Thermolysis of benzoenyne - Allenes to form biradicals and subsequent intramolecular trapping with a tetraarylallene to generate two triarylmethyl radical centers

Article abstract of DOI:10.1021/jo982326k

Thermolysis of the benzoenyne - allene 20 in 1,4-cyclohexadiene (1,4-CHD) at 75°C produced the cycloaromatized adduct 23 in 22% yield. The reaction presumably proceeds through a cascade sequence involving an initial Myers cyclization reaction to form the biradical 21. The subsequent trapping of the aryl radical center in 21 with the tetraarylallenic moiety intramolecularly affords 22, having two stabilized triarylmethyl radical centers. Hydrogen-atom abstraction from 1,4-CHD by 22, manifesting its radical character, then produces 23. Similarly, thermolysis of benzoenyne -allenes 25 in 1,4-CHD furnished fluoranthenes 27 in essentially quantitative yields. The presence of the fused five-membered ring in 20 and 25 is necessary to direct the initial biradical-forming step toward the Myers cyclization reaction. Without the five-membered ring as in the cases of 31, the C2 - C6 cyclization reaction became the preferred pathway, leading to benzofluorenes 34.

Full text of DOI:10.1021/jo982326k

1650
J . Org. Chem. 1999, 64, 1650-1656
Th er m olysis of Ben zoen yn e-Allen es To F or m Bir a d ica ls a n d
Su bsequ en t In tr a m olecu la r Tr a p p in g w ith a Tetr a a r yla llen e To
Gen er a te Tw o Tr ia r ylm eth yl Ra d ica l Cen ter s
Kung K. Wang,* Hai-Ren Zhang, and J effrey L. Petersen†
Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506-6045
Received November 24, 1998
Thermolysis of the benzoenyne-allene 20 in 1,4-cyclohexadiene (1,4-CHD) at 75 °C produced the
cycloaromatized adduct 23 in 22% yield. The reaction presumably proceeds through a cascade
sequence involving an initial Myers cyclization reaction to form the biradical 21. The subsequent
trapping of the aryl radical center in 21 with the tetraarylallenic moiety intramolecularly affords
22, having two stabilized triarylmethyl radical centers. Hydrogen-atom abstraction from 1,4-CHD
by 22, manifesting its radical character, then produces 23. Similarly, thermolysis of benzoenyne-
allenes 25 in 1,4-CHD furnished fluoranthenes 27 in essentially quantitative yields. The presence
of the fused five-membered ring in 20 and 25 is necessary to direct the initial biradical-forming
step toward the Myers cyclization reaction. Without the five-membered ring as in the cases of 31,
the C2-C6 cyclization reaction became the preferred pathway, leading to benzofluorenes 34.
In tr od u ction
or even stable4 if proper substituents are placed at the
terminus of the allenic end of 1.
The use of the thermally-induced isomerization reac-
tions of organic molecules to generate the carbon-centered
biradicals has several potential advantages over the
conventional chemical or photochemical methods.1 Unlike
the chemical methods where overoxidation or overreduc-
tion of an organic compound could occur,2 such undesir-
able side reactions will not be a major concern in the
thermal process because the two radical centers are
generated simultaneously. In addition, the chemical
reagent needed to promote the formation of radicals and
the reaction byproducts of the chemical process have to
be removed at the end. Moreover, since heat can easily
permeate through material, a precursor could be incor-
porated inside an inert matrix and then be converted to
a biradical by simple heat treatment. On the other hand,
chemicals or light may not be able to penetrate through
the matrix barrier to induce the formation of radicals.
(1)
Sch em e 1
Of the few reported methods for generating biradicals
under thermal conditions, the Myers cyclization reaction
of (Z)-1,2,4-heptatrien-6-ynes (enyne-allenes) to R,3-
didehydrotoluene biradicals (eq 1) provides a particularly
attractive pathway to carbon biradicals because the
reaction occurs under mild thermal conditions and vari-
ous synthetic routes to enyne-allenes with diverse
chemical structures are becoming available.3 While the
aryl radical center in 2 is too reactive to be persistent
because H-atom abstraction generates a strong aryl C-H
bond, the benzylic radical center could become persistent
We recently reported that the enyne-allene 3 under-
goes a facile Myers cyclization reaction under refluxing
benzene (80 °C) in the presence of an excess of 1,4-CHD
to furnish 5 in 58% yield (Scheme 1).5 The reaction
presumably proceeds through the biradical 4 having an
R,R-di-tert-butylbenzylic radical center, which was re-
(3) (a) Myers, A. G.; Kuo, E. Y.; Finney, N. S. J . Am. Chem. Soc.
1989, 111, 8057-8059. (b) Myers, A. G.; Dragovich, P. S. J . Am. Chem.
Soc. 1989, 111, 9130-9132. (c) Nagata, R.; Yamanaka, H.; Okazaki,
E.; Saito, I. Tetrahedron Lett. 1989, 30, 4995-4998. (d) Nagata, R.;
Yamanaka, H.; Murahashi, E.; Saito, I. Tetrahedron Lett. 1990, 31,
2907-2910. (e) Nicolaou, K. C.; Maligres, P.; Shin, J .; de Leon, E.;
Rideout, D. J . Am. Chem. Soc. 1990, 112, 7825-7926. For recent
reviews, see: (f) Wang, K. K. Chem. Rev. 1996, 96, 207-222. (g)
Grissom, J . W.; Gunawardena, G. U.; Klingberg, D.; Huang, D.
Tetrahedron 1996, 52, 6453-6518.
† To whom correspondence concerning the X-ray structures should
be addressed.
(1) (a) Borden, W. T. Diradicals; Wiley-Interscience: New York,
1982. (b) Platz, M. S. Kinetics and Spectroscopy of Carbenes and
Biradicals; Plenum Press: New York, 1990.
(2) (a) Rajca, A.; Rajca, S. J . Am. Chem. Soc. 1996, 118, 8121-8126.
(b) Rajca, A. Chem. Rev. 1994, 94, 871-893. (c) Rajca, A.; Utamapanya,
S.; Xu, J . J . Am. Chem. Soc. 1991, 113, 9235-9241. (d) Tukada, H.;
Mutai, K. Tetrahedron Lett. 1992, 33, 6665-6668. (e) Veciana, J .;
Rovira, C.; Crespo, M. I.; Armet, O.; Domingo, V. M.; Palacio, F. J .
