Intramolecular behaviors of anthryldicarbenic systems: Dibenzo[b,f]pentalene and, 1H,5H-dicyclobuta[de,kl]anthracene

Article abstract of DOI:10.1021/jo010404p

9,10-Bis[methoxy(trimethylsilyl)methyl]anthracenes (24), synthesized from 9,10-dilithioanthracene (26) and bromomethoxytrimethylsilylmethane (27, 2 equiv), decompose (550-650 °C/10^-3 mmHg) carbenically to dibenzo[b,f]pentalene (28, >48%). 9,10-Anthryldicarbenes 39 or their equivalents convert to pentalene 28 rather than di-peri-cyclobutanthracenes 30 and 31, benzobiphenylene 32, or extended rearrangement products 33-38. Formation of 28 from 24 raises questions with respect to the behavior of 1,3,4,6-cycloheptatetraenyl-1-carbenes 49, 2,4,5,7-cyclooctatetraenylidene 51, 2,5,7-cyclooctatriene-1,4-diylidene 52, 1,2,4,5,7-cyclooctapentaene 53, and bicyclo[4.1.0]heptatrienyl-1-carbenes 54 and to carbon-skeleton and hydrogen rearrangements of anthryldicarbenes 39 and/or their equivalents at various temperatures. 1,5-Bis[methoxy(trimethylsilyl)methyl]anthracenes (25), prepared from 1,5-diiodoanthracene (63) and methoxytrimethylsilylmethylzinc bromide (57, 2 equiv) as catalyzed by PdCl₂(PPh₃)₂, yield the di-peri-carbenic reaction product 1H,5H-dicyclobuta[de,kl]anthracene (30, >40%) on pyrolysis at 550-650 °C/10^-3 mmHg. Proof of structure and various aspects of the mechanisms of formation of 30 are discussed.

Full text of DOI:10.1021/jo010404p

J . Org. Chem. 2001, 66, 6643-6649
6643
In tr a m olecu la r Beh a vior s of An th r yld ica r ben ic System s:
Diben zo[b,f]p en ta len e a n d 1H,5H-Dicyclobu ta [d e,kl]a n th r a cen e
J . Kirby Kendall† and Harold Shechter*
Department of Chemistry, The Ohio State University, Columbus, Ohio 43210
veit.3@osu.edu
Received April 18, 2001
9,10-Bis[methoxy(trimethylsilyl)methyl]anthracenes (24), synthesized from 9,10-dilithioanthracene
(26) and bromomethoxytrimethylsilylmethane (27, 2 equiv), decompose (550-650 °C/10-3 mmHg)
carbenically to dibenzo[b,f]pentalene (28, >48%). 9,10-Anthryldicarbenes 39 or their equivalents
convert to pentalene 28 rather than di-peri-cyclobutanthracenes 30 and 31, benzobiphenylene 32,
or extended rearrangement products 33-38. Formation of 28 from 24 raises questions with respect
to the behavior of 1,3,4,6-cycloheptatetraenyl-1-carbenes 49, 2,4,5,7-cyclooctatetraenylidene 51, 2,5,7-
cyclooctatriene-1,4-diylidene 52, 1,2,4,5,7-cyclooctapentaene 53, and bicyclo[4.1.0]heptatrienyl-1-
carbenes 54 and to carbon-skeleton and hydrogen rearrangements of anthryldicarbenes 39 and/or
their equivalents at various temperatures. 1,5-Bis[methoxy(trimethylsilyl)methyl]anthracenes (25),
prepared from 1,5-diiodoanthracene (63) and methoxytrimethylsilylmethylzinc bromide (57, 2 equiv)
as catalyzed by PdCl2(PPh3)2, yield the di-peri-carbenic reaction product 1H,5H-dicyclobuta[de,kl]-
anthracene (30, >40%) on pyrolysis at 550-650 °C/10-3 mmHg. Proof of structure and various
aspects of the mechanisms of formation of 30 are discussed.
In tr od u ction
carbenic systems undergo rearrangements that are dra-
matic extensions of that of monocarbenic analogues.
Thus, thermolyses of bis(methoxysilylmethyl)binaphthyls
14 (Scheme 2)7 give the di-peri-cyclobuta derivative 15,
which is dehydrogenated to di-peri-cyclobuta product 16.8
The products and mechanisms of thermal and pho-
tolytic rearrangements of arylmonocarbenes (ArCH) are
subjects of intense interest.1-3 As important examples of
such rearrangements, 2-naphthylcarbenes (1) isomerize
via 4,5-benzocyclohepta-1,2,4,6-tetraene (3) to 1-naphth-
ylcarbenes (5) that then convert to cyclobuta[de]naph-
thalene (6), 1-vinylideneindene (12), and 1H-cyclobuta-
[cd]indene (13) as stable products possibly as formalized
in Scheme 1.2,4-6 Although little investigated, arylpoly-
(4) (a) The CDH notation in
1 and in other carbenes in this
manuscript indicate that the species illustrated may exist in (E)- and
(Z)- forms in their singlet and triplet states.4b (b) Trozzolo, A. M.;
Wasserman, E.; Yager, W. A. J . Am. Chem. Soc. 1965, 87, 129.
(5) The questions as to intramolecular conversion of 5 to 6 by (1)
direct peri-C-H insertion as in A, (2) peri-C-H insertion as a singlet
or/and a triplet to give B with polar or (and) radical delocalization, (3)
addition as a singlet or (and) a triplet to C8 to give C or (and) D,
stabilization therein followed by hydrogen migration, (4) addition to
give E or (and) F and then hydrogen rearrangement, (5) carbenic
abstraction to give G or (and) H and then ring-closure, and (6)
spiroconjugative paths as in 10 will be discussed in future publications
from this laboratory and by associates. Similar questions may be raised
with respect to the conversions of 11 to 13 and of 64 and/or 67 to 30.
* To whom correspondence should be addressed.
† Present address, SASOL Chemical Industries, Ltd., Austin, TX
78729.
(1) (a) For details, discussions, and further references to studies of
the products and mechanisms of rearrangements of phenylcarbene
(C6H5-C¨ -H), a member of the C7H6 energy surface, see ref 1b-j. (b)
Gaspar, P. P.; Hsu, J .-P.; Chari, S.; J ones, M., J r. Tetrahedron 1985,
41, 1479. (c) Wentrup, C.; Mayor, C.; Becker, J .; Lindner, H. J .
