The site-selective functionalization of halogen-bearing phenols: An exercise in diversity-oriented organometallic synthesis

Article abstract of DOI:10.1016/j.tet.2004.10.103

The organometallic approach to diversity-oriented organic synthesis was subjected to a further test, this time in the phenol series. The model compounds selected were 2,3,6-trifluorophenol, the three isomers of (trifluoromethoxy) phenol and the three isomers of chlorophenol. A combination of optionally site selective metalations and protective group-controlled metalations enabled the selective generation of several isomeric intermediates in each case and their subsequent conversion into functionalized derivatives, in particular hydroxybenzoic acids.

Full text of DOI:10.1016/j.tet.2004.10.103

Tetrahedron 61 (2005) 3393–3401
The site-selective functionalization of halogen-bearing phenols:
an exercise in diversity-oriented organometallic synthesis
*
Elena Marzi and Manfred Schlosser
´ ´
Institute for Chemical Sciences and Engineering, Ecole Polytechnique Federale (EPFL, BCh), CH-1015 Lausanne, Switzerland
Received 2 August 2004; revised 16 September 2004; accepted 15 October 2004
Available online 30 November 2004
Abstract—The organometallic approach to diversity-oriented organic synthesis was subjected to a further test, this time in the phenol series.
The model compounds selected were 2,3,6-trifluorophenol, the three isomers of (trifluoromethoxy)phenol and the three isomers of
chlorophenol. A combination of optionally site selective metalations and protective group-controlled metalations enabled the selective
generation of several isomeric intermediates in each case and their subsequent conversion into functionalized derivatives, in particular
hydroxybenzoic acids.
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
most simple fashion, one needs only to select the
appropriate bromophenol, treat it with two equivalents of
an organometallic agent such as butyllithium or tert-
butyllithium and trap the generated (lithiooxy)phenyl-
lithium with a suitable electrophile. Such sequences have
been successfully carried out in several cases indeed.1 The
yields, in general moderate to good, can still be improved if
the phenolic hydroxyl group is protected as a methoxy-
methoxy or 2-tetrahydropyranyloxy unit prior to the crucial
halogen/metal permutation step.1
Phenols as a class of compounds do presently not attract
much attention. This happened to be different at the dawn of
organic chemistry. In these days they played a prominent
role as both targets and intermediates of structural
elaboration. In fact, they rapidly became one of the
cornerstones supporting the progress in a frenetically
developing area. The names of the researchers involved in
this process reads like an almanac of chemical nobility:
Baeyer, Bucherer, Claisen, Fries, Kolbe, Pechmann,
Reimer, Schmitt, Simonis, Tiemann, Ullmann and
Vilsmeier.
This scheme nevertheless suffers from a serious drawback.
Only the most simple bromophenols are commercially
available and even those are rarely inexpensive. Thus, the
access to the required starting material will often constitute
a major obstacle. It would be more straightforward and
economic to start from a bromine-free (or iodine-free)
phenol and to subject it to a permutational hydrogen/metal
rather than halogen/metal interconversion. Unfortunately,
the direct ‘metalation’ of halogen-devoid phenols has only
been accomplished with phenol itself2 and with 2-naphthol3,4
as the substrates (at the 2- and 3-position, respectively).
1-Naphthol was found to be attacked concomitantly at the 2-
and 8-position.4 Alkoxy- and aroxy-substituted phenols5–7
also tend to produce regioisomeric mixtures despite poor
yields, unless they dispose of no more than one vacant
position.8
Some of the classical phenol reactions give rise to mainly
ortho-substituted derivatives as they benefit from neighbor-
ing group assistance provided by the neutral or deprotonated
hydroxyl group or proceed in a concerted fashion, in
particular as a [3.3]-sigmatropic rearrangement. Others
favor, for steric and electronic reasons, the para isomers. By
and large, however, electrophilic substitutions of phenols
tend to give mixtures of ortho and para isomers, meta
isomers being formed only in trace amounts, if at all.
The only rigorous way to secure regiochemical predict-
ability and fidelity in phenol reactions is to transit
organometallic species wherein the nucleophilically active
center is unequivocally defined. To realize this idea in a
We wondered whether halogen-substituents would not
considerably facilitate the metalation of phenol-derived
acetals and, moreover, comprise an option on more
regioflexibility. This was anticipated on the basis of
Keywords: Butyllithium; Carboxylation; Halogens; Metalation; Phenols;
Superbases; Trialkylsilyl groups.
* Corresponding author. Tel.: C41 21 692 39 65;
e-mail: manfred.schlosser@epfl.ch
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.10.103

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E. Marzi, M. Schlosser / Tetrahedron 61 (2005) 3393–3401
optionally site selective metalations we had previously
carried out with a variety of halogenated substrates, in
particular fluorotoluenes,9,10 fluoroanisoles,11 fluoroani-
lines,12 chlorofluorobenzenes,13 bromofluorobenzenes,13
(trifluoromethyl)toluenes,9 (trifluoromethyl)anilines,12
fluorobenzotrifluorides,14 chlorobenzotrifluorides,14 bromo-
benzotrifluorides14 and bis- or tris(trifluoromethyl)ben-
zenes.15,16 Our first endeavors in this direction proved to
be quite encouraging.
Work of this kind contributes to the prospects of diversity-
oriented synthesis.18 Meanwhile the toolbox approach19,20
has been conceived to extend and perfect such oppor-
tunities. By virtue of sophisticated organometallic
protocols any vacant position in an aromatic or heterocyclic
substrate can be selectively metalated and subsequently
functionalized. To demonstrate the validity of the concept,
several model substrates were converted into all possible
isomeric derivatives by carrying out regioisomerically
exhaustive metalations and functionalizations. Mono-, di-
and trifluorophenols belong to the noteworthy examples in
this respect.21,22
The O-methoxymethyl protected 2- and 4-(trifluoromethyl)-
phenols reacted with the mixture of butyllithium and
potassium tert-butoxide (‘LIC-KOR’ superbase) under
proton abstraction from the oxygen-adjacent positions to
provide the corresponding hydroxybenzoic acids in 56 and
54% yield.17 The meta isomer featured another example of
optional site selectivity by undergoing metalation with LIC-
KOR at the 2-position flanked by both substituents and at
the coordinatively assisted 6-position with sec-butyllithium,
affording the corresponding hydroxybenzoic acids in 53 and
93% yield, respectively.17
The metalation of the three fluoro(methoxymethoxy)ben-
zenes with butyllithium or sec-butyllithium at the position
next to the oxygen substituent having already been reported,
we were still able to improve the yields of the isolated
fluorohydroxybenzoic acids (to 69–93%).17 At the same
time we installed optional site selectivity in the metalation
of the ortho and para isomers, which were deprotonated and
subsequently carboxylated (84 and 80% of the acids) at the
fluorine-adjacent positions when LIC-KOR was employed
as the base.17
2. Results and discussion
We wanted to complement our study of trifluorophenols by
including the 2,3,6-trifluoro isomer into the investigations.
This model compound represents a challenge. Although
there are only two vacant positions left, both of them are
activated in an almost identical manner each having a
fluorine atom as a direct neighbor. Actually, the metalation
of either the O-methoxymethyl or O-triisopropylsilyl
protected 2,3,6-trifluorophenol gave more or less random
mixtures of organolithium species, the latter being even-
tually trapped as the hydroxybenzoic acid 1a and 1b. The
highest regioselectivity of 5:95 was achieved when the
acetal was treated with lithium diisopropylamide (LIDA) in
tetrahydrofuran. The problem could be easily circumvented
by bromination of the phenol at the para position. Halogen/
metal permutation accomplished with butyllithium in
tetrahydrofuran afforded the acid 1b in 83% yield. The
isomeric acid 1a (40%) was prepared in a one-pot procedure
by consecutive deprotonation of the acetal with lithium
diisopropylamide, reaction with dry ice and debromination
of the intermediate with zinc powder in alkaline medium.

