Electrochemical Reduction of Substituted n-Alkyl Esters
J . Org. Chem., Vol. 62, No. 6, 1997 1787
77%). Spectroscopic data were identical to those of an
authentic sample.
Red u ction of p r op yl p yr id in e-4-ca r boxyla te (0.095 g,
0.58 mmol) produced methyl pyridine-4-carboxylate (0.073 g,
92%). Spectroscopic data were identical to those of an
authentic sample.
90% as estimated by NMR). The low yields are, in part, a
reflection of the difficulties in purification due to the very
similar Rf values. TLC and NMR experiments indicated there
were two other products present with peaks in the aromatic
region in low yield (ca. 5% each).
2f: oil; Rf 0.66 [ether/petroleum spirits (60-90 °C) 1:1]; IR
1
Redu ction of dipr opyl pyr idin e-2,3-dicar boxylate (0.100
g, 0.40 mmol) produced methyl propyl pyridine-2,3-dicarboxy-
late (and propyl methyl pyridine-2,3-dicarboxylate) (0.080 g,
90%): oil; Rf 0.16 [ether/petroleum spirits (60-90 °C) 1:1]; IR
(KBr) 1662 (OCdO), 1726 (SCdO) cm-1; H NMR [(CD3)2SO]
δ 0.85-0.94 (m, 6H), 1.51-1.66 (m, 4H), 2.91-3.05 (m, 4H),
3.81 (s, 3H), 4.43 (s, 2H) 7.36-7.42 (m, 2H), 7.49 (d, J ) 8.1
Hz, 1H), 7.70-7.73 (m, 2H), 8.00 (dd, J ) 1.97, 8.0 Hz, 1H),
8.32 (d, J ) 1.96 Hz, 1H); 13C NMR [(CD3)2SO] δ 13.18, 22.49,
22.55, 30.36, 30.51, 38.38, 52.50, 124.89, 126.82, 128.81,
129.24, 130.21, 130.43, 132.63, 134.15, 135.05, 136.87, 141.15,
146.72, 166.53, 190.17, 191.17; EIMS m/z 430 (M+, 2), 355
(100), 322, 165, 140, 47, 430 calcd for C23H26O4S2.
2g: oil; Rf 0.50 [ether/petroleum spirits (60-90 °C) 1:1]; IR
(KBr) 1661 (OCdO), 1778 (SCdO); EIMS m/z 428 (M+, 1), 353
(100), 35, 249, 146, 76, 47, 428 calcd for C23H24O4S2. Although
this compound was not isolated in pure form, the close
similarity in the NMR and IR data to compound 1c strongly
support the structure assigned (see the Supporting Informa-
tion for spectra).
1
(KBr) 1735 (OCdO) cm-1; H NMR (CDCl3) δ 0.89-0.94 (m,
3H), 1.66-1.76 (m, 2H), 3.83 and 3.90 (s, 3H), 4.20 and 4.28
(t, J ) 6.7 Hz, 2H), 7.40 (dd, J ) 4.8, 7.9 Hz, 1H), 8.10 (dd, J
) 1.7, 7.9 Hz, 1H), 8.67 (dd, J ) 1.6, 4.8 Hz, 1H); 13C NMR
(CDCl3) δ10.22, 21.72, 52.73, 52.89, 67.61, 67.73, 124.62,
124.80, 125.86, 126.43, 137.54, 151.206, 151.59, 151.726,
165.54, 166.27.
Redu ction of dipr opyl pyr idin e-2,4-dicar boxylate (0.111
g, 0.44 mmol) produced methyl propyl pyridine-2,4-dicarboxy-
late (or propyl methyl pyridine-2,4-dicarboxylate) (0.083 g,
85%): oil; Rf 0.16 [ether/petroleum spirits (60-90 °C) 1:1]; IR
1
(KBr) 1737 (OCdO) cm-1; H NMR (CDCl3) δ 0.93 (t, J ) 7.4
Hz, 3H), 1.73-1.80 (m, 2H), 3.90 (s, 3H), 4.28 (t, J ) 6.8 Hz),
7.93 (dd, J ) 1.7, 5.0 Hz, 1H), 8.52 (s, 1H), 8.82 (d, J ) 4.7 Hz,
1H); 13C NMR (CDCl3) δ 10.24, 21.89, 52.84, 67.63, 124.49,
125.80, 138.56, 149.23, 150.63, 164.39, 164.66.
