Tungsten-promoted diels-alder cycloaddition of pyridines: Dearomatization of 2,6-dimethoxypyridine generates a potent 2-azadiene synthon

Article abstract of DOI:10.1021/om800430p

The complex TpW(NO)(PMe₃)(DMP), where DMP is 2,6-dimethoxypyridine, features an η²-coordinated pyridine ligand that chemically resembles an electron-rich 2-azadiene. As such, it readily reacts with a full range of dienophiles including examples of both alkenes and alkynes to generate azabicyclo[2.2.2]octadiene complexes. Often, one diastereomer spontaneously precipitates from the reaction solution. The bicyclic ligand in these complexes can in some cases be directly removed from the metal by the action of an oxidant (e.g., CAN) and in other cases can be chemically modified prior to its removal. Crystal structures of five tungsten cycloadduct complexes are included. A related complex of 2,6-lutidine is found to react with the nitrile dienophile ethyl cyanoformate to form a new dihapto-coordinated pyridine complex that is derived from a purported diaza[2.2.2]octatriene intermediate.

Full text of DOI:10.1021/om800430p

Organometallics 2008, 27, 4513–4522
4513
Tungsten-Promoted Diels-Alder Cycloaddition of Pyridines:
Dearomatization of 2,6-Dimethoxypyridine Generates a Potent
2-Azadiene Synthon
George W. Kosturko,† Peter M. Graham,† William H. Myers,‡ Timothy M. Smith,‡
Michal Sabat,† and W. Dean Harman*,†
Department of Chemistry, UniVersity of Virginia, CharlottesVille, Virginia 22904-4319, and Department of
Chemistry, UniVersity of Richmond, Richmond, Virginia 23173
ReceiVed May 12, 2008
The complex TpW(NO)(PMe3)(DMP), where DMP is 2,6-dimethoxypyridine, features an η2-coordinated
pyridine ligand that chemically resembles an electron-rich 2-azadiene. As such, it readily reacts with a
fullrangeofdienophilesincludingexamplesofbothalkenesandalkynestogenerateazabicyclo[2.2.2]octadiene
complexes. Often, one diastereomer spontaneously precipitates from the reaction solution. The bicyclic
ligand in these complexes can in some cases be directly removed from the metal by the action of an
oxidant (e.g., CAN) and in other cases can be chemically modified prior to its removal. Crystal structures
of five tungsten cycloadduct complexes are included. A related complex of 2,6-lutidine is found to react
with the nitrile dienophile ethyl cyanoformate to form a new dihapto-coordinated pyridine complex that
is derived from a purported diaza[2.2.2]octatriene intermediate.
Introduction
The construction of numerous polyheterocyclic scaffolds has
been achieved utilizing hetero-Diels-Alder reactions.1-5 In
particular, the isoquinuclidine skeleton, found in a variety of
alkaloids (e.g., ibogaine, 1) and their pharmaceutically derived
analogues,6-9 has been prepared using azabutadienes,10-13
dihydropyridines,14,15 or pyridones,8 combined with various
dienophiles. Common pyridines would be attractive alternatives
as sources of azadienes, but their aromatic stability normally
renders them unsuitable for such cycloaddition reactions.
Recently, we reported the ability to form dihapto-coordinated
complexes of 2,6-lutidine and 2-(dimethylamino)pyridine with
a π-basic tungsten complex.16,17 Once coordinated, the pyridine
ring is dearomatized, activating this heterocycle toward cy-
cloaddition reactions. Unfortunately, only a narrow range of
dienophiles reacted with these pyridine complexes.16 We
postulated that if 2,6-dimethoxypyridine (η2-DMP) were bound
to {TpW(NO)(PMe3)}, the uncoordinated portion of this ring
should take on a chemical nature similar to that of Danishefsky’s
diene. Specifically, the combination of π-donation from both
tungsten and the methoxy groups was expected to render this
pyridine a potent reagent for cycloaddition reactions. The
following study explores the potential of TpW(NO)(PMe3)(4,5-
η2-DMP) as an azadiene synthon for azabicyclic frameworks.
* Corresponding author. E-mail: wdh5z@virginia.edu.
† University of Virginia.
‡ University of Richmond.
(1) Boger, D. L. Chem. ReV. 1986, 86, 781–793.
(2) Boger, D. L. Tetrahedron 1983, 39, 2869–2935.
(3) Behforouz, M. A. Tetrahedron 2000, 56, 5259–5288.
(4) Jørgensen, K. A. Angew. Chem. 2000, 39, 3558–3588.
(5) Boger, D. L.; Weinreb, S. M. Hetero Diels–Alder Methodology in
Organic Synthesis; Wasserman, H. H., Ed.; Academic Press: San Diego,
1987; Vol. 47, pp 167.
(6) Bo¨hm, M.; Lorthiois, E.; Meyyappan, M.; Vasella, A. HelV. Chim.
Acta 2003, 86, 3787–3817.
(7) Ye, Z.; Guo, L.; Barakat, K. J.; Pollard, P. G.; Palucki, B. L.; Sebhat,
L. K.; Bakshi, R. K.; Tang, R.; Kalyani, R. N.; Vongs, A.; Chen, A. S.;
Chen, H. Y.; Rosenblum, C. I.; MacNeil, T.; Weinberg, D. H.; Peng, Q.;
Tamvakopoulos, C.; Miller, R. R.; Stearns, R. A.; Cashen, D. E. Bioorg.
Med. Chem. Lett. 2005, 15, 3501–3505.
(8) Passarella, D.; Favia, R.; Giardini, A.; Lesma, G.; Martinelli, M.;
Silvani, A.; Danieli, B.; Efange, S.; Mash, D. C. Bioorg. Med. Chem. 2003,
11, 1007–1014.
(9) Sundberg, R. J.; Smith, S. Q. Alkaloids Chem. Biol. 2002, 59, 281.
(10) Sustmann, R.; Sicking, W.; Lamy-Schelkens, H.; Ghosez, L.
Tetrahedron Lett. 1991, 32, 1401–1419.
(11) Lamy-Schelkens, H.; Ghosez, L. Tetrahedron Lett. 1989, 30, 5891–
5894.
(12) Lamy-Schelkens, H.; Giomi, D.; Ghosez, L. Tetrahedron Lett. 1989,
30, 5887–5890.
Results and Discussion
The DMP complex TpW(NO)(PMe3)(4,5-η2-DMP) (3) is
prepared by stirring a suspension of the benzene complex
(13) Rivera, M.; Lamy-Schelkens, H.; Sainte, F.; Mbiya, K.; Ghosez,
L. Tetrahedron Lett. 1988, 29, 4573–4576.
(14) Weinstein, B.; Lin, L.-C.; W., F. F. J. Org. Chem. 1980, 45, 1657–
1661.
(16) Graham, P. M. D., D. A.; Liu, W.; Myers, W. H.; Sabat, M.;
Harman, W. D. J. Am. Chem. Soc. 2005, 127, 10568–10572.
(17) Delafuente, D. A; K, G. W.; Graham, P. M.; Harman, W. H.; Myers,
W. H.; Surendranath, Y.; Klet, R. C.; Welch, K. D.; Trindle, C. O.; Sabat,
M.; Harman, W. D. J. Am. Chem. Soc. 2007, 129, 406–416.
(15) Fowler, F. W. J. Org. Chem. 1972, 37, 1321–1323.
10.1021/om800430p CCC: $40.75
2008 American Chemical Society
Publication on Web 08/14/2008

4514 Organometallics, Vol. 27, No. 17, 2008
Kosturko et al.
Table 1. Cycloadditions with
TpW(NO)(PMe3)(η2-2,6-dimethoxypyridine) (3)
Scheme 1. Cycloaddition Reactions of 2,6-Dimethoxypyridine
Complex (3) to Form 4-8
dienophile dr (A:B) dr (exo:endo) yield (isolated)
4 Z ) COCH3
5 Z ) COCH2CH3
6 Z ) CN
7 Z ) SO2C6H5
8 Z ) CO2CH3
1:1.4
1:1.4
1:1
1:3.3
1.0:1
1.7:1a
1.9:1a
3.6:1a
1:3.0a
1.4:1a
4.6:1ab
6.0:1c
1.0:1a
1:8.2a
3.2:1a
N/A
84%
70%
89%
85%
89%
61%
60%
9 R-methylene-γ-butyrolactone 1:1.2
10 N-methylmaleimide
1:1
11 dimethyl maleate
12 dimethyl fumarate
13 DMAD
1:2.0
1: 1.1
1: 1.1
1: 1.5
81%
78%
81%
80%
14 3-butyne-2-one
N/A
a Determined for B isomer only. b Geometry of isomers unknown.
c Determined by NOE.
Table 2. Isomer(s) Isolated by Precipitation from DME Reaction
Mixture
compound
dienophile
major isomer yield of isolated isomer
4
6
7
8
11
12
13
14
H2CCHCOCH3
H2CCHCN
H2CCHSO2Ph
H2CCHCO2Me
dimethyl maleate endo 11B
dimethyl fumarate exo 12B
DMAD
exo/endo 4B
exo 6B
exo 7B
54%
32%
39%
17%
40%
39%
55%
56%
exo 8B
TpW(NO)(PMe3)(η2-benzene) (2) and DMP in hexanes for 26 h.
