Synthesis of polysubstituted bicyclo[3.3.1]nonane-3,7-diones from cyclohexa-2,5-dienones and dimethyl 1,3-acetonedicarboxylate

Article abstract of DOI:10.1016/S0040-4020(00)00680-3

Oxidation of polysubstituted phenols with phenyliodonium diacetate gives cyclohexa-2,5-dienones, which on reaction with dimethyl 1,3-acetonedicarboxylate afford double-Michael-addition derivatives, whose hydrolysis and decarboxylation provides polysubstituted bicyclo[3.3.1]nonane-3,7-diones. For steric and/or electronic reasons, the Michael reaction only works with 3,5-unsubstituted or 3-substituted cyclohexa-2,5-dienones, if the substituent is not an electron-releasing or a good electron-withdrawing group. Hydrolysis and decarboxylation of the double-Michael adducts from 2,4,4- or 2,4,4,6-substituted cyclohexa-2,5-dienones gives only products of partial hydrolysis and decarboxylation, which exist exclusively in the enol form. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4020(00)00680-3

TETRAHEDRON
Pergamon
Tetrahedron 56 (2000) 8141±8151
Synthesis of Polysubstituted Bicyclo[3.3.1]nonane-3,7-diones from
Cyclohexa-2,5-dienones and Dimethyl 1,3-Acetonedicarboxylate
a
a
a
Pelayo Camps,a, Albert Gonzalez, Diego MunÄoz-Torrero, Montserrat Simon,
*
Â
Adriana Zuniga, Miriam A. Martins, Merce Font-Bardia and Xavier Solans
a,²
a,³
b
b
Á
Â
Ä
a
 Á Á
Laboratori de Quõmica Farmaceutica, Facultat de Farmacia, Universitat de Barcelona, Av. Diagonal 643; E-08028, Barcelona, Spain
b
Á
Departament de Cristal.logra®a, Mineralogia i Diposits Minerals, Facultat de Geologia, Universitat de Barcelona,
 Á
Av. Martõ Franques s/n; E-08028, Barcelona, Spain
Received 5 June 2000; revised 10 July 2000; accepted 27 July 2000
AbstractÐOxidation of polysubstituted phenols with phenyliodonium diacetate gives cyclohexa-2,5-dienones, which on reaction with
dimethyl 1,3-acetonedicarboxylate afford double-Michael-addition derivatives, whose hydrolysis and decarboxylation provides polysubsti-
tuted bicyclo[3.3.1]nonane-3,7-diones. For steric and/or electronic reasons, the Michael reaction only works with 3,5-unsubstituted or
3-substituted cyclohexa-2,5-dienones, if the substituent is not an electron-releasing or a good electron-withdrawing group. Hydrolysis
and decarboxylation of the double-Michael adducts from 2,4,4- or 2,4,4,6-substituted cyclohexa-2,5-dienones gives only products of partial
hydrolysis and decarboxylation, which exist exclusively in the enol form. q 2000 Elsevier Science Ltd. All rights reserved.
The two-fold condensation of dimethyl 1,3-acetonedicar-
boxylate with 1,2-dicarbonyl compounds, the Weiss±Cook
reaction, has been shown to be a versatile method for the
formation of cis-bicyclo[3.3.0]octane-3,7-dione derivatives
(Scheme 1).1,2 A large number of cis-bicyclo[3.3.0]octane-
3,7-diones, mono- or di-substituted at positions 1 and/or 5,
are easily available by this procedure. These diketones have
been widely used as precursors for the synthesis of many
polyquinane natural products and non-natural polyquinanes
of theoretical interest.2,3 Bertz extended the above reaction
to a 1,3-dicarbonyl compound (malondialdehyde), making
bicyclo[3.3.1]nonane-3,7-dione readily available from
inexpensive starting materials (Scheme 1).4,5 Only a few
examples of this kind of reaction are known starting from
other 1,3-dicarbonyl compounds to give 1- or 9-mono-
substituted bicyclo[3.3.1]nonane-3,7-diones.4,6 In most
cases, under similar reaction conditions, phenols were the
only isolated products.7
Scheme 1. Synthesis of cis-bicyclo[3.3.0]octane-3,7-diones and bicyclo[3.3.1]nonane-3,7-diones from 1,2- and 1,3-dicarbonyl compounds.
Keywords: phenols, cyclohexenones; bicyclic aliphatic compounds; X-ray crystal structures.
* Corresponding author. Tel.: 134-93402-4536; fax: 134-93403-5941; e-mail: camps@farmacia.far.ub.es
²
Â
Current address: Instituto de Investigaciones en Quõmica Organica, Universidad Nacional del Sur, Av. Alem 1253; 8000-Bahõa Blanca, Argentine.
Current address: Departamento de Quõmica Organica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, 1428-Buenos Aires,
Â
Â
³
Â
Â
Argentine.
0040±4020/00/$ - see front matter q 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(00)00680-3

8142
P. Camps et al. / Tetrahedron 56 (2000) 8141±8151
Scheme 2. Synthesis of polysubstituted bicyclo[3.3.1]nonane-3,7-diones from phenols. (i) Phenyliodonium diacetate, MeOH, room temp., 4 h; (ii) dimethyl
1,3-acetonedicarboxylate, NaOMe, MeOH, re¯ux, 48 h; (iii) (a) NaOH, H2O, MeOH, re¯ux, 12 h; (b) 2N HCl, room temp., 1 h.
Several bicyclo[3.3.1]nonane-3,7-diones have been
prepared through an alternative approach, which involves
a double Michael condensation of dimethyl 1,3-aceto-
nedicarboxylate with p-benzoquinone monoacetals8,9 or
4,4-dialkylcyclohexa-2,5-dienones,10,11 followed by hydro-
lysis and decarboxylation of the resulting diesters to
give 9,9-dialkoxy- or 9,9-dialkyl-bicyclo[3.3.1]nonane-
3,7-diones. We published the synthesis of 9-methoxy-9-
(2) From the oxidation of phenol 7, 6,6-dimethoxycyclo-
hexa-2,4-dienone 21 was isolated after column chromatro-
graphy in 9% yield, which was stable enough to be fully
characterized through its spectroscopic data and elemental
analysis. However, from the oxidation of o-cresol, 10,
compound 24, a Diels±Alder dimer of 6-methoxy-6-
methylcyclohexa-2,4-dienone, was isolated in 11% yield.
Similarly, from the oxidation of 2,6-dimethylphenol, 11,
compound 27, a Diels±Alder dimer of 6-methoxy-2,6-
dimethylcyclohexa-2,4-dienone having the same structure
and stereochemistry as 24, was isolated in 16% yield. The
structure of both dimers 24 and 27 was fully established by
X-ray diffraction analysis of monocrystals obtained by
recrystallizaton from AcOEt (Figs. 1 and 2).
methylbicyclo[3.3.1]nonane-3,7-dione, 28, through
a
similar procedure.12
It is known that oxidation of phenols with phenyliodonium
diacetate (PIDA) to p-benzoquinone monoacetals and
4-alkoxy-4-alkylcyclohexa-2,5-dienones proceeds in good
yields under mild conditions.13 This prompted us to study
the scope of the sequence phenol oxidation-double Michael
addition of dimethyl 1,3-acetonedicarboxylate-hydrolysis-
decarboxylation for the synthesis of diversely substituted
bicyclo[3.3.1]nonane-3,7-diones, which is herein described
(Scheme 2).
It is known that oxidation of substituted phenols with PIDA
can yield either 4,4-disubstituted cyclohexa-2,5-dienones or
6,6-disubstituted cyclohexa-2,4-dienones, depending on the
structure of the starting phenol.17 The major or sole oxida-
tion product in this kind of reactions is usually the 4,4-
disubstituted cyclohexa-2,5-dienone but, in some cases,
especially in the oxidation of 2-substituted phenols, com-
petitive or preferential formation of 6,6-disubstituted cyclo-
hexa-2,4-dienones has been observed.17 Although several
6,6-disubstituted cyclohexa-2,4-dienones are stable at
room temperature,18 these kind of compounds usually
undergo rapid Diels±Alder dimerization to give 1,4-ethano-
naphthalene derivatives.16,18±22 In fact, dimer 27 is a known
compound, which was obtained by Adler et al. on oxidation
of 11 with anhydrous periodic acid in MeOH.16 Its structure
was assigned by analogy with that of related dimers, whose
structure had been established by X-ray diffraction
analysis.23,24 Thus, the Diels±Alder dimerization of
6-methoxy-6-methylcyclohexa-2,4-dienone and 6-methoxy-
2,6-dimethylcyclohexa-2,4-dienone to give compounds 24
and 27, respectively, takes place with the usual regio- and
diastereo-selectivities, i.e., the dienophile reacts by the C4±
C5 double bond (site selectivity); the diene and dienophile
approach each other in a de®ned relative orientation (C2
diene/C4 dienophile and C5 diene/C5 dienophile: regio-
selectivity) from their less hindered faces (those where
the less sterically demanding methoxy group is placed:
face selectivity) in an endo arrangement (diastereo-
selectivity).16,20,21 Moreover, it must be emphasized that
dimers 24 and 27 derive from the cycloaddition of two
units of the corresponding intermediate cyclohexadienones
of the same chirality, in spite of their racemic nature. Cyclo-
addition of two cyclohexadienone units of opposed chirality
with the same site-, regio-, and endo-diastereoselectivity
must take place by the less hindered methoxy-face of one
Results and Discussion
Table 1 summarizes the results obtained in the oxidation of
the commercially available phenols 1±3, 5, and 7±11, and
of the known phenols 414 and 6,15 with PIDA. Oxidation of
the 4-substituted phenols, 1±6 and 8, and the 4-unsubsti-
tuted phenols, 7 and 9±11, with one or 2 equiv. of PIDA,
respectively, in MeOH at room temperature led to the
expected, and in many cases known, 4-alkyl-4-methoxy-
or 4,4-dimethoxy-cyclohexa-2,5-dienones in good to
moderate yields. Only the oxidation of phenol 9 failed,
giving a complex mixture of products which did not contain
any cyclohexadienone.
