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Electrochemistry Communications
the internal standard. Mass spectra (EI, ionizing voltage
70 eV) were determined using a THERMOFISHER ITQ-
900 DIP/GC-MSn mass-selective detector. Elemental
analyses were performed on a Leco CHNS Model 932
analyzer. All starting materials were obtained from
commercial sources and used without purification.
= 3505, 2972, 2941, 2873, 1725, 1446, 1375, 1119, 1025,
935. H NMR (300 MHz; CDCl3) (ppm): 1.15 (d, 6H,
1
J= 3.0 Hz), 1.21 (t, 3H, J= 7.2 Hz), 1.22 (s, 3H), 1.51 (m,
2H), 1.73 (m, 3H), 1.84 (bs, 1H), 2.13 (m, 2H), 4.08 (q,
2H, J= 7.2 Hz). 13C NMR (75.4 MHz, CDCl3) : 14.1,
24.9, 26.5, 28.0, 28.3, 37.7, 38.2, 49.2, 49.6, 60.5, 71.6,
178.7. MS m/z (relative intensity) IE: 214 (M+, 6),
197(22), 156(28), 141(28), 123(52), 115(80), 86 (100), 81
(55), 67 (61), 59 (75). Anal. Calc. for C12 H22 O3: C,
67.29; H, 10.28. Found: C, 66.95; H, 10.61.
2,2-Dimethyl-3-(2-oxopropyl)cyclopentanone (4a): Oil.
B.p.: 264-268 ºC. IR (NaCl) /cm-1 = 2968, 2928, 2873,
1738, 1715, 1470, 1381, 1362, 1173, 1103, 1055. 1H
NMR (300 MHz; CDCl3) (ppm): 0.78 (s, 3H), 0.97 (s,
3H), 1.47 (m, 2H), 2.15 (s, 3H), 2.22 (m, 2H), 2.51 (m,
2H), 2.63 (m, 1H). 13C NMR (75.4 MHz, CDCl3) : 17.9,
22.0, 24.7, 30.0, 35.7, 41.8, 43.5, 46.8, 207.0, 221.8. MS
m/z (intensidad relativa) IE: 168 (M+, 13), 151(20),
111(100), 97(20), 67(35), 55(30). Anal. Calc. for C10 H16
O2: C, 71.43; H, 9.52. Found: C, 71.34; H, 9.58.
2.2 General Electrochemical Procedure.
The electrolyses were carried out at 20 ºC under
constant current conditions (0.2 A). An undivided beaker-
type cell equipped with a magnetic stirrer was employed.
The solvent-supporting electrolyte (SSE) was either
H2O/EtOH (1:1) / 0.3 M NaClO4 or / 0.3 M Na2CO3
solutions. As anode a platinum sheet (geometric area 8
cm2) (1 cm separation of the cathode) was used.
In order to get a clean and reproducible surface the
platinum electrode was heated in a flame and polished. As
cathode a carbon plate was used. The anolyte was 60 mL
of the SSE solution containing 2 x 10-3 mol of
electroactive substrate 1. The electrolyses were carried out
during 3h and 45 min., which corresponds to a 700%
circulated charge (2702 C) in a 2F/mol process.
Once the electrolysis was finished, the EtOH was
removed under reduced pressure. The residue was
extracted three times with ether and the organic phase
dried over Na2SO4 and concentrated by evaporation. The
resulting solid (or oil) was chromatographed on a GC-MS
(HP-5 cross linked 5% PhMe silicone) 30m-0,25mm-
0.25m chromatographic column) instrument and a silica
gel (18 3 cm) column using chloroform (2a) or
hexane/EtOAc (30/1) (3a, 4a) as eluents. In order to
isolate the water-soluble products (hydroxyl derivatives),
the aqueous phase (slightly alkaline with Na2CO3 as
electrolyte) was neutralized, ether extracted and dried. All
the products were identified by their spectroscopic data
(see below). The characterization of the known
compounds 4b and 5b was completed with their MS
spectra. Yields are defined as the ratio between the
number of moles of product and the number of moles of
the reactant consumed taking into account the
stoichiometric coefficients.
(Z)-6-Isobutyl-4-methyltetrahydropyran-2-one
(2b):
Oil, B.p.: 249-251 ºC [Lit. [10,11] B.p.: 110 ºC (5 torr)].
