12560 J. Am. Chem. Soc., Vol. 118, No. 50, 1996
Sustmann et al.
-
1
3
nitrile: Ea ) 14.5 ( 0.1 kcal mol , log A ) 14.71 ( 0.01,
3-H), 3.46 (s, 3 H, H-9), 3.18 (s, 3 H, H-7), 2.33 (ddd, J4-H,5a-H
)
q
-1
q
-1 -1
13.0 Hz,
3
J3-H,4-H ) 4.0 Hz,
3
J
) 2.8 Hz, 1 H, 4-H), 2.14 (dddd,
∆
∆
H ) 14.1 ( 0.1 kcal mol , ∆S ) 7.2 ( 0.2 cal mol K ,
G ) 11.95 kcal mol . There is a close resemblance,
4-H,5e-H
3
2
3
q
-1 3
12 lines, J4-H,5a-H ) 13.0 Hz, J5a-H,5e-H ) 17.5 Hz, J5a-H,6a-H ) 5.9
3
Hz, J5a-H,6e-H ) 5.5 Hz, 1 H, H-5a), 1.95-1.56 (m, 3 H, 5-He and
indicating that a similar process is observed in both cases. In
the former case we interpreted the new absorption as due to a
zwitterionic intermediate which disappears by cyclizing to a
cycloadduct, either to a (2 + 2) adduct which further rearranges
to the (4 + 2) adduct or directly to the (4 + 2) product. The
small positive value of the activation entropy was taken as
evidence that a solvated zwitterion has to lose its solvation shell
which is accompanied by a positive entropy contribution. In
the reaction of 1,1-dimethoxy-1,3-butadiene with TCNE we find
13
6
1
7
3 ,
-H). C NMR (75 MHz, CDCl , DEPT ) of 3a: δ 173.60 (s, C-8),
32.22 (d, C-2, could also be C-1), 124.53 (d, C-1, could also be C-2),
2.66 (d, C-3), 57.01 (q, C-7), 51.53 (q, C-9), 44.79 (d, C-4), 25.08 (t,
1
C-6), 18.67 (t, C-5). H NMR (300 MHz, C
6
D
6
) of 3b: δ ) 5.77
3
3
(
“dm”, J1-H,2-H ) 10.3 Hz, 1 H, 2-H), 5.55 (“dm”, J1-H,2-H ) 10.3
3
Hz, 1 H, 1-H), 4.30 (“dt”, J3-H,4-H ) 8.5 Hz, 1 H, 3-H), 3.39 (s, 3 H,
3
3
3
9-H), 2.73 (ddd, J3-H,4-H ) 8.5 Hz, J4-H,5a-H ) 11.0 Hz, J4-H,5e-H
) 3.8 Hz, 1 H, 4-H), 1.95-1.56 (m, 4 H, 5-H and 6-H). 13C NMR
(CDCl
3 ,
, DEPT ): δ 175.21 (s, C-8), 129.29 (d, C-2, could also be C-1),
126.16 (d, C-1, could also be C-2), 76.20 (d, C-3), 56.20 (q, C-7),
1.79 (q, C-9), 45.33 (t, C-4), 24.26 (t, C-6), C-5 (not found, perhaps
, cm ) 1730 (s, νCdO).
MS m/z (%) 3a: 170 (M , 1), 155 (10), 138 (23), 123 (9), 110 (22),
4 (100), 79 (75), 69 (32), 55 (11). 3b: 170 (M , 2), 155 (26), 138
19), 123 (28), 110 (65), 95 (18), 84 (100), 79 (82), 69 (32), 59 (12),
5(25). Anal. Calcd for C (170.04): C, 63.53; H, 8.24.
Found: C, 63.25; H, 8.60.
q
a small negative value of ∆S which is, however, far from the
5
highly negative values which are observed in concerted cy-
cloadditions. Thus we suggest that we have found additional
spectroscopic evidence for a zwitterionic intermediate and its
cyclization. The close relationship between the two cases is
borne out also in their behavior in dichloromethane. For both
reactions it was not possible to detect the UV/vis absorption at
λmax ) 420 nm in this solvent. The explanation proposed in
the first example was that the zwitterion which is also formed
in dichloromethane is not stabilized by solvation, with the
consequence that the rate-determining step is zwitterion forma-
tion and not cyclization, as suggested for the observations in
acetonitrile.
-1
hidden under signal at 18.67 of 3a). IR (CH
Cl
2 2
+
+
8
(
5
9 14 3
H O
Reactions of 1,1-Dimethoxy-1,3-butadiene with Methyl Acrylate,
Acrylonitrile, Dimethyl Fumarate, Dimethyl Maleate, Fumaroni-
trile, and Maleonitrile. Equimolar amounts of the reactants (2.6 mmol)
in 14 mL of toluene were kept at 60 °C in the dark. Progress of the
reactions was monitored by following the decrease in diene by GLC.