It is worth noting the byproducts isolated in several of these
reactions:
(1) From the oxidation of phenols 1 and 2, products 13 and
15, derived from the methoxylation of the benzylic position,
were isolated in 10 and 14% yield, respectively, after
column chromatography. The formation of these byproducts
suggests the intermediacy of a quinone methide inter-
mediate,16 which on nucleophilic addition of MeOH
would lead to the 4-(a-methoxyalkyl)phenols 13 and 15.
Although similar byproducts were not observed in other
oxidations of the phenols shown in Table 1, their possible
formation cannot be ruled out.

P. Camps et al. / Tetrahedron 56 (2000) 8141±8151
8143
Table 1. Synthesis of cyclohexa-2,5-dienones from substituted phenols
component and the more hindered methyl-face of its
enantiomer, that would be less favorable.
cyclohexa-2,5-dienone, 25, from the oxidation of 11 with
PIDA, under the standard conditions. Since acetal hydroly-
sis of 25 could take place during the silica-gel column
chromatography puri®cation of the crude reaction product,
in another assay, Et3N was added to the eluent during the
(3) 2,6-Dimethylbenzoquinone, 26, was obtained in 49%
yield, instead of the desired 4,4-dimethoxy-2,6-dimethyl-

8144
P. Camps et al. / Tetrahedron 56 (2000) 8141±8151
Table 2. Synthesis of bicyclo[3.3.1]nonane-3,7-diones from substituted
cyclohexa-2,5-dienones
Figure 1. Crystal structure (ortep) of dimer 24.
Figure 2. Crystal structure (ortep) of dimer 27.
chromatography, isolating the desired dienone 25 in 48%
yield. In this case no dimer 27 was isolated. In another
attempt in which 4 equiv. of Na2CO3 were added to the
reaction mixture to prevent the hydrolysis of the acetal
group, compounds 25 and 27 were isolated in only 15 and
8% yield, respectively.
The synthesis of differently substituted bicyclo[3.3.1]no-
nane-3,7-diones from the obtained cyclohexa-2,5-dienones
(Table 2) was carried out as described previously for the
preparation of diketone 28, i.e. by double Michael addition
of dimethyl 1,3-acetonedicarboxylate to the cyclohexa-2,5-
dienones under NaOMe catalysis in re¯uxing MeOH for
48 h, followed by hydrolysis and decarboxylation of the
resulting diketo diester by successive treatment with
NaOH/water under re¯ux for 12 h and with 2N HCl at
room temperature for 1 h.12 Products were isolated either
by column chromatography, sublimation or recrystalliza-
tion. Starting from 4,4-dimethoxycyclohexa-2,5-dienones,
the faces of the C3 and C5 sp2 carbon atoms are enantiotopic
and thus non-distinguishable by the anion derived from
dimethyl 1,3-acetonedicarboxylate. However, in the case
of 4-alkyl-4-methoxycyclohexa-2,5-dienones, these faces
are diastereotopic and thus the Michael addition would
take place preferentially by the less hindered face. In the
last case, after complete hydrolysis and decarboxylation,
the obtained bicyclo[3.3.1]nonane-3,7-dione would be the
same, no matter which face Michael addition had taken
place.
By this procedure, from dienone 14, diketone 29 was
obtained in 90% yield. However, starting from dienone
16, the yield of the obtained diketone 30 was only 15%,
taking into account the recovered unchanged starting
dienone (32%). Also, a small amount of the partially
hydrolyzed and decarboxylated product 31 (4%) was
isolated. The con®guration of compound 31 was assigned
on the basis of its 1H NMR data by comparison with related

P. Camps et al. / Tetrahedron 56 (2000) 8141±8151
8145
diketones. The chemical shift of the 6-Hexo and 8-Hexo
protons of 31 compared with the chemical shifts of the
2-Hexo/4-Hexo and the 6-Hexo/8-Hexo protons of 28,12
suggests them to be far from the methoxy group. This result
is concordant with the expected preferential Michael addi-
tion of the anion of dimethyl 1,3-acetonedicarboxylate by
the less hindered methoxy-face of dienone 16. The low yield
of the last reaction may be explained on the basis of the
higher steric hindrance of the isopropyl group as compared
with a methyl or ethyl group. Addition of the anion of
dimethyl 1,3-acetonedicarboxylate to dienone 16 by the
less hindered methoxy-face would give a cyclohexenone
derivative, which should adopt a conformation with the iso-
propyl group and the substituent derived from dimethyl 1,3-
acetonedicarboxylate in a pseudoaxial arrangement to be
able to give the second intramolecular Michael addition.
In this way, the isopropyl group would be an axial sub-
stituent for the cyclohexanone ring derived from the starting
cyclohexa-2,5-dienone. Steric hindrance may also explain
the isolation in this case of product 31, corresponding to the
partial hydrolysis and decarboxylation. This kind of
partially hydrolyzed and decarboxylated product had
already been observed in the preparation of a related 9,9-
disubstituted bicyclo[3.3.1]nonane-3,7-dione.8
Finally, reaction of dienones 23 and 25 with dimethyl
1,3-acetonedicarboxylate followed by hydrolysis and
decarboxylation of the intermediate diketo diesters, under
the standard conditions, gave the partially hydrolyzed and
decarboxylated compounds 35 and 36 as the only isolated
products in 52 and 28% yield, respectively. It is worth
noting that in the case of 36, similar results were obtained
using a higher excess of NaOH and longer reaction times
during the hydrolysis step. Moreover, several attempts to
hydrolyze and decarboxylate compound 36 by reaction
either with NaCl in wet DMSO at 170±1908C or with a
mixture of HOAc/conc. HCl/water in the ratio of 2:1:1
under re¯ux resulted in decomposition of the product.
The value of the coupling constant 8-H/1-H (Jˆ4.5 Hz) in
1
the H NMR spectrum of 35 and 6-H/5-H (Jˆ4.5 Hz) and
1
8-H/1-H (Jˆ4.0 Hz) in the H NMR spectrum of 36, are
indicative of the exo-axial arrangement of 6-H and 8-H in
36 and of 8-H in 35,27 and consequently of the endo-
equatorial arrangement of the methyl groups in both
compounds. This fact was con®rmed in the case of 36 by
X-ray diffraction analysis (Fig. 3). The relative position of
the methoxycarbonyl and methyl groups in compound 35
was established on the basis of the multiplicity of the signal
1
of 1-H in its H NMR spectrum. This proton appears as a
Reactions of the 3,4,4-trisubstituted cyclohexa-2,5-dienones
17±20 with dimethyl 1,3-acetonedicarboxylate were carried
out to prepare 1,9,9-trisubstituted bicyclo[3.3.1]nonane-3,7-
diones. Cyclohexadienone 17 was reacted with dimethyl
1,3-acetonedicarboxylate in the presence of NaOMe in
MeOH at room temperature to give a crude product in
which the corresponding diketo diester was a minor product.
Curiously, under similar conditions, using NaOEt in EtOH,
a crude product containing mainly the desired condensation
product was obtained. Hydrolysis and decarboxylation of
this product was carried out by using the method of Krapcho
et al. for the decarbalkoxylation of b-keto esters (NaCl in
wet DMSO at 140±1908C)25,26 to prevent hydrolysis of the
bridgehead ester. Under these conditions, compound 32 was
obtained in 56% yield. The reactions starting from cyclo-
hexadienones 18±20 were carried out under the standard
conditions. From dienone 18, diketone 33 was obtained in
44% yield, after hydrolysis and decarboxylation of the inter-
mediate condensation product. However, treatment of
dienone 19 under the same reaction conditions led to
compound 34, in 55% yield. Probably, 19 did not react
with dimethyl 1,3-acetonedicarboxylate due to the electron
releasing character of the acetamido group which reduces
the reactivity of the C2±C3 double bond of 19 towards
nucleophiles. Then, basic hydrolyis of 19 would give
aminocyclohexadienone 34.
doublet of doublets due to its vicinal coupling with 8-H
(Jˆ4.5 Hz) and its W-coupling with 5-H (Jˆ3.0 Hz), show-
ing the absence of protons at position 2. The formation of
compounds 35 and 36 instead of the corresponding fully
hydrolyzed and decarboxylated diketones could be
explained on steric grounds. Steric hindrance either with
the endo-8-methyl or syn-9-methoxy groups may prevent
compounds 35 and 36 existing in the keto ester form, in
which hydrolysis of the more electrophilic ester groups
should be more favorable.
In conclusion, the oxidation of differently substituted
phenols with PIDA, followed by double Michael addition
of dimethyl 1,3-acetonedicarboxylate to the resulting cyclo-
hexa-2,5-dienones, has allowed the synthesis of a series of
differently substituted bicyclo[3.3.1]nonane-3,7-diones,
Starting from the 3-acetylcyclohexadienone 20, a complex
mixture of products not containing the desired diketone was
obtained. In this case, the Michael addition of a nucleophile
at C2 could be more favorable than addition at C3. The
resulting intermediate could lose methoxide to give a phenol
derivative.
