Palladium-catalyzed [2 + 2 + 2] cycloadditions of 3,4-didehydrophenanthrene and 1,2-didehydrotriphenylene

Article abstract of DOI:10.1021/jo8013947

(Chemical Equation Presented) Palladium-catalyzed [2 + 2 + 2] cycloaddition reactions of 3,4-didehydrophenanthrene (3,4-phenanthryne) and 1,2-didehydrotriphenylene (1,2-triphenylyne) afford sterically congested polycyclic aromatic hydrocarbons with novel

Full text of DOI:10.1021/jo8013947

Palladium-Catalyzed [2 + 2 + 2] Cycloadditions of
3,4-Didehydrophenanthrene and 1,2-Didehydrotriphenylene
Carmen Romero, Diego Pen˜a,* Dolores Pe´rez,* and Enrique Guitia´n
Departamento de Qu´ımica Orga´nica, UniVersidad de Santiago de Compostela, 15782 Santiago de
Compostela, Spain
qodpena@usc.es; qodolopm@usc.es
ReceiVed June 26, 2008
Palladium-catalyzed [2 + 2 + 2] cycloaddition reactions of 3,4-didehydrophenanthrene (3,4-phenanthryne)
and 1,2-didehydrotriphenylene (1,2-triphenylyne) afford sterically congested polycyclic aromatic
hydrocarbons with novel structures.
SCHEME 1. Arynes 1 and 2 and Aryne Precursors 3 and 4
Introduction
In recent years, interest in fullerenes, nanographenes, and
carbon nanotubes has led to a remarkable revival in the
development of methods for the preparation of large and/or
sterically congested polycyclic aromatic hydrocarbons (PAHs).1
Aryne-based reactions2 have been extensively used for this
purpose;3 in particular, our group has applied the palladium-
catalyzed cyclotrimerization of arynes to the synthesis of a
number of strained or large PAHs.4-6
Recently, we reported the generation and palladium-catalyzed
[2 + 2 + 2] cycloaddition reactions of 2,3-didehydrotriph-
enylene (2,3-triphenylyne) to afford planar extended triph-
(1) (a) Watson, M. D.; Fechtenko¨tter, A.; Mu¨llen, K. Chem. ReV. 2001, 101,
1267. (b) Harvey, R. G. Curr. Org. Chem. 2004, 8, 303. (c) Bendikov, M.; Wudl,
F.; Perepichka, D. F. Chem. ReV. 2004, 104, 4891. (d) Grimsdale, A. C.; Mu¨llen,
K. Angew. Chem., Int. Ed. 2005, 44, 5592. (e) Pascal, R. A., Jr. Chem. ReV.
2006, 106, 4809. (f) Wu, J.; Pisula, W.; Mu¨llen, K. Chem. ReV. 2007, 107, 718.
(g) Anthony, J. E. Angew. Chem., Int. Ed. 2008, 47, 452.
(2) For some reviews of aryne reactivity, see: (a) Hoffmann, R. W.
Dehydrobenzene and Cycloalkynes; Academic Press: New York, 1967. (b)
Pellissier, H.; Santelli, M. Tetrahedron 2003, 59, 701.
(3) For some recent examples, see: (a) Lu, J.; Zhang, J.; Shen, X.; Ho, D. M.;
Pascal, R. A., Jr. J. Am. Chem. Soc. 2002, 124, 8035. (b) Duong, H. M.;
Bendikov, M.; Steiger, D.; Zhang, Q.; Sonmez, G.; Yamada, J.; Wudl, F. Org.
Lett. 2003, 5, 4433. (c) Wang, D. Z.; Katz, T. J.; Golen, J.; Rheingold, A. L. J.
Org. Chem. 2004, 69, 7769. (d) Lu, J.; Ho, D. M.; Vogelaar, N. J.; Kraml, C. M.;
Pascal, R. A., Jr. J. Am. Chem. Soc. 2004, 126, 11168. (e) Dolbier, W. R., Jr.;
Zhai, Y.-A.; Battiste, M. A.; Abboud, K. A.; Ghiviriga, I. J. Org. Chem. 2005,
70, 10336. (f) Sygula, A.; Sygula, R.; Rabideau, P. W. Org. Lett. 2005, 7, 4999.
