The reaction of 1,3,5-trinitrobenzene with methoxide and hypochlorite ions

Full text of DOI:10.1021/jo951784f

J . Org. Chem. 1996, 61, 1551-1554
1551
Sch em e 1
Th e Rea ction of 1,3,5-Tr in itr oben zen e w ith
Meth oxid e a n d Hyp och lor ite Ion s†
Frank B. Mallory,*,‡ Donna S. Amenta,‡,§
Clelia W. Mallory,| and J ih-J en J oy Chiang Cheung‡
Department of Chemistry, Bryn Mawr College,
Bryn Mawr, Pennsylvania 19010, and
Department of Chemistry, University of Pennsylvania,
Philadelphia, Pennsylvania 19104
Sch em e 2
Received October 2, 1995
Some years ago we reported a novel reaction involving
various heterocyclic systems in which an aromatic nitro
substituent and an adjacent ring hydrogen are replaced
by chloro and methoxy substituents, respectively, through
the action of a combination of methoxide and hypochlorite
ions in aqueous methanol solution.1 In Scheme 1 we
show a representative example of this so-called chlo-
romethoxy reaction along with our hypothesis about its
three-step mechanism: nucleophilic addition of methox-
ide ion, electrophilic chlorination by attack of hypochlo-
rite ion trans to the methoxy group, and base-induced
E2 elimination. All of the examples of this reaction in
our original work1 and also in subsequent work2 involved
heterocycles. In order to test our view that there is no
special role of the heterocycle in these systems other than
to provide electron-withdrawing stabilization for the
initial Meisenheimer-like intermediate we decided to
determine whether 1,3,5-trinitrobenzene (1), a nonhet-
erocyclic system that readily forms a Meisenheimer
adduct, would undergo the chloromethoxy reaction.
It was first reported more than a century ago3 that a
bright red color is produced when a methanol solution of
1,3,5-trinitrobenzene (1) is treated with methoxide ion
(generated by dissolving potassium hydroxide in the
solution). This phenomenon has been studied extensively
in the ensuing years. It is now understood,4 as illustrated
in Scheme 2, that with 1 equiv of methoxide ion these
red solutions contain predominantly the simple monoan-
ionic Meisenheimer adduct 2, and that with an excess of
methoxide ion the dianionic adduct 3 is produced. Al-
though the trianionic adduct 4 seems not to have been
reported specifically for 1 and methoxide ion, analogous
triple adducts of 1 are known for other nucleophiles.4a
We now report that treatment of these red methanolic
solutions with aqueous sodium hypochlorite gives 3,5-
dichloro-2,4,6-trimethoxynitrobenzene (5) as the major
isolated product and 1,3,5-trichloro-2,4,6-trimethoxyben-
zene (6) as a minor isolated product (Scheme 3).5 Al-
though products 5 and 6 are easily isolated the yields
are only 14% and 1%, respectively; the dominant reaction
Sch em e 3
of 1 under our reaction conditions is the well-precedented
total degradation of the aromatic ring by reaction with
hypochlorite ion to generate chloropicrin, Cl3CNO2, and
carbon dioxide.6 This type of degradative reaction ap-
parently is not a major competing pathway in the
previously reported heterocyclic examples of the chlo-
romethoxy reaction, which give yields in the 40-90%
range.1,2 The isolation of products 5 and 6 from the
reaction of 1 suggests that chemistry analogous to that
illustrated in Scheme 1 can indeed take place in a
nonheterocyclic system.
As depicted in Scheme 4 the structure of product 5 was
established by reducing it to amine 7, converting 7 to 1,3-
dichloro-2,4,6-trimethoxybenzene (8) by treatment with
nitrous acid and hypophosphorous acid, and comparing
this material to an authentic sample of 8 prepared by
the known reaction7 of 1,3,5-trimethoxybenzene (9) with
phosphorus pentachloride. The spectral properties and
elemental analysis of product 5 provide additional sup-
port for the assigned structure. Product 6 is a previously
known compound.8 The mp and spectral properties of
our sample of 6 are consistent with the assigned struc-
ture. We also confirmed the identity of this product by
comparing it to an authentic sample of 6 prepared by a
Sandmeyer reaction of amine 7 as shown in Scheme 4.
