Regioselective (biomimetic) synthesis of a pentasulfane from ortho-benzoquinone

Article abstract of DOI:10.1021/jo062677w

(Chemical Equation Presented) A mechanism is proposed for the formation of cyclic 5,6,7,8,9-pentathiabenzocycloheptene-1,2-diol, 4, from the reaction of o-benzoquinone with reduced elemental sulfur, H₂;S_x. 1,6-Conjugate addition to t

Full text of DOI:10.1021/jo062677w

Regioselective (Biomimetic) Synthesis of a Pentasulfane from
ortho-Benzoquinone
David Aebisher, Edyta M. Brzostowska, Adaickapillai Mahendran, and Alexander Greer*
Department of Chemistry, Graduate Center & The City UniVersity of New York (CUNY),
Brooklyn College, Brooklyn, New York 11210
agreer@brooklyn.cuny.edu
ReceiVed December 29, 2006
A mechanism is proposed for the formation of cyclic 5,6,7,8,9-pentathiabenzocycloheptene-1,2-diol, 4,
from the reaction of o-benzoquinone with reduced elemental sulfur, H2Sx. 1,6-Conjugate addition to the
quinone is favored over 1,4-conjugate addition. Hydrogen bonding to the quinone oxygen enhances the
nucleophilicity of H2Sx by facilitating the removal of the S-H proton. We propose that initially formed
3-polysulfidobenzene-diol intermediates are oxidized to their corresponding quinones and closure of the
polysulfur ring subsequently takes place at the C3-C4 bond leading to 4. A possible mechanism for the
formation of the pentasulfur linkage in 4 is discussed, which is the key moiety found in a number of
natural products.
SCHEME 1. Natural Polysulfanes
Introduction
Desmethyl varacin (1), lissoclinotoxin B (2), and 5-(meth-
ylthio)varacin (3) represent a class of cytotoxic polysulfanes
isolated from marine invertebrates (Scheme 1).1-20 These
compounds contain a dopamine core and a pentasulfur linkage.
(1) Compagnone, R. S.; Faulkner, D. J.; Carte, B. K.; Chan, G.; Hemling,
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Am. Chem. Soc. 1991, 113, 4709-4710.
Although natural benzopolysulfanes have been isolated,1-10 the
biosynthetic origin and mechanism for introduction of the sulfur
atoms into dopamine have not been examined. Two reactions
of sulfur and dopamine may relate to the biomimetic principles
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10.1021/jo062677w CCC: $37.00 © 2007 American Chemical Society
Published on Web 03/23/2007
J. Org. Chem. 2007, 72, 2951-2955
2951

Aebisher et al.
SCHEME 2. Compounds 4-12 Detected as the
Corresponding Di-, Tri-, or Tetraacetates
that underlie how benzopentathiepins arise biosynthetically.
First, benzopentathiepins may arise from a two-electron transfer
reaction of reduced elemental sulfur, H2Sx, with dopamine-o-
quinone. Second, benzopentathiepins may arise from a one-
electron oxidation of dopamine followed by a reaction with
neutral S8. We have examined the viability of the first reaction
in the laboratory generation of cyclic 5,6,7,8,9-benzopentathi-
epin-1,2-diol (4) using a o-benzoquinone-H2Sx reaction. Our
work with catechol [o-C6H4(OH)2] served as a model for
dopamine. A discussion is presented on the reaction of o-quinone
and H2Sx with specific interest in the mechanism of formation
of pentasulfane 4.
Results and Discussion
Reaction of Quinone with H2Sx. The reaction of o-
benzoquinone (180 mM) (generated in a reaction of Ag2O with
catechol in acetone)21 with H2Sx (3.9 M) (generated by sodium
sulfide nonahydrate heated with elemental sulfur and precipitated
with Cl3CCO2H)22 was conducted by stirring for 1 h at room
temperature. The red color of the quinone was rapidly converted
to pale yellow on addition of H2Sx. The reaction produced a
series of products of high and low molecular weight. Precipita-
tion of neutral elemental S8 also accompanied the reaction.