(g) Sygula, A.; Sygula, R.; Rabideau, P. W. Org. Lett. 2006, 8, 5909. (h) Wang,
Y.; Stretton, A. D.; McConnell, M. C.; Wood, P. A.; Parsons, S.; Henry, J. B.;
Mount, A. R.; Galow, T. H. J. Am. Chem. Soc. 2007, 129, 13193.
enylenes.7 In this paper, we describe cyclotrimerization reactions
of 3,4-didehydrophenanthrene (3,4-phenanthryne, 1, Scheme 1)
and 1,2-didehydrotriphenylene (1,2-triphenylyne, 2) to yield
nonplanar extended polyarenes,8 increasing the scope of this
synthetic methodology. Based on our experience in this field,
(5) (a) Pen˜a, D.; Pe´rez, D.; Guitia´n, E.; Castedo, L. Org. Lett. 1999, 1, 1555.
(b) Pen˜a, D.; Cobas, A.; Pe´rez, D.; Guitia´n, E.; Castedo, L. Org. Lett. 2000, 2,
1629. (c) Pen˜a, D.; Pe´rez, D.; Guitia´n, E.; Castedo, L. J. Org. Chem. 2000, 65,
6944. (d) Pen˜a, D.; Cobas, A.; Pe´rez, D.; Guitia´n, E.; Castedo, L. Org. Lett.
2003, 5, 1863. (e) Iglesias, B.; Cobas, A.; Pe´rez, D.; Guitia´n, E.; Vollhardt,
K. P. C. Org. Lett. 2004, 6, 3557. (f) Caeiro, J.; Pen˜a, D.; Cobas, A.; Pe´rez, D.;
Guitia´n, E. AdV. Synth. Catal. 2006, 348, 2466.
(6) For a review of palladium-catalyzed cycloaddition reactions of arynes,
´
see: Guit´ıan, E.; Perez, D.; Pen˜a, D. In Topics in Organometallic Chemistry;
(4) (a) Pen˜a, D.; Escudero, S.; Pe´rez, D.; Guitia´n, E.; Castedo, L. Angew.
Chem., Int. Ed. 1998, 37, 2659. (b) Pen˜a, D.; Pe´rez, D.; Guitia´n, E.; Castedo, L.
J. Am. Chem. Soc. 1999, 121, 5827.
Tsuji, J., Ed.; Springer-Verlag: Weinheim, 2005; Vol. 14, pp 109-146.
(7) Romero, C.; Pen˜a, D.; Pe´rez, D.; Guitia´n, E. Chem.sEur. J. 2006, 12,
5677.
7996 J. Org. Chem. 2008, 73, 7996–8000
10.1021/jo8013947 CCC: $40.75 2008 American Chemical Society
Published on Web 09/17/2008

Cycloadditions of 3,4-Didehydrophenanthrene and 1,2-Didehydrotriphenylene
SCHEME 2. [2 + 2 + 2] Cycloaddition Reactions of
Phenanthryne 1
FIGURE 1. [2 + 2 + 2] cocycloaddition product not detected from
route b described in Scheme 2.
SCHEME 3. Proposed Metallacyclic Intermediate 10
SCHEME 4. Retrosynthetic Analysis of Triflate 4
FIGURE 2. X-ray structure of saddle-shaped compound 7.
we chose o-(trimethylsilyl)aryl triflates 3 and 4 as 3,4-phenan-
thryne (1) and 1,2-triphenylyne (2) precursors, respectively.
Fluoride-induced decomposition of these triflates would generate
arynes 1 and 2 under mild and neutral conditions.
Results and Discussion
Palladium-catalyzed [2 + 2 + 2] cycloaddition reactions of
aryne 1 have previously been studied to some extent by our
group.5c,d In particular, generation of 3,4-phenanthryne (1) by
treatment of triflate 3 with CsF in the presence of 5 mol % of
Pd2(dba)3 afforded the double helicene 5 in 26% yield (Scheme
2).5d On the other hand, generation of 1 in the presence of an
excess of dimethyl acetylenedicarboxylate (DMAD) afforded
compound 8, resulting from the reaction of one aryne and two
alkyne moieties, in 74% yield.5c
As expected on the basis of the previously observed chemose-
lectivity of the palladium-catalyzed cycloadditions of arynes and
alkynes,4b here we confirmed that the use of Pd(PPh3)4 results
in the preferential reaction of two molecules of aryne and one
molecule of alkyne. In particular, treatment of triflate 3 with
CsF in the presence of DMAD and 10 mol % of Pd(PPh3)4 led
to the isolation of a mixture of polyarenes 6 and 7 in 49% yield
(ratio 6:7 ) 7:3), while heptahelicene 9 (Figure 1) was not
isolated. Assuming a [2 + 2 + 2] cycloaddition mechanism,9
selective formation of 6 and 7 (as opposed to 9) can be explained
on the basis of the preferential formation of metallacycle 10 as
an intermediate (Scheme 3). Reaction of DMAD with Pd(PPh3)4
led to the initial formation of the corresponding palladium(0)
alkyne complex. Coordination of aryne 1 to palladium followed
by oxidative coupling would afford metallacycle 10, avoiding
the unfavorable steric interaction between the phenanthrene
moiety and the triphenylphosphine coordinated to the metal
center. Reaction of this metallacycle with phenanthryne 1 can
exclusively afford polycyclic arenes 6 and 7.