Tetrahedron 1985, 41, 1601. (d) McMahon, R. J .; Abelt, C. J .; Chapman,
O. L.; J ohnson, J . W.; Kreil, C. L.; LeRoux, J . P.; Mooring, A. M.; West,
P. R. J . Am. Chem. Soc. 1987, 109, 2456. (e) Miller, P. C.; Gaspar, P.
P. J . Org. Chem. 1991, 56, 5101. (f) Matzinger, S.; Bally, T.; Patterson,
E. V.; McMahon, R. J . J . Am. Chem. Soc. 1996, 118, 1535. (g) Wong,
M. W.; Wentrup, C. J . Org. Chem. 1996, 61, 7022. (h) Schreiner, P. R.;
Karney, W. L.; Schleyer, P. v. R.; Borden, W. T.; Hamilton, T. P.;
Schaefer, H. F., III. J . Org. Chem. 1996, 61, 7030. (i) Patterson, E. V.;
McMahon, R. J . J . Org. Chem. 1997, 62, 4398. (j) Investigations of
and prior references to the various intramolecular reactions of
substituted phenylcarbenes are included in ref 1b-i.
(2) (a) The rearrangements of naphthylcarbenes 1 and 5 as sum-
marized in Scheme 1 are based on studies in refs 1b, 2b-g, and
references therein. (b) West, P. R.; Mooring, A. M.; West, P. R.;
McMahon, R. J .; Chapman, O. L. J . Org. Chem. 1986, 51, 1316. (c)
Albrecht, S. W.; McMahon, R. J . J . Am. Chem. Soc. 1993, 115, 855. (d)
Xie, Y.; Schreiner, P. R.; Schleyer, P. v. R.; Schaefer, H. F., III. J . Am.
Chem. Soc. 1997, 119, 1370. (e) Engler, T. A.; Shechter, H. J . Org.
Chem. 1999, 64, 4247. (f) Zheng, F.; McKee, M. L.; Shevlin, P. B. J .
Am. Chem. Soc. 1999, 121, 11237. (g) Bonvallet, P. A.; McMahon, R.
J . J . Am. Chem. Soc. 2000, 122, 9332.
(3) (a) For investigations of the rearrangements of substituted-
naphthyl and more complicated arylmonocarbenes see refs 1b,d, 2c,e,
and 3b,c and references therein. (b) Bailey, R. J .; Shechter, H. J . Am.
Chem. Soc. 1974, 96, 8116. (c) Kendall, J . K.; Engler, T. A.; Shechter,
H. J . Org. Chem. 1999, 64, 4255.
(6) (a) Spiro[2,4]heptatriene intermediates such as 10 (Scheme 1)
in rearrangements of arylcarbenes have been considered (Brown, W.
T.; J ones, W. M. J . Org. Chem. 1979, 44, 3092 and ref 1e) and may be
highly involved in carbenic conversions of 9-deuterio-10-[methoxy-
(trimethylsilyl)methyl]anthracene to 10(49%)- and 1(51%)-deutero-1H-
cyclobutanthracene at 650 °C/10-3 mm.3c (b) Syntheses, properties, and
the effects of spiroconjugation in spiroheptatrienes have been reviewed
in ref 6c-f and references therein. (c) Du¨rr, H.; Gleiter, R. Angew.
Chem., Int. Ed. Engl. 1978, 17, 559. (d) Du¨rr, H.; Albert, K.-H.; Kausch,
M. Tetrahedron 1979, 35, 1285. (e) Maksic, Z.; Kovacevic, K.; Mogus,
A. Theochem 1982, 2, 9. (f) Galasso, V. THEOCHEM 1992, 89, 181.
10.1021/jo010404p CCC: $20.00 © 2001 American Chemical Society
Published on Web 09/11/2001

6644 J . Org. Chem., Vol. 66, No. 20, 2001
Kendall and Shechter
Sch em e 1
Sch em e 3
tions with respect to preferred reaction routes and
transannular paths in single and multiple arylcarbene
rearrangement systems.
Resu lts a n d Discu ssion
P r ep a r a tion a n d P yr olysis of 9,10-Bis[(m eth oxy-
m eth yl)sila n es] 24. 9,10-Bis(silanes) 24 are obtained by
displacement reactions of bromo(methoxy)silylmethane
Sch em e 2
(9) (a) Baum, M. W.; Font, J . L.; Meislich, M. E.; Wentrup, C.; J ones,
M., J r. J . Am. Chem. Soc. 1987, 109, 2534.9b (b) Pyrolysis of bis-
tetrazole 17 at 600 °C/0.01 Torr also yields dibenzotricyclooctadiene I
(<0.5%, stereochemistry unassigned)9a apparently as formed by selec-
tive dimerization of 23.9c (c) Rieke, R. D.; Hudnall, P. M. J . Am. Chem.
Soc. 1973, 95, 2640. (d) Cyclobutabenzene (benzocyclobutadiene, 23)
has been kept as a monomer at low temperature in an argon-matrix.
In solution 23 converts rapidly to K presumably after formation of J .9e-i
(e) Chapman, O. L.; Chang, C. C.; Rosenquist, N. R. J . Am. Chem.
Soc. 1976, 98, 261. (f) Trahanovsky, W. S.; Arvidson, K. B. J . Org.
Chem. 1996, 61, 9528. (g) Gandhi, P. J . Sci. Ind. Res. 1982, 41, 495.
(h) Cava, M. P.; Mitchell, M. J . J . Am. Chem. Soc. 1959, 81, 5409. (i)
References in ref 9e-h and: Wang, K. W.; Liu, B.; Peterson, J . L. J .
Am. Chem. Soc. 1996, 118, 6860.
