Reaction of N-Vinylic Phosphazenes with R,â-Unsaturated Aldehydes
Ethyl 6-Methyl-3-pyridinecarboxylate (7d). The general pro-
cedure was followed using crotonaldehyde 2d (0.246 mL, 3 mmol).
The crude oil was chromatographed on silica gel (10:1 hexane/
AcOEt) to give 0.153 g (31%) of 7d as a yellow oil (Rf ) 0.30,
hexane/AcOEt 2:1): 1H NMR (300 MHz, CDCl3) δ 1.31 (t, 3J(H,H)
Calcd for C15H15NO2: C, 74.67; H, 6.27; N, 5.81. Found: C, 74.75;
H, 6.25; N, 5.80.
Preparation of a Mixture of Pyridines 7b and 7′a from
3-Azatriene 11b. Cinnamaldehyde 2b (0.378 mL, 3 mmol) and
crotonaldehyde 2d (0.250 mL, 3 mmol) were added to a 0-10 °C
solution of 3-azatriene 11b (3 mmol) in CHCl3 (10 mL) under N2,
3
) 7.1 Hz, 3H), 2.56 (s, 3H), 4.30 (q, J(H,H) ) 7.1 Hz, 2H), 7.17
3
3
1
(d, J(H,H) ) 8.1 Hz, 1H), 8.11 (d, J(H,H) ) 8.1 Hz, 1H), 9.04 (s,
1H); 13C NMR (75 MHz, CDCl3) δ 14.1, 24.5, 61.0, 122.7, 123.4,
137.0, 150.2, 162.8, 165.2; IR (NaCl) 1730; MS (EI) m/z 165 (M+,
93). Anal. Calcd for C9H11NO2: C, 65.44; H, 6.71; N, 8.48.
Found: C, 65.48; H, 6.69; N, 8.47.
and the mixture was stirred at 60 °C during 50 h until H NMR
indicated the disappearance of 3-azatriene. Evaporation of solvent
under reduced pressure afforded an oil that was chromatographed
on silica gel to give the compounds 7b and 7′a (10:1 hexane/
AcOEt).
Ethyl 6-Phenyl-3-pyridinecarboxylate (7b). A 0.102 g (15%)
portion of 7b was obtained as a brown oil (see the spectroscopic
data in the Supporting Information).
Ethyl 6-Methyl-3-pyridinecarboxylate (7′a). A 0.149 g (30%)
portion of 7′a were obtained as a yellow oil (see the spectroscopic
data for the pyridine 7d).
General Procedure the Preparation of Pyridines 7′. The excess
of unsaturated aldehyde 2, used for the preparation of the 3-azatriene
11 (3 mmol), was eliminated by reduced pressure from the mixture,
and then 10 mL of CHCl3 and 3 mmol of a different aldehyde 2
were added to a 0-10 °C solution of azatriene 11. The mixture
was stirred at 60 or 90 °C until 1H NMR indicated the disappearance
of 3-azatriene. Evaporation of solvent under reduced pressure
afforded an oil that was chromatographed on silica gel to give the
compounds 7′.
General Procedure A for the Preparation of 3-Azatrienes 11.
Unsaturated aldehyde 2 (4 mmol) was added to a 0-10 °C solution
of phosphazene 6 (4 mmol) in CHCl3 (10 mL) under N2, and the
mixture was stirred at room temperature or warmed at 60 °C until
1H NMR indicated the disappearance of phosphazene. 3-Azatrienes
11 are unstable during distillation and/or chromatography and were
used without purification for the following reactions.
General Procedure B for the Preparation of 3-Azatrienes 11.
Unsaturated aldehyde 2 (4 mmol) was added to a 0-10 °C solution
of phosphazene 6 (4 mmol), prepared “in situ” in CHCl3 (10 mL)
under N2, and the mixture was stirred at room temperature until
1H NMR indicated the disappearance of phosphazene. 3-Azatrienes
11 are unstable during distillation and/or chromatography and were
used without purification for the following reactions.
