Toward Antikekulene: Angular 1,2-Di-, 2,3-Di-, and 1,2,15,16-Tetrachloro[6]phenylene

Article abstract of DOI:10.1055/s-0034-1379140

The synthesis of the first ring-functionalized heliphenes is described, comprised of angular 1,2-di-, 2,3-di-, and 1,2,15,16-tetrachloro[6]phenylene, via a series of Sonogashira couplings and cobalt-catalyzed alkyne cyclotrimerization steps. These molecul

Full text of DOI:10.1055/s-0034-1379140

LETTER
▌2429
lTettoerward Antikekulene: Angular 1,2-Di-, 2,3-Di-, and 1,2,15,16-Tetrachlo-
ro[6]phenylene
Chloroheliphenes
a
b
b
a
b
Alexandr Fonari, Jens C. Röder, Hao Shen, Tatiana V. Timofeeva, K. Peter C. Vollhardt*
a
Department of Biology and Chemistry, New Mexico Highlands University, Las Vegas, NM 87701, USA
b
Department of Chemistry, University of California at Berkeley, Berkeley, CA 94720-1460, USA
Fax +1(510)6435208; E-mail: kpcv@berkeley.edu
Received: 16.06.2014; Accepted after revision: 20.08.2014
–
7
tion (6 × 10 torr) through a hot quartz tube at tempera-
tures up to 800 °C, beyond which it decomposed to black
soot. Hoping to achieve Scholl-type (at least) single-bond
Abstract: The synthesis of the first ring-functionalized heliphenes
is described, comprised of angular 1,2-di-, 2,3-di-, and 1,2,15,16-
tetrachloro[6]phenylene, via a series of Sonogashira couplings and
8
cobalt-catalyzed alkyne cyclotrimerization steps. These molecules formation across the termini, 2a was exposed to FeCl
3
are explored as potential precursors to antikekulene and their reac- (H O, 2 equiv, 100 °C) or Cu(SO CF ) –AlCl (CS ,
2
3
3 2
3
2
tivity compared to that of the parent angular [6]phenylene. An X- 20 °C), leading only to recovered starting material. VOCl3
ray structural determination of 1,2,15,16-tetrachloro[6]phenylene
reveals a structure with a considerably larger helical separation than
in [6]phenylene, caused by the bulk of the appended chlorine atoms.
(
CH Cl , 2.5 equiv, 23 °C), caused immediate decompo-
2 2
sition, while 30% Pd/C in boiling 1-methyl-4-(1-methyl-
ethyl)benzene (p-cymene, 177 °C) left 2a largely intact
Key words: alkynes, cobalt, cycloaddition, helical structures, poly-
cycles
(
(
ca. 20% decomposition). Finally, simple irradiation
Rayonet, THF, 300 and 350 nm, 4 h) also had no effect.
1
2
The cyclophenylene antikekulene (1), in which the min-
imization of cylobutadienoid circuits enhances the rela-
tive importance of a resonance form (shown) with
peripheral inside and outside antiaromatic superdelocal-
ization, has been elusive. The hitherto most promising
1
2
R R
strategy, based on a triple CpCo(CO) -catalyzed cy-
2
cloisomerization of a hexaethynyltribenzocyclyne, aimed
at generating the three benzene rings indicated in red in
structure 1 in a single operation, was upended by the (pre-
R3 R2
1
R4
1–4
2
a, R = H
3
1,2
3,4
sumed to be kinetic) failure of the last cyclization. The
2b, R = H, R = Cl
1
,3
2,4
2
2
c, R = Cl, R = H
subsequent preparation of the helical angular phenylenes
1
–3
4
d, R = Cl, R = H
4
4a
(
heliphenes), including [6]heliphene (2a), suggested an
alternative approach featuring the cross-coupling of its Figure 1
two terminal arene units (blue bonds in 1) in the final step
(
Figure 1). While this scheme is ambitious, it was thought
In view of the preceding failures, attention turned to end-
ring-functionalized derivatives of 2a, specifically chloro-
