Allenylporphyrins: a new motif on the porphyrin periphery

Article abstract of DOI:10.1016/j.tetlet.2009.03.097

Palladium-catalysed Suzuki-Miyaura cross-coupling proved to be the simplest and most efficient method for attaching an unsubstituted allene, a novel substituent and potential functional group, to the porphyrin periphery. Comparative studies on various all

Full text of DOI:10.1016/j.tetlet.2009.03.097

Tetrahedron Letters 50 (2009) 2566–2569
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Allenylporphyrins: a new motif on the porphyrin periphery
*
Oliver B. Locos, Katja Dahms, Mathias O. Senge
School of Chemistry, SFI Tetrapyrrole Laboratory, Trinity College Dublin, Dublin 2, Ireland
a r t i c l e i n f o
a b s t r a c t
Article history:
Palladium-catalysed Suzuki–Miyaura cross-coupling proved to be the simplest and most efficient method
for attaching an unsubstituted allene, a novel substituent and potential functional group, to the porphyrin
periphery. Comparative studies on various allenyl synthetic pathways show that this method, which
makes use of a bromoporphyrin and allenylboronate, affords the corresponding allenylporphyrin in the
presence of an appropriate base and THF.
Received 30 November 2008
Revised 3 March 2009
Accepted 12 March 2009
Available online 18 March 2009
Ó 2009 Elsevier Ltd. All rights reserved.
The synthesis and functionalisation of porphyrins are of interest
to organic chemists. Tetrapyrroles play pivotal, diverse roles in
Nature1 and there is a continuing desire to exploit their properties
for applications in medicine,2 catalysis3 and nano materials.4 As a
result, functional group interconversion and synthetic transforma-
tions spanning the field of porphyrin chemistry are constantly
being explored and improved.5 One niche in the area of synthetic
transformations that appear to have received little to no attention
with porphyrins, however, is the use of 1,2-propadiene, or allene.
Allenes represent a versatile functional group that can be uti-
lised as a building block in a variety of synthetic transformations.6
With the emergence of efficient protocols for their preparation, al-
lenes have allowed chemists to access a variety of structurally
interesting products that possess biological, chiral and optical
activity.7
While cumulenic porphyrin dimers linked by two carbons have
been explored for their impressive optical properties,8 these dimers
are quinoidal in nature, which results in exceptionally perturbed
electronic absorption spectra. To the best of our knowledge, no stud-
ies have been performed on the utilisation of cumulative double
bonds on porphyrins for their chiral and biological aspects, hence
this has become the aim of our investigation.
could be isolated by simple chromatography in very good yield.
Interestingly though, both in the one-pot procedure, and using
the isolated intermediate 2, the second olefination reaction could
not be realised under a variety of conditions. This olefination
Ph
Ph
Ni
NH
N
N
N
N
N
N
H
O
Br
Ph
Ph
HN
Ph
Ph
1
H25
O O
O P
Pd(OAc)2
PPh3
NaH
THF
0 ºC
O
O
P
O
K2CO3
DMF
O P
O O
Toluene
Ph
Ph
N
N
N
N
NH
N
N
O
O
O
O
Ni
Ph
Ph
P
O
P
O
HN
Of the methods we envisaged being successful for allene syn-
thesis on the macrocycle periphery, the Horner–Wadsworth–Em-
mons (HWE) reaction appealed the most due to its versatility in
allene generation9 and to its need for a formylporphyrin precursor.
