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18th July 2012 @ 07:58
Product obtained in 30% overall yield.


Cyclodehydration of PMY 57-1 using XtalFluor-E in 1,2-DCE and subsequent oxidation to the oxazole.


Reaction Start Time: 17.10 18/07/12
PMY 57-1 (103 mg, 0.3 mmol, 1 equiv.) was stirred in 1,2-DCE (4 mL) and heated to 90 °C under nitrogen. XtalFluor-E (141 mg, 0.6 mmol, 2 equiv.) was added. After 16 hours, reaction mostly complete by TLC. The reaction was cooled to room temperature (13 °C) and 1:1 saturated Na2CO3/water added (10 mL) and the reaction stirred for 10 minutes. The layers were separated and the aqueous extracted with DCM (3 × 10 mL). The organic extracts were washed with brine then dried (MgSO4) and concentrated under reduced pressure to a brown gum (93 mg). 1H NMR is consistent with expected intermediate product.

1440 19/07/12 The material was dissolved in DCM (5 mL) and bromotrichloromethane (91 μL, 0.92 mmol, 3 equiv.) and DBU (138 μL, 0.92 mmol, 3 equiv.) were added. TLC at 2 hours at 15 °C (room temperature) shows formation of a new product and SM. After 18 hours,, SM still remains. Reaction concentrated to approx 1 mL and purified by chromatography (5-15% acetone/hexane) to obtain a white solid (30 mg, 30% over 2 steps). 1H and 13C NMR are consistent with expected product.

TLC (10% MeOH/DCM) visualised with UV and vanillin:
TLC stage 1
TLC stage 2, 2 hours

1H NMR step 1
1H, 13C, 19F NMR PMY 58-1

Mass Spec:
Intermediate oxazoline:
HRMS (ESI+) found 317.13035 [M+H], C17H18N2O3F requires 317.12960.

Product oxazole:
HRMS (ESI+) found 337.09628 [M+Na], C17H15N2O3FNa requires 337.09589.

See also:
Coupling of pyrrole acid chloride and serine methyl ester (PMY 57-1)
Synthesis of aryl pyrrole oxazole ester from aldehyde and Serine methyl ester (PMY 46-1)
Synthesis of aryl pyrrole oxazole ester (PMY 45-1)


Risk and Hazard Assessment:
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Attached Files
TLC stage 1
TLC stage 2, 2 hours
1H NMR step 1
1H, 13C, 19F NMR PMY 58-1