to be facilitated by the close proximity of the carbons in-
volved (e.g., in 2a, H1–H15 = 2.36 Å).4
a
substituted versions, chosen to avoid interference of the
9
Encouraged by the observation of facile 2 H and 4 H loss halogen with the requisite Sonogashira coupling and Co-
in the mass spectrum of 2a (see Supporting Informa- catalyzed alkyne cyclotrimerization steps of the envis-
1
0
4
a
4
tion), unique in the series of available heliphenes, initial aged synthesis. Such ring-functionalized derivatives of
studies focused on this molecule. Closer scrutiny by ma- the heliphenes are unknown.1,3,4,7 For reasons of prepara-
trix-assisted laser desorption/ionization–time-of-flight tive ease, the (from a regiochemical stand point less desir-
5
mass spectrometry (MALDI–TOF-MS) revealed a pris- able) angular 2,3-dichloro[6]phenylene (2b) frame was
tine molecular ion (m/z = 448) at low laser power. Increas- targeted first, assembled by appropriate modification of
4a
ing the latter led to the emergence of major peaks at m/z = the approach to 2a, shown in Scheme 1 (see Supporting
4
46 and 444, accompanied by a fragment indicating loss Information). It commenced with 1,2-dichloro-4,5-
6
10
of C H . These findings suggested the preparative flash- diiodobenzene (3) and its nonselective heterobisalky-
2
2
vacuum-pyrolytic (FVP) treatment of 2a, which might en- nylation to 4 and selective deprotection to 5. Attachment
7
3
gender 1 and/or other novel structures. In the event, 2a of synthon 6 engendered 7, which was elaborated simi-
4
proofed to be remarkably resilient to change on sublima- larly, but now with building block 8, to assemble crucial
hexayne 9. Prototetradesilylation followed by Cp-
Co(CO) -catalyzed double cyclization ended in 2b. An al-
ternative triple cyclooligomerization strategy that
constructed 8 of the 11 rings in the final step from an oc-
2
SYNLETT 210 014, 25 17, 2429–2433
Advanced online publication: 17.09.2014
4
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
DOI: 10.1055/s-0034-1379140; Art ID: st-2014-s0520-l
Georg Thieme Verlag Stuttgart · New York
©

2430
A. Fonari et al.
LETTER
tayne pieced together from 6 and 7 was also successful but
suffered from low yields (see Supporting Information).
Finally, for purposes of comparison, the lower benzocy-
clobutadienologue 2,3-dichloro[5]phenylene (11) was
prepared (see Supporting Information), in analogy to the
double cyclization scheme depicted in Scheme 1, but sub-
stituting 1-iodo-2-(trimethylsilyl)ethynylbenzene for 8,
thus accessing 10 as the framework to be subjected to the
cobalt cyclization (Scheme 2).
1. K CO3 (10 equiv),
Et2O, MeOH, r.t.
2
2
.
I
SiMe3
R
R
(
1 equiv),
1
1
[PdCl2(PPh3)2] (4 mol%),
CuI (4 mol%), Et N,
3
100 °C, 36 h
7
8
4%
Cl
Cl
[
PdCl2(PPh3)2] (0.5 mol%),
CuI (0.5 mol%), Et3N, RC2H (1 equiv),
R = Si(Me2)C(Me2)CH(Me2)
r.t., 14 h,
then
Me3SiC2H (1 equiv),
r.t., 14 h
R
R
Cl
Cl
I
I
Cl
Cl
R
1
0
35%
6.29
6.86
3
SiMe3
1. NBu4F (5 equiv), THF,
r.t., 40 min
6
.29
6.99
R = Si(Me2)C(Me2)CH(Me2)
R
4
2
. CpCo(CO)2 (2 equiv),
m-xylene,
6.99
6
.50
1
39 °C, hν, 40 min
SiMe3
6.86
6.911
8
%
6
(1 equiv),
6.50
I
Cl
Cl
K2CO3 (3 equiv),
Et2O, MeOH,
R
2 3 2
[PdCl (PPh ) ] (1.5 mol%),
CuI (1.5 mol%), Et3N,
0 °C, 36 h
74%
Cl
r.t., 1 h
R
9
6.33
8
1%
6.33
Cl
6.908
1
1
5
H
1
1
2
. K2CO3 (12 equiv),
Et2O, MeOH, r.t.
Scheme 2 Synthesis of 11 [with H NMR data, δ (ppm), CD Cl ]
2 2
.
