Selective 1,4-addition of arenes to 3-chloro-3-cyclobutene-1,2-dione under friedel-crafts conditions. Synthesis and reactivity of 4-aryl-3-chloro-2- hydroxy-2-cyclobuten-1-ones

Article abstract of DOI:10.1021/jo952062r

The reaction of semisquaric chloride (7) with arenes 2 has been investigated. In the presence of 1.1 equiv of AlCl₃ and in the temperature range of -15° C to rt the arenes 2a-q afford the 4-aryl-3-chloro-2-hydroxy-2-cyclobuten-1-ones (chloroenols) 8a-q in good yield. By contrast, 7 reacts with 1,4-dimethoxybenzene (2l) in boiling CH ₂Cl₂ to give a mixture of (2,5-dimethoxyphenyl) cyclobutenedione (9a) (27% yield) and bis(2,5-dimethoxyphenyl)cyclobutenedione (10a) (8% yield). With 1,2,4-trimethoxybenzene (2r) in the presence of trifluoroacetic acid is generated (2,4,5-trimethoxyphenyl)-cyclobutenedione (9b) in 21% yield. The chloroenols 8 allow a series of valuable transformation reactions: with diazomethane the chloroenol methyl ethers 11 are generated, with chlorine the 3-aryl-4-chlorocyclobutenediones 12, and with bromine in MeOH the 3-aryl-4-methoxycyclobutenediones 13. In DMSO or in acetone/H₂O the chloroenols 8 eliminate HCl, furnishing the arylcyclobutenediones 14. In a mixture of acetone-d₆/D₂O/DCl are obtained 4-aryl-cyclobutenediones-3-d 15. For the latter two processes the corresponding 3-aryl-4-chlorocyclobutane-1,2-diones 16 are postulated as intermediates. Thermolysis of the chloroenols 8 and the chloroenol methyl ethers 11 in refluxing m-xylene afforded the 3-chloro-1,2-dihydroxynaphthalenes 17 and the 3-chloro-1-hydroxy-2-methoxynaphthalenes 18, respectively.

Full text of DOI:10.1021/jo952062r

J . Org. Chem. 1996, 61, 2085-2094
2085
Selective 1,4-Ad d ition of Ar en es to
3-Ch lor o-3-cyclobu ten e-1,2-d ion e u n d er F r ied el-Cr a fts Con d ition s.
Syn th esis a n d Rea ctivity of
4-Ar yl-3-ch lor o-2-h yd r oxy-2-cyclobu ten -1-on es1
Arthur H. Schmidt,* Gunnar Kircher, Stephan Maus, and Heinz Bach
Abteilung fu¨r Organische Chemie und Biochemie, Fachhochschule Fresenius, Kapellenstrasse 11-15,
D-65193 Wiesbaden, Germany†
Received November 22, 1995X
The reaction of semisquaric chloride (7) with arenes 2 has been investigated. In the presence of
1.1 equiv of AlCl3 and in the temperature range of -15° C to rt the arenes 2a -q afford the 4-aryl-
3-chloro-2-hydroxy-2-cyclobuten-1-ones (chloroenols) 8a -q in good yield. By contrast, 7 reacts with
1,4-dimethoxybenzene (2l) in boiling CH2Cl2 to give a mixture of (2,5-dimethoxyphenyl)cyclobutene-
dione (9a ) (27% yield) and bis(2,5-dimethoxyphenyl)cyclobutenedione (10a ) (8% yield). With 1,2,4-
trimethoxybenzene (2r ) in the presence of trifluoroacetic acid is generated (2,4,5-trimethoxyphenyl)-
cyclobutenedione (9b) in 21% yield. The chloroenols 8 allow a series of valuable transformation
reactions: with diazomethane the chloroenol methyl ethers 11 are generated, with chlorine the
3-aryl-4-chlorocyclobutenediones 12, and with bromine in MeOH the 3-aryl-4-methoxycyclobutene-
diones 13. In DMSO or in acetone/H2O the chloroenols 8 eliminate HCl, furnishing the
arylcyclobutenediones 14. In a mixture of acetone-d6/D2O/DCl are obtained 4-aryl-cyclobutenedi-
ones-3-d 15. For the latter two processes the corresponding 3-aryl-4-chlorocyclobutane-1,2-diones
16 are postulated as intermediates. Thermolysis of the chloroenols 8 and the chloroenol methyl
ethers 11 in refluxing m-xylene afforded the 3-chloro-1,2-dihydroxynaphthalenes 17 and the 3-chloro-
1-hydroxy-2-methoxynaphthalenes 18, respectively.
Sch em e 1
In tr od u ction
A great number of investigations have been made into
the reaction of substituted cyclobutenediones with arenes
2 under Friedel-Crafts conditions. In such reactions
halogenocyclobutenediones react as vinylogous acid ha-
logenides. Thus, 3,4-dichlorocyclobutenedione (squaric
dichloride) (1) affords 3-aryl-4-chlorocyclobutenediones
3a or diarylcyclobutenediones 4, depending upon the
amount of catalyst (AlCl3), the molar ratio of the educts,
and the reaction conditions (Scheme 1).2-4 Accordingly,
the 3-aryl-4-halogenocyclobutenediones 3a and 3b react
with arenes 2′ to give the diarylcyclobutenediones 4.2g,5
Monosubstituted cyclobutenediones such as 5, on the
other hand, behave as vinylogous aldehydes. They react
with arenes in the presence of 1 equiv of AlCl3 to give
2-hydroxy-2-cyclobuten-1-ones 6a and 6b.2g,5,6
In this context it was of interest to examine in which
way 3-chloro-3-cyclobutene-1,2-dione (semisquaric chlo-
ride) (7),7 which combines the structural elements of a
vinylogous carboxylic acid chloride and a vinylogous
aldehyde, would react with arenes 2 under Friedel-
Crafts conditions.
Resu lts a n d Discu ssion
Syn t h esis of 4-Ar yl-2-h yd r oxycyclob u t en on es
(Ch lor oen ols). Semisquaric chloride (7) was reacted
with equimolar amounts of benzene (2a ) and AlCl3 in 1,2-
dichloroethane. While a complex mixture of products was
generated when heating the reaction mixture, at -15 °C
(30 min, and then rt, 4.5 h) we obtained 3-chloro-2-
hydroxy-4-phenyl-2-cyclobuten-1-one (8a) in almost quan-
titative yield (96%). The structure of 8a was confirmed
by spectroscopic methods. The mass spectrum of 8a
exhibited molecular ions at m/ z ) 196 (15%) and m/ z )
194 (45%). The IR spectrum exhibited a broad absorption
at 3300-3100 cm-1 due to a chelated OH group and a
† New address: Abteilung fu¨r Organische Chemie und Biochemie,
Fachhochschule Fresenius, Limburger Strasse 2, D-65510 Idstein,
Germany.
strong CdO absorption at 1750 cm-1
.
The 1H NMR
X Abstract published in Advance ACS Abstracts, February 15, 1996.
(1) Oxocarbons and Related Compounds; Part 23. Part 22: Schmidt,
A. H.; Kircher, G.; Ku¨nz, Ch.; Wahl, S.; Hendriok, M. W. J . Org. Chem.
1995, 60, 3890.
spectrum was characterized by a signal at δ 4.47,
corresponding to the proton in the 4-position of the
cyclobutenone system. Finally, the 13C NMR spectrum
0022-3263/96/1961-2085$12.00/0 © 1996 American Chemical Society

2086 J . Org. Chem., Vol. 61, No. 6, 1996
Schmidt et al.
Sch em e 2
indication of the generation of 3-aryl-3-cyclobutene-1,2-
diones as byproducts of the chloroenols 8. However, in
further experiments2n it was found that semisquaric
chloride (7) reacts with 1,4-dimethoxybenzene (2l) in the
presence of AlCl3 with heating to give a mixture of the
monoarylated and the diarylated cyclobutenedione 9a
and 10a , respectively. On reaction of semisquaric chlo-
ride (7) with 1,2,4-trimethoxybenzene (2r ) in the pres-
ence of trifluoroacetic acid (rt, 24 h) we furthermore
obtained 3-(2,4,5-trimethoxyphenyl)-3-cyclobutene-1,2-
dione (9b) in 21% yield (Scheme 3).9
Ta ble 1. 4-Ar yl-3-ch lor o-2-h yd r oxy-2-cyclobu ten -1-on es 8
Obta in ed by th e Ad d ition of Ar en es to Sem isqu a r ic
Ch lor id e (7)
yielda
entry
Ar
temp (°C)/time (h) product (%)
Sch em e 3
1
2
3
4
5
6
7
8
9
phenyl
p-tolyl
-15/0.5, then rt/4.5
-15/0.5, then rt/4.5
-15/0.5, then rt/4.5
-15/0.5, then rt/6
-15/2
-15/0.5, then rt/6
-15/0.5, then rt/6
-15/0.5, then rt/6
-15/0.5, then rt/4.5
-15/0.5, then rt/4.5
8a
8bb
8c
8d
8e
96
79
77
70
47
90
47
80
67
95
89
-
4-isopropylphenyl
4-tert-butylphenyl
4-methoxyphenyl
4-chlorophenyl
4-bromophenyl
4-iodophenyl
8f
8g
8h
8i
2,4-dimethylphenyl
10 2,5-dimethylphenyl
8j
11 3,4-dimethoxyphenyl -15/5
12 2,5-dimethoxyphenyl -15/5
13 2,5-dichlorophenyl
14 2,3,4-trimethylphenyl -15/2.5
15 mesityl
8k
[8l]c
8m
8n
8o
8p
-15/0.5, then rt/48
90
45
69
93
-15/3
16 2,3,4,5-tetramethyl- -15/2.5
phenyl
17 naphthalen-1-yl
-15/0.5, then rt/4.5
8qd
85
a
Yields represent crude yields of products (ca. 90-95% pure
by 1H NMR) except for products 8a , 8c, 8e, 8f, 8g, and 8m , which
are isolated, recrystallized yields. b 8b was accompanied by ca. 15%
3-chloro-2-hydroxy-4-(o-tolyl)-2-cyclobuten-1-one. The ratio of
products was not substantially changed by repeated recrystalli-
zations. c Isolated at -15 °C; not characterized due to thermal
instability. On the basis of H NMR measurements we ascribe,
tentatively, the attack of 7 on naphthalene at the 1-position.
Chemical proof of this orientation is being pursued.
Rea ctivity of th e 4-Ar yl-2-h yd r oxycyclobu ten -
on es (Ch lor oen ols). Since satisfactory elemental analy-
ses were not obtained for several chloroenols 8, and to
explore their reactivity, several representatives were
treated with diazomethane. This yielded the chloroenol
methyl ethers 11 (Scheme 4), which were characterized
by correct elemental analyses. Their structure was
confirmed by spectroscopic methods (see Experimental
Section).
d
1
exhibited 8 signals (4 Cq and 4 Ctert), which is in
agreement with the structure of 8a . As illustrated in
Scheme 2 and summarized in Table 1, the reaction of
semisquaric chloride (7) with benzene (2a ) can be
extended to a large number of arenes containing one or
several substituents.
Further investigations into the reactivity of the chlo-
roenols 8 proved them valuable four-membered-ring
As can be seen from Table 1 it is necessary to adapt
the reaction conditions to the electron density of the
individual arene to obtain good product yields. Thus, the
reactions with the halobenzenes 2f-h and 2m (entries
6-8 and 13) were carried out mainly at rt, while the
reactions with the methoxybenzenes 2e, 2k , and 2l
(entries 5, 11, and 12) were conducted at -15°C. No
reaction took place with electron poor aromatics (ac-
etophenone, nitrobenzene, (trichloromethyl)benzene, (tri-
fluoromethyl)benzene). With the exception of 3-chloro-
4-(4-methoxyphenyl)-2-hydroxy-3-cyclobuten-1-one (8e),
4-(4-bromophenyl)-3-chloro-2-hydroxy-3-cyclobuten-1-
one (8g), and 3-chloro-4-(2,3,4-trimethylphenyl)-2-hy-
droxy-3-cyclobuten-1-one (8n ), the chloroenols 8 were
obtained in good to excellent yields. The chloroenols 8a -
q8 are white to off-white solids, which decompose easily
at rt, with the exception of 8m . The chloroenol 8l
obtained from the reaction of 7 with 1,4-dimethoxyben-
zene (2l) could be isolated at -15 °C; brought to rt it
decomposed rapidly with vigorous elimination of HCl. On
the other hand, 3-chloro-(2,5-dichlorophenyl)-2-hydroxy-
2-cyclobuten-1-one (8m ) was stable and could be stored
at rt. The thermal instability of the other chloroenols 8
was intermediate between these two. In agreement with
these findings several chloroenols (8b, 8f, 8g, 8o, 8p ) did
not analyze correctly. These investigations gave no
(2) For publications dealing completely or in part with the reaction
of squaric dichloride with aromatics and offering full to almost no
experimental details, see: (a) Maahs, G.; Hegenberg, P. Angew. Chem.
1966, 78, 927; Angew. Chem., Int. Ed. Engl. 1966, 5, 888. (b) DeSelms,
R. C.; Fox, C. J .; Riordan, R. C. Tetrahedron Lett. 1970, 781. (c) Becher,
H. J .; Fenske, D.; Langer, E. Chem Ber. 1973, 106, 177. (d) Green, B.
R.; Neuse, E. W. Synthesis 1974, 46. (e) Neuse, E. W.; Green, B. J .