E. Marzi, M. Schlosser / Tetrahedron 61 (2005) 3393–3401
3395
On the other hand, the bulky triisopropylsilyl group
sterically shields its immediate vicinity. Therefore, metal-
ation with sec-butyllithium in the presence of N,N,N0,N00,N00-
pentamethyldiethylenetriamine (‘PMDTA’) was deflected
to the remote OCF3-adjacent position. Carboxylation
and deprotection afforded the hydroxy(trifluoromethoxy)-
benzoic acids 2e–2g (in 69, 80 and 78% yield).
The (trifluoromethoxy)phenols, the next selection of model
substrates, are quite expensive starting materials. Therefore,
we contented ourselves to make only seven rather than all
ten of the corresponding carboxylic acids. Optional site
selectivity was this time not achieved by reagent matching18
but rather by an appropriate choice of the O-protecting
entity.
Trifluoromethoxy groups resemble chloro substituents in
several respects23 even if the latter are a bit less effective in
activating ortho-position toward metalation.24 For sake of
comparison, the three chlorophenols were protected as
methoxymethyl and triisopropylsilyl ethers before being
metalated with butyllithium and sec-butyllithium,
respectively.
1-Methoxymethoxy-2- and -4-(trifluoromethoxy)benzene
reacted smoothly at the acetal-adjacent sites thus leading
to the acids 2a (71%) and 2c (93%). The meta isomer
underwent metalation at the doubly activated position
flanked by the two substituents thus providing the acid 2b
(85%) after carboxylation and neutralization. When, instead
of the carboxy function, a trimethylsilyl group or a chlorine
atom was introduced in the lithiated 2-position (to give the
silane 3 or the chloroarene 4), the next metalation took place
at the methoxymethoxy-neighboring 6-position. This
opened an entry to the acids 2d (74%; after protodesilylation
using tetrabutylammonium fluoride hydrate [‘TBAF’]) and
5 (80%).
In analogy with the behaviour of the corresponding
(trifluoromethoxy)phenol derivatives, proton abstraction
from the chloro(methoxymethoxy)benzenes occurred
exclusively from oxygen-adjacent positions. The hydro-
xybenzoic acids 6a, 6b and 6c were isolated in 74, 84 and
79% yield. The metalation of 1-chloro-2-(methoxy-
methoxy)benzene has been reported previously.25
The weaker base26 lithium 2,2,6,6-tetramethylpiperidide
(LITMP) had to be employed with the meta-substituted
substrate as both butyllithium and sec-butyllithium provided
a mixture of the acid 6b and its isomer 6d. The latter
compound was selectively prepared in 35% yield by treating
the silane 7, obtained after mixing 1-chloro-3-

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E. Marzi, M. Schlosser / Tetrahedron 61 (2005) 3393–3401
(methoxymethoxy)benzene with LITMP and chloro-
trimethylsilane, consecutively with sec-butyllithium, dry
ice, hydrochloric acid and TBAF.
3.2. Derivatives of 2,3,6-trifluorophenol
3.2.1. 4-Bromo-2,3,6-trifluorophenol. A solution contain-
ing 2,3,6-trifluorophenol (15 g, 0.10 mol) and N-bromo-
succinimide (18 g, 0.10 mol) in chloroform (0.20 L) was
kept 2 h at 0 8C. After the addition of a saturated aqueous
solution (0.10 L) of sodium thiosulfate, the reaction mixture
was extracted with dichloromethane (3!0.10 L). The
organic layer was evaporated and the residue crystallized
from hexanes as colorless platelets; mp 44–45 8C; yield:
1
The O-triisopropylsilyl protected chlorophenols also fol-
lowed the previously encountered pattern. sec-Butyllithium
attacked solely the chlorine-adjacent positions remote from
the silyloxy entity. After trapping with dry ice the
hydroxybenzoic acids 6e, 6f and 6g were obtained in 49,
50 and 51% yield.
19.8 g (87%). H NMR: dZ7.16 (ddd, JZ9.7, 5.8, 2.6 Hz,
1H), 5.38 (broad s, 1H) ppm; 13C NMR: dZ148.0 (td,
JZ243, 4 Hz), 145.9 (ddd, JZ245, 12, 4 Hz), 141.7
(ddd, JZ248, 17, 6 Hz), 134.1 (ddd, JZ15, 13, 2 Hz),
114.3 (dd, JZ23, 4 Hz), 98.8 (dd, JZ20, 11 Hz) ppm;
MS (c.i.): m/z (%)Z244 (0) [MCCNH4], 229 (39) [MCC
3], 228 (99) [MCC2], 227 (28) [MCC1], 226 (61) [MC],
99 (100).
3.2.2. 1-Bromo-2,3,5-trifluoro-4-(methoxymethoxy)ben-
zene. Prepared at 0 8C, a solution of 4-bromo-2,3,6-
trifluorophenol (17 g, 75 mmol), chloromethyl methyl
ether30 (9.1 mL, 9.7 g, 90 mmol) and N-ethyldiisopropyl-
amine (14 mL, 12 g, 90 mmol) in dichloromethane (75 mL)
was kept at 25 8C for 2 h. The mixture was poured into a
3.0 M aqueous solution (0.15 L) of sodium hydroxide,
extracted with dichloromethane (2!75 mL) and distilled;
colorless liquid; bp 59–61 8C/3 mmHg; n2D0Z1.4902; yield:
1
17.9 g (88%). H NMR: dZ7.16 (ddd, JZ9.9, 6.1, 2.9 Hz,
1H), 5.20 (s, 2H), 3.61 (s, 3H) ppm; 13C NMR: dZ152.2 (td,
JZ248, 4 Hz), 146.0 (ddd, JZ254, 15, 6 Hz), 145.9 (ddd,
JZ249, 13, 4 Hz), 133.9 (ddd, JZ16, 12, 2 Hz), 114.6 (dd,
JZ24, 4 Hz), 103.2 (ddd, JZ29, 11, 2 Hz), 99.0 (t, JZ
4 Hz), 57.6 ppm; MS (c.i.): m/z (%)Z288 (0) [MCCNH4],
272 (2) [MCC2], 270 (3) [MC], 228 (62), 99 (100);
C8H6BrF3O2 (271.03): calcd C 35.45, H 2.23; found C
35.61, H 2.41.
Carboxylation is presumably the most common way to
characterize an organometallic intermediate by derivatiza-
tion. Despite its popularity, carbon dioxide remains just one
out of dozens if not hundreds of eligible electrophiles. The
metalation reactions disclosed above thus do not simply
open a route leading to rare benzoic acids but may be used to
access numerous classes of otherwise functionalized
compounds.
3.2.3. 2,4,5-Trifluoro-3-hydroxybenzoic acid (1a).