The resulting yellow precipitate is isolated in 79% yield as a
1:1 equilibrium mixture of coordination diastereomers (3A and
3B; Scheme 1).17 While 3 could be obtained from its conjugate
acid as a single coordination diastereomer,17 its rate of re-
equilibration (t1/2 ≈ 10 min) is significantly faster than that of
cycloaddition. Hence an equilibrium mixture was used in all
experiments.
Once coordinated to tungsten, DMP was found to react with
a broad range of alkene and alkyne dienophiles to form the
isoquinuclidine core (Scheme 1, Figure 1).
In a typical experiment, an excess of the dienophile was
dissolved in DME, complex 3 was added, and the resulting
13B
14B
3-butyne-2-one
solution was allowed to stir for 16 h at ambient temperature.
Large differences in the anodic peak currents and 183W-31P
coupling constants for 3 and its products (4-14) made cyclic
voltammetry and 31P NMR valuable tools for monitoring of
these reactions.16 In most cases (all but 5, 9, and 10), the product
spontaneously precipitated from solution. The filtrate was then
evaporated under reduced pressure, and the residue was dis-
solved in THF. This solution was then added to pentane to
induce precipitation of any remaining products. Analyses of the
product mixtures are reported in Table 1, where the reported
yield is the combined mass of all precipitated products.
The structural and stereochemical characterizations of the
isolated products (4-14) were assigned on the basis of CV,
1
IR, H and 13C NMR, NOE, and H-H coupling data, as first
described for the lutidine analogue.17 For example, diagnostic
chemical shifts for the B diastereomers include proton reso-
nances associated with the tungsten-bound carbons (H4 and H5)
near 2.5 ppm (ddd) and 1.8 ppm (dd), respectively. The former
exhibits a 31P coupling of ∼10 Hz. The A diastereomers have
their H5 proton resonances near 2.4 ppm (dd) coupled to 31P
(∼10 Hz), and the corresponding H4 signals are multiplets
upfield of the PMe3 signal (<1.3 ppm). The most downfield Tp
doublet for the A diastereomers is near 8.10 ppm, while for the
B-type isomers, one Tp signal is consistently in the range
8.6-8.8 ppm. NOESY data for the DMAD analogue 13B
indicate that this proton (H3A; see Figure 1) belongs to the
pyrazole ring trans to the PMe3 group and is in close proximity
to the bridgehead methoxy group. In every case where a
precipitate forms directly from the initial reaction solution, a B
coordination diastereomer was isolated exclusively (Table 2).
Structural and stereochemical assignments for exo-5B, exo-6B,
exo-8B, exo-11B, and exo-12B were confirmed by X-ray
crystallography, and the corresponding ORTEP diagrams appear
in Figures 1 and 2.18
Figure 1. Cycloadduct complexes 9-14 (only endo isomer shown
for 9-12; for 12B, the “endo” designation refers to the car-
bomethoxy group closest to the nitrogen).
(18) The crystal structure of exo-7B shows internal disorder. This
prevented us from obtaining meaningful bond lengths, but the stereochem-
istry was confirmed.

Tungsten-Promoted Diels-Alder Cycloaddition
Organometallics, Vol. 27, No. 17, 2008 4515
Scheme 2. Attempted Oxidative Demetalation of Cycloadducts
5-8
would release the W-alkene bond in complexes 4-14. A
similar strategy was successfully applied in our initial explora-
tion of pyridine cycloaddition reactions.16 Demetalation of the
azabicyclooctadiene core of nitrile 6 was ultimately achieved
by subjecting it to 1.1 equiv of ceric ammonium nitrate (CAN)
in deuterated acetone (16, Scheme 2). The crude 1H NMR
spectrum of 16 reveals the disappearance of protons associated
with metal-bound carbons (H4/H5) and the formation of two
olefinic proton signals near 6.4 ppm with 7 Hz vicinal coupling.
Silica chromatography led to the isolation of 16 in 35% yield.
This process was repeated with the sulfone cycloadduct (7),
producing 17 in 35% yield (Scheme 2). Interestingly, the
treatment of 6 with a solution of CuBr2 in deuterated acetone
or acetonitrile also effected decomplexation, but NMR analysis
revealed that the imidate group of the isoquinuclidine was
hydrolyzed by adventitious water to form the bicyclic amide
15 in a 30% yield. The 1H NMR spectrum of 15 shows the loss
of one of the methoxy groups and the appearance of an amide
proton at 7.9 ppm. An IR spectrum of the isolated product
revealed signals at 1688 and 1611 cm-1, indicating the presence
of an amide.18 Hydrolysis of the imidate was not observed for
any other cycloadduct complex or oxidant.
Figure 2. ORTEP diagrams for structures exo-5B, exo-6B, exo-
8B, exo-11B, and exo-12B.
In order to gain insight into the mechanism of the cycload-
dition, we examined the dependence of the reaction rate and
stereochemistry on solvent polarity. We postulated that if the
reaction was sequential (i.e., a Michael addition reaction
followed by an aldol), then it should be accelerated in a more
polar solvent. Hence, two solutions of methyl acrylate [6 × 10-4
M] were prepared, one in DME and one in DMF. To each, the
pyridine complex 3 [6 × 10-5 M] was added, and the reaction
was monitored by 1H NMR spectroscopy. The pseudo-first-order
rate constants were determined to be 8.7 × 10-5 and 1.2 ×
10-4 s-1 (22 °C). While the more polar solvent (DMF) did
accelerate the reaction, the solvent effect was minor, corre-
sponding to a difference in ∆Gq values of only 0.20 kcal/mol.
Further, the distribution of stereoisomers in the crude reaction
mixture was found to be virtually independent of solvent
polarity. These results are in contrast to the solvent dependence
predicted for 3,4-dihydropyridines by Ghosez et al.10 Finally,
if the reaction occurred through a stepwise mechanism, a trans
stereochemistry would be expected for the two ester groups
originating from maleate (11) or fumarate (12) dienophiles.
Indeed, such was the case for cycloaddition reactions with the
analogous 2,5-dimethylpyrrole complexes.19 However, the reac-
tions of 3 with maleate and fumarate methyl esters lead to two
different stereoisomers (see Figure 1) with no trace of the
complementary epimer. Taken together, these observations
suggest a concerted reaction mechanism.
When methyl ester 8 was subjected to CAN, the anticipated
1
isoquinuclidine was observed in the HNMR spectrum of the
crude product, but its signals were dwarfed by those of 2,6-
dimethoxypyridine, the product of a retro-cycloaddition reaction.
When the ketone-derived cycloadduct 5 was exposed to CAN,
the bicyclic structure opened, but in this case the recovered
product was the trisubstituted pyridine, 18 (Scheme 2). Aromatic
1
protons at 6.20 and 7.30 ppm were observed in the H NMR
Demetalation of Isoquinuclidine Scaffold. Various one- and
two-electron oxidants were screened with the expectation that
a more electron-deficient tungsten(I) or tungsten(II) species
spectrum of this compound along with two sets of geminal
protons near 2.7 ppm.
Speculating that both the retro-cycloaddition and ring-opening
decomposition pathways in Scheme 2 were likely facilitated by
the electron-withdrawing substituents originating from the
dienophile, we endeavored to modify this group prior to
(19) Welch, K. D.; Smith, P. L.; Keller, A. P.; Myers, W. H.; Sabat,
M.; Harman, W. D. Organometallics 2006, 25, 5067–5075.

4516 Organometallics, Vol. 27, No. 17, 2008
Kosturko et al.
Scheme 3. Reduction and Decomplexation of 4 and 8
Scheme 4. Oxidative Decomplexation of Azabarrelene Complexes
(13 and 14)
Nitrile Metathesis. The Diels-Alder/retro-Diels-Alder se-
quence above that ultimately resulted in the conversion of 2,6-
dimethoxypyridine to substituted arenes led us to postulate that
an analogous reaction might be accessible in which a η2-pyridine
reacts with a nitrile to form a new η2-pyridine and nitrile
combination. While unactivated nitriles have been observed to
undergo Diels-Alder reactions only under harsh reaction
conditions, Mander’s reagent (ethyl cyanoformate) has been
documented to undergo such a reaction with dienes at or below
20 °C.20 Hence, the pyridine complex 3 was subjected to this
decomplexation. This study also allowed us to evaluate the
compatibility of the metal system with nucleophilic/basic
regents. Reduction of the ketone and ester cycloadducts (4 and
8) with LiAlH4 yielded the secondary and primary alcohol
isoquinuclidines (20 and 21) with overall yields of 74% and
75%. Treating 20 and 21 with either 1 equiv of CAN or 2 equiv
of recrystallized m-CPBA (Caution: shock sensitiVe) led to the
oxidation of the tungsten complex and the isolation of the
isoquinuclidines 22 and 23 in a 51% and 34% yield, respectively
(Scheme 3). Further, the ketone cycloadduct (4) could be
olefinated using the Tebbe reagent, to generate 19 (25%; Scheme
3). To our surprise, oxidative demetalation of 19 with CAN,
CuBr2, or AgOTf yielded only the retro-cycloaddition product
2,6-dimethoxypyridine.
