Constant current electrolyses were carried out in a 100 mL undivided cylindrical cell, equipped with a platinum-coated titanium grid (50 g Pt/m2, 40 × 60 mm) as the anode (available from Magneto-Chemie) and a copper wire (0.5 mm diameter) as the cathode. Lithium perchlorate (LiClO4, purchased from Acros, 1.5 g, 14.0 mmol) was added as a supporting electrolyte to dry MeOH (50 mL). The starting material was introduced, and the electrolysis was then performed at 50 mA, provided by a Sodilec SDRL02-120 regulated DC power supply, until the desired charge passed (2.5 F/mol). All reactions were vigorously stirred. After electrolysis, the solution was evaporated, and the residue was diluted in CH2Cl2 (50 mL) and washed with H2O (3 × 30 mL). The layers were then separated, and the aqueous layer was extracted with CH2Cl2 (3 × 30 mL). The combined organic extracts were dried over Na2SO4, filtered, and evaporated to dryness. Procedure B. Constant potential electrolyses were performed according to the method we previously described.40
3,3,10,10-Tetramethoxytricyclo[6.2.2.02,7]dodeca-5,11-diene-4,9-dione (4a). Electrooxidation of a solution of guaiacol 1a (211 mg, 1.70 mmol) was performed according to the procedure A. The reaction mixture was then processed as described above, and the residue was purified by column chromatography, eluting with pentanes/Et2O [(2:1) . (1:1)], to furnish pure dimer 4a as fine off-white crystals (241 mg, 92%). All spectroscopic data were identical to those previously reported.32,40
4-Bromo-6,6-dimethoxycyclohexa-2,4-dienone (3b). Electrooxidation of a solution of 4- bromo-2-methoxyphenol (1b, 171 mg, 0.84 mmol)48 was performed according to the procedure A. The reaction mixture was then processed as described above, and the oily residue was purified by column chromatography, eluting with pentanes/Et2O (2:1), to furnish the pure orthoquinone monoketal 3b as a yellow oil (126 mg, 64%): IR (NaCl) 1689, 1631 cm-1; 1H NMR (CDCl3, 250 MHz) d 3.37 (s, 6H), 5.96 (d, J = 10.1 Hz, 1H), 6.66 (d, J = 1.8 Hz, 1H), 6.87 (dd, J = 1.8, 10.1 Hz, 1H); 13C NMR (CDCl3, 62.9 MHz) d 192.8, 143.2, 135.3, 126.6, 119.4, 92.9, 50.2; EIMS m/z (rel intensity) 234 (M+, 22), 232 (M+, 22), 219 (4), 217 (4), 204 (9), 203 (21), 202 (9), 201 (21), 153 (52), 125 (100).
6-Acetoxy-3-tert-butyl-6-methylcyclohexa-2,4-dienone (3e). 5-tert-Butyl-2-methylphenol (1e 100 mg, 0.61 mmol)49 was submitted to the DIB-mediated oxidative acetoxylation method we previously described18 to furnish 3e as an orangish oil (131 mg, 97%): IR (NaCl) 1750, 1672 cm-1; 1H NMR (CDCl3, 250 MHz) d 1.18 (s, 9H), 1.37 (s, 3H), 2.07 (s, 3H), 6.05 (d, J = 1.5 Hz, 1H), 6.22 (d, J = 10.1 Hz, 1H), 6.37 (dd, J = 1.5, 10.1 Hz, 1H); 13C NMR (CDCl3, 62.9 MHz) d 199.3, 169.4, 163.8, 140.9, 122.3, 119.4, 113.6, 78.0, 30.1, 23.8, 20.4; EIMS m/z (rel intensity) 222 (M+, 3), 180 (67), 165 (35), 163 (6), 57 (18), 43 (100); HRMS (EI) calcd for C13H18O3 222.1256, found 222.1254.
3-tert-Butyl-6-methoxy-6-methylcyclohexa-2,4-dienone (3e') and 5-tert-butyl-4, 4- dimethoxy- 2-methylcyclohexa-2,5-dienone (5). To a stirred solution of DIB (412 mg, 1.28 mmol) in dry MeOH (10 mL) was added a solution of 1e (200 mg, 1.22 mmol)49 in dry MeOH (2 mL). The reaction mixture immediately became bright yellow. After 30 min, TLC monitoring