2,2,6,6-Tetramethylpiperidine (4.2 mL, 3.5 g, 25 mmol),
potassium tert-butoxide (2.8 g, 25 mmol), N,N,N0,N00,N00-
pentamethylethylenediamine (5.2 mL, 4.3 g, 25 mmol)
and 1-bromo-2,3,5-trifluoro-4-(methoxymethoxy)benzene
(6.8 g, 25 mmol) were added consecutively to a solution
of butyllithium (25 mmol) in tetrahydrofuran (32 mL) and
hexanes (16 mL) kept at K125 8C. After 45 min, the
reaction mixture was poured onto freshly crushed dry ice
and evaporated. The residue was partitioned between water
(25 mL) and diethyl ether (50 mL). The aqueous phase was
acidified with concentrated hydrochloric acid and extracted
with diethyl ether (3!50 mL). After evaporation of the
solvents, the residue was dissolved in a 3.0 M aqueous
solution (25 mL) of sodium hydroxide and stirred with zinc
powder (4.9 g, 75 mmol) for 2 h at 25 8C. The reaction
mixture was acidified to pH 1 with concentrated hydro-
chloric acid and extracted with diethyl ether (3!25 mL).
After evaporation of the solvents, the residue was crystal-
lized from chloroform; colorless needles; mp 143–144 8C;
yield: 1.92 g (40%). 1H NMR*: dZ7.35 (ddd, JZ10.6, 8.3,
5.8 Hz, 1H) ppm; 13C NMR*: dZ163.5 (m), 149.3 (ddd,
JZ254, 5, 3 Hz), 147.0 (ddd, JZ242, 11, 3 Hz), 141.1 (ddd,
JZ251, 16, 5 Hz), 136.7 (ddd, JZ18, 12, 3 Hz), 114.7 (ddd,
JZ17, 7, 4 Hz), 108.1 (d, JZ21 Hz) ppm; MS (c.i.): m/z
3. Experimental
3.1. Generalities
Details concerning standard operations and abbreviations
can be found in previous publications from this labora-
tory.27–29 1H and (1H-decoupled) 13C NMR spectra were
recorded at 400 and 101 MHz, respectively, samples having
been dissolved in CDCl3 or, if marked by an asterisk (*), in
acetone-d6. Mass spectra were obtained by the chemical
ionization technique (c.i.) in an ammonia atmosphere at
100 8C source temperature. To avoid redundancy, only the
[35Cl] and [79Br] fragments, and not the [37Cl] or [81Br]
isotopomers, are listed in all cases. Whenever possible and
appropriate, yields and purities of products were deter-
mined, prior to isolation, by gas chromatographic compari-
son of their peak areas with that of a known amount of a
reference substance (‘internal standard’) and correction of
the ratios thus obtained by means of separately established
calibration factors. The stationary phases employed are
encoded as DB-23 (silicone type) and DB-WAX (poly-
ethylene glycol type).

E. Marzi, M. Schlosser / Tetrahedron 61 (2005) 3393–3401
3397
(%)Z210 (0) [MCCNH4], 194 (8) [MCC2], 193 (55)
[MCC1], 192 (76) [MC], 175 (100); C7H3F3O3 (192.09):
calcd C 43.77, H 1.57; found C 43.94, H 1.54.
mixture (80%) of the acids 1a and 1b as determined by gas
chromatographic analysis of the crude product after
esterification with ethereal diazomethane [30 m, DB-
WAX, 150 8C; 30 m, DB-23, 150 8C].
3.2.4. 2,3,5-Trifluoro-4-hydroxybenzoic acid (1b). 1-
Bromo-2,3,5-trifluoro-4-(methoxymethoxy)-benzene
(6.8 g, 25 mmol) was added to a solution of butyllithium
(25 mmol) in hexanes (17 mL) and tetrahydrofuran (33 mL)
kept in a dry ice/methanol bath. After 15 min at K75 8C, the
reaction mixture was poured onto freshly crushed dry ice.
After addition of water (25 mL) and washing with diethyl
ether (2!25 mL), the aqueous phase was acidified with
concentrated hydrochloric acid and extracted with diethyl
ether (3!50 mL). Evaporation of the solvents and crystal-
lization from toluene afforded colorless needles; mp 154–
3.3. Derivatives of (trifluoromethoxy)phenols
3.3.1. 1-(Methoxymethoxy)-2-(trifluoromethoxy)ben-
zene. Prepared at 0 8C, a solution of 2-(trifluoromethoxy)-
phenol (18 g, 0.10 mol), N-ethyldiisopropylamine (18 mL,
16 g, 0.12 mol) and chloromethyl methyl ether30 (9 mL,
10 g, 0.12 mol) in dichloromethane (80 mL) was kept for
2 h at 25 8C, before being poured into a 3.0 M aqueous
solution (0.20 L) of sodium hydroxide. Extraction with
dichloromethane (2!0.10 L) and distillation gave a color-
less liquid; bp 51–52 8C/6 mmHg; n2D0Z1.4320; yield:
1
156 8C; yield: 3.99 g (83%). H NMR*: dZ7.53 (ddd, JZ
10.6, 6.7, 2.2 Hz, 1H) ppm; 13C NMR*: dZ163.3 (m),
148.7 (ddd, JZ258, 12, 4 Hz), 147.8 (dt, JZ241, 4 Hz),
141.8 (ddd, JZ243, 16, 6 Hz), 140.1 (ddd, JZ17, 13, 5 Hz),
112.7 (symm. m), 109.8 (t, JZ8 Hz) ppm; MS (c.i.): m/z
(%)Z210 (0) [MCCNH4], 194 (5) [MCC2], 193 (12)
[MCC1], 192 [MC], 175 (100); C7H3F3O3 (192.09): calcd
C 43.77, H 1.57; found C 43.58, H 1.49.
1
16.2 g (73%). H NMR: dZ7.22 (symm. m, 3H), 7.0 (m,
1H), 5.25 (s, 2H), 3.51 (s, 3H) ppm. 13C NMR: dZ150.1,
139.2, 128.3, 123.5, 122.4, 121.1 (q, JZ256 Hz), 117.3, 95.4,
56.5 ppm. MS (c.i.): m/z (%)Z240 (0) [MCCNH4], 222 (0)
[MC], 202 (86), 184 (51), 132 (26), 107 (100). C9H9F3O3
(222.16): calcd C 48.66, H 4.08; found C 48.73, H 4.11.
3.3.2. 1-(Methoxymethoxy)-3-(trifluoromethoxy)ben-
zene. Prepared analogously from 3-(trifluoromethoxy)-
phenol (18 g, 0.10 mol); colorless liquid, bp 42–
43 8C/4 mmHg; n2D0Z1.4304; yield: 19.3 g (87%). 1H
NMR: dZ7.26 (t, JZ8.3 Hz, 1H), 6.96 (ddd, JZ8.3, 2.2,
0.6 Hz, 1H), 6.92 (broad s, 1H), 6.83 (dm, JZ8.3 Hz, 1H),
5.14 (s, 2H), 3.45 (s, 3H) ppm. 13C NMR: dZ158.7, 150.4
(q, JZ2 Hz), 130.5, 120.9 (q, JZ257 Hz), 114.8, 114.3,
109.9, 94.9, 56.4 ppm. MS (c.i.): m/z (%)Z240 (0) [MCC
NH4], 223 (37) [MCC1], 222 (100) [MC], 191 (22), 161
(29). C9H9F3O3 (222.16): calcd C 48.66, H 4.08; found C
48.77, H 3.88.
