Acetylketene and Acetimidoylketene
J . Org. Chem., Vol. 62, No. 21, 1997 7119
reported below. For the reported results of the competition
reactions, the integrations of the two tautomers were com-
bined.
For preparative FP, a mixture of 6 and a single trapping
agent were mixed and pyrolyzed as above. The product
acetone was removed by rotary evaporation, and the residue
was subjected to flash chromatography on silica gel, using
hexane/ether/ethyl acetate (65:30:5) as the eluent.
Solu tion P yr olyses. The precursor (6 or 9a ) and re-
agent(s) were placed in a thick-walled glass tube. This was
filled with sufficient toluene so that there was minimal dead
space when the tube was flushed with nitrogen and sealed with
a Teflon “Ace-thread” plug.36 The tube was then heated in an
oil bath, behind a blast shield for the time and at the
temperature reported in Table 2. (Caution: There is a risk of
explosion when heating closed glass containers.) The tube was
cooled to room temperature, and the contents were directly
injected onto the GC for analysis. For preparative solution
pyrolyses, the excess solvent and/or trapping reagents were
removed by rotary evaporation. The residue was then sub-
jected to flash column chromatography on silica gel, as above.
For compounds 9 and 11, hexane/ethyl acetate (95:5) was used
as the eluent.
2-Hexyl-6-m eth yl-1,3-d ioxin -4-on e (8b). Excess heptanal
was removed by high-vacuum distillation prior to column
chromatography: 1H NMR δ 0.84 (t, 3H, J ) 6.7 Hz), 1.26 (br
s, 6H), 1.46 (m , 2H), 1.85 (m, 2H), 1.98 (s, 3H), 5.23 (s, 1H),
5.39 (t ,1H, J ) 5.0 Hz); 13C NMR δ 13.9, 19.3, 22.4, 22.7, 28.7,
31.5, 32.9, 95.8, 100.9, 162.8, 172.1.
3-(P r op yla m in o)-2-bu ten oic a cid , 1,1-d im eth yleth yl
ester (9a ): 1,1-Dimethylethyl 3-oxopropenonate (2.02 g, 0.013
m) and 1-propylamine (0.76 g, 0.013m) was absorbed on silica
gel (2 g) in an open beaker and irradiated in a commercial
microwave oven for 2 min.31 The product was removed from
the silica gel by filtering, using hexane/ethyl acetate (90:10)
as the wash solvent. After concentration, the product was
obtained by flash chromatography (hexane/ethyl acetate (95:
5) on silica gel): 1H NMR δ 0.93 (t, J ) 8.6 Hz, 3H), 1.44 (s,
9H), 1.54 (m, 2H), 1.86 (s, 3H), 3.11 (pseudo q, 2H), 4.43 (s,
1H) 8.46 (br s, 1H); 13C NMR 11.43, 19.34, 23.78, 28.67, 44.74,
51.51, 83.38, 161.27, 172.00. A small amount of the imine
tautomer was also observed in the spectra: 1H NMR δ 2.20
(s, 3H), 4.54 (s, 2H); 13C NMR 27.9, 30.5, 82.0. 9a :imine
1
tautomer 25:1 by H NMR.
3-(P r op yla m in o)-2-bu ten oic a cid , 1-m eth yleth yl ester
(9b): 1H NMR δ 0.94 (t, J ) 7.4 Hz, 3 H), 1.19 (d, J ) 6.2 Hz,
6 H), 1.54 (m, 2H), 1.86 (s, 3H), 3.13 (pseudo q, 2H), 4.37 (s,
1H), 4.95 (septet, J ) 6.2 Hz, 1 H), 8.55 (br s, 1H); 13C NMR
δ 11.36, 19.34, 22.22, 28.64, 44.71, 64.90, 82.19, 161.81, 170.23.
3-(P r op yla m in o)-2-bu ten oic a cid , bu tyl ester (9c): 1H
NMR δ 0.89 (m, 6 H), 1.32 (m, 2H), 1.55 (m, 4H), 1.85 (s, 3H),
3.10 (pseudo q, 2H), 4.37 (s, 1H), 8.52 (br s, 1H); 13C NMR δ
11.26, 13.68, 19.15, 19.26, 23.54, 31.04, 44.61, 62.11, 81.61,
161.81, 170.67.