I
R
The NMR and UV/vis spectral data of the chloro-
phenylenes 2b and 11 (see Supporting Information) differ
R
4
a,12
only slightly from those of the parent systems,
attest-
R
ing to minimal perturbation by the halo substituents. In
contrast, the mass spectrum of 2b shows, in addition to the
base molecular ion peak envelope at m/z = 516, 518, and
8
(1 equiv),
PdCl2(PPh3)2] (5 mol%),
CuI (5 mol%), Et3N,
00 °C, 36 h
R
SiMe3
[
1
520 (9:6:1), a prominent fragment ion at m/z = 444
29%
Cl
(C H , 27%), signalling the loss of two HCl molecules.
3
6
12
MALDI–TOF confirms this ready fissure, with the frag-
ment ion becoming dominant at high laser power. As in
the case of 2a, it is tempting to associate this process with
the generation of antikekulene 1, now facilitated by 1,2-
hydrogen shifts of the phenyl radicals arising from Cl
atom extrusion. That it is the close proximity of the ter-
minal arene nuclei in 2b which is responsible for this be-
havior is indicated by the corresponding mass spectrum of
Cl
Cl
Cl
R
R
7
R
R
9
1
3
6
.37
6.31
1
2
. NBu4F (7 equiv),
THF, r.t., 40 min
6
.37
6.31
11: The parent ion at m/z = 442 is also the base peak, and
. CpCo(CO)2 (3 equiv),
m-xylene,
Cl loss is relatively minor.
6
.47
6.95
139 °C, hν, 1.5 h
Armed with this information, attempts were made to ac-
cess 1 from 2b preparatively, albeit unsuccessfully. Thus,
attempted FVP (850 °C, 6 × 10 torr) led to decomposi-
tion to soot. Similarly, 11, while stable up to 900 °C, dis-
integrated at 1000 °C. Turning to a transition-metal-
catalyzed C–H arylation protocol, particularly inspired
by the precedence for metal migration, which might re-
locate functionality from the 2,3- to the required 1,2-loci,
6
.96
6.2%
6.47
6
.95
6.86
Cl
–
6
6
.86
6
.47
Cl
6
.47
6.92
1
4
2
b
1
5
1
Scheme 1 Synthesis of 2b [with H NMR data, δ (ppm), CD Cl ]
2
2
2
b was exposed to [PdCl (PPh ) ] (Et N, MeCN, 120 °C,
2 3 2 3
2
0 h). Surprisingly, hydrodechlorination with simultane-
1
6
ous complete four-membered ring hydrogenolysis took
Synlett 2014, 25, 2429–2433
© Georg Thieme Verlag Stuttgart · New York

LETTER
Chloroheliphenes
2431
place to give what appears to be a mixture of sexiphenyl (TMSA)21 to give 15 (in addition to its metabissilyl iso-
isomers, as indicated by the mass spectrum (m/z = 458) mer, ratio = 3:1). Diiodination rendered 1,2-dichloro-7,8-
and the replacement of the characteristically shielded diiodobiphenylene (16), which constitutes a valuable
1
phenylene signals in the H NMR spectrum by ‘normal’ building block for the synthesis of other angular
2
1a
aromatic signals (δ = 7.1–7.8 ppm, m; see Supporting In- phenylenes. As observed for 1,2-diiodobiphenylene,
formation).17
this molecule underwent selective β-Sonogashira cou-
pling with TMSA to provide 17.
At this stage, it became apparent that the plan to utilize the
2
,3-dichloro topology as a latent 1,2-functional synthon The utilization of 13 and 17 in the creation of the final tar-
3
may have been too ambitious. Consequently, the identity gets is depicted in Scheme 4, starting from 18 and its
of the targets shifted to the much more attractive 2,3-di- gratifyingly selective single coupling with 13 to give 19.
and 1,2,15,16-tetrachloro[6]phenylenes 2c and 2d, re- The remaining steps followed the previous strategy to the
spectively. Contemplation of the alterations of Scheme 1 angular [6]phenylene nucleus.
required to reach these structures highlights the need for
4
a
1
3
1
,2-dichloro-3,4-diiodobenzene (12), not only to replace
, but also to construct a 1,2-dichloro analogue of 5 (i.e.,
4) and 7,8-dichloro derivative of 8 (i.e., 17; Scheme 3).