Org. Chem. 1974, 39, 1585. (f) Wendling, L. A.; Koster, S. A.; Murray,
J . E.; West, R. J . Org. Chem. 1977, 42, 1126. (g) Ried, W.; Vogl, M.
Liebigs Ann. Chem. 1977, 101. (h) Argyropoulos, N. G. Chem. Chron.
(New Series) 1986, 15, 119. (i) Kazmaier, P. M.; Burt, R. A.; Baranyi,
G. US Patent 4, 624, 904, 25. Nov. 1986; Xerox Corp., USA; Chem.
Abstr. 1987, 106, 205165m. Described here, with full experimental
details, is the preparation of 3-chloro-4-[4-(N,N-dimethylamino)phenyl]-
cyclobutenedione by the reaction of squaric dichloride (1) (1 equiv) with
N,N-dimethylaniline (0.33 equiv) in the presence of AlCl3 (3 equiv).
Yield 33%; mp 190-191 °C. (j) Akasaki, Y.; Tokida, A.; Torigoe, K.;
Imai, A. J apanese Patent 62,249,952; 30 Oct 1987; Fuji Xerox Co., Ltd.,
J apan; Chem. Abstr. 1988, 109, 170005s. Described here is the
preparation and characterization of fourteen 3-[4-(N,N-dialkylamino)-
phenyl]-4-chlorocyclobutenediones. The reaction between squaric dichlo-
ride (1) and the N,N-dialkylaniline is carried out in the presence of
BF3-etherate. However, the reaction proceeded more satisfactorily
without a catalyst. Thus, the desired compound is obtained in higher
purity than the product obtained in the presence of a Lewis acid
catalyst. (k) Akasaki, Y.; Tokida, A.; Saeki, S.; Torigoe, K.; Imai, A.
J apanese Patent 62,249,953; 30 Oct 1987; Fuji Xerox Co., Ltd., J apan;
Chem. Abstr. 1988, 109, 170004r. (l) Akasaki, Y.; Tokida, A.; Torigoe,
K.; Imai, A. J apanese Patent 01,146,865; 8 J une 1989; Fuji Xerox Co.,
Ltd., J apan; Chem. Abstr. 1989, 111, 232571a. (m) Matsuoka, M;
Soejima, H.; Kitao, T. Dyes and Pigments 1991, 16, 309. (n) Maus, St.
Diplomarbeit; Fachhochschule Fresenius: Wiesbaden, 1994.

Synthesis of 4-Aryl-3-chloro-2-hydroxy-2-cyclobuten-1-ones
J . Org. Chem., Vol. 61, No. 6, 1996 2087
Sch em e 4
Ch a r t 3.
3-Ar yl-4-m eth oxy-3-cyclobu ten e-1,2-d ion es 13
Ch a r t 4.
3-Ar yl-3-cyclobu ten e-1,2-d ion es 14
a
Method A: 14 was obtained quantitatively in solution (DMSO-
d6, rt, 24 h) from the corresponding 8. Proof of structure was
1
accomplished by H and 13C NMR spectroscopy. No physical data
b
taken. Method B: Reaction carried out in DMSO. Product
Ch a r t 1.
isolated. Physical and spectroscopic data obtained. c Method
C: Reaction carried out in acetone/water. Product isolated. El-
emental analysis, physical and spectroscopic data obtained.
4-Ar yl-3-ch lor o-2-m eth oxy-2-cyclobu ten -1-on es 11
Ch a r t 5.
4-Ar yl-3-cyclobu ten e-1,2-d ion es-3-d 15a
a
Incorporation of 1 D/mol indicated by 1H NMR: 15a : 87%; 15b:
75%; 15c: 75%; 15d : 95%.
Ch a r t 2.
oxyphenyl)-3-cyclobutene-1,2-dione (12g) had been gen-
erated. In the H NMR spectrum the two protons of the
1
3-Ar yl-4-ch lor o-3-cyclobu ten e-1,2-d ion es 12
aryl ring appear as two singlets at δ 7.01 and 7.38. A
coupling of these protons is not observed, thus excluding
another arrangement of the substituents in the phenyl
ring.
Besides the intensively investigated parent compound,
3-chloro-4-phenylcyclobutenedione (12a ),10 and several
representatives with simple substituent-patterns in the
phenyl ring,4g,11,12 a large number of 3-[4-(N,N dialkyami-
no)phenyl]-4-chlorocyclobutenediones4 have been pre-
pared. They are easily transformed into the correspond-
ing 3-aryl-4-hydroxycyclobutenediones, which are of great
interest as starting materials for the synthesis of
squaraines.13
a
Obtained from the chlorination of 8k .
synthons. As illustrated in Scheme 4, the chloroenols 8
can be dehydrogenated by chlorine to give the 3-aryl-4-
chlorocyclobutenediones 12 (Chart 2). The treatment of
4-(3,4-dimethoxyphenyl)-2-hydroxy-2-cyclobuten-1-one (8k)
with chlorine deserves special mention. In this case not
only dehydrogenation, but also chlorination of the aryl
When the dehydrogenation of the chloroenols 8 was
carried out with bromine and using methanol as the
(3) The results reported in the literature on the reaction of squaric
dichloride (1) with benzene (2a ) are partly contradictory: See refs 2a
and 2c. Furthermore, we were not able to establish one of the published
procedures as a general one for the generation of 3-aryl-4-chlorocy-
clobutenediones 12: Schmidt, A. H.; unpublished results. See also ref
2n.
1
substituent was observed. The H NMR spectrum pro-
vided clear evidence that 3-chloro-4-(2-chloro-4,5-dimeth-

2088 J . Org. Chem., Vol. 61, No. 6, 1996
Schmidt et al.
Sch em e 5
solvent, 3-aryl-4-bromo-cyclobutenediones were gener-
ated as intermediates. Because of their high reactivity
they experienced methanolysis, and the 3-aryl-4-meth-
oxycyclobutenediones 13a ,10 13b, and 13c were isolated
(Chart 3).
1
On measuring H NMR spectra of the chloroenols 8,
we observed that solutions of 8 in DMSO-d6 were
unstable. Within 24 h at rt the chloroenols 8 eliminated
HCl and were transformed into the corresponding 3-aryl-
cyclobutene-1,2-diones 1412 (method A) (Chart 4). This
finding led to a novel, preparatively simple means of
access to this class of compounds: the chloroenol 8a was
dissolved in DMSO and the solution kept at rt for 24 h
and then poured onto ice. Phenylcyclobutenedione 14a 10
precipitated and was isolated in 41% yield (method B).
In an optimized variant, the solution of a chloroenol 8 in
acetone/water was heated to reflux for 1.5 h. On cooling,
the arylcyclobutenedione 14 crystallized from the reaction
mixture (method C). We assume that the chloroenols 8
exist in a tautomeric equilibrium with the corresponding
3-aryl-4-chlorocyclobutane-1,2-diones 16 in the above
mentioned solvents. In an irreversible reaction HCl is
eliminated from the latter compounds, whereby the
3-aryl-cyclobutenediones 14 are formed14 (Scheme 5).
In agreement with this, heating of the chloroenols 8
in a mixture of acetone-d6/D2O/DCl or acetone-d6/D2O
afforded 4-aryl-cyclobutene-1,2-diones-3-d 15 (Scheme 4,
Chart 5). Incorporation of approximately 1 D/mol in the
1
products 15a -d was indicated by H NMR analyses.
Th er m a l Isom er iza tion of 4-Ar yl-2-h yd r oxy [a n d
2-m eth oxy]-cyclobu ten on es. Liebeskind15 et al. and
Moore16 et al. have investigated the thermally induced
isomerization of 4-aryl [and 4-hetaryl]-4-hydroxycy-
clobutenones and subsequently of 4-aryl-4-substituted-
cyclobutenones17 in depth and have developed this pro-
cess into a valuable method for the preparation of 1,4-
dihydroxynaphthalenes, 1,4-naphthoquinones, and R-
naphthols.18,19 Their work prompted us to investigate,
whether the 4-aryl-2-hydroxycyclobutenones (chloroenols)
8 were also susceptible to this rearrangement. On
heating solutions of the chloroenols 8 in m-xylene to
reflux for 3 h we obtained the 3-chloro-1,2-dihydroxy-
naphthalenes 17a ,20 17b, and 17d -g in moderate to good
yields. 8c constituted an exception, and, under the same
conditions, afforded a brown oil, consisting of several
compounds which were difficult to separate. The genera-
tion of hitherto unknown 3-chloro-1,2-dihydroxyphenan-
threne (17h ) according to this method deserves special
mention. The reactions are illustrated in Scheme 6 and
the results are summarized in Table 2. The thermal
(4) In extension of the patent cited in ref 2j, several recent patents
and papers describe the preparation of a large number of new 3-[4-
(N,N-dialkylamino)phenyl]-4-chloro-3-cyclobutene-1,2-diones as well as
structurally related compounds. For selected references, see: (a)
Nakazumi, H. J apanese Patent 06,184,109; 5 J uly 1994; Mitsubishi
Chem. Ind., J apan. Chem. Abstr. 1995, 122, 132976v. (b) Nakazumi,
H. J apanese Patent 06,184,134; 5 J uly 1994; Mitsubishi Chem. Ind.,
J apan. Chem. Abstr. 1995, 122, 105672m. (c) Nishikata, Y.; Tomono,
T.; Fu, R. J apanese Patent 06,100,511; 12. April 1994; Fuji Xerox Co.,
Ltd., J apan; Chem. Abstr. 1994, 121, 121397k. (d) Chen, H.; Herk-
stroeter, W. G.; Perlstein, J .; Law, K.-Y.; Whitten, D. G. J . Phys. Chem.
1994, 98, 5138. (e) Kitipichai, P.; La Peruta, R.; Korenowski, G. M.;
Wnek, G. E. J . Polymer. Sci., Part A: Polym. Chem. 1993, 31, 1365. (f)
Fu, R. J apanese Patent 04,202,166; 22. J uly 1992; Fuji Xerox Co., Ltd.,
J apan; Chem. Abstr. 1992, 117, 261281k. (g) Fu, R. J apanese Patent
04,202,165; 22 J uly 1992; Fuji Xerox Co., Ltd., J apan; Chem. Abstr.
1992, 117, 261280j. (h) Akasaki, Y.; Tokida, A.; Torigoe, K.; Imai, A.
J apanese Patent 01,146,848; 8 J une. 1989; Fuji Xerox Co., Ltd., J apan;
Chem. Abstr. 1989, 111, 232276h. (i) Akasaki, Y.; Torigoe, K.; Imai,
A.; Tokida, A.; Saeki, S. J apanese Patent 62,249,951; 30 Oct 1987; Fuji
Xerox Co., Ltd., J apan; Chem. Abstr. 1988, 109, 210668u.
(5) Ried, W.; Scha¨fer, D. P. Chem. Ber. 1969, 102, 4193. Presented
here are also mechanistic details on the reactions of 3-chloro-4-
phenylcyclobutene-1,2-dione and 3-phenylcyclobutene-1,2-dione with
arenes under Friedel-Crafts conditions.
(6) (a) Ried, W.; Schmidt, A. H.; Kuhn, W. Chem Ber. 1971, 104,
2622. (b) Ried, W.; Knorr, H.; Kuhn, W.; Weissert, U. Chem Ber. 1975,
108, 1413.
(14) The conversion of 2-(aroyloxy)-4-halogeno-3-aryl-2-cyclobuten-
1-ones IVa into arylcyclobutenediones 14 by treatment with sulfuric
acid (ref a) obviously occurs via IVb and offers early examples of the
“3-halogeno [and 4-halogeno]-2-hydroxy-2-cyclobuten-1-one
f cy-
(7) Schmidt, A. H.; Debo, M.; Wehner, B. Synthesis 1990, 237.
(8) The chloroenols 8 may be characterized by their “oxidation
number” (Bellus, D.; Fischer, H.; Greuter, H.; Martin, P. Helv. Chim.
Acta 1978, 61, 1784.) (ON 5) and may be regarded as derivatives of
the hitherto unknown 1,4-dihydrosemisquaric acid II (ON 5). It must
be pointed out that 1,4-dihydrosemisquaric acid II and semisquaric
acid I (ON 6) posess the same oxidation numbers as hydroquinone (ON
5) and p-benzoquinone (ON 6). One further vinylogous acid having the
ON 5, derives from semisquaric acid: the 1,2-dihydrosemisquaric acid
III. Like II, acid III is also hitherto unknown. However, derivatives
E. g.: Heerding, J . M.; Moore, H. W. J . Org. Chem. 1991, 56, 4048 of
III have already been described.
clobutenedione conversion”, including a halogenocyclobutane-1,2-dione
as an intermediate. (a) Schmidt, A. H. Dissertation, Universita¨t
Frankfurt am Main, 1970. (b) Ref 6a. (c) Schmidt, A. H.; Ried, W.;
Gildemeister, H. Liebigs Ann. Chem. 1976, 705.
(15) For selected references, see: (a) Liebeskind, L. S.; Iyer, S.;
J ewell, C. F., J r. J . Org. Chem. 1986, 51, 3065. (b) Liebeskind, L. S.
Tetrahedron 1989, 45, 3053. (c) Liebeskind, L. S.; Zhang, J . J . Org.
Chem. 1991, 56, 6379. (d) Liebeskind, L. S.; Granberg, K. L.; Zhang,
J . J . Org. Chem. 1991, 57, 4345. (e) Gurski Birchler, A.; Lin, F.;
Liebeskind, L. S. J . Org. Chem. 1994, 59, 7737.