Polymeric and insoluble material was removed by filtration. GC/
MS analysis revealed a large peak that is likely due to
pentathiepin 4 (see Supporting Information). The GC/MS data
are indicative of a pentathiepin [m/z ) 64 (43), 96 (12), 110
(48), 142 (66), 204 (100), 268 (10)] because they display a weak
molecular ion peak at m/z 268 [M+] and a strong base peak at
m/z 204 [M+ - 2S] representing the loss of two sulfur atoms.23
The M + 2 and M + 4 peaks caused by isotope ratios are as
predicted. Another reaction product observed by GC/MS cor-
responded to 3-mercaptobenzene-1,2-diol (5, x ) 1). However,
attempts to purify the raw mixture by preparative TLC and
HPLC were unsuccessful due to the high polarity of the
compounds. Therefore, the hydroxy and thiol groups of the
products were protected by acetylation with addition of DMAP
(0.18 mmol) and acetic anhydride (2.52 mmol) in ethyl acetate.
Ten products could then be chromatographically separated
through preparative TLC and HPLC and characterized as the
SCHEME 3
in the absence of H2Sx when quinone and catechol (1:1) were
stirred in a 5% NaHCO3 solution followed by a reaction with
pyridine and acetic anhydride. Such nucleophilic additions to
o-quinone are known.21,26-30
The NMR data pointed to diacetylated 4 not 4′ (Scheme 3).
The 1H NMR spectrum revealed two singlets corresponding to
methyls of acetyl groups protecting two OH groups adjacent to
each other at 2.31 and 2.35 ppm and two doublets for H1 and
3
H2 of the aromatic ring with δ ) 7.76 ppm and J13 ) 8.4 Hz
and δ)7.18 ppm and J13)8.4 Hz, respectively. The J13
3
coupling for 4 is comparable to that observed by Sato et al. for
6,7-dimethoxybenzopentathiepin (J ) 8.4 Hz, 1H, ArH).31 The
regioselective formation of the polysulfur ring at the C3-C4
bond of o-benzoquinone and the predominance of sulfur
products arising from o-quinone 1,6-conjugate addition (e.g, 5,
7, and 8) were not immediately understandable. This regio-
chemical discrimination for closure of the polysulfur ring at
the C3-C4 bond leading to 4 rather than the C4-C5 bond
leading to 4′ is interesting, which led us to consider the
mechanism of formation.
Mechanism of Formation of 4. A route is proposed to reach
4 from o-quinone and reduced elemental sulfur. The experi-
mental and theoretical evidence that supports the mechanism
outlined in Scheme 4 includes the following:
(1) H2Sx is more likely to react at C3 of o-quinone compared
to C4 because of possible carbonyl H-bonding in the former,
which enhances the nucleophilicity of H2Sx (Table 1, reaction
1
corresponding di-, tri-, or tetraacetates of 4-12 using H and
13C NMR and MS techniques (Scheme 2). Additional support
for the structures assigned to 5 (x ) 1), 6 (x ) 1), 7, and 8
came from their independent synthesis by the reaction of
o-benzoquinone (18 mmol) with thioacetic acid (26 mmol) as
described in the Supporting Information.
Of particular interest to us is the fact that 4 was formed in
the quinone-H2Sx reaction. The yield of 4 is low (3%), but it
demonstrates the viability of the quinone-H2Sx reaction in
generating a benzopolysulfane. The quinone-H2Sx reaction also
gives byproducts, namely, 15% 5 (x ) 1), 5% 6 (x ) 1), 0.2%
7, ∼1% 8, and ∼2% 9. Traces of known compounds 10-12
are observed (e1%) (assigned on the basis of GC/MS analysis),
which represent nucleophilic addition of catechol to the quinone.
Acetylated 10-12 were obtained in higher yield (>5% total)
(26) Klecka, G. M.; Gibson, D. T. Biochem. J. 1979, 180, 639-645.
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(23) The GC/MS results for 4 are in agreement with the MS fragmenta-
tion pattern seen in other pentathiepins.1,5,8,24,25
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5485.
