Tonino Caruso et al.
FULL PAPERS
7.1 Hz), 3.45 (t, 1H, J=7.2 Hz), 4.15 (q, 2H, J=7.1 Hz);
13C NMR: d=7.89, 14.23, 21.88, 29.18, 36.08, 39.23, 58.45,
61.61, 169.69, 203.14, 210.48.
less environment, avoiding metal, basic or EGB cata-
lysts. With respect to the traditional chemical meth-
ods, the electrochemical, metal-free conditions result-
ed in enhanced reactivity of the electrogenerated bare
carbon anion, so that the reactions with suitable ac-
ceptors were found to occur under mild conditions
and with short reaction times. Furthermore, easy set-
up and work-up procedures were established avoiding
the addition of a supporting electrolyte in the elec-
trolysis medium.
Methyl 2-Acetyl-5-oxoheptanoate (3ca): 1H NMR: d=
0.99 (t, 3H, J=7.2 Hz), 2.06–2.09 (m, 2H), 2.22 (s, 3H), 2.38
(q, 2H, J=7.4 Hz), 2.44 (q, 2H, J=7.2 Hz), 3.50 (t, 1H, J=
7.2 Hz), 3.7 (s, 3H); 13C NMR: d=7.92, 21.95, 29.26, 36.12,
39.24, 52.65, 58.27, 170.20, 203.08, 210.45
General Procedure for Electrochemically-Promoted
QCCs Construction via Michael Addition of 1e–g to
Michael Acceptors 2
Experimental Section
Pure 1, 20 mmol, was electrolysed under galvanostatic con-
trol (I=5 mAcmÀ2, Q=2 F, terminal voltage for 1c=130 V)
at 08C. At the end of the electrolysis, the Michael acceptor
2 (20 mmol) was added to the cathode compartment and the
reaction prolonged for about 1 hour at room temperature.
Crude mixtures yielded pure adducts 3 (3ea: 3.69 g, 3ec:
4.80 g, 3fa: 4.16 g, 3fc: 4.20 g, 3ga: 5.50 g) after simple filtra-
tion over silica gel. The isolated products 3ea[14] gave spec-
tral and analytical data in accordance with those reported in
the literature.
Ethyl 2-Methyl-3-oxo-2-(3-oxocyclohexyl)butanoate (3ec)
(1:1 mixture of two diastereoisomers): 1H NMR: d=1.24–
1.29 (m, 6H), 1.32 (s, 3H), 1.35 (s, 3H), 1.33–1.51 (m, 2H),
1.59–1.84 (m, 2H), 2.06–2.12 (m, 4H), 2.14 (s, 3H), 2.15 (s,
3H), 2.18–2.28 (m, 4H), 2.39–2.43 (m, 3H), 2.58–2.62 (m,
3H), 4.15–4.24 (m, 4H); 13C NMR; d=13.80, 14.90, 14.97,
24.57, 24.69, 26.12, 26.27, 26.36, 26.75, 40.88, 41.48, 41.63,
42.80, 43.27, 61.32, 62.51, 171.03, 171.28, 203.88, 209.89.
General Remarks
Constant current electrolyses were performed under an
argon atmosphere, using an Amel Model 552 potentiostat
equipped with an Amel Model 572 integrator. Unless other-
wise indicated, all the experiments were carried out in a di-
vided glass cell separated through a porous glass plug filled
up with a layer of agar gel (i.e., methyl cellulose 0.5% vol
dissolved in DMF-Et4NClO4 1.0 mol dmÀ3); Pt spirals (ap-
parent areas 0.8 cm2) were used both as cathode and anode.
Starting materials (1,3-dicarbonyl compounds or rather ni-
tromethane and nitroethane) were used both as catholyte
and anolyte.
Starting materials and all the others materials were pur-
chased from Aldrich or Fluka and used without any further
purification. Purification of the products were performed by
flash chromatography column (silica gel, Merck). The IR
spectra were recorded on an FT-IR instrument (Bruker
Vector 22). The NMR spectra (Bruker DRX 400; 1H
400 MHz; 13C 100 MHz) were recorded as CDCl3 solutions
and referenced to residual CHCl3 [7.26 ppm (1H); 77.23 ppm
(13C)]. Chemical shifts are reported in ppm, multiplicities
are indicated by s (singlet); brs (broad singlet); d (doublet);
dd (double doublet); t (triplet); q (quartet); m (multiplet).