1-Ethoxycarbonyl-3-azahepta-1,3,5-triene (11d). General pro-
cedure A was followed using phosphazene 6a (1.252 g, 4 mmol)
and crotonaldehyde 2d (0.328 mL, 4 mmol) (room temperature/24
h): 1H NMR (300 MHz, CDCl3) of crude reaction mixture (11d +
Ph2MePO) δ 1.23 (t, 3J(H,H) ) 7.2 Hz, 3H), 1.92 (dd, 4J(H,H) ) 1.2
Hz, 3J(H,H) ) 6.7 Hz, 3H), 1.96 (d, 3J(H,H) ) 13.0 Hz, 3H), 4.15 (q,
Ethyl 2-Phenyl-3-pyridinecarboxylate (7′d). The general pro-
cedure was following using 3-azatriene 11f and acrolein 2a (0.201
mL, 3 mmol), and the mixture was stirred at 90 °C for 36 h.
Evaporation of solvent under reduced pressure afforded an oil which
was chromatographed on silica gel (20:1 hexane/AcOEt) to give
0.552 g (81%) of 7′d as a yellow oil (Rf ) 0.43, hexane/AcOEt
2:1): 1H NMR (300 MHz, CDCl3) δ 0.96 (t, 3J(H,H) ) 7.2 Hz, 3H),
3
3J(H,H) ) 7.2 Hz, 2H), 6.00 (d, J(H,H) ) 13.1 Hz, 1H), 6.33 (ddd,
4J(H,H) ) 1.2 Hz, 3J(H,H) ) 15.3 Hz, 3J(H,H) ) 9.0 Hz, 1H), 6.48 (dq,
3J(H,H) ) 6.7 Hz, 3J(H,H) ) 15.3 Hz, 1H), 7.36-7.74 (m, 11H), 7.95
3
3
3
4.07 (q, J(H,H) ) 7.2 Hz, 2H), 7.24 (dd, J(H,H) ) 4.7 Hz, JHH
)
7.8 Hz, 1H), 7.32-7.50 (m, 5H), 8.02 (dd, 3J(H,H) ) 7.8 Hz, 4J(H,H)
3
(d, J(H,H) ) 9.0 Hz, 1H); 13C NMR (75 MHz, CDCl3) of crude
3
4
) 1.7 Hz, 1H), 8.68 (dd, J(H,H) ) 4.7 Hz, J(H,H) ) 1.7 Hz, 1H);
13C NMR (75 MHz, CDCl3) δ 13.5, 61.3, 121.4, 127.3, 127.7-
128.4, 137.6, 140.1, 151.0, 158.7, 167.9; IR (NaCl) 1720; M/S (EI)
m/z 227 (M+, 10). Anal. Calcd for C14H13NO2: C, 73.99; H, 5.77;
N, 6.16. Found: C, 74.05; H, 5.76; N, 6.16.
1
reaction mixture (11d + Ph2MePO) δ 14.0, 16.5 (d, J(P,C) ) 74
Hz), 18.8, 60.0, 117.8, 128.3-134.5, 147.4, 153.7, 155.5, 166.8,
169.4. General procedure B was followed using phosphazene 6b
(4 mmol), prepared “in situ”, and 0.328 mL (4 mmol) of
crotonaldehyde 2d (room temperature/5 h): 1H NMR (300 MHz,
CDCl3) of crude reaction mixture (11d + Me3PO) δ 1.23 (t, 3J(H,H)
Reaction of Phosphazene 6k and Cinnamaldehyde 2b. Cin-
namaldehyde 2b (0.378 mL, 3 mmol) was added to a 0-10 °C
solution of phosphazene 6k, prepared “in situ” (3 mmol), in CHCl3
(10 mL). The mixture was stirred at 60 °C during 2 h. Evaporation
of solvent under reduced pressure afforded an oil that was
chromatographed (5:1 hexane/AcOEt) to give compounds 7h and
13.
) 7.2 Hz, 3H), 1.47 (d, 2J(P,H) ) 12.8 Hz, 9H), 1.92 (dd, 4J(H,H)
)
3
3
1.2 Hz, J(H,H) ) 6.7 Hz, 3H), 4.15 (q, J(H,H) ) 7.2 Hz, 2H), 6.00
3
4
3
(d, J(H,H) ) 13.1 Hz, 1H), 6.33 (ddd, J(H,H) ) 1.2 Hz, J(H,H)
15.3 Hz, 3J(H,H) ) 9.0 Hz, 1H), 6.48 (dq, 3J(H,H) ) 6.7 Hz, 3J(H,H)
)
)
15.3 Hz, 1H), 7.68 (d, 3J(H,H) ) 13.1 Hz), 7.95 (d, 3J(H,H) ) 9.0 Hz,
1H); 13C NMR (75 MHz, CDCl3) of crude reaction mixture (11d
+ Me3PO) δ 14.0, 17.8 (d, 1J(P,C) ) 70 Hz), 18.8, 60.0, 117.8, 147.4,
153.7, 155.5, 166.8, 169.4.