R
R
1
3 (1 equiv),
[
PdCl2(PPh3)2] (2 mol%),
CuI (2 mol%), Et3N,
THF, 100 °C, 24 h
At the outset of this work, 12 was unknown, but conve-
1
8
nient access was developed by us recently, the yield of
which was further improved here on scale-up (255 mmol;
see Supporting Information).
Cl
7
9%
Cl
Me3SiC2H (1 equiv),
PdCl2(PPh3)2] (5 mol%),
CuI (5 mol%), Et3N, THF,
R
R
8 R = Si(Me2)C(Me2)CH(Me2)
Me3Si
[
Cl
I
Cl
I
1
19
r.t., 22 h
I
Cl
Cl
SiMe3
9
0%
X
I
P
12
13
X
1
2
. K2CO3 (1 equiv),
MeOH, r.t., 3 h
20
[X = H, P = Si(Me2)C(Me2)CH(Me2); 1 equiv]4a
or
Cl
SiMe3
. Me3SiC2SnMe3 (1.2 equiv),
PdCl2(PPh3)2] (5 mol%), Cl
toluene, 95 °C, 20 h
Me3SiC2H (5 equiv),
1. NBu4F (8 equiv),
THF, r.t., 2–12 h
2. CpCo(CO)2
(2 equiv),
toluene,
111 °C, hν, 45 min
[
17
CpCo(CO)2 (1.2 equiv),
P
(X = Cl, P = SiMe , 1 equiv), R
toluene, Δ, hν, 90 h
3
[
PdCl2(PPh3)2] (2 mol%),
73%
44%
CuI (2 mol%), Et3N, THF,
H
1
00 °C, 24 h
14
Cl
SiMe3
Cl
I
X
Cl
ICl (5 equiv),
CH2Cl2, r.t., 4 h
Cl
SiMe3
Cl
I
X
Cl
89%
15
16
R
Me3Si
2
1
Me3SiC2H (1.2 equiv),
PdCl2(PPh3)2] (5 mol%),
CuI (5 mol%),
[
X = H, P = Si(Me2)C(Me2)CH(Me2)], 55%
[
SiMe3
Cl
I
22
(
X = Cl, P = SiMe3), 41%
Cl
Et3N, THF, r.t., 24 h
6.31
61%
6.31
17
6.71−6.90
Scheme 3 Synthesis of dichloro building blocks 14 and 17
Cl
6
.71−6.90
6.88 6.45
Cl
From 12, the assembly of 14 and 17 proceeded as shown
in Scheme 3. The sterically controlled regioselectivity of
the single Sonogashira coupling18 to 13 was crucial and
confirmed by an independent synthesis of 13 from 2,3-di-
chloro-6-iodoaniline19 (see Supporting Information).
6
.67
Cl
6.45
Cl
6.27
7.01
Cl
Cl
6.25
6.65
2c (from 21), 5.5%
6.32
6.99
2
0
Desilylation of 13, followed by Stille coupling, fur-
nished the regiodifferentiated diyne 14, which was sub-
6.29
6.64
2d (from 22), 3.4%
jected
cocyclotrimerization
to
partly
selective
with (trimethylsilyl)acetylene
cobalt-catalyzed
1
Scheme 4 Assembly of 2c and 2d [with H NMR data, δ (ppm),
CDCl3]
©
Georg Thieme Verlag Stuttgart · New York
Synlett 2014, 25, 2429–2433

2432
A. Fonari et al.
LETTER
–
1
To determine the effect of the added chlorine atoms in 2d kcal mol . Finally, A and B form offset π-stacked pairs
4
a
on the helical structure of the parent 2a, an X-ray struc- (Figure 2), juxtaposing two angular [4]phenylene sub-
tural investigation was carried out (Figure 2).2 Com- structures, with close contacts C33···C20′ = 3.277 Å,
pound 2d crystallizes with two independent molecules A C20···C9′ = 3.290 Å, C32···C17′ = 3.380 Å, and
and B in the asymmetric unit, exhibiting very similar bond Cl1′···Cl4 = 3.494 Å (see Supporting Information).