Further, p-phenylenedicarbenes 18 (Scheme 3) or their
precursors, as generated thermally from bis-tetrazole 17,9
convert to phenylacetylene (19, 3%) in low yield possibly
by degenerate rearrangement of cyclobutabenzene (benzo-
cyclobutadiene, 23) upon eventual formation and ring
closures of o-phenylenedicarbenes 20, cyclooctatrienyl-
1,4-dicarbene 21, and/or cyclooctapentaene 22.9,10
Study is now reported of syntheses and flash-vacuum
pyrolyses of bis(methoxysilylmethyl)anthracenes 247 and
25.7 The present thermolysis experiments result in
formation of impressive products by efficient multiple
carbenic processes and raise significant mechanism ques-
(10) (a) o-Phenylenedicarbenes (20) are calculated to (1) have
isomeric (Z,Z-, E,Z-, and E,E) ground-state, quinoidal, singlet struc-
tures and (2) undergo cyclization to cyclobutabenzene (23) in preference
to ring-opening to octadienediyne L.10b (b) Nicolaides, A.; Nakayama,
T.; Yamazaki, K.; Tomioka, H.; Koseki, S.; Stracener, L. L.; McMahon,
R. J . J . Am. Chem. Soc. 1999, 121, 10563.
(7) Silanes 14, 24, and 25 are presumed to have been prepared as
mixtures of stereoisomers.
(8) J aworek, W.; Vo¨gtle, F. Chem. Ber. 1991, 124, 347.

Intramolecular Behaviors of Anthryldicarbenic Systems
J . Org. Chem., Vol. 66, No. 20, 2001 6645
Sch em e 4
2711a,b (Scheme 4, 2 equiv) with 9,10-dilithioanthracene
(26)12 as generated from 9,10-dibromoanthracene and
n-BuLi (2 equiv) in hexane.13 Flash-vacuum pyrolyses of
242e,3d at 550-650 °C/10-3 mmHg give dibenzo[b,f]pen-
talene (indeno[2,1-a]indene, 28, Scheme 4, >48%),14,15
a
bronze-red, volatile solid (C10H16). Pentalene 28 is as-
signed from its exact mass and upon comparison of its
color, fluorescence, decomposition temperatures, mass
Thermolyses of 24 (Scheme 4) to give pentalene deriva-
tive 28 rather than its benzobiphenylene isomer 32 is
important for synthesis and with respect to theory9a and
to mechanisms of rearrangements of anthrylmono- and
dicarbenes. Of relevance are that pentalene (40, C8H6)
is more stable thermodynamically than cyclobutabenzene
(23)17 and 2,4,5,7-cyclooctatetraenylidene (41) is a simple
ring-opened isomer of 40. Further, biphenylene (42)
rearranges at 940 °C in the gas-phase to benzo[a]-
pentalene (44, Scheme 5).18 The mechanism proposed for
isomerization of 42 to 44 involves 1,2-hydrogen migration
and ring-expansion (Scheme 5) to the developing carbenic
center as in 43.18,19
1
spectra (including its cracking patterns), detailed H and
13C NMR spectra, IR and UV absorptions, and chemical
behavior with that previously reported.14,15 Further, the
C16H10 thermolysis product from 24 exhibits no 1H NMR
at ∼5 ppm for cyclobuta protons2d or any other evidence
for di-peri-cyclobutanthracene 30, its more strained di-
peri-cyclobuta isomer 31, or any other cyclobutarene
structure. Of importance also is that the C16H10 reaction
product did not contain benzobiphenylene 32,16a-e cy-
clobutanthracenes 3316e or 34,16e anthrylacetylenes 35,16f
36,16g or 37,16h or aceanthrylene (38),16i,j products that
might be formed by rearrangements of anthryldicarbenes
39 or their equivalents via sequences that are extensions
of Schemes 1 and 2 or as previously proposed for
phenylenedicarbenes 189a (Scheme 3).
(11) (a) Christiansen, M. L.; Benneche, T.; Undheim, K. Acta Chem.
Scand. 1987, B41, 536. (b) J ohn E. Strode is thanked for suggesting
the use of 27 for preparing 24 and 25.
(12) Duerr, B. F.; Chung, Y.-S.; Czarnik, A. W. J . Org. Chem. 1988,
53, 2120.
Recently benzobiphenylene 32 (Scheme 6) has been
reported19 to rearrange at 900-1100 °C to dibenzopen-
talene 28 as in Scheme 6. Of interest now are how bis-
silanes 24 are converted carbenically at 550-650 °C to
(13) (a) Present efforts to prepare 24 by treatment of 9,10-bis-
(methoxymethyl)anthracene13b with t-BuLi (2.2 equiv) in pentane at
-100 °C followed by chlorotrimethylsilane (4.5 equiv) and allowing
the mixture to warm to room temperature failed. (b) Miller, M. W.;
Amidon, R. W.; Tawney, P. O. J . Am. Chem. Soc. 1955, 77, 2845.
(14) (a) Blood, C. T.; Linstead, R. P. J . Chem. Soc. 1952, 2263. (b)
Chuen, C. C.; Fenton, S. W. J . Org. Chem. 1958, 23, 1538. (c) Eliasson,
B.; Edlund, U. Org. Magn. Reson. 1983, 21, 322. (d) Anderson, M. J .;
Brown, R. F. C.; Coulston, K. J .; Eastwood, F. W.; Ward, A. Aust. J .
Chem. 1990, 43, 1137. (e) Brown, R. F. C.; Eastwood, F. W.; Wong, N.
R. Tetrahedron Lett. 1993, 34, 3607.
(15) (a) The product assigned as dibenzopentalene 28 also exhibits
C-H IR absorptions at (1) ∼3047 cm-1 for aryl and olefinic protons,
(2) 746 (s) cm-1 for out of plane C-H bending vibration of the 4
adjacent aromatic hydrogen atoms, and (3) none for cyclobuta or
acetylenic hydrogens. (b) Further, the 1H and the 13C NMR chemical
shifts of the product presently assigned as 28 correspond excellently
with that of the ring protons and carbon atoms in 5, 10-dimethylindeno-
[2,1-a]indene14c (see the Experimental Section).
(16) (a) J ensen, F. R.; Coleman, W. E. Tetrahedron Lett. 1959, 7.
(b) Baker, W.; Barton, J . W.; McOmie, J . F. W.; Searle, R. J . G. J .
Chem. Soc. 1962, 2633. (c) Barton, J . W.; Rowe, D. J . Tetrahedron 1985,
41, 1323. (d) Barton, J . W.; Shepherd, M. K.; Willis, R. J . J . Chem.
