To
compound SI-1 (500 mg, 2.31 mmol, 1.0 equiv)
was added a solution of
DMDO
in
acetone (69 mL of a 0.1 M solution, 6.9 mmol, 3.0
equiv) at -78°C. The reaction was warmed to room temperature and stirred for three hours, after which a 0.5 mL sample was taken and the solvent removed under
reduced pressure. Examination of the reaction mixture by 1H-NMR
showed that the reaction had proceeded approximately 30%, and the reaction was allowed to proceed for two more hours (analysis of the reaction mixture by 1H-NMR is necessary,
as an over-oxidized byproduct that is co-polar with the product forms during extended reaction times) after which the solvent was removed under reduced pressure to yield a
pale yellow oil that was purified by
flash column
chromatography on silica gel (5% to 20% ethyl acetate in hexanes gradient as eluent) to yield recovered starting material (283 mg, 1.31 mmol, 57%) and the desired
epoxide ±SI-2 (220 mg, .95 mmol, 41%) as a colorless oil. Rf=.29 (20% ethly acetate in hexanes); IR (neat) v= 2979, 2935, 2834, 1743, 1443, 1368, 1348, 1307, 1248, 1217,
1156, 1121, 1070, 978, 896, 850 cm-1; HRMS (ESI-TOF) calculated for C11H20O5Na [M+Na+] 255.1203; found 255.1202.
Compound (±)-SI-2 (130 mg, 0.560 mmol, 1.0 equiv)
was dissolved in
DMF
(5 mL) to which
sodium azide (109 mg, 1.68 mmol, 3.0 equiv)
and
ammonium chloride (90 mg, 1.68 mmol, 3.0 equiv) were added. The reaction was then heated to 60 ºC for 14 h. After cooling to room temperature,
the reaction was poured into water (50 mL) and
extracted with ether
(4 x 30 mL). The combined organics were washed with water (2 x 20 mL), brine (20 mL), dried with MgSO4, and the solvent was removed under reduced pressure. The resulting yellow oil was purified
by flash column chromatography on silica gel (10% to 30% ethyl acetate in hexanes as eluent) to yield
compound (±)-SI-3 (128 mg, 0.465 mmol, 83%) as a pale yellow oil.
Rf = 0.31 (30% ethyl acetate in hexanes); IR (neat) ν = 3466, 2980, 2936, 2834, 2109,
1734, 1457, 1394, 1370, 1254, 1153, 1127, 1060, 969, 841 cm-1; HRMS (ESI-TOF) calculated for C11H21N3O5Na [M+Na+] 298.1373; found 298.1371.