Reactions of dimethoxycarbene with cyclic perchlorinated olefins and ketones

Article abstract of DOI:10.1021/jo9823846

Reactions of dimethoxycarbene (2), a carbonyl group equivalent, with perchlorinated olefins and ketones were investigated. Thermolysis of 2,2- dimethoxy-5,5-dimethyl-Δ³-1,3,4-oxadiazoline (1) at 110 °C generated 2, which reacted with hexachlorocyclopentadiene (4), octachlorocycloheptatriene (12), octachlorobicyclo[3.2.0]hepta-3,6-diene (24), hexachlorotropone (28), hexachlorobicyclo[3. 2.0]-hepta-3,6-dien-2-one (32), and tetrachloro-1,4- benzoquinone (35). Reactions of 2 with perchlorinated olefins 4, 12, and 24 led to esters or, in the case of 12, to a ketene acetal. Their formation is rationalized in terms of Michael-like addition and displacement (S(N)2' or S(N)2', if concerted) of allylic chlorine atoms by 2, yielding ion pairs that either dechloromethylate to esters or dechlorinate to a ketene acetal. In contrast, the reactions of 2 with unsaturated perchloroketones 28, 32, and 35 led to ring contraction, ring expansion, and aromatization, respectively. The products from these reactions are consistent with nucleophilic addition of 2 at the carbonyl moiety rather than Michael-type addition. Dimethoxycarbene- d₃ was used to show that demethylation in the latter reaction was intermolecular. Mechanisms for the different reaction courses are proposed.

Full text of DOI:10.1021/jo9823846

4344
J . Org. Chem. 1999, 64, 4344-4352
Rea ction s of Dim eth oxyca r ben e w ith Cyclic P er ch lor in a ted
Olefin s a n d Keton es
J ames A. Dunn,†,‡ J ohn Paul Pezacki,†,‡ Michael J . McGlinchey,* and J ohn Warkentin*
Department of Chemistry, McMaster University, 1280 Main Street West,
Hamilton, Ontario L8S 4M1, Canada
Received December 4, 1998
Reactions of dimethoxycarbene (2), a carbonyl group equivalent, with perchlorinated olefins and
ketones were investigated. Thermolysis of 2,2-dimethoxy-5,5-dimethyl-∆3-1,3,4-oxadiazoline (1) at
110 °C generated 2, which reacted with hexachlorocyclopentadiene (4), octachlorocycloheptatriene
(12), octachlorobicyclo[3.2.0]hepta-3,6-diene (24), hexachlorotropone (28), hexachlorobicyclo[3.2.0]-
hepta-3,6-dien-2-one (32), and tetrachloro-1,4-benzoquinone (35). Reactions of 2 with perchlorinated
olefins 4, 12, and 24 led to esters or, in the case of 12, to a ketene acetal. Their formation is
rationalized in terms of Michael-like addition and displacement (SN2′ or SN2′′, if concerted) of allylic
chlorine atoms by 2, yielding ion pairs that either dechloromethylate to esters or dechlorinate to a
ketene acetal. In contrast, the reactions of 2 with unsaturated perchloroketones 28, 32, and 35 led
to ring contraction, ring expansion, and aromatization, respectively. The products from these
reactions are consistent with nucleophilic addition of 2 at the carbonyl moiety rather than Michael-
type addition. Dimethoxycarbene-d3 was used to show that demethylation in the latter reaction
was intermolecular. Mechanisms for the different reaction courses are proposed.
In tr od u ction
methoxycyclopropane,6 and 2,2-dimethoxy-5,5-dimethyl-
∆3-1,3,4-oxadiazoline (1, eq 1).7 We chose 1 to study the
reactions of 2 with various perchlorinated olefins and
perchloroketones.
Singlet dimethoxycarbene (2) is a nucleophile,1 as a
consequence of donation by the lone pairs of the methoxy
oxygens into the formally vacant p-orbital of the carbene
carbon, which strongly stabilizes the singlet state2,3 and
causes dipolar character. This resonance interaction
stabilizes not only the ground state of 2 but also the
transition states and dipolar intermediates arising from
nucleophilic reactions of 2.
Dimethoxycarbene (2) has been generated from 7,7-
dimethoxynorbornadienes,4 dimethoxydiazirine,5 hexa-
The nucleophilic character of 2 is exemplified by its
preference for reaction with electron-deficient olefins such
as dimethylfumarate, dimethylmaleate,8 and styrene,4c
as well as strained olefins,7d over more electron-rich
olefins such as tetramethylethylene.1,9 It also undergoes
[1+4] cycloadditions with tetraphenylcyclopentadienone,10
with tropone to give 3 (eq 2),10 and with tetrazines,11 by
either stepwise or concerted addition of 2.
Addition of 2 to electron-deficient alkynes such as
dimethyl acetylenedicarboxylate (DMAD)8 can yield cy-
clopropenone acetal intermediates that can open ther-
mally to give dioxyvinylcarbenes. Thermal ring openings
* Corresponding author: Professor J . Warkentin, Department of
Chemistry, McMaster University, 1280 Main St. West, Hamilton,
Ontario, Canada, L8S 4M1 *Phone: 905 525-9140, ext 23478. Fax:
905 522 2509. E-mail: warkent@mcmaster.ca.
† NSERC Scholar 1996-1998.
‡ These authors contributed equally to the work presented here.
(1) (a) Moss, R. A. Acc. Chem. Res. 1989, 22, 15. (b) Moss, R. A. Acc.
Chem. Res. 1980, 13, 58.
(2) Rondan, N. G.; Houk, K. N.; Moss, R. A. J . Am. Chem. Soc. 1980,
102, 1770.
(3) Moss, R. A.; Włostowski, M.; Shen, S.; Krogh-J espersen, K.;
Matro, A. J . Am. Chem. Soc. 1988, 110, 4443.
(4) (a) Hoffmann, R. W. Acc. Chem. Res. 1985, 18, 248. (b) Hoffmann,
R. W.; Hagenbruch, B.; Smith, D. M. Chem. Ber. 1977, 110, 23. (c)
Moss, R. A.; Huselton, J . K. J . Chem. Soc., Chem. Commun. 1976, 950.
(d) Hoffmann, R. W.; Steinbach, K.; Lilienblum, W. Chem. Ber. 1976,
109, 1759. (e) Hoffmann, R. W.; Steinbach, K.; Dittrich, B. Chem. Ber.
1973, 106, 2174. (f) Hoffmann, R. W. Angew. Chem., Int. Ed. Engl.
1971, 10, 529. (g) Hoffmann, R. W.; Wunsche, C. Chem. Ber. 1967,
100, 943. (h) Lemal, D. M.; Gosselink, E. P.; McGregor, S. D. J . Am.
Chem. Soc. 1966, 88, 582. (i) Lemal, D. M.; Lovald, R. W.; Harrington,
R. W. Tetrahedron Lett. 1965, 2779. (j) Hoffmann, R. W.; Hauser, H.
Tetrahedron 1965, 21, 891. (k) Hoffmann, R. W.; Hauser, H. Tetrahe-
dron Lett. 1964, 197. (l) Lemal, D. M.; Gosselink, E. P.; Ault, A.
Tetrahedron Lett. 1964, 579.
(6) Moss, R. A.; Cox, D. P. Tetrahedron Lett. 1985, 26, 1931.
(7) (a) El-Saidi, M.; Kassam, K.; Pole, D. L.; Tadey, T.; Warkentin,
J . J . Am. Chem. Soc. 1992, 114, 8751. (b) Win, W. W.; Kao, M.;
Eiermann, M.; McNamara, J . J .; Wudl, F.; Pole, D. L.; Kassam, K.;
Warkentin, J . J . Org. Chem. 1994, 59, 5871. (c) Colomvakos, J . D.;
Egle, I.; Ma, J .; Pole, D. L.; Tidwell, T. T.; Warkentin, J . J . Org. Chem.