Soc., Perkin Trans. 1 1986, 967. (e) Dewar, M. J . S.; Gleicher, G. J .
Tetrahedron 1965, 21, 1817. (f) Akiyama, S.; Ogura, F.; Nakagawa,
M. Bull. Chem. Soc. J pn. 1971, 44, 3443. (g) Akiyama, S.; Nakagawa,
M. Bull. Soc. Chem. J pn. 1960, 33, 1291. (h) Moroz, A. A.; Piskunov,
A. V.; Shvartsberg, M. S. Izv. Akad. Nauk SSSR. Ser. Khim. 1981,
368. (i) Plummer, B. F.; Al-Saigh, Z. Y.; Arfan, M. J . Org. Chem. 1984,
49, 2069. (j) Becker, H.-D.; Hanson, L.; Anderson, K. J . Org. Chem.
1985, 50, 277.
(17) (a) Dewar, M. J . S.; Merz, K. M. J r. J . Am. Chem. Soc. 1985,
107, 6175. (b) Schulman, J . M.; Disch, R. L. J . Am. Chem. Soc. 1993,
115, 11153. (c) Bally, T.; Zhu, Z.; Neuenschwander, M.; Chai, S. J . Am.
Chem. Soc. 1997, 119, 1869 and references therein. (d) References in
ref 17b,c. (e) Pentalene (40) may be kept as a monomer in matrix at
low temperature, dimerizes in solution to M, and has been trapped
with various reagents.17c
(18) (a) Wiersurn, U. E.; J enneskens, L. W. Tetrahedron Lett. 1993,
34, 6615. (b) Brown, R. F. C.; Choi, N.; Coulston, K. J .; Eastwood, F.
W.; Wiersurn, U. E.; J enneskens, L. W. Tetrahedron Lett. 1994, 35,
4405.
(19) (a) Preda, D. V.; Scott, L. T. Org. Lett. 2000, 2, 1490.19c (b) Scott,
L. T.; Hashemi, M. M.; Schultz, T. H.; Wallace, M. B. J . Am. Chem.
Soc. 1991, 113, 9692. (c) Further, 28 undergoes ring-opening, phenyl
rearrangement, and ring-closure at 900-1100 °C to give fluoranthene.19a
(d) Rearrangement of 28 to fluoranthene is not observed in the present
thermolyses of 24 at 550-650 °C. (e) In studies made prior to that in
ref 19a, Hartree-Fock calculations (6-31 G) were found to reveal that
28 is of lower energy [∆(∆E°) ) 16.3 kcal/mol] than 32. Dr. O.
Alekseeva is thanked for these calculations.

6646 J . Org. Chem., Vol. 66, No. 20, 2001
Kendall and Shechter
Sch em e 5
Sch em e 8
Sch em e 6
Sch em e 9
Sch em e 7
allenic intermediates 48-50 and, in particular, benzo-
cycloocta-2,4,5,7-tetraenylidene 51 which converts to
pentalene 28 simply by 1,5-transannular ring-closure (as
for 41 to 40).20 Because of the eventual cyclobutadienic
character and the strain in the reaction transition states,
rearrangements of 49, 50, and 51 to 52 and/or 53 and
then benzobiphenylene 28 are expected to be re-
pressed.17,19-21 Whether 9,10-anthryldicarbenes 39 are
generated in the present thermolyses of disilanes 24 is
not known. However, carbon-skeleton monorearrange-
ments in dicarbenes 39 as in Scheme 8 will give simply
54, which may convert to 1,3,4,6-cycloheptatetraenyl-
carbene 49 (Scheme 7) and then pentalene 28. Of further
note is that the thermal carbenic behaviors of bis-
(methoxysilylmethyl)anthracenes 24 (Schemes 4, 7, and
8) are very different from that reported for bis-tetrazole
17 (Scheme 3).9a Studies should now be made of (1)
whether various phenylenedicarbenic systems yield pen-
talene (40) and products thereof17d,e and (2) the products
and mechanisms of rearrangements of varied arenyl-
dicarbenes and hetarenyldicarbenes or their equivalents.
Syn th esis a n d Th er m olysis of 1,5-Bis[(m eth oxy-
m eth yl)sila n es] 25. 1,5-Bis(silanes) 25 are prepared as
in Schemes 9 and 10 from methoxytrimethylsilylmeth-
ylzinc bromide (57), 1,5-diiodoanthracene (63), and cata-
lytic amounts of PdCl2(PPh3)2.22,23
28 and the relation of the reaction mechanisms with that
in Scheme 6.
In the present experiments, pentalene 28 might be
formed from bis-silanes 24 (Scheme 7) upon (1) loss of
(CH3)3SiOCH3 (1 equiv), rearrangement of the initial
carbene (46) generated, further elimination of (CH3)3-
SiOCH3 (1 equiv), and isomerization of 51 and/or (2)
complete elimination of (CH3)3SiOCH3 (2 equiv) to give
dicarbenes 39 and then rearrangements as will be
explained. Scheme 7 illustrates a monocarbenic sequence
by which 24 is converted to 28 by mechanisms involving
only carbon skeleton rearrangements.20,21 The monocar-
benic rearrangments in Scheme 7 are similar to or
extensions of that in Scheme 1.20 Scheme 7 includes
Thermolysis of bis(silanes) 25 at 550-650 °C/10-3
mmHg produces a pyrolysate that has a GC-MS trace
with only one peak with a mass (202) for C16H10
.
Purification by MPLC/hexane yields di-peri-dicyclobut-
anthracene 30 (>40%), a white solid, presumably formed
from monocarbenes 64 and 67 and (less likely) dicarbenes
66 as in Scheme 11. Effective synthesis of such a highly
strained product as 30 at 550-650 °C by two peri-
cyclobuta ring-closure processes is impressive. Sealed
under argon, 30 turns red and decomposes rapidly at ∼60
°C. Dicyclobuta derivative 30 is air-sensitive and yellows
noticeably at room temperature under N2. At -20 °C
under argon, 30 is more stable. Pentalene 28 and possible
isomers 31-38 are not found as products of thermal
decompositions of bis-silanes 25.