Red u ction of S,S-d ip r op yl p yr id in e-2,5-d ica r both ioa te
(0.124 g, 0.44 mmol) produced methyl-2-[(propylthio)carbonyl]-
pyridine-5-carboxylate (3b) (0.086 g, 82%) and methyl 5-[(pro-
pylthio)carbonyl]pyridine-2-carboxylate (3c) (0.011 g, 10%).
3b: mp 46-47 °C (ether); Rf 0.55 [ether/petroleum spirits
(60-90 °C) 1:1]; IR (KBr) 1666 (OCdO), 1724 (SCdO); 1H
NMR (CDCl3) δ 1.00 (t, J ) 7.3 Hz, 3H), 1.65-1.73 (m, 2H),
3.07 (t, J ) 7.2 Hz, 2H), 3.99 (s, 3H), 8.17 (d, J 8.1 Hz, 1H),
8.31 (dd, J ) 2.2, 8.2 Hz, 1H), 9.20 (d, J 1.8 Hz, 1H); 13C NMR
(CDCl3) δ 13.32, 22.66, 31.21, 53.17, 124.87, 134.85, 135.60,
148.23, 150.79, 164.74, 189.58; EIMS m/z 239 (M+, 1), 211,
164, 136 (100), 92, 77, 59, 239 calcd for C11H13NO3S.
3c: mp 42-44 °C (ether); Rf 0.30 [ether/petroleum spirits
(60-90 °C) 1:1]; IR (KBr) 1661 (OCdO), 1721 (SCdO); 1H
NMR (CDCl3) δ 1.01 (t, J ) 7.4 Hz, 3H), 1.65-1.72 (m, 2H),
3.01 (t, J ) 7.1 Hz, 2H), 3.95 (s, 3H), 7.99 (dd, J ) 0.7, 7.7 Hz,
1H), 8.40 (dd, J ) 2.1, 8.2 Hz, 1H), 9.21 (s, 1H); 13C NMR
(CDCl3) δ 13.45, 22.57, 30.76, 52.71, 119.77, 129.13, 138.44,
150.16, 154.45, 164.79, 189.54, 192.88; EIMS m/z 239 (M+, 1),
164 (100), 136, 106, 78, 59, 239 calcd for C11H13NO3S.
Red u ction of S,S-d ip r op yl ben zen e-1,4-d ica r both ioa te
(0.114 g, 0.40 mmol) produced methyl-4-[(propylthio)carbonyl]-
pyridine-1-carboxylate (4b) (0.081 g, 85%): oil; Rf 0.59 [ether/
petroleum spirits (60-90 °C) 1:1]; IR (KBr) 1665 (OCdO), 1729
(SCdO); 1H NMR (CDCl3) δ 1.00 (t, J ) 7.4 Hz, 3H), 1.68 (m,
2H), 3.04 (t, J ) 7.1 Hz, 4H), 3.90 (s, 3H) 7.97 (dd, J ) 1.9, 6.9
Hz, 2H), 8.06 (dd, J ) 1.59, 6.6 Hz, 2H); 13C NMR (CDCl3) δ
13.35, 22.78, 31.088, 52.37, 127.02, 129.73, 133.93, 140.46,
166.06, 191.47.
