Reactions of polychlorophenyllithium compounds with electrophiles

Article abstract of DOI:10.1007/s11172-005-0341-1

Polychloroaromatic compounds lithiated by BuⁿLi in THF react with several electrophilic agents of which aldehydes and epoxides seem to be the most promising from the preparative point of view.

Full text of DOI:10.1007/s11172-005-0341-1

964
Russian Chemical Bulletin, International Edition, Vol. 54, No. 4, pp. 964—969, April, 2005
Reactions of polychlorophenyllithium compounds with electrophiles*
A. S. Burukin, A. A. Vasil´ev, M. I. Struchkova, V. V. Kachala, and S. G. Zlotinꢀ
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (095) 135 5328. Eꢀmail: zlotin@ioc.ac.ru
Polychloroaromatic compounds lithiated by BunLi in THF react with several electrophilic
agents of which aldehydes and epoxides seem to be the most promising from the preparative
point of view.
Key words: polychloroarenes, hexachlorobenzene, nꢀbutyllithium, organolithium comꢀ
pounds, carbonyl compounds, aldehydes, epoxides.
Polychloroaromatic compounds, such as insecticides
Me3SiCl, and some other organoelement reagents are
documented,3—5,7 whereas carbonyl compounds as elecꢀ
trophiles are virtually unexplored.6
of the first generation and polychlorodioxines, are ecoꢀ
logically hazardous materials. The most popular method
for their chemical utilization is the catalytic hydrogenolysis
of the С—Cl bond.1 Other chemical transformations of
polychloroarenes are little studied. At the same time, the
development of methods for substitution of С—С and
С—Het (Het is a heteroatom) bonds for C—Cl bonds
usually of low reactivity can provide wide potentialities
for polychloroarene processing to practically useful aroꢀ
matic compounds. Available literature data indicate the
mutual activating effect of chlorine atoms, due to which
they undergo nucleophilic aromatic substitution (see,
e.g., Ref. 2).
A more rare type of reactions of polychloroarenes is
the exchange of chlorine by a metal to give the correꢀ
sponding organometallic compounds. For instance, they
react with alkyllithium reagents (BunLi, ButLi) affording
the expected polychlorophenyllithium derivatives,3—7 unꢀ
like monochloroarenes that are stable toward the action
of AlkLi.8 Since the prepared organometallic compounds
contain vicinal metal and chlorine atoms, these can be
eliminated with formation of benzynes.9 Nevertheless,
polychloroaryllithium derivatives are stable at –50 °C,
whereas C6Cl5MgCl is stable even in boiling ether.10
The purpose of the present work is a comparative study
of lithiation of hexachlorobenzene (1), 1,2ꢀdimethoxyꢀ
tetrachlorobenzene (2), and compounds 3 and 4 containꢀ
ing hydrogen atoms in the aromatic ring and further reacꢀ
tions of the resulting ArClLi with electrophiles. Different
carbonyl compounds, halogenating agents, and methylꢀ
oxirane were used as electrophiles. It should be noted
that the reactions of ArClLi with D2O, CO2, HgCl2,
The interaction of hexachlorobenzene (1) with BunLi
in THF results in the Cl→Li exchange to form pentaꢀ
chlorophenyllithium (cf. Refs 3—5). We studied the reacꢀ
tions of in situ prepared C6Cl5Li with several electrophiles
(Scheme 1, Table 1). Aldehydes with different structures
add C6Cl5Li affording the corresponding secondary
alcohols 5а—с in preparative yields (entries 1—3). The
reactions of C6Cl5Li with ketones afford no tertiary
alcohols. In this case, the main product is pentachloroꢀ
benzene C6HCl5 (δH 7.54, [М]+ 248), which results from
protonation of C6Cl5Li with either mobile αꢀH atoms of
enolizable ketones or water during workꢀup (for instance,
in the case of benzophenone that remains unchanged in
the reaction). The reactions of benzoyl chloride (entry 4)
and methyl benzoate (entry 5) even with excess C6Cl5Li
stop at the step of formation of 2,3,4,5,6ꢀpentachloroꢀ
benzophenone 6b (yields 7—9%). NꢀMethoxyꢀNꢀmethylꢀ
* Dedicated to Corresponding Member of the Russian Acadꢀ
emy of Sciences E. P. Serebryakov on the occasion of his
70th birthday.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 941—946, April, 2005.
