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20th February 2012 @ 05:47
Target synthesised in 80% yield.

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Synthesis of 1-(4-fluorophenyl)-2,5-dimethyl-1H-pyrrole-3-carbaldehyde by Vilsmeier-Haack formylation of 1-(4-Fluoro-phenyl)-2,5-dimethyl-1H-pyrrole.

Reaction Scheme PY14.png

Reaction Start Time: 15.45 EST 20/02/12
DMF (15 mL) was stirred under a nitrogen atmosphere in an ice-bath. Phosphoryl chloride (
3.5 mL, 38.1 mmol, 1.2 equiv.) was added and the reaction stirred for 25 minutes. Reaction still colourless. A solution of pyrrole PMY 1-6 (6.00 g, 31.5 mmol, 1 equiv.) in DMF (10 mL) was added dropwise over 5 minutes. The reaction was removed from the ice-bath and allowed to warm to room temperature. After 30 minutes, TLC shows reaction almost complete. After 45 minutes, reaction was poured into ice/water (200 mL) and 5M NaOH added until pH 6. The green suspension was allowed to stand. After 16 hours, the mixture was a brown suspension. pH was now 1, adjusted to 10 by addition of 5M NaOH. Allowed to stand for 20 minutes, then filtered. The pale brown solid was recrystallised from warm acetonitrile (approx 100-150 mL) and water. The brown crystals were filtered out, washed with water and dried under vacuum (5.51 g, 80%).

TLC (20% EtOAc/hexane) visualised with UV and vanillin:
TLC


Risk and Hazard Assessment:
See: Formylation of 1-(4-fluorophenyl)-2,5-dimethyl-1H-pyrrole (PMY 2-1)

See also:
Preparation of 1-(4-fluorophenyl)-2,5-dimethyl-1H-pyrrole-3-carbaldehyde
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TLC