Am. Chem. Soc. 1991, 113, 2552-2561.
(4) Griller, D.; Ingold, K. U. Acc. Chem. Res. 1976, 9, 13-19.
(5) Wang, K. K.; Wang, Z.; Sattsangi, P. D. J . Org. Chem. 1996, 61,
1516-1518.
10.1021/jo982326k CCC: $18.00 © 1999 American Chemical Society
Published on Web 02/06/1999

Thermolysis of Benzoenyne-Allenes
J . Org. Chem., Vol. 64, No. 5, 1999 1651
Sch em e 2
Sch em e 4
Sch em e 3
aryl radical to the more stable benzylic radical via a 1,5-
hydrogen shift.
Resu lts a n d Discu ssion
The success in producing a stabilized triarylmethyl
radical and in transforming the aryl radical to the
benzylic radical shown in Scheme 3 prompted us to
design new ways to capture the aryl radical intramo-
lecularly. Examples of trapping the aryl radical center
with an intramolecular double or triple bond have been
reported.8 We envisioned that if the aryl radical could
be captured by a tetraarylallenic moiety intramolecularly,
then the initially formed biradical could be transformed
to a new biradical having two triarylmethyl radical
centers. To test the feasibility of this strategy, the
benzoenyne-allene 20 was synthesized from 1-iodo-9-
fluorenone 169 (Scheme 4). The Pd(PPh3)4-catalyzed
cross-coupling reaction between 16 and (trimethylsilyl)-
acetylene furnished 17, which was desilylated to form 18.
Cross-coupling between 18 and 16 was also promoted by
Pd(PPh3)4 to afford 19, which was readily converted to
20 by treatment with phosphinoxy carbanion 7a for the
Horner reaction.
ported to be persistent in dilute solution at room tem-
perature for several days.6 The EPR spectrum of the R,R-
di-tert-butylbenzylic radical indicates that it prefers a
conformation in which the p orbital of the radical center
is perpendicular to the π bonds of the benzene ring in
order to minimize steric interactions.
Enyne-allenes 9 having two phenyl substituents at the
allenic terminus were synthesized by using readily
available enynyl aldehydes 8 for the Horner reaction with
phosphinoxy carbanion 7b.7 Thermolysis of these enyne-
allenes under mild thermal conditions produced the
cycloaromatized adducts 11 via biradicals 10 having a
stabilized triarylmethyl radical center (Scheme 2).
In the absence of 1,4-CHD, thermolysis of 12 under
refluxing benzene for 96 h afforded the cycloaromatized
adduct 15 in 40% yield (Scheme 3). Apparently, a 1,5-
hydrogen shift of the initially formed R,3-didehydrotolu-
ene biradical 13 to form 14 followed by an intramolecular
radical-radical combination led to 15. This example
demonstrates the feasibility of converting the reactive
Thermolysis of 20 in 1,4-CHD at 75 °C produced the
cycloaromatized adduct 23 in 22% yield (Scheme 5). The
structure assignment of 23 is based on the high-resolu-
1
tion mass spectrum and the H and 13C NMR spectra.
(8) (a) Wang, K. K.; Wang, Z.; Tarli, A.; Gannett, P. J . Am. Chem.
Soc. 1996, 118, 10783-10791 and references therein. (b) Grissom, J .
W.; Klingberg, D.; Huang, D.; Slattery, B. J . J . Org. Chem. 1997, 62,
603-626 and references therein. (c) Bharucha, K. N.; Marsh, R. M.;
Minto, R. E.; Bergman, R. G. J . Am. Chem. Soc. 1992, 114, 3120-
3121. (d) Lin, C.-F.; Wu, M.-J . J . Org. Chem. 1997, 62, 4546-4548. (e)
Cobas, A.; Guitia´n, E.; Castedo, L. J . Org. Chem. 1997, 62, 4896-4897.
(9) (a) Huntress, E. H.; Pfister, K., III.; Pfister, K. H. T. J . Am. Chem.
Soc. 1942, 64, 2845-2849. (b) Kharasch, N.; Bruice, T. C. J . Am. Chem.
Soc. 1951, 73, 3240-3244.
(6) Schreiner, K.; Berndt, A. Angew. Chem., Int. Ed. Engl. 1974,
13, 144-145.
(7) Liu, B.; Wang, K. K.; Petersen, J . L. J . Org. Chem. 1996, 61,
8503-8507.

1652 J . Org. Chem., Vol. 64, No. 5, 1999
Wang et al.
Sch em e 5
Sch em e 6
The molecular ion was detected by a high-resolution mass
spectrometer (m/z ) 932.5297). The presence of only one
1
tert-butyl signal in the H NMR spectrum suggests that
23 is a symmetrical molecule. The appearance of a set of
AB doublets in the aromatic region is also consistent with
the presence of the para-disubstituted benzene rings in
23. While the 1H NMR signal for the two tertiary
hydrogens on the sp3 carbons is buried in the aromatic
region, their presence can be clearly discerned in the 13C
NMR spectrum. The 13C NMR signal at δ 54.77 was found
to arise from the methine carbon attached with one
hydrogen by using the DEPT technique and can be
attributed to the two sp3 C-H carbons in 23. The 13C
NMR signals for one type of tert-butyl group were also
observed. In the aromatic region, nine signals are from
the C-H carbons and the remaining 10 signals are from
carbons without hydrogen attached to them, consistent
with what can be expected from the structure of 23. The
four signals with higher intensities at δ 148.97, 138.22,
129.36, and 125.01 can be attributed to the carbons on
the para-disubstituted benzene rings.
Apparently, the transformation from 20 to 23 pro-
ceeded through an initial Myers cyclization reaction to
produce the biradical 21. The aryl radical center in 21
was then captured by the allenic moiety to form 22
having two stabilized triarylmethyl radical centers.
Because of nonbonded steric interactions, the molecular
model of 22 indicates that it cannot achieve the planar
quinonoid form and can be best regarded as a biradical
with the p orbital of the radical centers perpendicular to
the π bonds of the central chrysene ring. In addition, the
quinonoid form of 22 would cause a complete disruption
of aromaticity of the central chrysene system. This is
reminiscent of a sterically hindered Chichibabin hydro-
carbon, which also cannot achieve coplanarity and con-
sequently exhibits paramagnetic properties.10 The sub-
sequent hydrogen-atom abstraction from 1,4-CHD by 22,
manifesting its radical behavior, then furnished 23.