(20) The cycloheptatrienylidene possibly formed by ring-opening of
47 and leading to cycloheptatetraene 48 in Scheme
7 and the
cycloheptatrienediylidene related to cycloheptatetraenylcarbene 49 in
Scheme 7 have not been included in the sequences illustrated in order
to save space and because the carbenes are expected to be of higher
energies than their corresponding allenes.1a-j
(21) Dicarbene 52 and/or diallene 53, if formed in thermolyses of
24 and of 32, might convert to 51 by multiple 1,2-carbon-skeleton
rearrangements or/and, as in ref 19a, by hydrogen migration. Pentalene
28 can then result upon ring-closure of 51 (Scheme 7). Study of the
behavior of labeled 24 and 32 in the gas-phase at 550-1100 °C might
allow further definition of the mechanism(s) of formation of 28.19a

Intramolecular Behaviors of Anthryldicarbenic Systems
J . Org. Chem., Vol. 66, No. 20, 2001 6647
Sch em e 10
F igu r e 1. 1H NMR of 1H,5H-Dicyclobuta[de,kl]anthracene
(30).
substituent, 30 has only one out-of-plane IR C-H bend-
ing band. The 1H NMR spectrum (Figure 1) of the product
shows absorption expected for cyclobuta methylene hy-
drogens at 4.83 ppm (s, 4H),2e the hydrogens ortho to the
methylene groups give a doublet at 7.05 ppm (2H, J )
5.97 Hz, AX system), the meta hydrogens absorb at 7.51
ppm (dd, 2H, J ) 5.97, 8.86 Hz, AX and AB systems),
and the para hydrogens give NMR at 7.60 ppm (d, 2H, J
) 8.87 Hz, AB system). The 13C NMR of 30 reveals
absorption for the methylene carbons at 44.7 ppm. There
are only six distinct peaks from δ 113-144 for the
remaining seven carbon atoms. Apparently, two of these
carbons have coincident chemical shifts. As yet it has
been impossible to obtain satisfactory stable crystals of
30 for X-ray analysis. The chemistry of 30 and its
derivatives is to be determined.
Sch em e 11
Thermolyses of 1,5-bis(silanes) 25 to give the di-peri-
cyclobuta product 30 (Scheme 11), whereas 9,10-bis-
(silanes) 24 yield the multiple rearrangment derivative
pentalene 28 (Schemes, 4, 7, and 8), are also of interest
with respect to preferred carbenic reaction mechanisms.
1-Anthrylcarbenes 64 (Scheme 11), as singlets or (and)
triplets, are more energetic than 9-anthrylcarbenes 46
(Scheme 7) of corresponding spin states. Similarly, 1,5-
anthryldicarbenes 66 have higher energies than 9,10-
anthryldicarbene analogues 39. Since pentalene 28 is
more stable than di-peri-cyclobutanthracene 30, on the
basis of thermodynamic equilibrative control, thermal
carbenic decompositions of 1,5-bis(silanes) 25 should yield
28 in preference to 30. Mechanistic schemes (see the
Supporting Information), however, for such carbenic
conversions of 25 to 28 via 64 and/or 66 involve inter-
mediates and/or transition states that do not have
naphthalenoid, benzenoid, and other favorable structures
for stabilization, and therefore, more preferable reaction
routes to 30, as will be proposed, are expected to be
followed.
The structural assignment as 30 is based primarily on
spectral data. The mass spectrum of the hydrocarbon
1
gives M+ ) 202 amu. The IR, H NMR, and 13C NMR
provide evidence for the symmetry of 30. The GC-FTIR
trace of 30 has three bands: aromatic C-H stretching
at 3062 cm-1, methylene C-H stretching at 2936 cm-1
,
and C-H out-of-plane bending at 767 cm-1. Since the
anthryl ring hydrogens are not separated by any other
(22) (a) In the preparation of 56 by the method of Magnus and Roy
(Magnus, P.; Roy, G. Organometallics 1982, 1, 533) in which sec-BuLi
reacts with methoxysilane 55 and THF in a 1:10 ratio at -78 °C and
the solution is warmed to -30 °C, CH3OCH2Si(CH3)2CH2Li is also
formed in substantial yield. Synthesis of 56 has now been found to be
greatly improved by using 55 and THF in a 1:2 ratio and lowering the
reaction temperature. A reliable method for preparing 56 is to add 55
in THF to a solution of sec-BuLi and THF (the ratio of 55/THF is 1:2)
frozen by liquid nitrogen and allowing the mixture to warm to -30
°C. (b) In the preparation of halozinc reagents [CH3OCH(ZnX)Si(CH3)3]
from 56 (Scheme 9), ZnBr2 and ZnI2 give comparable yields and better
than that from ZnCl2. ZnBr2 is preferred in the present preparation
because ZnI2 decomposes extensively while drying. (c) In further
development of this advantageous new synthetic methodology, (1)
iodobenzene, 57, and catalytic amounts of PdCl2(PPh3)2 in dioxane have
been found to give [methoxy(trimethylsilyl)methyl]benzene (>66%) and
biphenyl (10%) and (2) 1-iodonaphthalene is converted by 57 and PdCl2-
(PPh3)2 in dioxane to 1-[methoxy(trimethylsilyl)methyl]naphthalene
(>39%) and 1, 1′-binaphthyl (25%). (d) For coupling of iodoarenes with
other organozinc reagents using palladium chloride catalysts, see:
Erdik, E. Tetrahedron 1992, 48, 9577 and Negishi, E.; Gulevich, Y.
V.; Noda, Y. Tetrahedron Lett. 1993, 34, 1437.
The double carbenic reactions of 1,5-bis(silanes) 25 to
give the highly strained di-peri-cyclobuta derivative 30,
whereas 9,10-bis(silanes) 24 do not are of further interest
(23) (a) The present method for converting diaminoquinone 58 to
diiodoquinone 59 is simpler and more convenient than that by: Scholl,
R.; Hass, S.; Meyer, H. K. Chem. Ber. 1929, 107. (b) Syntheses of
diiodide 63 and 25 from 59 as in Scheme 10 are completely new. (c) It
is advantageous to reduce 59 with NaBH4 in 2-propanol to diols 60.
Methanol, methanol/diglyme, and methanol/THF as solvents lead to
extensive iodine removal during reactions of 59 with NaBH4. (d) For
other methodologies for reductions of 9,10-anthraquinones to an-
thracenes, see ref 23e-h. (e) Criswell, T. R.; Klandermann, B. H. J .
