Synthesis of peri-cyclobutarenes by thermolysis of [methoxy(trimethylsilyl)methyl]arenes

Article abstract of DOI:10.1021/jo981104j

[Methoxy(trimethylsilyl)methyl]arenes are readily prepared by reactions of chlorotrimethylsilane with (α-methoxy)arenylmethyllithium reagents as obtained from (methoxymethyl)arenes and t-BuLi. The [methoxy(trimethylsilyl)methyl]arenes eliminate methoxytrimethylsilane at 525-675 °C/0.05-0.10 mm to yield peri-cyclobutarenes as derived from arenylcarbenes. Of importance is the fact that the initial arenylcarbenes generated insert into adjacent peri C-H bonds and/or isomerize to other arenylcarbenes that insert into their peri C-H bonds to give peri- cyclobutarenes. Thus, flash-vacuum pyrolysis of 1- [methoxy(trimethylsilyl)methyl]naphthalene (13) at 575-675 °C/0.05-0.10 mm yields 1H-cyclobuta[de]naphthalene (6, up to 39%) in practical quantities. 2- [Methoxy(trimethylsilyl)methyl]naphthalene (23) also affords 6 as a major thermolysis product. At 510 °C/0.05-0.10 mm 4-methoxy-1- [methoxy(trimethylsilyl)methyl]naphthalene (29) decomposes to 4-methoxy-1H- cyclobuta[de]naphthalene (31, 46%). Under similar conditions, 2-methoxy-1- [methoxy(trimethylsilyl)methyl]naphthalene (33) converts to 1,2- dihydronaphtho[2,1-b]furan (35, 64%) and naphtho[2,1-b]furan (36, 31%), presumably by insertion of 2-methoxy-1-naphthylcarbene (34) into a C-H bond of its o-methoxy group and then dehydrogenation of the resultant dihydrofuran. Further, 1-[methoxy(trimethylsilyl)methyl]-6-methylnaphthalene (39) pyrolyzes (510 °C/0.10-0.20 mm) to 6-methyl-1-naphthylcarbene (40), which isomerizes in part to 7-methyl-1-naphthylcarbene (49); carbenes 40 and 49 then undergo peri C-H insertion to give 3-methyl-1H- cyclobuta[de]naphthalene (41) and 2-methyl-1H-cyclobuta[de]naphthalene (42) in an 8:1 ratio and a combined yield of 44%. The pyrolytic method is particularly valuable for preparing higher peri single carbon atom bridged arenes such as 4H-cyclobuta[jk]phenanthrene (53, 65%) and 3H- cyclobuta[cd]pyrene (59, 86%).

Full text of DOI:10.1021/jo981104j

J . Org. Chem. 1999, 64, 4247-4254
4247
Syn th esis of per i-Cyclobu ta r en es by Th er m olysis of
[Meth oxy(tr im eth ylsilyl)m eth yl]a r en es
Thomas A. Engler† and Harold Shechter*
Department of Chemistry, The Ohio State University, Columbus, Ohio 43210
Received J une 9, 1998
[Methoxy(trimethylsilyl)methyl]arenes are readily prepared by reactions of chlorotrimethylsilane
with (R-methoxy)arenylmethyllithium reagents as obtained from (methoxymethyl)arenes and t-BuLi.
The [methoxy(trimethylsilyl)methyl]arenes eliminate methoxytrimethylsilane at 525-675 °C/0.05-
0.10 mm to yield peri-cyclobutarenes as derived from arenylcarbenes. Of importance is the fact
that the initial arenylcarbenes generated insert into adjacent peri C-H bonds and/or isomerize to
other arenylcarbenes that insert into their peri C-H bonds to give peri-cyclobutarenes. Thus, flash-
vacuum pyrolysis of 1-[methoxy(trimethylsilyl)methyl]naphthalene (13) at 575-675 °C/0.05-0.10
mm yields 1H-cyclobuta[de]naphthalene (6, up to 39%) in practical quantities. 2-[Methoxy-
(trimethylsilyl)methyl]naphthalene (23) also affords 6 as a major thermolysis product. At 510 °C/
0.05-0.10 mm 4-methoxy-1-[methoxy(trimethylsilyl)methyl]naphthalene (29) decomposes to 4-meth-
oxy-1H-cyclobuta[de]naphthalene (31, 46%). Under similar conditions, 2-methoxy-1-[methoxy-
(trimethylsilyl)methyl]naphthalene (33) converts to 1,2-dihydronaphtho[2,1-b]furan (35, 64%) and
naphtho[2,1-b]furan (36, 31%), presumably by insertion of 2-methoxy-1-naphthylcarbene (34) into
a C-H bond of its o-methoxy group and then dehydrogenation of the resultant dihydrofuran.
Further, 1-[methoxy(trimethylsilyl)methyl]-6-methylnaphthalene (39) pyrolyzes (510 °C/0.10-0.20
mm) to 6-methyl-1-naphthylcarbene (40), which isomerizes in part to 7-methyl-1-naphthylcarbene
(49); carbenes 40 and 49 then undergo peri C-H insertion to give 3-methyl-1H-cyclobuta[de]-
naphthalene (41) and 2-methyl-1H-cyclobuta[de]naphthalene (42) in an 8:1 ratio and a combined
yield of 44%. The pyrolytic method is particularly valuable for preparing higher peri single carbon
atom bridged arenes such as 4H-cyclobuta[jk]phenanthrene (53, 65%) and 3H-cyclobuta[cd]pyrene
(59, 86%).
Sch em e 1
Naphthalenes have been bridged in peri-positions by
single carbon atom moieties by (1) photolysis of 8-halo-
1-naphthyldiazomethanes (1, X ) Br, and 3, X ) I; eq
1),1 (2) pyrolysis of 1(5)- and 2(7)-naphthyldiazomethanes
(Scheme 1), sodium 1- and 2-naphthaldehyde p-tosylhy-
drazonates, and 5-(1)- and 5-(2-naphthyl)tetrazoles, re-
spectively at 450-700 °C/10-2-10-4 mm,2 and (3) cou-
pling of 1,8-dilithionaphthalene (8, Scheme 1) with
dichloromethane and 1,8-bis(iodomagnesio)naphthalene
(9, Scheme 1) with methylene bis(toluene-p-sulfonate).3
The above synthetic methods are often unsatisfactory,
however, for preparative purposes. Practical syntheses
of various peri-methanonaphthalenes (11) by vacuum
thermolyses of [methoxy(trimethylsilyl)methyl]naph-
thalenes (10) as illustrated in eq 2 are now described in
† Present address: Lilly Corporate Center, Eli Lilly and Company,
Indianapolis, IN, 46285.
(1) (a) Bailey, R. J .; Shechter, H. J . Am. Chem. Soc. 1974, 96, 8116.
(b) Bailey, R. J .; Card, P. J .; Shechter, H. J . Am. Chem. Soc. 1983,
105, 6096.
(2) (a) Becker, J .; Wentrup, C. J . Chem. Soc., Chem. Commun. 1980,
190.2c (b) Wentrup, C.; Mayor, C.; Becker, J .; Lindner, H. J . Tetrahe-
dron 1985, 41, 1601.2c (c) The p-tosylhydrazonates and the (naphthyl)-
tetrazoles decompose to 5 or 7 prior to formation of 6.2a,b
(3) Yang, L. S.; Engler, T. A.; Shechter, H. J . Chem. Soc., Chem.