1066ꢀ5285/05/5404ꢀ0964 © 2005 Springer Science+Business Media, Inc.

Polychlorophenyllithiums
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 4, April, 2005
965
Scheme 1
R = Me (5a, 6a), Ph (5b, 6b), CH=CHMe (5c); Hal = Br (9a), I (9b)
Table 1. Reactions of lithiated polychloroaromatic compounds
siderable amounts of pentachlorobenzene. Methyloxirane
reacts smoothly with C6Cl5Li in the presence of 1 equiv.
of HMPA to form secondary alcohol 7 (entry 6). Ethyl
chloroformate, like other derivatives of carboxylic acids,
reacts with C6Cl5Li to afford, even with an excess of the
latter, ethyl pentachlorobenzoate (8) as the main product
(entry 7; however, according to the data from mass specꢀ
trometry, the reaction mixture contains certain amount of
diethyl tetrachlorobenzenedicarboxylates with [М]+ 358).
Cyanogen bromide reacts with C6Cl5Li as a brominating
agent to form bromopentachlorobenzene (9а) (entry 8).
When C6Cl5Li is quenched with a solution of iodine,
pentachloroiodobenzene (9b) is formed (entry 9). An atꢀ
tempt to synthesize pentachlorophenylboronic acid by the
treatment of C6Cl5Li with trimethyl borate or triisopropyl
borate was unsuccessful.
1,2ꢀDimethoxytetrachlorobenzene deactivated by two
methoxy groups (2) is lithiated less efficiently than
hexachlorobenzene (1) (Scheme 2, see Table 1). When
acetaldehyde was used as a trap for ArClLi, 1ꢀ(3,4ꢀdiꢀ
methoxyꢀ2,5,6ꢀtrichlorophenyl)ethanꢀ1ꢀol (10) was obꢀ
tained in a low yield (entry 10). The position of the
1ꢀhydroxyethyl substituent in the product (10) was inꢀ
ferred on the basis of 2D NMR experiments (NOESY and
НМВС). The NOESY experiment showed no interaction
between protons of the methoxy groups and СН(ОН)Ме
fragment. No correlation between the СН(ОН) proton
and aromatic carbon atoms of =С—ОМе were observed
in the HMBC experiment but correlations of this proton
with electrophiles (THF, arene : BunLi ~1 : 0.85)
Entry Startꢀ
ing
Electrophile
(molar ratio
to arene)
Proꢀ
duct
Yield
(%)
arene
1
2
3
4
5
6
7
8
1
1
1
1
1
1
1
1
1
2
3
3
3
3
MeCHO (0.8)
PhCHO (1.0)
5а
5b
5c
6b
6b
7
52
81
68
9
7
46
MeCH=CHCHO (1.0)
PhC(O)Cl (0.32)
PhCO2Me (0.32)
Methyloxiranea (1.2)
ClC(O)OEt (0.5 and 1.3)
BrCN (0.9)
I2 (0.8)
MeCHO (1.0)
MeCHO (1.6)
PhCHO (1.2)
8
34 and 18
~45b
41
9a
9b
10
11a
11b
9
10
11
12
13
14
17
51
23
PhCO2Me (1.0 and 0.5) 12b
PhC(O)Cl (0.5)
55 and 12
с
12b
13
14
—
12
13
15
4
MeCHO (1.0)
a In the presence of 1 equiv. of HMPA.
b According to the GLC data.
c Not determined.
benzamide, which usually reacts with organolithium comꢀ
pounds to form the corresponding phenones,11 does not
react with C6Cl5Li. Like ketones, acetyl chloride acts as a
proton donor in the reaction with C6Cl5Li to form conꢀ

966
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 4, April, 2005
Burukin et al.
