (3 mL), H₂O (3 mL), alkyne (1 mmol), CuSO₄·5H₂O (30 mol%), and sodium l-ascorbate (30 mol%) were added, and the mixture was stirred at r.t. for 12 h. The reaction mixture was then extracted using EtOAc, the combined organic layers were evaporated, and the resulting reaction mixture was purified by column chromatography, eluting with EtOAc–hexanes (50:50), to afford the product 4a as a colorless liquid. Yield: 82% (238 mg). FT-IR (neat): ν = 3375, 2954, 1731, 1450, 1223, 1091 cm^–1. ¹H NMR (400 MHz, CDCl₃): δ = 7.57 (s, 1 H), 7.41–7.28 (m, 10 H), 6.70 (dd, J ₁ = 15.6 Hz, J ₂ = 7.2 Hz, 1 H), 6.52–6.47 (m, 2 H), 4.79 (s, 2 H), 3.36 (br s, 1 H). ¹³C NMR (100 MHz, CDCl₃): δ = 147.8, 137.7, 135.5, 134.7, 129.2, 128.8, 128.7, 128.6, 127.5, 126.9, 125.5, 121.2, 66.5, 56.4. ESI-HRMS: m/z calcd for C₁₈H₁₈N₃O [M + H]⁺: 292.1450; found: 292.1100.

The nano Fe₃O₄ used in this work was purchased from Sigma-Aldrich, and the size of the particles was checked through HRTEM analysis/images (see the Supporting Information) before using the nano Fe₃O₄. For communications dealing with the preparation and characterization of nano Fe₃O₄, see:
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