Dienone 22 failed to react with dimethyl 1,3-aceto-
nedicarboxylate, probably due to steric hindrance. The
starting product was mainly recovered after the hydrolysis
and decarboxylation step.
Figure 3. Crystal structure (ortep) of compound 36.

8146
P. Camps et al. / Tetrahedron 56 (2000) 8141±8151
such as 29, 30, 32 and 33, and related derivatives, such as
compounds 35 and 36, not previously described and
not easily available by other procedures. The steric and
electronic effects of the substituents attached to the reaction
centers of the intermediate cyclohexa-2,5-dienones play an
important role in the success of the Michael addition step,
while steric effects due to substituents at positions 6 and/or 8
of the adducts (from 2- and/or 6-substituted cyclohexa-2,5-
dienones) may prevent, at least partly, the hydrolysis and
decarboxylation of these bicyclic intermediates.
was isolated as a white solid, mp 78±808C (CH2Cl2) [lit.28
mp 79±808C (hexane)].
Spectroscopic data of 12. IR (NaCl): n 1689, 1634 cm21. 1H
NMR (300 MHz, CDCl3): d 1.44 (s, 3H, 4-CH3), 3.21 (s,
3H, OCH3), 6.31 [d, Jˆ10.2 Hz, 2H, 2(6)-H], 6.77 [d,
Jˆ10.2 Hz, 2H, 3(5)-H]. 13C NMR (75.4 MHz, CDCl3): d
26.1 (CH3, 4-CH3), 53.1 (CH3, OCH3), 72.4 (C, C4), 130.3
[CH, C2(6)], 151.6 [CH, C3(5)], 184.9 (C, C1).
Spectroscopic data of 13: IR (KBr): n 3286 cm21. 1H NMR
(300 MHz, CDCl3): d 3.38 (s, 3H, OCH3), 4.40 (s, 2H,
4-CH2), 5.49 (s, 1H, OH), 6.77 [d, Jˆ8.5 Hz, 2H, 2(6)-H],
7.21 [d, Jˆ8.5 Hz, 2H, 3(5)-H]. 13C NMR (75.4 MHz,
CDCl3): d 57.6 (CH3, OCH3), 74.5 (CH2, 4-CH2), 115.3
[CH, C2(6)], 129.2 (C, C4), 129.8 [CH, C3(5)], 155.7 (C,
C1).
Experimental
General
Melting points were determined with a MFB 595010 M
Gallenkamp melting point apparatus. 500 MHz H NMR
spectra were performed on a Varian VXR 500 spectrometer,
1
4-Ethyl-4-methoxycyclohexa-2,5-dienone (14)29 and
4-(1-methoxyethyl)phenol (15).30 This reaction was
carried out according to the procedure described above,
from a solution of PIDA (13.1 g, 40.7 mmol) in anhydrous
MeOH (250 mL) and a solution of phenol 2 (5.00 g,
41.0 mmol) in anhydrous MeOH (60 mL). On elution with
hexane/AcOEt 80:20, cyclohexadienone 14 (3.48 g, 56%
yield) was isolated as a yellowish oil. On elution with
hexane/AcOEt 70:30, phenol 15 (0.86 g, 14% yield) was
isolated as a white solid, mp 97±998C (CH2Cl2) [lit.30 mp
98±100.58C (Et2O/hexane)].
1
300 MHz H and 75.4 MHz 13C NMR spectra on a Varian
Gemini 300, and 50.3 MHz 13C NMR spectra on a Varian
Gemini 200. Chemical shifts (d) are reported in ppm related
to internal tetramethylsilane (TMS). Assignments given for
the NMR spectra of the polycyclic compounds are based on
DEPT, 1H/1H and 1H/13C COSY experiments (HMQC
sequence) and it was much facilitated by the observation
in many cases of W-couplings between all or part of the
following pairs of protons: 1-H/5-H, 2-Hexo/8-Hexo,4-
Hexo/6-Hexo, 2-Hendo/4-Hendo and 6-Hendo/8-Hendo
protons. Differentiation of the 2(4)-Hexo and 8(6)-Hexo
protons in 29 and 30 was carried out by comparison with
the data of 2812 for which NOESY experiments were
performed. IR spectra were recorded on a FT/IR Perkin±
Elmer spectrometer, model 1600. Unless otherwise stated,
silica gel SDS 60 (60±200 mm) was utilized for the column
chromatography. Elemental analyses were carried out at the
Spectroscopic data of 14. IR (NaCl): n 1669, 1632 cm21. 1H
NMR (300 MHz, CDCl3): d 0.83 (t, Jˆ7.5 Hz, 3H,
CH2CH3), 1.77 (q, Jˆ7.5 Hz, 2H, CH2CH3), 3.23 (s, 3H,
OCH3), 6.38 [d, Jˆ10.3 Hz, 2H, 2(6)-H], 6.72 [d,
Jˆ10.3 Hz, 2H, 3(5)-H]. 13C NMR (75.4 MHz, CDCl3): d
7.7 (CH3, CH2CH3), 32.1 (CH2, CH2CH3), 53.1 (CH3,
OCH3), 76.3 (C, C4), 131.6 [CH, C2(6)], 150.9 [CH,
C3(5)], 185.4 (C, C1).
Â
Microanalysis Service of the Centro de Investigacion y
Desarrollo (C.I.D.), C.S.I.C., Barcelona, Spain.
Spectroscopic and analytical data of 15: IR (KBr): n
3214 cm21
.
1H NMR (300 MHz, CDCl3): d 1.44 (d,
General procedure for the preparation of cyclohexa-2,5-
dienones from phenols
Jˆ6.5 Hz, 3H, CHCH3), 3.22 (s, 3H, OCH3), 4.28 (q,
Jˆ6.5 Hz, 1H, CHOCH3), 5.83 (br. s, 1H, OH), 6.82 [d,
Jˆ8.5 Hz, 2H, 2(6)-H], 7.18 [d, Jˆ8.5 Hz, 2H, 3(5)-H].
13C NMR (75.4 MHz, CDCl3): d 23.6 (CH3, CHCH3),
56.1 (CH3, OCH3), 79.3 (CH, CHCH3), 115.3 [CH,
C2(6)], 127.7 [CH, C3(5)], 135.1 (C, C4), 155.3 (C, C1).
A solution of PIDA (1.0±1.6 mmol for the oxidation of
4-substituted phenols, 2.0±2.2 mmol for the oxidation of
4-unsubstituted phenols) in anhydrous MeOH (6±10 mL)
was added dropwise over 40 min to a stirred solution of
the phenol (1 mmol) in anhydrous MeOH (2 mL). The reac-
tion mixture was stirred at room temperature for 4 h and
evaporated at reduced pressure. The resulting yellow oily
residue was submitted to column chromatography through
silica gel (hexane/AcOEt mixtures, gradient elution), afford-
ing the corresponding cyclohexa-2,5-dienones.
4-Isopropyl-4-methoxycyclohexa-2,5-dienone (16).29 This
compound was prepared according to the procedure
described above, from a solution of PIDA (14.2 g,
44.1 mmol) in anhydrous MeOH (100 mL) and a solution
of phenol 3 (5.00 g, 36.8 mmol) in anhydrous MeOH
(30 mL). On elution with hexane/AcOEt 80:20, cyclohexa-
dienone 16 (2.90 g), slightly contaminated with starting 3,
was separated. This product was taken up in CH2Cl2
(100 mL) and the resulting solution was washed with 1N
NaOH (50 mL) and water (50 mL), dried with anhydrous
Na2SO4 and evaporated at reduced pressure, to give pure
cyclohexadienone 16 (2.34 g, 38% yield) as a colorless
4-Methoxy-4-methylcyclohexa-2,5-dienone (12)17 and
4-(methoxymethyl)phenol (13). This reaction was carried
out according to the procedure described above, from a
solution of PIDA (16.4 g, 50.9 mmol) in anhydrous
MeOH (400 mL) and a solution of phenol 1 (5.00 g,
46.3 mmol) in anhydrous MeOH (100 mL). On elution
with hexane/AcOEt 95:5, cyclohexadienone 12 (4.20 g,
66% yield) was isolated as a yellowish oil. On elution
with hexane/AcOEt 80:20, phenol 13 (0.67 g, 10% yield)
oil. IR (NaCl): n 1668, 1632 cm21. H NMR (300 MHz,
1
CDCl3): d 0.93 [d, Jˆ6.9 Hz, 6H, CH(CH3)2], 1.99 [heptet,
Jˆ6.9 Hz, 1H, CH(CH3)2], 3.21 (s, 3H, OCH3), 6.41 [d,

P. Camps et al. / Tetrahedron 56 (2000) 8141±8151
8147
Jˆ10.2 Hz, 2H, 2(6)-H], 6.73 [d, Jˆ10.2 Hz, 2H, 3(5)-H].
described above, from a solution of PIDA (15.0 g,
46.6 mmol) in anhydrous MeOH (240 mL) and a solution
of phenol 7 (3.00 g, 22.1 mmol) in anhydrous MeOH
(135 mL), and using silica gel (40±60 mm) for the column
chromatography. On elution with hexane/AcOEt 80:20,
dienone 21 (0.39 g, 9% yield) and dienone 20 (0.96 g,
22% yield) were consecutively isolated as yellowish oils.
13C NMR (50.3 MHz, CDCl3): d 17.0 [CH3, CH(CH3) ],
36.5 [CH, CH(CH3)2], 53.0 (CH3, OCH3), 78.3 (C, C4),
132.2 [CH, C2(6)], 150.1 [CH, C3(5)], 183.0 (C, C1).