Org. Chem. 1974, 39, 770, (f) Norves, S. J . Org. Chem. 1993, 58, 2414,
(g) Marquardt, D. J .; McCormick, F. A. Tetrahedron Lett. 1994, 1131.
(h) Clark, K. J . J . Chem. Soc. 1956, 1911.

6648 J . Org. Chem., Vol. 66, No. 20, 2001
Kendall and Shechter
in that the C-H bond strengths at C10 in monocarbenes
64 and 67 (Scheme 11), C9 and C10 in dicarbenes 66
(Scheme 11), C1 in monocarbenes 46 (Scheme 7), C1 and
C5 in dicarbenes 39, and C1 and C8 in monocarbenes 68,
are all expected to be similar.24 Therefore, differences in
the abilities of C-H bonds to undergo direct insertion or
hydrogen abstraction-recombination do not explain the
carbenic products from 24 and 25.
states, the stabilizations by two phenyl groups will
continue to be more significant than that from a naphthyl
and an olefinic group and be important in the conversion
of 25 to the di-peri-cyclobuta product 30.27
Of relevance with respect to differences in the carbenic
behaviors of 24 and 25 is that attacks on the π-electron
systems of anthracenes by unencumbering electrophilic,
homolytic, and electron-transfer reagents usually occur
much more rapidly at C9 than at C1 and C2 positions.25
Carbenic ring-closure reactions of 1-anthrylcarbenes such
as 64 and 67 and (even) 1,5-dicarbenes 66 as singlets are
thus expected to be significantly expedited by the stabi-
lizing effects involving two phenyl groups as illustrated
in dipolar transition states 69-71.26 Similar conclusions
can be drawn for ring closures of 64, 67, and 66 to give
diradical analogues of 69-71.26 In peri ring-closures of
9-anthrylcarbene 46, cyclobut-9-anthrylcarbenes 68, and
9,10-anthryldicarbenes 39, the corresponding transition
states 72-74 are stabilized by single naphthyl and
olefinic interactions.26 Since delocalization by two phenyl
groups will be greater than for a naphthyl and an olefinic
group, transition states 69-71 will be favored over that
in 72-74, respectively, and thus conversions to cyclobuta
derivatives can occur more readily from 69-71 than from
72-74. Of further note with respect to the above mech-
anisms of carbenic decompositions of 24 and 25 to 30 is
that the transition states might develop earlier than
represented in 69-74 and involve C-H insertive interac-
tion on hydrogen on the carbon atoms, C9 or C1, at which
cyclobuta bridging is occurring.27 In such transition
The effects of substituents on the intramolecular
reactions of anthrylcarbenes will be reported.3c,28
Exp er im en ta l Section
Meth od s, Tech n iqu es, Rea gen ts, a n d An a lyses. The
methods, techniques, handling of reagents, and the various
analyses and spectral determinations used in the present
experiments are essentially identical with that in ref 3c.
Br om o[m eth oxy(tr im eth ylsilyl)]m eth a n e (27). Bromine
(9.7 g, 60.6 mmol) in CCl4 (50 mL) was added dropwise in 1 h
to a solution of methoxy(trimethylsilyl)methane29 (10 mL, 63.6
mmol) in dry CCl4 (100 mL). The resulting mixture was stirred
overnight. The solvent was removed, and the concentrate was
distilled fractionally under reduced pressure to give 27 as a
colorless oil: 4.3 g (34%); bp 41 °C/10.5 mmHg (lit.11a bp 40
1
°C/10 mmHg); H NMR (CDCl3) δ 0.18 (s, 9H), 3.52 (s, 3H),
5.76 (s, 1H).
9,10-B is [m e t h o x y (t r im e t h y ls ily l)m e t h y l]a n t h r a -
cen es (24). n-BuLi in hexane (10.5 mL, 1.4 M, 15.0 mmol)
was slowly added to 9,10-dibromoanthracene30 (1.25 g, 3.75
mmol) in dry Et2O (100 mL) at 0 °C. An orange solid formed,
and the mixture was stirred for 30 min at room temperature.
Bromomethoxysilylmethane 27 (2.95 g, 15.0 mmol) was added
in one portion. The solution warmed as the solid reacted. The
mixture was stirred for 2 h and then washed with H2O and
brine. Silica gel was added, and the mixture was concentrated.
Column chromatography using petroleum ether-toluene as
eluent yielded 24. Recrystallization from hexane gave yellow
crystals of 24 (0.70 g, 45%) apparently as an isomeric mixture:7
(24) (a) Calculated [B3LYP/6-31G(d)] bond dissociation energies
(BDE, kcal mol-1, 298 K) for cleavage of the C-H bonds at the
indicated carbon atom in anthracene are: C9 (111.4), C1 (111.0), and
C2 (110.9). Such calculated BDEs for C-H in naphthalene are: C1
1
the mp of 24 is broad,7 mp 140-146 °C; H NMR (CDCl3) δ
(111.1) and C2 (110.9). For benzene the calculated BDE is 110.8 kcal
24b
mol-1
.
(b) Barckholtz, C.; Barckholtz, T. A.; Hadad, C. M. J . Am.
-0.05 (s, 9H), 0.01 (s, 9H), 3.23 (s, 3H), 3.29 (s, 3H), 5.70 (m,
2H), 7.45 (m, 4H), 8.30 (m, 2H), 9.05 (m, 2H); 13C NMR (CDCl3)
δ -1.5, -1.4, 59.2, 59.3, 76.8, 76.9, 123.4, 123.5, 123.5, 123.6,
124.3, 124.4, 124.4, 125.1, 127.7, 127.8, 128.5, 128.6, 128.6,
129.8, 130.1, 130.1, 130.2, 131.8, 131.9, 131.9 (several indis-
tinguishable shoulder absorptions are not listed); exact mass
calcd 410.2097, obsd 410.2101. Anal. Calcd for C24H34O2Si2:
C, 70.19; H, 8.34. Found: C, 70.12; H, 8.30.
