Phenylated benzotetraphenes (Dibenzanthracenes) by nickel-catalyzed diphenylacetylene cycloadditions to linear [3]phenylenes

Article abstract of DOI:10.1055/s-0033-1338500

Ni(COD)(PMe₃)₂ catalyzes the cycloaddition of diphenylacetylene to the four-membered rings of linear [3]phenylene and its 2,3,7,8-tetrakis(trimethylsilyl) derivative. The reaction proceeds via initial formation of the 5,6-diphenylbenzo[3,4]cyclobuta[1,2-b]phenanthrene frame, followed by a competitive second, nonregio selective alkyne insertion to furnish the corresponding phenyl-substituted benzo[k]- and -[m]tetraphenes.

Full text of DOI:10.1055/s-0033-1338500

PAPER
▌2469
paper
Phenylated Benzotetraphenes (Dibenzanthracenes) by Nickel-Catalyzed
Diphenylacetylene Cycloadditions to Linear [3]Phenylenes
Phenylene Cycloadditions
Zhenhua Gu, K. Peter C. Vollhardt*
Department of Chemistry, University of California at Berkeley, Berkeley, CA 94720-1460, USA
Fax +1(510)6435208; E-mail: kpcv@berkeley.edu
Received: 01.05.2013; Accepted after revision: 04.06.2013
fied by the smallest representative, linear [3]phenylene
7a. It was therefore of interest to establish its basic feasi-
bility to serve as a substrate in these reactions and, if suc-
cessful, compare their outcome with that observed for 1
Abstract: Ni(COD)(PMe3)2 catalyzes the cycloaddition of diphen-
ylacetylene to the four-membered rings of linear [3]phenylene and
its 2,3,7,8-tetrakis(trimethylsilyl) derivative. The reaction proceeds
via initial formation of the 5,6-diphenylbenzo[3,4]cyclobuta[1,2-
b]phenanthrene frame, followed by a competitive second, nonregio- under identical conditions.
selective alkyne insertion to furnish the corresponding phenyl-
substituted benzo[k]- and -[m]tetraphenes.
Key words: alkynes, arenes, cycloaddition, nickel, polycycles
Substituted polycyclic aromatic hydrocarbons are the sub-
ject of immense current interest because they feature as
components of optoelectronic materials,1 as building
blocks for the bottom-up assembly of novel carbon allo-
tropes,2 as platforms for the construction of functional
1
2
3
molecular assemblies,3 in biological studies of the metab-
olism of environmental pollutants,4 and as scaffolds in
natural products synthesis.5 The functionalization of the
parent systems (if available) by classical electrophilic ar-
omatic substitution is limited by the rules of regioselectiv-
ity, solubility problems, and side reactions, particularly in
the case of larger systems. Consequently, substantial ef-
fort has been devoted to the development of synthetic
methods that assemble targets with controlled topolo-
gies.1–6 In this vein, we have recently reported on the
nickel-catalyzed cycloaddition of diphenylacetylene (and,
briefly, two other alkynes) to the four-membered rings of
angular phenylenes 1–3 (Figure 1).7,8 This transformation
features a haptotropic Ni(PMe3) unit that undergoes kinet-
ically controlled, remarkably regioselective, sequential Ni
insertions along the bay-regions to furnish primarily
phenacene (oligophenanthrene) derivatives. Thus, and
most pertinent for the results to be described, 1 converted
with 1 equivalent of diphenylacetylene into only 11,12-di-
Figure 1
6.43
7.04
Ph
Ph,
8.31
8.53
Ni(COD)(PMe3)2
(10 mol%), THF,
75 °C, 23 h
6
5
7
10
4
1
1
+
11
12
4.01
Ph
Ph
4 (20%)
Ph
Ph
but no
Ph
Ph
Ph
Ph
Ph Ph
5 (59%)
6
Scheme 1 Outcome of the nickel-catalyzed addition of diphenyl-
acetylene to 1; pertinent chemical shifts in 4 are shown in blue (see
discussion)7
phenylbenzo[3,4]cyclobuta[1,2-a]phenanthrene
4 and
phenacene 5, in the absence of regioisomer 6 (Scheme 1).