Formylporphyrins are commonly used precursors the utility of
which has recently been expanded successfully from solely metal-
loporphyrins to include their metal-free analogues.10
Applying the one-pot double olefination procedure designed by
Tomioka and co-workers11 to formylporphyrin 1 (Scheme 1), the
HWE reaction using tetraisopropyl methylenebisphosphonate
and NaH worked well and the extremely polar intermediate 2
Ph
Ph
2
6
68%
88%
t-BuOK
PhCHO
THF
LDA
PhCHO
THF
LDA
LDA
PhCHO
THF
Pentyl-CHO
THF
-78 ºC
-78 ºC
-78 ºC
-78 ºC
Ph
Ph
Ni
Starting material
N
N
N
Ni
N
N
N
N
N
O
O
O
Ph
H
Ph
P
N
Ph
Ph
3
31%
4
77%
* Corresponding author. Tel.: +353 1 896 8537; fax: +353 1 896 8536.
E-mail address: sengem@tcd.ie (Mathias O. Senge).
Scheme 1.
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.03.097

O. B. Locos et al. / Tetrahedron Letters 50 (2009) 2566–2569
2567
reaction occurs through nucleophilic substitution of an in situ gen-
erated carbanion intermediate by an aldehyde.11 However, in our
case, when using either benzaldehyde or hexanal in conjunction
with LDA, the result was the unexpected substitution of diisopro-
pylamine from the base onto the alkenephosphonate to generate
porphyrin 4. Reaction of diisopropylamine with 2 occurred seem-
ingly regardless of the temperature used (À80 °C to 60 °C). Use of
base and metalloporphyrin used, either the 1-propynyl-, 7, alle-
nyl-, 8, or 2-propynylporphyrin, 9 could be isolated after column
chromatography. The results of the investigations to find the opti-
mum conditions for attaching the allene to the porphyrin are
shown in Table 1.
Except for when K3PO4 was used as base, the Suzuki coupling
was relatively unsuccessful when carried out at reflux in THF. Even
using K3PO4, coupling only occurred with the NiII bromoporphyrin,
and the use of this with a strong base resulted in rearrangement of
the allene to the more stable 1-propynylporphyrin Ni7, along with
the formation of unidentifiable side products. Our first successful
attempt at isolating the allenylporphyrin Ni8 came from heating
in THF to 80 °C in a sealed Schlenk tube and using a 20-fold excess
of K3PO4 (9% yield). Porphyrin Ni7 was also isolated from this reac-
tion in 14% yield along with unidentifiable side products. Interest-
ingly, using the same conditions, but in 1,4-dioxane at 80 °C, 100 °C
and 120 °C, no allenyl- or propynyl-porphyrin was isolated.
On varying the Pd catalyst, the best coupling results were
achieved with PdII salts with the bidentate ligands 1,2-(diphenyl-
phosphino)ethane and 1,3-(diphenylphosphino)propane. In partic-
ular, the allenyl-porphyrin Ni8 was isolated in up to 50% yield
when K2CO3 was used as the base in 10-fold excess.14 Interestingly,
while PdCl2(dppe) and PdCl2(dppp) were found to be equally effec-
tive in coupling, when a twofold excess of Cs2CO3 was used, the
PdCl2(dppp) caused ꢀ25% rearrangement from the allene to the
1-propynylporphyrin (entry 7). The use of PdCl2(dppe) gave no
such rearrangement, so it was considered the catalyst of choice
for the remaining optimisation experiments. It should be noted
that the PdII catalysts were synthesised according to the procedure
of Miyaura and Suzuki,15 and these represent new applications for
the catalysts PdCl2(dppe) and PdCl2(dppp).
The amount of base, strength of base and type of metallopor-
phyrin used in the coupling reactions were also found to have a
profound effect on the outcome of the reaction. Using a twofold ex-
cess of Cs2CO3 resulted in Ni8 solely being isolated from the reac-
tion, while a 10-fold excess resulted in Ni7 being the only Suzuki
product in 61% yield.14b Cs2CO3 was found to be an inappropriate
base when either a ZnII or free-base porphyrin was used, the result
being unidentifiable products. Using the less labile alkali base,
K2CO3 in 10-fold excess led to Ni8 again being isolated as the only
product from Ni5, while quite surprisingly, the kinetically rear-
ranged Zn9 was the only product isolated from the reaction of
Zn5.14c K2CO3 was ineffective for porphyrin H25, while Na2CO3
did not aid in Suzuki coupling for any of the metalloporphyrins.
