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18th October 2011 @ 03:47

Repeat of PMY 15-1: Reduction of pyrrole-3-ester PMY 6-1 using LiAlH4.

Reaction Scheme

Reaction start time: 08.50 18/10/11
LiAlH4 (72 mg, 1.91 mmol, 1 equiv, 4 hydride equiv.) was stirred in Et2O (5 mL) at room temperature (water bath). PMY 6-1 (500 mg, 1.91 mmol, 1 equiv.) in Et2O (10 mL) was added dropwise over 5 minutes. After 6 hours, a saturated solution of Rochelle's salt (approx 10 mL) was added, shaken and left to separate. Diluted with EtOAc (30 mL). Separated and aqueous extracted with EtOAc (3 × 20 mL), dried (MgSO4) and concentrated under reduced pressure. The residue was then purified by chromatography (2-30% EtOAc/hexane) to obtain an off-white solid (264 mg, 63%). Emulsion did not break fully, potentially cause of poor yield. Also suspect product is slightly unstable on silica, requires 2D TLC to check. Undeveloped TLC spots turn blue over time. 25/10/11 Sample has turned very dark with some purple precipitate over the weekend. Sample was stored in the dark at room temperature. 19F NMR shows mostly new product. 1H shows 2 peaks at 4.53 and 4.40 compared to 4.50 on original sample. TLC shows 3 spots.

TLC (25% EtOAc/hexane) visualised with UV and vanillin:
TLC 5 hours

1H, 19F, 13C NMR

1H, 19F NMR after 3 days

Risk and Hazard Assessment:
See:Reduction of pyrrole-3-ester PMY 6-1 using lithium aluminium hydride (PMY 15-1)

See also:
Synthesis of Ethyl 1-(4-fluorophenyl)-2,5-dimethyl-1H-pyrrole-3-carboxylate (PMY 6-1)

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Attached Files
TLC 5 hours
1H, 19F, 13C NMR
1H, 19F NMR after 3 days