Commun. 1983, 866.
detail.4-6 The present method has also been extended to
synthesis of various benzannelated derivatives of 11.
10.1021/jo981104j CCC: $18.00 © 1999 American Chemical Society
Published on Web 05/26/1999

4248 J . Org. Chem., Vol. 64, No. 12, 1999
Engler and Shechter
Ta ble 1. Effects of Tem p er a tu r e a n d P r essu r e on th e
Con ver sion s to a n d th e Yield s of 6 on P yr olysis of 13
1-[Methoxy(trimethylsilyl)methyl]naphthalene (13) is
readily prepared (100%, eq 3) by deprotonation of 1-(meth-
6
temp
(°C)
pressure
(mm)
13 %
% conversiona
% yieldb
recoveryc
490-510
500-510
500-510
560
650
695-700
750
0.005
2.0
0
0
92
35
51
65
0
0
0
0
6-11
17
11
39
27
4
9-12
35
32
39
27
4
0.35-0.40
0.07-0.10
0.05-0.15
0.05-0.07
0.05-0.07
3.0
oxymethyl)naphthalene (12) with t-BuLi in TMEDA/Et2O
at -78 °C and reaction of the subsequent lithio derivative
with chlorotrimethylsilane.7 Vacuum pyrolysis of 13 upon
volatilization through a packed quartz tube at 650 °C/
0.05-0.10 mm occurs with loss of methoxytrimethylsi-
lane to yield 1H-cyclobuta[de]naphthalene (6, eq 3) as a
major product (39%)8 along with 12 (8%), naphthalene
(14, 3%), 1-naphthaldehyde (9%), R-methyl-1-naphtha-
lenemethanol (7%), 1-methylnaphthalene (5%), and in-
tractables. Cyclobutanaphthalene 6 is obtainable, after
chromatography of the pyrolysate, as the major compo-
800
0
0
a
b
The percentage of 6 formed from 13 in a single pass. The
percentage of 6 formed from 13 that decomposed. c The percentage
of initial 13 recovered.
nitrate to give pure 4-nitro-1H-cyclobuta[de]naphthalene
(15).9 Purification of 6 (>90%) can be effected by frac-
tional distillation, preparative GC, or preparation of its
picrate followed by recrystallization and decomposition
of the complex on silica gel.
1
nent (60-70% by H NMR) of a mixture containing 14,
1-methylnaphthalene, and unidentified minor products.
This mixture can be used conveniently for preparing
derivatives of 6 as demonstrated by nitration with acetyl
(4) (a) A portion of these results were communicated: Engler, T.
A.; Shechter, H. Tetrahedron Lett. 1982, 23, 2715. (b) For application
of this chemistry, see: J aworek, W.; Vo¨gtle, F. Chem. Ber. 1991, 124,
347.
(5) (a) Other methods for generating arenylcarbenes at elevated
temperatures for preparing peri-cyclobutarenes are frequently imprac-
tical because of the instabilities of aryldiazomethanes and their facile
conversions to azines, the low vapor pressures of sulfonylhydrazonate
and sulfinate salts, the problems in introducing solids which are not
free-flowing into pyrolysis equipment at low pressures, and the
inefficiencies in decompositions of aryltetrazoles to their corresponding
arylcarbenes.2b,5b-d (b) The principal thermal reactions of aryltetrazoles
are conversions to nitriles and hydrogen azide.2b,5c,d (c) Golden, A. H.;
J ones, M., J r. J . Org. Chem. 1996, 61, 4460. (d) Kumar, A.; Narayanan,
R.; Shechter, H. J . Org. Chem. 1996, 61, 4462.
(6) (a) Photolysis of 2-diazoacenaphthenone in argon at 8 K to 1,8-
naphthyleneketene and irradiation of 8-hydroxy-1-naphthylglyoxylic
acid lactone at -195 °C to give 1H-cyclobuta[de]naphthalen-1-one have
been of significance to structural principles and mechanistic theory.6b
These transformations as yet, however, are not usable preparatively.
(b) Chapman, O. Chem. Eng. News 1978, Sept 18, p 78. (c) Hayes, R.
A.; Hess, T. C.; McMahon, R. J .; Chapman, O. L. J . Am. Chem. Soc.
1983, 105, 7787.
(7) (a) R-Lithio(aryl)methyl alkyl ethers [ArCH(Li)OR] rearrange
readily to lithio alkoxides [ArCH(R)OLi].7b-e Such Wittig rearrange-
ments are retarded at low temperatures by TMEDA. (b) Wittig, G.;
Lo¨hmann, L. Liebigs Ann. Chem. 1942, 550. (c) Schafer, H.; Scho¨llkopf,
U.; Walter, D. Tetrahedron Lett. 1968, 2809. (d) Scho¨llkopf, U. Angew.
Chem., Int. Ed. Engl. 1970, 9, 763. (e) Hoffmann, R. W.; Ru¨hl, T.;
Harbach, J . Liebigs Ann. Chem. 1992, 725. (f) That R-lithio(aryl)methyl
methyl ethers can be used synthetically in the presence of TMEDA at
low temperatures without significant rearrangement was developed4a,7g
on knowledge that the migratory abilities of alkyl groups in isomer-
ization of R-lithiobenzyl alkyl ethers in TMEDA/THF/Et2O at -60 °C
increase in the order methyl, ethyl, iso-propyl, and tert-butyl (krel 1:40:
162:2080).7c (g) Engler, T. A.; Shechter, H. Tetrahedron Lett. 1983, 24,
4645. (h) Yeh, M. K. J . Chem. Soc., Perkin Trans. 1 1981, 1652. The
author found that benzyl methyl ether is deprotonated by n-BuLi/
TMEDA in hexane at -10 °C and the R-lithiobenzyl methyl ether
formed is alkylated by 1-bromobutane (80% yield) and adds to
nonenolizable ketones. (i) Azzena, U.; Demartis, S.; Fiori, M. G.;
Melloni, G.; Pisano, L. Tetrahedron Lett. 1995, 36, 5641. The authors
have communicated that R-lithio(aryl)methyl methyl ethers, as gener-
ated by metalation of arylmethyl methyl ethers with n-BuLi in THF
at -40 °C in the absence of TMEDA, react with various electrophiles
without serious complications from Wittig rearrangements.
Pyrolysis of 13 is conducted in simple equipment (see
Experimental Section) at readily attainable temperatures
and pressures. More than 10 g of 13 has been thermo-
lyzed in a single experiment, and the decompositions can
be conducted on a larger scale.10 Varying the pyrolysis
temperature and pressure greatly affect the conversions
and yields of 6 from 13. As shown in Table 1, tempera-
tures of at least 500 °C are required, and the best yields
of 6 are obtained at lower pressures (<0.10 mm) and
short contact times. Temperatures of 750-800 °C, even
at low pressures, give poor yields of 6, and production of
intractables is extensive.
The mechanism of formation of 6 is presumed to
involve R-elimination of methoxytrimethylsilane from 13
to form 1-naphthylcarbene (16),11 which then inserts into
the peri C-H bond of its naphthalene ring (Scheme 2).1,2,8
Although details of the ring closure are not known, a
rational explanation is singlet reaction of 16 with its
naphthalene π-system at C-8 to give 17, followed by
hydrogen migration from C-8 to the bridging carbon.12
Alternatively, at temperatures of 500-750 °C, carbene
1 might react intramolecularly via its triplet and thus
involve biradical 18. Intramolecular hydrogen abstrac-
(9) Friedli, F. E.; Shechter, H. J . Org. Chem. 1985, 50, 5710.
