Copper-Catalyzed Cross-Dehydrogenative-Coupling Reaction of N-Arylglycine Esters with Imides or Amides for Synthesis of α-Substituted α-Amino Acid Esters

Abstract

A simple and highly efficient cross-dehydrogenative-­coupling (CDC) reaction between N-aryl glycine esters and imides or amides by the catalysis of a copper salt without the requirement of ­peroxide agents is described. The novel reaction provides a facile ­approach for the synthesis of α-substituted α-amino acid esters through C–H/N–H oxidative cross-coupling. A possible mechanism for the CDC reaction by using copper as a catalyst and air as the terminal oxidant is also proposed. This synthetic approach has the advantages of good yields, simple operation and mild reaction conditions.

Key words

copper catalysis - cross-dehydrogenative-coupling - glycine esters - imides - amides

• References and Notes


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• 9 General Procedure for the Synthesis of α-Substituted α-Amino Acid Esters 3: To a solution of N-arylglycine esters 1 (0.3 mmol) in MeCN (2 mL) were added imides or amides 2 (0.2 mmol) and CuCl (2.0 mg, 0.02 mmol). Then, the reaction mixture was stirred at 60 °C under air atmosphere until the reaction was completed. Then, the resulting mixture was concentrated under vacuum, and the residue was purified by column chromatography (silica gel, petroleum ether/EtOAc as an eluent) to afford the corresponding products 3.
• 10 Analytical Data of Ethyl 2-(1,3-Dioxoisoindolin-2-yl)-2-(p-tolylamino)acetate (3aa): light yellow solid; yield: 65.6 mg (97%); mp 119.2–119.7 °C. ¹H NMR (400 MHz, CDCl₃): δ = 7.82–7.84 (m, 2 H), 7.70–7.72 (m, 2 H), 6.99 (d, J = 8.0 Hz, 2 H), 6.74 (d, J = 8.4 Hz, 2 H), 6.19 (d, J = 9.6 Hz, 1 H), 5.20 (d, J = 9.2 Hz, 1 H), 4.30 (q, J = 7.2 Hz, 2 H), 2.20 (s, 3 H), 1.25 (t, J = 7.2 Hz, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 167.5, 167.2, 141.6, 134.4, 131.7, 130.0, 128.9, 123.7, 114.0, 63.0, 60.4, 20.4, 14.1. HRMS (ESI): m/z [M + H⁺] calcd for C₁₉H₁₉N₂O₄: 339.1339; found: 339.1352.