1996, 61, 9522. (d) de Meijere, A.; Kozhushkov, S. I.; Yufit, D. S.; Boese,
R.; Haumann, T.; Pole, D. L.; Sharma, P. K.; Warkentin, J . Liebigs
Ann. Chem. 1996, 601. (e) Couture, P.; Pole, D. L.; Warkentin, J . J .
Chem. Soc., Perkin Trans. 2 1997, 1565.
(5) (a) Ge, C.-S.; J efferson, E. A.; Moss, R. A. Tetrahedron Lett. 1993,
34, 7549. (b) Moss, R. A.; Włostowski, M.; Terpinski, J .; Kmiecik-
Lawrynowicz, G.; Krogh-J espersen, K. J . Am. Chem. Soc. 1987, 109,
3811. (c) Du, X.-M.; Fan, H.; Goodman, J . L.; Kesselmayer, M. A.;
Krogh-J espersen, K.; LaVilla, J . A.; Moss, R. A.; Shen, S.; Sheridan,
R. S. J . Am. Chem. Soc. 1990, 112, 1920. (d) Moss, R. A.; Włostowski,
M.; Shen, S.; Krogh-J espersen, K.; Matro, A. J . Am. Chem. Soc. 1988,
110, 4443. (e) Moss, R. A.; Shen, S.; Włostowski, M. Tetrahedron Lett.
1988, 29, 6417.
(8) Hoffmann, R. W.; Lilienblum, W.; Dittrich, B. Chem. Ber. 1974,
107, 3395.
(9) Enders, D.; Breuer, K.; Runsink, J .; Teles, J . H. Liebigs Ann.
Chem. 1996, 2019.
(10) Lilienblum, W.; Hoffmann, R. W. Chem. Ber. 1977, 110, 3405.
(11) (a) Ku¨mmell, A.; Seitz, G. Tetrahedron Lett. 1991, 32, 2743.
(b) Gerninghaus, C.; Ku¨mmell, A.; Seitz, G. Chem. Ber. 1993, 126, 733.
(c) Frenzen, G.; Ku¨mmell, A.; Meyer-Dulheuer, C.; Seitz, G. Chem. Ber.
1994, 127, 1803.
10.1021/jo9823846 CCC: $18.00 © 1999 American Chemical Society
Published on Web 05/20/1999

Dimethoxycarbene and Perchlorinated Olefins/Ketones
J . Org. Chem., Vol. 64, No. 12, 1999 4345
of cyclopropenone acetals were used in the construction
of complex products, including the natural product
colchicine, as well as its analogues, via Boger cycloaddi-
tions.12-14
Dipolar intermediates may be common in reactions
involving nucleophilic attack by 2. Thermal reactions of
2 with aryl isocyanates or aryl isothiocyanates yield 5,5-
dimethoxyhydantoins or 5,5-(dimethoxy)thiohydantoins,
respectively.15 The proposed mechanism involves nucleo-
philic attack of 2 at the central carbon atom of the
isocyanate or isothiocyanate to give a dipolar intermedi-
ate that adds to a second molecule of ArNCO or ArNCS.
Competition experiments, involving aryl isocyanates,16
gave a Hammett F ) +2.0, consistent with the proposed
mechanism. Reactions of 2 with vinylisocyanates lead to
highly functionalized pyrrolinones via formal [1+4] cyclo-
additions17 and constitute a key step in the synthesis of
tazettine and some analogues,17 and attack of 2 on 2,4-
dinitrofluorobenzene and hexafluorobenzene affords
acetals of aroyl fluorides, by nucleophilic aromatic sub-
stitution.18
In view of the diversity of the known reactions of 2 with
unsaturated moieties, it was of interest to ask whether
perchlorinated olefins and ketones would also react.
Moreover, unsaturated perchloroketones would provide
for internal competition between attack by 2 at CC and
CO double bonds. Therefore, we undertook a study of
reactions of 2, a carbonyl group equivalent, with cyclic,
unsaturated perchloro compounds.
F igu r e 1.
Sch em e 1
Resu lts a n d Discu ssion
Rea ction of 2 w ith Hexa ch lor ocyclop en ta d ien e
(4). Thermolysis of 1 at 110 °C in benzene containing 4
afforded 6, 7, and 8, which were isolated by radial
chromatography in 24%, 29%, and 34% yields, respec-
tively (Scheme 1). Analysis by GC-MS prior to chroma-
tography showed that 6, 7, and 8 were formed in 1.2:
1.8:1 ratios. Isomers of 7 and 8 were detected by GC-
MS, but they could not be isolated and characterized.
Products with molecular weights corresponding to [1+2]
or [1+4] adducts were not detected, and none of the minor
products had a molecular weight exceeding that of 8.
Thermolysis of 1 in 10-fold excess (relative to 4, 0.1 M)
resulted in a change in the ratios of products. Only a trace
of 6 was observed (GC-MS), whereas 7 and 8 were
formed in 12% and 76% yields (isolated), respectively.
Structures of many of the perchloro products in this
report could not be assigned unambiguously by means
(12) Boger, D. L.; Brotherton, C. E. J . Org. Chem. 1985, 50, 3425.
(13) (a) Boger, D. L.; Brotherton-Pleiss, C. E. In Advances in
Cycloaddition; Curran, D. P., Ed.; J AI Press: Greenwich, CT, 1990;
Vol. 2, p 147. (b) Boger, D. L.; Brotherton, C. E. J . Am. Chem. Soc.
1986, 108, 6695. (c) Boger, D. L.; Brotherton, C. E. Tetrahedron Lett.
1984, 25, 5611.
(14) Boger, D. L.; Brotherton, C. E. J . Am. Chem. Soc. 1986, 108,
6713.
(15) Hoffmann, R. W.; Steinbach, K.; Dittrich, B. Chem. Ber. 1973,
106, 2174.
(16) Hoffmann, R. W.; Reiffen, M. Chem. Ber. 1976, 109, 2565.
(17) (a) Rigby, J . H.; Cavezza, A.; Heeg, M. J . J . Am. Chem. Soc.
1998, 120, 3664. (b) Rigby, J . H.; Cavezza, A.; Ahmed, G. J . Am. Chem.
Soc. 1997, 118, 12848.
(18) Ross, J . P.; Couture, P.; Warkentin, J . Can. J . Chem. 1997, 75,
1331.
1
of H and 13C NMR spectroscopies and were confirmed
by means of X-ray crystallography. Those of 7 and 8 are
in Figure 1.
1
Variable-temperature H NMR experiments with 6, 7,
and 8, from -80 to 0 °C (CD2Cl2) and from 25 to 110 °C
(toluene-d8), showed that the products did not result from
1,5-chlorine or 1,5-ester migrations. Ester groups at-
tached to an sp2 site, δ ∼3.85, were distinguishable from
those on sp3 hybridized centers, δ ∼3.75. Fluxionality in
6-8 was not observed. Compound 8 was stable in
solution over a period of 24 h at 110-140 °C, and only

4346 J . Org. Chem., Vol. 64, No. 12, 1999
Dunn et al.
Sch em e 2
Sch em e 3
F igu r e 2.
from the relative stabilities of transition states, modeled
with the localized 9 and the allylic 11 (Scheme 2). We
cannot account for the regioselective formation of 8 to
the exclusion of the 1,2,3-triester that would result from
addition at the alternative site of 7.
Rea ction of 2 w ith Octa ch lor ocycloh ep ta tr ien e
(12).21,22 Thermolysis of 1 at 110 °C in benzene containing
12 (initially 0.1 M) for 24 h yielded dimethoxy(hexa-
chloro)heptafulvene (16, 12%) and dodecachlorohepta-
fulvalene (19, 56%) as major products, Scheme 3. Analy-
sis of the crude reaction mixture by GC-MS prior to
chromatography revealed octachlorotoluene, a known
product of thermal decomposition of 12.21 Heating of 12
in benzene (110 °C, 24 h) resulted in only 10% conversion
to octachlorotoluene, but in two weeks it was fully
converted.
at g160 °C were products associated with 1,5-ester
migrations observed (NMR, sealed tubes). These results
are in keeping with high barriers for ester migrations in
cyclopentadienes; the calculated barrier for a [1,5]-
sigmatropic ester shift in 5-chloro-1,2,3,4,5-pentakis-
(carbomethoxy)cyclopentadiene is ca. 32 kcal mol-1 19
.
