Table I. Electrochemical and Chemical Oxidations of Isosafrole Glycol 3a
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Experimental Section
The 1H and 13C NMR spectra were measured in CDCl3 with Me4Si as an internal standard on a JEOL FX-9OQ spectrometer. The IR spectra were obtained with a JASCO IRA-1 spectrometer.
Electrolysis of Isosafrole (2). Preparation of 1-[3,4-(Methylenedioxy)phenyl]propane-1,2-diol (3a).
A mixture of 2 (100 mg, 0.62 mmol) and NaBr (192 mg, 1.9 mmol) dissolved in MeCN (7 mL) and H2O (3 mL) was electrolyzed in a beaker-type undivided cell (3 cm in diameter and 10 cm in height). A
constant current (20 mA, 2.83 F/mol) was passed for 140 min by using platinum foils (2 x 1.5 cm2) as electrodes and a Metronix
Model 543B DC power supply. After the electrolysis at room temperature, 0.5 mL of 1% aqueous H2SO4 was added to the mixture, which was stirred for 1 h and neutralized with aqueous NaHCO3. After evaporation of solvents under reduced pressure, the organic substances were extracted with ethyl acetate. The
extracts were washed with brine, dried (Na2SO4), and concentrated in vacuo to give a colorless oil, which was chromatographed (Mallinckrodt Silica CC-7 Special), affording 3a (116 mg, 98%) as colorless crystals8 whose spectral data were identical with those reported. In an another experiment, after the electrolysis as mentioned above, the mixture was concentrated in vacuo and the organic substances were extracted with ethyl acetate. The usual
workup and chromatography provided 3a (28 mg, 23%) and 4 (78 mg, 71 %). The structure of 4 was identified spectroscopically by comparison with IR and 1H NMR spectra of the authentic sample prepared by mCPBA oxidation of 2.9
2-Bromo-1-[3,4-(methylenedioxy)phenyl]-l-propanol (3b).
A mixture of 2 (lOO mg) and NaBr (96 mg) dissolved in MeCN (7 mL)-1% aqueous H2SO4 (3 mL) was electrolyzed (20 mA for 125 min, 2.5 F/mol) in a similar manner as described above,
affording 3b9a (160 mg, quantitative yield) as a colorless oil: bp 110-112°C (0.02 mmHg); IR (neat) 3520, 3400 (OH), 1490, 1440, 1240, 1040, 790 cm-1; 1H NMR (CDCl3) ä 6.85 (br s, 1 H, Ar H), 6.77 (br s, 2 H, Ar H), 5.92 (s, 2 H, CH2), 4.87 (d, J = 4 Hz, 1 H, CHOH), 4.32 (dq, J1 = 7 Hz, J24 Hz, 1 H, CHBr), 2.54 (br s, 1 H, OH), 1.56 (d, J = 7 Hz, 3 H, CH3). Anal. Calcd for C10H11O3Br: C, 46.35; H, 4.28. Found: C, 46.10; H, 4.20.
Electrolysis of 3a, Preparation of Piperonal (1).
Glycol 3a (100 mg, 0.51 mmol) dissolved in benzene (6 mL) and 0.5% aqueous NaOH (4 mL) was electrolyzed at 65°C (18 mA for 3 h, 4 F/mol) in a similar manner as described above, affording 1 (76 mg, 99%) as colorless crystals whose spectral and TLC data
were consistent with those of an authentic sample.
Oxidation of 3a with NaIO4.
A solution of NaIO4 (82 mg, 0.38 mmol) was added to 3a (50 mg, 0.26 mmol) dissolved in MeOH (8 mL) at 0-5°C. The mixture was stirred at the temperature for 30 min. The usual workup provided 1 (36 mg, 94 % ).
Oxidation of 3a with CAN.
Into a solution of 3a (100 mg, 0.51 mmol) dissolved in AcOH-H2O (1:2,3 mL) was added CAN (587 mg, 1.07 mmol) dissolved in AcOH-H2O (1:2,12 mL). The mixture was stirred at room temperature for 30 min. The usual workup provided 1 (71 mg, 93% ).
Oxidation of 3a with Ca(ClO)2.
A suspension of Ca(ClO)2 (61 mg, 0.26 mmol) in benzene (2 mL)-H2O (1 mL) was added to a solution of 3a (100 mg, 0.51 mmol) dissolved in benzene (4 mL)-H2O (2 mL). After vigorous stirring at 65 °C for 1 h, Ca(ClO)2 (183 mg, 0.77 mmol) suspended in benzene (2 mL)-H2O (1 mL) was added again and the mixture was stirred for additional 2 h. After adding AcOEt and centrifuging a precipitate, the organic substances were extracted with AcOEt and the usual workup provided 1 (75 mg, 98%).
1-[2-Chloro-4,5-(methylenedioxy)phenyl]propane-l,2-diol (6).
A suspension of Ca(ClO)2 (60% purity, 92 mg, 0.39 mmol) in AcOH (0.12 mL)-H2O (1.2 mL) was added drop wise to a solution of 3a (50 mg, 0.26 mmol) dissolved in MeCN (2 mL)-CH2Cl2 (1 mL). The reaction mixture was stirred at room temperature for 1 h. Ether extraction followed by usual workup and chromatography provided 6 (50 mg, 85%) as colorless crystals: mp 85-86°C: IR (CHCl3) 3560 (OH), 3380 (OH), 1475, 1220, 1120, 1035, 935, 850 cm-1; 1H NMR (CDCl3) ä 6.96 (s, 1 H, Ar H), 6.80 (s, 1 H, Ar H), 5.97 (s, 2 H, CH2), 4.86 (d, J = 7 Hz, 1 H, CH), 3.84 (quint, J = 7 Hz, 1 H, CH), 3.04 (br s, 1 H, OH), 2.64 (br s, 1 H, OH), 1.14 (d, J = 7 Hz, 3 H, CH3); 13C NMR (CDCl3) ä 147.6 (s), 147.1 (s), 132.4 (s), 124.5 (s), 109.6 (d), 107.7 (d), 101.8 (t), 74.4 (d), 71.8 (d), 18.8 (q). Anal. Calcd for C10H11O4Cl: C, 52.07; H, 4.81. Found: C, 52.26; H, 4.99.
1-[3,4-(Methylenedioxy)phenyl]-2-propanone (5).
A solution of 3a (lOO mg, 0.5 mmol) and p-TsOH (200 mg) dissolved in a distilled benzene (20 mL) was refluxed for 20 min. The usual workup gave 5 (75 mg, 84% ).8,9
Registry No. 1, 120-57-0; 2, 120-58-1; 3a, 62512-79-2; 3b, 57961-85-0; 5, 4676-39-5; 6, 89321-20-0; CAN, 16774-21-3; NaIO4, 7790-28-5; Ca(ClO)2, 7778-54-3.
References will be added during this week. From https://www.thevespiary.org/rhodium/Rhodium/projects/typing/propenylbenzenes/isosafrole.electrochem.pdf (https://www.thevespiary.org/rhodium/Rhodium/projects/typing/propenylbenzenes/isosafrole.electrochem.pdf)
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References
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