1
reagent at -10 °C and the reaction followed by H NMR. We
also examined the unactivated pyridine complex derived from
2,6-lutidine, 27, for comparison. While reaction of 3 and
Mander’s reagent gave a complex mixture of products, when
the lutidine complex (27) was exposed to ethyl cyanoformate
1
With the hope of obtaining a rare example of an azabarrelene,
we treated the butynone-derived cycloadduct 14 with the mild
oxidant AgOTf. The reaction mixture was then subjected to
chromatography, and the new product 24 was isolated. 1H NMR
and IR spectra indicated an acetyl group, two methoxy groups,
and three aromatic protons in the range 7-8 ppm. 13C NMR
data and MS confirmed the identity of 24 as a benzimidate
derivative (Scheme 4), purportedly the result of the ring-opening
of a liberated azabarrelene followed by proton transfer (Scheme
4). Attempts to purify this material were hampered by its slow
decomposition to what we suspect is the corresponding benza-
mide 25. A proton NMR spectrum of 25 indicates that it is
similar to 24 but contains one less methoxy group, and LRMS
(ESI+) shows a parent ion of 194 (M + 1). Repeating this
decomplexation procedure with the DMAD-derived cycloadduct
complex 13 delivers an arene product with only one methoxy
group. 13C NMR and LRMS data along with a high-frequency
carbonyl stretching absorption at 1762 cm-1 indicate that a ring-
opening process occurs similar to that postulated for the
formation of 24, but in this case hydrolysis and condensation
form the novel phthalimide 26.
at -10 °C, a single new complex (28) was isolated. H NMR
spectra identify the complex as a new η2-pyridine species in
which one of the methyl groups has been replaced by an ester
group, the product of a nitrile metathesis (Scheme 5). Attempts
to isolate the diazabicyclooctatriene intermediate were unsuc-
cessful, and the generation of free CH3CN was not verified.
With the tungsten preferentially coordinating the C4 and C5
carbons of the pyridine in 3, the uncoordinated portion of the
ring is analogous to the TMSO-disubstituted cyclic 2-azadiene
extensively explored by Ghosez et al.13 The regiochemical
preference in both systems is distinct, with the positively
polarized dienophile carbon forming a bond with the 4-position
of the 2-azadiene. Ghosez found the usual kinetic preference
for endo cycloaddition with cyclic dienophiles, but open-chain
dienophiles showed a distinct exo kinetic selectivity.13 In Table
1, the exo/endo ratios are not as dramatic as found by Ghosez
et al., but the same general trend is observed.
The activation of pyridine through dihapto coordination was
first documented using the examples of 2,6-lutidine and 2-(dim-
(20) McClure, C. K.; Link, J. S. J. Org. Chem. 2003, 68, 8256–8257.

Tungsten-Promoted Diels-Alder Cycloaddition
Organometallics, Vol. 27, No. 17, 2008 4517
Scheme 5. Nitrile Metathesis in the Reaction of Ethyl
Cyanoformate and Lutidine Bound to Tungsten
ethylamino)pyridine.16 Other than this report, the only example
that we are aware of involving cycloaddition to a pyridine are
those of Gompper21 and Neunhoeffer,22 who independently
described the cycloaddition of dimethyl 2,6-bis(dimethylami-
no)pyridine-3,4-dicarboxylate and DMAD (Scheme 6). How-
ever, in that case the azabarralene readily rearomatized via a
retrocycloaddition, yielding a pentasubstituted benzene. Other
relevant examples of pyridinium-like aromatic molecules un-
dergoing cycloaddition include reactions with isoquinolinium23
and azoniaanthracene.24 The Diels-Alder reaction of an η2-
benzene complex with N-methylmaleimide has also been
demonstrated.25,26
Scheme 6. Examples of Pyridine and Azoniaanthracene
Cycloaddition
In conclusion, the coordination of 2,6-dimethoxypyridine by
{TpW(NO)(PMe3)} and subsequent removal of the metal
provides the formal equivalent of a Diels-Alder cycloaddition
with this heterocycle, a reaction that typically is thermodynami-
cally unfavorable in the absence of extreme pressures. Once
formed, the cycloadduct is moderately stable and in some cases
can be isolated. The use of a dihapto-coordinated 2,6-
dimethoxypyridine allows access to a full range of alkene and
alkyne dienophiles, and in some cases, these azabicyclic
skeletons can be chemically modified while bound to the
tungsten fragment prior to their decomplexation.
Experimental Section
or was performed by the University of Illinois Urbana-Champaign
School of Chemical Sciences (UIUC when noted). The data for
metal complexes are reported using the five most intense peaks
from the isotopic envelope and are listed as m/z with the intensity
relative to the most abundant peak of the isotopic envelope given
in parentheses for both the calculated and the observed peaks. The
difference between calculated and observed peaks is reported in
ppm. For isolated organic products, the monoisotopic peak is
reported, with the observed, calculated, and ppm difference again
provided. Thin-layer chromatography was performed on a Uniplate
silica gel GF from Analtech Inc. Methylene chloride and benzene
were run down a column packed with activated alumina and purged
with nitrogen prior to use. All other solvents and chemicals were
used as received from Sigma-Aldrich, Acros Chemicals, or Fischer
Scientific. 3-Chloroperbenzoic acid (m-CPBA) was recrystallized
by using a procedure from Bortolini et al.27
General Methods. All NMR spectra were obtained on either a
300 or 500 MHz Varian INOVA or Bruker AVANCE spectrometer.
All chemical shifts are reported in ppm versus tetramethylsilane
using residual shifts of the deuterated solvent as the internal
standard. All coupling constants (J) are reported in hertz (Hz). All
31P NMR data are reported versus an external standard in acetone
(trimethylphosphate, -16.58 ppm). Infrared spectra were obtained
on a MIDAC Prospect Series spectrometer as a glaze on a horizontal
attenuated total reflectance (HATR) cell from Pike Industries.
Electrochemical measurements were taken under a nitrogen atmo-
sphere using a BAS Epsilon EC-2000 potentiostat. Cyclic volta-
mmetry data were obtained in a three-electrode cell from +1.7 to
-1.7 V, with a glassy carbon working electrode, a platinum wire
auxiliary electrode, and a platinum wire reference electrode. All
data were obtained using a 100 mV/s scan rate with tetrabutylam-
monium hexafluorophosphate (TBAH) as the electolyte in N,N-
dimethylacetamide (DMA) unless otherwise noted. All potentials
were reported versus the normal hydrogen electrode (NHE) using
cobalticinium hexafluorophosphate (E1/2 ) -0.78 V) as an internal
standard. For reversible waves the peak to peak separation was less
than 100 mV. High-resolution mass spectrometry data (HRMS) was
obtained using either a 1:1 water:/acetonitrile solution with sodium
trifluoroacetate as a standard on a Bruker BioTOF-Q instrument
Preparations. The cycloaddition reactions forming compounds
4-13 typically resulted in mixtures of several diastereomers. These
mixtures were inseparable using column chromatography, and
extensive overlap of NMR signals prevented their full characteriza-
tion. Detailed characterizations were possible only in cases where
one or two isomers cleanly precipitated from the reaction mixture
(see Table 2). The A/B ratio for each crude reaction mixture was
determined on the basis of NMR data (e.g., H4 and H5 chemical
shifts). The exo/endo ratio was determined specifically for the B
isomer, where X-ray data could identify one of the stereoisomers.
The only exception to this is compound 10, where endo isomers
were confirmed by NOE interactions between H10 or H11 and
protons originating from the maleimide ring (H2 and H6).
(21) Gompper, R.; Heinemann, U. Angew. Chem. Int. Ed. Engl. 1980,
19, 216–217.
(22) Neunhoeffer, H.; Lehmann, B. Liebigs Ann. Chem. 1975, 1113–
1119.
(23) Wuonola, M. A.; Smallheer, J. M.; Read, J. M.; Calabrese, J. C.
Tetrahedron Lett. 1991, 32, 5481–5484.
(24) Sasaki, S.; Ishibashi, N.; Kuwamura, T.; Sano, H.; Matoba, M.;
Nisikawa, T.; Maeda, M. Bioorg. Med. Chem. Lett. 1998, 8, 2983–2986.
(25) Graham, P.; Meiere, S. H.; Sabat, M.; Harman, W. D. Organome-
tallics 2003, 22, 4364–4366.
[TpW(NO)(PMe3)(4,5-η2-1-(1,3-dimethoxy-2-azabicyclo[2.2.2]octa-
2,5-dien-7-yl)ethanone))] (4). A 2-dram vial containing 0.100 g of
methyl vinyl ketone (1.43 × 10-3 mol, 6 equiv) was solvated with
(26) Chordia, M. D.; Smith, P. L.; Meiere, S. H.; Sabat, M.; Harman,
W. D. J. Am. Chem. Soc. 2001, 123, 10756–10757.
(27) Bortolini, O.; Campestrini, S.; Di Furia, F.; Modena, G. J. Org.
Chem. 1987, 52, 5093–5095.

4518 Organometallics, Vol. 27, No. 17, 2008
Kosturko et al.