2
4,4-Dimethoxy-3-(methoxycarbonyl)cyclohexa-2,5-dienone
(17). This compound was prepared according to the pro-
cedure described above, from a solution of PIDA (5.14 g,
16.0 mmol) in anhydrous MeOH (100 mL) and a solution of
phenol 4 (2.00 g, 11.0 mmol) in anhydrous MeOH (50 mL).
On elution with hexane/AcOEt 80:20, cyclohexadienone 17
(1.92 g, 82% yield) was isolated as a yellowish oil, which
decomposed after few days at room temperature or on heat-
Spectroscopic and analytical data of 20. IR (NaCl): n 1685,
1
1662, 1634 cm21. H NMR (300 MHz, CDCl3): d 2.53 (s,
3H, COCH3), 3.40 (s, 6H, OCH3), 6.45 (dd, Jˆ10.1 Hz,
J0ˆ2.3 Hz, 1H, 6-H), 6.76 (d, Jˆ2.3 Hz, 1H, 2-H), 6.82
(d, Jˆ10.5 Hz, 1H, 5-H). 13C NMR (75.4 MHz, CDCl3): d
29.7 (CH3, COCH3), 51.1 (CH3, OCH3), 95.2 (C, C4), 131.2
(CH) and 131.8 (CH) (C2 and C6), 143.2 (CH, C5), 150.1
(C, C3), 185.3 (C, C1), 197.9 (C, COCH3). Anal. Calcd for
C10H12O4: C, 61.21; H, 6.17. Found: C, 61.17; H, 6.15.
ing. IR (NaCl): n 1736, 1678, 1639 cm21 1H NMR
.
(300 MHz, CDCl3): d 3.35 (s, 6H, OCH3), 3.89 (s, 3H,
COOCH3), 6.47 (dd, Jˆ10.4 Hz, J0ˆ2.2 Hz, 1H, 6-H),
6.85 (d, Jˆ10.4 Hz, 1H, 5-H), 6.89 (d, Jˆ2.2 Hz, 1H,
2-H). 13C NMR (75.4 MHz, CDCl3): d 51.3 (CH3, OCH3),
52.2 (CH3, COOCH3), 94.6 (C, C4), 130.6 (CH, C6), 134.6
(CH, C2), 144.2 (C, C3), 144.4 (CH, C5), 163.9 (C,
COOCH3), 184.6 (C, C1). Anal. Calcd for C10H12O5: C,
56.60; H, 5.70. Found: C, 56.52; H, 5.64.
Spectroscopic and analytical data of 21. IR (NaCl): n 1731,
1
1672, 1625 cm21. H NMR (300 MHz, CDCl3): d 2.46 (s,
3H, COCH3), 3.24 (s, 6H, OCH3), 6.25 (dd, Jˆ9.7 Hz,
J0ˆ1.2 Hz, 1H, 2-H), 7.03 (dd, Jˆ9.7 Hz, J0ˆ6.3 Hz, 1H,
3-H), 7.17 (dd, Jˆ6.3 Hz, J0ˆ1.2 Hz, 1H, 4-H). 13C NMR
(75.4 MHz, CDCl3): d 29.2 (CH3, COCH3), 50.9 (CH3,
OCH3), 94.0 (C, C6), 129.6 (CH, C2), 131.5 (CH) and
138.5 (CH) (C3 and C4), 145.4 (C, C5), 194.6 (C, C1),
196.8 (C, COCH3). Anal. Calcd for C10H12O4. 1/5H2O: C,
60.11; H, 6.26. Found: C, 60.10; H, 6.16.
4-Methoxy-3,4-dimethylcyclohexa-2,5-dienone (18).31 This
compound was prepared according to the procedure
described above, from a solution of PIDA (8.22 g,
25.5 mmol) in anhydrous MeOH (100 mL) and a solution
of phenol 5 (2.00 g, 16.4 mmol) in anhydrous MeOH
(30 mL). On elution with hexane/AcOEt 90:10, cyclohexa-
dienone 18 (1.46 g, 59% yield) was isolated as a yellowish
solid, mp 35±368C (acetonitrile) (Lit.31 oil). IR (KBr): n
4-Methoxy-3,4,5-trimethylcyclohexa-2,5-dienone (22).32
This compound was prepared according to the procedure
described above, from a solution of PIDA (7.80 g,
24.2 mmol) in anhydrous MeOH (120 mL) and a solution
of phenol 8 (3.00 g, 22.1 mmol) in anhydrous MeOH
(45 mL), with a reaction time of 1 h, and using silica gel
(40±60 mm) for the column chromatography. On elution
with hexane/AcOEt 90:10, cyclohexadienone 22 (2.05 g,
56% yield) was isolated as colorless crystals, mp 70±718C
[Lit.32 mp 50±528C (sublimed)]. IR (KBr): n 1674,
1
1671, 1636 cm21. H NMR (300 MHz, CDCl3): d 1.41 (s,
3H, 4-CH3), 1.99 (d, Jˆ1.4 Hz, 3H, 3-CH3), 3.08 (s, 3H,
OCH3), 6.19 (dq, Jˆ1.9 Hz, J0ˆ1.4 Hz, 1H, 2-H), 6.30 (dd,
Jˆ10.0 Hz, J0ˆ1.9 Hz, 1H, 6-H), 6.76 (d, Jˆ10.0 Hz, 1H,
5-H). 13C NMR (75.4 MHz, CDCl3): d 17.7 (CH3, 3-CH3),
25.4 (CH3, 4-CH3), 52.6 (CH3, OCH3), 74.4 (C, C4), 129.0
(CH) and 130.0 (CH) (C2 and C6), 152.0 (CH, C5), 160.5
(C, C3), 185.5 (C, C1).
1
1621 cm21. H NMR (300 MHz, CDCl3): d 1.35 (s, 3H,
3-Acetamido-4-ethyl-4-methoxycyclohexa-2,5-dienone (19).
This compound was prepared according to the procedure
described above, from a solution of PIDA (1.78 g,
5.53 mmol) in anhydrous MeOH (30 mL) and a solution
of phenol 6 (770 mg, 4.30 mmol) in anhydrous MeOH
(10 mL). On elution with hexane/AcOEt 60:40, cyclohexa-
dienone 19 (310 mg, 34% yield) was isolated as a white
solid, mp 134±1358C (CH2Cl2). IR (KBr): n 3274, 1717,
4-CH3), 1.97 [s, 6H, 3(5)-CH3], 2.92 (s, 3H, OCH3), 6.13
[s, 2H, 2(6)-H]. 13C NMR (75.4 MHz, CDCl3): d 17.7 (CH3,
4-CH3), 24.8 [CH3, 3(5)-CH3], 52.2 (CH3, OCH3), 76.8 (C,
C4), 129.0 [C, C2(6)], 160.7 [C, C3(5)], 185.2 (C, C1).
4,4-Dimethoxy-2-methylcyclohexa-2,5-dienone (23)22 and
(1RS,2RS,3SR,7SR,8SR,10SR)-3,10-dimethoxy-3,10-di-
methyltricyclo[6.2.2.02,7]dodeca-5,11-diene-4,9-dione
(24). This reaction was carried out according to the pro-
cedure described above, from a solution of PIDA (12.5 g,
38.8 mmol) in anhydrous MeOH (190 mL) and a solution of
phenol 10 (2.00 g, 18.5 mmol) in anhydrous MeOH
(35 mL), with a reaction time of 1 h. On elution with
hexane/AcOEt 90:10, dienone 23 (1.51 g, 49% yield) was
isolated as a colorless oil. On elution with hexane/AcOEt
80:20, compound 24 (290 mg, 11% yield) was isolated as
colorless crystals, mp 191±1928C (AcOEt).
1
1665, 1607 cm21. H NMR (300 MHz, CDCl3): d 0.78 (t,
Jˆ7.5 Hz, 3H, CH2CH3), 1.90 (m, 2H, CH2CH3), 2.24 (s,
3H, NHCOCH3), 3.22 (s, 3H, OCH3), 6.41 (dd, Jˆ10.2 Hz,
J0ˆ1.9 Hz, 1H, 6-H), 6.56 (d, Jˆ10.2 Hz, 1H, 5-H), 7.38
(broad s, 1H, NHCOCH3), 7.41 (d, Jˆ1.9 Hz, 1H, 2-H). 13
C
NMR (75.4 MHz, CDCl3): d 7.7 (CH3, CH2CH3), 25.0
(CH3, NHCOCH3), 32.5 (CH2, CH2CH3), 53.2 (CH3,
OCH3), 77.5 (C, C4), 114.7 (CH, C2), 132.2 (CH, C6),
145.0 (CH, C2), 150.9 (C, C3), 169.2 (C, NHCOCH3),
186.8 (C, C1). Anal. Calcd for C11H15NO3: C, 63.14; H,
7.23; N, 6.69. Found: C, 62.89; H, 7.04; N, 6.56.
Spectroscopic data of 23: IR (NaCl): n 1679, 1650 cm21. 1H
NMR (300 MHz, CDCl3): d 1.92 (d, Jˆ1.5 Hz, 3H, 2-CH3),
3.37 (s, 6H, OCH3), 6.27 (d, Jˆ10.5 Hz, 1H, 6-H), 6.62 (dq,
Jˆ3.3 Hz, J0ˆ1.5 Hz, 1H, 3-H), 6.81 (dd, Jˆ10.5 Hz,
J0ˆ3.3 Hz, 1H, 5-H). 13C NMR (75.4 MHz, CDCl3): d
3-Acetyl-4,4-dimethoxycyclohexa-2,5-dienone (20) and
5-acetyl-6,6-dimethoxycyclohexa-2,4-dienone (21). This
reaction was carried out according to the procedure

8148
P. Camps et al. / Tetrahedron 56 (2000) 8141±8151
15.6 (CH3, 2-CH3), 50.2 (CH3, OCH3), 92.8 (C, C4), 129.8
(CH, C6), 136.7 (C, C2), 138.3 (CH, C3), 142.8 (C, C5),
185.6 (C, C1).