To probe more closely the Myers cyclization reaction
from 20 to the biradical 21, the benzoenyne-allenes 25
were synthesized from 16 by using a similar reaction
sequence outlined in Scheme 6. Thermolysis of 25 in 1,4-
CHD at 75 °C for 1.5 h produced the cycloaromatized
adducts 27 in essentially quantitative yields.
The structure of 27a was unequivocally established by
an X-ray structural analysis.11 It is interesting to note
that the benzylic C-H bond lies essentially on the plane
of the fluoranthene ring with only a 17° twist angle and
is pointed toward the phenyl substituent in the crystal
lattice. The two 4-tert-butylphenyl groups are situated
above and below the plane of the fluoranthene ring.
Compared to 9, the fixed s-cis benzoenyne-allene
system in 25 presumably is an important factor in
promoting cycloaromatization efficiently.12 This result
also suggests that the initial Myers cyclization reaction
from 20 to 21 probably is not responsible for relatively
low yield in producing 23.
The presence of the fused five-membered ring in 20
and 25 is crucial in directing the initial biradical-forming
step toward the Myers cyclization reaction. By using the
benzophenones 30, readily prepared from 2813 (Scheme
7), for condensation with phosphinoxy carbanion 7a or
7b, the 11H-benzo[b]fluorenes 34 were produced (Scheme
8). The structures of 34a and 34b were established by
X-ray structural analyses.11 Presumably, the initial Hor-
ner reactions produced the benzoenyne-allenes 31,
which then underwent a facile C2-C6 cyclization at room
temperature to form the biradicals 32. The subsequent
intramolecular radical-radical coupling produced 33,
leading to the 11H-benzo[b]fluorenes 34 through tau-
(11) The authors have deposited atomic coordinates for this struc-
ture with the Cambridge Crystallographic Data Centre. The coordi-
nates can be obtained, on request, from the Director, Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge, CB2 1EZ,
UK.
(12) Naoe, Y.; Kikuishi, J .; Ishigaki, K.; Iitsuka, H.; Nemoto, H.;
Shibuya, M. Tetrahedron Lett. 1995, 36, 9165-9168.
(13) Fairfax, D. J .; Austin, D. J .; Xu, S. L.; Padwa, A. J . Chem. Soc.,
Perkin Trans 1 1992, 2837-2844.
(10) Mu¨ller, E.; Rieker, A.; Scheffler, K.; Moosmayer, A. Angew.
Chem., Int. Ed. Engl. 1966, 5, 6-15.

Thermolysis of Benzoenyne-Allenes
J . Org. Chem., Vol. 64, No. 5, 1999 1653
Sch em e 7
Sch em e 9
Sch em e 10
Sch em e 8
37 having a strained bicyclo[3.3.0]octatrienyl system
(Scheme 10). Apparently, the emergence of a similar ring
strain also prevented 9 from undergoing the C2-C6
cyclization. The effect of ring strain in deciding the
biradical-forming pathway from thermolysis of enyne-
allenes was clearly delineated by Schmittel and co-
workers previously.14a
Con clu sion s
The success in capturing the aryl radical center in 21,
derived from thermolysis of the benzoenyne-allene 20,
with the tetraarylallenic moiety intramolecularly dem-
onstrates the feasibility of generating 22 having two
triarylmethyl radical centers under mild thermal condi-
tions. Because of steric interactions, 22 cannot exist in
the planar quinonoid form and behaves like a biradical.
tomerization. There are ample precedents in the litera-
ture to support the formation of the formal Diels-Alder
adducts 33 through a two-step C2-C6 cyclization involv-
ing a biradical intermediate.14 Similarly, the 11H-benzo-
[b]fluorene 36 was obtained from condensation between
28b and 7b (Scheme 9).
The preference for 20 and 25 to undergo the Myers
cyclization reaction can be attributed to the emergence
of substantial ring strains in the resulting biradicals had
the reaction proceeded through the C2-C6 cyclization.
For example, the C2-C6 cyclization of 25 would produce
(14) (a) Schmittel, M.; Steffen, J .-P.; Auer, D.; Maywald, M. Tetra-
hedron Lett. 1997, 38, 6177-6180. (b) Schmittel, M.; Strittmatter, M.;
Kiau, S. Angew. Chem., Int. Ed. Engl. 1996, 35, 1843-1845. (c)
Schmittel, M.; Kiau, S.; Siebert, T.; Strittmatter, M. Tetrahedron Lett.
1996, 37, 7691-7694. (d) Schmittel, M.; Strittmatter, M.; Vollmann,
K.; Kiau, S. Tetrahedron Lett. 1996, 37, 999-1002. (e) Schmittel, M.;
Maywald, M.; Strittmatter, M. Synlett 1997, 165-166. (f) Schmittel,
M.; Strittmatter, M.; Kiau, S. Tetrahedron Lett. 1995, 36, 4975-4978.
(g) Gillmann, T.; Hulsen, T.; Massa, W.; Wocadlo, S. Synlett 1995,
1257-1259. (h) Garcia, J . G.; Ramos, B.; Pratt, L. M.; Rodriguez, A.
Tetrahedron Lett. 1995, 36, 7391-7394.

1654 J . Org. Chem., Vol. 64, No. 5, 1999
Wang et al.
mmol) were used to afford 0.425 g of 19 (1.11 mmol, 86%) as
orange crystalline needles: mp 281-283 °C; IR (KBr) 3057,
The central five-membered ring of the fluorene system
in 20 and 25 is crucial in directing the reaction toward
the Myers cycloaromatization pathway.
1
1714, 753, 670 cm-1; H NMR (CDCl3) δ 7.72-7.67 (4 H, m),
7.58-7.48 (8 H, m), 7.33 (2 H, td, J ) 7.2 and 1.4 Hz); 13C
NMR (CDCl3) δ 191.92, 144.80, 143.17, 134.55, 134.15, 134.05,
133.98, 133.66, 129.40, 124.28, 120.59, 120.36, 120.29, 92.21;
MS m/z 382 (M+), 354, 353, 324, 191; HRMS calcd for C28H14O2
382.0994, found 382.0982. Anal. Calcd for C28H14O2: C, 87.94;
H, 3.69. Found: C, 87.70; H, 3.61.