3-(P r op yla m in o)-2-bu ten oic a cid , m eth yl ester (9d ): 1H
NMR δ 0.93 (t, J ) 7.4 Hz, 3 H), 1.54 (m, 2H), 1.88 (s, 3H),
3.13 (pseudo q, 2H), 3.58 (s, 3H), 4.39 (s, 1H), 8.53 (br s, 1H);
13C NMR δ 11.31, 19.33, 23.60, 44.70, 49.82, 81.29, 162.07,
170.93.
Con ver sion of 4d a n d 10 to 9c a n d 11. An ether solution
was prepared containing 0.0263 g (1.665 × 10-4 mol) of 4d
and 0.0367 g (2.566 × 10-4 mol) of 10. The initial molar ratio
was 0.649:1. Then 0.1103 g (1.869 × 10-3 mol) of 1-propyl-
amine was added and 9c and 11 were formed in a 0.653:1
molar ratio as determined by GC.
3-Oxo-2-bu ten oic a cid , 1-m eth yleth yl ester (4b): 1H
NMR δ 1.15 (d, 6H, J ) 6.3 Hz), 2.18 (s, 3H), 3.33 (s, 2H),
4.97 (heptet, 1H, J ) 6.3 Hz); 13C NMR δ 21.5, 29.9, 50.2, 68.7,
166.5, 200.6. En ol ta u tom er 3b: 1H NMR δ 1.15 (d, 6H, J
) 6.3 Hz), 1.85 (s, 3H), 4.85 (s, 1H), 4.95 (heptet, 1H, J ) 6.3
Hz), 12.09 (s, 1H); 13C NMR δ 21.0, 21.7, 67.1, 90.0, 172.1,
1
175.0. GC peak ratio 1:2.9; 4b:3b 10.0:1 by H NMR.
3-Oxo-2-bu ten oic a cid , p en tyl ester (4c): 1H NMR δ
0.80 (t, 3H, J ) 6.7 Hz), 1.22 (m, 4H), 1.53 (m, 2H), 2.16 (s,
3H), 3.35 (s, 2H), 4.03 (t, 2H, J ) 6.7 Hz); 13C NMR δ 13.7,
22.0, 27.7, 27.9, 29.9, 49.9, 65.3, 167.0, 200.4. En ol ta u tom er
3c: 1H NMR δ 1.84 (s, 3H), 4.01 (t, 1H, J ) 6.7 Hz), 4.88 (s,
1H), 12.01 (s, 1H); 13C NMR δ 21.0, 63.0, 89.5, 172.5, 175.2.
3-(P r op yla m in o)-2-bu ten oic a cid , 2,2,2-tr iflu or oeth yl
ester (9e): 1H NMR δ 0.95 (t, J ) 7.2 Hz, 3H), 1.59 (m, 2H),
1.92 (s, 3H), 3.17 (pseudo q, 2H), 4.40 (q, J ) 8.7 Hz, 2H),
4.48 (s, 1H), 8.49 (br s, 1H); 13C NMR δ 11.28, 19.42, 23.49,
44.86, 58.56 (q, J ) 10.4 Hz), 80.00, 123.63 (q, J ) 138.8 Hz),
163.93, 168.08.
3-Oxo-2-bu ten oic a cid , p r op yla m id e (10): 1H NMR δ
0.89 (t, 3H, J ) 7.36 Hz), 1.47 (hextet, 2H, J ) 7.14 Hz), 2.23
(s, 3H), 3.19 (q, 2H, J ) 5.9 Hz), 3.38 (s, 2H), 7.04 (br s, 1H);
13C NMR δ 11.3, 22.6, 31.0, 41.2, 49.5, 165.4, 204.3.
3-(P r op yla m in o)-2-bu ten oic a cid , p r op yla m id e (11):
1H NMR δ 0.90 (m, 6H), 1.50 (hextet, 4H, J ) 7.36 Hz), 1.83
(s, 3H), 3.11 (m, 4H), 4.21 (s, 1H), 4.82 (br s, 1H), 9.04 (br s,
1H); 13C NMR δ 11.3, 19.2, 23.2, 23.7, 40.4, 44.5, 62.3, 84.2,
158.3, 170.9.
1
GC peak ratio 1:1.9; 4b:3b 10.2:1 by H NMR.