Of several hypothetical mechanisms that could account
for 6-8 from the reaction of 2 with 4, we favor a Michael
type of addition and loss of Cl-, possibly in concert, to
produce the ion pair 5, which affords 7 via 6. Analogous
subsequent processes provide a consistent account for the
three products (Scheme 1). Insertions of 2 into a C(sp3)-
Cl bond by concerted, radical pair, or halonium ylide
mechanisms are unlikely, given that chloroform and
1,1,2,2-tetrachloroethane did not react with 2. Radical
chemistry of 2 is unlikely in any case because its triplet
state lies ca. 76 kcal/mol above the singlet.3 The fact that
coupling products (e.g., decachlorobi(2,4-cyclopentadien-
1-yl) and/or octachloropentafulvalene)20 were not seen
from the reaction of 2 with 4 suggests that chlorine
abstraction by singlet 2 is also not an accessible pathway.
It is not surprising that 7 is more reactive than 4,
because CO2Me is more electron-withdrawing than Cl.
The regioselectivity that leads to 7 but not 10 follows
Dimethoxy(hexachloro)heptafulvene (16), a ketene ace-
tal, was stable enough to permit identification by con-
ventional spectroscopic techniques. However, it was
sensitive to atmospheric moisture that converted it into
17 (Scheme 3), the structure of which was secured by
X-ray crystallography (Figure 2).
A straightforward mechanism for the formation of 16
involves addition of 2 at one of the terminal double bonds
of 12 and loss of Cl- to yield ion pair 13. Subsequent
rearrangement through chloronium ion 14 would then
yield ion pair 15. Heptachlorocycloheptatrienyl cation is
known in a stable salt22 and, although the geometry has
(21) (a) West, R.; Kusuda, K. J . Am. Chem. Soc. 1968, 90, 7354. (b)
Kusuda, K.; West, R.; Mallikarjuna Rao, V. N. J . Am. Chem. Soc. 1971,
93, 3627.
(22) Dunn, J . A.; Gupta, H. K.; Bain, A. D.; McGlinchey, M. J . Can.
J . Chem. 1996, 74, 2258.
(19) (a) Hoffmann, R. W.; Schmidt, P.; Backes, J . Chem. Ber. 1976,
109, 1918. (b) Hoffmann, R. W.; Backes, J . Chem. Ber. 1976, 109, 1928.
(20) West, R. Pure Appl. Chem. 1971, 43, 379.

Dimethoxycarbene and Perchlorinated Olefins/Ketones
J . Org. Chem., Vol. 64, No. 12, 1999 4347
not been determined, it is unlikely to be planar.23 One of
the ion pairs, 14 or 15, must then undergo dechlorination
(the reverse of Cl2 addition to 16) rather than dechloro-
methylation.
Sch em e 4
The formation of syn-dodecachloroheptafulvalene (19)
was surprising. Selective formation of syn-19 in reactions
of n-BuLi24 and of various metals22 with 12 has been
observed previously, and hexachlorocycloheptatrienylidene
(18) was implicated in the selective formation of this
kinetic product.22,24b syn-19 is converted to anti-19 at
temperatures g270 °C.24 We postulate that 12 and 2
afford the dimethoxyacetal of phosgene and 18, which
dimerizes to 19. gem-Dechlorination (12 + 2 f 18 +
(MeO)2CCl2) is analogous to the reaction of organolithium
reagents with 12.25 Moreover a “carbene-to-carbene trans-
fer” (e.g., 2 + 12 f 18) has been observed previously in
reactions involving carbonyl groups.26 Ketene acetal 16
was stable for several days in benzene at 110 °C and was
therefore not the source of 18.
Cycloheptatrienylidene is known to exist in equilibrium
with cycloheptatetraene and phenylcarbene, as are benz-
annulated analogues of cycloheptatrienylidene.27 We
expect that the perchlorocycloheptatrienylidene would
also exist in equilibrium with the analogous perchlori-
nated isomers (eq 3) and that the nonplanar perchloro-
cycloheptatetraene would be favored to alleviate steric
interactions between the chlorine substituents.
to either a diradical (22) or a zwitterion and rearrange-
ment might be expected to give both E- and Z-23.
Fragmentation of 22 from the conformer with the leaving
groups antiperiplanar may account for the formation of
the Z-isomer exclusively. Although we cannot prove that
23 arises from 20,29 Cope rearrangements of this type
(Scheme 4) are known to occur readily at elevated
temperatures in cycloheptatrienes.
Trapping of cycloheptatrienylidene/cycloheptatetra-
ene and benzannulated analogues by way of [4+2]
cycloadditions with diphenylisobenzofuran (DPIBF) has
been reported.28 We attempted to trap the proposed
perchloro 18/18-allene, from the reaction of 2 and 12,
with DPIBF. Thermolysis of 1 in benzene at 110 °C in
the presence of 12 and DPIBF yielded 16 and 19, as well
as olefin 23 and an isomer of 23, which could not be
purified. The basic features of 23 followed from standard
spectroscopic techniques, and the Z-configuration was
determined by X-ray crystallography (Figure 2). One of
several explanations would have 23 originate from the
trapping of 18/18-allene by DPIBF via a [4+2] cyclo-
addition to give 20. An electrocyclic rearrangement would
afford norcaradiene 21 (Scheme 4), and its fragmentation
Rea ction of 2 w ith Octa ch lor obicyclo[3.2.0]h ep ta -
3,6-d ien e (24). Thermolysis of 1 at 110 °C in benzene
containing 24 (initially 0.1 M) for 24 h yielded dimethoxy-
(hexachloro)heptafulvene (16, 3%) and dodecachlorohep-
tafulvalene (19, 11%). The remainder was unreacted 24
and carbene dimer (tetramethoxyethylene). The products
from 24 are the same as those obtained with 12 in
roughly the same ratio, suggesting that they are formed
through a common intermediate. Following our previous
interpretation, 2 attacks 24 to give ion pair 25 (Scheme
5). Rearrangement by way of chloronium ion 26 affords
allylic cation 27, which is analogous to the cation
intermediate postulated for the aluminum chloride cata-
lyzed conversion of 24 to octachlorocycloheptatriene
(12).21 Disrotatory ring opening21 of 27 would lead to the
cycloheptatrienyl cation in ion pair 15, an intermediate
common to the reactions of 2 with both 12 and 24. The
lower yields from the latter may mean that 24 is less
reactive than 12 toward 2, possibly because 24 cannot
undergo overall SN2′′ substitution.
(23) Brydges, S.; Britten, J.; Chao, L. C. F.; Gupta, H. K.; McGlinchey,
M. J . Pole, D. L. Chem. Eur. J . 1998, 4, 1199.
(24) (a) Ishimori, M.; West, R.; Teo, B. K.; Dahl, L. F. J . Am. Chem.
Soc. 1971, 93, 7101. (b) Hu¨gel, H. M.; Horn, E.; Snow, M. R. Aust. J .
Chem. 1985, 38, 383.
(25) Kirmse, W. Carbene Chemistry, 2nd ed.; Academic Press: New
York, 1971.
(26) Kovacs, D.; Lee, M.-S.; Olson, D.; J ackson, J . E. J . Am. Chem.
Soc. 1996, 118, 8144 and references therein.
(27) (a) Matzinger, S.; Bally, T.; Patterson, E. V.; McMahon, R. J .
J . Am. Chem. Soc. 1996, 118, 1535. (b) 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. (c) J ohnson, R.
