Ethyl 2-oxocyclohexanecarboxylate [CAS 1655-07-8] (
4, 1 mmol, 1 eq), 2,6-lutidine [CAS 108-48-5] (5 mmol, 5 eq), 4-acetylamino-2,2,6,6-tetramethylpiperidine-1-oxoammonium tetrafluoroborate (
1, 7.5 mmol, 7.5 eq), acetonitrile (3 mL) and deionized water (1 mL) were added to a 40 mL-capacity glass tube equipped with a magnetic stir bar. The reaction mixture was sealed with a cap and placed into a CEM Discover SP microwave unit. The content of the vessel was heated to 100 °C and held at this temperature for 30 min, the microwave power automatically fluctuating to hold the reaction mixture at the desired temperature. The reaction mixture was stirred constantly. After the allotted time, the reaction mixture was allowed to cool to below 50 °C before taking the vessel out of the microwave unit. An intensely colored solution was obtained at this point. The product mixture was transferred from the glass tube to a separatory funnel whereupon water (2 mL) was added, followed by 1 M HCl (5 mL). An extraction with petroleum ether was performed (5 × 10 mL) in order to remove non-acidic byproducts. The organic layer was then washed with 0.5 M NaOH (2 × 25 mL) in order to extract the product in phenoxide anion form. At this point the color of the solution changed from yellow to green. The two basic aqueous fractions were collected and acidified with 2 M HCl until a pH of less than 3 was reached (~30 mL acid). At this point the solution turned a cloudy yellow color. This solution was extracted with petroleum ether (3 × 30 mL). The combined organic extracts were washed with brine (~30 mL) and dried over Na
2SO
4. The solvent was removed under reduced pressure by rotary evaporation affording pure phenol
6 as a yellow oil (66 mg, 40%).
1H-NMR (400 MHz, CDCl
3): δ ppm 10.84 (s, 1H), 7.85 (dd,
J = 8.0, 1.8 Hz, 1H), 7.45 (ddd,
J = 8.8, 7.2, 1.8 Hz, 1H), 6.98 (dd,
J = 8.4, 1.1 Hz, 1H), 6.88 (ddd,
J = 8.2, 7.2, 1.1 Hz, 1H), 4.41 (q,
J = 7.1 Hz, 2H), 1.42 (t,
J = 7.1 Hz, 3H).
13C-NMR (101 MHz, CDCl
3): δ ppm 170.36, 161.83, 135.73, 130.05, 119.22, 117.70, 112.79, 77.48, 77.16, 76.84, 61.55, 14.33. GC-MS: (EI),
m/
z (relative intensity, %), 166 ([M]
+, 39), 121 (28), 120 (100), 92 (37), 65 (11). Spectral data for this compound are consistent with those previously reported [
37,
38] (
Supplementary Materials).