After variable time from 15 d (methyl acrylate) to 5 d for fumaronitrile
no more diene could be detected. During these times a white solid
precipitate had been deposited which turned out not to be the expected
cycloadducts but rather polymeric material. Under these conditions
which were modeled after those of the reaction of 1-methoxy-1,3-
butadiene with these dienophiles polymerization is faster than cycload-
dition.
Experimental Section
Analytical Instruments. 1H and 13C NMR spectra (internal standard
TMS): Bruker AMX-300, Varian Gemini 200. MS(EI 70 eV):
Finnigan MAT 312/188. GC/MS (EI 70 eV): Hewlett Packard HP5971
A and HP 5890 Series II chromatograph. GC: Varian 3700, 50 m.
UV/vis: Cary 219. PE: Leybold-Heraeus UPG 200. P o¨ larography:
Bruker E 310, Metrohm Polarographiestand. Elemental analyses:
Heraeus EA 301. Melting points (uncorrected): B u¨ chi 510.
Methyl acrylate, acrylonitrile, dimethyl fumarate, dimethyl maleate,
fumaronitrile, and tetracyanoethylene (Aldrich) were purified by
fractional distillation over a 20 cm Vigreux column, by recrystallization
Cycloaddition of 2 to Dimethyl Dicyanofumarate. 1,1-Dimethoxy-
,3-butadiene (0.312 g, 2.7 mmol) and dimethyl dicyanofumarate (0.530
1
g, 2.7 mmol) were each dissolved in 18 mL of toluene The solutions
were cooled to -70 °C and combined at this temperature. Immediately
afterwards the solvent was removed at room temperature under vacuo
(10 Pa). The residue consisted of 0.82 g (97%) of colorless solid which
consisted of two isomers (NMR) and was recrystallized from petrolether
at low temperature. Crystals (0.73 g, 87%) with mp 134-136 °C were
isolated. The ratio of cycloadducts is 31:69 in the raw material and
19
20,21
or sublimation. Maleonitrile, dimethyl cyanomethylidenemalonate,
dimethyl dicyanomethylidenema-
lonate, dimethyl dicyanomaleate, dimethyl dicyanofumarate, and
1
9,22
methyl â,â-dicyanoacrylate,
2
0
23
24
1
1
35:65 in the recrystallized solid according to H NMR. 15a: H NMR
2
5
3
3
(
E)-1-methoxy-1,3-butadiene (purity >97%) were synthesized as
(CDCl ): δ 6.09 (ddd, J1-H,2-H ) 10.7 Hz, 3 J1-H,6a-H ) 4.6 Hz,
3
described in the literature. A description of the experimental procedures
is given for the cycloaddition of 1 to methyl acrylate and for the
cycloadditions and trapping experiments of 2 to dimethyl dicyanofu-
marate and methyl â,â-dicyanoacrylate. Experimental details for the
other reactions are given in the Supporting Information.
3
4
J1-H,6e-H ) 2.7 Hz, 1 H, 1-H), 5.76 (“dt”, J1-H,2-H ) 10.7 Hz,
J2-H,6e-H ) 2.4 Hz, J2-H,6a-H ) 2.0 Hz, 1 H, 2-H), 3.93 (s, 3 H, CO2-
4
CH ), 3.88 (s, 3 H, CO CH ), 3.60 (s, 3 H, OCH ), 3.46 (s, 3 H, OCH ),
3
2
3
3
3
2
3
4
3.25 (“dt”,
J6a-H,6e-H ) 18.4 Hz,
J1-H,6e-H ) 2.7 Hz,
J2-H,6e-H ) 2.4
) 18.4 Hz, J1-H,6a-H ) 4.6 Hz,
J2-H,6a-H ) 2.0 Hz, 1 H, 6-Ha). C NMR (CDCl , DEPT): δ 166.07
(s, CO CH , C-10 or C-13), 163.12 (s, CO CH , C-10 or C-13), 128.15
(d, C-2), 125.09 (d, C-1), 115.99 (s, CN, C-9 or C-12), 115.73 (s, CN,
C-9 or C-12), 96.79 (s, C-3), 54.93 (q, CO CH C-11 or C-14), 54.01
(q, CO CH , C-11 or C-14), 51.05 (q, OCH C-7 or C-8), 50.54 (q,
OCH C-7 or C-8), 55.14* (s, C-4 or C-5), 49.23 (s, C-4 or C-5), 33.20
2
3
Hz, 1 H, 6-He), 2.94 (ddd,
J6
a-H,6e-H
4
13
Cycloaddition of 1 to Methyl Acrylate. (E)-1-Methoxy-1,3-
butadiene (1) (0.501 g, 6.0 mmol) in toluene (11 mL) was mixed with
methyl acrylate (0.518 g, 6.0 mmol) in toluene (11 mL) at room
temperature. After 46 d, monitored by GLC, 1 had reacted. The solvent
was removed under reduced pressure (10 Pa) and the product was
purified by “Kugelrohr” distillation at 10 Pa, 85 °C. Yield: 0.86 g
3
2
3
2
3
2
3,
2
3
3,
3,
(
85%) of a 64:36 mixture of 3a and 3b as a colorless oil. The same
(t, C-6). (An asterisk indicates this could also be C-4 or C-5 of the
1
3
reaction at 60 °C needed 18 d for completion. Yield: 0.90 g (89%).