(16) For selected references, see: (a) Perri, S. T.; Foland, L. D.;
Decker, O. H. W.; Moore, H. W. J . Org. Chem. 1986, 51, 3067. (b)
Moore, H. W.; Perri, S. T. J . Org. Chem. 1988, 53, 996. (c) Perri, S. T.;
Rice, P.; Moore, H. W. Org. Synth. 1990, 69, 220. (d) Enhsen, A.;
Karabelas, K. Heerding, J . M.; Moore, H. W. J . Org. Chem. 1990, 55,
1177. (e) Heerding, J . M.; Moore, H. W. J . Org. Chem. 1991, 56, 4048.
(f) Gayo, L. M.; Winters, M. P.; Moore, H. W. J . Org. Chem. 1992, 57,
6896.
(17) (a) Xu, S. L.; Moore, H. W. J . Org. Chem. 1989, 54, 4024. (b)
Xu, S. L. Moore, H. W. J . Org. Chem. 1992, 57, 326.
(18) For an application of this methodology, see: Selwood, D. L.;
J andu, K. S. Heterocycles 1988, 27, 1191.
(19) For a review on the construction of complex organic molecules
by thermally induced ring expansion of 4-hydroxy-2-cyclobuten-1-ones,
see: Moore, H. W.; Yerxa, B. R. Chemtracts: Org. Chem. 1992, 5, 273.
(20) Zincke, Th. Ber. Dtsch. Chem. Ges. 1886, 19, 2493.
(9) We are actively involved at the present time in finding out (a)
conditions, (b) catalysts, and/or (c) substituent patterns of arenes 2
which allow the production of 3-arylcyclobutenediones 14 on a prepara-
tive scale by reacting 7 with 2.
(10) Smutny, E. J .; Caserio, M. C.; Roberts, J . D. J . Am. Chem. Soc.
1960, 82, 1793.
(11) Bellus, D. J . Am. Chem. Soc. 1978, 100, 8026.
(12) For reviews on phenyl- and arylcyclobutenediones and their
derivatives, see: (a) Ried, W.; Schmidt, A. H. Angew. Chem. 1972, 84,
1048. Angew. Chem., Int. Ed. Engl. 1972, 11, 997. (b) Schmidt, A. H.;
Ried, W. Synthesis 1978, 1. (c) Knorr, H.; Ried, W. Synthesis 1978,
649.
(13) For reviews on squaraines, see : (a) Sprenger, H. E.; Ziegenbein,
W. Angew. Chem. 1968, 80, 541. Angew. Chem., Int. Ed. Engl. 1968,
7, 530. (b) Schmidt, A. H. Synthesis 1980, 961. (c) Schmidt, A. H. In
Oxocarbons, West, R., Ed.; Academic Press: New York, 1980; Chapter
10, p 185. (d) Law, K-Y. Chem. Rev. 1993, 93, 449.

Synthesis of 4-Aryl-3-chloro-2-hydroxy-2-cyclobuten-1-ones
J . Org. Chem., Vol. 61, No. 6, 1996 2089
Ta ble 2. Da ta for 3-Ch lor o-1,2-d ih yd r oxyn a p h th a len es
17 a n d 3-Ch lor o-1-h yd r oxy-2-m eth oxyn a p h th a len es 18
Obta in ed by Th er m a l Isom er iza tion of
Sch em e 6
4-Ar yl-3-ch lor o-2-h yd r oxy [a n d
2-m eth oxy]-cyclobu ten -1-on es 8 a n d 11
isomerization described previously could be extended to
4-aryl-2-methoxycyclobutenones 11. To our great satis-
faction, the isomerization of the 3-chloro-2-methoxycy-
clobutenones 11 proceeded even more smoothly than that
of the corresponding 3-chloro-2-hydroxycyclobutenones 8.
We realized furthermore that the 3-chloro-1-hydroxy-
2-methoxynaphthalenes 18a -f were generated in high
purity and with good yields (Scheme 6; Table 2). The
3-chloro-1-hydroxynaphthalenes 18, selectively methoxy-
lated in the 2-position represent a class of naphthalene
derivatives with a novel substitution pattern. Related
work has recently been published by Gurski and Liebe-
skind.21 They have prepared 4-aryl-3-organyl-2-cy-
clobuten-1-ones by the 1,4-addition of organocopper
reagents to monosubstituted cyclobutenediones and rear-
ranged them at 140 °C for 20 h to give 3-organyl-2-(1,3,6-
trioxaheptyl)-1-naphthols.
Con clu sion s
In summary, we have presented the synthesis of easily
accessible 4-aryl-3-chloro-2-hydroxy-2-cyclobuten-1-ones
8. They are distinguished by a unique substitution
pattern and have proved to be versatile synthons for the
preparation of arylcyclobutenediones and their deriva-
tives. Furthermore, we have added a “Friedel-Crafts
approach”, starting with semisquaric chloride (7) and
leading to 4-aryl-2-hydroxycyclobutenones, to the widely
used “aryllithium approach” for the preparation of 4-aryl-
4-hydroxycyclobutenones. The thermal isomerization of
the 4-aryl-2-hydroxycyclobutenones and that of their
methyl ethers affords 1,2-dihydroxy [and 1-hydroxy-2-
methoxy]-naphthalenes, respectively, thus enlarging sub-
stantially the repertoire of naphthalene derivatives
obtainable by the thermal isomerization of 4-arylcy-
clobutenones. The syntheses and the thermal isomer-
izations of 4-substituted-2-hydroxycyclobutenones with
more complex and polynuclear aromatic substituents, as
well as representatives with heterocyclic and nonaro-
matic substituents, are currently under investigation.
Exp er im en ta l Section
Melting points were measured in capillary tubes and are
uncorrected. IR spectra were recorded as solids in KBr pellets.
Mass spectra were determined by electron impact at an
ionizing voltage of 70 eV. 1H NMR spectra were recorded at
400 MHz using TMS and/or CDCl3 as internal standard. 13C
NMR spectra were recorded at 100.6 MHz using CDCl3 or
DMSO-d6 as solvent and as internal standard (δ ) 76.99 and
δ ) 39.50, respectively), unless otherwise stated. Elemental
analyses were performed by the Institute of Chemistry,
University of Mainz. Analytical thin layer chromatography
was performed on precoated sheets of silica gel (silica gel 60,
F 254, layer thickness 0.2 mm; Riedel de Haen, Seelze).
Column chromatography was performed with silica gel (silica
gel 60, 70-230 mesh; Merck, Darmstadt). The abbreviation
“rt” is used for ambient temperature.
Sta r tin g Ma ter ia ls. Semisquaric chloride (7) was obtained
by reacting semisquaric acid22 with phosgene7 or with oxalic
(21) Gurski, A.; Liebeskind, L. S. J . Am. Chem. Soc. 1993, 115, 6101.
(22) (a) Schmidt, A. H.; Maibaum, H. Synthesis 1987, 134. Improved
procedure: (b) Schmidt, A. H.; Ku¨nz, Ch.; Debo, M.; Mora-Ferrer, J .
P. Synthesis 1990, 819.

2090 J . Org. Chem., Vol. 61, No. 6, 1996
Schmidt et al.
dichloride.23 All aromatics 2 were commercially available and
were used as received.
for C10H6Cl2O2: C, 52.44; H, 2.64; Cl, 30.95. Found: C, 51.76;
H, 2.87; Cl, 31.13.
3-Ch lor o-2-h yd r oxy-4-p h en yl-2-cyclobu ten -1-on e (8a )
(Ta ble 1, En tr y 1). Typ ica l P r oced u r e. A solution of
semisquaric chloride (7) (2.32 g, 20 mmol) and benzene (2a )
(1.57 g, 20 mmol) in 1.2-dichloroethane (30 mL) was cooled to
-15 °C with magnetic stirring. AlCl3 (2.92 g, 22 mmol) was
added portionwise over 5 min, and the reaction mixture was
stirred at this temperature for 30 min. The temperature was
then raised to rt, and stirring was continued for further 4.5 h.
During this period the reaction mixture took on a dark brown
color. It was poured onto a mixture of crushed ice (150 g) and
concd HCl (10 mL). The mixture was diluted with ether (100
mL). The organic layer was separated, and the aqueous layer
was extracted with ether (3 × 60 mL). The combined organic
layers were dried over MgSO4. On evaporation in vacuo a solid
remained and was recrystallized to give 8a : white crystals;
mp 147 °C dec (toluene); yield 3.74 g (96%); IR 3080-3020 (s,
br), 1760 (vs), 1620 (s) (OH, CdO, CdC) cm-1; 1H NMR (CDCl3)
δ 4.47 (s, 1H), 7.22-7.44 (m, 5H); 13C NMR (CDCl3) δ 62.04,
127.26, 128.30, 128.88, 134.09, 136.76, 148.43, 185.93; MS m/ z
(relative intensity) 196 (M+, 15), 194 (M+, 45), 159 (34), 131
(100), 102 (85). Anal. Calcd for C10H7ClO2: C, 61.27; H, 3.63;
Cl, 18.26. Found: C, 61.68; H, 3.54; Cl, 18.32.
4-(4-Br om op h en yl)-3-ch lor o-2-h yd r oxy-2-cyclobu ten -
1-on e (8g): white crystals; mp 117-119 °C dec (toluene); yield
2.57 g (47%); IR 3080-3020 (m, br), 1765 (vs), 1625 (s) (OH,
CdO, CdC) cm-1; 1H NMR (CDCl3) δ 4.43 (s, 1H), 7.11 (d, 2H,
J ) 8.4 Hz), 7.48 (d, 2H, J ) 8.4 Hz); 13C NMR (CDCl3) δ 61.41,
122.42, 128.88, 132.07, 133.03, 136.80, 148.55, 185.53; MS m/ z
(relative intensity) 276 (M+, 1), 274 (M+, 5), 272(M+, 4) 194
(100), 182 (99), 180 (93), 165 (93). Anal. Calcd for C10H6-
BrClO2: C, 43.91; H, 2.21; Br, 29.22; Cl, 12.96. Found: C,
43.55; H, 2.24; Br, 29.03; Cl, 12.63.
3-Ch lor o-2-h yd r oxy-4-(4-iod op h en yl)-2-cyclob u t en -1-
on e (8h ): white crystals; mp 127 °C dec (CCl4); yield 5.13 g
(80%); IR 3120-3000 (vs, br), 1770-1730 (vs, br), 1660 (s),
1
1630-1600 (vs, br), 1580 (s) (OH, CdO, CdC) cm-1; H NMR
(CDCl3) δ 4.41 (s, 1H), 6.98 (d, 2H, J ) 8.4 Hz), 7.68 (d, 2H, J
) 8.4 Hz); 13C NMR (CDCl3) δ 61.62, 93.92, 129.13, 133.81,
136.30, 138.03, 148.69, 185.35; MS m/ z (relative intensity) 322
(M+, >1), 320 (M+, 2), 228(74) 193 (61), 165 (20), 101 (100).
Anal. Calcd for C10H6IClO2: C, 37.47; H, 1.89; Cl, 11.06; I,
39.59. Found: C, 38.36; H, 1.76; Cl, 11.96; I, 39.51.
3-Ch lor o-4-(2,4-d im et h ylp h en yl)-2-h yd r oxy-2-cyclo-
bu ten -1-on e (8i): white crystals; mp 137-138 °C dec (tolu-
ene); yield 2.98 g (67%); IR 3200 (vs, br), 1755 (vs), 1670 (s)
3-Ch lor o-2-h yd r oxy-4-a r yl-2-cyclob u t en -1-on es 8b -q
were similarily prepared on a 20 mmol scale. Yields and
physical, spectroscopic, and analytical data for the compounds
are reported as follows.
1
(OH, CdO, CdC) cm-1; H NMR (CDCl3) δ 2.31 (s, 3H), 2.37
(s, 3H), 4.74 (s, 1H), 7.00-7.08 (m, 3H), 8.93 (s, 1H, OH); 13C
NMR (CDCl3) δ 19.44, 21.04, 58.57, 125.82, 126.90, 129.35,
131.60, 136.98,137.71, 137.81, 148.12, 187.96; MS m/ z (rela-
tive intensity) 224 (M+, 33), 222 (M+, 99), 187 (54), 159 (90),
115 (100). Anal. Calcd for C12H11ClO2: C, 64.73; H, 4.98; Cl,
15.92. Found: C, 64.33; H, 4.95; Cl, 16.14.
3-Ch lor o-2-h yd r oxy-4-(p-tolyl)-2-cyclobu ten -1-on e (8b):
white crystals; mp 117-118 °C dec (toluene); yield 3.30 g
(79%); IR 3160-3140 (s, br), 1740 (vs), 1660 (m) (OH, CdO,
CdC) cm-1; 1H NMR (CDCl3) δ 2.35 (s, 3H), 4.45 (s, 1H), 7.15
(d, 2H, J ) 8.1 Hz), 7.19 (d, 2H, J ) 8.1 Hz); 13C NMR (CDCl3)
δ 21.18, 61.56, 127.24, 129.64, 130.87, 138.04, 138.27, 148.44,
187.31; MS m/ z (relative intensity) 210 (M+, 14), 208 (M+, 45),
173 (27), 145 (58), 115 (100). Anal. Calcd for C11H9ClO2: C,
63.32; H, 4.35; Cl, 17.00. Found: C, 62.41; H, 4.46; Cl, 17.21.