Disubstituted dibenzopicene 7 has an interesting nonplanar
structure, as determined by single-crystal X-ray diffraction
studies (Figure 2). In the crystalline state, compound 7 adopts
a saddle-shaped conformation, a molecular structure with few
reported precedents in the field of polycyclic aromatic hydro-
carbons.10 The streric demand present in the two fjord regions
of the molecule causes this distorted conformation, with a
C(20)-C(21)-C(22)-C(23) dihedral angle of 31.9°.
We next planned to apply these cyclotrimerization reactions
to a polycyclic aryne of increased size and structural complexity:
1,2-didehydrotriphenylene (2, Scheme 1). Triflate 4, the precur-
sor of aryne 2, should be readily accessible from triphenylenol
(12, Scheme 4) by selective ortho-bromination followed by a
simple one-pot transformation previously developed by us for
the transformation of o-bromophenols into o-(trimethylsilyl)aryl
triflates.11
We first considered the synthesis of triphenylenol (12) by
palladium-catalyzed [2 + 2 + 2] cocycloaddition of one
molecule of 3-methoxybenzyne (16) and two molecules of
benzyne (17, Scheme 5). There are seven possible products from
the homo- and heterocyclotrimerization of these arynes: triph-
enylene, 1-methoxytriphenylene (15), 1,5-, 1,8-, and 1,12-
dimethoxytriphenylenes, and 1,5,9- and 1,5,12-trimethoxytriph-
enylenes.12 The composition of the mixture would depend on
the ratio of reagents, the rate of formation of the different
aryne-palladium complexes, and the rate of transformation of
these into the different products. Although a priori the selective
synthesis of one of the cotrimers seems to be a difficult task,
we tried to obtain 1-methoxytriphenylene (15) by this methodol-
(8) Arynes 1 and 2 have been proposed as intermediates in the flash vacuum
pyrolysis of the corresponding dicarboxylic anhydrides. See: Brown, R. F. C.
Eur. J. Org. Chem. 1999, 3211.
(9) (a) Schore, N. E. Chem. ReV. 1988, 88, 1081. (b) Lautens, M.; Klute,
W.; Tam, W. Chem. ReV. 1996, 96, 49.
(10) Krebs, F. C.; Jørgensen, M.; Larsen, M. J. Org. Chem. 1999, 64, 8758.
(11) Pen˜a, D.; Cobas, A.; Pe´rez, D.; Guitia´n, E. Synthesis 2002, 1454.
(12) See the Supporting Information for details.
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Romero et al.
SCHEME 5. Cocyclotrimerization of Aryne 16 with
Benzyne (17)
FIGURE 3. Optimized geometry (MM2) for the proposed conformation
of double helicene 21.
SCHEME 6. Synthesis of 1-Triphenylenol (12) by
Diels-Alder Cycloaddition of 9,10-Phenanthryne (20) with
Furan
FIGURE 4. [2 + 2 + 2] cycloaddition products not detected from the
reactions described in Scheme 8.
thryne (20) with furan (Scheme 6).14 Reaction of triflate 18,
the precursor of phenanthryne 20,5b with tetrabutylammonium
fluoride (TBAF) in the presence of an excess of furan in THF
afforded compound 19 in 81% yield. Acidic treatment of this
compound gave a quantitative yield of 1-triphenylenol (12).
ortho-Bromination of compound 12 with N-bromosuccinimide
(NBS), catalyzed by i-Pr2NH in DCM, led to the isolation of
compound 11. One-pot treatment with hexamethyldisilazane
(HMDS) in refluxing THF, followed by successive addition of
n-BuLi and Tf2O at -100 °C, afforded triflate 4 in 32% overall
yield from 12 (Scheme 7).
Next, we applied the palladium-catalyzed cyclotrimerization
procedures to 1,2-triphenylyne (2). Generation of this intermedi-
ate by treatment of triflate 4 with CsF in the presence of 5 mol%
of Pd2(dba)3 in MeCN at 40 °C resulted in the formation of the
sterically congested trimer 21 in 10% yield (route a, Scheme
8).15 The structure of nonplanar polycyclic arene 21 contains a
double helicene with a heptahelicene and a pentahelicene with
two rings in common. Comparison of its characteristic 1H NMR
spectrum with that of double helicene 5,5d suggested that 21
was isolated in the conformation in which both helicenes rotate
in opposite senses (Figure 3).12 The other possible cyclotrim-
erization product 24 (Figure 4) was not detected from the
reaction mixture.
