Zinc Chloride Catalyzed Ring Opening of N-Arylsulfonyl Aziridines by Thioamides: A New Approach to the Synthesis of Amidines

Abstract

The first zinc chloride catalyzed ring opening of N-arylsulfonyl aziridines by thioamides is described. Various thioamides were reacted with N-arylsulfonyl aziridines in the presence of a catalytic amount of dry zinc chloride to provide the corresponding N-arylsulfonyl amidine derivatives with good to excellent yields.

Key words

amides - Lewis acids - nitrogen - homogeneous catalysis - sulfur

• References and Notes

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• 21 Complete experimental procedures and relevant ¹H NMR and ¹³C NMR spectra and elemental microanalysis for new compounds are available in the Supporting Information. Typical Procedure for the Synthesis of N-Arylsulfonyl Amidine 3a A suspension of anhydrous ZnCl₂ (3.2 mg, 2 mol%) in anhydrous CH₂Cl₂ (2.0 mL) was refluxed for 5 min, a solution of 2-phenyl-1-tosylaziridine (2a, 328 mg, 1.2 mmol) in anhydrous CH₂Cl₂ (1.0 mL) was added slowly, and the mixture was stirred at 40 °C for a further 5 min. Morpholino(phenyl) methanethione (1a, 207 mg, 1 mmol) was then added, and the mixture was stirred at the same temperature for 2 h. The reaction mixture was then triturated with H₂O (5 mL) to remove ZnCl₂ and extracted with CH₂Cl₂ (3 × 5 mL). The combined organic layers were dried over MgSO₄, filtered, and concentrated under vacuum. Finally, the residue was subjected to column chromatog-raphy on silica gel eluting with PE–EtOAc (1:1) to furnish amidine 3a as a white solid (314 mg, 91%).