3.2.5. 1,2,4-Trifluoro-3-(methoxymethoxy)benzene. Pre-
pared analogously as 1-bromo-2,3,5-trifluoro-4-(methoxy-
methoxy)benzene (see above) from 2,3,6-trifluorophenol
(15 g, 0.10 mol), colorless liquid; bp 33–39 8C/3 mmHg;
n2D0Z1.4429; yield: 16.7 g (87%).1H NMR: dZ6.87 (m,
2H), 5.20 (s, 2H), 3.63 (s, 3H) ppm; 13C NMR: dZ152.8 (td,
JZ244, 3 Hz), 148.1 (ddd, JZ235, 11, 3 Hz), 145.6 (ddd,
JZ246, 15, 6 Hz), 134.8 (ddd, JZ14, 12, 2 Hz), 111.2 (dd,
JZ20, 9 Hz), 110.7 (ddd, JZ22, 8 Hz), 99.3 (t, JZ4 Hz),
57.5 ppm; MS (c.i.): m/z (%)Z200 (0) [MCCNH4], 192
(100) [MC], 141 (32), 82 (43); C8H7F3O2 (192.14): calcd C
50.01, H 3.67; found C 50.08, H 3.52. Upon reaction of the
acetal with butyllithium or lithium diisopropylamide in
tetrahydrofuran followed by carboxylation, a mixture of the
acids 1a and 1b was obtained in the ratios of 40:60 (61%)
and 5:95 (83%) respectively, as determined by gas
chromatographic analysis of the crude product after
esterification with ethereal diazomethane [30 m, DB-
WAX, 150 8C; 30 m, DB-23, 150 8C].
3.3.3. 1-(Methoxymethoxy)-4-(trifluoromethoxy)ben-
zene. Prepared analogously from 4-(trifluoromethoxy)-
phenol (18 g, 0.10 mol); colorless liquid, bp 47–
49 8C/5 mmHg; n2D0Z1.4295; yield: 14.2 g (64%). 1H
NMR: dZ7.18 (d, JZ9.2 Hz, 2H), 7.07 (d, JZ9.2 Hz,
2H), 5.18 (s, 2H), 3.50 (s, 3H) ppm. 13C NMR: dZ156.2,
144.0 (q, JZ2 Hz), 122.7 (2 C), 121.0 (q, JZ257 Hz), 117.5
(2 C), 95.0, 56.2 ppm. MS (c.i.): m/z (%)Z240 (0) [MCC
NH4], 223 (48) [MCC1], 222 (63) [MC], 192 (81), 137
(100). C9H9F3O3 (222.16): calcd C 48.66, H 4.08; found C
48.41, H 4.22.
3.2.6. Triisopropyl(2,3,6-trifluorophenoxy)silane. 2,3,6-
Trifluorophenol (15 g, 0.10 mol), chlorotriisopropylsilane
(22 mL, 20 g, 0.10 mol) and imidazole (6.8 g, 0.10 mol)
were dissolved in N,N-dimethylformamide (50 mL). After
20 h at 25 8C, the mixture was poured into water (100 mL)
and extracted with dichloromethane (3!50 mL). Distilla-
tion under reduced pressure gave a colorless liquid; bp 101–
102 8C/3 mmHg; n2D0Z1.4695; yield: 25.0 g (82%). 1H
NMR: dZ6.76 (dddd, JZ11.8, 9.6, 7.4, 2.2 Hz, 2H), 6.68
(symm. m, 1H), 1.30 (hept., JZ7.4 Hz, 3H), 1.09 (d, JZ7.4,
18 Hz) ppm; 13C NMR: dZ151.4 (dt, JZ241, 3 Hz), 148.2
(ddd, JZ245, 12, 3 Hz), 144.2 (ddd, JZ247, 15, 5 Hz),
135.2 (ddd, JZ15, 12, 3 Hz), 110.0 (ddd, JZ21, 8, 3 Hz),
107.5 (dd, JZ20, 8 Hz), 18.0 (3 C), 13.2 (6 C) ppm; MS
(c.i.): m/z (%)Z322 (0) [MCCNH4], 305 (4) [MCC1], 304
(4) [MC], 262 (100); C15H23F3OSi (304.42): calcd C 59.18,
H 7.62; found C 59.16, H 7.79. Consecutive treatment of the
silyl ether with lithium 2,2,6,6-tetramethylpiperidide in
diethyl ether, dry ice and hydrochloric acid afforded a 10:90
3.3.4. Triisopropyl[2-(trifluoromethoxy)phenoxy]silane.
2-(Trifluoromethoxy)phenol (8.9 g, 50 mmol), chlorotriiso-
propylsilane (11 mL, 10 g, 50 mmol) and imidazole (3.4 g,
50 mmol) were dissolved in N,N-dimethylformamide
(25 mL). After 20 h at 25 8C, the mixture was poured into
water (50 mL) and extracted with dichloromethane (3!
25 mL). Upon distillation under reduced pressure a colorless
liquid was collected; bp 92–94 8C/7 mmHg; n2D0Z1.4582;
1
yield: 12.9 g (77%). H NMR: dZ7.24 (dm, JZ8.0 Hz,
1H), 7.17 (ddd, JZ8.9, 7.4, 1.6 Hz, 1H), 6.95 (dd, JZ8.0,
1.6 Hz, 1H), 6.9 (m, 1H), 1.30 (sept, JZ7.4 Hz, 3H), 1.13
(d, JZ7.4 Hz, 18H) ppm. 13C NMR: dZ149.0, 140.5,
127.9, 123.2, 121.4, 121.2 (q, JZ257 Hz), 121.2, 18.1 (3 C),
13.2 (6 C) ppm. MS (c.i.): m/z (%)Z352 (0) [MCCNH4],

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E. Marzi, M. Schlosser / Tetrahedron 61 (2005) 3393–3401
334 (5) [MC], 291 (14), 139 (100). C16H25F3O2Si (334.45):
calcd C 57.46, H 7.53; found C 57.55, H 7.35.
(trifluoromethoxy)benzene (5.6 g, 25 mmol) using sec-
butyllithium alone; colorless needles (from chloroform);
mp 119–120 8C yield: 4.72 g (85%). 1H NMR*: dZ7.57 (t,
JZ8.6 Hz, 1H), 7.06 (d, JZ8.6 Hz, 1H), 6.92 (d, JZ
7.4 Hz, 1H) ppm. 13C NMR*: dZ170.5, 163.7, 148.7 (q,
JZ2 Hz), 135.4, 121.1 (q, JZ256 Hz), 117.3, 113.6,
108.2 ppm. MS (c.i.): m/z (%)Z240 (0) [MCCNH4], 223
(25) [MCC1], 222 (36) [MC], 205 (53), 204 (88), 107
(100). C8H5F3O4 (222.12): calcd C 43.26, H 2.27; found C
43.28, H 2.17.
3.3.5. Triisopropyl[3-(trifluoromethoxy)phenoxy]silane.
Prepared analogously from 3-(trifluoromethoxy)phenol
(8.9 g, 50 mmol); colorless liquid; bp 82–83 8C/4 mmHg;
1
n2D0Z1.4549; yield: 15.0 g (90%). H NMR: dZ7.24 (t,
JZ8.3 Hz, 1H), 6.9 (m, 2H), 6.79 (broad s, 1H), 1.31
(sept, JZ7.4 Hz, 3H), 1.14 (t, JZ7.4 Hz, 18H) ppm. 13C
NMR: dZ157.6, 150.4 (q, JZ2 Hz), 130.3, 120.9 (q, JZ
257 Hz), 118.8, 113.7, 113.4, 18.2 (3 C), 13.0 (6 C) ppm.
MS (c.i.): m/z (%)Z352 (0) [MCCNH4], 335 (8) [MCC1],
334 (1) [MC], 293 (18), 292 (100). C16H25F3O2Si (334.45):
calcd C 57.46, H 7.53; found C 57.47, H 7.54.