SCHEME 7. Synthesis of Triflate 4
SCHEME 8. [2 + 2 + 2] Cycloaddition Reactions of
Triphenylyne 2
Treatment of triflate 4 with CsF in the presence of DMAD
and 10 mol % of Pd(PPh3)4 led to the isolation of polyarene 22
in 19% yield (route b, Scheme 8). Remarkably, neither of the
two other cocyclotrimerization products resulting from the
reaction of two arynes and one alkyne were obtained (25 and
26, Figure 4). By contrast, when 5 mol % of Pd2(dba)3 and an
excess of DMAD were used, polycyclic arene 23, resulting from
the reaction of one aryne and two alkynes, was isolated as the
major product in a good yield (72%, route c, Scheme 8).16
Therefore, triphenylyne 2 exhibits in its reactions with DMAD
ogy. After some experimentation, we found that treatment of a
1:4 molar ratio of aryne precursors 13 and 14 with CsF in the
presence of 10 mol % of Pd(PPh3)4 allowed us to isolate
compound 15 in a remarkable 33% yield.13 Treatment of this
compound with NaCN in DMSO at 180 °C led to the isolation
of 1-triphenylenol (12) in 85% yield.
Alternatively, 1-triphenylenol (12) was prepared in higher
yield by means of Diels-Alder cycloaddition of 9,10-phenan-
(14) (a) Wittig, G.; Uhlenbrock, W.; Weinhold, P. Chem. Ber. 1962, 95, 1692.
(b) Stringer, M. B.; Wege, D. Tetrahedron Lett. 1980, 21, 3831. (c) Best, W. M.;
Collins, P. A.; McCulloch, R. K.; Wege, D. Aust. J. Chem. 1982, 35, 843.
(13) Triphenylene was also obtained in 57% yield.
7998 J. Org. Chem. Vol. 73, No. 20, 2008

Cycloadditions of 3,4-Didehydrophenanthrene and 1,2-Didehydrotriphenylene
(s, 2H), 6.38 (s, 2H); 13C NMR (62.8 MHz, CDCl3) δ 146.8 (2C),
the chemoselectivity pattern previously described for benzyne
and other polycyclic arynes.6
143.9 (2CH), 128.7 (2C), 127.1 (2C), 126.7 (2CH), 125.9 (2CH),
123.4 (2CH), 123.1 (2CH), 82.0 (2CH); MS (EI) m/z 244 (100).
1-Triphenylenol (12) via 19. Concentrated aqueous HCl solution
(36%, 0.4 mL) was added to a solution of 19 (22 mg, 0.090 mmol)
in THF (2 mL), and the mixture was stirred at 85 °C for 4 h. Then,
this mixture was cooled to room temperature, H2O (2 mL) and Et2O
(2 mL) were added, the phases were separated, and the aqueous
layer was extracted with Et2O (2 × 4 mL). The combined organic
layers were dried over anhydrous Na2SO4, filtered, and concentrated
under reduced pressure. The residue was purified by column
chromatography (SiO2; 1:2 EtOAc/hexane), affording 1-triphenyle-
nol (12, 22 mg, 100%) as a white solid.18
In conclusion, new sterically congested polycyclic aromatic
hydrocarbons have been prepared by successive aryne cycload-
dition reactions. Remarkably, the polycyclic arynes studied here
have been only reported sporadically, and their reaction products
have provided some insights into the palladium-catalyzed
cyclotrimerization of arynes.
Experimental Section
1-Methoxytriphenylene (15).17 Finely powdered anhydrous CsF
(1.90 g, 12.5 mmol) was added to a solution of triflate 13 (410
mg, 1.25 mmol), triflate 14 (1.49 g, 5.00 mmol), and Pd(PPh3)4
(720 mg, 0.62 mmol) in CH3CN (21 mL), and the mixture was
stirred at room temperature for 14 h. The solvent was removed
under reduced pressure, and the residue was purified by column
chromatography (SiO2; 1:9 CH2Cl2/hexane), affording
triphenylene4a (246 mg, 57%) and 1-methoxytriphenylene (15, 106
mg, 33%) as white solids. Data for 15: mp 165-167 °C (lit.17 mp
172 °C); 1H NMR (250 MHz, CDCl3) δ 9.65 (m, 1H), 8.68-8.61
(m, 3H), 8.33 (d, J ) 7.9 Hz, 1H), 7.66-7.57 (m, 5H), 7.22 (dd,
J ) 7.9, 0.9 Hz, 1H), 4.14 (s, 3H); 13C NMR (62.8 MHz, CDCl3)
δ 158.8 (C), 132.3 (C), 130.2 (C), 130.1 (C), 129.7 (C), 129.5 (C),
129.1 (CH), 127.3 (CH), 127.0 (2CH), 126.6 (CH), 126.5 (CH),
123.9 (CH), 123.1 (CH), 122.6 (CH), 120.3 (C), 115.9 (CH), 109.8
(CH), 55.8 (CH3); MS (EI) m/z 258 (100).