2952 J. Org. Chem., Vol. 72, No. 8, 2007

Synthesis of a Pentasulfane from ortho-Benzoquinone
TABLE 1. Ratios of Catechol Products That Arise from Nucleophilic Addition to o-Benzoquinones
reaction
R
nucleophile
1,6-product(s)
1,4-product
ref
a
1
2
3
4
H
H
H2Sx
74
98
26
2
-
-
this work
CH3C(dO)SHb
cysteine
N-acetylcysteine
this work
d
CH2CH2NH2
CH2CH2NH2
∼100
e
99
5
6
7
8
H
-
-
-
-
∼100
∼100
this work
f
H or CH3
CH2CH2NHAc
H or CH3
1,2,4-triazolium-3-thiolate
thiourea
thiourea
g
h
∼100
80-90
a
NMR detection of products formed in acetone-d6 at 25 °C after addition of H2Sx to o-benzoquinone. b NMR detection of products formed in CD3Cl at
25 °C after addition of thioacetic acid to o-benzoquinone. c NMR detection of products formed in acetone-d6 at 25 °C after addition of H2Sx and 5% aqueous
NaHCO3 to o-benzoquinone. d Relative ratios were not reported; however, the 5-S-cysteinyl conjugate of dopamine is the predominant product. Ref 44. e At
pH 2, the ratio of the two 1,6-products, 2-S-(N-acetylcysteinyl)dopamine to 5-S-(N-acetylcysteinyl)dopamine, is 10:89. A small amount of the di-1,6-adduct
2,5-S,S′-di(N-acetylcysteinyl)dopamine is also produced. Ref 45. A similar result is reported for reactions of N-acetyldopamine-o-quinone or N-â-alanyldopamine-
o-quinone with N-acetylcysteine. Ref 47. f This mesoionic mercaptan adds to o-quinone and 4-methyl-o-quinone to form salt products. TsO- is the counter
salt. Ref 46. g Relative ratios were not reported; however, the 6-S-thiourea conjugate of N-acetyldopamine is the predominant product. A similar result is also
h
reported for reactions of N-â-alanyldopamine-o-quinone with thiourea. Ref 47. Based on isolated yields. The 1,6-products were not observed. Ref 48.
(reaction 6),46 and thiourea (reactions 7 and 8)47,48 readily
SCHEME 4. Mechanism of Closure of the Polysulfide Ring 4
undergo 1,4-addition reactions to quinones because these sulfur
nucleophiles lack an ionizable S-H proton so that H-bonding
to the quinone oxygen cannot take place.49
(2) 3,4-Dimercaptobenzene-1,2-diol 9 is present in the
quinone-H2Sx reaction mixture. However, other related dimer-
captobenzene-1,2-diol isomers are not observed. 4,5-Dimercap-
tobenzene-1,2-diol (15), 3,5-dimercaptobenzene-1,2-diol (16),
and 3,6-dimercaptobenzene-1,2-diol (17) are not found to within
the experimental error for their detection, ∼0.1 mM. The
quinone-H2Sx reaction contains a large excess of H2Sx but does
not show the production of the C3/C6 product 17. A second
1,6-addition would have been expected with the anticipated
regioselectivity to give 17. Furthermore, we find that over the
course of a few days the peak for 9 increases and concomitantly
the magnitude of the peak for 4 decreases (Scheme 5), which
is reminiscent of thiol-disulfide interconversions seen in many
1). As a consequence, 3- and 4-mercaptobenzene-1,2-diols
organic reactions and biological systems.50 It is an important
[triacetylated 5 and 6 (x ) 1)] are found in the product mixtures
in a 74:26 ratio. The corresponding 3- and 4-hydrosulfidoben-
(36) (a) Behroozi, S. J.; Kim, W.; Gates, K. S. J. Org. Chem. 1995, 60,
zene-1,2-diols [5 and 6 (x g 2)] are assumed to be present but
are unstable to isolation.32 The regioselectivity of the H2Sx
addition to o-quinone is in the same direction as the addition
of thioacetic acid (reaction 2). Thioacetic acid was added to an
acetone solution containing 0.3 equiv of o-quinone and indicated
a preference for the 1,6-addition product to the 1,4-addition
product (98:2). Similar biological examples exist where 1,6-
addition processes are favored, such as the reaction of cysteine
with dopamine-o-quinone in the formation of 5-S-cysteinyl-
dopamine, which is relevant to the mechanism underlying in
vivo neuronal degeneration37-41 (Parkinson’s disease) (Table
1, reactions 3 and 4).42-45 In contrast, thioacetic acid in the
presence of 5% NaHCO3 (reaction 5), triazolium thiolate
3964-3966. (b) Sawwan, N.; Brzostowska, E. M.; Greer, A. J. Org. Chem.
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than a 1,4-addition.
(32) Hydropolysulfides (RSxH) are unstable and usually cannot be directly
detected because equilibration processes lead to a series of RSSxSR
products.33-36
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J. Org. Chem, Vol. 72, No. 8, 2007 2953

Aebisher et al.
