Figure 2. Current density 0.20 A/cm2. Symbols follow: la ( ), 2a (A), and 3a (•).Scheme I anol would produce the ring opening product 3a via the cation intermediate c. In the course of the electrolysis two-electrons oxidation of formaldehyde is also expected to afford methyl formate. After all, the conversion of 2a to 3a should require four electrons on the anode. As shown in Figure 1, the conversion of ca. 80% of 2a was achieved when 4 Faradays/mol of electricity was passed.
Experimental SectionAll the boiling points are uncorrected. NMR spectra were recorded on a Hitachi R-24 spectrometer. Ir spectra were measured on neat liquids using a JASCO model IRA-1 spectrometer.Materials. Commercially available furfuryl alcohol (la) and furfural (4) were distilled under reduced pressure before use. 2-Acetoxymethylfuran (2a)13 and 2-furoic acid (6)14 were prepared according to the procedure described in the literature.General Procedure of the Electrolysis. 2-Substituted furans la, lb, 2a, 4, 5, and 6 were dissolved in MeOH (20 ml) containing Et4NC104, Et4NC104-EtgN, and/or NH4Br-EtgN as a supporting electrolyte. The solutions were electrolyzed under a constant current in a compartment cell equipped with two platinum foil electrodes (2 X 3 cm2). The solution was condensed under reduced pressure, taken up in EtOAc, washed with aqueous NaHCOg and brine, and dried (Na2S04). After evaporation of the solvent the residue was distilled by using a short-path distillation apparatus, to give the products 2a, 2b, 3a, 3b, and 5. The detailed reaction conditions and results of electrolyses of 2-substituted furans and the related compounds are listed in Table I. Analytically pure samples were obtained by column chromatography on silica gel with benzene-EtOAc (20/1).2,5-Dimethoxy-2-hydroxymethyl-2,5-dihydrofuran (2a): bp 82-85 °C (7.5 mm) [lit.15 bp 106-110 °C (18 mm)]; ir (neat) 3440 (OH), 2820 (CHgO), 1633 cm"1 (C=C); NMR (CDClg) 2.68 (m, 1 , OH), 3.15-3.72 (8 H, 2 CHgO, CH20), 5.45-6.16 (3 H, CHO, CH=CH). 2-Acetoxymethyl-2,5-dimethoxy-2,5-dihydrofuran (2b): bp 105-109 °C (11 mm) [lit.15 bp 117-119 °C (12 mm)]; ir (neat) 2820(CHgO), 1745 (C=0), 1632 cm"1 (C=C); NMR (CDClg) 2.07 (s, 3 H, CHgCO), 3.15, 3.24 (2 s, 3 H, CHgO), 3.43, 3.51 (2 s, 3 H, CHgO), 3.88-4.48 (m, 2 H, CH20), 5.45-6.23 (3 H, CHO, CH=CH). Methyl (Z)-4,4-Dimethoxy-2-butenoate (3a): bp 74-78 °C (12 mm); ir (neat) 2820 (CHgO), 1728 (C=0), 1657 cm"1 (C=C); NMR