(10) A particular advantage of the present method is that 13 is a
low-melting solid (mp 40.5-43.0 °C) and with slight heating can be
conveniently admitted at low pressure into the pyrolysis equipment
as a liquid or by simple distillation.
(11) Sekiguchi, A.; Ando, W. Tetrahedron Lett. 1979, 4077. Sekigu-
chi, A.; Ando, W. J . Org. Chem. 1980, 45, 5286. These authors report
that substituted phenyl(trimethylsilyl)methanols eliminate trimeth-
ylsilanol at ∼500 °C to give products of the phenylcarbenes generated.
(12) For recent summaries and treatments of the theory of isomer-
ization of arylcarbenes, see: (a) Xie, Y.; Schreiner, P. R.; Schleyer,
P. v. R.; Schaefer, H. F., J r. J . Am. Chem. Soc. 1997, 119, 1370. (b)
Matzinger, S.; Bally, T.; Patterson, E V.; McMahon, R. J . J . Am. Chem.
Soc. 1996, 118, 1535. (c) Wong, M. W.; Wentrup, C. J . Org. Chem. 1996,
51, 7022. (d) Schreiner, P. R.; Karney, W. L.; Schleyer, P. v. R.; Borden,
W. T.; Hamilton, T. P.; Schaeffer, H. F. J . Org. Chem. 1996, 61, 7030
and (e) references therein.
(8) Piptopyrolysis of sodium 1-naphthaldehyde p-tosylhydrazonate
at 600 °C/10-3 to 10-1 mm is reported to give 6, 14, and 1-methyl-
naphthalene in 39%, 15%, and 21% yields, respectively.2b At 700 °C/
10-3 to 10-1 mm, 5-(1-naphthyl)tetrazole yields 6 (26%), 1-methyl-
naphthalene (6%), and naphthalene-1-carbonitrile (61%).2b In the
present investigation, piptopyrolysis of 5H-(1-naphthyl)tetrazole at 600
°C/0.05-0.1 mm in a quartz tube packed with quartz chips yields
naphthalene-1-carbonitrile and hydrogen cyanide essentially totally.

Synthesis of peri-Cyclobutarenes
J . Org. Chem., Vol. 64, No. 12, 1999 4249
Sch em e 2
Sch em e 3
Sch em e 4
tion-recombination via biradical 19, although theoreti-
cally less likely, cannot be excluded at present.12
Of further interest is that 14 might be formed by
rearrangement of 16 and loss of atomic carbon from 20
+
(eq 4) and/or ipso displacement of (CH3)3SiCHOCH3
from 13 on acidic surfaces in the pyrolysis chamber (eq
5).5c,d,13 The thermal decompositions of 13 to 12, 1-naph-
Ta ble 2. Effects of Tem p er a tu r e a n d P r essu r e on th e
Con ver sion s to a n d th e Yield s of 31 on P yr olysis of 29
31
temp
(°C)
pressure
(mm)
29
% conversiona % yieldb % recoveryc
445-455 0.2-0.3
87
510
520
0.05-0.10
0.05-0.10
29
27
6
46
35
7
35
21
10
0
535-545 0.1-0.4
560 0.2-0.3
tr
tr
thaldehyde, R-methyl-1-naphthalenemethanol, and 1-me-
thylnaphthalene are minor processes that are discussed
in the Supplemental Information.
a
b
The percentage of 31 formed from 29 in a single pass. The
percentage of 31 formed from 29 that decomposed. c The percent-
age of initial 29 recovered.
The thermal behavior of 2-[methoxy(trimethylsilyl)-
methyl]naphthalene (23), prepared (82%, Scheme 3) by
reaction of 2-(methoxymethyl)naphthalene (22) with t-
BuLi/TMEDA and then displacement of chlorotrimeth-
ylsilane, was then investigated. A purpose of this experi-
ment was to obtain evidence that carbenes 24 and (then)
16 are generated. The result of pyrolysis of 23 to 6 are
similar to that for 7.2,12,14 The difference in the yields of
6 from 13 (39%) and from 23 (12%) is attributable to the
lengthy path for isomerization of 24 to 6; the intermedi-
ates prior to 16 have many opportunities to be inter-
cepted by various species in the reaction system.
Decomposition of 4-methoxy-1-[methoxy(trimethylsi-
lyl)methyl]naphthalene (29), as prepared from 4-meth-
oxy-1-methoxymethylnaphthalene (28, Scheme 4), then
became of interest. Pyrolysis of 29 at 510 °C/0.05-0.1
mm yields 4-methoxy-1H-cyclobuta[de]naphthalene (31,
46%), a liquid of proper elemental analysis and spectral
properties.
Formation of 31 from 29 presumably involves carbene
30 as a reaction intermediate. Methanonaphthalene 31
is the first 1H-cyclobuta[de]naphthalene in which the
aromatic nucleus contains an oxygen substituent. Con-
version of 29 to 31 is much more sensitive to the pyrolysis
temperature (Table 2) than is conversion of 13 to 6.
Temperatures greater than 450 °C are required to
eliminate methoxytrimethylsilane from 29. Extensive
decomposition of 31 occurs, however, above 520 °C.
(13) In other studies from this laboratory, loss of carbon atoms from
arylcarbene precursors become major processes at temperatures above
650 °C.
(14) Carbon-carbon rearrangements of arylcarbenes were initially
reported by (a) Vander Stouw, G. G. Ph.D. Dissertation, The Ohio State
University, Columbus, Ohio, 1964; Dissertation Abstracts, Ann Arbor,
Michigan, 1965. (b) J oines, R. C.; Turna, A. B.; J ones, W. J . Am. Chem.
Soc. 1969, 91, 7754. (c) Crow, W. D.; Wentrup, C. Chem. Commun.
1969, 1387. (d) Schissel, P.; Kent, M. E.; McAdoo, D. J .; Hedeya, E. J .
Am. Chem. Soc. 1970, 92, 2147. (e) Baron, W. J .; J ones, M., J r.; Gaspar,
P. P. J . Am. Chem. Soc. 1970, 92, 4739. (f) For excellent summaries
and discussion of arylcarbene rearrangements, see: Gaspar, P. P.; Hsu,
J .-P.; Chari, S.; J ones, M., J r. Tetrahedron 1985, 41, 1479 and ref 2b.

4250 J . Org. Chem., Vol. 64, No. 12, 1999
Engler and Shechter
Sch em e 5
Sch em e 6
Sch em e 7
To determine the preference of a 1-naphthylcarbene
for reaction with an ortho substituent as compared to
insertion into a peri C8-H center, synthesis and vacuum
pyrolysis of 2-methoxy-1-[methoxy(trimethylsilyl)methyl]-
naphthalene (33) were investigated as summarized in
Scheme 5. Decomposition of 33 at 610 °C/0.05-0.10 mm
gives 1,2-dihydronaphtho[2,1-b]furan (35, 64%) and naph-
tho[2,1-b]furan (36, 31%). The structures of 35 and 36
are assigned from their exact masses and by comparison
of their 1H NMR, IR, and MS results with literature
values. Dihydrofuran 35 apparently results from inser-
tion of 2-methoxy-1-naphthylcarbene (34) into a C-H
bond of its o-methoxy group. Such cyclizations have been
reported for arylcarbenes having o-dialkylamino, o-thio-
alkyl, o-methoxy, and certain o-alkyl substituents.15
Dehydrogenation of 35 yields 36. There is no evidence
for formation of 2-methoxy-1H-cyclobuta[de]naphthalene
(37) in the pyrolysis of 33.