SCHEME 5
more, the presence of nucleophiles can facilitate equilibria
between 14 and stable 4. Such nucleophile-dependent equilibria
of polysulfane compounds25,63-67 and difficulties in the isolation
and purification of polysulfanes have been previously reported
in the literature.68,69
An alternative mechanism that we deem unlikely is the
bimolecular addition of H2Sx with 5 (x ) 1-8) (followed by
subsequent ring closure). The absence of 15-17 provides an
argument for a unimolecular ring closure by 3-polysulfi-
doquinone with subsequent formation of 4. The absence of 15-
17 in the reaction is probably due to the lesser efficiency of a
bimolecular reaction of H2Sx with 13. The mechanistic conclu-
sions may be reasonable even though it is difficult to know
exactly what is taking place due to the many equilibration
processes and possible intermediate radicals that may be present
in the formation of the polysulfanes. The quinone-H2Sx reaction
is reminiscent of thiol chemistry reported in the literature based
on formation of sulfur-containing adducts of catechols,38-44
although the present work describes the formation of polysul-
fanes. Catechol-amines can undergo autoxidation yielding
semiquinones, quinones, protonated superoxide ions, and H2O2
under aerobic conditions.70-72 A competing 1,4-addition and
radical addition reaction take place in the reaction of HS- with
the p-quinone-containing natural product juglone, where the
radical addition is favored at higher pH.73 We have not
investigated whether radical scavengers influence the o-quinone-
H2Sx reaction.
SCHEME 6. Compounds Not Observed in the Reaction
SCHEME 7. Unlikely Unimolecular Ring Closure Pathway
observation that 9 is derived from 4 in a decomposition process.
Tri- and tetrasulfur addition products of quinone and H2Sx are
also not detected (Scheme 6).
(3) Control experiments show that there is no reaction
between catechol and neutral S8. Furthermore, a direct pathway
to polysulfur ring closure of 5 (x ) 8) is predicted to be
endothermic and probably irrelevant to the chemistry to form 4
based on energetic demands (Scheme 7). B3LYP/6-31G(d)
calculations were used to predict the energetics of the alternative
cyclization of 5, where x ) 8. We compared the energy
difference of 5 (x ) 8) relative to 1-hydroxy-4aH-5,6,7,8,9-
pentathiabenzocyclohepten-2-one (18) with H2S3. The control
experiments with neutral S8 and the computational results
provide evidence that the new C-S bonds in 4-9 come only
from reactions between quinones and reduced sulfur compounds.
The above data taken together provide support for the
mechanism in Scheme 4. H2Sx incorporates regioselectively into
o-benzoquinone to give 3-hydrosulfidobenzene-1,2-diols 5 (x
) 1-8). A second oxidation can then take place, where 5 is
oxidized by unreacted o-benzoquinone producing 13 and
catechol as a byproduct (Scheme 4B). Unimolecular attack of
the polysulfur chain ion onto the C4 of 13 should occur at some
point when the sulfur chain is sufficiently long, e.g., x ) 8.
Formation of 4 is consistent with an oxidation of 3-polysulfi-
dobenzene-diols with a dependence on the chain length of the
3-polysulfidoquinone, thus leading to unimolecular ring closure.
A subsequent equilibration between benzooctathiecin 14 and
pentathiepin 4 (Scheme 4C) can be envisioned similar to the
one observed previously in an o-benzyne-S8 reaction.25 The
odd-membered ortho-benzofused polysulfane o-(HO)2C6H2Sx
rings (except x ) 1 which suffers from ring strain) are likely to
possess enhanced conformational stability compared to the even-
membered rings. Pentasulfane structures are quite common and
often formed in polysulfur heterocycle syntheses.51-62 Further-
Conclusion
The reaction of o-benzoquinone and H2Sx leads to pentathi-
epin 4 and several byproducts. The proposed mechanism
involves a unimolecular cyclization of 3-polysulfidoquinone
intermediates 13, e.g., where x ) 8. It is likely that the quinone-
H2Sx reaction can be used to synthesize natural product
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2954 J. Org. Chem., Vol. 72, No. 8, 2007

Synthesis of a Pentasulfane from ortho-Benzoquinone
Rf ) 0.48 (2:3 EtOAc/hexanes). 1H NMR (CDCl3) δ 2.28 (s, 3H),
2.29 (s, 3H), 7.12-7.16 (m, 2H), 7.44 (dd, J ) 8.0 Hz, J ) 1.5
Hz, 1H). UV (CH2Cl2) λmax 280, 321 nm. Mass spectrum (EI): m/z
) 110 (20), 142 (11), 250 (100, M-4Ac), 292 (60, M-3Ac), 334
(41, M-2Ac), 376 (19, M-Ac), 418 (12).
polysulfanes. We are currently exploring dopamine-o-quinone
as an intermediate in an H2Sx reaction to generate polysulfane
1.