Notably, double insertion to give 5 competed with single
addition to give 4.7
Thus, linear [3]phenylene 7a (1 equiv), diphenylacetylene
(0.83 equiv), and Ni(COD)(PMe3)2 (0.1 equiv) in tetra-
hydrofuran were heated to 75 °C for two days, during
which time the solution turned red and a colorless solid
consisting of 5,6,12,13-tetraphenylbenzo[k]tetraphene
(5,6,12,13-tetraphenyldibenz[a,h]anthracene) (9a) pre-
cipitated. A combination of filtration and column
chromatography allowed the isolation of 5,6-diphenyl-
benzo[3,4]cyclobuta[1,2-b]phenanthrene (8a), 9a, and
As such, and in view of the plethora of phenylene frames
that have become available during the past decades,9 this
methodology provides, in principle, a useful complement
to existing strategies toward specifically substituted poly-
cyclic benzenoids. However, a considerable number of
the phenylenes contain linear substructures, as exempli-
SYNTHESIS 2013, 45, 2469–2473
Advanced online publication: 24.06.2013
5,6,8,9-tetraphenylbenzo[m]tetraphene
phenyldibenz[a,j]anthracene) (10a) (Scheme 2) in good
combined yield (81%). After benzo[3,4]cyclobuta[1,2-
(5,6,8,9-tetra-
0
0
3
9
-
7
8
8
1
1
4
3
7
-
2
1
0
X
DOI: 10.1055/s-0033-1338500; Art ID: SS-2013-M0329-OP
© Georg Thieme Verlag Stuttgart · New York

2470
Z. Gu, K. P. C. Vollhardt
PAPER
b]phenanthrene-7,12-dicarbonitrile,10 lacking 13C NMR predicated on their unencumbrance by differences in their
data, fused biphenylene 8a is only the second (and fully local environment. Further corroboration of this notion
characterized) member of this type of carbon frame. Sim- was sought by X-ray analysis, an initiative also stimulated
ilarly, but now obviating the complication of insolubility, by the dearth of such data for similar phenylenes.12 Unfor-
the tetrakis(trimethylsilyl)phenylene 7b9a converted into tunately, 8a produced only amorphous powders. Howev-
the analogous pentacycles 8b, 9b, and 10b. In this case, an er, X-ray quality crystals of 8b could be grown from a
NMR experiment demonstrated that the reaction goes saturated toluene–propan-2-ol solution followed by slow
cleanly to completion (2.2 equiv of alkyne, 9b/10b ~1:1). vapor diffusion of methanol (Figure 2).13 While the pres-
ence of the silyl groups compromises a strict comparison
of the bond distances in 8b with those of 4,7 their perturb-
R
R
ing substituent effect tapers off rapidly beyond the ring of
attachment,14 justifying a cautious structural evaluation of
the relative aromaticity of the central phenanthrene ring.