with the carbon atoms of the =C—Cl fragment of the
benzene ring were found. The direction of the attack of
BunLi on the chlorine atom in position 4 is related, most
likely, to its greater spatial accessibility than that in posiꢀ
tion 3, although lithium can preliminarily be complexed
by the oxygen atom in the case of the alternative lithiation
route. Noticeable amounts of the dimerization products
of polychloroarene 2 are formed in the reaction along
with compound 10.
taining hydrogen atoms in the benzene ring react with
BunLi with replacement of one or two hydrogen atoms by
metal. Monolithium arene derivative 3 was identified folꢀ
lowing its reactions with aldehydes and methyl benzoate
to give products 11 and 12 (Scheme 3, see Table 1, enꢀ
tries 11—13). The dilithium derivative was identified by
the isolation of diketone 13, although in low yield, when
0.5 equiv. of benzoyl chloride was added to the reaction
mixture (entry 14). Similarly to C6Cl5Li, lithiated 3 does
not react with ketones.
The lithiation product of dichloroarene 4 does not reꢀ
act with acetaldehyde; instead of the expected alcohol,
biaryl 14 is formed (Scheme 4, see Table 4, entry 15). The
structure of compound 14 was established by 2D NMR
experiments (COSY, HSQC, and HMBC). The HMBC
experiment identified the junction carbon atom С(1) corꢀ
relating with the protons H(5) (doublet) and H(6´) (singlet).
orthoꢀDeprotonation of aryl ethers by alkyllithium reꢀ
agents is well known.12 In our case, the preferential
deprotonation of the proton from position 2, which is
more hindered but activated by the adjacent chlorine, is
noteworthy. Probably, aryllithium 15 that formed is less
stable than organolithium derivatives of compounds 1—3
and, hence, it reacts with excess dichloroarene 4 substiꢀ
tuting the chlorine atom in position 3, which is not deacꢀ
tivated by the mesomeric effect of the methoxy group. An
alternative dimerization mechanism including the formaꢀ
tion of 6ꢀchloroꢀ3ꢀmethoxybenzyne (16) and addition of
aryllithium 15 is also probable.
Scheme 2
Unlike polychloroarenes 1 and 2, 1,2,4,5ꢀtetrachloroꢀ
benzene (3) and 3,4ꢀdichloroꢀ1ꢀmethoxybenzene (4) conꢀ
Scheme 3
R = Me (11a, 12a), Ph (11b, 12b)

Polychlorophenyllithiums
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 4, April, 2005
967
Scheme 4
the biaryl type. We failed to isolate individual compoꢀ
nents from this mixture.
Thus, for the first time we performed a comparative
study of the lithiation processes of polychloroaromatic
compounds of different structures and the reactivities of
aryllithium derivatives that formed. The preparative value
of the studied reactions is determined, in particular, by
the reaction of ArClLi with aldehydes and epoxides. This
process can be considered as a method for the preparation
of secondary alcohols containing polychloroaromatic fragꢀ
ments. The latter can serve as intermediates in the synꢀ
theses of polychlorinated ketones by oxidation, while these
compounds are poorly accessible by other methods.
Experimental
Melting points were not corrected. Standard NMR spectra
were recorded on a Bruker AMꢀ300 spectrometer in CDCl3 at
300.13 MHz (1Н) and 75.47 MHz (13С). 2D NMR experiments
(COSY, NOESY, HSQC, and HMBC) were carried out on a
Bruker DRXꢀ500 AVANS spectrometer at 500.13 MHz (1Н)
and 125.76 MHz (13С) in DMSOꢀd6 at 30 °C. All NMR experiꢀ
ments were performed using standard Bruker procedures.