3.3.10.
[2-Methoxymethoxy-6-(trifluoromethoxy)-
phenyl]trimethylsilane (3). The metalation was carried
out as described for the preparation of the acid 2b, but the
reactant dry ice was replaced by chlorotrimethylsilane
(3.2 mL, 2.7 g, 25 mmol). Upon distillation, a colorless
liquid was collected; bp 75–76 8C/5 mmHg; n2D0Z1.4514;
3.3.6. Triisopropyl[4-(trifluoromethoxy)phenoxy]silane.
Prepared analogously from 4-(trifluoromethoxy)phenol
(8.9 g, 50 mmol); colorless liquid; bp 126–
127 8C/5 mmHg; n2D0Z1.4551; yield: 14.4 g (86%). 1H
NMR: dZ7.13 (d, JZ8.6 Hz, 2H), 6.91 (dd, JZ8.9,
1.6 Hz, 2H), 1.30 (sept, JZ7.4 Hz, 3H), 1.14 (d, JZ
7.4 Hz, 18H) ppm. 13C NMR: dZ155.1, 143.4 (q, JZ2 Hz),
122.6 (2 C), 121.0 (q, JZ254 Hz), 121.0 (2 C), 18.2 (3 C),
13.0 (6 C) ppm. MS (c.i.): m/z (%)Z352 (0) [MCCNH4],
336 (28) [MCC2], 335 (47) [MCC1], 334 (81) [MC], 236
(100). C16H25F3O2Si (334.45): calcd C 57.46, H 7.53; found
C 57.50, H 7.58.
1
yield: 4.78 g (65%). H NMR: dZ7.30 (t, JZ8.3 Hz, 1H),
7.01 (d, JZ8.3 Hz, 1H), 6.89 (dm, JZ8.3 Hz, 1H), 5.18 (s,
2H), 3.45 (s, 3H), 0.34 (s, 9H) ppm. 13C NMR: dZ163.5,
154.8 (q, JZ2 Hz), 131.8, 121.1 (q, JZ257 Hz), 121.0,
113.5, 111.6, 94.6, 56.4, 1.3 ppm. MS (c.i.): m/z (%)Z314
(0) [MCCNH4], 296 (15) [MCC2], 295 (24) [MCC1],
294 (61) [MC], 279 (70), 105 (100). C12H17F3O3Si
(294.32): calcd C 48.67, H 5.82; found C 48.66, H 5.99.
3.3.11. 2-Hydroxy-4-(trifluoromethoxy)benzoic acid
(2d). [1-(Methoxymethoxy)-6-(trifluoromethoxy)phenyl]-
trimethylsilane (3, 2.9 g, 10 mmol) in tetrahydrofuran
(14 mL) was treated with sec-butyllithium in cyclohexane
(6 mL) at K75 8C for 6 h before being poured on dry ice.
The residue was neutralized with ethereal hydrogen chloride
and dissolved in diethyl ether (10 mL) containing tetra-
butylammonium fluoride trihydrate (3.2 g, 10 mmol). After
2 h at 25 8C, a 10% aqueous solution (10 mL) of
hydrochloric acid was added and the reaction mixture was
extracted with diethyl ether (3!15 mL). The combined
organic layers were dried and evaporated; colorless needles
3.3.7. 2-Hydroxy-3-(trifluoromethoxy)benzoic acid (2a).
1-(Methoxymethoxy)-2-(trifluoromethoxy)benzene (5.6 g,
25 mmol)00was added to a solution of sec-butyllithium and
N,N,N0,N ,N00-pentamethyldiethylenetriamine (5.2 mL,
4.3 g, 25 mmol) in tetrahydrofuran (30 mL) and cyclo-
hexane (20 mL), cooled in a dry ice/methanol bath. After
2 h at K75 8C, the reaction mixture was poured onto an
excess of freshly crushed dry ice. After evaporation of the
solvents, the residue was partitioned between water (25 mL)
and diethyl ether (50 mL). The aqueous phase was acidified
with concentrated hydrochloric acid to pH 1 and extracted
with diethyl ether (3!25 mL). After evaporation of the
combined organic layers, the residue was crystallized from
hexanes; colorless needles; mp 132–133 8C; yield: 3.94 g
1
(from toluene); mp 122–123 8C; yield: 1.62 g (73%). H
NMR: dZ7.59 (d, JZ8.6 Hz, 1H), 6.5 (m, 1H), 6.40 (dm,
JZ8.6 Hz, 1H) ppm. 13C NMR: dZ174.2, 164.0, 155.8 (q,
JZ2 Hz), 133.2, 120.6 (q, JZ260 Hz), 111.9, 109.9,
109.3 ppm. MS (c.i.): m/z (%)Z240 (4) [MCCNH4], 223
(5) [MCC1], 222 (41) [MC], 176 (100). C8H5F3O4
(222.12): calcd C 43.26, H 2.27; found C 43.27, H 2.15.
When sec-butyllithium was replaced by butyllithium as the
metalating agent, the yield dropped to 47%.
1
(71%). H NMR*: dZ7.94 (dd, JZ8.1, 1.5 Hz, 1H), 7.57
(dm, JZ8.1 Hz, 1H), 7.06 (t, JZ8.0 Hz, 1H) ppm. 13C
NMR*: dZ172.0, 155.8, 137.8 (q, JZ2 Hz), 130.3, 129.9,
121.7 (q, JZ256 Hz), 119.6, 115.6 ppm. MS (c.i.): m/z
(%)Z240 (0) [MCCNH4], 223 (4) [MCC1], 222 (29)
[MC], 205 (13), 204 (100). C8H5F3O4 (222.12): calcd C
43.26, H 2.27; found C 43.19, H 2.29.
3.3.12. 1-Chloro-2-(methoxymethoxy)-6-(trifluoro-
methoxy)benzene (4). Prepared analogously as the silane
3 but replacing the reactant chlorotrimethylsilane by 1,1,2-
trichloro-1,2,2-trifluoroethane (3.1 mL, 4.8 g, 25 mmol).
Direct distillation of the reaction mixture afforded a
colorless liquid; bp 61–63 8C/4 mmHg; n2D0Z1.4554;
3.3.8. 2-Hydroxy-5-(trifluoromethoxy)benzoic acid (2c).
Prepared analogously from 1-(methoxymethoxy)-4-(tri-
fluoromethoxy)benzene (5.6 g, 25 mmol); colorless stars
(from toluene); mp 133–134 8C (lit.31: mp 128–129 8C);
yield: 5.16 g (93%). 1H NMR*: dZ7.80 (dd, JZ2.9, 1.0 Hz,
1H), 7.55 (ddd, JZ9.0, 2.9, 0.6 Hz, 1H), 7.08 (d, JZ9.0 Hz,
1H) ppm. 13C NMR*: dZ171.1, 161.3, 140.9 (q, JZ2 Hz),
129.7, 123.0, 121.0 (q, JZ254 Hz), 119.4, 113.2 ppm. MS
(c.i.): m/z (%)Z240 (0) [MCCNH4], 223 (12) [MCC1],
222 (16) [MC], 205 (16), 204 (30), 107 (100).