Experimental Section
Acetic Acid 2-Acetoxy-3-(2,3-diacetoxy-phenyldisulfanyl)-
phenyl Ester or “Tetraacetylated 8”. Yield 0.0048 g. Silica gel
TLC Rf ) 0.42 (2:3 EtOAc/hexanes). 1H NMR (acetone-d6) δ 2.28
(s, 6H), 2.30 (s, 6H), 7.25 (dd, J ) 1.5, 7.3 Hz, 2H), 7.34 (t, J )
7.3 Hz, 2H), 7.51 (dd, J ) 1.5, 7.3 Hz, 2H). 13C NMR (acetone-
d6) 20.1, 20.5, 124.5, 127.8, 131.7, 142.0, 144.4, 168.2, 168.6. UV
(CH2Cl2) λmax 280, 320 nm. Mass spectrum (EI): m/z ) 83 (6),
111 (10), 142 (71), 184 (22), 282 (100, M-4Ac), 324 (60, M-3Ac),
366 (91, M-2Ac), 408 (29, M-Ac), 450 (41). HRMS calcd for
C20H18O8S2 (M + NH4)+ 468.0781, found 468.0784.
5,6,7,8,9-Pentathiabenzocycloheptene-1,2-diol (4) was sepa-
rated by preparative silica gel TLC, Rf ) 0.5 EtOAc/hexanes (1:
3). Mass spectrum (EI): m/z ) 64 (43), 96 (12), 110 (48), 142
(66), 204 (100), 268 (10).
Acetic Acid 2-Acetoxy-5,6,7,8,9-pentathiabenzocyclohepten-
1-yl Ester or “Diacetylated 4”. Yield 0.0007 g. Silica gel TLC,
1
Rf ) 0.4 (THF/hexanes, 1:3). H NMR (CDCl3) δ 2.31 (s, 3H),
2.35 (s, 3H), 7.18 (d, 1H, J ) 8.4 Hz), 7.76 (d, 1H, J ) 8.4 Hz).
13C NMR (CDCl3) δ 20.4, 20.6, 117.8, 124.8, 125.5, 133.7, 142.5,
144.5, 167.7, 167.8. UV (CH2Cl2) λmax 232 nm. Mass spectrum
(EI): m/z ) 64 (23), 102 (10), 131 (21), 139 (15), 172 (6), 204
(100), 246 (34), 288 (26), 352 (0.9). Peaks at 246 and 204 represent
the loss of two ketene CH2dCdO fragments.
1
3,4-Dimercapto-benzene-1,2-diol or “Tetraacetylated 9”. H
NMR 400 MHz (acetone-d6) δ 2.30 (s, 3H), 2.31 (s, 3H), 2.42 (s,
3H), 2.42 (s, 3H), 7.22 (d, J ) 8.7 Hz, 1H), 7.40 (d, J ) 8.7 Hz,
1H). Mass spectrum (EI): m/z ) 342 (3), 300 (44, M-Ac), 258
(55, M-2Ac), 216 (70, M-3Ac), 174 (100, M-4Ac).
Acetic Acid 3,2′,3′-Triacetoxy-biphenyl-2-yl Ester or “Tet-
raacetylated 10”. Catechol acts as an ambident nucleophile in a
reaction between the carbanion tautomer of catechol and o-quinone.
Mass spectrum (EI): m/z ) 386, 344 (M-Ac), 302 (M-2Ac), 260
(M-3Ac), 218 (M-4Ac).
Acetic Acid 2-(3,4-Diacetoxy-phenoxy)-phenyl Ester or “Tri-
acetylated 11”. Mass spectrum (EI): m/z ) 344, 302 (M-Ac),
260 (M-2Ac), 218 (M-3Ac).
Acetic Acid 1-Acetoxy-dibenzo1,4dioxin-2-yl Ester or “Di-
acetylated 12”. Mass spectrum (EI): m/z ) 300, 258 (M-Ac),
216 (M-2Ac).