Inspired by the base-catalysed kinetic rearrangement of the al-
lene in the ZnII porphyrin to form Zn9, the same rearrangement
was attempted for Zn7 (Scheme 3). Zn7 was prepared by a method
adapted from Newman-Evans et al. for phenylprop-2-yne from
phenylacetylene,16 which subjects the alkyne to a strong base with
t
the non-nucleophilic base, BuOK, only resulted in partial dehy-
drophosphonation to yield the alkynylporphyrin 3 in modest
amounts when the reaction mixture was heated to 60 °C after addi-
tion of the base. Using the metal-free analogue 6, which was syn-
thesised by Heck coupling, only starting material was retrieved
from the reaction mixture.
As the double HWE reaction did not afford the desired result, we
tried a more unconventional synthetic route to allenes by using the
allenylboronic acid pinacol ester reagent and Suzuki coupling
(Scheme 2). Previously, this particular reagent has been used mainly
to take advantage of the allene in three- and four-component reac-
tions and in RuII catalysis to generate alkenylboronates.12,13
All Suzuki coupling reactions were attempted using a ten-fold
excess of the allenylboronate, and the reaction mixture was de-
gassed by three freeze-pump-thaw cycles before being heated to
the desired temperature. Using a variety of conditions to couple
the allenylboronate to the bromoporphyrin, it was discovered that
very few conditions resulted in the consumption of the bromo
starting material. However, when successful, depending on the
Ph
N
N
N
N
O
B
O
+
M
Br
Ph
Ph
5
M Ni, Zn, 2H
Pd Catalyst
Base
Ph
Ph
M
THF
H
N
N
N
N
N
N
N
N
Ph
M
M
CH3
Ph
Ph
H
H
N
N
N
N
Ph
Ph
7
Ph
9
Ph
8
Scheme 2.
Table 1
Yields of the Suzuki–Miyaura coupling reaction between 5 and allenylboronate in THF
Entry
M
Catalyst
Cat. Conc. (% mol)
Time (h)
Base (excess)
Temp °C
Yield 7 (%)a
Yield 8 (%)a
Yield 9 (%)a
1
Ni
Ni
Ni
Ni
Ni
Ni
Ni
Ni
Ni
Ni
Zn
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
15
15
15
25
15
15
15
15
15
15
15
15
15
15
15
5
15
15
15
15
15
15
Cs2CO3 (twofold)
K3PO4 (twofold)
K3PO4 (20-fold)
Cs2CO3 (twofold)
Cs2CO3 (twofold)
Cs2CO3 (twofold)
Cs2CO3 (twofold)
Cs2CO3 (twofold)
Cs2CO3 (10-fold)
K2CO3 (10-fold)
K2CO3 (10-fold)
80
67
80
80
80
80
80
80
80
80
80
—
25
14
—
—
—
9
—
61
—
—
2
—
9
—
—
—
—
—
—
—
—
—
—
46
2b
3b
4
PdCl2(PPh3)2/AsPh3
PdCl2(PPh3)2/AsPh3
Pd2(dba)3/AsPh3
PdCl2(dppp)
PdCl2(dppe)
PdCl2(dppe)
PdCl2(dppe)
PdCl2(dppe)
8
5
6
7
8
9
10
11
10
10
37
41
—
50
—
a
Isolated yield.
b
The strength of the base resulted in another porphyrin product that was not identifiable by 1H NMR and MS analysis.

2568
O. B. Locos et al. / Tetrahedron Letters 50 (2009) 2566–2569
(d) Langa, F.; Gomez-Escalonilla, M. J.; de la Cruz, P. J. Porphyrins
CH
3
Phthalocyanines 2007, 11, 348.