Exp er im en ta l Section
All reactions were conducted in oven-dried (120 °C) glass-
ware under a nitrogen atmosphere. Tetrahydrofuran (THF)
and diethyl ether (Et2O) were distilled from benzophenone
ketyl prior to use. Pyridinium chlorochromate, diisopropyl-
ethylamine, 1,4-cyclohexadiene, 2-bromobenzaldehyde, fluo-
ranthene, Pd(PPh3)4, CuI, 2.5 M solution of n-butyllithium in
hexanes, 1.7 M solution of tert-butyllithium in pentane, 1.0 M
solution of phenylmagnesium bromide in THF, and 2.0 M
solution of 4-tert-butylphenylmagnesium bromide in diethyl
ether were purchased from Aldrich Chemical Co. and were
used as received. Phenylacetylene, (4-tert-butylphenyl)acety-
lene, and (trimethylsilyl)acetylene were purchased from Farch-
an Laboratories Inc. and were used without further purifica-
tion. 1-Iodo-9-fluorenone was prepared from fluoranthene
according to the reported procedure.9 Diphenyl(2,2-diphenyl-
1-iodoethenyl)phosphine oxide (6b) was prepared by treatment
of diphenyl(phenylethynyl)phosphine oxide with phenylmag-
nesium chloride in the presence of CuBr followed by iodine as
reported previously.7 Similarly, diphenyl[2,2-di(4-tert-butylphe-
nyl)-1-iodoethenyl]phosphine oxide (6a ) was synthesized from
diphenyl[(4-tert-butylphenyl)ethynyl]phosphine oxide and 4-tert-
butylphenylmagnesium bromide in 83% yield as a pale yellow
solid. 2-(Phenylethynyl)benzaldehyde (28b) was prepared ac-
cording to the reported procedure.13 Melting points are uncor-
rected. Silica gel (230-400 mesh) was purchased from Baker.
1H (270 MHz) and 13C (67.9 MHz) NMR spectra were recorded
in CDCl3 using CHCl3 (1H δ 7.26) or CDCl3 (13C δ 77.00) as
internal standard unless otherwise indicated.
Dia llen e 20. To a solution of diphenyl[2,2-di(4-tert-bu-
tylphenyl)-1-iodoethenyl]phosphine oxide (6a , 2.41 g, 3.90
mmol) in 120 mL of THF was added 4.6 mL (7.8 mmol) of a
1.7 M solution of tert-butyllithium in pentane at -78 °C. After
30 min at -78 °C, the resulting mixture was added via cannula
to a solution of diketone 19 (0.573 g, 1.50 mmol) in 280 mL of
THF at 0 °C. The reaction mixture was stirred at room
temperature for 5 h before 50 mL of water was added. The
solution was concentrated in vacuo to about 150 mL, and then
100 mL of water and 200 mL of methylene chloride were
introduced. The organic layer was separated, washed with
water, dried over MgSO4, and concentrated. The residue was
purified by flash chromatography (silica gel/2% diethyl ether
in pentane) to furnish 1.186 g of 20 (1.28 mmol, 85%) as a
yellow solid: IR 3052, 1916, 753 cm-1; 1H NMR (CDCl3) δ 7.75
(2 H, d, J ) 7.3 Hz), 7.65 (2 H, dd, J ) 7.4 and 1.0 Hz), 7.60
(2 H, d, J ) 7.1 Hz), 7.36 (2 H, td, J ) 7.4 and 1.0 Hz), 7.28 (2
H, td, J ) 7.4 and 1.0 Hz), 7.07 (16 H, s), 6.98 (2 H, t, J ) 7.5
Hz), 6.90 (2 H, dd, J ) 7.7 and 1.0 Hz), 1.15 (36 H, s); 13C
NMR (CDCl3) δ 207.41, 150.17, 138.81, 138.24, 138.04, 137.66,
132.59, 131.15, 128.52, 127.55, 127.16, 126.68, 124.82, 122.48,
119.91, 119.54, 119.14, 116.36, 107.30, 92.59, 34.26, 31.05; MS
m/z 930 (M+), 929, 915, 914, 913, 905, 889, 873, 812, 797;
HRMS calcd for C72H65 (M+ - 1) 929.5086, found 929.5115.
Ch r ysen e 23. A degassed solution of diallene 20 (0.368 g,
0.396 mmol) in 10 mL of 1,4-CHD was heated at 75 °C, and
the progress of the reaction was monitored by TLC. The color
of the solution became dark green gradually. After 1 h at 75
°C, the starting diallene 20 disappeared completely. The
reaction mixture was concentrated, and the residue was
purified by flash chromatography (silica gel/2% CH2Cl2 in
hexanes) to afford 0.080 g of 23 (0.086 mmol, 22%) as a yellow
solid that gradually turns to brown color beginning at 180 °C
in a sealed capillary tube. At 220 °C, it starts to soften and
eventually melts and decomposes at 332 °C to produce a brown
liquid. 23: IR 3057, 1510 cm-1; 1H NMR (CDCl3) δ 8.16 (2 H,
d, J ) 8.5 Hz), 7.85 (2 H, d, J ) 6.9 Hz), 7.80 (2 H, d, J ) 7.3
Hz), 7.4-7.2 (24 H, m), 6.93 (2 H, td, J ) 7.6 and 0.8 Hz),
1-[2-(Tr im eth ylsilyl)eth yn yl]-9-flu or en on e (17). The pro-
cedure for the preparation of 28b was adopted.13 To a degassed
solution containing 0.116 g of Pd(PPh3)4 (0.100 mmol), 0.061
g of CuI (0.32 mmol), 0.60 g of 1-iodo-9-fluorenone9 (1.96
mmol), and 0.78 g of diisopropylethylamine (6.0 mmol) in 3
mL of N,N-dimethylformamide (DMF) was added via cannula
a degassed solution of 0.79 g of (trimethylsilyl)acetylene (8.1
mmol) in 1.8 mL of DMF. After 12 h at room temperature,
the reaction mixture was poured into a beaker containing 30
mL of a saturated NH4Cl solution and 100 mL of pentane.