Gratifyingly, and in consonance with computational pre-
dictions (vide supra),11 the averaged sum of its C–C bond
lengths decreases along the series 4 (1.437 Å),7 9,10-di-
phenylphenanthrene (1.428 Å),15 and 8b (1.423 Å), a ten-
tative sign of increasing delocalization.11 Similarly, the
average deviation of these distances from that of benzene
(1.388 Å), also decreases (0.334, 0.276, and 0.247 Å, re-
spectively). Finally, the best indicator of relative electron-
ic activation is the HOMO–LUMO gap, as measured by
the longest wavelength absorptions in the respective UV
spectra. Indeed, λmax (log ε) (8a) = 405 nm (3.93), where-
as λmax (log ε) (4) = 420 nm (3.66).7 While the effect is at-
tenuated relative to 4, 8a still incorporates a considerably
electronically activated phenanthrene nucleus [cf. phen-
anthrene: highest λmax = 345 nm, or the ‘hexagonal
squeeze’16 tetraphene (benz[a]anthracene) λ = 384 nm].17
One notes in this connection that areno-fused phenylenes
are garnering increasing attention as air-stable organic
electronic materials.18
R
8.57
8.90
Ph
Ph,
R
6.91
7.31
8.01
Ni(COD)(PMe3)2
(10 mol%), THF,
75 °C, 48 h
1
8.06
4
R
R
11
8
12
7
7.49
7.82
+
5
6
Ph
Ph
6.744
7.09
6.736
6.78
8a 37%
8b 33%
7a R = H
7b R = SiMe3
R
R
R
R
R
R
Ph
13
1
4
R
R
Ph
13
9
1
14
4
10
12
+
5
7
14
7
6
5
Ph
11
6
8
8
Ph
Ph
Ph
R
Ph
7.63
7.65
Ph
R
10a 29%
10b 18%
9a 21%
9b 26%
Scheme 2 Outcome of the nickel-catalyzed addition of diphenyl-
acetylene to 7; pertinent chemical shifts of 8 and 10 are shown in blue
for a and red for b (see discussion)
The structural assignments of 8–10 rest on their character-
istic spectral data. Thus, 8 exhibits the typical pattern of
relatively shielded hydrogens adjacent to the cyclobutadi-
enoid four-membered ring,9 in conjunction with the diag-
nostic bay region phenanthrene signals (Scheme 2). In
proceeding from 8a to 8b, the hydrogens ortho to trimeth-
ylsilyl experience the expected downfield displacement of
~0.3–0.4 ppm. One notes that an absorption correspond-
ing to the extraordinarily high field signal for H10 in 4, the
result of the shielding effect of the adjacent phenyl group,7
is now absent in 8 due to its altered topology. Phenylene
8a is an isomer of 4, and it is of interest to compare their
spectral properties. Consideration of their respective dom-
inant resonance forms in which the cyclobutadienoid
character of the four-membered ring is minimized,9 as
drawn in Schemes 1 and 2, shows that the aromaticity of
the central ring of the phenanthrene portion in 4 is disrupt-
ed, in contrast to that of the corresponding ring in 8a
where it is enhanced, relative to phenanthrene. To put it
differently, the benzocyclobuta[a] fusion in 4 is less read-
ily accommodated than the corresponding [b] fusion in
8a. This simple analysis has been quantified by DFT cal-
culations for the parent frames.11 A tentative indication of
decreased antiaromaticity in the latter is found in the rela-
tive deshielding of H11 (δ = 6.91, CDCl3) compared to
H7 in 4 (δ = 6.43, CDCl3), the choice of these hydrogens
Figure 2 ORTEP diagram of 8b; thermal ellipsoids are set at 50%
probability, selected bond lengths (Å) are averaged over two mole-
cules in the unit cell and rounded off in the last decimal (individual
values ±0.006–9)
Turning to the benzotetraphenes 9 and 10, their spectral
data are in agreement with those of the parent systems19
and related tetraaryl derivatives.20 The two topologies are
readily distinguished by the NMR spectra, which reveal
Synthesis 2013, 45, 2469–2473
© Georg Thieme Verlag Stuttgart · New York

PAPER
Phenylene Cycloadditions
2471
9a
an additional carbon and proton signal for the less sym-
metrical 10. Noticeable in 10 is the substantial shielding
of H7 relative to that of this hydrogen in the parent com-
pound (δ = 8.36, CDCl3),19b caused by the cumulative ef-
fect of the two adjacent phenyl substituents.
Tetraarylbenzotetraphenes of this type have been scruti-
nized for electronic applications,21 which have also
spurred increasing synthetic efforts to improve access to
the general framework.1o,5a,22
Colorless solid; mp >360 °C (dec; from THF, washed with CH2Cl2).
IR (KBr): 3053, 1489, 1440, 1433, 1069, 759, 704 cm–1.