3-Ch lor o-2-h ydr oxy-4-(4-isopr opylph en yl)-2-cyclobu ten -
1-on e (8c): white crystals; mp 88-91 °C dec (toluene); yield
3.65 g (77%); IR 3060-3020 (m, br), 1770 (vs), 1630 (s) (OH,
CdO, CdC) cm-1; 1H NMR (CDCl3) δ 1.22 (d, 6H, J ) 6.9 Hz),
2.85-2.91 (m, 1H), 4.44 (s, 1H), 7.16 (d, 2H, J ) 8.2 Hz), 7.21
(d, 2H, J ) 8.2 Hz); 13C NMR (CDCl3) δ 23.86, 33.83, 61.70,
126.95, 127.19, 131.33, 137.09, 148.35, 149.07, 186.54; MS m/ z
(relative intensity) 238 (M+, 0.2), 236 (M+, 0.6), 194 (100), 129
(75). Anal. Calcd for C13H13ClO2: C, 65.97; H, 5.54; Cl, 14.98.
Found: C, 65.52; H, 5.41; Cl, 15.21.
3-Ch lor o-4-(2,5-d im et h ylp h en yl)-2-h yd r oxy-2-cyclo-
bu ten -1-on e (8j): white crystals; mp 138 °C dec (toluene);
yield 4.23 g (95%); IR 3160-3160 (vs, br), 1755-1735 (vs,br),
1
1670 (vs) (OH, CdO, CdC) cm-1; H NMR (CDCl3) δ 2.30 (s,
3H), 2.37 (s, 3H), 4.75 (s, 1H), 6.98(s, 1H), 7.03 (d, 1H, J )
8.0Hz), 7.10 (d, 1H, J ) 8.0 Hz), 8.99 (s, 1H, OH); 13C NMR
(CDCl3) δ 18.97, 20.99, 58.73, 126.43, 128.68, 130.59, 132.03,
133.91, 135.72, 137.56, 148.09, 187.67; MS m/ z (relative
intensity) 224 (M+, 32), 222 (M+, 94), 207 (52), 187 (58), 159
(76), 115 (100). Anal. Calcd for C12H11ClO2: C, 64.73; H, 4.98;
Cl, 15.92. Found: C, 64.28; H, 4.78; Cl, 16.50.
4-(3,4-Dim eth oxyp h en yl)-3-ch lor o-2-h yd r oxy-2-cyclo-
bu ten -1-on e (8k ): white crystals; mp 111 °C dec (CCl4); yield
4.53 g (89%); IR 3130-3100 (vs, br), 1760-1740 (vs,br), 1660
(s) (OH, C)O, CdC) cm-1 1H NMR (CDCl3) δ 3.83 (s, 3H),
;
4-(4-ter t-Bu tylph en yl)-3-ch lor o-2-h ydr oxy-2-cyclobu ten -
1-on e (8d ): white crystals; mp 149-151 °C dec (CCl4); yield
3.51 g (70%); IR 3230-3180 (s, br), 1760 (vs), 1665 (s) (OH,
CdO, CdC) cm-1; 1H NMR (CDCl3) δ 1.30 (s, 9H), 4.45 (s, 1H),
7.17 (d, 2H, J ) 8.3 Hz), 7.38 (d, 2H, J ) 8.4 Hz); 13C NMR
(CDCl3) δ 31.30, 34.61, 61.53, 125.86, 126.97, 130.93, 137.50,
148.37, 151.41, 186.89; MS m/ z (relative intensity) 252 (M+,
0.2), 250 (M+, 0.7), 194 (46), 143 (39), 57 (100). Anal. Calcd
for C14H15ClO2: C, 67.07; H, 6.03; Cl, 14.14. Found: C, 66.82;
H, 6.00; Cl, 14.58.
3.84 (s, 3H), 4.39 (s, 1H), 6.70 (d, 1H, J ) 1.6Hz), 6.78 (dd,
1H, J ) 8.2 Hz, J ) 1.6 Hz), 6.83 (d, 1H, J ) 8.2 Hz); 13C
NMR (CDCl3) δ 56.02, 61.61, 110.51, 111.72, 119.74, 126.62,
137.35, 148.57, 149.14, 149.37, 186.63; MS m/ z (relative
intensity) 256 (M+, 32), 254 (M+, 100), 219 (44), 191 (70), 162
(84). Anal. Calcd for C12H11ClO4: C, 56.60; H, 4.35; Cl, 13.92.
Found: C, 56.53; H, 4.37; Cl, 14.50.
3-Ch lor o-4-(2,5-d ich lor op h e n yl)-2-h yd r oxy-2-cyclo-
bu ten -1-on e (8m ): white crystals; mp 134-136 °C dec (tolu-
ene); yield 4.74 g (90%); IR 3160-3140 (s, br), 1755 (vs), 1665
(s) (OH, CdO, CdC) cm-1 1H NMR (CDCl3) δ 5.01 (s, 1H),
;
3-Ch lor o-2-h ydr oxy-4-(4-m eth oxyph en yl)-2-cyclobu ten -
1-on e (8e): white crystals; mp 111 °C dec (CCl4); yield 2.12 g
(47%); IR 3160-3140 (m, br), 1760 (vs), 1660 (m) (OH, CdO,
CdC) cm-1; 1H NMR (CDCl3) δ 3.78 (s, 3H), 4.42 (s, 1H), 6.89
(d, 2H, J ) 8.7 Hz), 7.15 (d, 2H, J ) 8.7 Hz); 13C NMR (CDCl3)
δ 55.31, 61.38, 114.42, 126.05, 128.40, 137.41, 148.30, 159.72,
186.64; MS m/ z (relative intensity) 226 (M+, 13), 224 (M+, 38),
188 (30), 161 (46), 132 (100). Anal. Calcd for C11H9ClO3: C,
58.66; H, 4.03; Cl, 15.74. Found: C, 58.57; H, 4.14; Cl, 15.49.
3-Ch lor o-4-(4-clor op h en yl)-2-h yd r oxy-2-cyclobu ten -1-
on e (8f): white crystals; mp 109-111 °C dec (toluene); yield
4.12 g (90%); IR 3080-3040 (s, br), 1760, 1750 (vs), 1620 (vs)
7.18 (d, 1H, J ) 2.4 Hz), 7.22 (dd, 1H, J ) 8.5 Hz, J ) 2.4 Hz),
7.33 (d, 1H, J ) 8.5 Hz); 13C NMR (CDCl3) δ 58.89, 127.68,
129.51, 131.13, 132.72, 133.22, 133.69, 135.89, 148.93, 184.54;
MS m/ z (relative intensity) 264 (M+, 1), 262 (M+, 2), 227 (100),
170 (49), 135 (52). Anal. Calcd for C10H5Cl3O2: C, 45.58; H,
1.91; Cl, 40.36. Found: C, 45.38; H, 2.00; Cl, 40.38.
3-Ch lor o-2-h yd r oxy-4-(2,3,4-t r im e t h ylp h e n yl)-2-cy-
clobu ten -1-on e (8n ): white crystals; mp 148-149 °C dec
(CCl4); yield 2.13 g (45%); IR 3240 (vs, br), 1760 (vs), 1670 (s)
1
(OH, CdO, CdC) cm-1; H NMR (CDCl3) δ 2.19 (s, 3H), 2.26
(s, 3H), 2.29 (s, 3H), 4.81 (s, 1H), 6.94 (d, 1H, J ) 7.9 Hz),
6.99 (d, 1H, J ) 7.9 Hz); 13C NMR (CDCl3) δ15.71, 20.86, 30.92,
59.36, 122.98, 127.41, 130.21, 135.40, 135.92, 136.35, 136.94,
148.12, 187.24; MS m/ z (relative intensity) 238 (M+, 29), 236
(M+, 88), 221 (100), 173 (54), 144 (62), 129 (88). Anal. Calcd
for C13H13ClO2: C, 65.97; H, 5.54; Cl, 14.98. Found: C, 65.50;
H, 5.37; Cl, 15.38.
1
(OH, CdO, CdC) cm-1; H NMR (CDCl3) δ 4.44 (s, 1H), 7.17
(dd, 2H, J ) 8.5 Hz, J ) 1.9 Hz), 7.32 (dd, 2H, J ) 8.5 Hz, J
) 1.9 Hz); 13C NMR (CDCl3) δ 61.31, 128.58, 129.12, 132.52,
134.34, 136.89, 148.61, 185.87; MS m/ z (relative intensity) 230
(M+, 3), 228 (M+, 4), 193 (60), 165 (63), 136 (100). Anal. Calcd
3-Ch lor o-2-h yd r oxy-4-m esityl-2-cyclobu ten -1-on e (8o):
white crystals; mp 140 °C dec (toluene); yield 3.27 g (69%); IR
(23) Schmidt, A. H.; Ku¨nz, Ch.; Malmbak, M.; Zylla, J . Synthesis
1994, 422.

Synthesis of 4-Aryl-3-chloro-2-hydroxy-2-cyclobuten-1-ones
J . Org. Chem., Vol. 61, No. 6, 1996 2091
3200-3140 (vs, br), 1750-1730 (vs,br), 1660 (s), 1600 (m) (OH,
CdO, CdC) cm-1; 1H NMR (CDCl3) δ 2.25 (s, 3H), 2.30 (s, 6H),
4.94 (s, 1H), 6.83 (s, 2H); 13C NMR (CDCl3) δ20.79, 20.91,
58.15, 126.04, 130.46, 137.73, 137.96, 139.21, 147.52, 189.59;
MS m/ z (relative intensity) 238 (M+, 20), 236 (M+, 60), 221
diazomethane (11.5 mmol) in diethyl ether was added over 5
min, and stirring was continued for further 30 min. Then the
solution was carefully evaporated. The remaining yellow oil
was submitted to column chromatography, using dichlo-
romethane as the eluent. Exceptionally, 11h crystallized after
removal of the diethyl ether.
(100), 201 (90), 173 (42), 129 (42). Anal. Calcd for C13H13
-
ClO2: C, 65.97; H, 5.54; Cl, 14.98. Found: C, 66.16; H, 5.45;
Cl, 14.25.
3-Ch lor o-2-m eth oxy-4-ph en yl-2-cyclobu ten -1-on e (11a):
white crystals; mp 36 °C (n-hexane); yield 1.54 g (74%); IR
1
; H NMR (CDCl3) δ
3-Ch lor o-2-h yd r oxy-4-(2,3,4,5-tetr a m eth ylp h en yl)-2-cy-
clobu ten -1-on e (8p ): white crystals; mp 135 °C dec (toluene);
yield 4.66 g (93%); IR 3250 (vs, br), 1770 (vs), 1675 (s) (OH,
CdO, CdC) cm-1; 1H NMR (CDCl3) δ 2.17 (s, 3H), 2.21 (s, 3H),
2.24 (s, 3H), 2.28 (s, 3H), 4.81 (s, 1H), 6.82 (s, 1H); 13C NMR
(CDCl3) δ15.76, 16.10, 16.37, 20.81, 59.31, 124.73, 129.30,
132.84, 133.82, 134.94, 135.90, 137.16, 147.89, 187.31; MS m/ z
(relative intensity) 252 (M+, 11), 250 (M+, 33), 235 (100), 207
(36), 158 (23), 143 (30). Anal. Calcd for C14H15ClO2: C, 67.07;
H, 6.03; Cl, 14.14. Found: C, 66.07; H, 5.72; Cl, 14.30.
3-Ch lor o-2-h yd r oxy-4-(n a p h th a len -1-yl)-2-cyclobu ten -
1-on e (8q): white crystals; mp 153-156 °C dec (toluene); yield
4.16 g (85%); IR 3140 (s, br), 1745 (vs), 1655 (s) (OH, CdO,
CdC) cm-1; 1H NMR (CDCl3) δ 5.31 (s, 1H), 7.40-7.58 (m, 4H),
7.80 (d, 1H, J ) 7.8 Hz), 7.86 (d, 1H, J ) 7.8 Hz), 8.11 (d, 1H,
J ) 8.3 Hz); 13C NMR (CDCl3) δ 58.55, 123.31, 123.68, 125.27,
126.14, 126.58, 128.58, 128.66, 130.73, 132.11, 133.84, 136.50,
147.95, 186.27; MS m/ z (relative intensity) 246 (M+, 7), 244
(M+, 22), 181 (22), 152 (100). Anal. Calcd for C14H9ClO2: C,
68.73; H, 3.71; Cl, 14.50. Found: C, 68.13; H, 3.93; Cl, 15.40.
R ea ct ion of Sem isq u a r ic Ch lor id e (7) w it h 1,4-Di-
m et h oxyb en zen e (2l) in Dich lor om et h a n e a t R eflu x
Tem p er a tu r e. To a solution of semisquaric chloride (7) (2.00
g, 17 mmol) and 1,4-dimethoxybenzene (2l) (4.75 g, 34 mmol)
in dichloromethane (50 mL) was added AlCl3 (4.53 g, 34 mmol)
in portions with stirring. The reaction mixture was heated to
reflux for 1 h. During this period the color changed from
yellow to dark violet. The reaction mixture was poured onto
crushed ice (100 g) and the yellow solid which precipitated was
collected by filtration. The filtrate was transferred to a
separatory funnel and extracted with CH2Cl2 (3 × 50 mL). The
organic layers were combined, dried (MgSO4), and evaporated
to dryness, leaving yellow crystals. The crystal fractions were
combined and triturated with boiling ether (100 mL). The
yellow crystals left behind were treated with boiling acetone.
The major part went into solution and crystallized on cooling
to give 3-(2,5-dimethoxyphenyl)-3-cyclobutene-1,2-dione (9a ):
yellow crystals; mp 195-197 °C (acetone); yield 1.03 g (27%);
IR 3100 (w), 2960 (w), 2920 (w), 2820 (w), 1760 (s), 1610 (w),
1540 (m), 1490 (m), 1270 (m), 1250 (m) (C-H, CdO, CdC, C-O-
C) cm-1; MS m/ z (relative intensity) 218 (M+, 80), 162 (100),
147 (71). Anal. Calcd for C12H10O4: C, 66.05; H, 4.62.