Coupling constants, J, are reported in Hz.
Ethyl
2-Oxo-1-(3-oxopentyl)cyclohexanecarboxylate
1
(3fa): H NMR: d=1.03 (t, 3H, J=8.0 Hz), 1.27 (t, 3H, J=
6.8 Hz), 1.46–2.10 (m, 10H), 2.32–2.55 (m, 4H), 4.20 (q, 2H,
J=6.8 Hz); 13C NMR: d=7.41, 13.91, 22.01, 27.14, 28.05,
35.43, 36.19, 36.96, 40.61, 59.59, 60.93, 171.58, 207.43, 209.90.
Ethyl 2-Oxo-1-(3-oxopentyl)cyclohexanecarboxylate (3fc)
(1:1 mixture of two diastereoisomers): 1H NMR: d=1.29
(m, 3H), series of multiplets between 1.5–2.6 (17H), 4.2–4.6
(m, 2H); 13C NMR: d=13.47, 20.21, 21.83, 22.04, 24.28,
25.81, 26.44, 26.64, 31.17, 32.78, 40.50, 40.77, 42.26, 42.66,
59.52, 60.64, 62.50, 62.72, 169.82, 170.12, 205.35, 205.34,
209.67.
General Procedure for Electrochemically-Promoted
Addition Reactions of 1a–d to Michael Acceptors
2a–f
Diethyl 2-Methyl-3-oxo-2-(3-oxopenthyl)succinate (3ga):
1H NMR: d=0.94 (t, 3H, J=11.8 Hz), 1.19 (t, 3H, J=
11.2 Hz), 1.28 (t, 3H, J=11.4 Hz), 1.34 (s, 3H), 2.05–2.15
(m, 2H), 2.25–2.45 (m, 2H), 4.07 (q, 2H, J=11.2 Hz), 4.22
(q, 2H, J=11.4 Hz); 13C NMR: d=6.81; 13.04 (2C), 18.79,
27.76, 34.83, 35.70, 54.63, 60.61, 61.63, 159.44, 170.74, 190.44,
208.41.
Pure 1, 5 mL, was electrolysed under galvanostatic control
(I=5 mAcmÀ2, Q=0.3 F, terminal voltage for 1b=110 V) at
room temperature. At the end of the electrolysis, the Mi-
chael acceptor 2 (3 mmol) was added to the cathode com-
partment and the reaction prolonged for the time reported
in Table 2. Surplus starting materials was distilled under
vacuum at room temperature and recovered for recycling in
a glass trap cooled at À788C. Crude mixtures yielded pure
adducts 3 (3ba: 0.53 g; 3ca: 0.50 g; 3da: 0.60 g; 3db: 0.73 g;
3dc: 0.68 g; 3dd: 0.42 g; 3de: 0.40 g, 3df: 0.80 g) after simple
filtration over silica gel. The isolated products 3da,[13a]
3db,[13b] 3dc,[13c] 3dd,[13d] 3de[13e] and 3df[13f] gave spectral and
analytical data in accordance with those reported in the lit-
erature.
General Procedure for Electrochemically-Promoted
Nitroaldol Reactions of Nitromethane to Aldehydes 5
Pure nitromethane, 5 mL, was electrolysed under galvano-
static control (I=10 mAcmÀ2, Q=0.3 F) at 08C. At the end
of the electrolysis, the aldehyde 5 (3 mmol) was added to
the cathode compartment and the reaction prolonged, at
room temperature, for the time reported in Table 4. Surplus
nitromethane was evaporate under vacuum and the residue
purified by flash chromatography to afford pure product 6
(6a: 0.47 g, 6b: 0.47 g, 6c: 0.35 g, 6d: 0.29 g). The isolated
1
Ethyl 2-Acetyl-5-oxoheptanoate (3ba): H NMR: d=0.99
(t, 3H, J=7.1 Hz), 1.22 (t, 3H, J=7.0 Hz), 2.01–2.08 (m,
2H), 2.2 (s, 3H), 2.36 (q, 2H, J=7.4 Hz), 2.43 (q, 2H, J=
1946
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2006, 348, 1942 – 1947