1H NMR (500 MHz, CD2Cl2): δ = 8.94 (s, 2 H), 8.38 (d, J = 7.5 Hz,
2 H), 7.58–7.52 (m, 2 H), 7.50–7.42 (m, 4 H), 7.42–7.38 (m, 4 H),
7.38–7.33 (m, 6 H), 7.33–7.27 (m, 4 H), 7.27–7.20 (m, 6 H).
1H NMR (400 MHz, CDCl3): δ = 8.98 (s, 2 H), 8.39 (d, J = 7.2 Hz,
2 H), 7.57–7.50 (m, 4 H), 7.60 (d, J = 7.6 Hz, 2 H), 7.40–7.29 (m,
10 H), 7.29–7.19 (m, 10 H).
HRMS-FAB: m/z [M]+ calcd for C46H30: 582.2348; found:
582.2346.
In summary, we have complemented earlier work on the
nickel-catalyzed cycloaddition of alkynes to angular
phenylenes with that to the linear variant, as exemplified
by the prototype linear [3]phenylene 7. Unlike the former,
which shows extensive regioselectivity, strained ring
opening occurs from both the same and opposite sides of
the fused array to assemble substituted benzotetraphenes.
While this apparent flaw may be detrimental in the design
of routes to specific systems, it can be advantageous when
structural diversity is the goal. It will be interesting to ap-
ply this method to the larger phenylenes,9a as one can en-
visage the generation of a plethora of hitherto unobserved
polycyclic benzenoid hydrocarbon systems.
UV/Vis (CH2Cl2): λmax (log ε) = 288 (sh, 4.55), 299 (4.79), 311
(4.85), 333 (sh, 4.18), 347 (4.12), 363 (4.04), 403 nm (3.29).
10a
Colorless solid; mp >360 °C (dec; CH2Cl2).
IR (KBr): 3060, 1514, 1482, 1439, 1070, 1029, 1000, 767, 696 cm–1.
1H NMR (500 MHz, CDCl3): δ = 10.23 (s, 1 H), 9.18 (d, J = 8.0 Hz,
2 H), 7.78 (t, J = 8.0 Hz, 2 H), 7.63 (s, 1 H), 7.60 (d, J = 8.5 Hz, 2
H), 7.55 (t, J = 7.0 Hz, 2 H), 7.26–7.15 (m, 10 H), 7.03–6.94 (m, 10
H).
13C NMR (125 MHz, CDCl3): δ = 139.5, 138.9, 137.5, 136.8, 132.4,
131.04, 130.98, 130.6, 130.2, 128.3, 128.1, 127.63, 127.60, 127.3,
126.9, 126.6, 126.5, 126.0, 122.7, 115.8.
HRMS-FAB: m/z [M]+ calcd for C46H30: 582.2348; found:
582.2346.
Et2O and THF were dried over Na with benzophenone as indicator.
Toluene and m-xylene were distilled from CaH2. UV/Vis spectra
were recorded on a Hewlett-Packard HP 8453 UV/Vis ChemSta-
tion. NMR spectra were recorded on Bruker AVQ-400, AVB-400,
DXR-500, and AV-500 instruments. THF-d8 was purchased from
Cambridge Isotope Labs and degassed before use. Reactions moni-
tored by NMR were conducted in THF-d8.
UV/Vis (CH2Cl2): λmax (log ε) = 267 (4.46), 302 (4.71), 314 (4.87),
336 (sh, 4.17), 349 (4.08), 366 nm (sh, 3.66).
