Copper(II) Triflate Catalyzed Rearrangement of Amino 2,3-Epoxides to α-Amino Ketones

Abstract

α-Amino ketones were synthesized by a Meinwald rearrangement of biomass-based amino epoxides using copper(II) triflate as a catalyst. The regioselectivity of the rearrangement can be rationalized in terms of the reaction proceeding via the most stable carbocationic intermediate to give various α-amino α′-aryl ketones in moderate to good yields. This is an attractive method to prepare α-amino ketones using a benign and inexpensive catalyst.

Key words

Meinwald rearrangement - amino ketones - amino epoxide - copper catalysis - copper triflate

Publication History

Received: 23 April 2024

Accepted after revision: 08 May 2024

Article published online:
23 May 2024

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• 18 Rearrangement of α-Amino Epoxides 1; General Procedure A dried tube was charged with Cu(OTf)₂ (1 mol%) then capped and flushed with argon. A solution of the appropriate α-amino epoxide 1 (1 mmol) in anh 1,4-dioxane (4 mL) was added, and the mixture was stirred at 80 °C for 2 h. Sat. aq NaHCO₃ was added, and the mixture was extracted with EtOAc. The combined organic layers were dried (Na₂SO₄) and the solvent was evaporated under reduced pressure, then the mixture was then purified by column chromatography (silica gel, EtOAc–hexane gradient). N-Cyclohexyl-2-nitro-N-(2-oxo-3-phenylpropyl)benzenesulfonamide (2a) Yellow oil; yield: 250 mg (60%). ¹H NMR (400 MHz, CDCl₃): δ = 8.16–8.11 (m, 1 H), 7.72–7.60 (m, 3 H), 7.39–7.23 (m, 5 H), 4.21 (s, 2 H), 3.80 (s, 2 H), 3.71 (tt, J = 12.1, 3.5 Hz, 1 H), 1.74–1.52 (m, 5 H), 1.31–1.20 (m, 2 H), 1.09–0.81 (m, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 203.3, 148.0, 134.1, 133.5, 133.3, 131.7, 131.2, 129.5 (2C), 128.9 (2C), 127.3, 124.1, 58.2, 51.2, 46.7, 31.2 (2 C), 25.7 (2 C), 25.1. HRMS (ESI): m/z [M + Na]⁺ calcd for C₂₁H₂₄N₂NaO₅S: 439.1298; found: 439.1368.