IR (NaCl) /cm-1 = 2960, 2931, 2873, 1734, 1461, 1379,
1
1239, 1097, 988. H NMR (300 MHz; CDCl3) (ppm)
0.90 (d, 6H, J=6.7 Hz), 1.00 (d, 3H, J= 5.9 Hz), 1.23 –
1.35 (m, 3H), 1.62 (m, 1H), 1.86 (dd, 2H, J1= 4.87 Hz,
J2=12.7 Hz), 2.00 (d, 1H, J=11.5 Hz), 2.65 (d, 1H, J=11.7
Hz), 4.30 (m, 1H). 13C NMR (75.4 MHz, CDCl3) : 21.7,
22.0, 23.0, 23.9, 26.7, 37.5, 38.1, 45.2, 78.8, 171.6. MS
m/z (relative intensity) IE: 170 (M+, 60), 153 (9), 113 (3),
95 (3), 85 (8), 69 (10), 67 (5), 56 (3).
Ethyl 5-hydroxy-3,7-dimethyl octanoate (3b): Oil,
[Lit.[12] B.p.: 100 -105 ºC (2 torr)]. IR (NaCl) /cm-1
=
3512, 2958, 2925, 2874,1735, 1435, 1382, 1249, 1123,
1
945. H NMR (300 MHz; CDCl3) (ppm): 0.90 (d, 6H,
J= 6.7), 0.95 (d, 3H, J= 6.6 Hz), 1.23 (t, 3H, J= 7.3 Hz),
1.23 – 1.35 (m, 3H), 1.62 (m, 1H), 1.86 (m, 2H), 2.00 (m,
1H), 2.65 (m, 1H), 3.20 (m, 1H), 4.10 (q, 2H, J= 7.3 Hz).
13C NMR (75.4 MHz, CDCl3) : 14.3, 20.3, 23.4, 25.4,
29.7, 40.7, 42.6, 44.6, 60.2, 73.2, 172.9. MS m/z (relative
intensity) IE: 216 (M+, 3), 199 (100), 154 (16), 153 (14),
115 (67), 109 (18), 87 (90), 69 (46), 67 (10).
1-Isopropyl-4-methyl-2-oxa-bicyclo[2.2.1]heptan-3-one
(2a): Oil. B.p.: 244-247 ºC. IR (NaCl) /cm-1 = 2962,
1
2929, 2872, 1732, 1464, 1277, 1161, 1095, 951. H NMR
2-Ethoxy-2-isopropyl-5-methyl-cyclohexanone[13]
(4b): MS m/z (relative intensity) IE: 198(M+, 44),
155(M+-iPr, 20), 153 (M+-EtO, 18), 137(15), 115(98), 109
(72), 95(17), 87(100), 69(56).
2-Hydroxy-2-isopropyl-5-methyl-cyclohexanone[14]
(5b): MS m/z (relative intensity) IE: 170 (M+, 17),
153(M+-17, 30), 152 (M+-18, 19), 137(23), 127(M+-iPr,
5), 110(44), 109 (M+-18, 40), 95(100), 87(17), 85(18),
69(32).
(300 MHz; CDCl3): (ppm): 1.27 (s, 3H), 1.35 (d, 6H, J=
7.2 Hz), 1.53 (m, 2H), 1.87 (m, 3H), 2.07 (m , 2H). 13C
NMR (75.4 MHz, CDCl3) (ppm): 20.4, 24.6, 26.2, 28.3,
35.1, 37.0, 43.7, 44.9, 84.1, 176.7. MS m/z (relative
intensity) IE: 168 (M+, 19), 153 (12), 125 (13), 81(84),
67(100). Anal. Calc. for C10 H16 O2: C, 71.43; H, 9.52.
Found: C, 71.06; H, 9.72.
1,4,4-Trimethyl-3-oxa-bicyclo-[3.2.1]octan-2-one (2a´):
MS m/z (relative intensity) IE: 168 (M+, 100), 151 (54),
111 (93), 109 (12).
Ethyl
3-hydroxy-3-isopropyl-1-methylcyclopentane
carboxylate (3a): Oil. B.p.: 278-280 ºC. IR (KBr) /cm-1