1
yield: 4.29 g (67%). H NMR: dZ7.20 (t, JZ8.1 Hz, 1H),
7.13 (dd, JZ8.1, 1.8 Hz, 1H), 7.00 (dm, JZ8.2 Hz, 1H),
5.26 (s, 2H), 3.49 (s, 3H) ppm. 13C NMR: dZ154.9, 146.7
(q, JZ2 Hz), 127.6, 120.8 (q, JZ256 Hz), 118.0, 115.7,
114.5, 95.7, 56.8 ppm. MS (c.i.): m/z (%)Z274 (14) [MCC
NH4], 258 (20) [MCC2], 257 (8) [MCC1], 256 (100)
[MC]. C9H8ClF3O3 (256.61): calcd C 42.13, H 3.14; found
C 42.25, H 3.11.
3.3.9. 2-Hydroxy-6-(trifluoromethoxy)benzoic acid (2b).
Prepared analogously from 1-(methoxymethoxy)-3-

E. Marzi, M. Schlosser / Tetrahedron 61 (2005) 3393–3401
3399
3.3.13. 3-Chloro-2-hydroxy-4-(trifluoromethoxy)benzoic
3.4. Derivatives of chlorophenols
acid (5). The chloroarene 4 (2.6 g, 10 mmol) in tetra-
hydrofuran (14 mL) was treated with butyllithium
(10 mmol) in hexanes (6 mL) at K75 8C for 6 h before
being poured onto an excess of freshly crushed dry ice.
Acidification with concentrated hydrochloric acid, extrac-
tion with diethyl ether (3!15 mL) and crystallization from
toluene afforded colorless tiny needles; mp 186–187 8C;
yield: 2.05 g (80%). 1H NMR*: dZ8.01 (d, JZ8.9 Hz, 1H),
7.11 (dm, JZ8.9 Hz, 1H), ppm. 13C NMR*: dZ171.3,
160.9, 150.2 (q, JZ2 Hz), 130.0, 120.7 (q, JZ259 Hz),
115.1, 112.9, 112.1 (q, JZ2 Hz) ppm. MS (c.i.): m/z (%)Z
274 (0) [MCCNH4], 257 (3) [MCC1], 256 (30) [MC], 240
(31), 238 (100). C8H4ClF3O4 (256.56): calcd C 37.45, H
1.57; found C 37.23, H 1.43.
3.4.1. 1-Chloro-3-(methoxymethoxy)benzene. Mixed at
0 8C, a solution of 2-chlorophenol (13 g, 10 mL, 0.10 mol),
chloromethyl methyl ether30 (9.1 mL, 9.7 g, 0.12 mol) and
N-ethyldiisopropylamine (18 mL, 16 g, 0.12 mol) in
dichloromethane (80 mL) was kept at 25 8C for 2 h. The
mixture was then poured into a 3.0 M aqueous solution
(0.20 L) of sodium hydroxide. Extraction with diethyl ether
(2!100 mL) and distillation gave a colorless liquid; bp 59–
61 8C/5 mmHg; n2D0Z1.5209; yield: 9.4 g (55%). 1H NMR:
dZ7.20 (t, JZ8.3 Hz, 1H), 7.06 (tm, JZ2.2 Hz, 1H), 6.99
(dm, JZ8.0 Hz, 1H), 6.92 (dm, JZ8.3 Hz, 1H), 5.16 (s,
2H), 3.53 (s, 3H) ppm. 13C NMR: dZ158.4, 135.2, 130.6,
122.4, 117.2, 115.0, 94.8, 56.4 ppm. MS (c.i.): m/z (%)Z
190 (0) [MCCNH4], 174 (3) [MCC2], 173 (97) [MCC1],
172 (100) [MC]. C8H9ClO2 (172.61): calcd C 55.67, H 5.26;
found C 55.75, H 5.19.
3.3.14. 3-Hydroxy-2-(trifluoromethoxy)benzoic acid (2e).
Triisopropyl[2-(trifluoromethoxy)-phenoxy]silane (3.4 g,
10 mmol) was added to a solution of sec-butyllithium
(10 mmol) and N,N,N0,N00,N00-pentamethyldiethylenetri-
amine (2.1 mL, 1.7 g, 10 mmol) in tetrahydrofuran
(12 mL) and cyclohexane (8 mL) kept in a dry ice/methanol
bath. After 2 h at K75 8C, the reaction mixture was poured
onto an excess of freshly crushed dry ice. Acidification with
a 1.0 M aqueous solution (10 mL) of citric acid, extraction
with diethyl ether (3!15 mL) and evaporation of the
solvents afforded a residue which was treated with
tetrabutylammonium fluoride trihydrate (3.2 g, 10 mmol)
in diethyl ether (10 mL). After 2 h at 25 8C, the mixture was
evaporated to dryness. The residue crystallized from toluene
as colorless platelets; mp 152–153 8C; yield: 1.53 g (69%).
1H NMR*: dZ7.42 (dd, JZ7.4, 1.9 Hz, 1H), 7.3 (m, 2H)
ppm. 13C NMR*: dZ165.5, 151.4, 135.3, 128.4, 122.3,
121.6 (2 C), 121.2 (q, JZ257 Hz) ppm. MS (c.i.): m/z (%)Z
240 (0) [MCCNH4], 223 (3) [MCC1], 222 (62) [MC], 202
(47), 136 (100). C8H5F3O4 (222.12): calcd C 43.26, H 2.27;
found C 43.52, H 2.19.
3.4.2. (2-Chlorophenoxy)triisopropylsilane. 2-Chloro-
phenol (6.4 g, 5.1 mL, 50 mmol), chlorotriisopropylsilane
(11 mL, 10 g, 50 mmol) and imidazole (3.4 g, 50 mmol)
were dissolved in N,N-dimethylformamide (25 mL). After
20 h at 25 8C, the mixture was poured into water (50 mL)
and extracted with dichloromethane (3!25 mL). Distilla-
tion under reduced pressure gave a colorless liquid; bp 108–
109 8C/5 mmHg; n2D0Z1.5216; yield: 12.3 g (83%). 1H
NMR: dZ7.34 (dd, JZ8.0, 1.3 Hz, 1H), 7.11 (td, JZ8.0,
1.3 Hz, 1H), 6.93 (dd, JZ8.0, 1.3 Hz, 1H), 6.86 (t, JZ
8.0 Hz, 1H), 1.33 (sept, JZ7.4 Hz, 3H), 1.18 (d, JZ7.4 Hz,
18H) ppm. 13C NMR: dZ152.4, 130.7, 127.8, 125.7, 122.0,
120.5, 18.3 (3 C), 13.3 (6 C) ppm. MS (c.i.): m/z (%)Z302
(0) [MCCNH4], 287 (1) [MCC3], 284 (0) [MC], 241
(100). C15H25ClOSi (284.90): calcd C 63.24, H 8.84; found
C 63.18, H 8.94.
3.4.3. (3-Chlorophenoxy)triisopropylsilane. Prepared
analogously from 3-chlorophenol (6.4 g, 5.1 mL,
50 mmol); colorless liquid; bp 110–112 8C/6 mmHg;
n2D0Z1.4968; yield: 6.43 g (45%). H NMR: dZ7.13 (t,
1
3.3.15. 4-Hydroxy-2-(trifluoromethoxy)benzoic acid (2f).