The transformation of 1,3,5-trinitrobenzene (1) to a
mixture of 5 and 6 obviously involves a multistep
pathway that is very complicated mechanistically. At one
mechanistic extreme one might imagine that products 5
and 6 each are formed by three consecutive chloromethoxy-
type reactions. In this context (Scheme 5) the mecha-
† Taken in part from the Ph.D. dissertation of Donna S. Amenta,
Bryn Mawr College, and in part from the Senior Honors Thesis of J ih-
J en J oy Chiang, Bryn Mawr College.
‡ Bryn Mawr College.
§ Current address: Department of Chemistry, J ames Madison
University, Harrisonburg, VA 22807.
| University of Pennsylvania.
(1) (a) Mallory, F. B.; Varimbi, S. P. J . Org. Chem. 1963, 28, 1656.
(b) Mallory, F. B.; Wood, C. S.; Hurwitz, B. M. J . Org. Chem. 1964,
29, 2605.
(2) Eckroth, D. R.; Cochran, T. G.; Taylor, E. C. J . Org. Chem. 1966,
31, 1303.
(3) (a) Hepp, P. Liebigs Ann. Chem. 1882, 215, 345. (b) Lobry de
Bruyn, C. A.; Van Leent, F. H. Recl. Trav. Chim. Pays-Bas 1895, 14,
150.
(4) (a) Strauss, M. J . Chem. Rev. 1970, 70, 667. (b) Servis, K. L. J .
Am. Chem. Soc. 1967, 89, 1508. (c) Bernasconi, C. F.; Bergstrom, R.
G. J . Am. Chem. Soc. 1974, 96, 2397.
(5) A small amount (3% yield) of 3,5-dinitroanisole also is obtained
under these reaction conditions. This compound is the major product
from the reaction of 1,3,5-trinitrobenzene (1) with methoxide ion in
methanol solution in the absence of hypochlorite ion. (a) Lobry de
Bruyn, C. A. Recl. Trav. Chim. Pays-Bas 1890, 9, 208. (b) Reverdin,
F. Organic Syntheses; Wiley: New York, 1932; Collect. Vol. I, p 219.
(c) Gold, V.; Rochester, C. H. J . Chem. Soc. 1964, 1692.
(6) Butler, A. R.; Wallace, H. F. J . Chem. Soc. (B) 1970, 1758.
(7) Lloyd, G.; Whalley, W. B. J . Chem. Soc. 1956, 3209.
(8) Strating, J .; Thijs, L.; Zwanenburg, B. Recl. Trav. Chim. Pays-
Bas 1966, 85, 291.
0022-3263/96/1961-1551$12.00/0 © 1996 American Chemical Society

1552 J . Org. Chem., Vol. 61, No. 4, 1996
Notes
Sch em e 4
Sch em e 8
Sch em e 5
Sch em e 6
Sch em e 7
version of 1 to the mixture of 5 and 6, we feel obliged to
present at least a plausible rationalization. In that spirit
we offer as a working hypothesis the pathway shown in
Scheme 8 in which we imagine, at another mechanistic
extreme, that the three M steps and the three C steps
all are complete10 before any E step takes place. This
pathway would involve a cyclohexane of type 16 as a key
intermediate.11 One might think that the six-step trans-
formation of 1 to 16 could be very complicated stereo-
nistic pathways each would involve methoxide addition
(M), chlorination (C), and elimination (E) steps in the
sequence M-C-E-M-C-E-M-C-E, and compounds 10 and
11 would be formed as intermediates. To test the validity
of this idea we synthesized the putative intermediates
10 and 11 by the reactions shown in Scheme 6. By
demonstrating that these independently synthesized
samples of compounds 10 and 11 fail to undergo conver-
sion to products 5 and 6 under the reaction conditions
employed for the formation of these two products from
1, we ruled out the mechanistic pathway shown in
Scheme 5. We did find, however, that under these
reaction conditions compounds 10 and 11 each are
chemically because many different stereoisomers are
possible for 16. On the basis of steric and stereoelectronic
considerations, however, we suggest that the three M
steps and the first two C steps may lead preferentially
to a single species, anion 17. From consideration of
molecular models it appears that the trans pathway for
the chlorination of anion 17, which would generate
stereoisomer 16b, would be disfavored by steric interac-
tions between the incoming hypochlorite ion and the two
axial chlorine atoms in 17. As a consequence we suggest
that for this final C step the normal preference for overall
transformed to the substituted cyclohexadiene 14.