After filtration, the organic layer was separated, washed with
water, dried over MgSO4, and concentrated. The residue was
purified by flash chromatography (silica gel/2% diethyl ether
in hexanes) to afford 0.427 g of 17 (1.55 mmol, 79%) as a
1
1.27 (36 H, s); H NMR (CD2Cl2) δ 8.16 (2 H, d, J ) 8.3 Hz),
7.89 (2 H, d, J ) 6.9 Hz), 7.84 (2 H, d, J ) 7.5 Hz), 7.38 (8 H,
d, J ) 8.7 Hz), 7.4-7.3 (6 H, m), 7.30 (8 H, d, J ) 8.5 Hz),
7.23 (2 H, t, J ) 7.3 Hz), 6.96 (2 H, td, J ) 7.6 and 1.0 Hz),
1.28 (36 H, s); 13C NMR (CDCl3) δ 148.97, 140.90, 139.35,
138.22, 137.69, 137.62, 136.39, 135.93, 132.58, 129.36, 128.62,
127.70, 127.02, 126.67, 126.40, 126.18, 125.01, 120.07, 118.49,
54.77, 34.35, 31.32; MS m/z 932 (M+), 875, 797, 279; HRMS
calcd for C72H68 932.5321, found 932.5297.
viscous yellow liquid: IR (neat) 2155, 1715 cm-1 1H NMR
;
(CDCl3) δ 7.67 (1 H, dt, J ) 7.3 and 1 Hz), 7.5 (2 H, m), 7.48-
7.45 (1 H, m), 7.41 (1 H, t, J ) 7.5 Hz), 7.35-7.27 (2 H, m),
0.33 (9 H, s); 13C NMR (CDCl3) δ 191.77, 144.70, 142.92,
134.48, 134.03, 133.72, 133.65, 129.39, 124.21, 120.62, 120.18,
120.04, 101.87, 101.05, -0.18; MS m/z 276 (M+), 261, 202;
HRMS calcd C18H16OSi 276.0970, found 276.0961.
1-Eth yn yl-9-flu or en on e (18). To 0.356 g of 17 (1.29 mmol)
in 50 mL of diethyl ether was added a mixture of 20 mL of
10% NaOH and 50 mL of methanol. After 30 min at room
temperature, 50 mL of diethyl ether and 50 mL of water were
added, and the organic layer was separated, washed with 2 N
HCl and water, and dried over MgSO4. Evaporation of solvent
furnished 0.263 g of 18 (1.29 mmol, 100%) as a yellow solid:
1-(P h en yleth yn yl)-9-flu or en on e (24). The same proce-
dure was repeated as described for 17 except that 1.013 g of
1-iodo-9-fluorenone (3.308 mmol) in 5 mL of DMF and 0.505 g
of phenylacetylene (4.95 mmol) in 4 mL of DMF were used to
afford 0.818 g of 24 (2.92 mmol, 88%) as a yellow solid: mp
98-99 °C; IR (KBr) 2213, 1717 cm-1; 1H NMR (CDCl3) δ 7.74-
7.66 (3 H, m), 7.5-7.27 (9 H, m); 13C NMR (CDCl3) δ 191.91,
144.78, 142.95, 134.44, 134.06, 133.81, 133.28, 132.88, 132.14,
129.32, 128.80, 128.32, 124.08, 122.92, 120.91, 120.20, 119.76,
95.77, 86.28; MS m/z 280 (M+), 252, 250; HRMS calcd for
mp 129-131 °C; IR (KBr) 3244, 2109, 1708, 750, 668 cm-1
;
1H NMR (CDCl3) δ 7.68 (1 H, dt, J ) 7.5 and 1 Hz), 7.54-7.49
(3 H, m), 7.44 (1 H, t, J ) 7.5 Hz), 7.37 (1 H, dd, J ) 7.6 and
1.3 Hz), 7.32 (1 H, ddd, J ) 7.3, 6.3, and 2.2 Hz), 3.50 (1 H, s);
13C NMR (CDCl3) δ 191.73, 144.84, 142.90, 134.66, 133.97,
133.90, 129.47, 124.41, 120.46, 120.24, 119.57, 83.40, 79.90;
MS m/z 204 (M+), 176; HRMS calcd C15H8O 204.0575, found
204.0573. Anal. Calcd for C15H8O: C, 88.22; H, 3.95. Found:
C, 88.24; H, 3.94.
C
21H12O 280.0888, found 280.0889. Anal. Calcd for C21H12O:
C, 89.98; H, 4.31. Found: C, 89.96; H, 4.40.
9-[Di(4-ter t-bu tylph en yl)vin yliden e]-1-(ph en yleth yn yl)-
9H-flu or en e (25a ). To a solution of 0.587 g of diphenyl[2,2-
di(4-tert-butylphenyl)-1-iodoethenyl]phosphine oxide (6a , 0.950
mmol) in 35 mL of THF was added 1.1 mL (1.9 mmol) of a 1.7
M solution of tert-butyllithium in pentane at -78 °C, and the
color of the solution changed to dark red immediately. After
30 min at -78 °C, the reaction mixture was introduced via
Dik eton e 19. The same procedure was repeated as de-
scribed for 17 except that 0.403 g of 1-iodo-9-fluorenone (16,
1.31 mmol) and 0.263 g of 1-ethynyl-9-fluorenone (18, 1.29

Thermolysis of Benzoenyne-Allenes
J . Org. Chem., Vol. 64, No. 5, 1999 1655
cannula to a flask containing 0.206 g of 24 (0.736 mmol) in 50
mL of THF at 0 °C. After 5 h at room temperature, 40 mL of
diethyl ether and 60 mL of water were added. The organic
layer was separated, washed with water, dried over MgSO4,
and concentrated. The residue was purified by column chro-
matography (silica gel/hexanes) to afford 0.246 g of 25a (0.44
131.41, 128.39, 127.19, 127.13, 125.52, 119.25, 96.60, 84.26,
34.88, 31.12; MS m/z 262 (M+), 247, 229, 219, 202; HRMS calcd
for C19H18
O 262.1358, found 262.1348. Anal. Calcd for
C19H18O: C, 86.99; H, 6.92. Found: C, 87.15; H, 6.77.