P. Chem. Rev. 1989, 89, 1111 and references therein. For organo-
metallic trapping of C7H6 carbene/allene, see: (d) Winchester, W. R.;
J ones, W. M. Organometallics 1985, 4, 2228. (e) Abboud, K. A.; Lu, Z.;
J ones, W. M. Acta Crystallogr., Sect. C 1992, C48, 909. (f) Lu, Z.; J ones,
W. M.; Winchester, W. R. Organometallics 1993, 12, 1344.
(28) (a) Kirmse, W.; Sluma, H.-D. J . Org. Chem. 1988, 53, 763. (b)
Saito, K.; Ishihara, H. Bull. Chem. Soc. J pn. 1985, 58, 2664. (c) Saito,
K.; Omura, Y.; Mukai, T. Bull. Chem. Soc. J pn. 1985, 58, 1663. (d)
Saito, K.; Omura, Y.; Mukai, T. Chem. Lett. 1980, 349.
Rea ction of 2 w ith Hexa ch lor otr op on e (28). Facile
rearrangements of 2-substituted tropones or tropolones
to benzenoid derivatives in reactions with nucleophiles
have been explored vigorously.30 Although the chemis-
tries of 12 and 28 have been investigated less thoroughly,
Scherer31 and West et al.21 reported independently that
(29) Our attempts to trap 18/18-allene, from the reaction of n-BuLi
and 13, with DPIBF led to minor products with the mass of 23, which
we could not isolate in pure form.
(30) (a) Pauson, P. L. Chem. Rev. 1955, 55, 1. (b) Doering, W. von
E.; Knox, L. H. J . Am. Chem. Soc. 1952, 74, 5683. (c) Doering, W. von
E.; Hiskey, C. F. J . Am. Chem. Soc. 1952, 74, 5688.
(31) Scherer, K. V. J . Am. Chem. Soc. 1968, 90, 7352.

4348 J . Org. Chem., Vol. 64, No. 12, 1999
Dunn et al.
Sch em e 5
F igu r e 3.
Sch em e 6
both afford methyl pentachlorobenzoate upon dissolution
in methanol. Thermolysis of 1 in benzene at 110 °C in
the presence of 28 gave ester 31 as the major product
(44%), in keeping with the reported rearrangements of
troponoids to benzenoid derivatives.30 Analysis of the
crude product mixture by GC-MS prior to chromatog-
raphy confirmed that 31 was the major fraction (ca. 69%)
(Figure 3). Methyl pentachlorobenzoate (ca. 7%), penta-
chlorobenzoyl chloride (ca. 2%), and hexachlorobenzene
(ca. 2%) were also found. The latter two are known
products of thermal decomposition of 28 and presumably
arise via a norcaradienone intermediate.21b,32 We suggest
that 31 arises through nucleophilic attack by 2 at the
carbonyl carbon of 29, generating a zwitterion intermedi-
ate 30 (Scheme 6), possibly in equilibrium with the
corresponding oxirane (not shown). There is precedence
for the formation of such intermediates in reactions of 2
with other carbonyl compounds.33 Ring opening of 30 and
demethylation is analogous to the formation of methyl
pentachlorobenzoate from the reaction of 12 with metha-
nol.21
Reactions of hexachlorotropone with nucleophiles,
including thiols, amines, 30 and organolithium reagents,34
give exclusively benzenoid products rather than products
of nucleophilic addition without ring contraction. Al-
though 31 could also arise from reaction of 2 with
pentachlorobenzoyl chloride, analogous to the reaction of
2 with benzoyl chloride,35 heating of 28 in benzene at 110
°C gave only ca. 5% of pentachlorobenzoyl chloride and
ca. 2% of hexachlorobenzene. Therefore, reaction of
pentachlorobenzoyl chloride with 2 can be only a minor
contributor to the formation of 31.
philic aromatic substitution by 2, leading to products of
formal carbon-halogen insertion, have been reported,18
and insertion of 2 into a C-Cl bond of hexachlorobenzene,
followed by hydrolysis on exposure to air, was also
considered. However, thermolysis of 1 in the presence of
hexachlorobenzene did not lead to methyl pentachlo-
robenzoate.
Although other mechanisms involving nucleophilic
attack at the chlorine-bearing carbons have been sug-
gested for analogous systems and cannot be discounted,30a,b
they are less likely to occur in the formation of 31,
because 28 is far from planar.36 The boatlike geometry
of 28 should increase its susceptibility to attack at the
carbonyl carbon while inhibiting the double bond shift
associated with attack at C-2.31 In contrast, C-7 in 12
should be more sterically encumbered, and as a result,
the double bonds in 12 would be more likely sites for
attack by 2. Possible pathways which could result in the
same end products have been reviewed for 2-chloro-
tropones and tropolones, and similar arguments probably
apply to hexachlorotropone.30
R ea ct ion of 2 a n d Hexa ch lor ob icyclo[3.2.0]-3,6-
d ien -2-on e (32). Ketone 3237 is known to react with
anions (e.g., MeLi) to afford the corresponding alcohols,37b
with no evidence for Michael addition products. Oxa-
diazoline 1 and 32, when heated at 110 °C in benzene,
gave 1,4,5,6,7,8-hexachloro-2,2-dimethoxybicyclo[4.2.0]-
The origin of methyl pentachlorobenzoate is uncertain.
Loss of CO from keto ester 31 is one possibility. Nucleo-
(32) Mukai, T.; Nakazawa, T.; Okayama, K. Tetrahedron Lett. 1968,
14, 1695.
(33) For an example, see: Pole, D. L.; Warkentin, J . J . Org. Chem.
1997, 62, 4065.
(34) Dunn, J . A.; Pezacki, J . P.; Warkentin, J .; McGlinchey, M. J .,
manuscript in preparation.
(36) (a) Dodge, R. P.; Sime, R. J .; Templeton, D. H., personal
communication cited in ref 31b. (b) Su¨nkel, R. J . Organomet. Chem.
1990, 391, 247.
(35) Hoffman, R. W.; Lilienblum, W.; Dittrich, B. Chem. Ber. 1974,
107, 3395.
(37) (a) Roedig, A.; Ho¨rnig, L. Liebigs Ann. Chem. 1956, 598, 208.
(b) Roedig, A.; Fo¨rsch, M. Liebigs Ann. Chem. 1977, 297.

Dimethoxycarbene and Perchlorinated Olefins/Ketones
J . Org. Chem., Vol. 64, No. 12, 1999 4349
Sch em e 8
F igu r e 4.
Sch em e 7
Sch em e 9
octa-4,7-dien-3-one (34) in quantitative yield. 1H and 13C
NMR data included two methoxy signals, and in the IR,
νCO ) 1740 cm-1 suggested that the R,â-unsaturated
carbonyl unit had remained intact; X-ray crystallography
confirmed the structure, Figure 4.
Compound 34 is the result of a formal carbene inser-
tion into a carbon-carbon bond. Reactions of 2 with
carbonyl groups of anhydrides,36 biacetyl, and benzoyl
chloride35 appear to involve nucleophilic addition of 2 at
the carbonyl carbon, followed by rearrangement of the
resulting dipolar intermediates. In the case of anhy-
drides, formal insertion of 2 into carbon-oxygen bonds
occurs; analogous insertions into carbon-sulfur bonds
have also been observed.39
Formation of 34 probably involves nucleophilic attack
by 2 at the carbonyl carbon of 32 to yield intermediate
33 (Scheme 7), which rearranges by a 1,2-carbon migra-
tion, with retention of stereochemistry, to form 34. The
reaction of 2 with 32 is the first example of an overall
carbon-carbon bond insertion reaction for an alkoxy- or
dialkoxycarbene.
The aromatization of 35 presumably occurs via initial
attack of 2 at the carbonyl carbon to yield dipolar
structure 36, which is probably equilibrated with oxirane
37 and dipole 38 (Scheme 8). An alternative pathway,
from 35 directly to 38, may also be feasible. The latter
could then react with another 38 by way of a methyl
transfer to give 42 and 43, which undergo a subsequent
intermolecular methyl transfer to yield the major product
39. One possibility for the origins of the minor products
40 and 41 that is consistent with the labeling studies
(below) is that they arise from the collapse of ions 42 and
43 (Scheme 9).
