Oxidation of 3-(4-methoxyphenyl)prop-2-yn-1-ol by an Oxoammonium Salt; 3-(4-Methoxyphenyl)propiolaldehyde
Submitted Dec 22, 2012, published Dec 28, 2012
(Prepared In-House, See Comment 1) 3-(4-methoxyphenyl)prop-2-yn-1-ol
(Prepared in house, see Synthetic Page 507
Dichloromethane (≥99.5%, ACS Reagent Grade, Sigma-Aldrich)
Silica Gel (Dynamic Adsorbants Inc. Flash Silica Gel, 60Å porosity, 32-63 µm)
To a 500 mL flask equipped with stirbar was added the 3-(4-methoxyphenyl)prop-2-yn-1-ol (2.75 g, 0.01696 mol, 1 equiv) and DCM (170 mL, 0.1M in the alcohol). After mixing for a few minutes, 4-acetamido-2,2,6,6-tetramethylpiperidine-1-oxoammonium tetrafluoroborate1 (5.34 g, 0.01780 mol, 1.05 equiv.) was added followed by 2.75 g of SiO2 (1 mass equiv. to substrate)2. The flask was sealed with a rubber septa and the mixture was allowed to stir vigerously3 for 24 hours at room temperature. Upon reaction completion4 (confirmed by GC/MS analysis), the slurry was filtered solvent filtered through a coarse porosity fritted funnel. The solids were rinsed thoroughly with CH2Cl2 (≈ 300 mL). The filtrate was then adhered to silica gel by mixing it with 1.5 weight equivalents silica gel (relative to the theoretical yield, in this case 4.08 g) and removing the solvent in vacuo by rotary evaporation. A plug of silica was then assembled (A diagram of this apparatus is in the Data Files). This was done by adding 3-4 weight equivalents of silica (again relative to the theoretical yield) to a 60 mL coarse-porosity fritted glass funnel. An appropriately sized piece of filter paper relative to the size of the funnel was used to the top of the dry silica gel layer and this layer was pre-wet with hexanes. The dry packed material was gentle added evenly atop the filter paper. Another piece of appropriately sized filter paper was added atop this layer. The plug was eluted with a 9:1 by volume mixture of Hex:EtOAc (2-3 column volumes). The solvent was removed in vacuo by rotary evaporation to afford the pure aldehyde (1.72 g, 63%) as a tan solid.
1H NMR (CDCl3, 400 MHz) δ ppm 3.83 (s, 3 H) 6.89 (d, J = 8.80 Hz, 2 H) 7.54 (d, J = 8.80 Hz, 2 H) 9.37 (s, 1 H)
13C NMR (CDCl3, 100 MHz) δ ppm 55.7 (CH3) 89.0 (C) 96.8 (C) 111.3 (C) 114.7 (CH) 135.6 (CH) 162.4 (C) 176.9 (CH)
GC-MS (EI) 161 ([M]+2, 11%), 160 ([M]+, 100%), 159 (59%), 144 (13%), 132 (46%), 117 (34%), 116 (11%), 89 (44%), 88 (11%), 63 (20%), 62 (16%), 44 (10%), 40 (36%).
HRMS (ESI+) calcd for C9H9F3O2 [M + H]+ 161.0603, found: 161.0604
Kelly, C. B; Mercadante, M. A.; Hamlin, T. A.; Fletcher, M. H.; Leadbeater, N. E. J. Org. Chem., 2012, 77, 8131.
Bobbitt, J. M. J. Org. Chem. 1998, 63, 9367.
Bobbitt, J. M.; Bruckner, C.; Merbouh, N. Organic Reactions 2010, 74, 103.
Plug Diagram (Plug Apperatus.jpg)
1H NMR (HNMR.jpg)
13C NMR (13C NMR.jpg)
Keywords: aldehydes, alkynes, Organic Oxidants, oxidation, Oxoammonium Salts