1.723 g of DME that was dried over basic alumina. This stock
solution was added to a preweighed 2-dram vial containing 0.153
g of 3 (2.379 × 10-4 mol, 1 equiv). The resulting homogeneous
mixture was allowed to react at room temperature for 16 h. The
resulting heterogeneous mixture was filtered over a 30 mL fine
fritted glass disk and washed with 50 mL of fresh Et2O. An off-
white precipitate 4B was isolated and dried under vacuum. The
isolated yield of the pure B isomer was 54% in a diastereomer
ratio of 1.7:1 exo/endo. Overall, the reaction yield was 84% (A
and B). 1H NMR (CDCl3, ambient temperature, 300 MHz, δ): 4B
exo 8.79 (1H, d, J ) 2.0 Hz, Tp), 8.13 (1H, d, J ) 2.0 Hz, Tp),
7.69 (1H, d, J ) 2.0 Hz, Tp), 7.63 (1H, d, J ) 2.0 Hz, Tp), 7.45
(1H, d, J ) 2.0 Hz, Tp), 7.29 (1H, d, J ) 2.0 Hz, Tp), 7.26 (CDCl3),
6.28 (2H, m, Tp major and minor), 6.12 (2H, m, Tp major and
minor), 6.08 (1H, t, J ) 2.2, 4.1 Hz, Tp), 3.82 (3H, s, H11), 3.76
(3H, s, H12), 3.39 (1H, dd, J ) 4.1,9.8 Hz; H8), 3.06 (1H, m, H3),
2.45 (1H, m, H7), 2.37 (1H, m, H4 major and minor), 2.27 (3H, s,
H10), 1.76 (1H, m, H7′) 1.43 (1H, dd, J ) 2.6, 10.4 Hz, H5), 1.23
(9H, d, J ) 8.4 Hz, PMe3). 4B exo 13C NMR (CDCl3, ambient
temperature, 300 MHz, δ): 210.2 (C9), 168.2 (C2), 149.3 (Tp d),
143.0 (Tp d), 140.8 (Tp d), 136.7 (Tp d), 135.7 (Tp d), 134.6 (Tp
d), 106.5 (Tp t), 105.9 (Tp t), 105.2 (Tp t), 100.3 (C6), 77.0 (CDCl3,
t), 55.4 (C5), 54.3 (C8), 54.2 (d, J ) 16.0 Hz, C4), 53.6 (C11),
49.8 (C12), 41.0 (C3), 34.0 (C7), 32.2 (C10), 14.0 (d, J ) 27.5
d, J ) 2.0 Hz, Tp), 6.28 (2H, m, Tp major and minor), 6.21 (1H,
t, Tp), 6.12 (2H, m, Tp major and minor), 3.89 (3H, s, H11), 3.55
(1H, dd, J ) 4.4,9.6 Hz; J ) 4.1, 9.8 Hz, H8), 3.23 (3H, s, H12),
3.17 (1H, m, H3), 2.45 (1H, m, H7), 2.37 (2H, m, H4 major and
minor), 2.20 (3H, s, H10), 2.05 (1H, m, H7′) 1.43 (2H, dd, J) 2.6,
10.4 Hz, H5 major and minor), 1.28 (9H, d, J ) 8.4 Hz, PMe3).
5B endo 13C NMR (d6-acetone, ambient temperature, 300 MHz,
δ): 211.5 (C9), 166.8 (C2), 148.4 (Tp d), 143.2 (Tp d), 140.3 (Tp
d), 136.9 (Tp d), 135.9 (Tp d), 134.8 (Tp d), 106.6 (Tp t), 105.8
(Tp t), 105.7 (Tp t), 100.8 (C6), 77.0 (CDCl3, t), 58.9 (C8), 54.7
(C11), 54.6 (C5), 53.8 (d, J ) 15.1 Hz, C4), 51.3 (C12), 41.2 (C3),
36.0 (C7), 28.9 (C10), 14.2 (d, J ) 28.2 Hz, PMe3). IR: ν(NO) )
1574 cm-1 (vs), ν(imidate) ) 1648 cm-1 (s), ν(CO) ) 1698 cm-1
(s). CV: Ep,a ) + 0.62 V. HRMS (UIUC) (m/z, obsd (%), calcd
(%), error (ppm)): 725.2261 (81.7%), 725.2235 (82.8%), 3.6;
726.2286 (80.3%), 726.2256 (80.5%), 4.1; 727.2286 (100%),
727.2248 (100%), 5.2; 728.2325 (45.4%); 728.2314 (45%), 1.5;
729.23180 (83.4%), 729.2300 (83.3%) 2.5.
[TpW(NO)(PMe3)(4,5-η2-(1,5-dimethoxybicyclo[2.2.2]octa-5,7-
diene-2-carbonitrile))] (6). The synthesis is similar to compound
1
4. H NMR (d6-acetone, ambient temperature, 300 MHz, δ): 8.90
(1H, d, J ) 1.7 Hz, Tp), 8.18 (1H, d, J ) 1.8 Hz, Tp), 7.96 (1H,
d, J ) 2.3 Hz, Tp), 7.91 (1H, d, J ) 2.1 Hz, Tp), 7.67 (1H, d, J )
2.4 Hz, Tp), 7.62 (1H, d, J ) 2.0 Hz, Tp), 6.42 (1H, t, J ) 2.1, 4.3
Hz, Tp), 6.28 (1H, t, J ) 2.3, 4.4 Hz, Tp), 6.17 (1H, t, J ) 2.1, 4.3
Hz, Tp), 3.73 (3H, s, H10), 3.58 (3H, s, H11), 3.45 (3H, DME),
3.27 (3H, DME), 3.19 (1H, m, H3) 3.16 (1H, dd, J ) 4.6, 10.1
Hz, H8), 2.59 (1H, ddd, J) 2.7,10.5, 13.0 Hz, H4), 2.37 (1H, ddd,
J) 2.4,10.8, 12.7 Hz, H7′), 2.12 (1H, ddd, J) 2.4, 4.6, 12.4 Hz;
H7), 2.05 (d6-acetone) 1.86 (1H, dd, J ) 2.7, 10.5 Hz, H5), 1.29
(9H, d, J ) 8.4 Hz, PMe3). 13C NMR (CDCl3, ambient temperature,
300 MHz, δ): 167.2 (C2), 149.0 (Tp d), 142.7 (Tp d), 140.4 (Tp
d), 136.5 (Tp d), 135.6 (Tp d), 134.3 (Tp d), 122.4 (C9), 106.3
(Tp t), 105.7 (Tp t), 105.3 (Tp t), 98.4 (C6), 71.7 (DME), 59.0
(DME), 53.8 (C5), 53.7 (C10), 53.6 (d, J ) 15.6 Hz, C4), 49.7
(C11), 40.0 (C8), 37.5 (C7), 33.0 (C3), 13.6 (d, J ) 28.2 Hz, PMe3).
IR: ν(NO) ) 1562 cm-1 (vs), ν(imidate) ) 1645 cm-1 (s), ν(CN)
) 2231 cm-1 (w). CV: Ep,a ) +0.65 V. HRMS (m/z, obsd(I);
calcd(I); error (ppm)): 694.19216 (87%), 694.19452 (84%), 3.40;
695.19634 (82%), 695.19705 (80%), 1.02; 696.19659 (100%),
696.19692 (100%), 0.47; 697.20037 (50%), 697.20099 (44%), 0.88;
698.19977 (95%), 698.20016 (84%), 0.58.
1
Hz, PMe3). 4B endo H NMR (CDCl3, ambient temperature, 300
MHz, δ): 8.62 (1H, d, J ) 2.0 Hz, Tp), 8.06 (1H, d, J ) 2.0 Hz,
Tp), 7.71 (1H, d, J ) 2.0 Hz, Tp), 7.67 (1H, d, J ) 2.0 Hz, Tp),
7.51 (1H, d, J ) 2.0 Hz, Tp), 7.26 (CDCl3), 7.24 (1H, d, J ) 2.0
Hz, Tp), 6.28 (2H, m, Tp major and minor), 6.21 (1H, t, Tp), 6.12
(2H, m, Tp major and minor), 3.89 (3H, s, H11), 3.55 (1H, dd, J
) 4.4,9.6 Hz; H8), 3.23 (3H, s, H12), 3.17 (1H, m, H3), 2.45 (1H,
m, H7), 2.37 (2H, m, H4 major and minor), 2.20 (3H, s, H10),
2.05 (1H, m, H7′) 1.43 (2H, dd, J) 2.6, 10.4 Hz, H5 major and
minor), 1.28 (9H, d, J ) 8.4 Hz, PMe3). 4B endo 13C NMR (CDCl3,
ambient temperature, 300 MHz, δ): 211.5 (C9), 166.8 (C2), 148.4
(Tp d), 143.2 (Tp d), 140.3 (Tp d), 136.9 (Tp d), 135.9 (Tp d),
134.8 (Tp d), 106.6 (Tp t), 105.8 (Tp t), 105.7 (Tp t), 100.8 (C6),
77.0 (CDCl3, t), 58.9 (C8), 54.7 (C11), 54.6 (C5), 53.8 (d, J )
15.1 Hz, C4), 51.3 (C12), 41.2 (C3), 36.0 (C7), 28.9 (C10), 14.2
(d, J ) 28.2 Hz, PMe3). IR: ν(NO) ) 1574 cm-1 (vs), ν(imidate)
) 1648 cm-1 (s), ν(CO) ) 1698 cm-1 (s). CV: Ep,a ) +0.62 V.