Rea ction of 2 w ith Tetr a ch lor o-1, 4-ben zoqu in on e
(35). Thermolysis of 1 for 24 h at 110 °C in benzene
containing 35 yielded 4-methoxy-2,3,5,6-tetrachloro-
phenyl methyl carbonate (39, 82% isolated yield), bis-
carbonate 40 (5%), and 1,4-dimethoxy-2,3,5,6-tetrachlo-
robenzene (41, 1%). Analysis by GC-MS prior to chro-
matography gave 39:40:41 ca. 57:4:1. Although 35 is a
good one-electron acceptor,40 an electron-transfer mech-
anism for the formation of the products is unlikely
because the energy difference between dihydroxycarbene,
Carbene precursor 1-d3 was used to determine whether
products 39-41 are formed via intermolecular or in-
tramolecular methyl transfers. Methyl group transfer
with crossover should lead to deuterium-labeled 39-41
with the isotopomer distribution ∼25% d0, ∼50% d3, and
∼25% d6 based on statistics and ignoring kinetic isotope
effects. Analysis by GC-MS showed that 39-41 had
molecular ion isotopic distributions consistent with such
a CD3 crossover (Figure 5). Although those isotopic
distributions were complicated somewhat by the Cl
isotopes, the overlap of signals from d3 and d6 isotopomers
a model for 2, and its radical cation is ca. 120 kcal mol-1 41
.
(38) Pole, D. L.; Warkentin, J . Liebigs Ann. Chem. 1995, 1907.
(39) Reid, D.; Warkentin, J ., unpublished results.
(40) (a) Eberson, L. Electron-Transfer Reactions in Organic Chem-
istry; Springer-Verlag: New York, 1987. (b) Photoinduced Electron
Transfer, Vol. A-D; Fox, M. A., Chanon, M., Eds.; Elsevier: New York,
1988.
(41) (a) Burgers, P. C.; McGibbon, G. A.; Terlouw, J . K. Chem. Phys.
Lett. 1994, 224, 539. (b) Burgers, P. C.; Mommer, A. A.; Holmes, J . L.
J . Am. Chem. Soc. 1983, 105, 5976.

4350 J . Org. Chem., Vol. 64, No. 12, 1999
Dunn et al.
prior to use if necessary. Purities of reagents and solvents were
determined by GC and GC-MS.
2,2-Dim eth oxy-5,5-d im eth yl-∆3-1,3,4-oxa d ia zolin e (1).
Oxadiazoline 1 was prepared by oxidative cyclization of the
carbomethoxyhydrazone of acetone with lead tetraacetate
(LTA) as described previously.7a The product was purified by
radial chromatography on SiO2 using 10:1 hexanes/ethyl
acetate as the eluent: yield 78%, clear oil; 1H NMR (200 MHz,
CDCl3) δ 1.53 (s, 6 H), 3.45 (s, 6 H); 13C NMR (50.3 MHz,
CDCl3) δ 23.7, 51.5, 118.8, 137.0; IR (neat, KBr) 2982, 2949,
2887, 2847, 1577, 1459, 1448, 1376, 1137, 1078 cm-1; MS (EI)
m/z (molecular ion not observed), 129 [M - OMe]+, 105, 91,
90, 75, 74, 73, 59 (100%); MS (CI, NH3) m/z 178 [M + NH4]+;
UV (pentane) λmax 328 nm (ꢀ 500).
2-Meth oxy-2-m eth oxy-d 3-5, 5-d im eth yl-∆3-1,3,4-oxa d i-
a zolin e (1-d 3). Oxadiazoline 1, prepared by LTA oxidation of
the carbomethoxyhydrazone of acetone in CH2Cl2, was treated
with methanol-d4 as described previously.33
Octa ch lor obicyclo[3.2.0]h ep ta -3,6-d ien e (24). Diene 24
was synthesized according to a literature procedure:37a white
solid, mp 53-54 °C (lit.37a 53 °C); 13C NMR (50.3 MHz, CDCl3)
δ 137.4, 134.2, 133.4, 132.2, 89.0, 81.8, 78.7; MS (EI) m/z 364
[M]+, 329 (100%) [C7Cl7]+, 294 [C7Cl6]+, 259 [C7Cl5]+, 189
[C7Cl3]+, 154 [C7Cl2]+, 119 [C7Cl]+; MS (CI, NH3) m/z 382 [M
+ NH4]+.
Octa ch lor ocycloh ep ta tr ien e(12). The triene, synthesized
according to a literature procedure,21 was a pale yellow solid:
mp 85 °C (lit.21 86 °C); 13C NMR (50.3 MHz, CD2Cl2) δ 134.5,
134.1, 129.2, 84.3; MS (EI) m/z 364 [M]+, 329 (100%) [C7Cl7]+,
294 [C7Cl6]+, 259 [C7Cl5]+, 189 [C7Cl3]+, 154 [C7Cl2]+, 119
[C7Cl]+; MS (CI, NH3) m/z 382 [M + NH4]+.
Hexa ch lor otr op on e (28). A literature procedure21b for the
synthesis of 28 gave a yellow solid: mp 82-83 °C (lit.21b 82.5
°C); 13C NMR (50.3 MHz, CDCl3) δ 177.5, 136.6, 134.5, 132.4;
MS (EI) m/z 310 [M]+, 284 (100%) [M - CO]+, 247 [C7Cl5]+,
212 [C7Cl4]+, 177 [C7Cl3]+, 142 [C7Cl2]+, 107 [C7Cl]+; MS (CI,
NH3) m/z 328 [M + NH4]+.
Hexa ch lor obicyclo[3.2.0]h ep ta -3,6-d ien -2-on e (32). Di-
enone 32 was prepared by means of a modified literature
procedure.37a Sulfuric acid (concentrated, 5.0 mL) was added
to octachlorobicyclo[3.2.0]hepta-3,6-diene (24) (1.947 g, 5.30
mmol), and the solution was heated at 80 °C for 20 h. The
solution was cooled, poured over ice, and extracted with ether.
Radial chromatography of the extract using petroleum ether
eluent yielded 32 as a white powder (1.034 g, 63%): mp 84.5-
85 °C (lit.37a 85-86 °C); 13C NMR (50.3 MHz, CDCl3) δ 182.5,
157.0, 136.1, 132.1, 131.6, 75.6, 73.7; IR (neat, KBr) 1746, 1622,
1573, 1226, 1155, 1129, 1030 cm-1; MS (EI) m/z 310 [M]+, 282
[M - CO]+, 247 [C6Cl5]+, 212 [C6Cl4]+, 177 [C6Cl3]+, 142 (100%)
[C6Cl2]; MS (CI, NH3) m/z 328 [M + NH4]+, 311 [M + H]+;
HRMS calcd for C7Cl6O 309.8080, found 309.8092.
F igu r e 5.
could be corrected for. On the basis of these findings, a
cascade of intermolecular methyl transfers is implicated.
Con clu sion s
Dimethoxycarbene reacts with perchloro olefins (e.g.,
4 and 12) by overall nucleophilic substitution leading to
ion pair intermediates. The latter undergo nucleophilic
substitution by Cl- either at Me of (MeO)2C+R to afford
esters and MeCl or at Cl to afford a ketene acetal and
Cl2. These results are consistent with reaction of 2 as an
“acyl anion” equivalent. Unsaturated perchloroketones,
including tetrachloro-1, 4-benzoquinone, are attacked at
the carbonyl carbon atom to afford dipolar intermediates
that can rearrange without loss of a Cl- moiety. Alter-
natively, such intermediates can form ion pairs that also
lead to MeCl and esters.