Prepared analogously from triisopropyl[3-(trifluoro-
methoxy)phenoxy]silane (3.4 g, 10 mmol); colorless
needles (from chloroform); mp 129–130 8C; yield: 1.73 g
JZ8.0 Hz, 1H), 6.93 (ddd, JZ8.0, 1.9, 0.6 Hz, 1H), 6.88 (t,
JZ2.2 Hz, 1H), 6.75 (ddd, JZ8.0, 2.0, 0.6 Hz, 1H), 1.24
(sept, JZ7.4 Hz, 3H), 1.08 (t, JZ7.4 Hz, 18H) ppm. 13C
NMR: dZ157.3, 135.0, 130.4, 121.7, 120.8, 118.6, 18.3 (3
C), 13.1 (6 C) ppm. MS (c.i.): m/z (%)Z302 (0) [MCC
NH4], 286 (25) [MCC2], 285 (31) [MCC1], 284 (15)
[MC], 157 (100). C15H25ClOSi (284.90): calcd C 63.24, H
8.84; found C 63.43, H 8.62.
1
(78%). H NMR*: dZ7.99 (d, JZ8.6 Hz, 1H), 6.98 (dd,
JZ8.6, 2.2 Hz, 1H), 6.87 (symm. m, 2H) ppm. 13C
NMR*: dZ164.9, 162.7, 149.8, (q, JZ2 Hz), 134.5, 120.8
(q, JZ257 Hz), 116.3, 114.6, 110.2 ppm. MS (c.i.): m/z
(%)Z240 (0) [MCCNH4], 223 (77) [MCC1], 222 (100)
[MC], 206 (66), 205 (90). C8H5F3O4 (222.12): calcd C
48.66, H 4.08; found C 48.77, H 3.88.
3.4.4. (4-Chlorophenoxy)triisopropylsilane. Prepared
analogously from 4-chlorophenol (6.4 g, 4.9 mL,
50 mmol); colorless liquid; bp 91–93 8C/5 mmHg; n2D0Z
1.5031; yield: 13.6 g (96%). 1H NMR: dZ7.18 (t, JZ
8.9 Hz, 2H), 6.82 (d, JZ8.9 Hz, 2H), 1.3 (m, 3H), 1.12 (d,
JZ7.4 Hz, 18H) ppm. 13C NMR: dZ155.1, 129.7 (2 C),
126.3, 121.5 (2 C), 18.3 (3 C), 13.0 (6 C) ppm. MS (c.i.): m/z
(%)Z302 (0) [MCCNH4], 286 (9) [MCC2], 285 (17)
[MCC1], 284 (15) [MC], 185 (100). C15H25ClOSi
(284.90): calcd C 63.24, H 8.84; found C 63.25, H 8.86.
3.3.16. 5-Hydroxy-2-(trifluoromethoxy)benzoic acid
(2g). Prepared analogously as described above for the acid
2e from triisopropyl[4-(trifluoromethoxy)phenoxy]silane
(3.4 g, 10 mmol); colorless tiny needles (from dichloro-
methane); mp 201–202 8C; yield: 1.78 g (80%). 1H NMR*:
dZ7.45 (d, JZ3.2 Hz, 1H), 7.28 (dm, JZ9.0 Hz, 1H), 7.14
(dd, JZ9.0, 3.2 Hz, 1H) ppm. 13C NMR*: dZ165.0, 156.6,
140.4 (q, JZ2 Hz), 126.9, 124.8, 121.0 (q, JZ255 Hz),
120.4, 118.3 ppm. MS (c.i.): m/z (%)Z240 (0) [MCC
NH4], 223 (22) [MCC1], 222 (100) [MC], 205 (18), 136
(31). C8H5F3O4 (222.12): calcd C 43.26, H 2.57; found C
43.52, H 1.99.
3.4.5. 3-Chloro-2-hydroxybenzoic acid (6a). 1-Chloro-2-
(methoxymethoxy)benzene25,32 (4.3 g, 25 mmol) was added
to a solution of butyllithium (25 mmol) in tetrahydrofuran

3400
E. Marzi, M. Schlosser / Tetrahedron 61 (2005) 3393–3401
(35 mL) and hexanes (15 mL), cooled in a dry ice/methanol
bath. After 6 h at K75 8C, the reaction mixture was poured
onto an excess of freshly crushed dry ice. After evaporation
of the solvents, the residue was taken up in water (25 mL)
and washed with diethyl ether (2!15 mL). The aqueous
phase was acidified to pH 1 and extracted with diethyl ether
(3!25 mL). After evaporation of the combined and dried
organic layers, the residue was crystallized from toluene;
colorless needles; mp 176–178 8C (lit.33: mp 183–183.5 8C);
yield: 3.19 g (74%). 1H NMR: dZ7.89 (dd, JZ8.0, 1.6 Hz,
1H), 7.67 (dd, JZ8.0, 1.6 Hz, 1H), 6.96 (t, JZ8.0 Hz, 1H)
ppm. 13C NMR: dZ172.0, 158.2, 136.2, 129.5, 121.9,
119.7, 114.2 ppm. MS (c.i.): m/z (%)Z192 (0) [MCC
NH4], 174 (6) [MCC2], 173 (3) [MCC1], 172 (26) [MC],
154 (100).
141.6, 131.5, 127.1, 124.1, 111.9, 94.6, 56.5, 2.6 ppm. MS
(c.i.): m/z (%)Z262 (22) [MCCNH4], 246 (11) [MCC2],
245 (2) [MCC1], 244 (16) [MC], 199 (100). C11H17ClO2Si
(244.18): calcd C 53.97, H 7.00; found C 54.38, H 7.41.
3.4.9. 2-Hydroxy-4-chlorobenzoic acid (6d). [2-(Chloro)-
6-(methoxymethoxy)phenyl]trimethylsilane (7, 2.4 g,
10 mmol) in tetrahydrofuran (15 mL) was treated with
sec-butyllithium in cyclohexane (6 mL) at K75 8C for 6 h
before being poured on dry ice. After evaporation of the
solvents, the residue was partitioned between water (10 mL)
and diethyl ether (50 mL). The aqueous phase was acidified
with concentrated hydrochloric acid to pH 1 and extracted
with diethyl ether (3!15 mL). After evaporation of the
combined organic layers, the residue was dissolved in
N,N-dimethylformamide (10 mL) containing tetrabutyl-
ammonium fluoride trihydrate (3.2 g, 10 mmol) and heated
to 100 8C for 48 h. A 10% aqueous solution (20 mL) of
hydrochloric acid was then added. The product was isolated
by extraction with diethyl ether (3!15 mL); colorless stars
(from dichloromethane); mp 206–208 8C (lit.36: mp
3.4.6. 5-Chloro-2-hydroxybenzoic acid (6c). Prepared
analogously from 1-chloro-4-(methoxymethoxy)ben-
zene25,32 (4.3 g, 25 mmol); colorless needles (from toluene);
mp 173–175 8C (lit.34: mp 172 8C); yield: 3.41 g (79%). 1H
NMR: dZ7.85 (d, JZ2.9 Hz, 1H), 7.54 (dd, JZ9.0, 2.9 Hz,
2H), 6.99 (d, JZ9.0 Hz, 1H) ppm. 13C NMR: dZ171.5,
161.7, 136.5, 130.3, 124.1, 120.1, 114.4 ppm. MS (c.i.): m/z
(%)Z190 (0) [MCCNH4], 173 (13) [MCC1], 172 (0)
[MC], 154 (100).
1
207 8C); yield: 0.60 g (35%). H NMR*: dZ7.92 (d, JZ
8.6 Hz, 1H), 7.02 (d, JZ1.9 Hz, 1H), 7.00 (dd, JZ8.6,
1.9 Hz, 1H) ppm. 13C NMR*: dZ171.6, 163.1, 141.2,
132.2, 120.0, 117.5, 111.7 ppm. MS (c.i.): m/z (%)Z190 (0)
[MCCNH4], 174 (12) [MCC2], 173 (6) [MCC1], 172
(34) [MC], 156 (34), 154 (100).