HRMS (m/z, obsd(I); calcd(I); error (ppm)): 711.20967 (94%),
711.20985 (83%), 0.25; 712.21195 (83%), 712.21240 (80%), 0.63;
713.21097 (100%), 713.21228 (100%), 1.83; 714.21493 (47%),
714.21635 (44%), 1.98; 715.21481 (89%), 715.21551 (83%), 0.97.
[TpW(NO)(PMe3)(4,5-η2-(1,3-dimethoxy-7-(phenylsulfonyl)-2-
azabicyclo[2.2.2]octa-2,5-diene))] (7). The synthesis is similar to
1
[TpW(NO)(PMe3)(4,5-η2-(1-(1,3-dimethoxy-2-azabicyclo[2.2.2]octa-
2,5-dien-7-yl)propan-1-one))] (5). The synthesis is similar to
compound 4. 1H NMR (d6-acetone, ambient temperature, 300 MHz,
δ): 5B exo 8.81 (1H, d, J ) 1.5 Hz, Tp), 8.17 (1H, d, J ) 1.9 Hz,
Tp), 7.93 (1H, d, J ) 2.3 Hz, Tp), 7.88 (1H, d, J ) 2.2 Hz, Tp),
7.62 (1H, d, J ) 2.2 Hz, Tp), 7.49 (1H, d, J ) 1.9 Hz, Tp), 6.39
(2H, m, Tp major and minor), 6.29 (2H, m, Tp major and minor),
6.12 (1H, t, J ) 2.2, 4.1 Hz, Tp), 3.74 (3H, s, H12), 3.72 (3H, s,
H13), 3.45 (DME), 3.35 (1H, dd, J ) 4.0,9.7 Hz, H8), 3.27 (DME),
3.10 (1H, m, H3), 2.45 (1H, m, H7), 2.37 (1H, m, H4 major and
minor), 2.27 (3H, s, H10), 1.76 (1H, m, H7′) 1.43 (1H, dd, J) 2.6,
10.4 Hz, H5), 1.28 (9H, d, J ) 8.5 Hz, PMe3), 0.88 (3H, t, J )
7.2,14.3 Hz, H13). 5B exo 13C NMR (d6-acetone, ambient tem-
perature, 300 MHz, δ): 210.3 (C9), 167.8 (C2), 148.9 (Tp d), 143.0
(Tp d), 141.0 (Tp d), 136.9 (Tp d), 135.8 (Tp d), 134.6 (Tp d),
106.2 (Tp t), 105.8 (Tp t), 104.8 (Tp t), 100.1 (C6), 71.6 (DME),
57.9 (DME), 54.4 (C5), 53.9 (d, J ) 15.2 Hz, C4), 53.4 (C8), 52.6
(C12), 48.7 (C13), 40.8 (C3), 36.6 (C10), 33.9 (C7), 12.8 (d, J )
28.2 Hz, PMe3) 7.43 (C11). 5B endo 1H NMR (d6-acetone, ambient
temperature, 300 MHz, δ): 8.62 (1H, d, J ) 2.0 Hz, Tp), 8.06 (1H,
d, J ) 2.0 Hz, Tp), 7.71 (1H, d, J ) 2.0 Hz, Tp), 7.67 (1H, d, J )
2.0 Hz, Tp), 7.51 (1H, d, J ) 2.0 Hz, Tp), 7.26 (CDCl3), 7.24 (1H,
compound 4. H NMR (CDCl3, ambient temperature, 300 MHz,
δ): 8.53 (1H, d, J ) 1.1 Hz, Tp), 8.08 (1H, m, H13), 8.06 (1H, m,
H11), 8.01 (1H, d, J ) 1.8 Hz, Tp), 7.70 (1H, d, J ) 2.0 Hz, Tp),
7.67 (1H, d, J ) 2.0 Hz, Tp), 7.54 (1H, m, H14), 7.52 (1H, m,
H10), 7.50 (1H, d, J ) 1.3 Hz, Tp), 7.48 (1H, m, H12), 7.26
(CDCl3), 7.22 (1H, d, J ) 1.6 Hz, Tp), 6.25 (1H, t, Tp), 6.20 (1H,
t, Tp), 6.10 (1H, t, Tp), 4.22 (1H, dd, J ) 5.1, 9.7 Hz; 5.5, 10.1
Hz, H8), 3.50 (3H, s, H15), 3.08 (1H, m, H3), 2.92 (3H, s, H16),
2.45 (1H, ddd, J ) 2.8, 5.5; 14.0 Hz, H7), 2.33 (1H, ddd, J ) 2.0,
10.1, 12.6 Hz, H7′), 2.22 (1H, ddd, J ) 2.6, 11.5, 13.4 Hz, H4)
1.59 (1H, dd, J ) 2.4, 11.0 Hz, H5), 1.23 (9H, d, J ) 8.4 Hz,
PMe3). 13C NMR (CDCl3, ambient temperature, 300 MHz, δ): 165.7
(C2), 148.2 (Tp d), 142.8 (Tp d), 140.4 (C9), 139.9 (Tp, d), 136.6
(Tp d), 135.7 (Tp d), 134.6 (Tp d), 132.7 (C12), 130.1 (C11, C13),
128.4 (C10, C14), 106.3 (Tp t), 105.7 (Tp t), 105.4 (Tp t), 98.8
(C6), 68.5 (C8), 54.1(C4), 53.9 (C15), 52.6 (C5), 51.2 (C16), 40.5
(C3), 34.9 (C7), 13.7 (d, J ) 28.2 Hz, PMe3). IR: ν (NO) ) 1565
cm-1 (vs), ν(imidate) ) 1650 cm-1 (s). CV: Ep,a ) +0.74 V.
HRMS (m/z, obs(I); calc(I); error (ppm)): 809.19249 (69%),
809.19255 (78%); 0.07; 810.19511 (79%), 810.19501 (79%), 0.12;
811.19437 (100%), 811.19480 (100%), 0.53; 812.19890 (50%),
812.19829 (50%), 0.75; 813.19961 (73%), 813.19786 (84%), 2.15.

Tungsten-Promoted Diels-Alder Cycloaddition
Organometallics, Vol. 27, No. 17, 2008 4519
as a tan powder. IR: ν(NO) ) 1566 cm-1, ν(CO) ) 1692 cm-1
[TpW(NO)(PMe3)(4,5-η2-(methyl 1,3-dimethoxy-2-azabicyclo-
[2.2.2]octa-2,5-diene-7-carboxylate))] (8). The synthesis is similar
to compound 4. 1H NMR (CDCl3, ambient temperature, 300 MHz,
δ): 8.81 (1H, d, J ) 1.6 Hz, Tp), 8.11 (1H, d, J ) 1.8 Hz, Tp),
7.69 (1H, d, J ) 2.0 Hz, Tp), 7.63 (1H, d, J ) 2.0 Hz, Tp), 7.44
(1H, d, J ) 2.0 Hz, Tp), 7.31 (1H, d, J ) 1.6 Hz, Tp), 6.27 (1H,
t, J ) 2.0, 4.2 Hz, Tp), 6.12 (1H, t, J ) 2.2, 4.1 Hz, Tp), 6.08 (1H,
t, J ) 2.2, 4.1 Hz, Tp), 3.80 (3H, s, H11), 3.67 (3H, s, H12), 3.60
(3H, s, H10), 3.13 (1H, dd, J ) 4.6, 10.0 Hz, H8), 3.08 (1H, m,
H3), 2.44 (1H, ddd, J ) 2.6,10.5, 13.3 Hz, H4), 2.21 (1H, ddd J )
2.1, 4.6, 12.1 Hz; H7), 2.08 (1H, buried, H7′) 1.70 (1H, dd, J )
2.6, 10.5 Hz, H5), 1.23 (9H, d, J ) 8.2 Hz, PMe3). 13C NMR
(CDCl3, ambient temperature, 300 MHz, δ): 174.8 (C9), 167.4 (C2),
149.0 (Tp d), 142.7 (Tp d), 140.4 (Tp d), 136.2 (Tp d), 135.4 (Tp
d), 134.2 (Tp d), 106.1 (Tp t), 105.6 (Tp t), 105.1 (Tp t), 99.7
(C6), 77.0 (CDCl3, t), 54.5 (C5), 54.4 (d, J ) 15.3 Hz, C4), 53.3
(C11), 51.5 (C12), 49.3 (C10), 46.9 (C8), 40.6 (C3), 35.8 (C7),
13.7 (d, J ) 27.1 Hz, PMe3). IR: ν(NO) ) 1561 cm-1 (vs),
ν(imidate) ) 1648 cm-1 (s), ν(CO2Me) ) 1725 cm-1 (w). CV:
Ep,a ) +0.65 V. HRMS (m/z, obsd (%), calcd (%), error (ppm)):
727.2056 (87.9%), 727.2054 (83.2%), 0.27; 728.2087 (80.9%),
728.2079 (80.2%), 1.10; 729.2083 (100%), 729.2078 (100%), 0.68;
730.2116 (44.1%), 730.2119 (44.4%), 0.41; 731.2111 (84.4%),
731.2110 (83.6%), 0.13.