Cycloaddition of Diphenylacetylene to 7b: 5,6-Diphenyl-
2,3,9,10-tetrakis(trimethylsilyl)benzo[3,4]cyclobuta[1,2-
b]phenanthrene (8b), 5,6,12,13-Tetraphenyl-2,3,9,10-tetra-
kis(trimethylsilyl)benzo[k]tetraphene (9b), and 5,6,8,9-Tetra-
phenyl-2,3,11,12-tetrakis(trimethylsilyl)benzo[m]tetraphene
(10b)
Under N2, an Ace-glass tube was charged with phenylene 7b (30.8
mg, 0.06 mmol), diphenylacetylene (8.90 mg, 0.05 mmol),
Ni(COD)(PMe3)2 (0.08 M in THF, 63 μL, 0.005 mmol), and THF
(5 mL). The tube was sealed with a screw cap and the contents
stirred at 75 °C for 48 h. The solvent was removed by rotary evap-
oration and the residue purified by flash chromatography (silica gel,
hexanes–CH2Cl2, 5:1) to give 5,6-diphenyl-2,3,9,10-tetrakis(tri-
methylsilyl)benzo[3,4]cyclobuta[1,2-b]phenanthrene (8b) (11.3 mg,
33%), 5,6,12,13-tetraphenyl-2,3,9,10-tetrakis(trimethylsilyl)ben-
zo[k]tetraphene (9b) (5.7 mg, 26%), and 5,6,8,9-tetraphenyl-
2,3,11,12-tetrakis(trimethylsilyl)benzo[m]tetraphene (10b) (4.0
mg, 18%).
Cycloaddition of Diphenylacetylene to 7a: 5,6-Diphenylben-
zo[3,4]cyclobuta[1,2-b]phenanthrene (8a), 5,6,12,13-Tetra-
phenylbenzo[k]tetraphene (9a), and 5,6,8,9-
Tetraphenylbenzo[m]tetraphene (10a)
Under N2, an Ace-glass tube was charged with phenylene 7a (22.6
mg, 0.10 mmol), diphenylacetylene (14.8 mg, 0.083 mmol),
Ni(COD)(PMe3)2 (2.6 mg, 0.0082 mmol), and THF (5 mL). The
tube was sealed with a screw cap and the contents stirred at 75 °C
for 48 h, during which the mixture turned red and colorless
5,6,12,13-tetraphenylbenzo[k]tetraphene (9a) (5.1 mg, 21%) pre-
cipitated. After its removal by filtration, the remainder was subject-
ed to flash chromatography (silica gel, hexanes–CH2Cl2, gradient
10:1 to 5:1) to afford 5,6-diphenylbenzo[3,4]cyclobuta[1,2-b]phen-
anthrene (8a) (12.3 mg, 37%) and 5,6,8,9-tetraphenylbenzo[m]tet-
raphene (10a) (7.0 mg, 29%).
8b
8a
Pale yellow solid; mp 278–280 °C (CH2Cl2–hexanes).
Pale yellow solid; mp 264–265 °C (CH2Cl2).
IR (KBr): 3056, 2951, 1602, 1494, 1442, 1411, 1249, 1142, 1066,
1027, 854, 836, 755, 699 cm–1.
1H NMR (400 MHz, CDCl3): δ = 8.90 (s, 1 H), 8.06 (s, 1 H), 7.82
(s, 1 H), 7.31 (s, 1 H), 7.29–7.16 (m, 6 H), 7.124 (t, J = 9.0 Hz, 2 H),
7.120 (t, J = 9.0 Hz, 2 H), 7.09 (s, 1 H), 6.78 (s, 1 H), 0.52 (s, 9 H),
0.39 (s, 9 H), 0.33 (s, 9 H), 0.21 (s, 9 H).
13C NMR (100 MHz, CDCl3): δ = 150.0, 149.9, 149.7, 149.5, 148.9,
148.7, 142.51, 142.47, 139.9, 139.2, 138.5, 137.3, 135.4, 133.1,
131.0, 130.9, 130.7, 130.4, 129.6, 128.9, 127.6, 127.4, 126.42,
126.37, 124.40, 124.37, 116.0, 110.7, 2.17, 2.11, 2.02, 1.61.
IR (KBr): 3055, 1483, 1442, 1422, 764, 741, 698 cm–1.