Rea ction of 2 w ith 4. A solution of 1 (0.268 g, 1.68 mmol)
in freshly distilled benzene (18.3 mL) containing 4 (0.1 M,
0.500 g, 1.83 mmol), in a 40 mL thermolysis tube fitted with
Teflon valves, was degassed by means of three successive
freeze-pump-thaw cycles. The sealed tube was then heated
at 110 °C in a constant temperature oil bath for 24 h.
Immediate analysis by GC-MS showed 6, 7, and 8 as major
products in a 1.2:1.8:1 ratio, respectively. These products were
isolated by means of radial chromatography, with hexanes and
1:1 hexanes/CH2Cl2. Minor isomers of 6, 7, and 8 were detected
by GC-MS, but they could not be isolated by chromatography.
A degassed solution of 1 (0.587 g, 3.67 mmol) in benzene (3.7
mL) containing 4 (0.100 g, 0.37 mmol) was also heated in a
thermolysis tube at 110 °C for 24 h. Analysis by GC-MS gave
8:7 ≈ 4:1 with only trace amounts of 6 present. The identities
of 7 and 8 were confirmed by isolation of those products.
5-Ca r b om et h oxy-1,2,3,4,5-p en t a ch lor ocyclop en t a d i-
Exp er im en ta l Section
Gen er a l In for m a tion . For GC-MS analyses, a gas chro-
matograph equipped with a mass-selective detector and a DB-1
capillary column (12 m × 0.2 mm) was used. Mass spectra were
obtained with a double-focusing instrument, and infrared
spectra (FT) are from samples in KBr windows. Frequencies
below 1000 cm-1 are omitted. All values of m/z for polychlo-
rinated compounds are the lowest in the envelope and cor-
respond to 35Cl; the signal intensities matched the pattern
required for the number of Cl atoms in the fragment. Not all
observed signals are listed.
1
en e (6). Yield 24%, white solid, mp 93-94 °C; H NMR (500
MHz, CD2Cl2) δ 3.82 (s); 13C NMR (125.7 MHz, CD2Cl2) δ 162.5,
131.0, 130.1, 72.6, 55.1; IR (neat, KBr) 2956, 2920, 2850, 1756,
1648, 1601, 1448, 1441, 1283, 1234, 1179, 1148, 1123, 1010
cm-1; MS (EI) m/z 294 [M]+ (100%), 259 [C7H3O2Cl4]+, 235
[C5H3O2Cl4]+ (based on the isotopic distribution within the
Ma ter ia ls. Benzene (Aldrich) was distilled from sodium. All
other solvents and reagents were of the highest purity com-
mercially available (Aldrich) and were distilled/recrystallized

Dimethoxycarbene and Perchlorinated Olefins/Ketones
J . Org. Chem., Vol. 64, No. 12, 1999 4351
fragment envelope); MS (CI, NH3) m/z 312 [M + NH4]+; HRMS
calcd for C7H3O2Cl5 293.8576, found 293.8573.
diphenylisobenzofuran (0.2 M, 294 mg, 1.09 mmol) was heated
as described above. Radial chromatography with a solvent
gradient ranging from hexanes to 1:1 hexanes/ethyl acetate
yielded 16, 19, and 23, as well as the product of hydrolysis of
diphenylisobenzofuran. An isomer of 23 (identical mass spec-
trum) was also isolated, but it could not be obtained in either
a high enough purity or yield to be fully characterized.
(Z)-2-(2-Ben zoylph en yl)-1-ch lor o-1-pen tach lor oph en yl-
2-p h en yleth en e (23). Yield 16%, white solid, mp 158-9 °C;
1H NMR (500 MHz, CD2Cl2) δ 7.05-7.80 (m, 14 H); 13C NMR
(125 MHz, CD2Cl2) δ 126.9, 128.1, 128.2, 128.4, 128.5, 128.7,
128.8, 129.5, 130.1, 130.4, 130.6, 130.8, 131.1, 131.3, 132.3,
132.9, 133.3, 134.8, 137.7, 140.4,196.7; IR (neat, KBr) 2924,
2852, 1771, 1736, 1661, 1597, 1579, 1492, 1447, 1315, 1276,
1199, 1179, 1154, 1103, 1074, 1061, 1025, 1001 cm-1; MS (EI)
4,5-Dica r bom eth oxy-1,2,3,5-tetr a ch lor ocyclop en ta d i-
1
en e (7). Yield 28%, white solid, mp 84-85 °C; H NMR (500
MHz, CD2Cl2) δ 3.84 (s, 3 H), 3.75 (s, 3 H); 13C NMR (125.7
MHz, CD2Cl2) δ 163.4, 159.9, 143.7, 137.0, 132.3, 132.0, 68.4,
54.9, 52.7; IR (neat, KBr) 3007, 2956, 2848, 1783, 1756, 1697,
1681, 1653, 1628, 1603, 1557, 1436, 1327, 1289, 1254, 1226,
1161, 1120, 1094, 1048 cm-1; MS (EI) m/z 318 [M]+, 287
[C8H3O3Cl4]+, 274 [C8H6O2Cl4]+ (based on isotopic distribution
within the fragment envelope), 259 [C7H3O2Cl4]+, 228 [C6OCl4]+,
180 [C6H3Cl3]+, 165 [C5Cl3]+, 130 [C5Cl2]+, 95 [C5Cl]+, 59
[CO2Me]+ (100%), 43; MS (CI, NH3) m/z 338 [M + NH4]+;
HRMS calcd for C9H6O4Cl4 317.9020, found 317.9012.
4,5,5-Tr ica r b om et h oxy-1,2,3-t r ich lor ocyclop en t a d i-
en e (8). Yield 33%, white solid, mp 104-105 °C; 1H NMR (200
MHz, CD2Cl2) δ 3.80 (s, 3 H), 3.75 (s, 6 H); 13C NMR (50.3
MHz, CD2Cl2) δ 162.8 (CO2Me), 160.5 (CO2Me), 142.4, 133.2,
132.0, 129.0, 71.1, 54.5, 52.3; IR (neat, KBr) 3013, 2959, 2848,
1785, 1754, 1625, 1597, 1552, 1437, 1325, 1290, 1255, 1228,
1161, 1055, 1043 cm-1; MS (EI) m/z 342 [M]+, 298 [C10H9O4-
Cl3]+, 267 [C11H9O6Cl3]+; MS (CI, NH3) m/z 360 [M + NH4]+,
343 [M + H]+; HRMS (EI) HRMS calcd for C11H9O6Cl3
341.9465, found 341.9463.
m/z 564 [M]+, 529[C27H14OCl5]+, 494 [C27H14OCl4]+, 459 [C27H14
-
OCl3]+, 209 (100%); MS (CI, NH3) m/z 582 [M + NH4]+; HRMS
calcd for C27H14OCl6 563.9176, found 563.9179.
Rea ction of 2 w ith 28. A solution of 1 (0.093 g, 0.58 mmol)
in benzene (6.4 mL) containing 28 (0.1 M, 0.200 g, 0.64 mmol)
was heated as described above. Analysis by GC-MS revealed
methyl 2-pentachlorophenyl-2-oxo-ethanoate (31) (69%), pen-
tachlorobenzoyl chloride (2%), methyl pentachlorobenzoate
(7%), hexachlorobenzene (1%), and remaining 28 (20%). Keto-
ester 31 was isolated using radial chromatography with a
gradient of solvents ranging from hexanes to 1:1 hexanes/
CH2Cl2. Hexachlorotropone (28), heated under identical condi-
tions, gave (by GC-MS) pentachlorobenzoyl chloride (5%),
hexachlorobenzene (2%), and starting material (93%). Pro-
longed thermolysis times (2.5 weeks) converted hexachloro-
tropone fully to hexachlorobenzene and pentachlorobenzoyl
chloride. A solution of 1 (0.102 g, 0.64 mmol) in freshly distilled
benzene (7.0 mL) containing hexachlorobenzene (0.1 M, 0.200
g, 0.70 mmol) was heated as described previously. The only
product from this reaction, other than acetone, detected by
GC-MS was tetramethoxyethylene.
