A New Approach to Ring Expansion of Keto Aziridines to 2,5-Diaryloxazoles

Abstract

Ring expansion of keto aziridines to the corresponding 2,5-diaryl oxazoles in the presence of dicyclohexyl carbodiimide and iodine under refluxing acetonitrile conditions is described. A plausible mechanism is proposed.

Key words

ring expansion - keto aziridine - oxazole

• References and Notes

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• 24 Typical Experimental Procedure for the Preparation of 2,5-Oxazoles: 2-(2,4-Dichlorophenyl)-5-phenyloxazole (Table 2 Entry 3)I₂ (1.0 mmol) was added to a solution of 2-benzoyl-3-(2,4-dichlorphenyl)aziridine (1.0 mmol) and dicyclohexyl carbodiimide (1.0 mmol) in MeCN (10 mL). The mixture was refluxed for 2 h, cooled, and the crude product was purified by column chromatography (silica gel, EtOAc–hexane = 2:5) to provide the desired 2-(2,4-diclorophenyl)-5-phenyloxazole (86%); yellow solid, mp 90–92 °C. IR (KBr): ν = 3064, 1662, 1590, 1482, 1101, 867, 828, 756, 685 cm^–1. ¹H NMR (400 MHz, CDCl₃): δ = 7.25–7.31 (m, 1 H), 7.34–7.39 (m, 2 H), 7.42 (s, 1 H), 7.47 (d, J = 2.0 Hz, 1 H), 7.65 (d, J = 8.1 Hz, 2 H), 7.97 (d, J = 8.1 Hz, 2 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 121.1, 123.8, 124.5, 124.6, 127.4, 129.0, 129.1, 129.2, 130.0, 131.8, 148.7, 152.4, 158.8 ppm. Anal. Calcd (%) for C₁₅H₉Cl₂NO: C, 62.09; H, 3.13; N, 4.83. Found: C, 62.11; H, 3.05; N, 4.77.