Y. Zhao et al. / Tetrahedron Letters 42 (2001) 7721–7723
7723
(e) Campbell, K.; McDonald, R.; Branda, N. R.; Tykwin-
ski, R. R. Org. Lett. 2001, 3, 1045–1048.
2. (a) Diederich, F. Chem. Commun. 2001, 219–227; (b)
Faust, R.; Go¨belt, B.; Weber, C.; Krieger, C.; Gross, M.;
Gisselbrecht, J.-P.; Boudon, C. Eur. J. Org. Chem. 1999,
205–214; (c) Bryce, M. R.; Coffin, M. A.; Skabara, P. J.;
Moore, A. J.; Batsanov, A. S.; Howard, J. A. K. Chem.
Eur. J. 2000, 6, 1955–1962; (d) Wang, W. L.; Helgeson,
R.; Ma, B.; Wudl, F. J. Org. Chem. 2000, 65, 5862–5867;
(e) Song, Y.; Spencer, L.; Euler, W. B.; Rosen, W. Org.
Lett. 1999, 1, 561–564.
3. (a) Hopf, H. Angew. Chem., Int. Ed. 1984, 23, 948–960;
(b) Hopf, H. Classics in Hydrocarbon Synthesis; Wiley-
VCH: Weinheim, 2000; Chapter 11.
4. Phelan, N. F.; Orchin, M. J. Chem. Ed. 1968, 45, 633–
637.
Figure 3. Electronic absorption spectra (m [L M−1 cm−1]) in
CHCl3 comparing the effects of substitution for 4a–b.
5. (a) Schreiber, M.; Tykwinski, R. R.; Diederich, F.; Spre-
iter, R.; Gubler, U.; Bosshard, C.; Poberaj, I.; Gu¨nter, P.;
Boudon, C.; Gisselbrecht, J.-P.; Gross, M.; Jonas, U.;
Ringsdorf, H. Adv. Mater. 1997, 9, 339–343; (b) Nielsen,
M. B.; Schreiber, M.; Baek, Y. G.; Seiler, P.; Lecomte, S.;
Boudon, C.; Tykwinski, R. R.; Gisselbrecht, J.-P.; Gram-
lich, V.; Skinner, P. J.; Bosshard, C.; Gu¨nter, P.; Gross,
M.; Diederich, F. Chem. Eur. J. 2001, 7, 3263–3280.
6. Siemsen, P.; Livingston, R. C.; Diederich, F. Angew.
Chem., Int. Ed. 2000, 39, 2633–2657.
The electronic absorption spectra for dimeric 2a–c are
shown in Fig. 2. Three low energy absorptions at ca.
290, 310 and 330 nm are observed for all three deriva-
tives, and the energy of these absorptions changes little
as a result of the different pendant groups of 2a–c. The
most surprising observation, however, is found in the
spectrum of 2b, where a significant shoulder absorption
is found near 350 nm. Whereas previous studies have
suggested enhanced communication in cross-conjugated
molecules resulting from increasingly electron rich sub-
stitution,5 in tetraynes such as 2, it is clearly the elec-
tron poor functionality that has the more dramatic
effect.
7. Hay, A. S. J. Org. Chem. 1962, 27, 3320–3321.
8. Compound 2a: Mp 185°C (decomp). IR (mscope) 2904,
1
2202, 2133, 1609, 1585, 1521, 1363. H NMR (300 MHz,
CDCl3) 7.32 (d, J=9.0 Hz, 4H), 6.61 (d, J=9.0 Hz, 4H),
2.95 (s, 12H), 2.086 (s, 6H), 2.084 (s, 6H). 13C NMR (75.5
MHz, CDCl3) 155.9, 150.1, 132.6, 111.9, 110.2, 101.4,
93.1, 83.4, 79.4, 75.7, 40.3, 23.0(2×). HRMS calcd for
C32H32N2 (M+) 444.2566, found 444.2559.
The UV–vis spectra for 4a–b are shown in Fig. 3. In the
spectrum of both 4a–b, three low energy absorptions
are visible, centered at approximately 327, 346, and 366
nm. Although electron rich 4a shows a slightly higher
molar absorptivity, the overall electronic absorption
characteristics for 4a–4b are quite analogous. Thus, the
anomalous behavior resulting from p-electron acceptors
appears limited to molecules such as 2.
Compound 2b: Mp=176–178°C. IR (mscope) 3103, 2910,
1
2209, 1515, 1342. H NMR (400 MHz, CDCl3) 8.16 (d,
J=8.4 Hz, 4H), 7.57 (d, J=8.4 Hz, 4H), 2.14 (s, 12H).
13C NMR (100 MHz, CDCl3, APT) 160.7, 147.0, 132.0,
130.0, 123.6, 100.4, 90.4, 90.2, 78.5, 76.1, 23.3(2×).
HRMS calcd for C28H20O4N2 (M+) 448.1423, found
448.1419.
Compound 4a: Mp=148°C (decomp). IR (mscope) 2903,
2198, 2134, 1522 cm−1 1H NMR (500 MHz, CDCl3) l
.
7.36 (d, J=9.0 Hz, 4H), 6.59 (d, J=9.0 Hz, 4H), 2.97 (s,
12H), 2.09 (s, 6H). 13C NMR (125 MHz, CDCl3, APT) l
159.4, 150.4, 133.6, 111.6, 108.0, 100.8, 84.0, 77.1, 77.0,
72.2, 40.1, 23.3. EI HRMS calcd for C28H26N2 (M+)
390.2096, found 390.2099.
Acknowledgements
Financial support for this work has been provided by
the University of Alberta, the Alberta Science,
Research, and Technology Authority, and NSERC. We
thank Dr. R. McDonald for the X-ray structural deter-
mination of 4a.
Compound 4b: Mp=117°C (decomp). IR (mscope) 3103,
2931, 2201, 1343 cm−1 1H NMR (400 MHz, CDCl3) l
.
8.18 (d, J=8.6 Hz, 4H), 7.62 (d, J=8.6 Hz, 4H), 2.15 (s,
6H). 13C NMR (100 MHz, CDCl3, APT) l 165.0, 147.5,
133.2, 128.6, 123.7, 99.8, 80.2, 79.6, 78.6, 76.2, 23.5. EI
HRMS calcd for C24H14N2O4 (M+) 394.0954, found
394.0954.
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