5. For recent examples of porphyrin functionalization, see: (a) Senge, M. O.;
Richter, J. J. J. Porphyrins Phthalocyanines 2004, 8, 934; (b) Sugiura, K.-i.; Kato,
A.; Iwasaki, K.; Miyasaka, H.; Yamashita, M.; Hino, S.; Arnold, D. P. Chem.
Commun. 2007, 2046; (c) Esdaile, L. J.; Jensen, P.; McMurtrie, J. C.; Arnold, D. P.
Angew. Chem., Int. Ed. 2007, 46, 2090; (d) Atefi, F.; Locos, O. B.; Senge, M. O.;
Arnold, D. P. J. Porphyrins Phthalocyanines 2006, 10, 176; (e) Baba, H.; Chen, J.;
Shinokubo, H.; Osuka, A. Chem. Eur. J. 2008, 14, 4256; (f) Hori, T.; Peng, X.;
Aratani, N.; Takagi, A.; Matsumoto, T.; Kawai, T.; Yoon, Z. S.; Yoon, M.-C.; Yang,
J.; Kim, D.; Osuka, A. Chem. Eur. J. 2008, 14, 582; (g) Senge, M. O.; Fazekas, M.;
Notaras, E. G. A.; Blau, W. J.; Zawadzka, M.; Locos, O. B.; Ni Mhuircheartaigh, E.
M. Adv. Mater. 2007, 19, 2737; (h) Senge, M. O. Acc. Chem. Res. 2005, 38, 733; (i)
Horn, S.; Sergeeva, N. S.; Senge, M. O. J. Org. Chem. 2007, 72, 5414; (j) Horn, S.;
Senge, M. O. Eur. J. Org. Chem. 2008, 4881; (k) Hao, E. H.; Fronczek, F. R.; Vicente,
M. G. H. Chem. Commun. 2006, 4900; (l) Fan, D. Z.; Taniguchi, M.; Lindsey, J. S. J.
Org. Chem. 2007, 72, 5350; (m) Mori, G.; Shinokubo, H.; Osuka, A. Tetrahedron
Lett. 2008, 49, 2170; (n) Maes, W.; Ngo, T. H.; Vanderhaeghen, J.; Dehaen, W.
Org. Lett. 2007, 9, 3165.
6. (a) Castro, A. M. M. Chem. Rev. 2004, 104, 2939; (b) Sydnes, L. K. Chem. Rev.
2003, 103, 1133; (c) Mikami, K.; Shimizu, M. Chem. Rev. 1992, 92, 1021; (d)
Nakai, T.; Mikami, K. Chem. Rev. 1986, 86, 885; (e) Smadja, W. Chem. Rev. 1983,
83, 263; (f) Taylor, D. R. Chem. Rev. 1967, 67, 317; (g) Pasto, D. J. Tetrahedron
1984, 40, 2805; (h) Krause, N.; Hoffmann-Roeder, A. Tetrahedron 2004, 60,
11671; (i) Hoffmann-Roder, A.; Krause, N. Angew. Chem., Int. Ed. 2002, 41, 2933.
7. (a) Ma, S.; Hou, H.; Zhao, S.; Wang, G. Synthesis 2002, 1643; (b) Hoffmann-
Roeder, A.; Krause, N. Angew. Chem., Int. Ed. 2004, 43, 1196.
Ph
Ph
N
N
N
N
N
N
N
N
Zn
Zn
CH3
Ph
Ph
MeLi
MeI
THF
-30 ºC
Ph
Ph
Zn7 88%
n-BuLi
THF
0 ºC
Ph
Ph
N
N
N
N
NH
N
N
Zn
Ph
CH3
Ph
HN
Ph
Zn9
Ph
H27 25%
8. (a) Blake, I. M.; Rees, L. H.; Claridge, T. D. W.; Anderson, H. L. Angew. Chem., Int.
