Highly Regioselective Aminolysis of Alkynyl Epoxide Catalyzed by LiOTf

Background: Aminolysis of alkynyl epoxides was accomplished with excellent regioselectivity and good yields using microwave reactor. The reactions occurred exclusively at carbon atom next to the triple bond. Interestingly, aminolysis of alkynyl epoxide containing an ester group at γ-C (to the oxirane ring) led to a mixture of products. The first step of this reaction involved the attacks of amine to oxirane ring and ester group to form a lactone and an amide epoxide, respectively. Then intramolecular and intermolecular amine attacks of the former and intramolecular aminolysis of the latter formed a mixture of four products. Method: Aminolysis of alkynyl epoxide was carried out in a microwave reactor 110°C, 200 W for 1.5 h with catalyst lithium triflate. All reactions were monitored by thin-layer chromatography (TLC) using silica gel (Merck, 60-120 mesh). Column chromatography for isolation of products was performed using Merck silica gel (40-63 μm) packed by the slurry method, under a positive pressure of air. 1H and 13C NMR spectra were recorded on a Varian Inova NMR Spectrometer (1H NMR running at 500 MHz and 13C NMR running at 125 MHz) instrument. CDCl3 was used as the NMR solvent. Low-resolution mass spectra were obtained on a Shimadu GC spectrometer (EI) or Water LCZ single quadropole (ESI). High resolution spectra were obtained on a VG Autospec mass spectrometer (EI) or Waters QTOF (ESI). Infrared spectra were obtained as neat samples on a Smart Omni-Sampler Avator ESP Nicolet-Brand. The melting points were recorded on a Gallenhamp MF-370 carpillary tube, melting point apparatus and are uncorrected. The values are expressed in degree Celcius (°C). Uncertanties in the quoted values are ±2°C. Result: Aminolysis of alkynyl epoxide 3,4 occurred exclusively at the α carbon in good yield (72-76%), while with amine 8, the reaction produced a mixture of four products. Structure of all products was elucidated using IR, NMR, low-resolution MS, high-resolution MS. Conclusion: We examined the ring opening reaction of some alkynyl epoxides by amines catalysed by lithium triflate using microwave reactor. These reactions were accomplished with excellent regioselectivity and good yields. Because of time constraint, only three alkynyl epoxides were studied. In future, more alkynyl epoxides will need to be prepared and examined for the aminolysis reaction. Other amines will be also examined for the aminolysis of alkynyl epoxides.