2-Bromo-1-triphenylenol (11). A solution of NBS (130 mg, 0.73
mmol) in CH2Cl2 (7.3 mL) was added to a solution of 1-triph-
enylenol (12, 160 mg, 0.66 mmol) and i-Pr2NH (10 µL, 0.070
mmol) in CH2Cl2 (8.3 mL) at -78 °C. The resulting mixture was
stirred for 8 h while the temperature reached 20 °C. Then, H2O
(15 mL) was added, and the mixture was acidified to pH 1 by careful
addition of concentrated aqueous H2SO4 solution. The phases were
separated, and the aqueous layer was extracted with CH2Cl2 (3 ×
20 mL). The combined organic layers were dried over anhydrous
Na2SO4, filtered, and concentrated under reduced pressure. The
residue was purified by column chromatography (SiO2; 1:4 Et2O/
hexane), affording 2-bromo-1-triphenylenol (11, 135 mg, 63%) as
1
a white solid: mp 143-145 °C; H NMR (250 MHz, CDCl3) δ
9.64 (m, 1H), 8.54 (d, J ) 7.8 Hz, 1H), 8.68-8.62 (m, 2H), 8.11
(d, J ) 9.0 Hz, 1H), 7.70-7.57 (m, 5H), 6.63 (s, OH); 13C NMR
(62.8 MHz, CDCl3) δ 150.2 (C), 132.0 (C), 130.2 (C), 129.3 (CH),
129.1 (CH), 129.0 (2C), 128.9 (C), 127.6 (CH), 127.0 (2CH), 126.9
(CH), 123.6 (CH), 123.2 (CH), 122.7 (CH), 119.5 (C), 116.5 (CH),
110.3 (C); MS (EI), m/z (%): 324 (59), 322 (59); HRMS (EI) for
C18H11O79Br calcd 321.9993, found 321.9991; HRMS (EI) for
C18H11O81Br calcd 323.9973, found 323.9966; UV/vis (CHCl3) λmax
(ꢀ) 294 (18060), 284 (21450), 267 (79900), 260 (sh, 64800 mol-1
dm3 cm-1) nm.
1-Triphenylenol (12) via 15. NaCN (321 mg, 6.55 mmol) was
added to a solution of 15 (249 mg, 0.97 mmol) in dry DMSO (3.4
mL), and the mixture was stirred at 180 °C for 8 h. Then, the
mixture was cooled to room temperature, H2O (10 mL) was added,
and the mixture was acidified to pH 1 by careful addition of 20%
aqueous HCl solution (CAUTION: HCN evolution). The aqueous
phase was extracted with CH2Cl2 (3 × 10 mL). The combined
organic layers were dried over anhydrous Na2SO4, filtered, and
concentrated under reduced pressure. The residue was purified by
column chromatography (SiO2; 1:2 EtOAc/hexane), affording
1-triphenylenol (12, 201 mg, 85%) as a white solid: mp 178-180
2-(Trimethylsilyl)triphenylenyl 1-Trifluoromethanesulfonate
(4). A solution of 2-bromo-1-triphenylenol (11, 140 mg, 0.43 mmol)
and HMDS (100 µL, 0.47 mmol) in THF (1.5 mL) was refluxed
for 1 h. The solvent was evaporated under reduced pressure, and
the residue was subjected to vacuum to remove excess NH3 and
unreacted HMDS. 1H NMR of the crude residue showed quantitative
formation of the corresponding silyl ether. This crude product was
dissolved in THF (3.0 mL), and the solution was cooled to -100
°C (external temperature). n-BuLi (190 µL, 2.42 M, 0.47 mmol)
was added dropwise, and the reaction mixture was stirred for 30
min while the temperature reached -80 °C. The mixture was again
cooled to -100 °C, Tf2O (90 µL, 0.52 mmol) was added dropwise,
and stirring was continued for 30 min while the temperature returned
to -80 °C. Then, saturated aqueous NaHCO3 (2 mL) was added at
low temperature, the phases were separated, and the aqueous layer
was extracted with Et2O. The combined organic layers were dried
over anhydrous Na2SO4, filtered, and concentrated under reduced
pressure. The residue was purified by column chromatography
(SiO2; 6:4 CH2Cl2/hexane), affording 4 (100 mg, 52%) as a white
°C (lit.18 mp 180-182 °C); H NMR (250 MHz, CDCl3) δ 9.62
1
(m, 1H), 8.69-8.59 (m, 3H), 8.21 (d, J ) 8.2 Hz, 1H), 7.66-7.60
(m, 4H), 7.49 (dd, J ) 8.0 Hz, 1H), 7.02 (d, J ) 7.7 Hz, 1H), 5.62
(s, OH); 13C NMR (62.8 MHz, CDCl3) δ 154.4 (C), 132.8 (C),
130.3 (C), 130.1 (C), 129.7 (C), 129.5 (C), 128.9 (CH), 127.4 (CH),
127.1 (CH), 126.9 (CH), 126.8 (CH), 126.6 (CH), 124.0 (CH), 123.2
(CH), 122.8 (CH), 118.9 (C), 116.2 (CH), 114.7 (CH); MS (EI)
m/z 244 (100).
