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7th September 2011 @ 01:04
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Pinnick oxidation at 60 °C of recovered material from PMY 3-7 to the corresponding carboxylic acid.

Reaction Scheme PY3_5.png

Experiment start time: 0900 EST 07/09/11
Aldehyde PMY 2-3 (99 mg, 0.46 mmol, 1 equiv.), NaH2PO4 (0.44 g, 3.7 mmol, 8 equiv.) and 2,3-dimethyl-2-butene (0.55 mL, 4.6 mmol, 10 equiv.) were dissolved in THF/Water/t-BuOH (4:4:1, 10 mL). Emulsion forms on stirring, all solids dissolved. Heated to 60 °C NaClO2 ( 0.17 g, 1.8 mmol, 4 equiv.) was dissolved in THF/Water/t-BuOH (4:4:1, 4 mL) and added to the reaction portionwise over 3.5 hrs hrs. TLC (50% EtOAc/petrol) shows no UV active product, potentially overlapping. After a further 1.30 minutes, TLC (25% acetone/petrol or EtOAc/petrol) shows some new UV active product. Further NaClO2 ( 0.17 g, 1.8 mmol, 4 equiv.) added as a solution in reaction solvent (4 mL) dropwise over 40 minutes. TLC 7.5 hrs shows some progression. Another NaClO2 ( 0.34 g, 3.6 mmol, 8 equiv.) and NaH2PO4 (0.44 g, 3.7 mmol, 8 equiv.) in solvent mix (4 mL) were added over 40 mins. A further 2,3-dimethyl-2-butene (0.55 mL, 4.6 mmol, 10 equiv.) was added a couple of drops into the addition of NaClO2. Reaction mostly complete by TLC at approx 8.7 hrs. Reaction was diluted with EtOAc (50 mL) and then washed with 1M HCl (3 × 20 mL), brine then dried (MgSO4) and concentrated under reduced pressure to obtain an orange oil (0.61 g). The oil was redissolved in EtOAc (10 mL) and extracted with 1M NaOH (3 × 10 mL). The Ethyl acetate layer was then washed with brine, dried (MgSO4) and concentrated to a yellow oil, PMY 3-8b (144 mg). The NaOH extract was acidified with 2M HCl and extracted with EtOAc (3 × 10 mL). The extract was washed with brine, dried (MgSO4) and concentrated under reduced pressure to obtain a pale yellow oily solid, PMY 3-8a (71 mg). PMY 3-8a was recrystallised to obtain a tan solid (31 mg).

TLC visualised with UV and vanillin:
TLC 170 min and 235 min
TLC 5 hrs
TLC 7.5 hrs and 8.7 hrs

170 and 235 min TLC 50% EtOAc/petrol, drops AcOH.
5 hr TLC: 25% acetone/petrol (left) and 25% EtOAc/petrol (right).
7.5 and 8.7 hrs TLC: 25% EtOAc/petrol.

PMY 3-8 a and b

Post work-up, PMY 3-8a and b

NMR Spectra:
PMY 3-8-a
PMY 3-8-b
PMY 3-8-a recrystallised (EtOH wet)


References:
DOI: 10.1021/jm2001053
DOI: j.bmcl.2010.10.079

See also:

Oxidation of Pyrrole-3-carbaldehyde PMY 2-3, to corresponding acid using hydrogen peroxide (PMY 3-7)
Comparison of Chlorite and Permanganate in the Oxidation of Pyrrole-3-carbaldehyde PMY 2-3, to corresponding acid (PMY 3-6)
Pinnick Oxidation of Pyrrole-3-carbaldehyde PMY 2-3, to corresponding acid (PMY 3-5)
Oxone oxidation of Pyrrole-3-carbaldehyde PMY 2-3, to corresponding acid (PMY 3-4)
Sodium chlorite oxidation of Pyrrole-3-carbaldehyde PMY 2-2, to corresponding acid (PMY 3-3)
Oxidation of pyrrole-3-carbaldehyde PMY 2-2, to corresponding acid (PMY 3-2)
Oxidation of pyrrole-3-carbaldehyde PMY 2-2, to corresponding acid (PMY 3-1)


Risk and Hazard Assessment:
As for Sodium chlorite oxidation of Pyrrole-3-carbaldehyde PMY 2-2, to corresponding acid (PMY 3-3).
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Attached Files
TLC 5 hrs
TLC 170 min and 235 min
TLC 7.5 hrs and 8.7 hrs
PMY 3-8 a and b
PMY 3-8-a
PMY 3-8-b
PMY 3-8-a recrystallised (EtOH wet)