3-Mercaptobenzene-1,2-diol (5). 1H NMR (acetone-d6) δ 4.03
(s, 1H), 6.60 (t, J ) 7.82 Hz, 1H), 6.66 (dd, J ) 1.6, 7.8 Hz, 1H),
6.74 (dd, J ) 1.6, 7.8 Hz, 1H), 7.76 (s, 1H), 8.50 (s, 1H).
Acetic Acid 2-Acetoxy-3-acetylsulfanyl-phenyl Ester or “Tri-
acetylated 5”. Yield 0.0006 g. Triacetylated 5 was isolated from
silica gel TLC, Rf ) 0.42 (EtOAc/hexanes, 1:3), from the quinone-
H2Sx reaction or via recrystallization in chloroform as white crystals
(mp 80-83 °C) from the quinone-thiolacetic acid reaction (method
1, Supporting Information). The 1H NMR spectrum of triacetylated
5 shows three singlets corresponding to methyls of the acetyl groups
on two OH and SH groups adjacent to each other at 2.27, 2.29,
1
and 2.41 ppm, respectively. H NMR (acetone-d6) δ 2.27 (s, 3H),
2.29 (s, 3H), 2.41 (s, 3H), 7.37-7.46 (m, 3H). 13C NMR (acetone-
d6) δ 20.2, 20.3, 30.1, 124.6, 126.4, 134.5, 144.6, 168.1, 168.5,
Acknowledgment. This work was supported by research
grants from the National Institutes of Health (S06 GM076168-
01) and PSC-CUNY (67341-0036). Cliff Soll (Hunter College
Mass Spectrometry Facility) and Kym Faull and Ken Conklin
(Pasarow UCLA Mass Spectrometry Laboratory) were respon-
sible for conducting several mass measurements. Computational
support was provided by the CUNY Graduate Center compu-
tational facility.
192.0. IR (KBr) ν 1765, 1703, 1466, 1368, 1262, 1213, 1005 cm-1
.
Mass spectrum (EI): m/z ) 83 (2), 96 (1), 113 (2), 142 (100,
M-3Ac), 184 (55, M-2Ac), 226 (27, M-Ac), 268 (8). HRMS calcd
for C12H12O5S (M + H)+ 269.0478, found 269.0476.
4-Mercaptobenzene-1,2-diol (6). 1H NMR (acetone-d6) δ 3.10
(s, 1H), 6.68 (dd, J ) 2.1, 8.2 Hz, 1H), 6.73 (d, J ) 8.2 Hz, 1H),
6.84 (d, J ) 2.1 Hz, 1H), 8.03 (s, 1H), 7.93 (s, 1H).
Acetic Acid 2-Acetoxy-5-acetylsulfanyl-phenyl Ester or “Tri-
acetylated 6”. Prepared from the quinone-H2Sx reaction and the
quinone-thiolacetic acid reaction (method 2). Purification was
accomplished by column chromatography using EtOAc/hexanes (1:
4). Yellow crystals were obtained (mp 79-82 °C). 1H NMR
(acetone-d6) δ 2.47 (s, 3H), 2.48 (s, 3H), 2.62 (s, 3H), 7.49 (d, J )
8.4 Hz, 1H), 7.51 (s, 1H), 7.54 (dd, J ) 2.1, 8.4 Hz, 1H). 13C
NMR (acetone-d6) δ 19.5, 19.5, 29.2, 124.0, 126.0, 129.3, 132.6,
142.4, 143.3, 168.0, 193.0. IR (KBr) ν 1773, 1752, 1703, 1491,
1364 cm-1. Mass spectrum (EI): m/z ) 268 (7), 226 (39, M-Ac),
184 (48, M-2Ac), 142 (100, M-3Ac). HRMS calcd for C12H12O5S
(M + H)+ 269.0478, found 269.0478.
Note Added after ASAP Publication. In the text,
“[o-C6H4(OH)2]” was incorrectly displayed as “[o-C6H4(HO)2]”
and “ambident” was spelled “ambient” in the version published
ASAP March 23, 2007; the corrected version was published
March 27, 2007.
Supporting Information Available: Experimental procedures
and spectroscopic data for new compounds 4-9 and HRMS data
for 5, 6, and 8. This material is available free of charge via the
Internet at http://pubs.acs.org.
Acetic Acid 2-Acetoxy-6-(2,3-diacetoxy-phenylsulfanyl)-phen-
yl Ester or “Tetraacetylated 7”. Yield 0.0012 g. Silica gel TLC
JO062677W
J. Org. Chem, Vol. 72, No. 8, 2007 2955