Rea ction of 2 w ith 12. A solution of 1 (0.118 g, 0.74 mmol)
in benzene (8.1 mL) containing 12 (0.1 M, 0.300 g, 1.1 mmol)
was heated as described above. Major products 16 and 19 were
isolated using radial chromatography with a gradient of
solvents ranging from hexanes to 1:1 hexanes/CH2Cl2. Octa-
chlorotoluene was isolated as a minor product. Heating of 12
under identical conditions converted ∼10% to octachloro-
toluene, whereas heating for two weeks resulted in complete
conversion.
Dim eth oxy(h exa ch lor o)h ep ta fu lven e (16). Yield 12%,
white solid, mp 91-91.5 °C; 1H NMR (500 MHz, CD2Cl2) δ
3.89 (s, 6 H); 13C NMR (125.7 MHz, CDCl3) δ 162.1, 132.0,
130.4, 126.0, 86.8, 57.9; IR (neat, KBr) 3007, 2956, 2856, 1618,
Meth yl 2-P en tach lor oph en yl-2-oxo-eth an oate (31). Yield
44%, white solid, mp 127-28 °C; 1H NMR (300 MHz, CD2Cl2)
δ 3.95; 13C NMR (75 MHz, CD2Cl2) δ 181.3, 159.0, 136.2, 135.4,
132.8, 129.4, 54.1; IR (neat, KBr) 3046, 2967, 2850, 1763, 1738,
1555, 1467, 1430, 1320, 1266, 1223, 1192, 1165, 1120 cm-1
;
MS (EI) m/z 368 [M]+, 353 [C9H3O2Cl6]+, 333 [C10H6O2Cl5]+;
MS (CI, NH3) m/z 369 [M + H]+; HRMS calcd for C10H6O2Cl6
367.8499, found 367.8492.
1646, 1545, 1439, 1352, 1322, 1273, 1230, 1138, 1031 cm-1
;
Dod eca ch lor oh ep ta fu lva len e (19). Fulvalene 19 was
identified from MS (EI) and 13C NMR data, which were
consistent with those in the literature;22,24b yield 56%. Oc-
ta ch lor otolu en e. Yield 5%, white solid, mp 69-71 °C (lit.21b
71-72 °C); 13C NMR (50.3 MHz, CD2Cl2) δ 138.0, 136.1, 134.7,
132.9, 93.5; MS (EI) m/z 364 [M]+, 329 (100%) [C7Cl7]+, 294
[C7Cl6]+; MS (CI, NH3) m/z 382 [M + NH4]+.
MS (EI) m/z 334 [M]+, 275 (100%) [C7OCl5]+; MS (CI, NH3)
m/z 352 [M + NH4]+; HRMS (EI) calcd for C9H3O3Cl5 333.8525,
found 333.8536.
P en ta ch lor oben zoyl Ch lor id e. Identified from the mass
spectral (GC-MS) fragmentation pattern:21 MS (EI) m/z 310
[M]+, 275 (100%) [C7OCl5]+, 247 [C6Cl5]+, 212 [C6Cl4]+, 177
[C6Cl3]+, 142 [C6Cl2]+, 107 [C6Cl]+.
Attem p ted Th er m olysis of Dim eth oxy(h exa ch lor o)-
h ep ta fu lven e (16). A solution of 16 (0.05 M, 0.020 g, 0.054
mmol) in 1 mL of benzene-d6 in an NMR tube was degassed
by means of three successive freeze-pump-thaw cycles before
the tube was flame-sealed. The solution was heated at 110 °C
Meth yl P en ta ch lor oben zoa te. Identified from the mass
spectral (GC-MS) fragmentation pattern: MS (EI) m/z 306
[M]+, 275 (100%) [C7OCl5]+, 247 [C6Cl5]+, 212 [C6Cl4]+, 177
[C6Cl3]+, 142 [C6Cl2]+, 107 [C6Cl]+, 83, 71, 59 [CO2Me]+.
Hexa ch lor oben zen e. Yield 1%, white solid, mp 225-227
°C (lit.21 227-29 °C); 13C NMR (50.3 MHz, CD2Cl2) δ 132.3;
MS (EI) m/z 282 (100%) [M]+, 247 [C6Cl5]+; MS (CI, NH3) m/z
300 [M + NH4]+.
Rea ction of 2 w ith 32. A solution of 1 (0.1 M, 116 mg,
0.73 mmol) in benzene (8.0 mL) containing 32 (0.1 M, 0.250
mg, 0.80 mmol) was heated as described above. Analysis by
TLC suggested that only 34 was formed during the thermoly-
sis. It was purified by recrystallization from a 19:1 hexanes/
CH2Cl2 solvent mixture.
1
for 24 h and then analyzed by H NMR (500 MHz) spectros-
copy. Thermal decomposition products of 16 were not observed.
Rea ction of 2 w ith 24. A solution of 1 (0.118 g, 0.74 mmol)
in benzene (8.1 mL) containing 24 (0.1 M, 0.300 g, 0.82 mmol)
was heated as described above. Products 16 (11%) and 19 (3%)
were isolated by means of radial chromatography.
7-Ca r b om e t h oxy-1,2,3,4,5,6-h e xa ch lor ocycloh e p t a -
tr ien e (17). Ketene acetal 16 hydrolyzed to 17 on prolonged
exposure to air. In a deliberate hydrolysis, a solution of 16
(0.05 M, 0.100 g, 0.27 mmol) in dichloromethane (5.5 mL) was
stirred with 2 mL of distilled water at room temperature for
2 days. Radial chromatography (hexanes) gave 17 as a white
solid (85 mg, 89%): mp 86-87 °C; 1H NMR (200 MHz, CD2Cl2)
δ 4.65 (s, 1H), 3.71 (s, 3H); 13C NMR (50.3 MHz, CD2Cl2) δ
165.4, 133.2, 130.6, 127.9, 60.4, 54.2; IR (neat, KBr) 3007, 2954,
2844, 1751, 1641, 1616, 1597, 1575, 1449, 1436, 1291, 1274,
1230, 1152, 1090, 1003 cm-1; MS (EI) m/z 354 [M]+, 319
[C9H4O2Cl5]+, 295 (100%) [C7HCl6]+; MS (CI, NH3) m/z 372 [M
+ NH4]+; HRMS calcd for C9H4O2Cl6 353.8342, found 353.8339.
Rea ction of 2 w ith 12 Con ta in in g Dip h en ylisoben zo-
fu r a n . A solution of 1 (0.1 M, 0.087 g, 0.54 mmol) in benzene
(5.4 mL) containing 12 (0.1 M, 0.200 g, 0.54 mmol) and
2,2-Dim eth oxy-1,4,5,6,7,8-h exa ch lor obicyclo[4.2.0]octa -
4,7-d ien -3-on e (34). Yield 98%, white solid, mp 154.5-155
1
°C; H NMR (500 MHz, CD2Cl2) δ 3.52 (s, 3H), 3.18 (s, 3H);
13C NMR (125.7 MHz, CD2Cl2) δ 183.2, 143.3, 133.5, 132.3,
129.8, 100.3, 80.0, 77.0, 52.0, 51.4; IR (neat, KBr) 2996, 2986,
2944, 2984, 1740, 1637, 1592, 1530, 1458, 1441, 1249, 1194,
1181, 1161, 1086, 1019 cm-1; MS (EI) m/z (molecular ion not
obsd) 349 (100%) [C10H6O3Cl5]+, 321 [C9H6O2Cl5]+; MS (CI,
NH3) m/z 402 [M + NH4]+; HRMS calcd for fragment C10H6O3-
Cl5 348.8760, found 348.8762.