Methyl 2-Methyl-6-phenyl-3-pyridinecarboxylate (7h). A
0.219 g (30%) portion of 7h was obtained as a yellow oil (Rf )
0.55, hexane/AcOEt 2:1): 1H NMR (300 MHz, CDCl3) δ 2.85 (s,
3
General Procedure for the Preparation of Pyridines 7a-g
from 3-Azatrienes 11. The same unsaturated aldehyde 2 (3 mmol),
used for the preparation of 3-azatriene 11, was added to a 0-10
°C solution of 3-azatriene 11, prepared “in situ” in anhydrous CHCl3
(10 mL) under N2, and the mixture was stirred at 60 or 90 °C until
1H NMR indicated the disappearance of 3-azatriene 11. Evaporation
of solvent under reduced pressure afforded an oil that was
chromatographed on silica gel.
Ethyl 6-Methyl-2-phenyl-3-pyridinecarboxylate (7e). The
general procedure was followed using 3-azatriene 11e and cro-
tonaldehyde 2d (0.246 mL, 3 mmol). The mixture reaction was
stirred at 90 °C during 62 h. The crude oil was chromatographed
on silica gel (10:1 hexane/AcOEt) to give 0.398 g (55%) of 7e as
a brown oil (Rf ) 0.49, hexane/AcOEt 2:1): 1H NMR (300 MHz,
CDCl3) δ 0.94 (t, 3J(H,H) ) 7.2 Hz, 3H), 2.56 (s, 3H), 4.03 (q, 3J(H,H)
) 7.2 Hz, 2H), 7.10 (d, 3J(H,H) ) 7.9 Hz, 1H), 7.19-7.85 (m, 5H),
7.93 (d, 3J(H,H) ) 7.9 Hz, 1H); 13C NMR (75 MHz, CDCl3) δ 13.5,
24.6, 61.1, 121.1, 124.3, 126.0, 128.2, 128.4, 138.1, 140.5, 158.6,
160.6, 168.0; IR (NaCl) 1726; M/S (EI) m/z 241 (M+, 86). Anal.
3H), 3.86 (s, 3H), 7.35-7.51 (m, 3H), 7.56 (d, J(H,H) ) 8.3 Hz,
3
3
1H), 7.99 (d, J(H,H) ) 7.3 Hz, 2H), 8.19 (dd, J(H,H) ) 8.3 Hz,
3J(H,H) ) 1.8 Hz, 1H); 13C NMR (75 MHz, CDCl3) δ 25.2, 52.1,
117.3, 123.3, 127.3, 128.8, 129.7, 138.5, 139.3, 159.2, 160.1, 167.0;
IR (NaCl) 1723; M/S (EI) m/z 243 (M+, 15). Anal. Calcd for C14H13-
NO2: C, 73.99; H, 5.77; N, 6.16. Found: C, 74.02; H, 5.76; N,
6.15.
Dimethyl 2,6-Dimethyl-4-phenylethenyl-1,4-dihydro-3,5-pyr-
idinedicarboxylate (13). A 0.245 g (25%) portion of 13 was
obtained as a yellow solid: mp 169-170 °C (recrystallized from
AcOEt/hexane); 1H NMR (300 MHz, CDCl3) δ 2.27 (s, 6H), 3.66
(s, 6H), 4.54 (m, 1H), 5.59 (s, 1H), 6.10-6.17 (m, 2H), 7.09-
7.27 (m, 5H); 13C NMR (75 MHz, CDCl3) δ 19.5, 36.2, 51.1, 101.4,
126.3-131.7, 137.7, 145.1, 167.9; IR (KBr) 3334, 1698, 1649; M/S
(EI) m/z 327 (M+, 56). Anal. Calcd for C19H21NO4: C, 69.71; H,
6.47; N, 4.28. Found: C, 69.68; H, 6.49; N, 4.27.
Acknowledgment. We thank the Ministerio de Ciencia y
Tecnolog´ıa (MCYT, Madrid DGI, PPQ2003-0910), Ministerio
J. Org. Chem, Vol. 71, No. 16, 2006 6029