The behavior of 6-methyl-1-naphthylmethylene (40),
as generated from 1-[methoxy(trimethylsilyl)methyl]-6-
methylnaphthalene (39), was then examined. Synthesis
of silane 39 and the overall results of its pyrolysis are
summarized in Scheme 6.
reactants, 2- and 3-substituted-1H-cyclobuta[de]naph-
thalenes are preparable from naphthylmethylene precur-
sors.
Cyclobutanaphthalenes 41 and 42 are differentiated
1
1
Of interest in the thermolysis of 39 at 510 °C/0.1-0.2
mm is the fact that 3-methyl-1H-cyclobuta[de]naphtha-
lene (41) and 2-methyl-1H-cyclobuta[de]naphthalene (42)
are formed in an 8:1 ratio in 44% overall yield along with
1,6-dimethylnaphthalene (43, 3%). The three hydrocar-
bon products 41-43 were partially separated by GC; the
major peri-bridged naphthalene 41 and dimethylnaph-
thalene 43 were isolated pure. The minor peri-bridged
naphthalene 42 could not be obtained free of 41 and 43,
and the assignments of 41 and 42 will be explained. The
results of importance are (1) carbenic ring closure of 40
at C-8 with hydrogen rearrangement to yield 41 is a
major process, (2) 42 is apparently formed by multiple
carbene-carbene rearrangements as partially illustrated
in Scheme 7 to give 7-methyl-1-naphthylcarbene (49)12,14
which then cyclizes at its peri C-H position with
hydrogen migration, and (3) with proper choice of initial
by their H NMR as follows. A feature of the H NMR of
1H-cyclobuta[de]naphthalenes is that aromatic protons
which are ortho to peri-bridges absorb upfield (at 6.6-
7.1 ppm) from that of their meta and para protons (at
7.2-8.1 ppm). In symmetrical 1-substituted-1H-cyclob-
uta[de]naphthalenes, the ortho hydrogens give reso-
nances as doublets of doublets, whereas the meta and
para protons exhibit multiplets. The 300 MHz aromatic
1H NMR of 41 consists of a singlet at δ 6.97 (1H), a
doublet at 7.04 (1H, J ) 6 Hz), and a multiplet at 7.35-
7.48 (3H), which corresponds to a structure having two
protons ortho to the 1,8-methano bridge. H-2 gives a
singlet (meta coupling to H-4 is small), and H-7 gives a
doublet coupled to H-6. At 90 MHz the resonances of H-2
and H-7 overlap. Isomer 42 exhibits a 1H NMR (spec-
trum) at 200 MHz as a doublet at δ 7.02 (1H, J ) 5 Hz)
and a multiplet at δ 7.2-7.8 (4H). This pattern is
consistent with a structure having only one proton ortho
to the peri-methylene bridge, H-7, in which there is
splitting resulting from H-6. Coupling between H-5 and
(15) (a) Garner, R. Tetrahedron Lett. 1968, 221. (b) Garner, G. V.;
Mobbs, D. B.; Suschitsky, H.; Millership, J . S. J . Chem. Soc. C 1971,
3693. (c) Bailey, R. J . Ph.D. Dissertation, The Ohio State University,
1974, and ref 11.
1
H-7 is too small to be observed. H NMR signals for the

Synthesis of peri-Cyclobutarenes
J . Org. Chem., Vol. 64, No. 12, 1999 4251
Sch em e 8
Sch em e 9
Ta ble 3. Effects of Tem p er a tu r e a n d P r essu r e on th e
Con ver sion s, Yield s, a n d th e Ra tios of 53 a n d 54 on
P yr olysis of 51
53, 54
temp
(°C)
pressure
(mm)
51 %
53/54
% conversiona % yieldb recoveryc ratio
500-520 0.05-0.10
7
21
38
35
56
31
56
72
57
77
80
63
48
39
27
>100
590
590
0.3-0.5
10
9
0.10
600-650 0.2-0.4
6
4
650
0.10-0.15
a
b
The percentage of 53 and 54 from 51 in a single pass. The
percentage of 53 and 54 formed from 51 that decomposed. c The
percentage of initial 51 recovered.
bridging in CH2 in 41 and 42 appear at δ 4.76 and 4.70,
respectively.
Investigation was then initiated of the thermal behav-
ior of benzannelated naphthylcarbenes as generated from
methyl R-(trimethylsilyl)arylmethyl ether precursors. The
first such carbene studied was 9-phenanthrylcarbene (52)
upon synthesis and decomposition of 9-[methoxy(trim-
ethylsilyl)methyl]naphthalene (51, Scheme 8).4,16 Pyroly-
sis of 51 at 590 °C/0.1 mm gives 4H-cyclobuta[jk]-
phenanthrene (53) and 4H-cyclopenta[def]phenanthrene
(54) in a 9:1 ratio and a combined yield of 72%. The yield
of 53 and the ratio of 53 to 54 vary greatly with the
thermolysis conditions (Table 3). Indeed, no 54 is ob-
tained when the pyrolysis is conducted at low conversion
of 51 to products. In general, purification of 53 is much
simpler when the decompositions are effected at lower
temperatures. As expected, conversion of 52 to rear-
rangement product 54 increases with temperature.
The major product, 53, is obtained pure by recrystal-
lization and is assigned from its combustion analysis,
exact mass, and spectral properties. The important
pyrolysis mixture of 53 and 54 with 54 that had been
synthesized independently.
The mechanisms of rearrangement of 52 are similar
to those of naphthylcarbenes. Thus, 53 is formed by
cyclization of 52 at C-1 with hydrogen migration. Cyclo-
pentaphenanthrene 54 results (Scheme 9) after at least
20 formal rearrangement steps in the isomerization of
52 to 4-phenanthrylcarbene (55), which then inserts into
its C-H bond at C-5. Rearrangement of 52 to 55 and then
54 is also of interest in that carbenic migration through
a fused ring juncture occurs.16
1
spectral features of 53 are its H NMR absorptions at δ
Synthesis of 1-[methoxy(trimethylsilyl)methyl]pyrene
(57, 77%) from 1-methoxymethylpyrene (56), its ther-
molysis to 1-pyrenylmethylene (58), and the formation
of 3H-cyclobuta[cd]pyrene (59, Scheme 10) were then
studied. Indeed, volatilization of 57 through a quartz tube
at 520-525 °C at 0.05-0.07 mm produces 59 in 86%
yield. Identification of 59 is made from its exact mass
4.80 (s, 2H, CH2), 7.25 (dd, 1H, H-3 on the phenanthrene
nucleus, J ) 2 and 6 Hz), 7.31 (s, 1H, H-5, this signal
and that of H-3 partially overlap), and 7.5-8.5 (m, 7H,
aromatic) and 13C NMR absorption at 46.6 (CH2), as well
as the proper number of aromatic C-H and quaternary
C signals. Cyclobutaphenanthrene 53 is a sublimable,
white crystalline material and forms a bright orange
complex with 2,4,7-trinitrofluoren-9-one. Identification of
1
and spectral properties including H NMR absorptions
1
at δ 5.19 (s, 2H, CH2), 7.50 (s, 1H, H-4 on aromatic ring),
7.62 (d, 1H, H - 2, J ) 6 Hz), and 7.8-8.2 (m, 6H,
aromatic) and a 13C NMR signal at δ 53.0 (CH2). Pyrene
59 is a sublimable, white crystalline solid that reacts
rapidly with air on standing at room temperature;
however, 59 forms an air-stable bright maroon-purple
54 resulted from H NMR and HPLC comparison of the
(16) Reference 2b reports that piptopyrolysis of 5-(9-phenanthryl)-
tetrazole at 700 °C/10-3 to ∼5 × 10-1 mm and sodium phenanthrene-
9-carboxaldehyde p-tosylhydrazonate at 650 °C/10-3 to 10-1 mm each
yield 53 and 54 in ∼7% and 1% yields; phenanthrene, 9-meth-
ylphenanthrene and 9-phenanthrenecarbonitrile are also formed.