1H NMR (500 MHz, CDCl3): δ = 8.57 (d, J = 8.0 Hz, 1 H), 8.01 (s,
1 H), 7.58 (ddd, J = 1.5 Hz, 7.5, 8.5 Hz, 1 H), 7.49 (d, J = 7.5 Hz, 1
H), 7.40 (t, J = 7.5 Hz, 1 H), 7.26–7.15 (m, 6 H), 7.15–7.09 (m, 4
H), 6.94–6.84 (m, 2 H), 6.91 (d, J = 7.5 Hz, 1 H), 6.744 (d, J = 8.0
Hz, 1 H), 6.736 (s, 1 H).
13C NMR (125 MHz, CDCl3): δ = 150.9, 150.8, 148.6, 148.4, 139.9,
139.5, 138.1, 137.3, 132.6, 131.8, 130.96, 130.95, 130.93, 130.4,
129.2, 129.1, 127.8, 127.6, 127.5, 126.40, 126.39, 126.2, 126.1,
122.5, 118.9, 118.8, 115.6, 110.7.
HRMS-FAB: m/z [M]+ calcd for C44H52Si4: 692.3146; found:
692.3130.
MS (EI, 70 eV): m/z (%) = 404 ([M]+, 18), 91 (100).
HRMS-EI: m/z [M]+ calcd for C32H20: 404.1565; found: 404.1571.
UV/Vis (CH2Cl2): λmax (log ε) = 250 (4.66), 304 (4.94), 317 (sh,
UV/Vis (CH2Cl2): λmax (log ε) = 289 (4.71), 303 (sh, 4.59), 314 (sh,
4.85), 334 (4.67), 371 (4.27), 392 (4.06), 413 nm (4.12).
4.43), 326 (4.49), 364 (3.70), 384 (3.86), 405 nm (3.93).
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2013, 45, 2469–2473

2472
Z. Gu, K. P. C. Vollhardt
PAPER
Casado, J.; Ding, J.; Wu, J. J. Am. Chem. Soc. 2012, 134,
Anal. Calcd for C44H52Si4: C, 76.23; H, 7.56. Found: C, 76.13; H,
7.49.
14913. (l) Zeng, Z.; Sung, Y. M.; Bao, N.; Tan, D.; Lee, R.;
Zafra, J. L.; Lee, B. S.; Ishida, M.; Ding, J.; López
Navarrete, J. T.; Li, Y.; Zeng, W.; Kim, D.; Huang, K.-W.;
Webster, R. D.; Casado, J.; Wu, J. J. Am. Chem. Soc. 2012,
134, 14513. (m) Kumar, B.; Strasser, C. E.; King, B. T.
J. Org. Chem. 2012, 77, 311. (n) Gu, X.; Luhman, W. A.;
Yagodkin, E.; Holmes, R. J.; Douglas, C. J. Org. Lett. 2012,
14, 1390. (o) Umeda, R.; Miyake, S.; Nishiyama, Y. Chem.
Lett. 2012, 41, 215. (p) Wu, T.-C.; Wu, Y.-T. Synlett 2011,
741.
9b
Colorless solid; mp >360 °C (dec; CH2Cl2–hexanes).
IR (KBr): 3051, 2950, 1490, 1462, 1441, 1251, 1152, 1120, 1062,
854, 834, 755, 699 cm–1.
1H NMR (400 MHz, CDCl3): δ = 8.97 (s, 2 H), 8.75 (s, 2 H), 7.87
(s, 2 H), 7.42–7.36 (m, 4 H), 7.36–7.30 (m, 6 H), 7.29 (d, J = 6.8 Hz,
4 H), 7.26–7.21 (m, 6 H), 0.33 (s, 18 H), 0.20 (s, 18 H).
13C NMR (100 MHz, CDCl3): δ = 143.7, 143.1, 139.5, 139.2, 137.8,
137.1, 135.1, 131.2, 131.0, 130.9, 130.8, 129.6, 128.5, 128.4, 127.8,
127.6, 126.8, 126.5, 121.5, 1.78, 1.59.