A
mechanistic rationalization for these unusual transfor-
mations is offered in Scheme 7. The structure of 14 was
proved by its spectral properties and its elemental
analysis, and also by the spectral properties and elemen-
tal analysis of ketone 15, which is obtained from the
thermal decomposition of 14 in chloroform solution.9
Although we do not have enough information to make
a well-founded mechanistic proposal regarding the con-
(10) Five permutations are conceivable for the sequence of these six
steps: M-C-M-C-M-C, M-C-M-M-C-C, M-M-C-C-M-C, M-M-C-M-C-C,
and M-M-M-C-C-C.
(11) We speculate further that intermediates related to 16, especially
those formed from hydroxide addition rather than methoxide addition,
might be involved in the formation of the dominant product chloro-
picrin6 by way of base-induced ring-opening followed by a series of
chlorination and fragmentation reactions.
(9) The conversion of 14 to 15 has a close parallel in the reported
formation of 1,2-naphthoquinone from 1-chloro-1-nitro-2-keto-1,2-
dihydronaphthalene in chloroform solution by the thermally induced
loss of nitrosyl chloride. Perrin, C. L. J . Org. Chem. 1971, 36, 420.

Notes
J . Org. Chem., Vol. 61, No. 4, 1996 1553
and then for 24 h at room temperature. The mixture was diluted
with 40 mL of water, and the resulting precipitate was collected
and washed with 20% aqueous NaOH and water. The crude
product was recrystallized twice from hexane to yield 0.25 g
(53%) of 8: mp 125.3-126.8 °C (lit.7 mp 129 °C); mixed mp with
authentic sample (see below) 125.6-127.0 °C; 1H NMR δ 6.38
(s, 1 H), 3.92 (s, 6 H), 3.89 (s, 3 H).
Chlorination of 1.0 g (6 mmol) of 1,3,5-trimethoxybenzene by
a previously reported method7 (Scheme 4) gave, after recrystal-
lization of the crude product from hexane, 1.2 g (75%) of an
authentic sample of 8: mp 126.7-127.4 °C (lit.7 mp 129 °C).
5-Ch lor o-4-m eth oxy-1,3-d in itr oben zen e (10). 2-Chloro-
4-nitrophenol (12) (4.35 g, 25 mmol) was treated with anhydrous
K2CO3 (12.5 g, 93 mmol) and methyl iodide (10 mL, 160 mmol)
in refluxing acetone for 3 h. The residue after evaporation of
the solvent was washed with 150 mL of water and collected.
Sublimation of the crude product (60 °C, 0.05 Torr) yielded 4.40
g (93%) of 2-chloro-4-nitroanisole: mp 93.0-95.0 °C (lit.14 mp
96 °C).
trans addition of the chloro and methoxy groups might
be skewed, by default, in favor of overall cis addition to
give mostly stereoisomer 16a . For simplicity we assume
that all of the subsequent base-induced elimination
reactions of 16a and 16b are of the E2 type, with anti
conformations strongly preferred in the transition struc-
tures. Thus 16a and 16b would undergo aromatization
only after conformational isomerization to 16a ′ and 16b′,
respectively. By a sequence of three consecutive E2
eliminations stereoisomer 16a ′ would give the major
isolated product 5, and similarly stereoisomer 16b′ would
give the minor isolated product 6.
Exp er im en ta l Section
Melting points were measured in an oil-bath apparatus and
are uncorrected. Elemental analyses were performed by M-H-W
Laboratories, Phoenix, AZ. Unless specified otherwise 1H NMR
spectra were measured in CDCl3 solution at 300.1 MHz.
Sublimations at reduced pressure were carried out as described
previously.12
A previously reported method15 (Scheme 6) was used to
convert 4.0 g (21 mmol) of 2-chloro-4-nitroanisole to 4.0 g (83%)
of 10: mp 34.8-35.2 °C (lit.15 mp 36 °C); 1H NMR δ 8.66 and
8.60 (ABq, 2H, J ) 2.2 Hz), 4.20 (s, 3 H).
3,5-Dich lor o-2,4,6-tr im eth oxyn itr oben zen e (5) a n d 1,3,5-
Tr ich lor o-2,4,6-tr im eth oxyben zen e (6) fr om 1,3,5-Tr in i-
t r ob en zen e (1). Samples of 4.26 g (20 mmol) of 1,3,5-
trinitrobenzene (1) and 11.2 g (170 mmol) of 85% KOH were
dissolved in 300 mL of methanol to give a red solution. This
color gradually changed to yellow as 250 mL (176 mmol) of 5.25%
aqueous NaOCl (Clorox) was added over 3 h at 25-28 °C. After
48 h at room temperature some inorganic salts were filtered off
and the filtrate was chilled to 0 °C. The resulting precipitate
was collected, washed with cold water, and air-dried to give 1.0
g of white crystalline material that was shown by gas chroma-
tography (GC) to consist of an approximately 80:15:5 mixture
of three components.