(CH, C1), 42.7 (CH, C2), 43.0 (CH, C7), 50.7 (CH3) and
51.7 (CH3) (3-OCH3 and 10-OCH3), 53.8 (C, C8), 76.1 (C)
and 77.9 (C) (C3 and C10), 133.7 (CH, C12), 135.1 (CH,
C11), 136.5 (CH, C6), 137.6 (C, C5), 201.6 (C, C4), 210.6
(C, C9).
Spectroscopic and analytical data of 24: IR (KBr): n 1736,
1
1695 cm21. H NMR (500 MHz, CDCl3): d 1.23 (s, 3H, 3-
CH3), 1.44 (s, 3H, 10-CH3), 3.13±3.17 (complex signal, 2H,
2-H and 8-H), 3.29 (ddd, Jˆ8.0 Hz, J0ˆ4.0 Hz, J0ˆ2.0 Hz,
1H, 7-H), 3.33 (ddd, Jˆ7.0 Hz, J0ˆJ00ˆ1.5 Hz, 1H, 1-H),
3.34 (s, 3H) and 3.45 (s, 3H) (3-OCH3 and 10-OCH3), 5.84
(ddd, Jˆ8.0 Hz, J0ˆ6.5 Hz, J00ˆ1.5 Hz, 1H, 12-H), 5.95
(dd, Jˆ10.0 Hz, J0ˆ2.0 Hz, 1H, 5-H), 6.27 (dd, Jˆ
10.0 Hz, J0ˆ4.0 Hz, 1H, 6-H), 6.31 (ddd, J<J0<7.5 Hz,
J00ˆ1.0 Hz, 1H, 11-H). 13C NMR (75.4 MHz, CDCl3): d
19.9 (CH3, 3-CH3), 25.0 (CH3, 10-CH3), 38.9 (CH, C7),
41.8 (CH, C2), 42.9 (CH, C1), 51.0 (CH3) and 51.7 (CH3)
(3-OCH3 and 10-OCH3), 52.7 (CH, C8), 76.0 (C) and 77.9
(C) (C3 and C10), 128.4 (CH, C12), 129.8 (CH, C5), 135.8
(CH, C11), 144.0 (CH, C6), 200.6 (C, C4), 208.8 (C, C9).
Anal. Calcd for C16H20O4: C, 69.54; H, 7.30. Found: C,
69.60; H, 7.40.
General procedure for the preparation of bicyclo-
[3.3.1]nonane-3,7-diones from cyclohexa-2,5-dienones
To a stirred mixture of sodium (0.1±0.2 mmol) in anhy-
drous MeOH (3 mL), a solution of cyclohexadienone
(1 mmol) in anhydrous MeOH (4 mL) and a solution of
dimethyl 1,3-acetonedicarboxylate (2.1 mmol) in anhy-
drous MeOH (4 mL) were successively added dropwise,
and the reaction mixture was heated under re¯ux for 48 h.
The resulting solution was cooled to room temperature and
treated with water (6 mL) and NaOH pellets (4 mmol). The
mixture was heated under re¯ux overnight. The organic
solvent was evaporated in vacuo, and the resulting aqueous
mixture was made acidic with 2N HCl (4 mL), stirred at
room temperature for 1 h, and extracted with CH2Cl2
(3£10 mL). The combined organic extracts were dried
with anhydrous Na2SO4 and evaporated at reduced pressure
to give a residue, which was puri®ed by column chromato-
graphy through silica gel, recrystallization or sublimation.
4,4-Dimethoxy-2,6-dimethylcyclohexa-2,5-dienone (25)33
and (1RS,2RS,3SR,7SR,8SR,10SR)-3,10-dimethoxy-3,5,
8,10-tetramethyltricyclo[6.2.2.02,7]dodeca-5,11-diene-
4,9-dione (27).16 This reaction was carried out according to
the procedure described above, from a solution of PIDA
(10.6 g, 32.9 mmol) in anhydrous MeOH (160 mL) and a
solution of phenol 11 (1.96 g, 16.1 mmol) in anhydrous
MeOH (30 mL), with a reaction time of 1 h. On elution
with a mixture of hexane/AcOEt/Et3N 90:10:1, dienone 25
(1.42 g, 48% yield), slightly contaminated with 2,6-
dimethyl-1,4-benzoquinone, was isolated as a colorless oil.
9-Ethyl-9-methoxybicyclo[3.3.1]nonane-3,7-dione (29).
This compound was prepared according to the procedure
described above, from sodium (30 mg, 1.30 mmol) in anhy-
drous MeOH (20 mL), a solution of 14 (2.00 g, 13.2 mmol)
in anhydrous MeOH (40 mL) and a solution of dimethyl 1,3-
acetonedicarboxylate (4.57 g, 26.3 mmol) in anhydrous
MeOH (40 mL). The obtained solid residue consisted of
pure diketone 29 (2.50 g, 90% yield). The analytical sample
of 29 was obtained by recrystallization: white solid, mp
Note 1: When the reaction was carried out in the presence of
Na2CO3 (4 equiv.), dienone 25 (15% yield) and compound
27 (8% yield) were isolated after column chromatography.
141±1428C (Et2O). IR (KBr): n 1710, 1697 cm21 1H
.
NMR (500 MHz, CDCl3): d 0.99 (t, Jˆ7.5 Hz, 3H,
CH2CH3), 1.95 (q, Jˆ7.4 Hz, 2H, CH2CH3), 2.13 [br. d,
Jˆ15.5 Hz, 2H, 2(4)-Hendo], 2.33 [br. d, Jˆ16.5 Hz, 2H,
6(8)-Hendo], 2.60 [dm, Jˆ16.5 Hz, 2H, 6(8)-Hexo], 2.64
[m, 2H, 1(5)-H], 2.90 [dm, Jˆ15.5 Hz, 2H, 2(4)-Hexo],
3.31 (s, 3H, OCH3). 13C NMR (50.3 MHz, CDCl3): d 6.5
(CH3, CH2CH3), 22.3 (CH2, CH2CH3), 36.5 [CH, C1(5)],
43.8 [CH2, C2(4)], 44.7 [CH2, C6(8)], 48.4 (CH3, OCH3),
74.7 (C, C9), 207.8 (C, C7), 209.5 (C, C3). Anal. Calcd for
C12H18O3: C, 68.54; H, 8.63. Found: C, 68.70; H, 8.73.
Note 2: When no base was used during the reaction and no
Et3N was added to the mixture of eluents for the chromato-
graphic puri®cation, 2,6-dimethyl-1,4-benzoquinone, 26,
(49% yield) and dimer 27 (16% yield) as a white solid
were isolated after column chromatography.
Spectroscopic data of 25. IR (NaCl): n 1682, 1652,
1
1619 cm21. H NMR (300 MHz, CDCl3): d 1.83 [s, 6H,
2(6)-CH3], 3.27 (s, 6H, OCH3), 6.51 [s, 2H, 3(5)-H]. 13C
NMR (75.4 MHz, CDCl3): d 15.9 [CH3, 2(6)-CH3], 50.2
(CH3, OCH3), 92.7 (C, C4), 136.6 [CH, C3(5)], 138.3 [C,
C2(6)], 186.2 (C, C1).
9-Isopropyl-9-methoxybicyclo[3.3.1]nonane-3,7-dione
(30) and methyl 3-hydroxy-anti-9-isopropyl-syn-9-meth-
oxy-7-oxobicyclo[3.3.1]non-2-ene-2-carboxylate (31). This
compound was prepared according to the procedure
described above, from sodium (50 mg, 2.17 mmol) in anhy-
drous MeOH (10 mL), a solution of 16 (2.00 g, 12.0 mmol)
in anhydrous MeOH (30 mL) and a solution of dimethyl 1,3-
acetonedicarboxylate (4.63 g, 26.6 mmol) in anhydrous
MeOH (30 mL). The resulting residue was submitted to
column chromatography through silica gel (hexane/AcOEt
mixtures, gradient elution), isolating consecutively starting
16 (640 mg), compound 31 (100 mg, 3% yield, 4% yield
based on recovered 16), and diketone 30 (270 mg, 10%
yield, 15% yield based on recovered 16). The analytical
samples of 30 and 31 were obtained by recrystallization.
Spectroscopic and analytical data of 27: mp 143±1448C
(AcOEt) [described: mp 134±1358C (i-Pr2O)16]. IR (KBr):
n 1727, 1697 cm21. 1H NMR (500 MHz, CDCl3): d 1.21 (s,
3H, 3-CH3), 1.29 (s, 3H, 8-CH3), 1.39 (s, 3H, 10-CH3), 1.77
(dd, JˆJ0ˆ1.5 Hz, 3H, 5-CH3), 2.83 (ddm, Jˆ8.0 Hz,
J0ˆ3.5 Hz, 1H, 7-H), 3.11 (dd, Jˆ8.0 Hz, J0ˆ1.5 Hz, 1H,
2-H), superimposes in part 3.32 (dm, Jˆ7.5 Hz, 1H, 1-H),
3.33 (s, 3H) and 3.44 (s, 3H) (3-OCH3 and 10-OCH3), 5.46
(dd, J<8.0 Hz, J0ˆ1.0 Hz, 1H, 12-H), 6.11 (br. d,
J<3.5 Hz, 1H, 6-H), 6.24 (dd, JˆJ0ˆ7.5 Hz, 1H, 11-H).