1,4-Dihydro-1,4-epoxytriphenylene (19).14 NBu4F (4.6 mL, 1
M in THF, 4.6 mmol) was added dropwise to a solution of triflate
18 (1.5 g, 3.77 mmol) and furan (2.7 mL, 37.2 mmol) in THF (50
mL) at 0 °C. The mixture was stirred under argon at room
temperature for 2 h. Then, H2O (30 mL) and Et2O (30 mL) were
added, the phases were separated, and the aqueous layer was
extracted with Et2O (2 × 20 mL). The combined organic layers
were dried over anhydrous Na2SO4, filtered, and concentrated under
reduced pressure. The residue was purified by column chromatog-
raphy (SiO2; 1:2 CH2Cl2/hexane), affording 1,4-dihydro-1,4-ep-
oxytriphenylene (19, 745 mg, 81%) as a yellow solid: mp 179-180
°C (lit.14c mp 180-181 °C); 1H NMR (250 MHz, CDCl3) δ
8.89-8.53 (m, 2H), 7.96-7.89 (m, 2H), 7.67-7.56 (m, 4H), 7.26
1
solid: mp 168-170 °C; H NMR (250 MHz, CDCl3) δ 8.77 (d, J
) 8.2 Hz, 1H), 8.60-8.52 (m, 4H), 7.76-7.56 (m, 5H), 0.55 (s, 9
H); 13C NMR (62.8 MHz, CDCl3) δ 149.9 (C), 134.4 (C), 134.0
(C), 133.1 (CH), 130.6 (C), 130.4 (C), 128.8 (CH), 128.3 (C), 128.2
(CH), 128.0 (CH), 127.7 (CH), 126.8 (C), 126.6 (CH), 124.2 (C),
123.6 (CH), 123.4 (CH), 123.3 (CH), 122.2 (CH), 118.3 (q, J )
321 Hz, CF3), 0.4 (3CH3, TMS); MS (EI) m/z 448 (75); HRMS
(EI) for C22H19O3F3SiS, calcd 448.0776, found 448.0776; UV/vis
(CHCl3) λmax (ꢀ) 284 (12400), 267 (18000), 260 (15260 mol-1 dm3
cm-1) nm.
(15) Pd2(dba)3 usually affords higher yields than Pd(PPh3)4 in homocyclo-
trimerization reactions of sterically demanding arynes, probably due to the
presence of bulky and strongly coordinated phosphine ligands in the latter catalyst.
(16) The “lightly stabilized” complex Pd2(dba)3 reacts with two molecules
of DMAD leading to the corresponding metallacycle, which upon reaction with
aryne 2 would afford compound 23. See ref 4b.
Dimethyl Naphtho[2,1-c]pentahelicene-15,16-dicarboxylate
(6) and Dimethyl Dibenzo[a,o]picene-13,14-dicarboxylate (7).
Finely powdered anhydrous CsF (61 mg, 0.40 mmol) was added
to a solution of triflate 3 (80 mg, 0.20 mmol), dimethyl acetylene-
(17) Rapson, W. S. J. Chem. Soc. 1941, 15.
(18) Thakker, D. R.; Boehlert, C.; Mirsadeghi, S.; Levin, W.; Ryan, D. E.;
Thomas, P. E.; Yagi, H.; Pannell, L. K.; Sayer, J. M.; Jerina, D. M. J. Biol.
