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 110ºC, 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. 1
C NMR spectra were recorded on a Varian Inova NMR Spectrometer (1
H NMR running at 500 MHz
C 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 (ºC). Uncertanties in
the quoted values are ±2ºC.
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.