3-Oxo-2-bu ten oic a cid , bu tyl ester (4d ): 1H NMR δ 0.89
(t, J ) 7.3 Hz, 3 H), 1.33 (m, 2H), 1.60 (m, 2H), 2.24 (s, 3H),
3.42 (s, 2H), 4.09 (t, J ) 6.7 Hz, 2H); 13C NMR δ 13.60, 18.98,
30.10, 30.42, 50.08, 65.23, 167.16, 200.63. E n ol t a u t om er
3d : 1H NMR δ 1.92 (s, 3H), 4.08 (t, 1H, J ) 6.7 Hz), 4.94 (s,
1H), 12.08 (s, 1H); 13C NMR δ 21.1, 30.6, 63.7, 89.7, 172.5,
1
175.2. GC peak ratio 1:1.9; 4b:3b 11.4:1 by H NMR.
3-Oxo-2-bu ten oic a cid , p r op yl ester (4e): 1H NMR δ
0.82 (t, 3H, J ) 7.3 Hz), 1.55 (hextet, 2H, J ) 7.3 Hz), 2.14 (s,
3H), 3.34 (s, 2H), 3.97 (t, 2H, J ) 6.7 Hz); 13C NMR δ 10.0,
21.6, 29.8, 49.8, 67.0, 166.6, 200.4. En ol ta u tom er 3e: 1H
NMR δ 0.82 (t, 3H, J ) 7.3 Hz), 1.55 (hextet, 2H, J ) 7.3 Hz),
1.82 (s, 3H), 3.95 (t, 2H, J ) 6.7 Hz), 4.86 (s, 1H), 11.98 (s,
1H); 13C NMR δ 10.0, 20.9, 21.8, 65.2, 89.5, 172.5, 175.2. GC
Ab In itio Ca lcu la tion s. The ab initio molecular orbital
calculations were carried out using Gaussian 92.37 Geometry
optimizations were performed at the MP2(FC)/6-31G* level.
MP2 optimizations give reasonable agreement with MCSCF-
geometries for orbital symmetry allowed pericyclic reactions.38
Frequency calculations verified the identity of each stationary
point as a minimum or transition state. Full geometries and
vibrational frequencies are available in the Supporting Infor-
mation. Single-point energies of each structure were obtained
at the MP4(FC, SDQ)/6-31G* level. The zero-point vibrational
energy (ZPE) corrections were obtained by scaling the MP2/
1
peak ratio 1:1.9; 4b:3b 8.8:1 by H NMR.
3-Oxo-2-bu ten oic a cid , 2,2,2-tr iflu or oeth yl ester (4g):
1H NMR δ 2.24 (s, 3H), 3.54 (s, 2H), 4.49 (q, 2H, J ) 8.4 Hz);
13C NMR δ 30.0, 49.2, 60.7 (q, J ) 36.9 Hz), 122.7 (q, J ) 277.1
Hz), 165.5, 199.2. En ol ta u tom er 3g: 1H NMR δ 1.96 (s,
3H),4.47 (q, 2H, J ) 8.4 Hz), 5.06 (s, 1H), 11.58 (s, 1H); 13C
NMR δ 21.3, 59.6 (q, J ) 36.6 Hz), 88.5, 123.2 (q, J ) 277.1
Hz), 170.7, 177.7. GC peak ratio 1:1.4; 4b:3b 8.9:1 by 1H NMR.
4-Meth yl-1,5-d ioa sp ir o[5,5]u n d ec-3-en -2-on e (8a ). Ex-
cess cyclohexanone was removed by high-vacuum distillation
prior to column chromatography: 1H NMR δ 1.46 (m, 2H), 1.62
(m, 4H), 1.96 (a sharp singlet overlapping with a small
multiplet, 7H), 5.17 (s, 1H); 13C NMR δ 20.0, 22.2, 24.6, 33.7,
94.0, 107.0, 161.2, 168.3.
(37) Frisch, M. J .; Trucks, G. W.; Head-Gordon, M.; Gill, P. M. W.;
Wong, M. W.; Foresman, J . B.; J ohnson, B. G.; Schlegel, H. B.; Robb,
M. A.; Replogle, E. S.; Gomperts, R.; Andres, J . L.; Raghavachari, K.;
Binkley, J . S.; Gonzalez, C.; Martin, R. L.; Fox, D. J .; Defrees, D. J .;
Baker, J .; Stewart, J . J . P.; Pople, J . A. Gaussian, Inc.: Pittsburgh,
PA, 1992.
(38) (a) Houk, K. N.; Li, Y.; Evanseck, J . D. Angew. Chem., Int. Ed.
Engl. 1992, 31, 682-708. (b) Houk, K. N.; Gonzalez, J .; Li, Y. Acc.
Chem. Res. 1995, 28, 81. (c) J iao, H.; Schleyer, P. v. R. Angew. Chem.,
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(36) Inconsistent results were obtained with larger dead space,
presumably due to selective vaporization of the more volatile of the
traps.