3,5-Dich lor o-2,4-d im eth oxyn itr oben zen e (11). A pow-
dered sample of 1.65 g (6.3 mmol) of 2,3,4,5-tetrachloronitroben-
zene (13) was added to a stirred solution prepared previously
by the reaction of 1.5 g (65 mmol) of sodium with 65 mL of
methanol. This mixture was heated under reflux for 1 h and
then was poured over 60 g of crushed ice. The resulting
precipitate was collected and recrystallized twice from aqueous
methanol to yield 1.0 g (63%) of 11: mp 72.8-73.6 °C; 1H NMR
δ 7.89 (s, 1 H), 4.03 (s, 3 H), and 3.99 (s, 3 H); GC/MS m/ z 251,
253, 255; IR (KBr) 1525, 1345, 1210, 1071 cm-1. Anal. Calcd
for C8H7Cl2NO4: C, 38.12; H, 2.80. Found: C, 38.22; H, 2.97.
1,3,5-Tr ich lor o-2,4,4-tr im eth oxy-1-n itr o-2,5-cycloh exa d i-
en e (14) a n d 3,5-Dich lor o-2,4,4-tr im eth oxy-2,5-cycloh exa -
d ien on e (15). Samples of 1.0 g (4.0 mmol) of 11 and 2.8 g (42
mmol) of 85% KOH were dissolved in 200 mL of methanol to
give a yellow solution to which 80 mL (56 mmol) of 5.25%
aqueous NaOCl (Clorox) was added dropwise over 15 min at 25-
31 °C. After two days at room temperature the reaction mixture
was diluted with 1 L of water and placed in a freezer for 12 h.
The resulting precipitate was collected, washed with water, and
The crude product mixture was chromatographed on alumina
with a 1:4 mixture of benzene and hexane as the eluent to yield
0.8 g (14%) of 5: mp 81.8-82.8 °C; 1H NMR δ 3.98 (s, 6 Η), 3.95
(s, 3 H). Anal. Calcd for C9H9Cl2NO5: C, 38.32; H, 3.22; N,
4.97. Found: C, 38.49; H, 3.33; N, 4.88.
This same chromatographic separation also yielded 0.05 g
(1%) of 6: mp 125-128 °C (lit.8 mp 130-131 °C); 1H NMR δ
3.90 (s, 9 H). The identity of this compound was confirmed by
comparisons (infrared spectrum and GC retention time) with
an authentic sample of 6 synthesized as described below.
The relative yield of the other minor product increased at
higher reaction temperatures, rising from about 15% at 28 °C
to about 60% at 70 °C. Recrystallization of the crude product
mixture from a reaction at 70 °C gave, in addition to 0.3 g of 5
and a trace of 6, 0.4 g (10%) of 3,5-dinitroanisole: mp 105.0-
106.5 °C (lit.5b mp 105.5-106.5 °C). The identity of this material
was confirmed by comparisons (mixed mp 105.0-106.5 °C,
infrared spectrum, and GC retention time) with an authentic
sample prepared as described previously.5b
1
air-dried to yield 0.5 g (39%) of 14: mp 90.0-91.0 °C; H NMR
δ 6.56 (s, 1 H), 4.13 (s, 3 H), 3.35 (s, 3 H), 3.25 (s, 3 H); IR (KBr)
1645, 1570, 1345, 1100 cm-1; UV (ethanol) no peaks above 205
nm. Anal. Calcd for C9H10Cl3NO5: C, 33.94; H, 3.16; Cl, 33.39.
Found: C, 33.25; H, 2.97; Cl, 33.48.
Samples of 0.32 g (1.4 mmol) of 5-chloro-4-methoxy-1,3-
dinitrobenzene (10) and 1.4 g (21 mmol) of 85% KOH were
dissolved in 35 mL of methanol to give a red solution. The color
gradually changed to yellow as 40 mL (28 mmol) of 5.25%
aqueous NaOCl (Clorox) was added dropwise over 1 h at 15-18
°C. After two days at room temperature the reaction mixture
was placed in a freezer for 3 h. The resulting precipitate was
collected, washed with water, and air-dried to yield 0.1 g (22%)
of material identified as 14 by 1H NMR and GC comparisons
with the sample of 14 produced from 11 as described above.