13C NMR (75.4 MHz, CDCl3): d 15.7 (CH3, 8-CH3), 16.4
(CH3, 5-CH3), 20.1 (CH3, 3-CH3), 24.7 (CH3, 10-CH3), 41.5

P. Camps et al. / Tetrahedron 56 (2000) 8141±8151
8149
Spectroscopic and analytical data of 30: white solid, mp
145±1468C (Et2O). IR (KBr): n 1716, 1703 cm21 1H
2H, 2(8)-Hendo], 2.83 (s, 1H, 5-H), 2.84 [m, 2H, 4(6)-
Hexo], 3.37 [d, Jˆ15.5 Hz, 2H, 2(8)-Hexo], 3.37 (s, 6H,
9-OCH3), 3.73 (s, 3H, COOCH3). 13C NMR (75.4 MHz,
CDCl3): d 37.7 (CH, C5), 43.8 [CH2, C4(6)], 47.7 [CH2,
C2(8)], 49.5 (CH3, 9-OCH3), 52.3 (C, C1), 52.9 (CH3,
COOCH3), 100.3 (C, C9), 171.8 (C, COOCH3), 206.3 [C,
C3(7)]. Anal. Calcd for C13H18O6: C, 57.77; H, 6.72. Found:
C, 57.82; H, 6.86.
.
NMR (500 MHz, CDCl3): d 1.22 [d, Jˆ7.0 Hz, 6H,
CH(CH3)2], 2.16 [br. d, Jˆ13.5 Hz, 2H, 2(4)-Hendo], 2.35
[br. d, Jˆ17.0 Hz, 2H, 6(8)-Hendo], 2.37 [heptet, Jˆ7.0 Hz,
1H, CH(CH3)2], 2.61 [dm, Jˆ17.0 Hz, 2H, 6(8)-Hexo],
2.86±2.93 [complex signal, 4H, 1(5)-H and 2(4)-Hexo],
3.48 (s, 3H, OCH3). 13C NMR (50.3 MHz, CDCl3): d 17.3
[CH3, CH(CH3)2], 30.2 [CH, CH(CH3)2], 35.8 [CH, C1(5)],
44.3 [CH2, C2(4)], 44.6 [CH2, C6(8)], 52.5 (CH3, OCH3),
76.0 (C, C9), 208.0 (C, C7), 209.5 (C, C3). Anal. Calcd for
C13H20O3: C, 69.61; H, 8.99. Found: C, 69.60; H, 9.00.
9-Methoxy-1,9-dimethylbicyclo[3.3.1]nonane-3,7-dione
(33). This compound was prepared according to the general
procedure described above, from a mixture of sodium
(12 mg, 0.52 mmol) in anhydrous MeOH (10 mL), a solu-
tion of 18 (700 mg, 4.60 mmol) in anhydrous MeOH
(20 mL) and a solution of dimethyl 1,3-acetonedicarboxy-
late (2.00 g, 11.5 mmol) in anhydrous MeOH (20 mL).
Sublimation of the resulting residue (800 mg) at 1108C/
1 Torr afforded pure diketone 33 (430 mg, 44% yield) as a
white solid. The analytical sample of 33 was obtained by
recrystallization: mp 186±1888C (isopropanol). IR (KBr): n
Spectroscopic and analytical data of 31: white solid, mp
145±1488C (Et2O). IR (KBr): n 1713, 1652, 1613 cm21
.
1H NMR (500 MHz, CDCl3): d 1.15 (d, Jˆ6.5 Hz, 3H)
and 1.24 (d, Jˆ7.0 Hz, 3H) [CH(CH3)2], 2.07 (dd, Jˆ
18.5 Hz, J0ˆ1.0 Hz, 1H, 4-Hendo), 2.26 (ddd, Jˆ16.5 Hz,
J0ˆ2.5 Hz, J00ˆ1.5 Hz, 1H, 6-Hendo), 2.37 [heptet,
Jˆ6.5 Hz, 1H, [CH(CH3)2], 2.43 (ddd, Jˆ16.0 Hz,
J0ˆJ00ˆ3.0 Hz, 1H, 8-Hendo), 2.53±2.60 (complex signal,
2H, 6-Hexo and 8-Hexo), 2.62 (m, 1H, 5-H), 2.89 (ddd,
Jˆ18.5 Hz, J0ˆ7.0 Hz, J00ˆ1.5 Hz, 1H, 4-Hexo), 3.30 (s,
3H, OCH3), 3.42 (m, 1H, 1-H), 3.78 (s, 3H, COOCH3),
12.1 (s, 1H, OH). 13C NMR (75.4 MHz, CDCl3): d 16.4
(CH3) and 17.8 (CH3) [CH(CH3)2], 30.8 [CH, CH(CH3)2],
32.3 (CH, C1), 34.8 (CH2, C4), 34.9 (CH, C5), 43.1 (CH2,
C8), 45.8 (CH2, C6), 51.7 (CH3, COOCH3), 53.3 (CH3,
OCH3), 76.2 (C, C9), 98.3 (C, C2), 171.6 (C) and 172.3
(C) (C3 and COOCH3), 210.0 (C, C7). Anal. Calcd for
C15H22O5: C, 63.81; H, 7.86. Found: C, 63.67; H, 7.95.
1
1710 cm21. H NMR (500 MHz, CDCl3): d 1.02 (s, 3H,
1-CH3), 1.53 (s, 3H, 9-CH3), 1.96 (dd, Jˆ15.5 Hz, J0ˆ
2.5 Hz, 1H, 2-Hendo), 2.15 (dd, Jˆ13.5 Hz, J0ˆ2.5 Hz,
1H, 4-Hendo), 2.20 (dd, Jˆ16.5 Hz, J0ˆ2.5 Hz, 1H,
8-Hendo), 2.38 (ddd, Jˆ16.5 Hz, J0ˆJ00ˆ2.5 Hz, 1H,
6-Hendo), 2.46 (dd, Jˆ16.5 Hz, J0ˆ2.5 Hz, 1H, 8-Hexo),
2.58 (dm, Jˆ16.5 Hz, 1H, 6-Hexo), 2.70±2.78 (complex
signal, 2H, 4-Hexo and 5-H), 2.91 (dd, Jˆ15.5 Hz,
J0ˆ2.5 Hz, 1H, 2-Hexo), 3.34 (s, 3H, 9-OCH3). 13C NMR
(75.4 MHz, CDCl3): d 16.6 (CH3, 9-CH3), 23.3 (CH3,
1-CH3), 37.6 (CH, C5), 43.3 (C, C1), 43.9 (CH2, C4), 45.1
(CH2, C6), 48.9 (CH3, 9-OCH3), 50.8 (CH2, C2), 52.4 (CH2,
C8), 75.0 (C, C9), 207.4 (C, C3), 209.3 (C, C7). Anal. Calcd
for C12H18O3: C, 68.54; H, 8.63. Found: C, 68.51; H, 8.62.
Methyl 9,9-dimethoxy-3,7-dioxobicyclo[3.3.1]nonane-1-
carboxylate (32). To a stirred mixture of sodium (25 mg,
1.09 mmol) in absolute EtOH (10 mL), a solution of 17
(1.12 g, 5.28 mmol) in absolute EtOH (10 mL) and a
solution of dimethyl 1,3-acetonedicarboxylate (1.01 g,
5.80 mmol) in absolute EtOH (10 mL) were successively
added dropwise, and the reaction mixture was heated at
room temperature for 48 h. The resulting solution was
evaporated in vacuo and the resulting residue was taken
up in CHCl3 (30 mL), and washed with 5N HCl (20 mL)
and water (20 mL). The organic solution was dried with
anhydrous Na2SO4 and evaporated at reduced pressure to
give a crude product (2.05 g), which consisted mainly of
the corresponding bicyclic diester (1H NMR). A thoroughly
stirred solution of an aliquot of this crude product (1.00 g) in
a mixture of DMSO (6 mL) and water (1 mL) was heated at
1708C for 30 min. NaCl (420 mg) was added and the
reaction mixture was heated at 1708C for an additional
1-h-period and at 1908C for 30 min, and was cooled to
room temperature. To the cold mixture, CHCl3 (7 mL)
was added and the resulting precipitate was ®ltered off in
vacuo. The ®ltrate was concentrated by distillation of the
organic solvents at reduced pressure. The resulting residue
was taken up in CH2Cl2 (30 mL), and the organic solution
was washed with water (3£25 mL), dried with anhydrous
Na2SO4, and evaporated at reduced pressure. Sublimation of
the resulting residue (460 mg) at 1408C/0.5 Torr afforded
pure diketone 32 (390 mg, 56% yield). The analytical
sample of 32 was obtained by recrystallization, mp 138±
Attempted synthesis of 1-acetamido-9-ethyl-9-methoxy-
bicyclo[3.3.1]nonane-3,7-dione from 19: obtention of
3-amino-4-ethyl-4-methoxycyclohexa-2,5-dienone (34).
From sodium (6 mg, 0.26 mmol) in anhydrous MeOH
(10 mL), a solution of 19 (430 mg, 2.06 mmol) in anhydrous
MeOH (15 mL) and a solution of dimethyl 1,3-aceto-
nedicarboxylate (1.00 g, 5.74 mmol) in anhydrous MeOH
(15 mL), slightly impure cyclohexadienone 34 (190 mg,
55% yield) was obtained. An analytical sample of 34 was
obtained by recrystallization: white solid, mp 165±1668C
(CHCl3). IR (KBr): n 3363, 3175, 1677, 1652, 1556 cm21
.