Found: C, 65.85; H, 4.48.
The acetone-insoluble residue from above was recrystallized
from 1-propanol to give 3,4-bis(2,5-dimethoxyphenyl)-3-cy-
clobutene-1,2-dione (10a ): yellow crystals; mp 228-230 °C (1-
propanol); yield 0.48 g (8%); IR 3000 (w), 2960 (w), 2920 (w),
2830 (w), 1775 (s), 1755 (s), 1620 (m), 1500 (m), 1480 (m), 1460
(m) (CsH, CdO, CdC) cm-1. Anal. Calcd for C20H18O6: C,
67.79; H, 5.12. Found: C, 67.82; H, 5.11.
3-(2,4,5-Tr im et h oxyp h en yl)-3-cyclob u t en e-1,2-d ion e
(9b). A solution of semisquaric chloride (7) (1.16 g, 10 mmol),
1,2,4-trimethoxybenzene (2r ) (1.68 g, 10 mmol), and trifluo-
roacetic acid (1 mL) in dichloromethane was stirred at rt for
24 h. During this period the reaction mixture took on a dark
green color. The reaction mixture was evaporated in vacuo
and the remaining residue triturated with hexane (2 × 20 mL).
The crystals obtained were recrystallized from acetone with
the aid of charcoal to give 9b: yellow crystals; mp 226-228
°C (acetone); yield 0.52 g (21%); IR 3095 (w), 2980 (w), 2930
(w), 2830 (w), 1765 (s, br), 1610 (m), 1540 (s), 1520 (s), 1450
(m), 1250 (m), 1220 (m) (CsH, CdO, CdC, CsOsC) cm-1; MS
m/ z (relative intensity) 248 (M+, 49), 192 (100), 177 (45), 149
(19). Anal. Calcd for C13H12O5: C, 62.90; H, 4.87. Found: C,
62.65; H, 4.87.
1760 (vs, br), 1635 (s) (CdO, CdC) cm-1
4.08 (s, 3H), 4.41 (s, 1H), 7.24-7.38 (m, 5H); 13C NMR (CDCl3)
δ 58.49, 62.28, 127.29, 128.18, 128.88, 134.36, 134.95, 150.01,
183.15; MS m/ z (relative intensity) 210 (M+, 2), 208 (M+, 7),
165 (22), 137 (31), 102 (100). Anal. Calcd for C11H9ClO2: C,
63.32; H, 4.35; Cl, 16.99. Found: C, 63.11; H, 4.29; Cl, 17.18.
3-Ch lor o-2-m eth oxy-4-(p-tolyl)-2-cyclobu ten -1-on e (11b):
white crystals; mp 43-44 °C (n-hexane); yield 1.54 g (69%);
1
IR 1780-1750 (vs, br), 1630 (s) (CdO, CdC) cm-1; H NMR
(CDCl3) δ 2.33 (s, 3H), 4.08 (s, 3H), 4.38 (s, 1H), 7.14 (d, 2H,
J ) 8.4 Hz), 7.17 (d, 2H, J ) 8.4 Hz); 13C NMR (CDCl3) δ 21.12,
58.41, 62.96, 127.13, 129.53, 131.22, 135.15, 137.94, 149.87,
183.34; MS m/ z (relative intensity) 224 (M+, 13), 222 (M+, 40),
207 (42), 179 (49), 115 (100). Anal. Calcd for C12H11ClO2: C,
64.73; H, 4.98; Cl, 15.92. Found: C, 64.69; H, 5.00; Cl, 16.01.
4-(4-ter t-Bu tylph en yl)-3-ch lor o-2-m eth oxy-2-cyclobu ten -
1-on e (11c): white crystals; mp 56-57 °C (n-hexane); yield
1
1.61 g (61%); IR 1755 (vs, br), 1635 (s) (CdO, CdC) cm-1; H
NMR (CDCl3) δ 1.30 (s, 9H), 4.08 (s, 3H), 4.39 (s, 1H), 7.19 (d,
2H, J ) 8.3 Hz), 7.38 (d, 2H, J ) 8.3 Hz); 13C NMR (CDCl3) δ
31.28, 34.55, 58.40, 61.83, 125.75, 126.87, 131.20, 135.09,
149.81, 151.11, 183.36; MS m/ z (relative intensity) 266 (M+,
1), 264 (M+, 4), 208 (97), 193 (47), 115 (26), 57 (100). Anal.
Calcd for C15H17ClO2: C, 68.01; H, 6.47; Cl, 13.39. Found: C,
67.90; H, 6.42; Cl, 13.53.
3-Ch lor o-2-m eth oxy-4-(4-m eth oxyph en yl)-2-cyclobu ten -
1-on e (11d ): white crystals; mp 48-50 °C (n-hexane); yield
1.43 g (60%); IR 1770-1740 (vs, br), 1630 (s), 1605 (m) (CdO,
CdC) cm-1; 1H NMR (CDCl3) δ 3.77 (s, 3H), 4.07 (s, 3H), 4.35
(s, 1H), 6.88 (d, 2H, J ) 8.7 Hz), 7.16 (d, 2H, J ) 8.7 Hz); 13
C
NMR (CDCl3) δ 55.29, 58.40, 61.59, 114.35, 126.24, 128.38,
135.37, 149.80, 159.63, 183.60; MS m/ z (relative intensity) 240
(M+, 33), 238 (M+, 98), 223 (61), 195 (100), 175 (70), 132 (96).
Anal. Calcd for C12H11ClO3: C, 60.39; H, 4.65; Cl, 14.85.
Found: C, 60.45; H, 4.60; Cl, 14.84.
3-Ch lor o-4-(4-ch lor op h en yl)-2-m eth oxy-2-cyclobu ten -
1-on e (11e): white crystals; mp 39-41 °C (n-hexane); yield
1.80 g (74%); IR 1755 (vs), 1650 (s) (CdO, CdC) cm-1; 1H NMR
(CDCl3) δ 4.05 (s, 3H), 4.37 (s, 1H), 7.17 (d, 2H, J ) 8.5 Hz),
7.31 (d, 2H, J ) 8.5 Hz); 13C NMR (CDCl3) δ 58.37, 61.49,
128.48, 128.91, 132.79, 133.91, 134.31, 150.01, 182.25; MS m/ z
(relative intensity) 246 (M+, 1), 244 (M+, 9), 242 (M+, 14), 207
(58), 199 (48), 171 (51), 136 (100). Anal. Calcd for C11H8-
Cl2O2: C, 54.35; H, 3.32; Cl, 29.17. Found: C, 54.34; H, 3.36;
Cl, 29.20.
3-Ch lor o-4-(4-iod op h en yl)-2-m eth oxy-2-cyclobu ten -1-
on e (11f): white crystals; mp 59-61 °C (n-hexane); yield 2.61
g (78%); IR 1760 (vs, br), 1630 (s) (CdO, CdC) cm-1; 1H NMR
(CDCl3) δ 4.06 (s, 3H), 4.34 (s, 1H), 6.99 (d, 2H, J ) 8.3 Hz),
7.67 (d, 2H, J ) 8.3Hz); 13C NMR (CDCl3) δ 58.56, 61.86, 93.71,
129.16, 134.15, 134.38, 138.00, 150.24, 182.20; MS m/ z (rela-
tive intensity) 336 (M+, 2), 334 (M+, 6), 207 (78), 164 (100),
136 (39), 101 (61). Anal. Calcd for C11H8ClIO2: C, 39.49; H,
2.41; Cl, 10.60; I, 37.93. Found: C, 40.04; H, 2.55; Cl, 10.77;
I, 37.46.
3-Ch lor o-4-(2,5-d im e t h oxyp h e n yl)-2-m e t h oxy-2-cy-
clobu ten -1-on e (11g): white crystals; mp 59-61 °C (n-
hexane); yield 1.88 g (70%); IR 1755 (vs, br), 1640 (s), 1605
1
(m) (CdO, CdC) cm-1; H NMR (CDCl3) δ 3.73 (s, 3H), 3.76
(s, 3H), 4.05 (s, 3H), 4.81 (s, 1H), 6.70 (d, 1H, J ) 2.9 Hz),
6.76 (dd, 1H, J ) 8.9 Hz, J ) 2.9 Hz), 6.81 (d, 1H, J ) 8.9 Hz);
13C NMR (CDCl3) δ 55.71, 56.55, 56.91, 58.32, 112.55, 113.33,
114.03, 123.89, 134.60, 149.66, 152.60, 153.78, 183.48; MS m/ z
(relative intensity) 270 (M+, 22), 238 (M+, 80), 249 (76), 210
(100), 191 (46), 121 (56). Anal. Calcd for C13H13ClO4: C, 58.11;
H, 4.88; Cl, 13.19. Found: C, 58.06; H, 4.79; Cl, 13.25.
3-C h lo r o -4-(2,5-d ic h lo r o p h e n y l)-2-m e t h o x y -2-c y -
clobu ten -1-on e (11h ): white crystals; mp 96-97 °C (EtOAc);
Gen er ation of 4-Ar yl-3-ch lor o-2-m eth oxy-2-cyclobu ten -
1-on es (Ch lor oen ol Meth yl Eth er s) 11. Gen er a l P r oce-
d u r e. The solution of a chloroenol 8 (10 mmol) in diethyl ether
(100 mL) was cooled to -15 °C. With stirring, a solution of
yield 2.39 g (86%); IR 1770 (vs, br), 1635 (s) (CdO, CdC) cm-1
;

2092 J . Org. Chem., Vol. 61, No. 6, 1996
Schmidt et al.
1H NMR (CDCl3) δ 4.08 (s, 3H), 4.93 (s, 1H), 7.17-7.31 (m,
3H); 13C NMR (CDCl3) δ 58.54, 59.15, 127.53, 129.22, 131.03,
132.71, 133.03, 133.29, 134.01, 150.46, 180.95; MS m/ z (rela-
tive intensity) 278 (M+, 3), 276 (M+, 3), 241 (81), 205 (47), 170
(100), 99 (44). Anal. Calcd for C11H7Cl3O2: C, 47.61; H, 2.54;
Cl, 38.32. Found: C, 47.69; H, 2.63; Cl, 38.05.
3-Ch lor o-4-(2,5-d im eth ylp h en yl)-3-cyclobu ten e-1,2-d i-
on e (12f): yellow crystals; mp 64 °C (i-Pr2O); yield 1.24 g
(56%); IR 1790-1775 (vs), 1560 (w) (CdO, CdC) cm-1; 1H NMR
(CDCl3) δ 2.36 (s, 3H), 2.46 (s, 3H), 7.24 (d, 1H, J ) 7.9 Hz),
7.29 (d, 1H, J ) 7.9 Hz), 7.49 (s, 1H); 13C NMR (CDCl3) δ 20.64,
20.85, 125.79, 128.87, 131.60, 134.30, 135.64, 135.88, 182.68,
191.51, 193.52, 195.50; MS m/ z (relative intensity) 222 (M+,
23), 220 (M+, 69), 164 (100), 157 (49), 129 (95). Anal. Calcd
for C12H9ClO2: C, 65.32; H, 4.11; Cl, 16.07. Found: C, 64.98;
H, 4.46; Cl, 16.16.
3-Ch lor o-4-(2-ch lor o-4,5-d im et h oxyp h en yl)-3-cyclo-
bu ten e-1,2-d ion e (12g): obtained from the chlorination of 8k ;
yellow crystals; mp 128 °C (CCl4/n-hexane); yield 2.12 g (74%);
IR 1810 (s), 1785-1755 (vs,br), 1585 (s) (CdO, CdC) cm-1; 1H
NMR (CDCl3) δ 3.91 (s, 3H), 3.95 (s, 3H), 7.01 (s, 1H), 7.38 (s,
1H); 13C NMR (CDCl3) δ 56.39, 56.51, 111.74, 113.74, 117.80,
127.67, 148.02, 154.02, 181.74, 190.22, 191.55, 193.20; MS m/ z
(relative intensity) 290 (M+, 4), 288 (M+, 28), 286 (M+, 43),
230 (100), 152 (21). Anal. Calcd for C12H8Cl2O4: C, 50.20; H,
2.81; Cl, 24.70. Found: C, 50.20; H, 3.14; Cl, 24.26.
Gen er a tion of 3-Ar yl-4-m eth oxy-3-cyclobu ten e-1,2-d i-
on es 13. Gen er a l P r oced u r e. To the solution of a chloroenol
8 (5 mmol) in MeOH (25 mL) was added bromine 0.80 g (5
mmol). When the reaction mixture was shaken vigorously the
product started to precipitate from the solution. After 5 min
of shaking the suspension was cooled to -15 °C. The precipi-
tate was collected by filtration.
3-Meth oxy-4-p h en yl-3-cyclobu ten e-1,2-d ion e (13a ): yel-
low crystals; mp 148-150 °C (MeOH), (lit.10 mp 151-152 °C);
yield 1.05 g (56%); IR 1780-1770 (vs, br), 1740-1720 (vs, br),
1590-1570 (vs, br) (CdO, CdC) cm-1; 1H NMR (CDCl3) δ 4.56
(s, 3H), 7.44-7.50 (m, 3H), 7.97-8.00 (m, 2H); 13C NMR
(CDCl3) δ 61.71, 127.61, 127.74, 129.10, 132.74, 173.73, 192.33,
192.70, 194.84; MS m/ z (relative intensity) 188 (M+, 24), 145
(48), 132 (29), 117 (35), 89 (100). Anal. Calcd for C11H8O3:
C, 70.21; H, 4.29. Found: C, 69.88; H, 4.38.