2
lengths and angles, but differing substantially in the de-
gree of helical separation, the latter much more pro-
nounced than in 2a. Thus, the shortest intramolecular
With small amounts of 2c and 2d in hand, their feasibility
as precursors to antikekulene (1) was assessed. Disap-
pointingly, inspection of the mass spectrum of 2c showed
contacts in 2d are between Cl1 and Cl4: 3.471 Å for A,
it to be essentially identical to that of 2b, with the molec-
and 3.416 Å for B, held roughly at van der Waals distanc-
ular ion at m/z = 516 constituting the base peak, and loss
2
3
es (ca. 3.50 Å) by increasing the distance and interplanar
angle of the terminal benzene nuclei to 5.885 Å and
of two HCl molecules [m/z (%) = 444 (37)] not being rel-
+
atively accentuated. Similarly, 2d exhibits the [M] pat-
33.40° (A), and 6.374 Å and 39.83° (B), respectively. At
tern expected for a tetrachloride [m/z (%) = 591 (4), 590
the B3LYP/6-311G** level, the geometries of both mole-
(
5
14), 589 (19), 588 (56), 587 (39), 586 (100), 585 (31)+,
cules (A and B) converged to a single symmetrical C to-
2
84 (78)], the fragment at m/z (%) = 444 (20) ([M – 4 Cl]
pology with a Cl1···Cl4 distance of 3.669 Å and
corresponding separation and interplanar angle of the ter-
minal benzenes of 6.302 Å and 39.61°, respectively. In
contrast, the shortest contact in 2a is between the terminal
hydrogens H1 and H4 (adopting the numbering for Cl
from above) at 2.364 Å, necessitating lesser distortion of
the helix (terminal benzene ring distances and angles:
also not especially pronounced. For comparison, 1,2-di-
chlorobiphenylene (accessed by protodesilylation of 15;
see Supporting Information) displays m/z (%) = 220 (100,
+
[
M] ) and single [185 (15)] and double loss of Cl [150
40)] to a similar degree. Since these data were unencour-
(
aging with respect to pyrolytic attempts to generate 1, a
1
(
substance) limited foray ( H NMR experiments, mg
5.62 Å and 22.8°).
scale, THF-d ) into the intramolecular cross-coupling of
8
2
5
2
d was taken, with mixed results. Thus, nickel-catalyzed
2
6
methods led to complete decomposition, while Mg; Mg–
Cu(AcO) ; Na; (activated) Cu; or Na–CuI proved inert.
2
7
2
Most promising was activated Cu–Na–CuI at room tem-
perature, which led reproducibly to the clean emergence
of a singlet at δ = 5.97 ppm, before complete decomposi-
1
3
tion set in, thus precluding the recording of a C NMR
spectrum. This behavior, in addition to the unique chemi-
2
8
cal shift outside the range of plausible impurities and
tantalizingly close to that calculated for 1 (δ = 6.20
2
e
ppm), are promising. Corroboration of this speculation
will have to await large-scale syntheses of 2d and its pre-
parative conversion.
In conclusion, we have synthesized the first ring-function-
alized heliphenes 2b–d, in which the halogen should pro-
vide a general handle with respect to structural
2
9
modification, particularly for materials applications.
Some evidence, albeit speculative, has been obtained sug-
gesting 2d as a hopeful precursor to antikekulene (1).
Figure 2 ORTEP plot of 2d showing two molecules (A, top; B, bot-
tom) in the unit cell
Acknowledgment
This study was facilitated by support from the NSF (CHE-0907800;
KPCV; DMR 0934212 (PREM), and IIA-1301346; TVT). JCR is
grateful to the Alexander von Humboldt Foundation for a Feodor
Lynen Research Fellowship. We thank Ms. Sze Lyn Alycia Tan for
The data are a testament to the pronounced flexibility of
the heliphenes and the phenylenes in general. This facet
is also reflected in the variance of interplanar angles be-
4
24
tween successive fused six- and four-membered rings: for carrying out the chemical structure proof of 13.