1H NMR (300 MHz, CDCl3): d 0.76 (t, Jˆ7.5 Hz, 3H,
CH2CH3), 1.78 (q, Jˆ7.5 Hz, 2H, CH2CH3), 3.16 (s, 3H,
OCH3), 5.30 (br. signal, 2H, NH2), 5.61 (d, Jˆ1.7 Hz, 1H,
2-H), 6.30 (dd, Jˆ10.0 Hz, J0ˆ1.7 Hz, 1H, 6-H), 6.39 (d,
Jˆ10.0 Hz, 1H, 5-H). 13C NMR (75.4 MHz, CDCl3): d 7.5
(CH3, CH2CH3), 33.4 (CH2, CH2CH3), 53.0 (CH3, OCH3),
78.0 (C, C4), 101.8 (CH, C2), 132.4 (CH, C6), 143.4 (CH,
C5), 164.0 (C, C3), 185.6 (C, C1). No correct elemental
analysis was obtained for this compound.
Attempted synthesis of 9,9-dimethoxy-2-methylbicy-
clo[3.3.1]nonane-3,7-dione from 23: obtention of methyl
3-hydroxy-9,9-dimethoxy-endo-8-methyl-7-oxobicyclo-
[3.3.1]non-2-ene-2-carboxylate (35). Ester 35 was
obtained when 23 was submitted to the reaction conditions
of the general procedure described above. From sodium
(120 mg, 5.22 mmol) in anhydrous MeOH (60 mL), a
1
1408C (Et2O). IR (KBr): n 1737, 1712 cm21. H NMR
(500 MHz, CDCl3): d 2.24 [m, 2H, 4(6)-Hendo], 2.27 [m,

8150
P. Camps et al. / Tetrahedron 56 (2000) 8141±8151
solution of 23 (1.16 g, 6.90 mmol) in anhydrous MeOH
(25 mL) and a solution of dimethyl 1,3-acetonedicarboxyl-
ate (2.61 g, 15.0 mmol) in anhydrous MeOH (25 mL), a
brown oily residue (1.23 g), was obtained. An aliquot of
this crude product (1.13 g) was recrystallized from CHCl3
(1 mL), affording pure ester 35 (450 mg) as a white solid.
The mother liquors were evaporated at reduced pressure and
the resulting residue was submitted to column chromato-
grahy through silica gel (25 g, 40±60 mm) (hexane/AcOEt
mixtures, gradient elution). On elution with hexane/AcOEt
85:15, pure ester 35 (480 mg) (52% total yield) was isolated,
mp 139±1408C (CHCl3). IR (KBr): n 3397, 1708, 1654,
Calcd for C15H22O6: C, 60.39; H, 7.44 Found: C, 60.52; H,
7.49.
X-Ray crystal-structure determination of 2434
A prismatic crystal was selected and mounted on a Enraf-
Nonius CAD4 four-circle diffractometer. Unit-cell para-
meters were determined by automatic centering of 25
re¯ections (12 , u , 218) and re®ned by the least-squares
method. Intensities were collected with graphite-mono-
chromatized Mo-Ka radiation, using v/2u scan technique.
4039 re¯ections were measured in the range 2:41 # u #
30:12; 4011 of which were non-equivalent by symmetry
[Rint (on I)ˆ0.021]. 2432 re¯ections were assumed as
observed by applying the condition I . 2sꢀI†: Three re¯ec-
tions were measured every two hours as orientation and
intensity control; signi®cant intensity decay was not
observed. Lorentz polarization but no absorption correc-
tions were made. The structure was solved by Direct meth-
ods, using the shelxs computer program35 and re®ned by
the full-matrix least-squares method with the shelx-93
computer program36 using 3961 re¯ections (very negative
intensities were not assumed). The function minimized was
SwꢀuFou2 2 uFcu2†2; where w ˆ ‰s2ꢀI† 1 ꢀ0:1735P†2Š21; and
P ˆ ꢀuFou2 1 2uuFcu2†=3: f; f 0 and f 00 were taken from Inter-
national Tables of X-ray Crystallography.37 4H Atoms were
located from a difference synthesis and re®ned with an over-
all isotropic temperature factor and 16H atoms were
computed and re®ned with an overall isotropic temperature
factor using a riding model. Goodness of ®t on F2ˆ0.967
for all observed re¯ections. Mean shift/e.s.d.ˆ0.0 (Table 3).
1618 cm21 1H NMR (500 MHz, CDCl3): d 0.88 (d,
.
Jˆ7.0 Hz, 3H, 8-CH3), 2.16 (dd, Jˆ16.5 Hz, J0ˆ3.5 Hz,
1H, 6-Hendo), 2.21 (d, Jˆ18.0 Hz, 1H, 4-Hendo), 2.67±
2.74 (complex signal, 3H, 4-Hexo, 5-H, 6-Hexo), 2.97 (dq,
Jˆ4.5 Hz, J0ˆ7.0 Hz, 1H, 8-H), 3.19 (s, 3H) and 3.35 (s,
3H) [9-(OCH3)2], 3.31 (dd, Jˆ4.5 Hz, J0ˆ3.0 Hz, 1H, 1-H),
3.71 (s, 3H, COOCH3), 12.28 (br. s, 1H, OH). 13C NMR
(75.4 MHz, CDCl3): d 12.1 (CH3, 8-CH3), 34.5 (CH, C5),
35.0 (CH2, C4), 40.5 (CH, C1), 45.1 (CH2, C6), 45.2 (CH,
C8), 48.0 (CH3) and 48.5 (CH3) [9-(OCH3)2], 51.4 (CH3,
COOCH3), 95.9 (C, C2), 99.7 (C, C9), 171.9 (C) and
172.2 (C) (C3 and COOCH3), 211.3 (C, C7). Anal.
Calcd for C14H20O6: C, 59.14; H, 7.10. Found: C, 58.86;
H, 7.09.
Attempted synthesis of 9,9-dimethoxy-2,4-dimethyl-
bicyclo[3.3.1]nonane-3,7-dione from 25: obtention of
methyl 3-hydroxy-9,9-dimethoxy-endo-6,endo-8-dimethyl-
7-oxobicyclo[3.3.1]non-2-ene-2-carboxylate (36). Ester
36 was obtained when 25 was submitted to the reaction
conditions of the general procedure described above.
From sodium (209 mg, 9.09 mmol) in anhydrous MeOH
(12 mL), a solution of 25 (1.40 g, 7.69 mmol) in anhydrous
MeOH (18 mL) and a solution of dimethyl 1,3-aceto-
nedicarboxylate (2.77 g, 15.9 mmol) in anhydrous MeOH
(18 mL), a brown oily residue (1.57 g) was obtained. An
aliquot of this crude product (0.89 g) was submitted to
column chromatograhy through silica gel (27 g, 40±
60 mm) (hexane/AcOEt mixtures, gradient elution). On
elution with hexane/AcOEt 80:20, pure ester 36 (367 mg)
(28% yield) was isolated as a white solid. Note: In a reaction
carried out by using a higher excess of NaOH (13 equiv.)
with a hydrolysis time of 60 h, and a higher excess of 2N
HCl (9 mL/mmol starting cyclohexadienone) with a reac-
tion time of 3 h, ester 36 was obtained in the same yield. The
analytical sample of 36 was obtained by recrystallization:
mp 159±1638C (AcOEt). IR (KBr): n 3401, 1710, 1650,
X-Ray crystal-structure determination of 2734
The same procedure described above was followed. 4523
re¯ections were measured in the range 2.27#u#29.96,
4493 of which were non-equivalent by symmetry [Rint (on
I)ˆ0.003]. 3530 re¯ections were assumed as observed by
applying the condition I.2s(I). The structure was solved as
before using 4493 re¯ections (very negative intensities were
not assumed). The function minimized was SwꢀuFou2 2
uFcu2†2; where w ˆ ‰s2ꢀI† 1 ꢀ0:1056P†2 1 0:0543PŠ21; and
P ˆ ꢀuFou2 1 2uFcu2†=3: f; f 0 and f 00 were taken from Inter-
national Tables of X-ray Crystallography.37 45H Atoms
were located from a difference synthesis and re®ned with
an overall isotropic temperature factor and 3H atoms were
computed and re®ned with an overall isotropic temperature
factor using a riding model. Goodness of ®t on F2ˆ1.038 for
all observed re¯ections. Mean shift/e.s.d.ˆ0.00 (Table 3).
1617 cm21 1H NMR (500 MHz, CDCl3): d 0.86 (d,
.