Chem. Soc. 1999, 121, 491. (c) The BDE for C-H in benzene has been
found experimentally to be 111.2 ( 0.8 24d and 113.5 ( 0.524e kcal mol-1
at 300 K. The experimental BDE for C-H in naphthalene (gas-phase
ion)24f is 111 ( 3 kcal mol-1. (d) Berkowitz, J .; Ellison, G. B.; Gutman,
D. J . Phys. Chem. 1994, 98, 2744. (e) Davico, G. E.; Bierbaum, V. M.;
DePuy, C. H.; Ellison, G. B.; Squires, R. R. J . Am. Chem. Soc. 1995,
117, 2590. (f) Kass, S. Private communication.
(25) (a) Various reactions and reactivities of anthracene have been
reviewed by: (b) Sainsbury, M. Rodd’s Chemistry of Carbon Com-
pounds, 2nd. ed.; Elsevier Scientific Publishing Company: Amsterdam,
1979; Vol. III H, pp 1-91. (c) Bolton, R. Rodd’s Chemistry of Carbon
Compounds, 2nd. ed.; Elsevier Science Publishers B.V.: Amsterdam,
The Netherlands, 1988; Vol. III, Supplement, pp 1-17. (d) For
comprehensive summary and mechanistic interpretations of various
electrophilic reactions of anthracenes, see: Taylor, R. Electrophilic
Aromatic Substitution; J . Wiley & Sons: Chichester, 1990; pp 1-513.
(26) In 69-71, there will be delocalization by two phenyl groups at
P yr olysis of 9,10-Disila n es 24 to Diben zo[b,f]p en ta len e
(28). Flash-vacuum decomposition of 24 (200 mg, 0.49 mmol)
was effected at 650 °C/10-3 mmHg in a horizontal quartz
furnace filled with quartz chips as described in ref 3d. The
pyrolysate upon trituration with degassed benzene gave 28
(28) (a) 9- and 1-anthrylcarbenes, upon generation at 500-600 °C,
yield 1H-cyclobuta[de]anthracene1c,3c,5,6a,28b,c and other products. (b)
Engler, T. A.; Shechter, H. Tetrahedron Lett. 1982, 23, 2715. (c) The
mechanisms of these reactions will be interpreted further.6a
(29) Speier, J . L. J . Am. Chem. Soc. 1948, 70, 4142.
C
10 and by a phenyl group at the bridging carbenic (cyclobuta) carbon.
Delocalization in 72-74 at C4 will involve interaction with a single
2-naphthyl group and an olefinic group and at the cyclobuta carbon
with a 1-naphthyl group.
(27) Such insertive-addition transition states are similar to B in
footnote 5.
(30) Heilbron, I. M.; Heaton, J . S. Organic Syntheses; Wiley: New
York, 1941; Collect. Vol. I, p 207.

Intramolecular Behaviors of Anthryldicarbenic Systems
J . Org. Chem., Vol. 66, No. 20, 2001 6649
as a bronze solid:14 38 mg (40%); mp 300-310 °C dec (lit.14c,d
mp >280 °C dec); IR (KBr) 3047 (w), 1582 (w), 1453 (w), 1428
57 generated, and the orange mixture was then stirred for 4
h. During this time, the mixture became dark blue.
(w), 1156 (w), 9.34 (w), 891 (w), 853 (m), 746 (s), 473 (w) cm-1
;
Et2O (ca. 20 mL) and H2O (ca. 20 mL) were added, and the
mixture was vacuum-filtered over Celite. The Et2O extract was
washed with H2O and brine, dried, concentrated on silica gel,
and column chromatographed on silica with petroleum ether
and petroleum ether-toluene as eluents to yield 25 (145 mg,
61%). The mp of 25 is broad and its NMR is complex as
expected for stereoisomers: mp 147-166 °C (lit.7 mp 147-
166 °C); 1H NMR (CDCl3) δ 0.19 (s, 18H),3.40 (s, 3H), 3.41 (s,
3H), 4.96 (s, 1H), 4.98 (s, 1H), 7.49 (m, 4H), 7.92 (dd, 2H), 8.64
(d, 2H); 13C NMR (CDCl3) δ -2.4, 59.4, 78.0, 78.3, 122.6, 122.7,
123.6, 123.7, 125.0, 126.9, 127.0, 129.3, 129.3, 131.6, 137.0;
exact mass calcd 410.2097, obsd 410.2108. Anal. Calcd for
1H NMR (CDCl3) δ 6.40 (s, 1H), 6.85-6.9 (m, 3H), 7.0-7.1 (m,
1H) [lit.14c,d 1H NMR (CDCl3) δ 6.40 (s, 1H), 6.85-6.9 (m, 3H),
7.0-7.1 (m, 1H)]; 13C NMR (CDCl3) δ 122.0, 123.0, 126.1, 127.1,
128.2, 134.6, 148.8, 150.1 [lit.14c,d 13C NMR (CDCl3) δ 122.1,
123.2, 126.3, 127.2, 128.3, 134.8, 149.0, 150.2]; M+ ) 202 amu;
m/z 202 (M, 100), 200 (14), 101 (9), 100 (6) [lit.14c,d m/Z 202
(M, 100), 200 (14), 101 (11), 100 (6)]. The NMR chemical shifts
of the ring hydrogens and carbons in 5,10-dimethylindeno[2,1-
a]indene are as follows: [lit.14c 1H NMR δ 6.9 (m, 3H), 7.1 (m,
2H); lit.14c,15 13C NMR (CDCl3) δ 120.5, 121.6, 126.9, 127.1,
135.5, 136.0, 143.0, 151.1]. (Pyrolysis of 24 at 550 °C/10-3
mmHg gave 28 in >48% yield).
C
24H34O2Si2: C, 70.21; H, 8.35. Found: C, 70.45; H, 8.35.
1,5-Diiod o-9,10-a n t h r a q u in on e (59). 1,5-Diamino-9,10-
anthraquinone (58, 50 g, 210 mmol) was suspended in chilled
concd H2SO4 (200 mL). Sodium nitrite (40 g, 580 mmol) was
added over 30 min. The resulting thick brown mixture was
stirred 3 h and poured into H2O (2.5 L). After the mixture had
been stirred for 30 min, the purple solids were filtered. To the
filtrate was added KI (50 g, 310 mmol). The solution bubbled
and turned black. After the mixture had stirred for 3 h,
NaHSO3 was added until the color of the solution changed to
brown. The orange solid formed was washed with H2O until
acid free, oven-dried, and identified as 59 (6.68 g, 7%).
