3860 J. Am. Chem. Soc., Vol. 118, No. 16, 1996
Qiao et al.
(CN), 125.4 (C2), 134.8 (C3), 165.4 (CdO); GC-MS (tR ) 6.8 min)
m/z 125 (M+, 2), 94 (33), 81 (27), 66 (100), 59 (93), 55 (71).
pyrolyzed at 630 °C with Ar as the carrier gas: IR (Ar, BaF2, 12 K)
3731.4 w (MeOH), 2145 vs, 1508 vw, 1420 vw, 1377 w, 1361 vw
(MeOH), 1332 vw, 1264.5 vw, 1177 vw, 1053 vw, 1035 w (MeOH),
Isomerization of Dipyrrolo[1,2-a:1′,2′-d]pyrazine-5,10-dione (3)
to 1H-Dipyrrolo[1,2-a:2′,3′-d]pyridine-5,9-dione (15) and 6H-Dipyr-
rolo[1,2-a:3′,2′-d]pyridine-5,9-dione (16). A 0.5 g (2.7 mmol) sample
of 3 was pyrolyzed at 850-900 °C in the course of 6 h, giving rise to
four new dimers, named A, B, C, and D. A and B were identified as
15 and 16 (or 16 and 15); C and D were identified as 17 and 18,
respectively. The four dimers were separated initially by flash
chromatography (SiO2/ethyl acetate-CH2Cl2, 1:1), giving a first fraction
containing unchanged 3 (0.44 g, 88%). The second fraction (0.05 g,
10%; mp 198 °C) was a mixture of dimers A and B (ratio 1.2-1.6 in
different experiments). The third fraction was a mixture of dimers C
and D (ca. 0.1% yield). Repeated flash chromatography (five times)
resulted in (i) a fraction containing A and B, enriched in A, (ii) almost
1013.7 vw, 906.3 w, 877 vw cm-1
.
(c) From Pyrrole-2-carboxylic Acid Chloride24a (1c). 1c was
sublimed (10-6 mbar) at 40 °C and pyrolyzed at 650 °C with Ar as the
carrier gas: IR (Ar, KBr, 12 K) 2864.5/2859.6 m (HCl), 2145.5 vs,
1507 vw, 1419.5 vw, 1377 w, 1333 vw, 1264.7 vw, 1177.5 vw, 1067
vw, 1014 vw, 907 w, 877 vw, 738.5 w, 575.5 vw, 518 vw cm-1
.
(Cyanovinyl)ketenes 6 and 7. (a) Pyrrole-2-carboxylic acid (1a)
or its methyl ester (1b) was pyrolyzed at 1010 °C with N2, and the
(cyanovinyl)ketenes 6 and 7 were isolated as a mixture in the matrix:
IR (N2, 12 K) 2234 w, 2141.8 vs, 2139.3 vs, 2134.7 vs, 1596.5 m,
1421.4 w, 1338 w, 962.5 w cm-1
. (b) Pyrrole-2-carboxylic acid
chloride (1c) at 850 °C gave (cyanovinyl)ketenes 6 and 7: IR (Ar, 12
K): 2226 vw, 2134 vs, 1593 m, 1419 w, 1339 w, 918.7 w cm-1. (c)
A mixture of compounds 8, 9, and 10 generated by photolysis of 11
was pyrolyzed at 850 °C: IR (Ar, 12 K) 2230 broad (CN), 2132 vs
pure B, (iii) a fraction enriched in C, and (iv) pure D. The 1H and 13
C
NMR spectra of A-D are given in the supporting information.
1
Data for Dimer A: H NMR (DMSO-d6) δ 6.42 (dd, J ) 3.5 Hz,
1H), 6.76 (dd, JNH ) 2.6 Hz, J ) 2.7 Hz, 1H), 7.11 (dd, J ) 3.8 Hz,
J ) 1.8 Hz, 1H), 7.32 (dd, JNH ) 2.6 Hz, J ) 2.7 Hz, 1H), 7.69 (dd,
J ) 3.1 Hz, J ) 1.5 Hz, 1H), 13.6 (br s, 1H, NH, exchanging with
D2O), NH couplings were confirmed by exchange with D2O; 13C NMR
(DMSO-d6) δ 109.9, 113.4, 119.3, 121.2, 123.5, 127.3, 131.3, 132.7,
156.3, 166.1.
(CdCdO) cm-1
.