4-ter t-Bu t yl-2′-[(4-ter t-b u t ylp h en yl)et h yn yl]b en zh y-
d r ol (29a ). To a solution of 0.715 g of 28a (2.73 mmol) in 10
mL of THF was added 1.7 mL of a 2.0 M solution of 4-tert-
butylphenylmagnesium bromide (3.4 mmol) in diethyl ether
at -30 °C under a nitrogen atmosphere. The reaction mixture
then was allowed to warm to room temperature. After 1.5 h,
18 mL of a dilute NH4Cl solution and 100 mL of diethyl ether
were introduced. The organic layer was separated, washed
with water, dried over Na2SO4, and concentrated. The residue
was purified by flash chromatography (silica gel/6% diethyl
ether in hexanes) to furnish 0.995 g of 29a (2.51 mmol, 92%)
as a white solid: mp 103-104 °C; IR (KBr) 3359, 2216, 834,
758 cm-1; 1H NMR (CDCl3) δ 7.60 (1 H, d, J ) 7.4 Hz), 7.50 (1
H, dd, J ) 7.7 and 1.2 Hz), 7.4-7.2 (10 H, m), 6.34 (1 H, d, J
) 3.7 Hz), 2.45, (1 H, d, J ) 3.7 Hz), 1.31 (9 H, s), 1.28 (9 H,
s); 13C NMR (CDCl3) δ 151.76, 150.31, 145.58, 140.23, 132.33,
131.21, 128.61, 127.24, 126.32, 126.23, 125.37, 125.30, 121.36,
120.00, 94.76, 86.90, 73.89, 34.81, 34.48, 31.33, 31.16; MS m/z
396 (M+), 381, 247; HRMS calcd for C29H32O 396.2453, found
396.2452. Anal. Calcd for C29H32O: C, 87.83; H, 8.13. Found:
C, 87.54; H, 8.18.
2-(P h en yleth yn yl)ben zh yd r ol (29b). To a solution of 1.59
g of 2-(phenylethynyl)benzaldehyde13 (28b, 7.72 mmol) in 18
mL of THF was added 9.3 mL of a 1.0 M solution of
phenylmagnesium bromide (9.3 mmol) in THF at -30 °C under
a nitrogen atmosphere. The reaction mixture then was allowed
to warm to room temperature. After 1.5 h, 18 mL of a dilute
NH4Cl solution and 100 mL of diethyl ether were introduced.
The organic layer was separated, washed with water, dried
over Na2SO4, and concentrated. The residue was recrystallized
from hexanes to furnish 1.77 g of 29b (6.23 mmol, 81%) as a
white solid: mp 99-101 °C; IR (KBr) 3333, 755, 689 cm-1; 1H
NMR (CDCl3) δ 7.59 (1 H, dm, J ) 7.9 and 0.6 Hz), 7.54 (1 H,
dm, J ) 7.6 and 1 Hz), 7.5-7.43 (4 H, m), 7.41-7.22 (8 H, m),
6.39 (1 H, s), 2.55 (1 H, br s); 13C NMR (CDCl3) δ 145.45,
143.05, 132.40, 131.46, 128.83, 128.48, 128.38, 127.51, 127.39,
126.65, 126.34, 122.94, 121.21, 94.58, 87.40, 74.03; MS m/z 284
(M+), 206, 178; HRMS calcd for C21H16O 284.1201, found
284.1198.
4-ter t-Bu tyl-2′-[(4-ter t-bu tylp h en yl)eth yn yl]ben zop h e-
n on e (30a ). To 0.646 g of pyridinium chlorochromate (3.00
mmol), suspended in 4 mL of anhydrous methylene chloride,
was added 0.719 g of 29a (1.82 mmol) in 4 mL of methylene
chloride at room temperature. After 2 h, the black reaction
mixture was diluted with 40 mL of diethyl ether, and the
solvent was decanted. The remaining black residue was
washed with diethyl ether. The combined organic layers were
passed through a short Florisil column. Solvent was then
evaporated, and the black residue was purified by flash
chromatography (silica gel/2% diethyl ether in hexanes) to
furnish 0.632 g of 30a (1.60 mmol, 88%) as a white solid: mp
110-111 °C; IR (KBr) 2217, 1663 cm-1; 1H NMR (CDCl3) δ 7.82
(2 H, d, J ) 8.4 Hz), 7.56 (1 H, td, J ) 7.7 and 1.9 Hz), 7.5-
7.38 (5 H, m), 7.17 (2 H, d, J ) 8.4 Hz), 6.90 (2 H, d, J ) 8.4
Hz), 1.31 (9 H, s), 1.24 (9 H, s); 13C NMR (CDCl3) δ 196.82,
156.81, 151.62, 141.80, 134.75, 132.29, 131.12, 130.26, 130.13,
128.63, 128.01, 125.29, 124.96, 122.00, 119.61, 95.36, 87.06,
35.14, 34.70, 31.08; MS m/z 394 (M+), 379; HRMS calcd for
C29H30O 394.2297, found 394.2299. Anal. Calcd for C29H30O:
C, 88.28; H, 7.66. Found: C, 88.36; H, 7.64.
(2-P h en yleth yn yl)ben zop h en on e (30b). The same pro-
cedure was repeated as described for 30a except that 0.345 g
of pyridinium chlorochromate (1.60 mmol) and 0.284 g of 29b
(1.00 mmol) were used to afford 0.256 g of 30b (0.91 mmol,
91%) as a yellow liquid: IR (neat) 2216, 1665, 755, 704, 690
cm-1; 1H NMR (CDCl3) δ 7.93-7.90 (1 H, m), 7.90-7.87 (1 H,
m), 7.66-7.41 (7 H, m), 7.28-7.16 (3 H, m), 7.09-7.03 (2 H,
m); 13C NMR (CDCl3) δ 197.04, 141.53, 137.34, 133.12, 132.53,
131.39, 130.29, 130.22, 128.66, 128.37, 128.16, 128.05, 122.57,
121.82, 95.12, 87.42; MS m/z 282 (M+), 281, 265, 253, 252, 176;
mmol, 60%) as a pale yellow solid: IR 1918, 1599, 1454 cm-1
;
1H NMR (CDCl3) δ 7.83-7.78 (2 H, m), 7.73 (1 H, dd, J ) 6.4
and 1.2 Hz), 7.53 (1 H, dd, J ) 7.7 and 1.0 Hz), 7.5-7.3 (11 H,
m), 7.25-7.1 (5 H, m), 1.33 (18 H, s); 13C NMR (CDCl3) δ
207.51, 150.75, 139.42, 138.22, 137.76, 137.55, 132.80, 131.81,
131.56, 128.71, 127.95, 127.84, 127.79, 127.52, 127.36, 125.37,
123.15, 122.53, 120.18, 119.98, 119.31, 116.48, 107.65, 95.30,
87.38, 34.57, 31.31.