TpW(NO)(PMe3)(4,5-η2-(1,3-Dimethoxy-4′,5′-dihydro-
2azaspiro[bicyclo[2.2.2]octa-2,5-diene-7-3′-furan]-2′-one)) (9). To
3 (0.085 g, 1.321 × 10-4 mol, 1 equiv) was added 4 mL of pentane.
To this solution was added a solution of R-methylene-γ-butyro-
lactone (0.039 g, 3.966 × 10-4 mol, 3 equiv) in DME (1 mL).
The reaction was then stirred overnight (18 h). The reaction mixture
was then added to pentane (50 mL). Residue on the sides of the
reaction vessel was taken in DME (1 mL) and also added to the
pentane. The resulting precipitate was then collected on a medium-
porosity filter funnel and dried in Vacuo to give 9 (0.059 g, 0.0805
mmol, 61%) as a white powder (dr ) 4.6:1 for the B isomers). 1H
NMR (acetone-d6, ambient temperature, 300 MHz, δ): 8.17 (1H,
d, Tp), 7.92 (1H, d, Tp), 7.90 (1H, d, Tp), 7.67 (1H, d, Tp), 7.59
(1H, d, Tp), 6.39 (1H, d, Tp), 6.27 (1H, d, Tp), 6.17 (1H, d, Tp),
4.32 (1H, ddd (J ) 7.2, 7.2, 7.2 Hz), 10a), 4.12 (1H, ddd (J ) 7.2,
7.2, 3.2 Hz), 10b), 3.79 (3H, s, 9), 3.61 (3H, s, 8), 3.14 (1H, d (J
) 2.4 Hz), 3), 2.88 (1H, ddd (J ) 12.9, 7.2, 3.2 Hz), 11a), 2.49
(1H, ddd (J ) 12.9, 10.2, 2.4 Hz), 4 (bound)), 2.27 (1H, dd (J )
12.0, 2.6 Hz), 7a), 2.17 (1H, m, 11b), 1.80 (1H, dd (J ) 12.0, 2.6
Hz), 7), 1.75 (1H, dd (J ) 10.2, 2.4 Hz), 5 (bound)), 1.26 (9H, d
(J ) 8.5 Hz), PMe3). 13C NMR (acetone-d6, ambient temperature,
300 MHz, δ): 181.5 (s, C9), 166.6 (s, C2), 149.3 (s, Tp), 143.9 (s,
Tp), 142.0 (s, Tp), 137.8 (s, Tp), 136.7 (s, Tp), 135.6 (s, Tp), 107.0
(s, Tp), 106.6 (s, Tp), 105.7 (s, Tp), 102.3 (s, C6), 66.1 (s, C10),
56.1 (s, C5), 55.2 (d (J ) 15.5 Hz), C4), 53.7 (s, C12), 50.9 (s,
C13), 47.3 (s, C7), 42.5 (s, C3), 40.8 (s, C8), 36.1 (s, C11), 13.4
(d (J ) 28.2 Hz), PMe3). 31P NMR (acetone-d6, δ): -12.14 (satellite
d (J ) 267), PMe3). IR: ν(NO) ) 1561 cm -1, ν(CO) ) 1757
cm-1. CV: Ep,a ) +0.66 V. HRMS (m/z, obsd(I); calcd(I); error
(ppm)): 739.20417 (90%), 739.20478 (83%), 0.82; 740.20656
(81%), 740.20733 (80%), 1.04; 741.20678 (100%), 741.20723
(100%), 0.61; 742.21039 (47%), 742.21125 (45%), 1.16; 743.20936
(82%), 743.21045 (83%), 1.46.
.
CV: Ep,a ) +0.79 V. 1H NMR (CDCl3, ambient temperature, 300
MHz, δ): 8.70 (1H, d, Tp), 8.05 (2H, d, 2 Tp), 8.03 (1H, d, Tp),
7.70 (1H, d, Tp), 7.69 (1H, d, Tp), 7.67 (2H, d, 2 Tp), 7.54 (1H,
d, Tp), 7.49 (1H, d, Tp), 7.24 (1H, d, Tp), 7.19 (1H, d, Tp), 6.28
(1H, t, Tp), 6.26 (1H, t, Tp), 6.20 (1H, t, Tp), 6.19 (1H, t, Tp),
6.17 (1H, t, Tp), 6.14 (1H, t, Tp), 3.78 (3H, s, 13A), 3.76 (3H, s,
12A), 3.72 (3H, s, 12B), 3.67 (1H, dd (J ) 2.5, 3.0 Hz), 3A), 3.60
(1H, t (J ) 2.8 Hz), 3B), 3.57 (1H, d (J ) 7.7 Hz), 8B), 3.45 (3H,
s, 13B), 3.43 (1H, d (J ) 7.9 Hz), 8A), 3.27 (1H, dd (J ) 3.2, 7.7
Hz), 7B), 3.08 (1H, dd (J ) 3.0, 7.9 Hz), 7A), 2.90 (1H, s, NMe
(A or B)), 2.89 (1H, s, NMe (A or B)), 2.71 (1H, dd (J ) 10.4,
12.4 Hz), 5A), 2.26 (1H, ddd (J ) 2.8, 10.6, 15.3 Hz), 4B), 1.72
(1H, dd (J ) 2.5, 10.6 Hz), 5B), 1.28 (9H, d (J ) 8.9 Hz), PMe3
A), 1.25 (9H, d (J ) 8.5 Hz), PMe3 B), 1.19 (1H, buried, 4A). 13
C
NMR (CDCl3, ambient temperature, 300 MHz, δ): 177.2 (s,
11A(CO)), 177.1 (s, 11B(CO)), 176.6 (s, 9A(CO)), 174.6 (s,
9B(CO)), 164.6 (s, 2A or B), 164.4 (s, 2A or B), 148.3 (s, Tp),
144.3 (s, Tp), 142.9 (s, Tp), 142.4 (s, Tp), 140.2 (s, Tp), 140.1 (s,
Tp), 136.7 (s, Tp), 136.5 (s, Tp), 135.9 (s, Tp), 135.7 (s, Tp), 134.8
(s, Tp), 134.5 (s, Tp), 106.4 (s, Tp), 106.3 (s, Tp), 106.0 (s, Tp),
105.8 (s, Tp), 105.7 (s, Tp), 105.5 (s, Tp), 99.5 (s, 6B), 98.7 (s,
6A), 60.2 (d (J ) 14.9 Hz), 5A), 54.5 (s, 8A), 54.3 (s, OMe), 53.9
(s, OMe), 53.3 (s, 4A + 5B), 52.4 (s, 7B), 52.1 (d (J ) 16.1 Hz),
4B), 51.9 (s, OMe + 7A), 51.1 (s, OMe), 49.6 (s, 8B), 43.7 (s,
3B), 42.7 (s, 3A), 24.5 (s, NMe A or B), 24.4 (s, NMe A or B),
14.3, 14.0 (d (J ) 28.7 Hz), PMe3 A or B), 13.8. 13.4 (d (J ) 28.1
Hz), PMe3 A or B). 31P NMR: -12.81 (satellite d (J PW ) 261
Hz), PMe3), -13.68 (satellite d (J PW ) 272 Hz), PMe3). HRMS
(UIUC) (m/z, obsd (%), calcd (%), error (ppm)): 752.2006 (81.22%),
752.1997 (82.5%), 1.2; 753.2031 (80.35%), 753.2002 (80.5%), 3.9;
754.2031 (100%), 754.2023 (100%), 1.1; 755.2070 (45.85%),
755.2062 (45.3%), 1.1; 756.2063 (83.41%), 756.2057 (83.3%), 0.8.