4252 J . Org. Chem., Vol. 64, No. 12, 1999
Engler and Shechter
Chemical shifts, unless otherwise specified, are reported in
ppm (δ) relative to tetramethylsilane (TMS) with TMS,
CH2Cl2, residual CHCl3, or ClCH2CH2Cl as internal standards.
P r oced u r e A; 1-[Meth oxy(tr im eth ylsilyl)m eth yl]n a p h -
th a len e (13). t-BuLi in pentane (1.9 M, 17 mL, 32 mmol) was
added to a mixture of 1-(methoxymethyl)naphthalene17 (12,
5.2 g, 30.0 mmol) and dry TMEDA (5.3 mL, 35 mmol) in dry
Et2O (100 mL) at -70 °C under argon. The purple-black
solution was stirred 20 min at -70 °C, chlorotrimethylsilane
(5.2 mL, 33 mmol) was added, and the dark green mixture
was allowed to warm to room temperature. After addition of
H2O to the colorless solution, the organic layer was separated,
washed with saturated aqueous NaHCO3, dried (MgSO4), and
concentrated to a light yellow oil (7.6 g, 100%) which was pure
Sch em e 10
1
by TLC and H NMR. Vacuum distillation yielded a colorless
oil, bp 123-125 °C/0.6 mm, which solidified in a freezer.
Sublimation (40-60 °C at 0.05 mm) gave 13 as a white waxy
1
solid: mp 40.5-43.0 °C; H NMR (CDCl3, CH2Cl2 as internal
standard) -0.02 (s, 9H), 3.33 (s, 3H), 4.83 (s, 1H), 7.3-8.2 (m,
7H); exact mass calcd 244.1283, obsd 244.1289. Anal. Calcd
for C15H20OSi: C, 73.71; H, 8.25. Found: C, 73.58, H, 8.13.
P yr olysis of [Meth oxy(tr im eth ylsilyl)m eth yl]a r en es.
Gen er a l P r oced u r e. All pyrolyses, unless otherwise de-
scribed, were performed by passing samples through a 3 cm
× 35 cm vertical quartz tube packed with a 4-5 cm column of
quartz chips placed approximately halfway down the tube. The
pyrolysis tube was heated with a 100 V Hoskins electric
furnace. A thermocouple was positioned between the furnace
wall and the quartz tube approximately one-third of the way
into the oven. Insulation material was packed around the tube
at the top and bottom of the oven. A receiver, with a sidearm
for vacuum connection, was attached to the bottom of the tube
and cooled in a dry ice-acetone bath.
Ta ble 4. Effects of Tem p er a tu r e a n d P r essu r e on th e
Con ver sion s to a n d th e Yield s of 59 on P yr olysis of 57
59
temp
(°C)
pressure
(mm)
57 %
% conversiona
% yieldb
recoveryc
510-530
520-525
520-540
660
0.02-0.05
0.05-0.07
0.05-0.10
0.05-0.20
29
32
47
86
47
39
62
34
26
31
<16d
<16
a
b
The percentage of 59 formed from 57 in a single pass. The
percentage of 59 formed from 57 that decomposed. c The percent-
d
age of 57 recovered. Part (∼35%) of a complex mixture.
Samples were introduced into the hot zone by (1) distillation
or sublimation by slowly heating a reservoir containing the
sample with an oil bath, flame, or Nichrome wire wrapped
around the reservoir, (2) dropping a neat sample into the tube
using a Hershberg pressure-equalizing dropping funnel, or (3)
dropping a solid sample into the tube utilizing a solid addition
funnel. Generally, the distillation technique gave better and
more reproducible results because stricter control over rate
and amount of addition could be maintained. Also, there is
less fluctuation in pressure during pyrolysis. Pressures were
monitored with a manometer fitted into the vacuum system
between the receiver and the vacuum pump.
complex with 2,4,7-trinitrofluoren-9-one. The excellent
yield in conversion of 57 to 59 presumably results from
the flexibility of the many ring-atom arene system, and
when there is carbene-carbene rearrangement, 58 is
formed repeatedly. The yield of 59 is, however, sensitive
to the pyrolysis temperature (Table 4).
In summary, various [methoxy(trimethylsilyl)methyl]-
arenes eliminate methoxytrimethylsilane preparatively
at 525-675 °C/0.05-0.10 mm in flow equipment to give
peri-cyclobutarenes as derived from precursor arenylcar-
benes. Of further value is information with respect to the
spectral and physical properties of various cyclobutarenes
from the present and previous1,3,9 investigations from this
P yr olysis of 1-[Meth oxy(tr im eth ylsilyl)m eth yl]n a p h -
th a len e (13); 1H-Cyclobu ta [d e]n a p h th a len e (6). Distilla-
tion of 13 (3.0 g, 12 mmol) at 0.05-0.10 mm through a quartz
tube heated to 650 °C afforded a dark brown pyrolysate that
was chromatographed on silica gel while changing the eluent
from hexane to benzene. The products obtained were (1) a
mixture (1.02 g) of 6 (63% of the mixture, 39% yield), 14 (3%
yield), and 1-methylnaphthalene (5% yield) in which the
components were identified and the yields were determined
1
laboratory. The H and 13C NMR spectra of peri-meth-
ylene-bridged arenes are very distinct with respect to the
positions of their peri-methano hydrogen and carbon
1
resonances. The H spectra show methylene signals at
4.39-5.15 ppm, depending upon the ring substituents.
The 13C NMR display carbon signals at 44.3-53.0 ppm.
Such resonances clearly indicate formation or retention
of a peri-methanoarene structure in assigning the prod-
ucts from various experiments. Of further note is the fact
that bridged arenes such as 6, 31, 41, 53, and 59 reveal
intense molecular ion patterns and very little fragmenta-
tion.
Studies of (1) improved methods for generating are-
nylcarbenes, (2) further synthesis of mono- and poly-peri-
methanoarenes, and (3) the varied chemistry of single-
atom, peri-bridged arenes are in progress.
1
by H NMR with ClCH2CH2Cl added as an internal standard
or by GC, (2) 1-(methoxymethyl)naphthalene 12 (0.11 g, 8%),
(3) 1-naphthaldehyde (0.12 g, 9%), (4) R-methyl-1-naphthale-
nemethanol (0.14 g, 7%), and (5) unidentified products.
The yields of 6 varied greatly with the temperature and
pressure at which the pyrolyses were conducted (Table 1).
Cyclobutanaphthalene 6 was usually obtained by chromatog-
raphy as the major component (60-70%) of a mixture with
14, 1-methylnaphthalene, and other minor products. This
mixture could be used directly for preparation of derivatives
of 6, as demonstrated by isolation of pure 4-nitro-1H-cyclobuta-
[de]naphthalene (15) from nitration of the mixture. Further
purification (>90% purity) of 6 could be effected by fractional
distillation or preparative GC (5% SE-30, 140 °C). Formation
of the picric acid complex of 6, followed by recrystallization
and decomposition of the complex on silica gel (hexane eluent),
afforded pure 6.