Method B: Pulsed Pyrolysis (PP). 2-Carbonyl-2H-pyrrole (2) was
generated by PP of 1b at 1000 °C: IR (Ar, 12 K) 2144 vs, 1377.8 w,
908 w, 737 w cm-1. (Cyanovinyl)ketenes 6 and 7 were generated by
PP at 1400 °C: IR (Ar, 12 K) 2226 vw, 2135 vs, 1593 m, 1419 w,
1339 w, 919 vw, 857 w 653 vw, 649 vw cm-1
.
1
Preparative FVP of Indole-2-carboxylic Acid (19) and Its Methyl
Ester (20). Diindolo[1,2-a:1′,2′-d]pyrazine-8,16-dione (21). Methyl
indole-2-carboxylate (20) (0.4 g, 2.29 mmol) was sublimed at 60 °C
and pyrolyzed in the 32 cm oven at 700 °C. The dimer 21 (33 mg,
10%) condensed on the glassware immediately outside the oven and
had properties identical with those of sample prepared according to
Data for Dimer B: H NMR (DMSO-d6) δ 6.42 (dd, J ) 3.5 Hz,
J ) 3.2 Hz, 1H), 6.76 (dd, JNH ) 2.6 Hz, J ) 2.7 Hz, 1H), 7.09 (dd,
J ) 3.6 Hz, J ) 1.5 Hz, 1H), 7.32 (dd, JNH ) 2.6 Hz, J ) 2.7 Hz, 1H),
7.66 (dd, J ) 3.0 Hz, J ) 1.5 Hz, 1H), 13.17 (br s, 1H, NH, exchanging
with D2O), NH couplings were confirmed by collapse on exchange
with D2O; 13C NMR (DMSO-d6) δ 107.9, 113.6, 119.4, 122.8, 126.8,
127.8, 128.4, 132.0, 152.0, 171.6; HRMS calcd for C10H6N2O2 m/z
186.04290, found 186.0428.
1
Ciamician:39 mp 325-327 °C; H NMR (DMSO-d6) δ 7.44 (t, J )
7.48 Hz, 1H), 7.61 (t, J ) 7.69 Hz, 1H), 7.83 (s, 1H), 7.87 (d, J )
7.49 Hz, 1H), 8.46 (d, J ) 8.3 Hz, 1H); IR (KBr) 1701 vs, 1583 w,
1560 s, 1451 m, 1368 vs, 1345.5 vs cm-1; GC-MS m/z 286 (M+,
100), 143 (47), 115 (45), 114 (21), 88 (12), 62 (8), 44 (6); HRMS
Data for Dimer C: 1H NMR (DMSO-d6) δ 7.68 (m, 1H), 7.85 (m,
1H), 12.7 (br s, 1H, NH, exchanging with D2O); 13C NMR (DMSO-
d6) δ 107.4, 125.1, 125.7, 132.9, 174.0.
12
calcd for C18H10N2O2 m/z 286.0754, found 286.0749. Crystal data:
1
Data for Dimer D: H NMR (DMSO-d6) δ 6.48 (d, J ) 2.6 Hz,
a light yellow crystal from DMSO was subjected to single-crystal X-ray
analysis at 298 K, C18H10N2O2, FW ) 286.28 g mol-1, space group
P21/c, a ) 5.805(3) Å, b ) 5.2000(6) Å, c ) 20.709(11) Å, â )
94.81(2)°, V ) 622.9 Å3, Z ) 2, Qcalc ) 1.526 mg/m3, µ(Mo KR) )
0.102 mm-1, number of unique reflections 1090, number of reflections
with I > 2σI ) 435, R ) 0.0598, wR2 ) 0.1408. The full data are
presented in the supporting information.
1H), 7.09 (d, J ) 2.6 Hz, 1H), 12.6 (s, 1H, NH, exchanging with D2O);
13C NMR (DMSO-d6) δ 107.8, 125.5, 127.3, 131.9, 168.3, 179.3; UV
(EtOH) λmax 288, 322, 459 nm; HRMS calcd for C10H6N2O2 m/z
186.04290, found 186.0428.
Photolysis of 6-Chloro-2-pyridone (11). Photolysis was conducted
according to the literature.15 A 200 mg sample of 6-chloro-2-pyridone
(11) was dissolved in 200 mL of absolute methanol in a quartz tube.