The purple solids filtered from the initial reaction mixture
were suspended in H2O (2.5 L) for 15 min. After filtering the
dark diazonium salt solution, KI (50 g) was added portionwise.
The solution bubbled vigorously, and the olive solid formed
was washed with H2O and oven-dried. Combination of the solid
fractions gave gold-orange 59 (79.2 g, 82%): mp 250-260 °C
dec (lit.23a mp 308-309 °C).
P yr olysis of 1,5-Disila n e 25 to 1H,5H-Dicyclobu ta [d e,-
kl]a n th r a cen e (30). Flash-vacuum decomposition of 25 (50
mg, 0.12 mmol) was conducted at 550 °C/10-3 mmHg in a
horizontal quartz apparatus filled with quartz chips as de-
scribed in ref 3c. MPLC (hexanes) of the pyrolysate yielded
two yellow fractions and one colorless fraction. GC-IR-MS
and 1H NMR of the two yellow fractions indicated each to be
complex mixtures containing incompletely pyrolyzed material.
The colorless fraction on concentration gave white crystals of
30: 10 mg (40%); mp (sealed capillary) 60-82 °C (dec, yellow-
red); FTIR (gas phase) 3062, 2967, 2936, 2832, 1613, 1458,
984, 767, 729 cm-1; 1H NMR (300 MHz, CDCl3) δ 4.83 (s, 4H),
7.05 (d, 2H, J ) 5.97), 7.51 (dd, 2H, J ) 5.97, 8.86 Hz), 7.60
(d, 2H, J ) 8.87 Hz); 13C NMR (300 MHz, CDCl3) δ 44.7, 114.1,
118.8, 120.3, 130.6, 143.7; UV (λ, hexane) 228, 262, 352, 368,
370, 386; exact mass 202.0783, obsd 202.0788. The instability
of 30 at room temperature has precluded elemental analysis.
Many experiments as above gave 30 in ∼40% yield.
1,5-Diiod oa n th r a cen e (63) fr om 59. Finely ground 59 (5.0
g, 10.87 mmol) was suspended in a mixture of 2-propanol (50
mL) and THF (50 mL). After the stirred mixture was cooled
to 0 °C, NaBH4 (1 g, 26.32 mmol) was added. The red-brown
suspension became homogeneous after 30 min. The mixture
was stirred at room temperature for 30 min, and H2O was
added. The crude 9,10-dihydro-9,10-dihydroxy-1,5-diiodoan-
thracenes (60, mp 250-270 °C dec) collected were washed with
H2O, dried, and added to phenylhydrazine (3.0 mL, 30.6 mmol)
in glacial acetic acid (50 mL). The mixture was heated at 80-
95 °C for 7 h, cooled, and diluted with H2O. The light brown
solids were vacuum-filtered, washed with H2O, oven-dried, and
then purified by continuous extraction on silica gel with
hexanes. (Sublimation of the product leads to substantial
losses; conventional chromatography requires massive amounts
of solvent because of the insolubility of diiodide 63.) Concen-
tration of the hexane mixture followed by recrystallization
from THF-EtOH yielded light orange 63: 0.84 g (18%); mp
236-238 °C; 1H NMR (CDCl3) δ 7.21 (t, 2H), 8.12 (t, 4H), 8.61
Ack n ow led gm en t. We thank the National Science
Foundation, the U.S. Department of Education, and M.
S. Newman Funds at The Ohio State University for
partial support of this research. We also thank Kathy
Veit for her enormous help in preparing this manu-
script, Kurt Loening for his extensive advice on chemical
nomenclature, and Christopher Hadad for important
discussions.
Su p p or tin g In for m a tion Ava ila ble: Discussion of mech-
anisms for possible conversions of 25 to 28 via 64 and/or 66,
1H and 13C NMR of 24, 25, and 63, 1H NMR of 28, and 13C
NMR of 30. Also included are experimental details for (1)
reaction of 55 with sec-BuLi in THF to give [(dimethyl-
(methoxymethyl)silyl)methyl]lithium (see ref 22a) and its
reaction with MgBr2 and then 1,5-dichloroanthracene/NiCl2
dppp to yield 1,5-bis[(dimethyl(methoxymethyl)silyl)methyl]-
anthracene, (2) development methodology and advantageous
synthesis of [methoxy(trimethylsilyl)methyl]benzene and
1-[methoxy(trimethylsilyl)methyl]naphthalene from iodoben-
zene and 1-iodonaphthalene, respectively, with 57 and PdCl2-
(PPh3)2, (3) alternate synthesis of 63 by diazotization of 1,5-
diaminoanthracene followed by KI, and (4) alternate preparation
of 25 from anthracene-1,5-dicarboxylic acid upon conversion
to dimethyl anthracene-1,5-dicarboxylate, 1,5-bis(hydroxym-
ethyl)anthracene, and 1,5-bis(methoxymethyl)anthracene. This
material is available free of charge via the Internet at
http://pubs.acs.org.
1
(s, 2H); H NMR (DMSO-d6) δ 7.32 (t, 2H), 8.27 (q, 4H), 8.66
(s, 2H); 13C NMR (CDCl3) δ 126.7, 129.7, 132.3, 132.6, 137.9;
exact mass calcd 429.8719, obsd 429.8713. Anal. Calcd for
C
14H8I2: C, 39.10; H, 1.88. Found: C, 39.17; H, 1.89.
1,5-Bis[m eth oxy(tr im eth ylsilyl)m eth yl]an th r acen es (25)
fr om 63. sec-BuLi in hexane (1.4 M, 2.1 mL, 2.88 mmol) was
added to THF (1 mL) at -78 °C, and the resulting solution
was frozen by liquid N2. (Methoxymethyl)trimethylsilane (55,
0.45 mL, 2.9 mmol) was injected. The mixture was melted and
warmed over 1 h to -10 °C. Addition of ZnBr2 in THF (0.77
M, 3.7 mL, 2.85 mmol) and diglyme (5 mL) was followed by 5
min of stirring. Diiodide 63 (250 mg, 0.96 mmol, 0.33 equiv)
and PdCl2(PPh3)2 (22 mg, 3.3 mol % of 63) were added to the
J O010404P