9-(Dip h e n ylvin ylid e n e )-1-(p h e n yle t h yn yl)-9H -flu o-
r en e (25b). The same procedure was repeated as described
for 25a except that 0.83 g of diphenyl(2,2-diphenyl-1-iodoet-
henyl)phosphine oxide (6b, 1.6 mmol), 1.9 mL of a 1.7 M
solution of tert-butyllithium (3.2 mmol) in pentane, and 0.352
g of 24 (1.26 mmol) were used to afford 0.508 g of 25b (1.15
mmol, 91%) as an orange solid: IR 1924, 1597, 1493, 1454
cm-1; 1H NMR (CDCl3) δ 7.82-7.78 (2 H, m), 7.72 (1 H, dd, J
) 7.3 and 1.2 Hz), 7.54-7.28 (14 H, m), 7.2-7.1 (5 H, m); 13
C
NMR (CDCl3) δ 207.51, 139.49, 138.03, 137.82, 137.35, 135.73,
131.74, 131.53, 129.01, 128.48, 128.07, 127.99, 127.93, 127.78,
127.72, 127.44, 123.02, 122.53, 120.27, 120.06, 119.42, 116.87,
107.84, 95.47, 87.15; MS m/z 442 (M+), 365, 289; HRMS calcd
for C35H22 442.1722, found 442.1713.
1-[Di(4-t er t -b u t ylp h e n yl)m e t h yl]-2-p h e n ylflu or a n -
th en e (27a ). A solution of 0.231 g of 25a (0.417 mmol) in 5
mL of 1,4-CHD was heated at 75 °C, and the progress of the
reaction was monitored by TLC. After 1.5 h at 75 °C, the
benzoenyne-allene 25a disappeared completely. The reaction
mixture was concentrated, and the residue was purified by
flash chromatography (silica gel/hexanes) to afford 0.218 g of
27a (0.392 mmol, 94%) as a pale yellow solid: mp 227-229
1
°C; IR (KBr) 3059, 752, 702 cm-1; H NMR (CDCl3) δ 7.99 (1
H, d, J ) 6.7 Hz), 7.91 (1 H, d, J ) 7.5 Hz), 7.85 (1 H, d, J )
8.3 Hz), 7.81 (1 H, s), 7.67 (1 H, dd, J ) 8.2 and 7.0 Hz), 7.4-
7.3 (3 H, m), 7.28-7.2 (7 H, m), 7.12 (4 H, d, J ) 8.3 Hz), 7.01
(1 H, d, J ) 7.9 Hz), 6.91 (1 H, td, J ) 7.5 and 1 Hz), 6.17 (1
H, s), 1.31 (18 H, s); 13C NMR (CDCl3) δ 148.79, 145.88, 142.69,
139.81, 139.56, 139.39, 139.27, 136.69, 136.38, 132.97, 129.63,
128.88, 128.40, 127.75, 127.63, 127.17, 126.90, 126.81, 126.56,
126.28, 125.04, 120.44, 119.15, 52.07, 34.30, 31.34; MS m/z 556
(M+), 555, 541, 499, 423, 421, 365, 289, 279; HRMS calcd for
C
43H40 556.3130, found 556.3155. Anal. Calcd for C43H40: C,
92.76; H, 7.24. Found: C, 92.59; H, 7.27. The fluoranthene
27a was recrystallized from a mixture of 5:3 ethanol and
pentane for the X-ray structure determination.11
1-(Dip h en ylm eth yl)-2-p h en ylflu or a n th en e (27b). The
same procedure was repeated as described for 27a except that
0.156 g of 25b (0.353 mmol) in 4.8 mL of 1,4-CHD was heated
at 75 °C for 1.5 h to afford 0.155 g of 27b (0.349 mmol, 99%)
as a yellow solid: mp 230-232 °C; IR (KBr) 3057, 1598, 740,
1
698 cm-1; H NMR (CDCl3) δ 7.97 (1 H, dd, J ) 6.9 and 0.6
Hz), 7.85 (2 H, t, J ) 7.9 Hz), 7.80 (1 H, s), 7.66 (1 H, dd, J )
8.1 and 6.9 Hz), 7.35-7.1 (16 H, m), 7.04 (1 H, d, J ) 7.9 Hz),
6.88 (1 H, td, J ) 7.6 and 1.0 Hz), 6.15 (1 H, s); 13C NMR
(CDCl3) δ 145.87, 142.47, 141.84, 139.83, 139.07, 138.92,
136.74, 136.65, 132.96, 129.55, 129.34, 128.88, 128.49, 128.20,
127.84 (two overlapping signals), 127.07, 126.96, 126.83,
126.74, 126.33, 126.12, 120.58, 119.30, 52.84; MS m/z 444 (M+),
367, 289, 165; HRMS calcd for C35H24 444.1878, found 444.1862.
Anal. Calcd for C35H24: C, 94.56; H, 5.44. Found: C, 94.27; H,
5.51.
2-[(4-ter t-Bu tylph en yl)eth yn yl]ben zaldeh yde (28a). The
same procedure was repeated as described for 28b13 except
that 2.22 g of (4-tert-butylphenyl)acetylene (14.1 mmol) and
1.85 g of 2-bromobenzaldehyde (10.0 mmol) were used to afford
2.025 g of 28a (7.73 mmol, 77%) as a yellow solid: mp 62.5-
64.5 °C; IR (KBr) 2214, 1698, 835, 762 cm-1; 1H NMR (CDCl3)
δ 10.64 (1 H, s), 7.93 (1 H, d, J ) 7.7 Hz), 7.62 (1 H, d, J ) 7.7
Hz), 7.56 (1 H, t, J ) 7.4 Hz), 7.5-7.36 (5 H, m), 1.32 (9 H, s);
13C NMR (CDCl3) δ 191.82, 152.49, 135.75, 133.74, 133.15,

1656 J . Org. Chem., Vol. 64, No. 5, 1999
Wang et al.