2D HSQC and HMBC spectra were recorded using a gradient
procedure. Mass spectra were obtained on a Kratos MSꢀ30 inꢀ
strument (ionizing voltage 70 eV) with the direct sample inlet
and heating 0→220 °C; mass numbers are presented for the 35Cl
and 79Br isotopes. Elemental analyses were carried out at the
Analytical Laboratory of the N. D. Zelinsky Institute of Organic
Chemistry (Russian Academy of Sciences). Hexane, AcOEt,
and CH2Cl2 were preꢀdistilled; THF was dried by refluxing over
The reaction of the lithiation products of 1,2ꢀdichloꢀ
robenzene with MeCHO affords a complex mixture of
nonpolar compounds with low volatilities, probably, of
Table 2. Physicochemical characteristics of the synthesized compounds
Compound
NMR (CDCl3), δ (J/Hz)
M.p./°С
Compositiona
(literature data)
1Н
13C
1ꢀ(Pentachlorophenyl)ꢀ
ethanꢀ1ꢀol (5a)
1.67 (d, 3 Н, Me, J = 8);
3.00 (d, 1 Н, ОН, J = 10);
5.69 (br.quintet, 1 Н, ОCН,
J = 8)
20.9 (Me); 69.8 (CН);
131.5, 132.6, 132.9,
140.0 (all C)
124—126
—
(123—124,6
12613
)
2,3,4,5,6ꢀPentachloroꢀ
benzhydrol (5b)
3.43 (d, 1 Н, ОН, J = 10);
6.76 (d, 1 Н, ОCН, J = 10);
7.20—7.42 (m, 5 Н, Ph)
1.75 (d, 3 Н, Me, J = 6);
73.9, 125.2, 127.7
114—116
(11714
—
(all CН); 132.9, 133.0,
133.8, 139.2, 140.2 (all C)
17.9 (Me); 73.8, 128.7,
130.0 (all CН); 132.0,
132.8, 133.1, 138.7 (all C)
)
1ꢀ(2,3,4,5,6ꢀ
104—106
Found (%):
Pentachlorophenyl)butꢀ 3.04 (d, 1 Н, ОН, J = 10);
2ꢀenꢀ1ꢀol (5c)
C, 37.26; Н, 2.33.
C10Н7Cl5O.
Calculated (%):
C, 37.48; Н, 2.20
—
5.65—6.10 (m, 3 Н, ОCН
and CН=CН)
2,3,4,5,6ꢀPentachloroꢀ
acetophenone (6a)
2,3,4,5,6ꢀPentachloroꢀ
benzophenone (6b)
2.60 (s, 3 Н, Me)
30.5 (Me); 127.6, 132.5,
134.4, 139.9, 196.7 (all C)
129.3 (CН); 129.4 (C);
129.7 (CН); 132.7, 134.4,
134.8 (all C); 134.9 (CН);
138.0, 189.9 (both C)
90—92
(9015
149—151
(15414
)
7.53 (t, 2 Н, CН, J = 8);
7.71 (t, 1 Н, CН, J = 7.3);
7.86 (d, 2 Н, CН, J = 8)
[М]+ 352
)
(to be continued)

968
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 4, April, 2005
Burukin et al.
Table 2 (continued)
Compound
NMR (CDCl3), δ (J/Hz)
M.p./°С
Compositiona
(literature data)
1Н
13C
1ꢀ(Pentachlorophenyl)ꢀ
propanꢀ2ꢀol (7)
1.36 (d, 3 Н, Me, J = 5.9);
1.53 (s, 1 Н, ОН); 3.16
(dd, 1 Н, CН, J = 5.6,
23.9 (Me); 42.8 (CH2);
67.4 (CН); 132.1,
133.6, 136.6 (all C)
119—120
Found (%):
C, 35.44; Н, 2.21.
C9Н7Cl5O.
J = 12.9); 3.31 (dd, 1 Н,
CН, J = 7.1, J = 12.9);
4.24 (sextet, ОCН, J = 7.6)
1.43 (t, 3 Н, Me, J = 8);
4.50 (q, 2 Н, ОCН2, J = 6.7)
Calculated (%):
C, 35.05; Н, 2.29
Ethyl pentachloroꢀ
benzoate (8)
14.1 (Me); 63.0 (CН2);
129.4, 132.4, 134.3,
135.0, 162.9 (all C)
123.8 (C—Br); 132.1,
133.0, 138.1 (all C)
103.2 (C—I); 130.6,
134.1, 138.1 (all C)
21.3 (Me); 61.1 (2 ОMe);
69.0 (CН); 126.9,
75—76
[М]+ 320
1ꢀBromoꢀ2,3,4,5,6ꢀpentaꢀ No signals
[М]+ 326
chlorobenzeneb (9a)
1,2,3,4,5ꢀPentachloroꢀ
6ꢀiodobenzeneb (9b)
1ꢀ(3,4ꢀDimethoxyꢀ
No signals
186—188а
(20716
Oil
)
1.63 (d, 3 Н, Me, J = 6.7);
2,5,6ꢀtrichlorophenyl)ꢀ 3.12 (d, 1 Н, ОН, J = 10);
[М]+ 284
ethanꢀ1ꢀol (10)
3.89 (s, 3 Н, ОMe); 3.91
(s, 3 Н, ОMe); 5.58 (br.