[TpW(NO)(PMe3)(4,5-η2-(dimethyl 1,3-dimethoxy-2-azabicyclo-
[2.2.2]octa-2,5-diene-7,8-dicarboxylate))] (11). The synthesis is
similar to compound 4. 1H NMR (CDCl3, ambient temperature,
300 MHz, δ): 8.63 (1H, d, J ) 1.8 Hz, Tp), 8.11 (1H, d, J ) 1.8
Hz, Tp), 7.70 (1H, d, J ) 2.3 Hz, Tp), 7.62 (1H, d, J ) 2.1 Hz,
Tp), 7.44 (1H, d, J ) 2.1 Hz, Tp), 7.28 (1H, d, J ) 2.0 Hz, Tp),
6.28 (1H, t, J) 2.0, 4.1 Hz, Tp), 6.12 (1H, t, J ) 2.0, 4.1 Hz, Tp),
6.08 (1H, t, J ) 2.1, 4.4 Hz, Tp), 3.82 (3H, s, H13), 3.72 (3H, s,
H14), 3.71 (3H, s, H11), 3.64 (3H, s, H12), 3.50 (1H d, J ) 1.7
Hz, H8), 3.41 (1H, m, H3), 3.11 (1H, ddd, J ) 2.7,10.8, 13.6 Hz,
H4), 2.97 (1H, dd, J ) 1.7, 10.8 Hz, H7), 1.69 (1H, dd, J ) 2.7,
10.8 Hz, H5), 1.31 (9H, d, J ) 8.4 Hz, PMe3). 13C NMR (CDCl3,
ambient temperature, 300 MHz, δ): 172.9 (C9 or C10), 172.1 (C10
or C9), 167.9 (C2), 148.7 (Tp d), 142.8 (Tp d), 140.5 (Tp d), 136.2
(Tp d), 135.4 (Tp d), 134.1 (Tp d), 106.1 (Tp t), 105.7 (Tp t), 104.9
(Tp t), 100.1 (C6), 56.1 (C5), 51.6 (C11), 51.5 (C12), 49.9 (C8),
49.7 (C7), 49.5 (C14) 49.6 (C14), 47.9 (d, J ) 15.3 Hz, C4), 42.6
(C3), 13.8 (d, J ) 28.2 Hz, PMe3). IR: ν(NO) ) 1560 cm-1 (vs),
ν(imidate) ) 1646 cm-1 (s), ν(CO2Me) ) 1733 cm-1 (m). CV:
Ep,a ) +0.66 V. HRMS (UIUC) (m/z, obsd (%), calcd (%), error
(ppm)): 785.2109 (80.7%), 785.2100 (81.8%), 1.1; 786.2134
(80.3%), 786.2112 (80.4%), 2.8; 787.2133 (100%), 787.2139
(100%), 0.8; 788.2173 (46.5%), 788.2158 (46%), 1.9; 789.2166
(83.3%), 789.2141 (83.2%), 3.2.
TpW(NO)(PMe3)(4,5-η2-(7,9-Dimethoxy-4-methyl-4,8-diaza-
tricyclo[5.2.2.02,6]undeca-8,10-diene-3,5-dione)) (10). To 3 (0.069
g, 1.082 × 10-4 mol, 1 equiv) was added 2 mL of THF. To this
solution was added a solution of NMM (0.143 g 1.288 × 10-3
mol, 12 equiv) in THF (1 mL). The reaction was then stirred
overnight (18 h). The solid generated by the reaction, presumably
NMM polymer, was filtered out with a 15 mL medium-porosity
filter funnel. The filtrate was than added to pentane (50 mL). The
resulting precipitate was then collected on a medium-porosity filter
funnel and dried in Vacuo to give 10 (48.5 mg, 0.0644 mmol, 60%)
[TpW(NO)(PMe3)(4,5-η2-(dimethyl 1,3-dimethoxy-2-azabicyclo-
[2.2.2]octa-2,5-diene-7,8-dicarboxylate))] (12). The synthesis is
similar to compound 4. 1H NMR (CDCl3, ambient temperature,
300 MHz, δ): 8.78 (1H, Tp), 8.11 (1H, Tp), 7.70 (1H, Tp), 7.65
(1H, Tp), 7.44 (1H, Tp), 7.29 (1H, Tp), 7.26 (CDCl3), 6.28 (1H,
Tp), 6.15 (1H, Tp), 6.09 (1H, Tp), 3.81 (3H, s, H13), 3.72 (3H, s,
H14), 3.71 (3H, s, H11), 3.64 (3H, s, H12), 3.50 (2H, s, H7 and
H8), 3.38 (1H, m, H3), 2.47 (1H, ddd, J) 2.0,10.2, 12.5 Hz, H4),
1.68 (1H, dd, J ) 2.0, 10.2 Hz, H5), 1.25 (9H, d, J ) 8.2 Hz,
PMe3). 13C NMR (CDCl3, ambient temperature, 300 MHz, δ): 173.6

4520 Organometallics, Vol. 27, No. 17, 2008
Kosturko et al.
(C9 or C10), 173.5 (C10 or C9), 165.4 (C2), 149.1 (Tp d), 142.8
(Tp d), 140.4 (Tp d), 136.4 (Tp d), 135.5 (Tp d), 134.3 (Tp d),
106.3 (Tp t), 105.7 (Tp t), 105.0 (Tp t), 99.3 (C6), 77.0 (CDCl3, t),
54.2 (C5), 53.7 (d, J ) 13.7 Hz, C4), 53.6 (C13), 53.3 (C8), 52.1
(C11), 51.9 (C12), 50.5 (C7) 49.6 (C14), 43.9 (C3), 13.7 (d, J )
28.2 Hz, PMe3). IR: ν(NO) ) 1566 cm-1 (vs), ν(imidate) ) 1650
cm-1 (s), ν(CO2Me) ) 1715 cm-1(m). CV: Ep,a ) +0.66 V. HRMS
(UIUC) (m/z, obsd (%), calcd (%), error (ppm)): 785.21090 (80.8%),
785.2100 (81.8%), 1.1; 786.213 (80.4%), 786.2133 (80.4%), 0.1;
787.2133 (100%), 787.2114 (100%), 2.4; 788.2173 (46.6%),
788.2185 (46%), 1.5; 789.2166 (83.5%), 789.2158 (83.2%), 1.0.
temperature. The resulting solution was evaporated to a residue,
redissolved with CH2Cl2, and purified via silica gel chromatography
(elution with 15% acetone/ethyl acetate). Isolated yield was 29%.
1H NMR (CDCl3, ambient temperature, 300 MHz, δ): 7.90 (1H,
br, H1), 6.67 (1H, dd, J ) 8.2, 9.3 Hz, H5), 6.61 (1H, dd, J ) 6.0,
8.2 Hz, H4), 3.64 (3H, s, H10), 3.44 (1H, m, H3), 3.17 (1H, dd, J
) 4.1, 9.7 Hz, H8), 2.40 (1H, ddd, J ) 2.4, 9.7, 12.8 Hz, H7′),
1.89 (1H, ddd, J ) 3.1, 4.1, 13.0 Hz, H7). 13C NMR (CDCl3,
ambient temperature, 300 MHz, δ): 174.2 (C2), 132.7 (C5), 132.4
(C4), 119.4 (C9), 89.4 (C6), 53.6 (C10), 43.0 (C3), 35.7 (C8), 28.9
(C7). IR: ν(CO) ) 1688 cm-1 (vs), ν(amide) ) 1611 cm-1 (m).
[TpW(NO)(PMe3)(4,5-η2-(dimethyl 1,3-dimethoxy-2-azabicyclo-
[2.2.2]octa-2,5,7-triene-7,8-dicarboxylate))] (13). The synthesis is
similar to compound 4. 1H NMR (CDCl3, ambient temperature,
300 MHz, δ): 8.59 (1H, d, J ) 1.8 Hz, Tp), 8.14 (1H, d, J ) 1.8
Hz, Tp), 7.72 (1H, d, J ) 2.2 Hz, Tp), 7.68 (1H, d, J ) 2.1 Hz,
Tp), 7.47 (1H, d, J ) 2.2 Hz, Tp), 7.31 (1H, d, J ) 1.8 Hz, Tp),
6.30 (1H, t, J ) 2.3, 4.3 Hz, Tp), 6.16 (1H, t, J ) 2.3, 4.3 Hz, Tp),
6.13 (1H, t, J ) 2.2, 4.4 Hz, Tp), 4.37 (1H, d, J ) 2.8 Hz, H3),
3.90 (3H, s, H13), 3.83 (3H, s, H12), 3.80 (3H, s, H11), 3.74 (3H,
s, H14), 2.73 (1H, ddd, J ) 3.0, 10.6, 13.2 Hz, H4), 2.16 (1H, dd,
J ) 2.8, 10.4 Hz, H5), 1.23 (9H, d, J ) 8.4 Hz, PMe3). 13C NMR
(CDCl3, ambient temperature, 300 MHz, δ): 169.7 (C2), 168.4
(C10), 164.3 (C9), 160.4 (C7), 148.6 (Tp), 142.9 (Tp), 140.8 (Tp),
136.7 (C8), 136.4 (Tp), 135.8 (Tp), 134.3 (Tp) 106.3 (Tp), 105.6
(Tp), 105.4 (Tp), 104.4 (C6), 77.0 (CDCl3, t), 63.6 (C5), 63.3 (d,
J ) 2.9 Hz, C4), 59.0 (C13), 55.0 (C14), 53.4 (C12), 52.1 (C11),
48.1 (C3), 13.8 (d, J ) 29.0 Hz, PMe3). IR: ν(NO) ) 1571 cm-1
(vs), ν(imidate) ) 1649 cm-1 (s), ν(CO2Me) ) 1730 cm-1(s). CV:
Ep,a ) +0.87 V. HRMS (UIUC) (m/z, obsd (%), calcd (%), error
(ppm)): 783.1952 (80.70%), 783.1946 (81.8%), 0.8; 784.1978
(80.26%), 784.1976 (80.4%), 0.3; 785.1977 (100%), 785.1979
(100%), 0.3; 786.2017 (46.49%), 786.2018 (46.0%), 0.1; 787.2009
(83.33%), 787.2007 (83.2%), 0.3.
