M. B. Nielsen et al.
SHORT COMMUNICATION
for 5 h, whereupon it was diluted with Et2O (100 mL) and washed
with saturated aqueous NH4Cl (2ϫ100 mL). The organic phase
was dried with MgSO4, filtered, and the solvents evaporated in
vacuo. Purification by column chromatography (SiO2, 40%
CH2Cl2/heptane) yielded 10 (196 mg, 45%) as a yellow to green
solid. Crystals were grown from pentane. M.p. 126–127 °C. 1H
NMR (300 MHz, CDCl3): δ = 7.72–7.76 (m, 2 H), 7.44–7.51 (m, 3
H), 6.88 (s, 1 H), 6.51–6.63 (m, 2 H), 6.31 (d, J = 5.9 Hz, 1 H),
6.16 (d, J = 4.6 Hz, 1 H), 3.80 (dd, J = 4.6, 1.5 Hz, 1 H), 1.09 (s,
21 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 141.3, 140.3, 132.7,
131.5, 130.5, 129.5, 126.6, 124.9, 123.3, 120.7, 115.1, 112.7, 105.3,
91.5, 51.0, 45.0, 18.9, 11.5 ppm; two overlapping signals.
C29H32N2Si (436.67): calcd. C 79.77, H 7.39, N 6.42; found C
79.66, H 7.49, N 6.33. HR-MS (ES): m/z = 437.2385 [MH+].
C29H33N2Si: m/z = 437.2413.
CCDC-718205 (for 7), 718204 (for 2-phenylazulene-1,3-dicar-
bonitrile), 718206 (for 9), 718207 (for 10) contain the supplemen-
tary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
Scheme 4.
Supporting Information (see also the footnote on the first page of
this article): NMR spectra of 3, 10, and 13; spectral evolution upon
irradiation of 10 in comparison to 1; detailed photolysis experi-
ments on 10; frontier orbitals of 10–13 devoid of silyl substituents.
partly to the 6-substituted isomer by irradiation followed
by thermal ring closure in the polar solvent acetonitrile. As
the two regioisomers exhibit different absorption maxima,
their ratio can be controlled by the wavelength of irradia-
tion. Isomerization can, however, be completely avoided by
using a nonpolar solvent. Access to DHA derivatives func-
tionalized in both the five- and seven-membered rings is
important for the future exploitation of the DHA/VHF
switch in for example molecular electronics devices.
Acknowledgments
The Danish Research Agency is gratefully acknowledged for sup-
porting this work (272-08-0540).
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Experimental Section
2-Phenyl-7-[(triisopropylsilyl)ethynyl]-1,8a-dihydroazulene-1,1-dicar-
bonitrile (10): Dibromide 5 (416 mg, 1.00 mmol) was dissolved in
dry THF (20 mL) at 0 °C. Lithium bis(trimethylsilyl)amide
(1.00 mL, 1.00 mmol, 1 in toluene) was added dropwise, and the
solution was stirred for 2 h, while the temperature was slowly raised
to room temperature. The reaction mixture was diluted with Et2O
(100 mL) and then washed with saturated aqueous NH4Cl
(2ϫ100 mL). The organic phase was dried with MgSO4, filtered,
and the solvents evaporated in vacuo yielding a black solid contain-
ing the bromide 8 plus minor by-products (according to NMR
analysis). [8: 1H NMR (300 MHz, CDCl3): δ = 7.74 (m, 2 H), 7.48
(m, 3 H), 6.89 (s, 1 H), 6.52 (m, 2 H), 6.30 (m, 1 H), 6.13 (dd, J =
4.4, 0.9 Hz, 1 H), 3.80 (dd, J = 4.4, 1.8 Hz, 1 H) ppm. 13C NMR
(75 MHz, CDCl3): δ = 141.6, 141.1, 132.9, 132.3, 131.8, 130.7,
131.1, 129.5, 126.6, 120.3, 120.2, 120.0, 114.8, 112.6, 51.2,
44.8 ppm.] The crude batch of 8 was redissolved in dry, argon-
degassed THF (10 mL). Then [PdCl2(PPh3)2] (70.19 mg,
0.10 mmol) and CuI (3.81 mg, 0.02 mmol) were added under ar-
gon, followed by iPr2NH (0.3 mL) and (triisopropylsilyl)acetylene
(0.5 mL, 2.2 mmol). The reaction mixture was stirred at 35–40 °C
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Received: March 19, 2009
Published Online: April 29, 2009
2736
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Eur. J. Org. Chem. 2009, 2733–2736