Ed. 2000, 39, 1818; (b) Piet, J. J.; Taylor, P. N.; Anderson, H. L.; Osuka, A.;
Warman, J. M. J. Am. Chem. Soc. 2000, 122, 1749; (c) Beljonne, D.; O’Keefe, G. E.;
Hamer, P. J.; Friend, R. H.; Anderson, H. L.; Bredas, J. L. J. Chem. Phys. 1997, 106,
9439.
Scheme 3.
9. (a) Nagaoka, Y.; Tomioka, K. J. Org. Chem. 1998, 63, 6428; (b) Nagaoka, Y.; Inoue,
H.; Tomioka, K. Phosphorus, Sulfur Silicon Relat. Elem. 2002, 177, 1843; (c)
Wadsworth, W. S., Jr.; Emmons, W. D. J. Am. Chem. Soc. 1961, 83, 1733; (d)
Fillion, H.; Refouvelet, B.; Pera, M. H.; Dufaud, V.; Luche, J. L. Synth. Commun.
1989, 19, 3343; (e) Fillion, H.; Hseine, A.; Pera, M. H. Synth. Commun. 1987, 17,
929.
10. (a) Runge, S.; Senge, M. O. Tetrahedron 1999, 55, 10375; (b) Dahms, K.; Senge,
M. O.; Bakar, M. B. Eur. J. Org. Chem. 2007, 3833; (c) Senge, M. O.; Hatscher, S. S.;
Wiehe, A.; Dahms, K.; Kelling, A. J. Am. Chem. Soc. 2004, 126, 13634; (d)
Takanami, T.; Wakita, A.; Sawaizumi, A.; Iso, K.; Onodera, H.; Suda, K. Org. Lett.
2008, 10, 685.
11. Inoue, H.; Tsubouchi, H.; Nagaoka, Y.; Tomioka, K. Tetrahedron 2002, 58, 83.
12. (a) Tonogaki, K.; Itami, K.; Yoshida, J. Org. Lett. 2006, 8, 1419; (b) Tonogaki, K.;
Itami, K.; Yoshida, J.-I. J. Am. Chem. Soc. 2006, 128, 1464.
13. Bustelo, E.; Guerot, C.; Hercouet, A.; Carboni, B.; Toupet, L.; Dixneuf, P. H. J. Am.
Chem. Soc. 2005, 127, 11582.
subsequent trapping of the anion intermediate with MeI. However,
only starting material and the demetallated H27 were retrieved
from the reaction mixture after column chromatography when
subjecting 2-propynylporphyrin Zn7 to 2 equiv of n-BuLi in THF
at 0 °C. This preliminary investigation is ongoing in our laboratory
with NiII derivatives.
In conclusion, for the first time, unsubstituted allenes and prop-
argyl substituents have been attached to the porphyrin periphery
by Suzuki coupling and trapping of an alkyne anion with MeI.
The phenomenon of allene rearrangement on the porphyrin
periphery is still being investigated. However, as allenes are partic-
ularly reactive functional groups, especially towards metal cataly-
sis,7,17,18 we have also begun exploring their reactivity on the
macrocycle.