quintet, 1 Н, ОCН, J = 6.0)
1.64 (d, 3 Н, Me, J = 7);
127.3, 127.7, 136.1,
149.5, 150.1 (all C)
1ꢀ(2,3,5,6ꢀTetrachloroꢀ
phenyl)ethanꢀ1ꢀol (11a) 3.00 (d, 1 Н, ОН, J = 8.1);
5.68 (br.quintet, 1 Н, ОCН,
20.9 (Me); 69.7, 129.9
(both CН); 130.7, 133.0,
142.2 (all C)
78—80
88—89
Found (%):
C, 36.97; Н, 2.18.
C8Н6Cl4O.
Calculated (%):
C, 36.96; Н, 2.33
Found (%):
C, 48.22; Н, 2.39.
C13Н8Cl4O.
J = 7.4); 7.56 (s, 1 Н, ОCН)
2,3,5,6ꢀTetrachloroꢀ
benzhydrol (11b)
3.44 (d, 1 Н, ОН, J = 8.4);
6.66 (d, 1 Н, ОCН, J = 11.1);
7.20—7.43 (m, 5 Н, Ph);
7.64 (s, 1 Н, =CН)
73.9, 125.3, 127.7,
128.6, 130.6 (all CН);
132.2, 133.1, 140.4,
141.6 (all C)
Calculated (%):
C, 48.49; Н, 2.50
—
2,3,5,6ꢀTetrachloroꢀ
acetophenone (12a)
2.58 (s, 3 Н, Me);
7.59 (s, 1 Н, CН)
30.6 (Me); 127.0 (C);
131.1 (CН); 132.6,
142.4, 197.5 (all C)
128.7 (C); 129.2, 129.7,
131.4 (all CН); 132.7,
55—57
129
2,3,5,6ꢀTetrachloroꢀ
benzophenone (12b)
7.51 (t, 2 Н, CН, J = 8.3);
7.65 (t, 2 Н, CН, J = 8.8);
7.71 (s, 1 Н); 7.83 (d, 2 Н,
CН, J = 9.3)
[М]+ 318
134.5 (both C); 134.8 (CН);
140.4, 190.5 (both C)
1,4ꢀDibenzoylꢀ2,3,5,6ꢀ
tetrachlorobenzene (13) 7.69 (t, 2 Н, CН, J = 8.3);
7.90 (2 Н, CН, J = 9.0)
7.58 (t, 4 Н, CН, J = 8.3);
129.4 (CH); 129.7 (C); 129.8
(CН); 134.2 (C); 135.1 (CН);
140.4, 190.3 (both C)
212
[М]+ 422
[М]+ 316
2,2´,3ꢀTrichloroꢀ5´,6ꢀ
3.72 (s, 3 Н, 6ꢀОMe); 3.78
55.5, 56.3 (both OMe);
122—124
dimethoxybiphenylс (14) (s, 3 Н, 5´ꢀОMe); 6.84
(br.s, 1 Н, H(6´)); 7.01
111.6 (CH(5)); 115.2 (CH(4´));
116.8 (CH(6´)); 122.9 (C(3));
124.0 (C(2´)); 128.5 (C(1));
129.8 (CH(3´)); 130.3 (CH(4));
131.2 (C(2)); 135.0 (C(1´));
156.3 (OC(6)); 158.0 (OC(5´))
(br.d, 1 Н, H(4´), J = 8.3);
7.18 (d, 1 Н, H(4), J = 8.7);
7.43 (d, 1 H, H(3´), J = 8.3);
7.64 (d, 1 H, H(5), J = 8.7)
a Data from mass spectrometry (m/z) or elemental analysis.
b The samples contained C6Cl6 (δC 132.5) in amounts of 55 (9а) and 20% (9b).
c The NMR spectra were recorded in DMSOꢀd6.