A, 3.01, 5.14, 3.51, 3.31, 4.76, 3.96, 5.86, 5.45, 5.68, and
2
7
4
.63°; for B, 1.60, 1.19, 1.92, 2.74, 4.87, 4.93, 8.67, 8.51,
Supporting Information for this article is available online
at http://www.thieme-connect.com/products/ejournals/journal/
.81, and 3.89° (computed for the C structure: 3.60, 5.42,
2
.54, 5.53, and 4.11°), revealing markedly uneven helical
1
0.1055/s-00000083. SunogIpimirf antoSuIpg
n
ori
m
turns. For comparison, the (experimentally symmetrical)
structure of 2a displays values of 1.49, 3.35, 2.41, 3.28,
and 3.28°.4a Despite these differences in topology, the
References and Notes
computed energies of A and B (at experimental geome-
tries) show the latter to be more energetic by only 0.12
(1) (a) For a review of the [N]phenylenes, see: Miljanić, O. Š.;
Vollhardt, K. P. C. In Carbon Rich Compounds: Molecules
Synlett 2014, 25, 2429–2433
© Georg Thieme Verlag Stuttgart · New York

LETTER
to Materials; Haley, M. M.; Tykwinski, R. R., Eds.; Wiley-
Chloroheliphenes
2433
(12) Schmidt-Radde, R. H.; Vollhardt, K. P. C. J. Am. Chem. Soc.
1992, 114, 9713.
(13) (a) Tsefrikas, V. M.; Scott, L. T. Chem. Rev. 2006, 106,
4868. (b) Brooks, M. A.; Scott, L. T. J. Am. Chem. Soc.
1999, 121, 5444.
VCH: Weinheim, 2005, 140. For recent work, see, for
example: (b) Gu, Z.; Vollhardt, K. P. C. Synthesis 2013, 45,
2
469. (c) Gu, Z.; Boursalian, G. B.; Gandon, V.; Padilla, R.;
Shen, H.; Timofeeva, T. V.; Tongwa, P.; Vollhardt, K. P. C.;
Yakovenko, A. A. Angew. Chem. Int. Ed. 2011, 50, 9413.
(14) (a) Chiusoli, G. P.; Catellani, M.; Costa, M.; Motti, E.; Della
Ca’, N.; Maestri, G. Coord. Chem. Rev. 2010, 254, 456.
(b) Livendahl, M.; Echavarren, A. M. Isr. J. Chem. 2010, 50,
630. (c) McGlacken, G. P.; Bateman, L. M. Chem. Soc. Rev.
2009, 38, 2447.
(
d) González Gómez, J. A.; Green, J.; Vollhardt, K. P. C.
Synlett 2011, 805. (e) Engelhardt, V.; Garcia, J. G.; Hubaud,
A. A.; Lyssenko, K. A.; Spyroudis, S.; Timofeeva, T. V.;
Tongwa, P.; Vollhardt, K. P. C. Synlett 2011, 280.
(
f) Mohler, D. L.; Kumaraswamy, S.; Stanger, A.; Vollhardt,
(15) Shi, F.; Larock, R. C. Top. Curr. Chem. 2010, 292, 123.
(16) For the hydrogenolysis of biphenylenes, see: (a) Edelbach,
B. L.; Vicic, D. A.; Lachicotte, R. J.; Jones, W. D.
Organometallics 1998, 17, 4784; and references cited
therein. For a monograph, see: (b) Shepherd, M. K.
Cyclobutarenes; Elsevier: Amsterdam, 1991.
K. P. C. Synlett 2006, 2981.
(
2) For a selection of recent computational treatments, see
(a) Luzanov, A. V. J. Struct. Chem. 2013, 54, 277.
(
5
b) Dickens, T. K.; Mallion, R. B. Chem. Phys. Lett. 2011,
17, 98. (c) Randić, M.; Balaban, A. T.; Plavšic, D. Phys.
Chem. Chem. Phys. 2011, 13, 20644. (d) Aihara, J. J. Phys.
Chem. A 2008, 112, 4382. (e) Schulman, J. M.; Disch, R. L.
J. Phys. Chem. A 2007, 111, 10010.
(17) For NMR data of sexiphenyls, see: (a) Mathew, S. M.;
Engle, J. T.; Ziegler, C. J.; Hartley, C. S. J. Am. Chem. Soc.
2013, 135, 6714. (b) Mathew, S. M.; Hartley, C. S.
Macromolecules 2011, 44, 8425. (c) Ozasa, S.; Fujioka, Y.;
Ibuki, E. Chem. Pharm. Bull. 1982, 30, 2698. (d) Ibuki, E.;
Ozasa, S.; Fujioka, Y.; Okada, M.; Yanagihara, Y. Chem.
Pharm. Bull. 1982, 30, 2369.
(18) Chinchilla, R.; Nájera, C. Chem. Rev. 2007, 107, 874.