3-Ch lor o-2-m et h oxy-4-(2,3,4,5-t et r a m et h ylp h en yl)-2-
cyclobu ten -1-on e (11i): white crystals; mp 81 °C (n-hexane);
yield 0.93 g (35%); IR 1750 (vs), 1645 (m), (CdO, CdC) cm-1
;
1H NMR (CDCl3) δ 2.18 (s, 3H), 2.22 (s, 3H), 2.26 (s, 3H), 2.30
(s, 3H), 4.08 (s, 3H), 4.77 (s, 1H), 6.85 (s, 1H); 13C NMR (CDCl3)
δ 15.74, 16.07, 16.35, 20.82, 58.35, 59.52, 124.57, 129.50,
132.87, 133.67, 134.70, 135.21, 135.81, 149,37 184.16; MS m/ z
(relative intensity) 266 (M+, 23), 264 (M+, 68), 249 (100), 221
(40), 201 (32), 143 (47). Anal. Calcd for C15H17ClO4: C, 68.05;
H, 6.47; Cl, 13.39. Found: C, 68.06; H, 6.41; Cl, 13.25.
3-Ch lor o-2-m eth oxy-4-(n a p h th a len -1-yl)-2-cyclobu ten -
1-on e (11j): white crystals; mp 82-83 °C (n-hexane); yield 1.37
g (53%); IR 1750 (vs), 1640 (s) (CdO, CdC) cm-1 1H NMR
;
(CDCl3) δ 4.10 (s, 3H), 5.26 (s, 1H), 7.44-7.59 (m, 4H), 7.79-
7.87 (m, 2H), 8.15 (d, 1H, J ) 8.1 Hz); 13C NMR (CDCl3) δ
58.49, 58.78, 123.48, 125.26, 126.09, 126.52, 128.40, 128.61,
131.08, 132.21, 133.85, 134.29, 149.51, 183.09; MS m/ z (rela-
tive intensity) 260 (M+, 4), 258 (M+, 12), 242 (58), 214 (47),
152 (100). Anal. Calcd for C15H11ClO2: C, 69.64; H, 4.29; Cl,
13.70. Found: C, 69.31; H, 4.30; Cl, 13.60.
Gen er a t ion of 4-Ar yl-3-ch lor o-2-cyclob u t en e-1,2-d i-
on es. Gen er a l P r oced u r e. Chlorine was introduced into a
magnetically stirred suspension of a chloroenol 8 (10 mmol)
in tetrachloromethane (100 mL). After ca. 15 min the suspen-
sion had turned into a clear orange solution. This solution
was heated to reflux for 30 min, and the solvent then was
removed in vacuo, leaving a solid behind.
3-Ch lor o-4-p h en yl-3-cyclobu ten e-1,2-d ion e (12a ): yel-
low crystals; mp 113-114 °C (CCl4/n-hexane), (lit.10 mp 114-
115 °C); yield 1.52 g (79%). Anal Calcd for C10H5ClO2: C,
62.36; H, 2.62; Cl, 18.41. Found: C, 62.19; H, 2.71; Cl, 18.19.
3-Meth oxy-4-(p-tolyl)-3-cyclobu ten e-1,2-dion e (13b): yel-
low crystals; mp 160 °C (MeOH); yield 1.42 g (70%); IR 1780,
3-Ch lor o-4-(p-tolyl)-3-cyclobu ten e-1,2-d ion e (12b): yel-
low crystals; mp 136-137 °C (CCl4/n-hexane); yield 1.03 g
(50%); IR 1800 (s), 1780-1760 (vs, br), 1600 (m) (CdO, CdC)
1780-1730 (vs, br), 1590 (vs) (CdO, CdC) cm-1 1H NMR
;
(CDCl3) δ 2.37 (s, 3H), 4.53 (s, 3H), 7.24 (d, 2H, J ) 7.9 Hz),
7.85 (d, 2H, J ) 8.1 Hz); 13C NMR (CDCl3) δ 21.90, 61.58,
124.96, 127.77, 129.84, 143.86, 173.76, 192.04, 192.91, 194.29;
MS m/ z (relative intensity) 202 (M+, 40) 159 (44), 146 (67),
131 (81), 103 (100). Anal. Calcd for C12H10O3: C, 71.28; H,
4.98. Found: C, 71.06; H, 4.97.
cm-1 1H NMR (CDCl3) δ 2.44 (s, 3H), 7.35 (d, 2H, J ) 8.0
;
Hz), 8.08 (d, 2H, J ) 8.2 Hz); 13C NMR (CDCl3) δ 22.19, 124.19,
128.94, 130.35, 146.79, 179.05, 188.80, 190.77, 194.52; MS m/ z
(relative intensity) 208 (M+, 7), 206 (M+, 23), 150 (91), 143
(51), 115 (100). Anal. Calcd for C11H7ClO2: C, 63.94; H, 3.41;
Cl, 17.16. Found: C, 63.94; H, 3.66; Cl, 16.74.
4-(4-Ch lor op h en yl)-3-m et h oxy-3-cyclob u t en e-1,2-d i-
on e (13c): yellow crystals; mp 129-130 °C (MeOH); yield 1.14
g (51%); IR 1780, 1750-1730 (vs, br), 1580 (vs, br) (CdO, CdC)
4-(4-ter t-Bu t ylp h en yl)-3-ch lor o-3-cyclob u t en e-1,2-d i-
on e (12c): yellow crystals; mp 92-93 °C (i-Pr2O); yield 1.94 g
(78%); IR 1800 (s), 1760-1720 (vs, br), 1610 (m) (CdO, CdC)
cm-1 1H NMR (CDCl3) δ 4.57 (s, 3H), 7.44 (d, 2H, J ) 8.5
;
Hz), 7.92 (d, 2H, J ) 8.5 Hz); 13C NMR (CDCl3) δ 61.87, 125.95,
128.86, 129.55, 138.97, 172.20, 192.00, 192.28, 194.79; MS m/ z
(relative intensity) 224 (M+, 10), 222 (M+, 30) 166 (59), 152
(67), 123 (100). Anal. Calcd for C11H7ClO3: C, 59.35; H, 3.17;
Cl, 15.92. Found: C, 59.19; H, 3.04; Cl, 16.04.
1
cm-1; H NMR (CDCl3) δ 1.34 (s, 9H), 7.59 (dd, 2H, J ) 6.7
Hz, J ) 1.9 Hz), 8.17 (dd, 2H, J ) 6.7 Hz, J ) 1.9 Hz); 13C
NMR (CDCl3) δ 30.84, 35.55, 124.07, 126.54, 128.83, 159.51,
179.16, 188.82, 190.78, 194.45; MS m/ z (relative intensity) 250
(M+, 3), 248 (M+, 9), 192 (58), 177 (100). Anal. Calcd for
C14H13ClO2: C, 67.61; H, 5.27; Cl, 14.25. Found: C, 67.21; H,
5.19; Cl, 14.59.
Gen er a t ion of 3-Ar yl-3-cyclob u t en e-1,2-d ion es 14.
Meth od A. A solution of a chloroenol 8 (40 mg) in DMSO-d6
(2.5 mL) was kept at rt for 24 h and was then submitted to
NMR spectroscopy.
Meth od B. A solution of 3-chloro-2-hydroxy-4-phenyl-2-
cyclobuten-1-one (8a ) (1.96g, 10 mmol) in DMSO (50 mL) was
kept at rt for 24 h. The solution was then poured onto an ice-
water mixture (100 g). The precipitate was collected by
filtration and recrystallized from acetone.
Meth od C. A solution of a chloroenol 8 (10 mmol) in a
mixture of acetone/H2O (30 mL; 3:2 vol:vol) was heated with
stirring to reflux for 1 h. During this period the product
started to crystallize. The reaction mixture was cooled in an
ice bath and the product collected by filtration.
3-P h en yl-3-cyclobu ten e-1,2-d ion e (14a ). Method A and
Method B: yellow crystals; mp 149-150 °C (acetone), (lit.10
mp 152-153 °C); yield 0.32 g (38%). IR 1765 (vs, br), 1590
(m) (CdO, CdC) cm-1; 1H NMR (CDCl3) δ 7.60-7.70 (m, 3H),
7.80-8.02 (m, 2H), 10.11 (s, 1H); 13C NMR (CDCl3) δ 127.36,
128.99, 129.43, 134.18, 180.61, 194.57, 196.10, 198.24; MS m/ z
(relative intensity) 158 (M+, 17), 102 (100), 91 (12), 76 (27).
Anal. Calcd for C10H6O2: C, 75.94; H, 3.82. Found: C, 75.75;
H, 3.79.
3-Ch lor o-4-(4-m et h oxyp h en yl)-3-cyclob u t en e-1,2-d i-
on e (12d ): yellow crystals; mp 119-121 °C (CCl4), (lit.11 mp
122-123 °C); yield 1.47 g (66%); IR 1800 (m), 1785, 1760 (vs,
1
br), 1590 (m) (CdO, CdC) cm-1; H NMR (CDCl3) δ 3.90 (s,
3H), 7.04 (dd, 2H, J ) 7.0 Hz, J ) 2.0 Hz), 8.20 (dd, 2H, J )
7.0 Hz, J ) 2.0 Hz); 13C NMR (CDCl3) δ 55.68, 115.13, 119.62,
131.35, 165.15, 176.86, 187.71, 190.37, 194.74; MS m/ z (rela-
tive intensity) 224 (M+, 19), 222 (M+, 57), 166 (100), 159 (49),
123 (46). Anal. Calcd for C11H7ClO3: C, 59.35; H, 3.17; Cl,
15.92. Found: C, 58.18; H, 3.43; Cl, 17.88.
3-Ch lor o-4-(4-ch lor op h en yl)-3-cyclob u t en e-1,2-d ion e
(12e): yellow crystals; mp 139-140 °C (CCl4/n-hexane), (lit.11
mp 142-142.5 °C; yield 1.45 g (64%); IR 1765 (vs, br), 1585
1
(m) (CdO, CdC) cm-1; H NMR (CDCl3) δ 7.55 (dd, 2H, J )
6.7 Hz, J ) 1.9 Hz), 8.17 (dd, 2H, J ) 6.7 Hz, J ) 1.9 Hz); 13
C
NMR (CDCl3) δ 125.16, 130.04, 130.15, 141.70, 180.63, 187.27,
190.40, 193.99; MS m/ z (relative intensity) 230 (M+, 3), 228
(M+, 19), 226 (M+, 29), 170 (100), 163 (36). Anal. Calcd for
C10H4Cl2O2: C, 52.90; H, 1.78; Cl, 31.23. Found: C, 52.77; H,
1.92; Cl, 31.86.

Synthesis of 4-Aryl-3-chloro-2-hydroxy-2-cyclobuten-1-ones
J . Org. Chem., Vol. 61, No. 6, 1996 2093
3-(p-Tolyl)-3-cyclobu ten e-1,2-d ion e (14b). Method C:
yellow crystals; mp 158-160 °C dec (acetone), (lit.24 mp 166
°C); yield 1.00 g (58%); IR 1765 (vs, br), 1600 (m) (CdO, CdC)
(relative intensity) 218 (M+, 73), 162 (100), 147 (86), 119 (20).
Anal. Calcd for C12H10O4: C, 66.05; H, 4.62. Found: C, 65.87;
H, 4.72.
cm-1 1H NMR (CDCl3) δ 2.43 (s, 3H), 7.34 (d, 2H, J ) 8.1
;
3-(2,5-Dich lor op h en yl)-3-cyclobu ten e-1,2-d ion e (14k ).
Method C: yellow crystals; mp 182 °C dec (acetone); yield 1.50
g (66%); IR 1775 (vs, br), 1580 (w) (CdO, CdC) cm-1; 1H NMR
(CDCl3) δ 7.52 (d, 2H, J ) 1.4 Hz), 8.42 (t, 1H, J ) 1.4 Hz),
9.88 (s, 1H); 13C NMR (CDCl3) δ 127.19, 130.95, 132.11, 133.74,
133.96, 134.56, 182.47, 190.56, 195.52, 196.93; MS m/ z (rela-
tive intensity) 230 (M+, >1), 228 (M+, 2), 226 (M+, 3), 170 (100),
135 (20), 99 (42). Anal. Calcd for C10H4Cl2O2: C, 52.90; H,
1.78; Cl, 31.23. Found: C, 52.81; H, 1.73; Cl, 31.15.
3-(2,3,4-Tr im eth ylph en yl)-3-cyclobu ten e-1,2-dion e (14l).
Method A: 1H NMR (DMSO-d6) δ 2.22 (s, 3H), 2.32 (s, 3H),
2.37 (s, 3H), 7.23 (d, 1H, J ) 7.9 Hz), 7.87 (d, 1H, J ) 7.9 Hz),
9.87 (s, 1H); 13C NMR (DMSO-d6) δ 15.50, 17.13, 21.09, 125.37,
126.78, 127.62, 136.58, 137.74, 143.20, 181.00, 194.45, 196.67,
199.17.
Hz), 7.86 (d, 2H, J ) 8.1 Hz), 9.45 (s, 1H); 13C NMR (CDCl3)
δ 22.07, 124.79, 129.50, 130.35, 146.17, 177.14, 195.44, 195.75,
198.06; MS m/ z (relative intensity) 172 (M+, 18), 116 (100),
89 (11). Anal. Calcd for C11H8O2: C, 76.73; H, 4.68. Found:
C, 76.50; H, 4.69.