LiAlH4 followed by distillation under argon. Hexachlorobenzene
(1) (Aldrich), 1,2,4,5ꢀtetrachlorobenzene (3) (Acros), and
cyanogen bromide were used as received. Acetaldehyde was preꢀ
pared by detrimerization of paraldehyde with Н3РО4, a fraction
with b.p. 20—21 °С was collected through a high Vigreux
column. Benzaldehyde, methyl benzoate, benzoyl chloride,
acetyl chloride, crotonaldehyde, and ethyl chloroformate were
freshly distilled. NꢀMethoxyꢀNꢀmethylbenzamide was syntheꢀ
sized by the reaction of benzoyl chloride with N,Oꢀdimethylꢀ
hydroxylamine hydrochloride in the presence of 2 equiv. of pyriꢀ

Polychlorophenyllithiums
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 4, April, 2005
969
dine and 1 equiv. of triethylamine in CH2Cl2 according to a
known procedure.11 1,2ꢀDimethoxytetrachlorobenzene (2) and
3,4ꢀdichloroꢀ1ꢀmethoxybenzene (4) were synthesized by meꢀ
thylation of tetrachloropyrocatechol (Lancaster) and 3,4ꢀdiꢀ
chlorophenol (Aldrich), respectively, with excess of MeI and
K2CO3 in boiling acetone. TLC analysis was carried out on
aluminum plates with Kieselgel 60 F254 (Merck, 1.05554). Colꢀ
umn chromatography was carried out on silica gel L (100/160).
Lithiation of polychloroarenes followed by the reaction with
electrophiles (general procedure). A 1.7 М solution of BunLi
(2.5 mL, ~4.25 mmol) in hexane (Merck) was added dropwise
for 5 min at –50 °С under argon to a mixture of polychloroarene
(5 mmol) in anhydrous THF (25 mL) (hexachlorobenzene was
not completely dissolved). The mixture was kept for 20 min.
During this time, the solution became gray. Then the mixture
was cooled to –78 °C, and a solution of the corresponding
electrophile (2—5 mmol, see Table 1) in THF (3 mL) was added.
Cooling was discontinued, and the mixture was warmed to room
temperature. The mixture was quenched with a solution of soꢀ
dium hydrogencarbonate, the organic layer was separated, the
aqueous layer was extracted with ether, and the combined exꢀ
tracts were dried with MgSO4 and concentrated in vacuo. The
residues were chromatographed on silica gel (gradient 10→100%
CH2Cl2 in hexane). Compounds 5—14 were thus obtained
(Tables 1 and 2).
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Ketones 6a,b and 12a,b (independent synthesis). A solution
of Na2Cr2O7 (1.5 g) and H2SO4 (1.13 mL) in water (7.5 mL) was
added for 10 min to a solution of the corresponding secondary
alcohol (15 mmol) in ether (4 mL), and the mixture was stirred
for 2—3 h (TLC monitoring). The ethereal layer was separated,
the aqueous layer was extracted with ether, and the combined
extracts were dried with CaCl2 and concentrated in vacuo. Keꢀ
tones were isolated by crystallization or, if necessary, column
chromatography in 51—99% yields.
10. D. E. Pearson and D. Cowan, Organic Syntheses,
1964, 44, 78.
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12. H. Gilman, Organic Reactions, 1954, 8, 258.
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The authors thank V. I. Kadentsev and N. G.
Kolotyrkina for mass spectrometric measurements.
This work was financially supported by the Russian
Science Support Foundation.
14. G. Lock, Chem. Ber., 1939, 72, 300.
15. G. Lock and E. Böck, Chem. Ber., 1937, 70, 916.
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Received July 27, 2004;
in revised form October 18, 2004