A high-pressure mercury lamp was used to photolyze the solution at
room temperature for 24 h until no starting material was left according
to monitoring by TLC. The solution was under nitrogen throughout
the course of photolysis. After reaction, the solvent was evaporated,
and the mixture was subjected to column chromatography (SiO2/ethyl
acetate). Two fractions were obtained. The first fraction (140 mg)
was a mixture of compounds 8, 9, and 10 in the ratio 14:15:13 (by 1H
NMR integration). Fraction 2 contained 54 mg of 2-methoxy-6-
pyridone:38 1H NMR (acetone-d6) δ 4.30 (s, 3H, CH3), 6.65 (d, J )
7.8 Hz, 1H, CH), 6.70 (d, J ) 8.1 Hz, 1H, CH), 8.02 (t, J ) 7.94 Hz,
1H, CH); 13C NMR (acetone-d6) δ 54.0 (OCH3), 98.2 (CH), 102.7 (CH),
142.6 (CH), 163.2 (C), 163.7 (C); IR (KBr) 1668 s, 1613 s, 1468 m,
1409 m, 1376 m, 1279 m, 1164 m, 1071 m 937 w, 770 w, 551 m
cm-1; GC-MS m/z 125 (M+, 98), 124 (75), 96 (43), 95 (45), 82 (85),
67 (40), 55 (35), 39 (100).
Matrix Isolation of 2-Carbonyl-2H-pyrrole (2) and Cyanovinyl
Ketenes 6 and 7. Method A: FlashVacuum Pyrolysis (FVP).
2-Carbonyl-2H-pyrrole (2). (a) From Pyrrole-2-carboxylic Acid
(1a). Pyrrole 2-carboxylic acid (1a) was pyrolyzed at 690 °C with N2
as the carrier gas. The pyrolyzed product was trapped on a BaF2
window (12 K) and assigned as 2-carbonyl-2H-pyrrole (2): IR (N2
matrix, 12 K) 2148 vs, 1509 vw, 1418 vw, 1376.5 w, 1333.5 vw, 1264
vw, 1179 vw, 1065.4 vw, 1014 vw, 908 w, 879 vw cm-1; UV (N2
matrix, 12 K) λmax 266 nm.
The same compound was obtained in similar yield on pyrolysis of
indole-2-carboxylic acid (19) at 600-850 °C.
Methyl (2-Cyanophenyl)acetate (23). Methyl indole-2-carboxylate
(20) (0.30 g, 1.71 mmol) was pyrolyzed in the 32 cm oven at 700 °C.
The volatile product was cocondensed with MeOH on a cold finger at
77 K, MeOH being introduced through a needle valve between the
oven exit and the cold finger. The resulting methanol solution was
concentrated and subjected to Kugelrohr distillation, giving 210 mg
(70%) of nitrile 23. This compound is known,40 but no spectral data
have been reported. The identity of the pyrolysis product with a sample
prepared according to Halford and Weissmann40a was established by
spectral comparison: 1H NMR (CDCl3) δ 7.31 (td, J ) 7.5 Hz, J ) 1
Hz, 1H, H-C4), 7.34 (d, J ) 7.8 Hz, 1H, H-C6), 7.49 (td, J ) 7.8 Hz,
J ) 1.3 Hz, 1H, H-C5), 7.59 (dd, J ) 7.5 Hz, J ) 0.8 Hz, 1H, H-C3);
13C NMR (CDCl3) δ 39.16 (td, CH2), 52.24 (q, CH3), 113.38 (m, C2),
127.74 (dd, C4), 130.56 (dq, C6), 132.70 (dd, C3), 132.81 (dd, C5),
1
137.49 (pent, C1), 170.02 (t, CO); the H and 13C NMR spectra were
correlated by a 2D (COLOG) spectrum; IR (film on KBr) 2955 m,
2227 s, 1742 s, 1490 m, 1437 s, 1343 s, 1227 s, 1167 s 760 s cm-1
HRMS calcd for C10H9NO2 175.0633, found 175.0634.
;
12
23 was also formed in 24% yield when no additional methanol was
used for trapping. 23 was formed in 50-52% yield by FVP of indole-
2-carboxylic acid (19) at 850 °C with trapping of the product in a MeOH
matrix at 77 K.
In experiments with both 19 and 20, without added methanol, a
polymer of (2-cyanophenyl)ketene (27) was formed. When the
(b) From Methyl Pyrrole-2-carboxylate (1b). Methyl pyrrole-2-
carboxylate (1b) was sublimed (10-6 mbar) at room temperature and
(39) Ciamician, G. L.; Zatti, C. Ber. Dtsch. Chem. Ges. 1888, 21, 1929.
(40) (a) Halford, J. O., Weissmann, B. J. Org. Chem. 1953, 18, 30. (b)
Arsenijevic, L.; Arsenijevic, V. Bull. Soc. Chim. Fr. 1968, 3403.
(38) Katritzky, A. R.; Popp, F. D.; Rowe, J. D. J. Chem. Soc. B 1966,
562.