A sample of 14 was found to undergo slow decomposition in
CDCl3 solution at 40-50 °C. After this reaction was substan-
tially complete, as monitored by 1H NMR, the solvent was
evaporated and the residue was dissolved in diethyl ether. The
ether solution was cooled to about -35 °C to give crystalline
(15): mp 41.2-42.0 °C; 1H NMR δ 6.66 (s, 1 H), 3.96 (s, 3 H),
3.24 (s, 6 H); GC/MS m/ z 256, 254, 252; IR (KBr) 1600, 1665
cm-1; UV (ethanol) 242.5 nm (ꢀ ) 26000), 298 nm. In confirma-
tion of this structural assignment for 15, the increases in δ
values that were observed16 to accompany the addition of tris-
(dipivalomethanato)europium to a CCl4 solution of 15 were
1,3,5-Tr ich lor o-2,4,6-tr im eth oxyben zen e (6) via Am in e
7. A previously reported method13 (Scheme 4) was used to
convert 1.0 g (3.5 mmol) of 5 to 0.45 g (51%) of 3,5-dichloro-
1
2,4,6-trimethoxyaniline (7): mp 62.6-64.0 °C; H NMR δ 3.90
(s, 2 H), 3.85 (s, 6 H), 3.83 (s, 3 H); IR (CCl4) 3500, 3400 cm-1
.
Amine 7 (0.10 g, 0.4 mmol) was diazotized at 0-5 °C in 10
mL of 8 M HCl by adding 0.17 g (2.5 mmol) of NaNO2 dissolved
in 4 mL of water. The resulting solution was added slowly to a
solution of 1.0 g (10 mmol) of cuprous chloride in 4 mL of 6 M
HCl at 8-10 °C. This mixture was heated at 70 °C for 30 min
and then filtered. The filtrate was chilled in an ice bath, and
the resulting precipitate was collected and recrystallized from
aqueous ethanol to yield 6: mp 128.0-129.5 °C (lit.8 mp 130-
1
131 °C); H NMR δ 3.90 (s, 9 H).
1,3-Dich lor o-2,4,6-tr im eth oxyben zen e (8). Amine 7 (0.50
g, 2.0 mmol) was diazotized at 0-5 °C in 9 mL of glacial acetic
acid by adding 0.17 g (2.5 mmol) of NaNO2 dissolved in 2 mL of
concd H2SO4. Then 5 mL (36 mmol) of 50% aqueous H3PO2 was
added, and the resulting mixture was stirred for 1 h at 0-5 °C
(14) Schouten, A. E. Recl. Trav. Chim. Pays-Bas 1937, 56, 541.
(15) (a) Reverdin, F.; Philipp, K. Chem. Ber. 1905, 38, 3774. (b)
Holleman, A. F.; de Mooy, W. J .; Terweel, J . Recl. Trav. Chim. Pays-
Bas 1916, 35, 1. (c) Terrier, F.; Halle´, J .-C.; Simonnin, M.-P. Org. Magn.
Reson. 1971, 3, 361. (d) Terrier, F.; Millot, F.; Schaal, R. J . Chem. Soc.,
Perkin Trans. 2 1972, 1192.
(12) Mallory, F. B. J . Chem. Educ. 1962, 39, 261.
(13) Oliverio, A.; Castelfranchi, G.; Borra, G. Gazz. Chim. Ital. 1952,
82, 115.
(16) We thank Professor David R. Dalton of Temple University for
these measurements.

1554 J . Org. Chem., Vol. 61, No. 4, 1996
Additions and Corrections
largest for the aryl signal at 6.66 ppm, 75% as large for the
methoxy signal at 3.96 ppm, and 31% as large for the methoxy
signal at 3.24 ppm. Anal. Calcd for C9H10Cl2O4: C, 42.71; H,
3.98; Cl, 28.08. Found: C, 42.78; H, 4.21; Cl, 27.57.
tions to Bryn Mawr College that enabled the purchase
of an NMR spectrometer and a GC/MS system.
A
Research Corporation grant to F.B.M. also is gratefully
acknowledged.
Ack n ow led gm en t . We thank the W. M. Keck
Foundation, Merck & Co., Inc., the Camille and Henry
Dreyfus Foundation, and PQ Corporation for contribu-
J O951784F
Additions and Corrections
Vol. 60, 1995
Hu -Min g He, P h illip E. F a n w ick , Ka r l Wood , a n d Ma r k
Cu sh m a n *. A Novel 1,3 O f C Silyl Shift and Deacylation
Reaction Mediated by Tetra-n-butylammonium Fluoride in an
Aromatic System.