Chem. 1988, 263, 98.
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Romero et al.
dicarboxylate (DMAD, 47 µL, 0.38 mmol), and Pd(PPh3)4 (23 mg,
0.020 mmol) in CH3CN (4 mL), and the mixture was stirred at
room temperature for 14 h. The solvent was removed under reduced
pressure, and the residue was purified by column chromatography
(SiO2; 1:1:2 CH2Cl2/Et2O/hexane), affording a mixture of 6 and 7
(24 mg, 49%, 7:3 6/7). Data for 6: 1H NMR (250 MHz, CDCl3) δ
8.60 (dd, J ) 8.2, 2.5 Hz, 1H), 8.19 (d, J ) 8.7 Hz, 1H), 8.11 (d,
J ) 8.5 Hz, 1H), 8.06-7.92 (m, 7H), 7.82 (d, J ) 8.5 Hz, 1H),
7.67-7.48 (m, 4H), 7.17 (dt, J ) 7.7, 1.3 Hz, 1H), 4.08 (s, 3H),
3.17 (s, 3H); MS (EI) m/z 494 (33); HRMS (EI) for C34H22O4 calcd
494.1518, found 494.1533. Data for 7: 1H NMR (250 MHz, CDCl3)
δ 9.02 (d, J ) 8.2 Hz, 2H), 8.84 (d, J ) 8.7 Hz, 2H), 8.19 (d, J )
8.7 Hz, 2H), 8.01-7.89 (m, 6H), 7.79 (t, J ) 8.2, 1.3 Hz, 2H),
7.67 (t, J ) 7.5, 1.1 Hz, 2H), 3.06 (s, 6H); MS (EI) m/z 494 (42);
HRMS (EI) for C34H22O4 calcd 494.1518, found 494.1519.
Dibenzo[f,r]triphenyleno[1,2-l]heptahelicene (21). Finely pow-
dered anhydrous CsF (31 mg, 0.21 mmol) was added to a solution
of triflate 4 (31 mg, 0.069 mmol) and Pd2(dba)3 ·CHCl3 (3.6 mg,
3.5 µmol) in 4:1 CH3CN/CH2Cl2 (2.4 mL), and the mixture was
stirred at 40 °C for 14 h. The resulting suspension was filtered,
and the solid residue was purified by column chromatography (SiO2;
1:1 CH2Cl2/hexane), affording 21: 1H NMR (500 MHz, CD2Cl2) δ
8.97 (s, 2H), 8.92 (d, J ) 8.6 Hz, 1H), 8.88 (d, J ) 9.0 Hz, 1H),
8.82-8.76 (m, 4H), 8.72 (d, J ) 7.9 Hz, 1H), 8.50 (d, J ) 8.0 Hz,
1H), 8.49 (d, J ) 8.5 Hz, 1H), 8.38 (d, J ) 7.9 Hz, 1H), 8.32 (d,
J ) 9.4 Hz, 1H), 8.28 (d, J ) 7.6 Hz, 1H), 8.10 (d, J ) 7.8 Hz,
1H), 7.94 (d, J ) 7.9 Hz, 1H), 7.83-7.79 (m, 2H), 7.77-7.64 (m,
4H), 7.63 (ddd, 8.0, 7.1, 1.3 Hz, 1H), 7.58 (ddd, J ) 8.2, 7.1, 1.3
Hz, 1H), 7.52 (ddd, J ) 8.2, 6.9, 1.3 Hz, 1H), 6.99 (ddd, J ) 7.9,
6.8, 1.2 Hz, 1H), 6.80 (ddd, J ) 8.1, 6.9, 1.2 Hz, 1H), 6.61 (dd, J
) 8.4, 1.2 Hz, 1H), 6.34 (ddd, J ) 8.1, 6.9, 1.1 Hz, 1H), 5.99
(ddd, J ) 8.2, 6.9, 1.2 Hz, 1H); MS (FAB) m/z 678 (100); HRMS
(FAB) for C54H30 calcd 678.2348, found 678.2351.
7.55 (dd, J ) 8.1, 7.2 Hz, 1H), 7.13 (dd, J ) 7.7, 7.3 Hz, 1H),
4.07 (s, 3H), 3.16 (s, 3H); 13C NMR (75 MHz, CDCl3) δ 169.4
(C), 168.5 (C), 134.5 (C), 133.2 (C), 131.6 (C), 131.5 (C), 131.0
(C), 130.8 (C), 130.4 (2C), 130.2 (C), 130.0 (C), 129.9 (CH), 129.5
(CH), 129.3 (C), 129.2 (C), 129.0 (CH), 128.9 (C), 128.3 (2C),
128.0 (CH), 127.7 (CH), 127.5 (2CH), 127.4 (C), 127.3 (CH), 127.1
(C), 127.0 (CH), 126.7 (CH), 125.8 (CH), 125.4 (C). 124.7 (CH),
124.1 (CH), 123.7 (CH), 123.6 (CH), 123.3 (4CH), 122.9 (CH),
120.2 (CH), 53.1 (CH3), 52.2 (CH3); MS (CI) m/z 594 (81); HRMS
(CI) for C42H26O4 calcd 594.1831, found 594.1852.