Exp er im en ta l Section
Gen er a l Meth od s. Melting points are uncorrected. El-
emental analyses were performed by Galbraith Laboratories,
Inc., Knoxville, TN, or Microanalysis, Inc., Wilmington, DE.
Mass spectra were determined at 70 eV unless otherwise
Nitr a tion of 1H-Cyclobu ta [d e]n a p h th a len e (6) Ob-
ta in ed by P yr olysis of 13; 4-Nitr o-1H-cyclobu ta [d e]n a p h -
th a len e (15). Acetyl nitrate (6.2 mmol) was prepared by slowly
described. 1H NMR were recorded at 90, 200, or 300 MHz. 13
C
NMR spectra were obtained at 20.1, 50.3, or 75.3 MHz.
(17) Sharp, D. B.; Patrick, T. M. J r. J . Org. Chem. 1961, 26, 1389.

Synthesis of peri-Cyclobutarenes
J . Org. Chem., Vol. 64, No. 12, 1999 4253
adding 70% nitric acid (0.4 mL, 6.2 mmol) to acetic anhydride
(5 mL) at 0-5 °C. After 5 min, the mixture was added dropwise
to 6 (1.02 g of pyrolysis product, 63% pure; 4.7 mmol) in acetic
anhydride (20 mL) at 0-5 °C. The resulting solution was
stirred for 1 h at 0-5 °C, allowed to warm to room tempera-
ture, stirred further for 1 h, and then poured into a mixture
of Et2O and 3.5 M aqueous KOH. After the mixture had been
stirred for 2 h, the Et2O layer was separated, dried (MgSO4),
and concentrated to a yellow solid, which was recrystallized
from hexane to give 15 as yellow needles (0.29 g, 34%); mp
120-123 °C, lit.9 mp 124-125 °C. The product was homoge-
neous by TLC and spectrally identical to reported values. The
mother liquor, upon chromatography on silica gel with 50%
hexane/benzene, afforded additional 15 as a yellow solid (0.12
g, 14%).
274.1398. Anal. Calcd for C16H22O2Si: C, 70.02; H, 8.08.
Found: C, 69.68; H, 8.17. The yield of 33 is 80% based on
recovered 47.
P yr olysis of 2-Met h oxy-1-[m et h oxy(t r im et h ylsilyl)-
m eth yl]n a p h th a len e (33). Slow distillation of 33 (0.26 g, 0.95
mmol) at 0.05-0.10 mm through a quartz tube heated to 610
°C gave a pale yellow oil, which on preparative TLC on silica
gel with hexane/benzene (5:1) yielded (1) naphtho[2,1-b]furan
(36, 0.05 g, 31%) as a light yellow oil, (2) 1,2-dihydronaphtho-
[2,1-b]furan (35, 0.10 g, 64%) as a colorless liquid, and (3)
initial 33 (0.01 g, 3%). Product 36 could be further purified by
preparative VPC (10 ft × 1/4 in. 5% SE-30 on chromosorb P,
isothermal at 160 °C) followed by sublimation at 35-40 °C
and 0.02 mm to yield white crystals: mp 51-54 °C (lit.18 mp
61-62 °C); 1H NMR18 (CDCl3, 200 MHz) 7.27 (d, 1H, J ) 2
Hz), 7.36-7.64 (m, 2H), 7.70 (d, 2H, J ) 5 Hz), 7.76 (d, 1H, J
) 2 Hz), 7.94 (d, 1H, J ) 8 Hz), 8.14 (d, 1H, J ) 8 Hz); MS
m/e (relative intensity) 169 (15), 168 (100, M+), 140 (18), 139
(27); exact mass calcd 168.0575, obsd 168.0580. Spectral data
for 35; 1H NMR19 (CDCl3, 90 MHz, CH2Cl2 as internal
standard) 3.46 (t, 2H, J ) 9 Hz), 4.78 (t, 2H, J ) 9 Hz), 7.1-
7.9 (m, 6H); MS m/e (relative intensity) 171 (14), 170 (100,
M+), 169 (58), 142 (13), 141 (30), 139 (13), 115 (21); exact mass
calcd 170.0732, obsd 170.0737.
2-[Meth oxy(tr im eth ylsilyl)m eth yl]n a p h th a len e (23).
Synthesis from 2-methoxymethylnaphthalene (22, 0.46 g) by
Procedure A and column chromatography of the product on
silica gel with 10% benzene/hexane as eluent yielded 23 (0.53
g, 82%) as a colorless liquid which crystallized at 0 to -10 °C:
mp 33-35 °C; 1H NMR (CDCl3, CH2Cl2 as internal standard)
0.23 (s, 9H), 3.48 (s, 3H), 4.18 (s, 1H), 7.1-7.9 (m, 7H); exact
mass calcd 244.1283, obsd 244.1276. Anal. Calcd for C15H20
OSi: C, 73.71; H, 8.25. Found: C, 73.57; H, 8.04.
-
P yr olysis of 2-[Meth oxy(tr im eth ylsilyl)m eth yl]n a p h -
th a len e (23). Silane 23 (1.0 g, 4.1 mmol) was distilled at 0.2-
0.3 mm through a quartz tube heated to 640-650 °C. Column
chromatography of the black pyrolysate on silica gel with
hexane as eluent afforded a complex mixture (0.25 g) in which
6 was shown to be a major component by 1H NMR (28% of the
mixture, 12% yield).
4-Met h oxy-1-[m et h oxy(t r im et h ylsilyl)m et h yl]n a p h -
th a len e (29). Crude 28 (3.5 g, 18 mmol) was converted by
Procedure A and chromatography on silica gel with benzene/
hexane (1:1) to 29 (4.2 g, 89%), a colorless oil which crystallized
at ∼5 °C: mp 55-60 °C; 1H NMR (CDCl3, CH2Cl2 as internal
standard) 0.02 (s, 9H), 3.31 (s, 3H), 4.00 (s, 3H), 4.69 (s, 1H),
6.85 (d, J ) 8 Hz, 1H), 7.3-7.5 (m, 3H), 8.0-8.2 (m, 1H), 8.3-
8.5 (m, 1H); exact mass calcd 274.1389, obsd. 274.1398. An
analytical sample was prepared by distillation at 86 °C/0.1
mm. Anal. Calcd for C16H22O2Si: C, 70.02; H, 8.08. Found: C,
70.12; H, 8.28.
1-[Meth oxy(tr im eth ylsilyl)m eth yl]-6-m eth yln a p h th a -
len e (39). Reactions of 6-methyl-1-naphthalenemethanol with
sodium hydride and then dimethyl sulfate followed by chro-
matography on silica gel using 1:5 benzene/hexane as eluent
yielded 1-methoxymethyl-6-methylnaphthalene (38, 78%) as
a colorless liquid: 1H NMR (CDCl3) 2.50 (s, 3H), 3.40 (s, 3H),
4.81 (s, 2H), 7.2-7.8 (m, 5H), 8.0 (d, 1H, J ) 9 Hz). Procedure
A was then followed to convert 38 (3.6 g) to 39 (4.9 g, 100%)
as light yellow oil (100%): 1H NMR (CDCl3, CH2Cl2 was an
internal standard) -0.08 (s, 9H), 2.41 (s, 3H), 3.19 (s, 3H),
4.67 (s, 1H), 7.1-7.6 (m, 5H), 7.9 (d, 1H, J ) 9 Hz); exact mass
calcd 258.1440, obsd. 258.1446. An analytical sample was
prepared as a colorless liquid by molecular distillation at 66-
68 °C/0.07 mm. Anal. Calcd for C16H22OSi: C, 74.36; H, 8.58.