(19) Shen, H.; Vollhardt, K. P. C. Synlett 2012, 23, 208.
(20) Lo Sterzo, C. Synlett 1999, 1704.
(21) Patterned after: (a) Schmidt-Radde, R. H.; Vollhardt, K. P.
C. J. Am. Chem. Soc. 1992, 114, 9713. (b) Hillard, R. L. III.;
Vollhardt, K. P. C. Angew. Chem., Int. Ed. Engl. 1977, 16,
399.
(22) CCDC 778109 contains the supplementary crystallographic
data for 2d. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
(
3) Eickmeier, C.; Junga, H.; Matzger, A. J.; Scherhag, F.; Shim,
M.; Vollhardt, K. P. C. Angew. Chem., Int. Ed. Engl. 1997,
3
6, 2103.
(
4) (a) Han, S.; Bond, A. D.; Disch, R. L.; Holmes, D.;
Schulman, J. M.; Teat, S. J.; Vollhardt, K. P. C.; Whitener,
G. D. Angew. Chem. Int. Ed. 2002, 41, 3223. (b) Han, S.;
Anderson, D. R.; Bond, A. D.; Chu, H. V.; Disch, R. L.;
Holmes, D.; Schulman, J. M.; Teat, S. J.; Vollhardt, K. P. C.;
Whitener, G. D. Angew. Chem. Int. Ed. 2002, 41, 3227.
5) We thank Professor Thomas Drewello, University of
Erlangen-Nürnberg, for providing preliminary data.
6) For a similar fragmentation of hexahelicene, see: Dougherty,
R. C. J. Am. Chem. Soc. 1968, 90, 5788.
(
(
(
7) (a) FVP of angular [4]phenylene causes isomerization to
‘
biphenylene dimer’: Dosa, P. I.; Gu, Z.; Hager, D.; Karney,
W. L.; Vollhardt, K. P. C. Chem. Commun. 2009, 45, 1967.
(23) Bondi, A. J. Phys. Chem. 1964, 68, 441.
For related reactions of angular and linear [3]phenylene, see:
(24) Holmes, D.; Kumaraswamy, S.; Matzger, A. J.; Vollhardt,
K. P. C. Chem. Eur. J. 1999, 5, 3399.
(b) Matzger, A. J.; Vollhardt, K. P. C. Chem. Commun.
1
997, 33, 1415. (c) Dosa, P. I.; Schleifenbaum, A.;
(25) For selected reviews, see: (a) Everson, D. A.; Weix, D. J.
J. Org. Chem. 2014, 79, 4793. (b) Nelson, T. D.; Crouch, R.
D. Org. React. 2004, 63, 265.
(26) See, for example: Colon, I.; Kelsey, D. R. J. Org. Chem.
1986, 51, 2627.
(27) Rieke, R. D.; Rhyne, L. D. J. Org. Chem. 1979, 44, 3445.
(28) See, for example: Fulmer, G. R.; Miller, A. J. M.; Sherden,
N. H.; Gottlieb, H. E.; Nudelman, A.; Stoltz, B. M.; Bercaw,
J. E.; Goldberg, K. I. Organometallics 2010, 29, 2176.
(29) For a recent review of the properties and applications of
helicenes, see: Gingras, M. Chem. Soc. Rev. 2013, 42, 1051.
Vollhardt, K. P. C. Org. Lett. 2001, 3, 1017.
(
8) Grzybowski, M.; Skonieczny, K.; Butenschön, H.; Gryko,
D. T. Angew. Chem. Int. Ed. 2013, 52, 9900.
9) For a recent review, see: Hierso, J.-C.; Beaupérin, M.; Saleh,
S.; Job, A.; Andrieu, J.; Picquet, M. C. R. Chim. 2013, 16,
(
5
80.
(
10) For the successful employment of chloroarenes in CpCo-
catalyzed cyclizations, see: Berris, B. C.; Hovakeemian, G.
H.; Lai, Y.-H.; Mestdagh, H.; Vollhardt, K. P. C. J. Am.
Chem. Soc. 1985, 107, 5670.
(
11) Nicolaou, K. C.; Dai, W. M.; Hong, Y. P.; Baldridge, K. K.;
Siegel, J. S.; Tsay, S. C. J. Am. Chem. Soc. 1993, 115, 7944.
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