X-Ray crystal-structure determination of 3634
Jˆ7.0 Hz, 3H, 8-CH3), 0.99 (d, Jˆ7.0 Hz, 3H, 6-CH3),
2.31 (d, Jˆ19.0 Hz, 1H, 4-Hendo), 2.45 (dd, Jˆ19.0 Hz,
J0ˆ7.0 Hz, 1H, 4-Hexo), 2.50 (ddd, Jˆ7.0 Hz, J0ˆ4.5 Hz,
J00ˆ3.5 Hz, 1H, 5-H), 2.85 (dqm, Jˆ4.5 Hz, J0ˆ7.0 Hz, 1H,
6-H), 2.99 (ddq, Jˆ1.0 Hz, J0ˆ4.0 Hz, J00ˆ7.0 Hz, 1H,
8-H), 3.18 (s, 3H) and 3.36 (s, 3H) [9-(OCH3)2], 3.30 (dd,
Jˆ4.0 Hz, J0ˆ3.5 Hz, 1H, 1-H), 3.70 (s, 3H, COOCH3),
12.2 (br. s, 1H, OH). 13C NMR (75.4 MHz, CDCl3): d
11.6 (CH3, 6-CH3), 11.8 (CH3, 8-CH3), 28.7 (CH2, C4),
41.1 (CH) and 41.2 (CH) (C1 and C5), 43.3 (CH, C6),
45.3 (CH, C8), 48.0 (CH3) and 48.5 (CH3) [9-(OCH3)2],
51.4 (CH3, COOCH3), 95.7 (C, C2), 100.1 (C, C9), 172.1
(C) and 172.3 (C) (C3 and COOCH3), 212.4 (C, C7). Anal.
The same procedure described above was followed. 4560
re¯ections were measured in the range 2.63#u#29.96,
4390 of which were non-equivalent by symmetry [Rint
(on I)ˆ0.031]. 2994 re¯ections were assumed as observed
by applying the condition I.2s(I). The structure was
solved as before using 4390 re¯ections (very negative inten-
sities were not assumed). The function minimized was
SwꢀuFou2 2 uFcu2†2; where w ˆ ‰s2ꢀI† 1 ꢀ0:1426P†2Š21; and
P ˆ ꢀuFou2 1 2uFcu2†=3: f; f 0 and f 00 were taken from Inter-
national Tables of X-ray Crystallography.37 15H Atoms
were located from a difference synthesis and re®ned with

P. Camps et al. / Tetrahedron 56 (2000) 8141±8151
8151
Table 3. Experimental data of the X-ray crystal structure determination of
compounds 24, 27 and 36
8. McDonald, I. A.; Dreiding, A. S. Helv. Chim. Acta 1973, 56,
2523±2534.
9. Stetter, H.; Lennartz, J. Liebigs Ann. Chem. 1977, 1807±1816.
10. Stetter, H.; Mayer, J. Chem. Ber. 1959, 92, 2664±2666.
11. Aranda, G.; Bernassau, J. M.; Fetizon, M.; Hanna, I. J. Org.
Chem. 1985, 50, 1156±1161.
24
27
36
Molecular formula
Molecular mass
Temperature
C16H20O4
276.32
293 (2)K
Triclinic
P1
C18H24O4
304.37
293(2) K
Triclinic
P1
C15H22O6
298.33
293(2)K
Monoclinic
P21/c
È
12. Camps, P.; El Achab, R.; Font-Bardia, M.; Gorbig, D.; Morral,
Crystal system
Space group
Cell parameters
J.; MunÄoz-Torrero, D.; Solans, X.; Simon, M. Tetrahedron 1996,
52, 5867±5880.
a
a
a
Ê
a [A]
6.941(8)
9.185(4)
11.978(3)
100.64(3)
101.70(5)
107.41(3)
688.5(9)
2
296
1.333
0.1£0.1£0.2
7.068(4)
9.647(2)
12.561(2)
71.01
79.01
76.92
782.5(5)
2
12.109(6)
8.059(3)
15.63(3)
90
98.00(8)
90
1510(3)
4
640
1.312
0.1£0.1£0.2
4560
13. Pelter, A.; Elgendy, S. M. A. J. Chem. Soc., Perkin Trans. 1
1993, 1891±1896.
È
14. Schmidt, U.; Bokens, H.; Lieberknecht, A.; Griesser, H.
Tetrahedron Lett. 1981, 22, 4949±4952.
Ê
b [A]
Ê
c [A]
a [8]
b [8]
g [8]
15. Meyers, A. I.; Tomioka, K.; Roland, D. M.; Comins, D.
Tetrahedron Lett. 1978, 1375±1378.
Ê 3
V [A ]
Z
F(000)
16. Adler, E.; Andersson, G.; Edman, E. Acta Chem. Scand. B
1975, 29, 909±920.
328
d (calcd) [Mg m23
]
1.292
0.1£0.1£0.2
4523
Size of crystal [mm]
Measured re¯ections
Independent re¯ections
Observed re¯ections
m(Mo-Ka) [mm21
17. Mitchell, A. S.; Russell, R. A. Tetrahedron Lett. 1993, 34,
545±548.
4039
4011
4493
3530
4390
2994
18. Adler, E.; Junghahn, L.; Lindberg, U.; Berggren, B.; Westin,
G. Acta Chem. Scand. 1960, 14, 1261±1273.
Â
19. Adler, E.; Dahlen, J.; Westin, G. Acta Chem. Scand. 1960, 14,
2432
0.100
0.190
0.967
0.601
20.559
134
0.0
b
]
0.100
0.051
0.141
0.335
20.291
286
0.100
0.063
0.172
0.368
20.301
258
R
Rw
Drmax (eA
Drmin (eA
1580±1596.
20. Adler, E.; Holmberg, K. Acta Chem. Scand. B 1974, 28, 465±
472.
c
Ê 23
Ê 23
)
)
d
Re®ned parameters
Max. shift/e.s.d
21. Adler, E.; Holmberg, K.; Ryrfors, L.-O. Acta Chem. Scand. B
1974, 28, 888±894.
22. McKillop, A.; Perry, D. H.; Edwards, M.; Antus, S.; Farkas,
0.00
0.00
a Determined by automatic centering of 25 re¯ections (12#u#218).
b m(Mo-Ka), linear absorption coef®cient. Radiation Mo-Ka
Â
Â
L.; Nogradi, M.; Taylor, E. C. J. Org. Chem. 1976, 41, 282±287.
23. Karlsson, B.; Kierkegaard, P.; Pilotti, A.-M.; Wiehager, A.-C.;
Lindgren, B. O. Acta Chem. Scand. 1973, 27, 1428±1430.
24. Vannerberg, N. G.; Brasen, S. Acta Chem. Scand. 1970, 24,
1894±1902.
Ê
(lˆ0.71069 A).
c Maximum peaks in ®nal difference synthesis.
d Minimum peaks in ®nal difference synthesis.
an overall isotropic temperature factor and 7H atoms were
computed and re®ned with an overall isotropic temperature
factor using a riding model. Goodness of ®t on F2ˆ0.970 for
all observed re¯ections. Mean shift/e.s.d.ˆ0.00. (Table 3)
25. Krapcho, A. P.; Lovey, A. J. Tetrahedron Lett. 1973, 957±960.
26. Krapcho, A. P.; Jahngen Jr, E. G. E.; Lovey, A. J. Tetrahedron
Lett. 1974, 1091±1094.
27. Peters, J. A.; Van der Toorn, J. M.; Van Bekkum, H.
Tetrahedron 1975, 31, 2273±2281.
28. Pattison, V. A.; Colson, J. G.; Carr, R. L. K. J. Org. Chem.
1968, 33, 1084±1087.
Acknowledgements
29. Capparelli, M. P.; DeSchepper, R. S.; Swenton, J. S. J. Chem.
Soc., Chem. Commun. 1987, 610±611.
Financial support from Comissionat per a Universitats i
Recerca of the Generalitat de Catalunya (project 1999-
SGR-00080) is gratefully acknowledged. We also thank
30. Ojika, M.; Wakamatsu, K.; Niwa, H.; Yamada, K.; Hirono, I.
Chem. Lett. 1984, 397±400.
Â
the Serveis Cientõ®co-Tecnics of the University of
Barcelona and particularly Dr M. Feliz and Dr A. Linares
Á
31. Mitchell, A. S.; Russell, R. A. Tetrahedron 1997, 53, 4387±
4410.
Á
for recording the NMR spectra, and Ms P. Domenech from
y Desarrollo (C.I.D.)
32. Islam, M. M.; Waring, A. J. J. Chem. Res. (S) 1980, 56;
J. Chem. Res. (M) 1980, 0768±0783.
Â
the Centro de Investigacion
(Barcelona, Spain) for carrying out the elemental analyses.
33. Lu, L.; Shoemaker, R. K.; Wheeler, D. M. S. Tetrahedron Lett.
1989, 30, 6993±6996.
34. Crystallographic data (excluding structure factors) for the
structures reported in this paper have been deposited with the
Cambridge Crystallographic Data Centre. Copies of the data can
be obtained free of charge on application to The Director, CCDC,
12 Union Road, Cambridge CB2 1EZ, UK (Fax: 11223-336-033;
e-mail: deposit@chemcrys.cam.ac.uk).
References
1. Weiss, U.; Edwards, J. M. Tetrahedron Lett. 1968, 4885±4887.
2. Gupta, A. K.; Fu, X.; Snyder, J. P.; Cook, J. M. Tetrahedron
1991, 47, 3665±3710.
3. Fu, X.; Cook, J. M. Aldrichimica Acta 1992, 25, 43±54.
4. Bertz, S. H.; Dabbagh, G. Angew. Chem., Int. Ed. Engl. 1982,
21, 306±307.
35. Sheldrick, G. M. Acta Crystallogr. A 1990, 46, 467±473.
36. Sheldrick, G. M. shelx-93, Program for Crystal Structure
È
Determinations. University of Gottingen, Germany, 1994.
37. International Tables of X-ray Crystallography, Birmingham:
Kynock Press, 1974, Vol. IV, pp 99±100 and 149.
5. Bertz, S. H. J. Org. Chem. 1985, 50, 3585±3592.
6. Sands, R. D. J. Org. Chem. 1983, 48, 3362±3363.
7. Bertz, S. H. Synthesis 1980, 708±710.