Red u ction of d ip r op yl p yr id in e-2,5-d ica r boxyla te (1.5
g, 6.0 mmol) produced methyl propyl pyridine-2,5-dicarboxy-
late (and propyl methyl pyridine-2,5-dicarboxylate) (1.25 g,
93%): oil; Rf 0.25 [ether/petroleum spirits (60-90 °C) 1:1]; IR
(KBr) 1737, 1718 (OCdO) cm-1; 1H NMR (CDCl3) δ 0.90-0.98
(m, 3H), 1.71-1.81 (m, 2H), 3.90 and 3.95 (s, 3H), 4.26 and
4.31 (t, J ) 6.6 Hz, 2H), 8.10-8.14 (m, 1H), 8.34-8.39 (m, 1H),
9.23 (s, 1H); 13C NMR (CDCl3) δ 10.26, 21.88, 52.64, 53.08,
67.32, 67.75, 124.50, 128.33, 128.84, 138.15, 150.64, 150.68,
151.07, 164.30, 164.79. Unmethylated product was further
reduced at -2.35 V (vs Ag/Ag+) to form (after methylation)
dimethyl pyridine-2,5-dicarboxylate (1.00 g, 85%). Analytical
and spectral data obtained were identical to those of an
authentic sample.
Redu ction of dipr opyl pyr idin e-3,4-dicar boxylate (0.105
g, 0.42 mmol) produced methyl propyl pyridine-3,4-dicarboxy-
late (and propyl methyl pyridine-3,4-dicarboxylate) (0.082 g,
88%): oil; Rf 0.22 [ether/petroleum spirits (60-90 °C) 1:1]; IR
1
(KBr) 1740 (OCdO) cm-1; H NMR (CDCl3) δ 0.89-0.95 (m,
3H), 1.65-1.73 (m, 2H), 3.86 (s, 3H), 4.20-4.24 (m, 2H) 7.40-
7.44 (m, 1H), 8.74 (d, J ) 4.8 Hz, 1H), 8.97 and 9.00 (s, 1H);
13C NMR (CDCl3) δC 10.25, 21.77, 52.73, 52.93, 67.56, 67.85,
121.67, 121.76, 125.17, 140.24, 140.42, 150.26, 150.39, 152.67,
165.04, 165.56, 166.16, 166.67.
Redu ction of dipr opyl pyr idin e-3,5-dicar boxylate (0.103
g, 0.41 mmol) produced methyl propyl pyridine-3,5-dicarboxy-
late (0.027 g, 30%): mp 41-43 °C [petroleum spirits (60-90
°C)]; Rf 0.30 [ether/petroleum spirits (60-90 °C) 1:1]; IR (KBr)
Ack n ow led gm en t. The authors gratefully thank M.
Sadek and P. Floria for discussion of NMR data and for
assistance in acquiring 13C INEPT spectra.
1729 (OCdO) cm-1 1H NMR (CDCl3) δ 0.96 (t, J ) 7.4 Hz,
;
3H), 1.80 (m, 2H), 3.91 (s, 3H), 4.27 (t, J ) 6.7 Hz, 2H), 8.77
(t, J ) 2.0 Hz, 1H), 9.34 (s, 2H); 13C NMR (CDCl3) δ 10.31,
21.89, 52.55, 67.23, 125.85, 126.2, 137.81, 153.95, 154.05,
164.32, 164.81.
Su p p or t in g In for m a t ion Ava ila b le: 1H and 13C NMR
(including in some cases INEPT or DEPT) spectra of all new
products of the reductions and spectral data of starting esters
(34 pages). This material is contained in libraries on micro-
fiche, immediately follows this article in the microfilm version
of the journal, and can be ordered from the ACS; see any
current masthead page for ordering information.
Red u ction of S,S-d ip r op yl ben zen e-1,3-d ica r both ioa te
(1.50 g, 5.3 mmol) produced 2f (0.68 g, 30%), 2g [0.23 g, 10%
(not pure)], and one compound in high yield (ca. 20% weight
of starting material) that was not identified. The compounds
were isolated as oils. These compounds account for a high
percentage of the total aromatic products of this reaction (70-
J O961492U