Rea ction of 2 w ith 35. A solution of 1 (0.296 g, 1.85 mmol)
in benzene (20.3 mL) containing 35 (0.1 M, 0.500 g, 2.03 mmol)
was heated as described above. Analysis by TLC and by GC-

4352 J . Org. Chem., Vol. 64, No. 12, 1999
Dunn et al.
MS indicated 39:40:41 in ca. 57:4.1:1 ratio (GC-MS). They
were isolated by means of radial chromatography with a
gradient of solvents ranging from hexanes to 20% CH2Cl2 in
hexanes.
4-Meth oxy-2,3,5,6-tetr a ch lor op h en yl Meth yl Ca r bon -
a te (39). Yield 82%, yellow solid, mp 106.5-108 °C; 1H NMR
(500 MHz, CD2Cl2) δ 3.95 (s, 3 H), 3.91 (s, 3 H); 13C NMR (125.7
MHz, CD2Cl2) δ 152.8, 152.1, 142.2, 128.3, 127.5, 61.3, 57.0;
IR (neat, KBr) 2952, 1784, 1462, 1443, 1408, 1383, 1316, 1254,
1199, 1166, 1031 cm-1; MS (EI) m/z 318 [M]+, 274 [C8H6O2-
Cl4]+, 259 (100%) [C7H3O2Cl4]+, 228 [C6OCl4]+; MS (CI, NH3)
m/z 336 [M + NH4]+; HRMS calcd for C9H6O4Cl4 317.9020,
found 317.9004.
fibers with epoxy cement. X-ray crystallographic data were
collected with a P4 Siemens diffractometer, equipped with a
Siemens SMART 1K charge-coupled device (CCD) area detec-
tor (employing the program SMART42) and a rotating anode
utilizing graphite-monochromated Mo KR radiation (λ )
0.71703 Å). The crystal-to-detector distance was 3.991 cm, and
the data collection was carried out in 512 × 512 pixel mode,
employing 2 × 2 pixel binning. In all cases, the initial unit
cell parameters were determined by a least-squares fit of the
angular settings of the strong reflections, collected using three
4.5° scans (15 frames each) over three different parts of
reciprocal space, and one complete hemisphere of data was
collected, to better than 0.8 Å resolution. Processing of the data
was carried out using the program SAINT,43 which applied
Lorentz and polarization corrections to three-dimensionally
integrated diffraction spots. The program SADABS44 was
employed for the scaling of diffraction data, the application of
a decay correction, and an empirical absorption correction
based on redundant reflections. All structures were solved by
the direct methods routine outlined in the Siemens SHELXTL
program library45 followed by full-matrix least-squares refine-
ment on F2 with anisotropic thermal parameters for all non-
hydrogen atoms. For 7, 17, and 34, hydrogen positions were
located on a Fourier difference map and then the coordinates
were refined with isotropic thermal parameters, whereas for
8 and 23, hydrogen atoms were added as fixed contributors at
calculated positions riding on the relevant carbon atoms.
1,4-(2,3,5,6-Tetr a ch lor op h en yl) Bis(m eth yl ca r bon a te)
(40). Yield 5%, orange solid, mp 169-170.5 °C; 1H NMR (500
MHz, CD2Cl2) δ 3.95 (s, 6 H); 13C NMR (50.3 MHz, CD2Cl2) δ
151.8, 144.0, 127.9, 57.2; IR (neat, KBr) 3005, 2847, 1779, 1715,
1688, 1574, 1455, 1442, 1414, 1384, 1330, 1247, 1194, 1171
cm-1; MS (EI) m/z 362 [M]+, 318 [C9H6O4Cl4]+, 274 [C8H6O2-
Cl4]+, 259 (100%) [C7H3O2Cl4]+; MS (CI, NH3) m/z 380 [M +
NH4]+; HRMS calcd for C10H6O6Cl4 361.8918, found 361.8933.
1,4-Dim eth oxy-2,3,5,6-tetr a ch lor oben zen e (41). Yield
1%, yellow solid, mp 98-99 °C; 1H NMR (500 MHz, CD2Cl2) δ
3.92; 13C NMR (50.3 MHz, CD2Cl2) δ 61.5, 128.7, 152.0; MS
(EI) m/z 274 [M]+, 259 (100%) [C7H3O2Cl4]+.
Rea ction of Dim eth oxyca r ben e-d 3 (2-d 3) w ith 35. A
solution of 2-methoxy-2-methoxy-d3-5,5-dimethyl-∆3-1,3,4-oxa-
diazoline (1-d 3, 0.120 g, 0.74 mmol) in benzene (8.1 mL)
containing 35 (0.1 M, 0.200 g, 0.82 mmol) was heated as
described above. Analysis by GC-MS revealed that the ratio
39:40:41 was again 57:4:1. The isotopic distribution of the
molecular ion envelope (IDME) from 39 was consistent with
a 1:2:1 distribution of isotopomers containing all hydrogens
(m/z 318), 3 deuterium atoms (m/z 321), and 6 deuterium
atoms (m/z 324), respectively. Relative intensities of the signals
from the molecular ion were 318 (8.1%), 319 (0.9%), 320 (9.7%),
321 (16.4%), 322 (6.6%), 323 (20.5%), 324 (9.2%), 325 (10.5%),
326 (9.4%), 327 (3.1%), 328 (4.2%), 329 (0.5%), and 330 (1.0%).
The IDME of 40 was also consistent with a 1:2:1 distribution
of isotopomers containing all hydrogens (m/z 362), 3 deuterium
atoms (m/z 365), and 6 deuterium atoms (m/z 368), respec-
tively. Relative intensities of the signals from the molecular
ion were 362 (5.8%), 363 (<0.1%), 364 (13.1%), 365 (19.4%),
366 (5.5%), 367 (29.4%), 368 (3.2%), 369 (11.3%), 370 (9.4%),
371 (<0.1%), 372 (2.9%), 373 (<0.1%), and 374 (<0.1%).
Finally, the IDME of 41 was consistent with a 1:2:1 distribu-
tion of isotopomers containing all hydrogens (m/z 274), 3
deuterium atoms (m/z 277), and 6 deuterium atoms (m/z 280).
The relative intensities of the signals from the molecular ion
were 274 (4.4%), 275 (<0.1%), 276 (10.9%), 277 (19.1%), 278
(5.6%), 279 (22.4%), 280 (11.8%), 281 (12.5%), 282 (10.2%), 283
(<0.1%), 284 (3.1%), 285 (<0.1%), and 286 (<0.1%).
Ack n ow led gm en t. We are indebted to Dr. J . F.
Britten for advice concerning X-ray crystallography and
to Dr. Don Hughes and Mr. Brian Sayer for help with
NMR spectroscopy. Some mass spectra were obtained
courtesy of Dr. Richard Smith of the McMaster Regional
Center for Mass Spectrometry. J .P.P. and J .A.D. grate-
fully acknowledge the Natural Sciences and Engineering
Council of Canada (NSERC) for graduate scholarships.
J .W. and M.J .M. thank NSERC for support through
operating grants. M.J .M. also acknowledges support
from the donors of the Petroleum Research Fund,
administered by the American Chemical Society.
Su p p or tin g In for m a tion Ava ila ble: Crystal and struc-
ture refinement data for compounds 7, 8, 17, 23, and 34. This
material is available free of charge via the Internet at
http://pubs.acs.org.
J O9823846
(42) SMART, Release 4.05; Siemens Energy and Automation Inc.,
Madison, WI 53719, 1996.
(43) SAINT, Release 4.05; Siemens Energy and Automation Inc.,
Madison, WI 53719, 1996.
(44) Sheldrick, G. M. SADABS (Siemens Area Detector Absorption
Corrections), unpublished, 1994.
(45) Sheldrick, G. M. SHELXTL, Release 5.03; Siemens Analytical
X-ray Instruments, Madison, WI, 1994.
X-r a y Cr ysta llogr a p h ic Da ta . Summaries of the crystal
data and structure refinement parameters are in Supporting
Information, Table S1. All crystals were grown by slow
evaporation of the solvent and were mounted on fine glass