(2) For a very recent monograph and reviews, see:
(a) Fragments of Fullerenes and Carbon Nanotubes:
Designed Synthesis, Unusual Reactions, and Coordination
Chemistry; Scott, L. T.; Petrukhina, M. A., Eds.; Wiley:
Hoboken, 2012. (b) Ivanovskii, A. L. Russ. Chem. Rev.
2012, 81, 571. (c) Itami, K. Pure Appl. Chem. 2012, 84, 907.
(d) Wen, B.; Wang, K. K. Pure Appl. Chem. 2012, 84, 893.
(e) Sygula, A. Eur. J. Org. Chem. 2011, 1611. For very
recent illustrative methodologies, see: (f) Luo, J.; Xu, X.;
Mao, R.; Miao, Q. J. Am. Chem. Soc. 2012, 134, 13796.
(g) Nishiuchi, T.; Feng, X.; Enkelmann, V.; Wagner, M.;
Müllen, K. Chem. Eur. J. 2012, 18, 16621. (h) Fort, E. H.;
Jeffreys, M. S.; Scott, L. T. Chem. Commun. 2012, 48, 8102.
(i) Li, H.; He, K.-H.; Liu, J.; Wang, B.-Q.; Zhao, K.-Q.; Hu,
P.; Shi, Z.-J. Chem. Commun. 2012, 48, 7028.
HRMS-FAB: m/z [M]+ calcd for C58H62Si4: 870.3929; found:
870.3921.
UV/Vis (CH2Cl2): λmax (log ε) = 240 (4.95), 299 (sh, 4.82), 308
(5.11), 321 (5.26), 341 (4.59), 355 (4.45), 372 (4.32), 410 nm
(3.65).
10b
Colorless solid; mp 350–351 °C (dec; CH2Cl2–hexanes).
IR (KBr): 3054, 2952, 1491, 1441, 1261, 1250, 1115, 1030, 855,
834, 701, 695 cm–1.
1H NMR (400 MHz, CDCl3): δ = 10.28 (s, 1 H), 9.47 (s, 2 H), 7.92
(s, 2 H), 7.65 (s, 1 H), 7.26–7.22 (m, 4 H), 7.21–7.15 (m, 6 H), 7.04–
6.94 (m, 10 H), 0.63 (s, 18 H), 0.25 (s, 18 H).
13C NMR (100 MHz, CDCl3): δ = 143.8, 143.2, 139.2, 138.9, 137.9,
136.8, 135.5, 131.3, 131.1, 131.0, 130.7, 129.5, 128.7, 128.2, 127.6,
127.5, 127.3, 126.5, 126.1, 115.2, 2.18, 1.70.
(j) Yamaguchi, R.; Hiroto, S.; Shinokubo, H. Org. Lett.
2012, 14, 2472. (k) Wan, X.; Chen, K.; Liu, D.; Chen, J.;
Miao, Q.; Xu, J. Chem. Mater. 2012, 24, 3906.
(l) Higashibayashi, S.; Tsuruoka, R.; Soujanya, Y.;
Purushotham, U.; Sastry, G. N.; Seki, S.; Ishikawa, T.;
Toyota, S.; Sakurai, H. Bull. Chem. Soc. Jpn. 2012, 85, 450.
(m) Mueller, A.; Amsharov, K. Yu. Eur. J. Org. Chem.
2012, 6155.
HRMS-FAB: m/z [M]+ calcd for C58H62Si4: 870.3929; found:
870.3961.
UV/Vis (CH2Cl2): λmax (log ε) = 249 (4.73), 280 (4.52), 300 (sh,
4.50), 311 (4.74), 324 (4.92), 342 (sh, 4.30), 359 (4.20), 370 nm (sh,
3.93).
(3) For a recent illustrative study, see: De Rouville, H.-P. J.;
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Acknowledgment
This work was made possible by support from the NSF (CHE
0907800).
Supporting Information (1H and 13C NMR spectra of
new compounds) for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synthesis.SnuIomprifgtooatrinSugpIoi
nnfomartit
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