3.4.7. 6-Chloro-2-hydroxybenzoic acid (6b). 2,2,6,6-
Tetramethylpiperidine (4.2 mL, 3.5 g, 25 mmol) and
1-chloro-3-(methoxymethoxy)benzene (4.3 g, 25 mmol)
were added consecutively to a solution of butyllithium
(25 mmol) in tetrahydrofuran (34 mL) and hexanes (16 mL)
kept in a dry ice/ methanol bath. After 2 h at K75 8C, the
reaction mixture was poured onto an excess of freshly
crushed dry ice. After addition of water (25 mL) and
washing with diethyl ether (2!30 mL), the aqueous phase
was acidified to pH 1 with concentrated hydrochloric acid,
extracted with dichloromethane (3!25 mL), dried and
evaporated under reduced pressure, crystallization of the
residue from toluene afforded colorless needles; mp 169–
170 8C (lit.35: mp 171.5–172.5 8C); yield: 3.62 g (84%). 1H
NMR: dZ7.37 (d, JZ8.0 Hz, 1H), 7.01 (dd, JZ8.0, 1.0 Hz,
1H), 6.91 (dd, JZ8.3, 1.3 Hz, 1H) ppm. 13C NMR: dZ
169.5, 161.1, 133.6 (2 C), 122.0, 116.2, 116.3 ppm. MS
(c.i.): m/z (%)Z192 (0) [MCCNH4], 174 (7) [MCC2], 173
(7) [MCC1], 172 (24) [MC], 154 (100). When butyllithium
was used instead of lithium 2,2,6,6-tetramethylpiperidide in
otherwise identical conditions, a mixture of 6-chloro-2-
hydroxybenzoic acid and 4-chloro-2-hydroxybenzoic acid
was obtained in the ratio 60:40 (89%) according to gas
chromatographic analysis (30 m, DB-WAX, 150 8C; 30 m,
DB-23, 150 8C).
3.4.10. 2-Chloro-3-hydroxybenzoic acid (6e). (2-Chloro-
phenoxy)triisopropylsilane (2.8 g, 10 mmol) was added to a
solution of sec-butyllithium in tetrahydrofuran (12 mL) and
cyclohexane (8 mL) kept at K100 8C. After 6 h at this
temperature, the reaction mixture was poured onto an excess
of freshly crushed dry ice. After acidification with 1.0 M
aqueous solution (10 mL) of citric acid and extraction with
diethyl ether (3!15 mL), the combined organic layers were
reduced to a volume of 10 mL and tetrabutylammonium
fluoride trihydrate (3.2 g, 10 mmol) was added. After
standing for 2 h at 25 8C, the solvents were evaporated
and the product crystallized from toluene to give colorless
platelets; mp 157–158 8C (lit.37: mp 157.5–158.5 8C); yield:
1
0.85 g (49%). H NMR: dZ7.34 (dd, JZ7.7, 1.9 Hz, 1H),
7.25 (t, JZ8.0 Hz, 1H), 7.16 (dd, JZ8.0, 1.6 Hz, 1H) ppm.
13C NMR: dZ166.6, 154.2, 132.9, 127.8, 122.1, 119.5,
119.4 ppm. MS (c.i.): m/z (%)Z190 (0) [MCCNH4], 174
(41) [MCC2], 173 (16) [MCC1], 172 (98) [MC], 155
(100).
3.4.11. 2-Chloro-4-hydroxybenzoic acid (6f). Prepared
analogously from (3-chlorophenoxy)triisopropylsilane
(2.8 g, 10 mmol); colorless tiny needles (from dichloro-
methane); mp 192–193 8C (lit.38: mp 159 8C); yield: 0.86 g
1
(50%). H NMR: dZ7.92 (d, JZ8.6 Hz, 1H), 6.95 (d, JZ
3.4.8. [2-Chloro-6-(methoxymethoxy)phenyl]trimethyl-
silane (7). 2,2,6,6-Tetramethylpiperidine (4.2 mL, 3.5 g,
25 mmol), 1-chloro-3-(methoxymethoxy)benzene (4.3 g,
25 mmol) and chlorotrimethylsilane (3.2 mL, 2.7 g,
25 mmol) were added consecutively to a solution of
butyllithium (25 mmol) in tetrahydrofuran (35 mL) and
hexanes (15 mL) kept in a dry ice/methanol bath. Upon
distillation, a colorless liquid was collected; bp 82–85 8C/
2.6 Hz, 1H), 6.89 (dd, JZ8.6, 2.6 Hz, 1H) ppm. 13C NMR:
dZ166.2, 162.0, 136.2, 134.8, 121.5, 118.6, 114.9 ppm. MS
(c.i.): m/z (%)Z192 (0) [MCCNH4], 174 (18) [MCC2],
173 (11) [MCC1], 172 (66) [MC], 155 (100).
3.4.12. 2-Chloro-5-hydroxybenzoic acid (6g). Prepared
analogously from (4-chlorophenoxy)triisopropylsilane
(2.8 g, 10 mmol); colorless needles (from toluene); mp
167–168 8C (lit.37: mp 168–169 8C); yield: 0.87 g (51%). 1H
NMR: dZ7.36 (d, JZ3.2 Hz, 1H), 7.34 (d, JZ8.6 Hz, 2H),
4 mmHg; n2D0Z1.5062; yield: 4.03 g (66%). H NMR: dZ
1
7.26 (t, JZ8.3 Hz, 1H), 7.05 (d, JZ8.3 Hz, 2H), 5.21 (s,
2H), 3.54 (s, 3H), 0.50 (s, 9H) ppm. 13C NMR: dZ163.4,

E. Marzi, M. Schlosser / Tetrahedron 61 (2005) 3393–3401
3401
7.04 (dd, JZ8.6, 2.9 Hz, 1H) ppm. 13C NMR: dZ166.2,
156.5, 132.1, 131.9, 120.1, 118.2, 118.1 ppm. MS (c.i.): m/z
(%)Z190 (0) [MCCNH4], 174 (27) [MCC2], 173 (16)
[MCC1], 172 (81) [MC], 155 (100).
14. Mongin, F.; Desponds, O.; Schlosser, M. Tetrahedron Lett.
1996, 37, 2767–2770.
15. Schlosser, M.; Porwisiak, J.; Mongin, F. Tetrahedron Lett.
1998, 54, 895–900.
16. Schlosser, M.; Mongin, F.; Porwisiak, J.; Dmowski, W.;
Bu¨ker, H. H.; Nibbering, N. M. M. Chem. Eur. J. 1998, 4,
1281–1286.
Acknowledgements
17. Marzi, E.; Mongin, F.; Spitaleri, A.; Schlosser, M. Eur. J. Org.
Chem. 2001, 2911–2915.
This work has been sponsored by the Schweizerische
¨
Nationalfonds zur Forderung der wissenschaftlichen
18. Schlosser, M. Eur. J. Org. Chem. 2001, 3975–3984.
19. Schlosser, M. In Soloshonok, V. A., Ed.; ACS Symposium
Series; American Chemical Society: Washington, DC, 2004;
in press.
Forschung, Bern (grant 20-1000336-02). The authors
express gratitude to Dr. F. Collet for his valuable help
during the finalization of this manuscript.
20. Schlosser, M. Review article to appear in Angew. Chem.
21. Marzi, E.; Schlosser, M.; unpublished results, 2003/2004;
Marzi, E.; Bobbio, C.; Collet, F.; Schlosser, M. Manuscript in
preparation.
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