14. (a) Ni8 was synthesised in the optimum yield using the following procedure:
To a 20 cm3 Schlenk tube, Ni5 (50 mg), PdCl2(dppe) (15 mol %, 10 mg) and
K2CO3 (107 mg) were added and dried under vacuum before the flask was
charged with argon. Dry THF (10 cm3) was added and the mixture was
degassed via three freeze-pump-thaw cycles. Allenylboronic acid pinacol ester
(140 lL, 10-fold excess) was subsequently added, and the flask was sealed and
Acknowledgements
heated to 80 °C overnight. The progress of the reaction was monitored by TLC
using CH2Cl2/n-hexane (1:2) as eluent. Upon complete consumption of the
starting material, the solvent was removed in vacuo and the residue was
chromatographed on silica gel using CH2Cl2/n-hexane (1:2). The first fraction
collected was Ni8 (24 mg, 50%). Analytical data: mp: >300 °C; 1H NMR
(400 MHz, CDCl3): 9.46 (d, 3J = 5.0 Hz, 2H, b-H), 8.80 (d, 3J = 5.0 Hz, 2H, b-H),
8.69 (d, 3J = 4.90 Hz, 2H, b-H), 8.67 (d, 3J = 4.90 Hz, 2H, b-H), 8.31 (t, 4J = 6.8 Hz,
1H, allene–CH), 8.01 (m, 6H, o-Ph–H), 7.70 (m, 9H, m,p-Ph–H), 5.32 (d,
4J = 6.8 Hz, 2H, allene–CH2); 13C NMR (150 MHz, CDCl3): 216.6, 142.1, 141.9,
141.4, 141.1, 140.5, 140.2, 133.2, 132.2, 132.0, 131.8, 131.7, 130.3, 128.2, 126.5,
This work was generously funded by a Science Foundation Ire-
land Research Professorship Award (SFI 04/RP1/B482) and we used
facilities provided by the Centre of Chemical Synthesis and Chem-
ical Biology funded by the HEA.
References and notes
125.5, 118.6, 109.3, 92.1; UV/Vis (CH2Cl2) kmax (log
575 (3.81); HRMS (MALDI) calcd for [M]+ C41H26N4Ni 632.1511, found
632.1530; IR cmÀ1
= 696 (aromatic H), 737 (aromatic H), 1537 (N–H),
e): 421 (5.41), 535 (4.31),
1. (a)The Porphyrin Handbook; Kadish, K. M., Smith, K. M., Guilard, R., Eds.;
Academic Press: San Diego, California, 2000; Vol. 1, (b) Milgrom, L. R. The Colors
of Life: An Introduction to the Chemistry of Porphyrins and Related Compounds;
Oxford University Press: London, 1997.
2. (a) Maillard, P.; Loock, B.; Grierson, D. S.; Laville, I.; Blais, J.; Doz, F.; Desjardins,
L.; Carrez, D.; Guerquin-Kern, J. L.; Croisy, A. Photodiagn. Photodyn. Ther. 2007, 4,
261; (b) Molinari, A.; Bombelli, C.; Mannino, S.; Stringaro, A.; Toccacieli, L.;
Calcabrini, A.; Colone, M.; Mangiola, A.; Maira, G.; Luciani, P.; Mancini, G.;
Arancia, G. Int. J. Cancer 2007, 121, 1149; (c) Kiesslich, T.; Berlanda, J.; Plaetzer,
K.; Krammer, B.; Berr, F. Photochem. Photobiol. Sci. 2007, 6, 619; (d) Moghissi, K.;
Dixon, K. Photodiagn. Photodyn. Ther. 2005, 2, 135; (e) Kessel, D.; Dougherty, T. J.
Rev. Contemp. Pharmacol. 1999, 10, 19; (f) Wiehe, A.; Shaker, Y. M.; Brandt, J. C.;
Mebs, S.; Senge, M. O. Tetrahedron 2005, 61, 5535.
3. (a) Aviv, I.; Gross, Z. Chem. Eur. J. 2008, 14, 3995; (b) Zhang, H.-J.; Liu, Y.; Lu, Y.;
He, X.-S.; Wang, X.; Ding, X. J. Mol. Catal. A: Chem. 2008, 287, 80; (c)
Korotchenko, V. N.; Severin, K.; Gagne, M. R. Org. Biomol. Chem. 2008, 6,
1961; (d) Chatterjee, D. Coord. Chem. Rev. 2008, 252, 176.