Found: C, 74.40; H, 8.48.
P yr olysis of 1-[Meth oxy(tr im eth ylsilyl)m eth yl]-6-m e-
th yln a p h th a len e (39); 3-Meth yl-1H-cyclobu ta [d e]n a p h -
th a len e (41), a n d 2-Meth yl-1H-cyclobu ta [d e]n a p h th a -
len e (42). Volatilization of 39 (0.83 g, 3.22 mmol) at 0.1-0.2
mm through a quartz tube at 510 °C gave a dark red-black
pyrolysate. Preparative TLC with hexane yielded (1) a mixture
(0.16 g) of 41 (27%), 42 (3%), and 1,6-dimethylnaphthalene
(43, 2%) in a ratio of 14.1:1.7:1 as determined by GC using 43
as an internal standard [partial separation of 41, 42, and 43
was achieved via GC (3% OV-17, 12 ft × 1/8 in., isothermal at
170 °C)] and (2) initial 39 (0.25 g, 28%). The properties of the
products were (1) for 41, a colorless liquid: 1H NMR (CDCl3,
300 MHz) 2.55 (s, 3H), 4.76 (s, 2H), 6.97 (s, 1H), 7.04 (d, 1H,
J ) 6 Hz), 7.35-7.48 (m, 3H); 13C NMR (CDCl3, 75 MHz) 23.7,
47.1, 116.3, 119.1, 120.2, 120.6, 125.4, 130.6, 140.9, 141.0,
141.2, 144.9; UV (λ, ꢀ, hexane) 322 nm (380), 312 (332), 305
(462), 274 (3 570), 228 (56 100); exact mass calcd 154.0782,
P yr olysis of 4-Met h oxy-1-[m et h oxy(t r im et h ylsilyl)-
m eth yl]n a p h th a len e (29); 4-Meth oxy-1H-cyclobu ta [d e]-
n a p h th a len e (31). Volatilization of 29 (0.54 g, 2.0 mmol) at
0.05-0.10 mm through a quartz tube heated to 510 °C gave a
dark red-black pyrolysate. Preparative thin-layer chromatog-
raphy on silica gel with hexane as the eluent yielded (1) 31
(0.10 g, 29%) as a light yellow liquid and (2) initial 29, a light
yellow oil (0.19 g, 35%) identified by comparison with an
1
authentic sample by TLC and H NMR. Spectral data for 31:
1H NMR (CDCl3, 90 MHz) 3.90 (s, 3H), 4.60 (s, 2H), 6.68 (d,
1H, J ) 7 Hz), 6.84-7.48 (m, 3H), 7.62 (d, 1H, J ) 9 Hz); 13
C
NMR (CDCl3, 75.4 MHz) 46.0, 55.8, 108.9, 117.7, 118.1, 118.2
(2C), 129.5, 133.0, 140.7, 147.1, 153.4; UV (λ, ꢀ, hexane) 324
nm (3 600), 315 (2 500), 310 (3 400), 304 (3 500), 296 (4 900),
292 (4 900), 285 (4 600), 242 (20 500), 234 (25 600), 216
(38 400); exact mass calcd 170.0732, obsd. 170.0737. An
analytical sample was prepared by molecular distillation (45-
50 °C/0.3 mm). Anal. Calcd for C12H10O: C, 84.68; H, 5.92.
Found: C, 84.89; H, 6.24. The yield of 31 is 46% based on
recovered 29.
obsd. 154.0787. Anal. Calcd for C12H10
: C, 93.46; H, 6.54.
Found: C, 93.29; H, 6.63; (2) for 42, a colorless liquid: 1H NMR
(CDCl3, 200 MHz) 2.38 (s, 3H), 4.70 (s, 2H), 7.02 (d, 1H, J )
5 Hz), 7.2-7.8 (m, 4H); and (3) for 43, a colorless liquid:
identified by comparison of its 1H NMR and GC with an
authentic sample (Aldrich). Yields of 41, 42, and 43 based on
recovered starting material were 39%, 5%, and 3%, respec-
tively. Cyclobuta[de]naphthalene 42 could not be cleanly
separated from 43 and thus was not characterized further.
9-[Meth oxy(tr im eth ylsilyl)m eth yl]p h en a n th r en e (51).
9-(Methoxymethyl)phenanthrene (50, 34.1 g, 0.15 mol) was
converted as in Procedure A to a white solid (43.7 g, 99%)
homogeneous by TLC. Recrystallization from hexane yielded
2-Met h oxy-1-[m et h oxy(t r im et h ylsilyl)m et h yl]n a p h -
th a len e (33). Procedure A was followed to convert 32 (0.28 g)
to 33, with the modification that in the deprotonation reaction
the mixture was warmed to -30 °C prior to the addition of
chlorotrimethylsilane. Workup and column chromatography
on silica gel with 20% benzene/hexane as eluent yielded (1)
33 (0.21 g, 55%), a white solid, mp 75.5-77.5 °C (pentane) and
(2) 32 (0.1 g, 36%), a colorless oil. Spectral data for 33: 1H
NMR (CDCl3, CH2Cl2 as internal standard) 0.02 (s, 9H), 3.24
(s, 3H), 3.88 (s, 3H), 5.18 (s, 1H), 7.2-7.5 (m, 3H), 7.65-7.85
(m, 2H), 8.65-8.75 (m, 1H); 13C NMR (CDCl3, 75.43 MHz)
-2.2, 56.3, 59.2, 74.1, 112.9, 122.1, 123.4, 125.4, 126.4, 128.0,
128.2, 129.6, 133.1, 154.3; exact mass calcd 274.1389, obsd.
(18) (a) Emmott, P.; Livingstone, R. J . Chem. Soc. 1957, 3144. (b)
Narasimhan, N. S.; Mali, R. S. Tetrahedron 1975, 31, 1005. (c)
Batterham, T. J .; Lamberton, J . A. Aust. J . Chem. 1964, 17, 1305. (d)
Loader, C. E.; Timmons, C. J . J . Chem. Soc. C 1967, 1677.
(19) Breuer, E.; Melumad, D. Tetrahedron Lett. 1969, 1875.

4254 J . Org. Chem., Vol. 64, No. 12, 1999
Engler and Shechter
1
white crystals of 51 (33.4 g, 76%): mp 106-108 °C; H NMR
(CDCl3, CH2Cl2 as internal standard) 0.05 (s, 9H), 3.38 (s, 3H),
4.78 (s, 1H), 7.5-7.8 (m, 6H), 8.0-8.2 (m, 2H), 8.58-8.88 (m,
2H); exact mass calcd 294.1440, obsd. 294.1450. Anal. Calcd
for C19H22OSi: C, 77.50; H, 7.53. Found: C, 77.62; H, 7.52.
1-[Meth oxy(tr im eth ylsilyl)m eth yl]p yr en e (57). Proce-
dure A was used to convert 56 (2.7 g, 11 mmol) to crude 57.