3-(4-Isop r op ylp h en yl)-3-cyclobu ten e-1,2-d ion e (14c).
Method A: 1H NMR (DMSO-d6) δ 1.22 (d, 6H, J ) 6.9 Hz),
2.98 (m, 1H), 7.52 (d, 2H, J ) 8.1 Hz), 7.96 (d, 2H, J ) 8.2
Hz), 10.08 (s, 1H); 13C NMR (DMSO-d6) δ 23.29, 33.73, 125.19,
127.53, 129.29, 155.65, 179.85, 194.42, 196.12, 198.54.
3-(4-ter t-Bu t ylp h en yl)-3-cyclob u t en e-1,2-d ion e (14d ).
Method C: yellow crystals; mp 163-164 °C (acetone); yield
1.35 g (63%); IR 1775 (vs), 1600 (m) (CdO, CdC) cm-1 1H
;
NMR (CDCl3) δ 1.33 (s, 9H), 7.56 (d, 2H, J ) 8.3 Hz), 7.91 (d,
2H, J ) 8.3 Hz), 9.48 (s, 1H); 13C NMR (CDCl3) δ 30.89, 35.44,
124.59, 126.52, 129.31, 158.98, 177.15, 195.20, 195.66, 197.96;
MS m/ z (relative intensity) 214 (M+, 34), 158 (41), 143 (100),
115 (32). Anal. Calcd for C14H14O2: C, 78.48; H, 6.59.
Found: C, 78.05; H, 6.76.
3-(4-Met h oxyp h en yl)-3-cyclob u t en e-1,2-d ion e (14e).
Method C: yellow crystals; mp 156-158 °C dec (acetone), (lit.6a
159-162 °C dec); yield 1.07 g (57%); IR 1755 (vs, br), 1595 (s)
(CdO, CdC) cm-1; 1H NMR (DMSO-d6) δ 3.87 (s, 3H), 7.20 (d,
2H, J ) 8.8 Hz), 8.02 (d, 2H, J ) 8.8 Hz), 9.96 (s, 1H); 13C
NMR (DMSO-d6) δ 55.72, 115.12, 120.07, 131.48, 164.12,
178.00, 193.48, 195.65, 198.81; MS m/ z (relative intensity) 188
(M+, 26), 132 (100), 117 (31), 89 (41). Anal. Calcd for
C11H8O3: C, 70.21; H, 4.29. Found: C, 70.29; H, 4.39.
3-(2,3,4,5-Tet r a m et h ylp h en yl)-3-cyclob u t en e-1,2-d i-
on e (14m ). Method A: 1H NMR (DMSO-d6) δ 2.19 (s, 3H),
2.20 (s, 3H), 2.23 (s, 3H), 2.30 (s, 3H), 7.72 (s, 1H), 9.80 (s,
1H); 13C NMR (DMSO-d6) δ 15.98, 16.61, 17.17, 20.11, 124.69,
127.91, 133.75, 135.23, 136.43, 141.93, 180.86, 194.54, 196.60,
199.07.
3-(Na p h t h a len -1-yl)-3-cyclob u t en e-1,2-d ion e (14n ).
Method C: orange crystals; mp 143 °C (acetone); yield 0.89 g
1
(43%); IR 1760 (vs, br), 1570 (w) (CdO, CdC) cm-1; H NMR
(DMSO-d6) δ 7.65-7.74 (m, 3H), 8.08 (d, 1H, J ) 9.3 Hz), 8.26
(d, 1H, J ) 8.2 Hz), 8.37-8.42 (m, 2H), 10.36 (s, 1H); 13C NMR
(DMSO-d6) δ 124.10, 124.52, 125.41, 127.00, 128.53, 129.18,
129.59, 129.86, 133.31, 134.92, 181.39, 192.68, 196.67, 198.78;
MS m/ z (relative intensity) 208 (M+, 1), 180 (12), 152 (100).
Anal. Calcd for C14H8O2: C, 80.76; H, 3.87. Found: C, 80.75;
H, 3.74.
Gen er a tion of 4-Ar yl-3-cyclobu ten e-1,2-d ion es-3-d 15.
Gen er a l P r oced u r es. Variant A. To the solution of either
chloroenol 8a or 8f (3 mmol) in a mixture of acetone-d6/D2O
(10 mL; 3:2 vol:vol) was added DCl (36% in D2O; 3 drops). The
mixture was heated with stirring to reflux for 1 h. During
this period the product started to crystallize. The reaction
mixture was cooled in an ice bath and the product collected
by filtration. Variant B. For the substrates 8b and 8d : As
Variant A but without the addition of DCl.
3-(4-Ch lor op h en yl)-3-cyclobu ten e-1,2-d ion e (14f). Me-
thod C: yellow crystals; mp 179-181 °C dec (acetone), (lit.24
mp 182 °C); yield 1.28 g (66%); IR 1765 (vs, br), 1585 (m) (CdO,
1
CdC) cm-1; H NMR (DMSO-d6) δ 7.73 (d, 2H, J ) 8.0 Hz),
8.05 (d, 2H, J ) 8.0 Hz), 10.16 (s, 1H); 13C NMR (DMSO-d6) δ
126.19, 129.74, 130.66, 138.91, 181.02, 193.16, 195.97, 197.88;
MS m/ z (relative intensity) 194 (M+, 13), 192 (M+, 39), 136
(100), 101 (48). Anal. Calcd for C10H5ClO2: C, 62.36; H, 2.62;
Cl, 18.41. Found: C, 62.24; H, 2.61; Cl, 18.15.
3-(4-Br om op h en yl)-3-cyclobu ten e-1,2-d ion e (14g). Me-
thod C: yellow crystals; mp 183-185 °C dec (acetone), (lit.24
mp 190 °C); yield 1.33 g (56%); IR 1765 (vs, br), 1585 (m) (CdO,
4-P h en yl-3-cyclobu ten e-1,2-d ion e-3-d (15a ). Variant
A: yellow crystals; mp 151 °C (EtOH); yield 0.23 g (49%); IR
1
CdC) cm-1; H NMR (DMSO-d6) δ 7.88 (d, 2H, J ) 8.4 Hz),
1785-1760 (vs, br), 1590 (m) (CdO, CdC) cm-1 1H NMR
;
7.95 (d, 2H, J ) 8.4 Hz), 10.14 (s, 1H); 13C NMR (DMSO-d6) δ
126.47, 128.10, 130.65, 132.68, 180.97, 193.28, 195.96, 197.84;
MS m/ z (relative intensity) 182 (M+, 78), 180 (M+, 81), 101
(100), 75 (85). Anal. Calcd for C10H5BrO2: C, 50.67; H, 2.13;
Br, 33.71. Found: C, 50.68; H, 1.92; Cl, 31.33.
(CDCl3) δ 7.53-7.65 (m, 3H), 7.98-7.99 (m, 2H), 9.54 (s,
0.13H); MS m/ z (relative intensity) 159 (M+, 13), 103 (100).
Anal. Calcd for C10H5DO2: C, 75.47; H/D, 4.43. Found: C,
75.09; H/D, 4.22.
4-(p-Tolyl)-3-cyclobu ten e-1,2-d ion e-3-d (15b). Variant
B: yellow crystals; mp 162-163 °C (acetone); yield 0.22 g
3-(2,4-Dim eth ylp h en yl)-3-cyclobu ten e-1,2-d ion e (14h ).
Method A: 1H NMR (DMSO-d6) δ 2.34 (s, 3H), 2.44 (s, 3H),
7.24 (d, 1H, J ) 8.0 Hz), 7.27 (s, 1H), 8.08 (d, 1H, J ) 7.9 Hz),
9.85 (s, 1H); 13C NMR (DMSO-d6) δ 20.98, 21.23, 124.37,
127.06, 129.54, 132.25, 139.95, 144.75, 180.57, 192.81, 196.73,
199.20.
1
(43%); IR 1765 (vs, br), 1600 (m) (CdO, CdC) cm-1; H NMR
(CDCl3) δ 2.44 (s, 3H), 7.35 (d, 2H, J ) 7.9 Hz), 7.87 (d, 2H, J
) 8.1 Hz), 9.46 (s, 0.25H); MS m/ z (relative intensity) 173 (M+,
6), 116 (100). Anal. Calcd for C11H7DO2: C, 76.29; H/D, 5.24.
Found: C, 76.20; H/D, 5.29.
3-(2,5-Dim eth ylp h en yl)-3-cyclobu ten e-1,2-d ion e (14i).
Method C: yellow crystals; mp 151-152 °C (acetone); yield
1.28 g (69%); IR 1775-1755 (vs, br), 1605 (w) (CdO, CdC)
4-(4-ter t-Bu tylph en yl)-3-cyclobu ten e-1,2-dion e-3-d (15c).
Variant B: yellow crystals; mp 165 °C dec (acetone); yield 0.33
g (51%); IR 1775(vs), 1600 (m) (CdO, CdC) cm-1 1H NMR
;
cm-1 1H NMR (CDCl3) δ 2.37 (s, 3H), 2.46 (s, 3H), 7.24 (d,
;
(CDCl3) δ 1.33 (s, 9H), 7.55 (d, 2H, J ) 8.1 Hz), 7.91 (d, 2H, J
) 8.2 Hz), 9.48 (s, 0.25H); MS m/ z (relative intensity) 215 (M+,
4), 144 (100), 128 (17), 116 (38). Anal. Calcd for C14H13DO2:
C, 78.11; H/D, 7.02. Found: C, 78.23; H/D, 6.91.
1H, J ) 7.8 Hz), 7.32 (d, 1H, J ) 7.8 Hz), 8.16 (s, 1H), 9.38 (s,
1H); 13C NMR (CDCl3) δ 20.64, 21.24, 126.81, 130.83, 131.52,
135.10, 136.52, 136.75, 179.22, 194.80, 196.20, 198.50; MS m/ z
(relative intensity) 186 (M+, 37), 130 (100), 115 (72). Anal.
Calcd for C12H10O2: C, 77.40; H, 5.41. Found: C, 77.02; H,
5.64.
4-(4-Ch lor op h en yl)-3-cyclobu ten e-1,2-d ion e-3-d (15d ).
Variant A: yellow crystals; mp 183 °C dec (EtOH); yield 0.33
1
g (57%); IR 1765 (vs), 1590 (m) (CdO, CdC) cm-1; H NMR
3-(2,5-Dim eth oxyp h en yl)-3-cyclobu ten e-1,2-dion e (14j).
Method C: yellow crystals; mp 196-197 °C dec (acetone); yield
1.13 g (52%); IR 1760 (vs), 1610 (w) (CdO, CdC) cm-1; 1H NMR
(CDCl3) δ 3.83 (s, 3H), 3.94 (s, 3H), 6.95 (d, 1H, J ) 9.2 Hz),
7.17 (dd, 1H, J ) 9.2 Hz, J ) 3.2 Hz), 7.88 (d, 1H, J ) 3.2 Hz),
9.52 (s, 1H); 13C NMR (CDCl3) δ 56.03, 112.14, 113.79, 117.02,
123.29, 153.57, 153.62, 180.90, 190.81, 197.06, 199.22; MS m/ z
(CDCl3) δ 7.54 (d, 2H, J ) 8.4 Hz), 7.93 (d, 2H, J ) 8.4 Hz),
9.52 (s, 0.05H); MS m/ z (relative intensity) 196 (M+, 6), 194
(M+, 17), 138 (100), 102 (12), 75 (14). Anal. Calcd for C10H4-
ClDO2: C, 62.04; H/D, 3.12. Found: C, 62.01; H/D 2.93.
Th er m a l Isom er iza tion of 4-Ar yl-3-ch lor o-2-h yd r oxy-
2-cyclobu ten -1-on es 8. Gen er a tion of 3-Ch lor on a p h th a -
len e-1,2-d iols 17. Gen er a l P r oced u r es. Variant A (for the
isomerization of 8a and 8i). A suspension of either chloroenol
8a or 8i (10 mmol) in m-xylene (30 mL) was purged with
nitrogen and heated with stirring to 139 °C for 3 h. The
(24) Brune, H. A.; Horlbeck, G.; Ro¨ttele, H.; Tanger, U. Z. Naturf.
1973, 28b, 68.

2094 J . Org. Chem., Vol. 61, No. 6, 1996
Schmidt et al.
solvent was removed in vacuo to give a brown oil. This oil
was extracted with hot hexane (6 × 15 mL). On cooling the
combined hexane fractions, the products crystallized and were
collected by filtration. Variant B: As described in variant A
with the difference that the xylene reaction solutions were
cooled to -15 °C. The products then crystallized and were
collected by filtration.
yl ether) 11 (5 mmol) in m-xylene (20 mL) was purged with
nitrogen and heated with stirring to 139 °C for 3 h. The
solvent was removed in vacuo to give a solid, which was
recrystallized from n-hexane or toluene.
3-Ch lor o-2-m eth oxy-1-n a p h th ol (18a ): white crystals; mp
80-81 °C (n-hexane); yield 1.34 g (64%); IR 3380 (vs, br), 1585
(m) (OH, CdC) cm-1; 1H NMR (DMSO-d6) δ 3.80 (s, 3H), 7.43-
7.46 (m, 2H), 7.53 (s, 1H), 7.75-7.77 (m, 1H), 8.09-8.11 (m,
1H), 10.07 (s, 1H, OH); 13C NMR (DMSO-d6) δ 60.78, 118.24,
121.84, 124.60, 125.10, 126.10, 126.55, 126.64, 130.49, 138.35,
145.57; MS m/ z (relative intensity) 210 (M+, 30), 208 (M+, 93),
193 (100), 165 (28), 101 (55). Anal. Calcd for C11H9ClO2: C,
63.32; H, 4.35; Cl, 16.99. Found: C, 63.14; H, 4.34; Cl, 16.66.