4. (a) Ren, D.-M.; Guo, Z.; Du, F.; Liu, Z.-F.; Zhou, Z.-C.; Shi, X.-Y.; Chen, Y.-S.;
Zheng, J.-Y. Int. J. Mol. Sci. 2008, 9, 45; (b) Nobukuni, H.; Shimazaki, Y.; Tani, F.;
Naruta, Y. Angew. Chem., Int. Ed. 2007, 46, 8975; (c) Kojima, T.; Nakanishi, T.;
Harada, R.; Ohkubo, K.; Yamauchi, S.; Fukuzumi, S. Chem. Eur. J. 2007, 13, 8714;
:
m
1947 (C@C@C), 3054 (aromatic H). (b) Ni7 was synthesised using Ni5
(0.074 mmol), PdCl2(dppe) (10 mg, 0.018 mmol) and Cs2CO3 (254 mg,
0.78 mmol). The residue was chromatographed on silica gel using CH2Cl2/n-
hexane (1:2). The first fraction collected was Ni7 (29 mg, 61%). mp: >300 °C; 1H
NMR (400 MHz, CDCl3): 9.63 (d, 3J = 4.7 Hz, 2H, b-H), 8.99 (d, 3J = 4.7 Hz, 2H, b-
H), 8.85 (d, 3J = 4.7 Hz, 2H, b-H), 8.84 (d, 3J = 4.7 Hz, 2H, b-H), 8.20 (m, 6H, o-Ph–
H), 7.75 (m, 9H, m,p-Ph–H), 5.99 (d, 4J = 2.6 Hz, 2H, CH2), 2.51 (t, 4J = 2.6 Hz, 1H,
acetylene–H); 13C (150 MHz, CDCl3): 144.8, 142.8, 142.4, 142.1, 140.6, 140.5,
133.5, 133.4, 132.5, 132.0, 131.9, 131.5, 127.6, 126.7, 119.7, 119.2, 100.1, 93.4,
79.7, 5.2; UV/Vis (CH2Cl2) kmax (log e): 420 (5.47), 553 (4.18); HRMS (ESI) calcd.
for [M]+ C41H26N4Ni 632.1449, found 632.1530. (c) Zn9 was obtained using
Zn5 (0.073 mmol), PdCl2(dppe) (10 mg, 0.018 mmol) and K2CO3 (107 mg,
0.78 mmol). The residue was chromatographed on silica gel using CH2Cl2/n-
hexane (1:2). The first fraction collected gave Zn9 (22 mg, 46%). mp: >300 °C;
1H NMR (400 MHz, CDCl3): 9.63 (d, 3J = 4.7 Hz, 2H, b-H), 8.99 (d, 3J = 4.7 Hz, 2H,
b-H), 8.85 (d, 3J = 4.7 Hz, 2H, b-H), 8.84 (d, 3J = 4.7 Hz, 2H, b-H), 8.20 (m, 6H, o-
Ph–H), 7.75 (m, 9H, m,p-Ph–H), 5.99 (d, 4J = 2.6 Hz, 2H, CH2), 2.51 (t, 4J = 2.6 Hz,
1H, acetylene–H); 13C NMR (150 MHz, CDCl3): 150.1, 150.0, 149.8, 149.6, 143.5,
134.5, 132.5, 131.6, 128.5, 127.1, 126.3, 126.2, 122.9, 120.4, 86.0, 73.1, 29.7;

O. B. Locos et al. / Tetrahedron Letters 50 (2009) 2566–2569
2569
UV/Vis (CH2Cl2) kmax (log
e
): 420 (5.47), 553 (4.18); LRMS (MALDI) calcd for
16. Newman-Evans, R. H.; Simon, R. J.; Carpenter, B. K. J. Org. Chem. 1990, 55, 695.
17. Ohno, H. Chem. Pharm. Bull. 2005, 53, 1211.
[M]+ C41H26N4Zn 638.1449, found 638.1467.
15. Miyaura, N.; Suzuki, A. Org. Synth. 1990, 68, 130.
18. Marshall, J. A. J. Org. Chem. 2007, 72, 8153.