minor product.) 15b: H NMR (CDCl ): δ 6.16 (ddd, J
1-H,2-H
)
3
1
3
3
3
H NMR (300 MHz, C
6
D
6
) of 3a: δ 5.81 (dddd, J1-H,2-H ) 10.3 Hz,
10.7 Hz, J
) 4.9 Hz, J
) 2.4 Hz, 1 H, 1-H), 5.99 (“dt”,
1
-H,6-H
1-H,6′-H
3
4
4
3
J1-H,2-H ) 10.7 Hz, 4J
4
J
2-H,3-H ) 4.0 Hz, J2-H,6-H ) 2.5 Hz, J2-H,6-H′ ) 1.5 Hz, 1 H, 2-H),
) 2.4 Hz, J
2-H,6′-H
) 1.8 Hz, 1 H,
2-H,6-H
3
5
1
.69 (dddd, J1-H,2-H ) 10.3 Hz, J) 5.4 Hz, J) 2.0 Hz, J ) 1.3 Hz,
2 3 2 3
2-H), 3.93 (s, 3 H, CO CH ), 3.92 (s, 3 H, CO CH ), 3.51 (s, 3 H,
H, 1-H), 3.97 (dd, “t”, 3J2-H,3-H ) 4.0 Hz, J3-H,4-H ) 4.0 Hz, 1 H,
3
2
3
OCH ), 3.46 (s, 3 H, OCH ), 3.05 (“dt”, J
3
3
6-H,6′-H
) 18.4 Hz, J
1-H,6-H
2
4
)
2.4 Hz, J2-H,6′-H ) 2.4 Hz, 1 H, 6-H), 2.95 (“dt”, J6-H,6′-H ) 18.4
(19) Liepins, R.; Campbell, D.; Walker, C. J. Polym. Sci. Polym. Chem.
13
Hz, J ) 2.4 Hz, 1 H, 6-H). C NMR (CDCl
3
, DEPT): δ 166.03 (s,
, C-10 or C-13), 127.73
d, C-2), 125.91 (d, C-1), 115.35 (s, CN, C-9 or C-12), 113.94 (s, CN,
C-9 or C-12), 99.13 (s, C-3), 54.70 (q, CO CH , C-11 or C-14), 54.37
(q, CO CH , C-11 or C-14), 52.26 (q, OCH , C-7 or C-8), 51.47 (q,
OCH3, C-7 or C-8), 57.03* (s, C-4 or C-5), 47.39 (s, C-4 or C-5), 33.94
t, C-6). (An asterisk indicates this could also be C-4 or C-5 of the
major product.) Two-dimensional CH- and CC-COSY spectra were
Ed. 1968, 6, 3059-3073.
2 3 2 3
CO CH , C-10 or C-13), 164.16 (s, CO CH
(
20) Hall, H. K., Jr.; Sentman, R. C. J. Org. Chem. 1982, 47, 4572-
(
4
577.
(
(
(
21) Hall, H. K., Jr.; Ykman, P. Macromolecules 1977, 10, 464-469.
2
3
22) Bernstein, Z.; Ben-Ishai, D. Tetrahedron 1977, 33, 881-883.
23) Gotoh, T.; Padias, A. B.; Hall, H. K., Jr. J. Am. Chem. Soc. 1986,
2
3
3
1
1
1
08, 4920-4931.
24) Ireland, C. J.; Jones, K.; Pizey, J. S.; Johnson, S. Synth. Commun.
976, 6, 185-191.
25) Montagna, A. E.; Hirsch, D. H. US 2905722, 1959; Chem. Abstr.
960, 22, 4628e.
(
(
-
1
also recorded. IR (KBr, cm ) 2984 (νCH2), 2230 (νCN), 1722 (νCO),
(
+
1650 (νCdC). MS m/z (%): 15a, 308 (M ,2), 276 (2), 268 (8), 252