3-Ch lor on a p h th a len e-1,2-d iol (17a ). Variant A: white
crystals; mp 112-114 °C (n-hexane), (lit.20 mp 116-117 °C);
yield 1.60 g (82%). IR 3400-3350 (vs, br), 1590 (m) (OH, CdC)
cm-1; MS m/ z (relative intensity) 196 (M+, 33), 194 (M+, 100),
131 (34), 113 (15), 102 (50). Anal. Calcd for C10H7ClO2: C,
63.32; H, 4.35; Cl, 17.00. Found: C, 63.37; H, 4.31; Cl, 16.57.
3-Ch lor o-7-m eth yln a p h th a len e-1,2-d iol (17b). Variant
B: white crystals; mp 160-162 °C (n-hexane); yield 1.67 g
3-Ch lor o-2-m eth oxy-7-m eth yl-1-n a p h th ol (18b): white
crystals; mp 84-86 °C (n-hexane); yield 1.93 g (81%); IR 3480-
3440 (s, br), 1595 (m) (OH, CdC) cm-1; 1H NMR (DMSO-d6) δ
2.44 (s, 3H), 3.78 (s, 3H), 7.27 (dd, 1H, J ) 8.4 Hz, J ) 1.6
Hz), 7.46 (s, 1H), 7.65 (d, 1H, J ) 8.4 Hz), 7.87 (s, 1H), 9.94 (s,
1H, OH); 13C NMR (DMSO-d6) δ 21.33, 60.75, 118.02, 120.73,
124.72, 125.56, 126.48, 128.25, 128.78, 134.43, 138.40, 145.04;
MS m/ z (relative intensity) 224 (M+, 32), 222 (M+, 98), 207
(100), 179 (25), 115 (47). Anal. Calcd for C12H11ClO2: C, 64.73;
H, 4.98; Cl, 15.92. Found: C, 64.62; H, 5.03; Cl, 16.10.
1
(80%); IR 3400-3340 (vs, br), 1600 (m) (OH, CdC) cm-1; H
NMR (DMSO-d6) δ 2.42 (s, 3H), 7.15 (dd, 1H, J ) 8.3 Hz, J )
1.4 Hz), 7.45 (s, 1H), 7.60 (d, 1H, J ) 8.3 Hz), 7.80 (s, 1H),
9.25 (s, 2H, OH); 13C NMR (DMSO-d6) δ 21.52, 118.23, 119.94,
122.53, 124.78, 126.35, 126.46, 126.59, 134.15, 136.95, 139.44;
MS m/ z (relative intensity) 210 (M+, 73), 208 (M+, 100), 173
(66), 145 (68), 115 (73). Anal. Calcd for C11H9ClO2: C, 63.32;
H, 4.35; Cl, 17.00. Found: C, 63.37; H, 4.31; Cl, 16.57.
3,7-Dich lor on a p h th a len e-1,2-d iol (17d ). Variant B: pale
red crystals; mp 172-173 °C (toluene); yield 1.63 g (71%); IR
7-(ter t-Bu tyl)-3-ch lor o-2-m eth oxy-1-n aph th ol (18c): white
crystals; mp 84-85 °C (n-hexane); yield 1.99 g (75%); IR 3490
3500, 3420 (vs, br), 1590 (m) (OH, CdC) cm-1 1H NMR
;
1
(s, br), 1590 (w) (OH, CdC) cm-1; H NMR (DMSO-d6) δ 1.33
(DMSO-d6) δ 7.31 (dd, 1H, J ) 8.8 Hz, J ) 2.1 Hz), 7.58 (s,
1H), 7.76 (d, 1H, J ) 8.8 Hz), 8.00 (s, 1H), 9.51 (s, 1H, OH),
9.64 (s, 1H, OH); 13C NMR (DMSO-d6) δ 118.75, 119.80, 124.00,
124.60, 125.32, 126.15, 129.05, 129.94, 138.26, 139.10; MS m/ z
(relative intensity) 232 (M+, 26), 230 (M+, 92), 228 (M+, 100),
193 (66), 165 (51), 136 (64). Anal. Calcd for C10H6Cl2O2: C,
52.44; H, 2.64; Cl, 30.95. Found: C, 52.36; H, 2.78; Cl, 30.84.
3-Ch lor o-7-iod on a p h th a len e-1,2-d iol (17e). Variant B:
pale red crystals; mp 148 °C (toluene); yield 2.12 g (66%); IR
(s, 9H), 3.78 (s, 3H), 7.45 (s, 1H), 7.53 (dd, 1H, J ) 8.7 Hz, J
) 1.8 Hz), 7.68 (d, 1H, J ) 8.7 Hz), 8.01 (s, 1H), 9.99 (s, 1H,
OH); 13C NMR (DMSO-d6) δ 30.86, 34.60, 60.72, 116.47, 117.73,
124.30, 124.91, 125.81, 126.40, 128.75, 138.42, 145.52, 147.42;
MS m/ z (relative intensity) 266 (M+, 22), 264 (M+, 70), 249,
(100). Anal. Calcd for C15H17ClO2: C, 68.01; H, 6.47; Cl, 13.39.
Found: C, 67.95; H, 6.40; Cl, 13.29.
3-Ch lor o-2,7-d im eth oxy-1-n a p h th ol (18d ): white crys-
tals; mp 106-107 °C (n-hexane); yield 1.79 g (75%); IR 3440-
3380 (vs, br), 1590 (s) (OH, CdC) cm-1; 1H NMR (DMSO-d6) δ
3.79 (s, 3H), 3.86 (s, 3H), 7.10 (dd, 1H, J ) 8.9 Hz, J ) 2.5
Hz), 7.39 (s, 1H), 7.46 (s, 1H), 7.68 (d, 1H, J ) 9.0 Hz), 9.93 (s,
1H, OH); 13C NMR (DMSO-d6) δ 55.05, 60.70, 100.31, 118.13,
118.59, 123.74, 125.69, 125.88, 128.36, 138.87, 144.60, 156.89;
MS m/ z (relative intensity) 240 (M+, 33), 238 (M+, 100), 223
(75), 195 (22). Anal. Calcd for C12H11ClO3: C, 60.39; H, 4.65;
Cl, 14.85. Found: C, 60.41; H, 4.61; Cl, 14.57.
3420-3360 (vs, br), 1580 (m) (OH, CdC) cm-1 1H NMR
;
(DMSO-d6) δ 7.51-7.57 (m, 3H), 8.38 (s, 1H), 9.54 (s, 2H, OH);
13C NMR (DMSO-d6) δ 91.07, 118.69, 124.22, 126.21, 126.36,
128.70, 129.50, 132.15, 137.98, 138.76; MS m/ z (relative
intensity) 322 (M+, 32), 320 (M+, 100), 165 (13), 101 (30). Anal.
Calcd for C10H6IClO2: C, 37.47; H, 1.89; Cl, 11.06; I, 39.59.
Found: C, 37.95; H, 1.95; Cl, 11.53; I, 39.02.
3-Ch lor o-5,8-d im eth yln a p h th a len e-1,2-d iol (17f). Vari-
ant A: white crystals; mp 95-96 °C (n-hexane); yield 1.25 g
(56%); IR 3480, 3400 (s, br), 1585 (w) (OH, CdC) cm-1 1H
;
3-Ch lor o-7-iodo-2-m eth oxy-1-n aph th ol (18e): white crys-
tals; mp 123-125 °C (n-hexane); yield 2.71 g (81%); IR 3380-
3320 (s, br), 1570 (m) (OH, CdC) cm-1; 1H NMR (DMSO-d6) δ
3.79 (s, 3H), 7.53 (s, 1H), 7.56 (d, 1H, J ) 8.6 Hz), 7.69 (d, 1H,
J ) 8.6 Hz), 8.44 (s, 1H), 10.27 (s, 1H, OH); 13C NMR (DMSO-
d6) δ 60.84, 91.17, 118.44, 126.20, 127.55, 128.60, 129.07,
130.36, 134.21, 139.11, 144.60; MS m/ z (relative intensity) 336
(M+, 32), 334 (M+, 100), 319 (58), 291 (14). Anal. Calcd for
C11H8ClIO2: C, 39.49; H, 2.41; Cl, 10.60; J , 37.93. Found: C,
39.91; H, 2.50; Cl, 10.85; I, 37.32.
NMR (DMSO-d6) δ 2.46 (s, 3H), 2.79 (s, 3H), 6.97 (d, 1H, J )
7.1 Hz), 7.01 (d, 1H, J ) 7.1 Hz), 7.43 (s, 1H); 13C NMR
(DMSO-d6) δ 19.35, 24.32, 115.01, 122.86, 123.86, 124.95,
127.33, 128.62, 130.38, 131.75, 137.13, 143.89; MS m/ z (rela-
tive intensity) 224 (M+, 76), 222 (M+, 100), 207 (72), 187 (58),
128 (67), 159 (36), 115 (68). Anal. Calcd for C12H11ClO2: C,
64.73; H, 4.98; Cl, 15.92. Found: C, 64.69; H, 4.87; Cl, 16.03.
3,5,8-Tr ich lor on a p h th a len e-1,2-d iol (17g). Variant B:
red crystals; mp 166-167 °C (toluene); yield 2.08 g (79%); IR
1
3500, 3450 (s), 1585 (w) (OH, CdC) cm-1; H NMR (DMSO-
3,5,8-Tr ich lor o-2-m eth oxy-1-n a p h th ol (18f): white crys-
tals; mp 139-140 °C (toluene); yield 1.97 g (71%); IR 3430 (s),
1575 (m) (OH, CdC) cm-1; 1H NMR (DMSO-d6) δ 3.80 (d, 3H,
J ) 2.3 Hz), 7.43 (dd, 1H, J ) 8.1 Hz, J ) 2.2 Hz), 7.53 (dd,
1H, J ) 8.1 Hz, J ) 2.1 Hz), 7.68 (d, 1H, J ) 2.2 Hz), 10.33 (s,
1H, OH); 13C NMR (DMSO-d6) δ 60.86, 114.72, 121.87, 126.45,
128.05, 128.28, 128.52, 129.10, 140.95, 147.75; MS m/ z (rela-
tive intensity) 282, (M+, 4), 280 (M+, 31), 278 (M+, 97), 276
(M+, 100), 261 (99), 233 (42). Anal. Calcd for C11H7Cl3O2: C,
47.61; H, 2.54; Cl, 38.32. Found: C, 48.00; H, 2.47; Cl, 37.77.
d6) δ 7.38 (d, 1H, J ) 8.0 Hz), 7.41 (d, 1H, J ) 8.0 Hz), 7.73 (s,
1H), 9.72 (s, 2H, OH); 13C NMR (DMSO-d6) δ 115.17, 122.10,
124.41, 125.52, 126.21, 127.20, 127.88, 128.56, 140.31, 141.99;
MS m/ z (relative intensity) 268 (M+, 4), 266 (M+, 31), 264 (M+,
98), 262 (M+, 100), 163 (21), 135 (19). Anal. Calcd for C10H5-
Cl3O2: C, 45.58; H, 1.91; Cl, 40.36. Found: C, 45.38; H, 2.00;
Cl, 40.38.
3-Ch lor op h en a n th r en e-1,2-d iol (17h ). Variant B: grey
powder; mp 168-170 °C (toluene); yield 1.57 g (64%); IR 3500
(s), 3360-3320 (s, br), 1610 (w), 1595 (w) (OH, CdC) cm-1; 1H
NMR (DMSO-d6) δ 7.52-7.62 (m, 2H), 7.72 (d, 1H, J ) 9.2
Hz), 7.89 (d, 1H, J ) 7.7 Hz), 8.02 (d, 1H, J ) 9.1 Hz), 8.34 (s,
1H), 8.65 (d, 1H, J ) 8.2 Hz), 9.47 (s, 1H, OH), 9.58 (s, 1H,
OH); 13C NMR (DMSO-d6) δ 114.30, 120.08, 122.07, 122.68,
122.88, 123.92, 125.70, 126.09, 126.80, 128.28, 129.01, 130.71,
138.74, 141.42; MS m/ z (relative intensity) 246 (M+, 31), 244
(M+, 100), 181 (28), 152 (32). Anal. Calcd for C14H9ClO2: C,
68.73; H, 3.71; Cl, 14.50. Found: C, 68.73; H, 3.71; Cl, 14.22.
Th er m a l Isom er iza tion of 4-Ar yl-3-ch lor o-2-m eth oxy-
2-cyclobu ten -1-on es 11. Gen er a tion of 3-Ch lor o-2-m eth -
oxy-1-n a p h th ols 18. Gen er a l P r oced u r e. The solution of
a 4-aryl-3-chloro-2-methoxy-2-cyclobuten-1-one (chloroenol meth-
Ack n ow led gm en t. The authors gratefully acknowl-
edge financial support of this work from the Deutsche
Forschungsgemeinschaft (DFG) Bonn-Bad Godesberg
(Grant: Schm 309-6/1). They are also grateful to S.
Goldschmidt, Fachhochschule Fresenius, Wiesbaden, for
technical assistance, to Prof. Dr. H. Meier, Universita¨t
Mainz, for permission to record NMR and mass spectra,
and to Dr. G. Penzlin, Beilstein-Institut, Frankfurt am
Main, for his advice on nomenclature.
J O952062R