HRMS calcd for C21H13O (M+ - 1) 281.0966, found 281.0959.
Anal. Calcd for C21H14O: C, 89.34; H, 5.00. Found: C, 89.31;
H, 5.00.
H, m), 5.15 (1 H, s); 13C NMR (CDCl3) δ 149.67, 144.20, 142.19,
140.32, 139.05, 138.36, 136.76, 136.42, 133.21, 133.05, 132.25,
130.46, 130.25, 130.21, 129.42, 129.17, 129.13, 128.29, 128.16,
127.82, 127.68, 126.91, 126.80, 126.38, 125.88, 125.70, 125.40,
125.27, 123.57, 53.69; MS m/z 444 (M+), 367; HRMS calcd for
7-ter t-Bu tyl-5,10,11-tr i(4-ter t-bu tylp h en yl)-11H-ben zo-
[b]flu or en e (34a ). To a solution of 1.446 g of diphenyl[2,2-
di(4-tert-butylphenyl)-1-iodoethenyl]phosphine oxide (6a , 2.340
mmol) in 95 mL of dry THF at -78 °C was added 2.8 mL (4.76
mmol) of a 1.7 M solution of tert-butyllithium in pentane under
a nitrogen atmosphere. After 30 min at -78 °C, 0.839 g of 30a
(2.13 mmol) in 15 mL of THF was introduced. After 5 h, the
reaction mixture was gradually warmed to room temperature.
After an additional 12 h at room temperature, 200 mL of
diethyl ether and 100 mL of water were added. The organic
layer was separated, washed with water, dried over MgSO4,
and concentrated. The residue was purified by flash chroma-
tography (silica gel/hexanes) to afford 1.077 g of 34a (1.61
mmol, 76%) as a white solid: mp 288-290 °C; IR (KBr) 3059,
C
35H24 444.1878, found 444.1904. Anal. Calcd for C35H24: C,
94.56; H, 5.44. Found: C, 94.51; H, 5.49. Benzofluorene 34b
was recrystallized from a 2:1 mixture of methanol and meth-
ylene chloride for the X-ray structure determination.11
5,10-Dip h en yl-11H-b en zo[b]flu or en e (36). The same
procedure was repeated as described for 34b except that 0.206
g of 28b (1.00 mmol) was used to afford 0.189 g of 36 (0.51
mmol, 51%) as a white solid: mp 194-196 °C; IR 3060, 762,
1
701 cm-1; H NMR (CDCl3) δ 7.7-7.35 (15 H, m), 7.21 (1 H,
td, J ) 7.4 and 1.2 Hz), 7.04 (1 H, t, J ) 7.7 Hz), 6.51 (1 H, d,
J ) 7.9 Hz), 3.89 (2 H, s); 13C NMR (CDCl3) δ 144.28, 141.40,
139.47, 139.25, 139.13, 136.91, 135.23, 133.15, 132.96, 131.50,
130.16, 129.95, 129.10, 128.65, 127.75, 127.39, 127.05, 126.49,
126.46, 125.75, 125.23, 125.07, 124.79, 123.71, 36.57; MS m/z
368 (M+), 291; HRMS calcd for C29H20 368.1565, found
368.1561. Anal. Calcd for C29H20: C, 94.53; H, 5.47. Found:
C, 94.63; H, 5.56.
833, 765, 728 cm-1 1H NMR (CDCl3) δ 7.68-7.61 (2 H, m),
;
7.56 (1 H, d, J ) 2.2 Hz), 7.53 (1 H, d, J ) 9 Hz), 7.46 (2 H, dt,
J ) 8.2 and 2 Hz), 7.42-7.35 (2 H, m), 7.30 (1 H, dd, J ) 7.9
and 2.0 Hz), 7.14-7.03 (2 H, m), 7.0-6.89 (2 H, m), 6.84 (2 H,
d, J ) 8.2 Hz), 6.48 (1 H, d, J ) 7.7 Hz), 6.4-6.33 (3 H, m),
5.08 (1 H, s), 1.49 (9 H, s), 1.38 (9 H, s), 1.23 (9 H, s), 1.19 (9
H, s); 13C NMR (CDCl3) δ 150.59, 149.76, 149.27, 148.07,
147.66, 144.33, 140.87, 139.12, 136.82, 136.09, 135.89, 135.60,
133.17, 133.07, 130.49, 129.93, 129.78, 128.91, 127.74, 127.29,
126.68, 125.83, 125.77, 125.60, 125.24, 124.90, 124.43, 123.85,
123.53, 121.60, 53.21, 34.80, 34.77, 34.47, 34.15, 31.58, 31.55,
31.36, 31.07; MS m/z 668 (M+), 653, 611, 535; HRMS calcd for
Ack n ow led gm en t. The financial support of the
National Science Foundation (CHE-9618676) to K.K.W.
is gratefully acknowledged. J .L.P. acknowledges the
support (CHE-9120098) provided by the Chemical In-
strumentation Program of the National Science Foun-
dation for the acquisition of a Siemens P4 X-ray
diffractometer in the Department of Chemistry at West
Virginia University.
C
51H56 668.4382, found 668.4385. Anal. Calcd for C51H56: C,
91.56; H, 8.44. Found: C, 91.49; H, 8.54. Benzofluorene 34a
was recrystallized from a 2:1 mixture of methanol and meth-
ylene chloride for the X-ray structure determination.11
5,10,11-Tr iph en yl-11H-ben zo[b]flu or en e (34b). The same
procedure was repeated as described for 34a except that 0.141
g of 30b (0.500 mmol) and 0.253 g of 6b (0.500 mmol) were
used to afford 0.11 g of 34b (0.25 mmol, 50%) as a white solid:
Su p p or t in g In for m a t ion Ava ila b le: 1H and 13C NMR
spectra for compounds 6a , 17-20, 23, 24, 25a ,b, 27a ,b, 28a ,
29a ,b, 30a ,b, 34a ,b, and 36 and the ORTEP drawings of the
crystal structures of 27a , 34a , and 34b. This material is
available free of charge via the Internet at http://pubs.acs.org.
mp 197-199 °C; IR 1595, 1493, 762, 698 cm-1
;
1H NMR
(CDCl3) δ 7.7-7.3 (14 H, m), 7.13-6.9 (6 H, m), 6.57-6.48 (3
J O982326K