Tetramethyl Benzo[g]chrysene-11,12,13,14-tetracarboxylate
(23). Finely powdered anhydrous CsF (78 mg, 0.51 mmol) was
added to a solution of triflate 4 (75 mg, 0.17 mmol), DMAD (0.15
mL, 1.19 mmol), and Pd2(dba)3 ·CHCl3 (18 mg, 0.018 mmol) in
4:1 CH3CN/CH2Cl2 (3.3 mL), and the mixture was stirred at room
temperature for 14 h. The solvent was removed under reduced
pressure, and the residue was purified by column chromatography
(SiO2; 1:1:2 CH2Cl2/Et2O/hexane), affording 23 (62 mg, 72%) as
1
a yellow solid: mp 187-190 °C; H NMR (250 MHz, CDCl3) δ
8.66-8.59 (m, 3H), 8.54 (d, J ) 7.4 Hz, 1H), 8.09 (d, J ) 8.0 Hz,
1H), 8.03 (d, J ) 9.0 Hz, 1H), 7.73-7.69 (m, 2H), 7.63 (dd, J )
7.4 Hz, 1H), 7.52 (dd, J ) 7.5 Hz, 1H), 4.09 (s, 3H), 3.98 (s, 3H),
3.96 (s, 3H), 3.12 (s, 3H); 13C NMR (62.8 MHz, CDCl3) δ 168.1
(C), 167.5 (C), 167.0 (C), 165.9 (C), 134.4 (C), 132.6 (C), 131.7
(C), 130.8 (C), 130.6 (C), 130.3 (C), 129.9 (C), 129.3 (C), 128.5
(C), 128.4 (C), 128.3 (CH), 128.2 (CH), 127.7 (CH), 127.6 (C),
127.3 (CH), 126.6 (CH), 125.3 (C), 124.3 (CH), 124.2 (CH), 124.0
(CH), 123.2 (2CH), 53.3 (CH3), 53.2 (CH3), 53.1 (CH3), 52.3 (CH3);
MS (EI) m/z 510 (23); HRMS (EI) for C30H22O8 calcd 510.1315,
found 510.1310; UV/vis (CHCl3) λmax (ꢀ) 342 (8650), 311 (36300),
269 (35800), 262 (37000 mol-1 dm3 cm-1) nm.
Acknowledgment. Financial support from the Spanish Min-
istry of Education and Science (MEC, CTQ2004-05752 and
CTQ2007-63244) and the Xunta de Galicia (DXPCTSUG2007/
090 and PGIDIT07PXIB209139PR) is gratefully acknowledged.
C.R. and D.P. thank MEC for the award of a FPU fellowship
and a Ramo´n y Cajal research contract, respectively.
Dimethyl Benzo[l]phenanthro[9,10-c]pentahelicene-7,8-dicar-
boxylate (22). Finely powdered anhydrous CsF (66 mg, 0.44 mmol)
was added to a solution of triflate 4 (80 mg, 0.20 mmol), DMAD
(28 µL, 0.23 mmol), and Pd(PPh3)4 (17 mg, 0.014 mmol) in 4:1
CH3CN/CH2Cl2 (2.9 mL), and the mixture was stirred at room
temperature for 14 h. The solvent was removed under reduced
pressure, and the residue was purified by column chromatography
(SiO2; 5:1:4 CH2Cl2/Et2O/hexane), affording 22 (8.1 mg, 19%) as
a yellow solid: 1H NMR (300 MHz, CDCl3) δ 8.81-8.66 (m, 5H),
8.63 (d, J ) 8.2 Hz, 1H), 8.55 (d, J ) 8.7 Hz, 1H), 8.48 (d, J )
7.9 Hz, 1H), 8.29 (s, 2H), 8.16-8.09 (m, 2H), 7.85-7.59 (m, 6H),
Supporting Information Available: Experimental, spectro-
scopic, and crystallographic data. This material is available free
of charge via the Internet at http://pubs.acs.org.
JO8013947
8000 J. Org. Chem. Vol. 73, No. 20, 2008