Recrystallization from hexane afforded 57 as yellow crystals
(2.7 g, 77%): mp 96.5-98.5 °C; 1H NMR (CDCl3, CHCl3 as
internal standard) 0.18 (s, 9H), 3.51 (s, 3H), 5.23 (s, 1H), 7.9-
8.5 (m, 9H); exact mass calcd 318.1440, obsd. 318.1449. Anal.
Calcd for C21H22OSi: C, 79.19; H, 6.97. Found: C, 79.42; H,
7.22.
4H-Cyclobu ta [jk]p h en a n th r en e (53) a n d 4H-Cyclo-
p en ta [d ef]p h en a n th r en e (54). Solid phenanthrene 51 (0.54
g, 1.8 mmol) was dropped at 0.1 mm into a quartz tube heated
to 590 °C. The black pyrolysate, on purification by preparative
TLC on silica gel using hexane as eluent, yielded first a 9:1
mixture (by 1H NMR) of 53 and 54 (0.13 g, 38%). Recrystal-
lization from pentane afforded pure 53 as white flakes: mp
87.5-88.5 °C; 1H NMR (CDCl3, 90 MHz) 4.80 (s, 2H), 7.25 (dd,
1H, J ) 6.2 Hz), 7.31 (s, 1H), 7.5-8.2 (m, 6H), 8.35-8.50 (m,
1H); 13C NMR (CDCl3, 75 MHz) 46.6, 117.6, 119.3, 119.6, 124.0,
125.4, 126.2, 126.6, 129.6, 129.9, 130.2, 137.4, 139.1, 141.1,
145.0; UV (λ, ꢀ, hexane) 345 nm (1,100), 338 (490), 330 (720),
323 (430), 314 (430), 294 (12 900), 282 (10 200), 275 (13 500),
264 (shoulder, 19 500), 249 (96 200), 244 (shoulder, 82 400),
228 (19 800), 223 (17 000), 205 (23 100); exact mass calcd
190.0782, obsd. 190.0788. An analytical sample (white crystals,
mp 87.5-88.5 °C) was prepared by sublimation at 55-58 °C
P yr olysis of 1-[Meth oxy(tr im eth ylsilyl)m eth yl]p yr en e
(57): 3H-Cyclobu ta [cd ]p yr en e (59). Silane 57 (0.50 g, 1.6
mmol) was slowly distilled at 0.05-0.07 mm through a quartz
tube at 520-525 °C. The pyrolysate, upon purification by
preparative TLC using hexane as eluent, yielded 59 (0.11 g,
32%) as a light yellow solid. Recrystallization from pentane
gave white crystals: mp 117-118 °C; 1H NMR (CDCl3, 90
MHz) 5.19 (s, 2H), 7.5 (s, 1H), 7.62 (d, 1H, J ) 6 Hz), 7.8-8.2
(m, 6H); 13C NMR (CDCl3, 20.1 MHz) 53.0, 116.8, 121.3, 123.3,
124.4, 124.8, 125.0, 125.8, 126.4 (2 C), 127.8, 128.4, 131.1,
135.6, 137.1, 139.8, 144.1; UV (λ, ꢀ, hexane) 375 nm (299), 340
(36 300), 335 (24 800), 324 (26 100), 310 (12 700), 275 (41 000),
265 (24 200), 254 (15 200), 244 (58 400), 235 (shoulder, 36 000);
exact mass calcd 214.0782, obsd. 214.0786. Anal. Calcd for
C17H10: C, 95.30; H, 4.70. Found: C, 94.71; H, 4.95. A further
product of chromatography is initial 57 (0.31 g, 62%), identical
and 0.02 mm. Anal. Calcd for C15H10
: C, 94.70; H, 5.30.
Found: C, 94.35; H, 5.53. Further chromatography of this
pyrolysate gave starting 51 (0.26 g, 48%) as a light yellow solid.
The yield of 53/54 was 72% based on recovered starting
material.
Identification of 54 as the minor component in the first
fraction was based on comparison of the mixture’s 1H NMR
spectrum and HPLC trace (Waters C-18 column; 1:1 methanol/
water) with those of authentic 54.20 No change other than
relative intensities of the peaks in the 1H NMR spectrum or
the HPLC trace was observed when authentic 54 was added
to the mixture obtained from the pyrolysis.
Amounts of 51 up to 10 g were pyrolyzed. Purification of 53
was accomplished by column chromatography on silica gel,
followed by recrystallization from pentane or methanol. Start-
ing material 51 could easily be recycled, and thus no material
was wasted.
4H-Cyclobu ta [jk]p h en a n th r en e:2,4,7-Tr in itr oflu or en -
9-on e Com p lex. Cyclobuta[jk]phenanthrene 53 (0.40 g, 2.1
mmol) in hot ethanol (10 mL) was added to a hot ethanolic
solution (40 mL) of 2,4,7-trinitrofluoren-9-one (0.70 g, 2.2
mmol). Benzene (30 mL) was slowly added until the boiling
solution became clear. Upon cooling of the reaction mixture,
bright orange crystals separated that were recrystallized from
benzene to give bright orange needles of the addition complex
(0.58 g, 54%): mp 209.5-211 °C. Anal. Calcd for C28H15N3O7:
C, 66.53; H, 2.99; N, 8.32. Found: C, 66.78; H, 3.09; N, 8.07.
Decomposition of the complex on silica gel using 1:1 benzene/
hexane as eluent regenerated initial 53.
1
to an authentic sample by TLC and H NMR. The yield of 59
based on recovered starting material is 86%.
Reanalysis of 59 after standing open to air for 1 day revealed
that it contained 91.51% carbon and 5.09% hydrogen, thus
indicating considerable oxidation. A more satisfactory analysis
could not be obtained even after repeated chromatography,
recrystallization, and sublimation (100 °C and 0.02 mm). All
analytical samples were sealed in ampules under argon.
3H -Cyclob u t a [cd ]p yr en e:2,4,7-Tr in it r oflu or en -9-on e
Com p lex. To a refluxing benzene solution (10 mL) of 2,4,7-
trinitrofluoren-9-one (0.30 g, 0.95 mmol) was added 59 (0.19
g, 0.89 mmol) in benzene (2 mL). Upon cooling of the mixture,
dark maroon crystals separated that recrystallized from
benzene as glistening, bright maroon-purple needles (0.27 g,
57%). The 3H-cyclobuta[cd]pyrene:2,4,7-trinitrofluoren-9-one
complex turned black when heated to 190 °C and charred to a
black dust at 220 °C, with no visible sign of melting. Anal.
Calcd for C30H15H3O7: C, 68.05; H, 2.86; N, 7.94. Found: C,
68.02; H, 3.10; N, 7.85.
Ack n ow led gm en t. We thank the National Science
Foundation for support of this research.
Su p p or tin g In for m a tion Ava ila ble: Discussion of mech-
anisms of formation of minor products from pyrolysis of 13,
procedures for preparing 4-methoxy-1-naphthalenemethanol,
2-methoxy-1-naphthalenemethanol, 6-methyl-1-naphthalen-
emethanol, 1-pyrenemethanol and methoxymethylarenes 12,
22, 28, 32, and 56, UV data, and copies of NMR spectra. This
material is available free of charge via the Internet at
http://pubs.acs.org.
(20) (a) Mendenwald, H. Chem. Ber. 1953, 86, 287. (b) Sadtler
Standard 1H NMR Spectrum 2349M. Sadtler Research Laboratories,
Inc., Philadelphia, PA.
J O981104J