Ka zu h ir o Kon d o, Mik ik o Sod eok a , a n d Ma sa k a tsu
Sh iba sa k i*. Regioselective Olefin Insertion in Asymmetric
Heck Reaction. Catalytic Asymmetric Synthesis of a Versatile
Intermediate for Diterpene Syntheses.
Page 5905. Structures 4, 5, and 20 were misassigned
and should be corrected as shown below. Consequently,
the reported 1,3-silyl migration occurs in the anions
generated on treatment of 3 and 19 with n-butyllithium,
and compounds 4, 5, and 20 deacylate in the presence of
tetra-n-butylammonium fluoride in THF. We are grate-
ful to Professor Scott Rychnovsky, University of Califor-
nia, Irvine, for bringing this error to our attention.
Page 4323, Scheme 3 should include the following
legend:
(a) LiAlH4, Et2O, 23 °C; (b) HMPA, 224 °C (81%, 2 steps); (c)
TBDMSCl, imidazole, DMF (98%); (d) LDA, THF, -78 °C, then
Tf2NPh, 0 °C (65%); (e) 12, 9-BBN, THF, 23 °C, then H2O; 14,
Pd(PPh3)4 (cat.), K3PO4, 60 °C (72%); (f) TBAF, THF; (g) Tf2O,
NEt3, -78 °C (63%, 2 steps); (h) Pd(OAc)2 (9 mol %), (R)-BINAP
(18 mol %), K2CO3 (3 molar equiv), toluene, 50 °C, 96 h;
naphthalene·Cr(CO)3 (20 mol %), THF, 50 °C (62%, 2 steps); (i)
OsO4, t-BuOH-H2O, then NaHSO3, pyridine (76%); (j) TBDMSCl,
DMAP, CH2Cl2 (94%); (k) SO3·Py, NEt3, DMSO (90%); (l) HF,
MeCN-H2O (70%); (m) PhOC(dS)Cl, DMAP, MeCN; (n) Bu3SnH,
AIBN, benzene, 90 °C (43%, 2 steps).
J O954033M
Tosh ir o Ha r a d a ,* Hir ok i Wa d a , a n d Ak ir o Ok u *. Prepara-
tion of (1-Cyclopropylidenealkyl)zinc Reagents by the Reaction
of Homopropargylic Sulfonates with Triorganozincates.
J O9540357
Page 5370, Scheme 1. The correct drawings for ho-
mopropargylic sulfonates 2a -g and intermediate 3 are
shown below.
Step h en R. Wilson * a n d Qin g Lu . 1,3-Dipolar Cycloaddition
of N-Methylazomethine Ylide to C70
.
Page 6497, column 2, last line, and page 6498, column
1, first line. With respect to the sentence “To our
knowledge, the structure proposed for 1c is the first
reported product of addition across the 22,23-bond in
C70.”, we regret our failure to cite an earlier study in
which the first adduct across the 22,23-bond in C70 was
described: Herrmann, A.; Diederich, F.; Thilgen, C.; ter
Meer, H.-U.; Mu¨ller, W. H. Helv. Chim. Acta 1994, 77,
1689.
J O954030+
J O954036Z
Dou gla ss F . Ta ber ,* Ra m a S. Bh a m id ip a ti, a n d La r r y
Yet. Phenyldimethylsilyl as an Alcohol Surrogate in Intra-
molecular Diels-Alder Cycloaddition: Synthesis of R-Dicty-
opterol.
Cu llen L. Ca va lla r o a n d J effr ey Sch w a r tz*. A Rapid
Synthesis of Pyranoid Glycals from Glycosyl Bromides.
Page 7056, column 2. Corrected Scheme 3 is shown
below:
Page 5537. We neglected to cite prior work on the
intramolecular Diels-Alder cycloaddition of silyl-substi-
tuted acrylates:
Kolb, H. C.; Ley, S. V.; Slawin, A. M. Z.; Williams, D.
J . J . Chem. Soc., Perkin Trans. 1 1992, 2735.
Kolb, H. C.; Ley, S. V.; Sheppard, R. N.; Slawin, A. M.
Z.; Smith, S. C.; Williams, D. J .; Wood, A. J . Chem. Soc.,
Perkin Trans. 1 1992, 2763.
J O954029A
J O954028I