1,3-Dimethoxy-2-azabicyclo[2.2.2]octa-2,5-diene-7-carbonitrile
(16). A sample containing 0.1025 g of 6 (1.47 × 10-4 mol) was
dissolved with 0.881 g of CD3CN and added to preweighed vial
containing 0.097 g (2.95 × 10-4 mol, 2 equiv) of cerric(IV)
ammonium nitrate. The reaction turned orange-brown instantly and
was allowed to react for 14 h at room temperature. The resulting
solution was evaporated to dryness and redissolved with 8 mL of
CH2Cl2 and 2 mL of saturated NaHCO3. The organic layer was
extracted, while the aqueous layer was rewashed with 4 mL of
CH2Cl2. The organic solution was dried over MgSO4, filtered over
a 30 mL fritted glass disk, and evaporated to a residue. The resulting
residue was taken up in 2 mL of CH2Cl2 and purified via silica gel
chromatography (elution with 75% Et2O/hexanes). The isolated
yield was 35%. 1H NMR (CDCl3, ambient temperature, 300 MHz,
δ): 6.63 (1H, d, J )7.7 Hz, H5), 6.50 (1H, dd, J ) 6.0, 7.7 Hz,
H4), 3.70 (3H, s, H10), 3.66 (3H, s, H11), 3.54 (1H, m, H3), 2.80
(1H, dd, J ) 4.8, 9.7, H8), 2.08 (1H, ddd, J ) 2.8, 9.7, 12.4 Hz,
H7′), 1.89 (1H, ddd, J ) 2.5, 4.8 Hz, 12.4 H7). 13C NMR (CDCl3,
ambient temperature, 300 MHz, δ): 172.3 (C2), 135.4 (C5), 130.8
(C4), 120.5 (C9), 94.0 (C6), 54.3 (C10), 51.9 (C11), 37.5 (C3),
32.3 (C8), 30.0 (C7). IR: ν(imidate) ) 1643 cm-1 (s). HRMS
(UIUC) (m/z, obsd (%), calcd (%), error (ppm)): 193.0969 (37.5%),
193.0977 (100%), 4.14; 194.1002 (4.7%), 194.1007 (11.8%), 2.57.
TpW(NO)(PMe3)(4,5-η2-(1,3-Dimethoxy-2-azabicyclo[2.2.2]octa-
2,5,7-trien-6-yl)ethanone) (14). To 3 (0.041 g, 6.372 × 10-4 mol,
1 equiv) was added 4 mL of pentane. To this solution was added
a solution of 3-butyne-2-one (0.018 g, 4 equiv) in DME (1 mL).
The reaction was then stirred overnight (18 h). The reaction mixture
was then added to pentane (50 mL). Residue on the sides of the
reaction vessel was taken in DME (1 mL) and also added to the
pentane. The resulting precipitate was then collected on a medium-
porosity filter funnel and dried in Vacuo to give 14B (36.0 mg,
0.0507 mmol, 80%) as a brown powder. 1H NMR (acetone-d6,
ambient temperature, 300 MHz, δ): 8.97 (1H, d, Tp), 8.23 (1H, d,
Tp), 7.96 (1H, d, Tp), 7.92 (1H, d, Tp), 7.67 (1H, d, Tp), 7.59
(1H, d, Tp), 7.17 (1H, d (J ) 5.7), 7), 6.42 (1H, t, Tp), 6.27 (1H,
t, Tp), 6.19 (1H, t, Tp), 3.91 (1H, dd (J ) 5.7, 3.1 Hz), 3), 3.82
(3H, s, 11), 3.54 (3H, s, 12), 2.81 (1H, m, 4), 2.25 (3H, s, 10),
2.00 (1H, d (J ) 13.9 Hz), 5), 1.30 (9H, d (J ) 8.5 Hz), PMe3).
13C NMR (acetone-d6, ambient temperature, 300 MHz, δ): 196.9
(s, 9), 169.2 (s, 2), 159.4 (s, 6), 150.0 (s, Tp), 145.1 (s, Tp), 144.0
(s, 7), 142.3 (s, Tp), 137.8 (s, Tp), 136.9 (s, Tp), 135.5 (s, Tp),
107.2 (s, Tp), 106.7 (s, Tp), 105.8 (s, Tp), 104.3 (s, 6), 65.5 (s, 5),
64.3 (d (J ) 18.4 Hz), 4), 54.7 (s, 11), 53.5 (s, 12), 49.0 (s, 3),
28.9 (s, 10), 13.5 (d (J ) 28.7 Hz), PMe3). 31P NMR: -12.08
(satellite d (JPW ) 257 Hz), PMe3). IR: ν(NO) ) 1575 cm-1(vs),
ν(CO) ) 1700 cm-1 (s). CV: Ep,a ) +0.88 V. HRMS (UIUC)
(m/z, obsd (%), calcd (%), error (ppm)): 709.1948 (82.53%),
709.1918 (83.4%), 4.2; 710.1973 (80.35%), 710.1948 (80.3%), 3.5;
711.1972 (100%), 711.1956 (100%), 2.2; 712.2103 (44.98), 712.1982
(44.2%), 4.4; 713.2004 (83.84%), 713.2007 (83.6%), 0.4.
1,3-Dimethoxy-7-(phenylsulfonyl)-2-azabicyclo[2.2.2]octa-2,5-di-
ene (17). A sample containing 0.1487 g of 7 (1.83 × 10-4 mol)
was dissolved with 0.881 g of CD3CN and added to preweighed
vial containing 0.067 g (2.02 × 10-4 mol, 1.1 equiv) of cerric(IV)
ammonium nitrate. The reaction turned orange-brown instantly and
was allowed to react for 3 h at room temperature. The resulting
solution was evaporated to dryness and redissolved with 8 mL of
CH2Cl2 and 2 mL of saturated NaHCO3. The organic layer was
extracted, while the aqueous layer was rewashed with 4 mL of
CH2Cl2. The organic solution was dried over MgSO4, filtered over
a 30 mL fritted glass disk, and evaporated to a residue. The resulting
residue was taken up in 1 mL of CH2Cl2 and purified via silica gel
chromatography (elution with 40% Et2O/hexanes, Rf 0.45). Overall
yield was 35%. 1H NMR (CDCl3, ambient temperature, 300 MHz,
δ): 7.92 (2H, d, J ) 7.3 Hz, H10, H14), 7.61 (H, t, J ) 7.5,14.6
Hz, H12), 7.53 (2H, t, J ) 7.8, 14.9 Hz, H11, H13), 6.52 (1H, d,
J )7.6 Hz, H5), 6.44 (1H, dd, J ) 6.1, 7.6 Hz, H4), 3.65 (3H, s,
H15), 3.51 (1H, m, H8), 3.48 (1H, m, H3), 3.27 (3H, s, H16), 2.08
(1H, ddd, J) 3.1, 9.6, 12.8 Hz, H7), 1.89 (1H, ddd, J) 2.1, 5.7,
12.7 Hz; H7′). 13C NMR (CDCl3, ambient temperature, 300 MHz,
δ): 173.4 (C2), 140.6 (C9), 134.8 (C5), 133.2 (C4), 129.8 (C12),
129.0 (C10, C14), 128.4 (C11, C13), 93.88 (C6), 77.0 (CDCl3),
66.0 (C8), 54.3 (C15), 51.1 (C16), 38.0 (C3), 27.9 (C7). IR:
ν(imidate) ) 1641 cm-1 (s).
1-(2,6-Dimethoxypyridin-3-yl)pentan-3-one (18). 5 (0.084 g,
1.182 × 10-4 mol) was dissolved in 0.892 g of d6-acetone and
added to a preweighed vial containing 0.039 g of ceric(IV)
ammonium nitrate (1.182 × 10-4 mol, 1 equiv). The reaction turned
orange-brown instantly and was allowed to react for 14 h at room
temperature. The resulting solution was evaporated to dryness and
redissolved with 8 mL of CH2Cl2 and 2 mL of saturated NaHCO3.
The organic layer was extracted, while the aqueous layer was
rewashed with 4 mL of CH2Cl2. The organic solution was dried
1-Methoxy-3-oxo-2-azabicyclo[2.2.2]oct-5-ene-7-carbonitrile (15).
A sample containing 0.099 g of 6 (1.33 × 10-4 mol) was dissolved
with 0.792 g of CD3CN and added to preweighed vial containing
0.059 g (2.66 × 10-4 mol, 2 equiv) of CuBr2. The reaction turned
green instantly and was allowed to react for 14 h at room

Tungsten-Promoted Diels-Alder Cycloaddition
Organometallics, Vol. 27, No. 17, 2008 4521
over MgSO4, filtered over a 30 mL fritted glass disk, and evaporated
to a residue. The resulting residue was taken up in 1 mL of CH2Cl2
and purified via silica gel chromatography (80% Et2O/hexanes, Rf
at 0.48). 1H NMR (CDCl3, ambient temperature, 300 MHz, δ): 7.33
(1H, dd, J )7.8 Hz, H5), 6.21 (1H, d, J ) 7.8 Hz, H4), 3.91 (3H,
s, H12), 3.87 (3H, s, H13), 2.75 (4H, m, H7, H7′ and H8, H8′),
2.43 (2H, q, J ) 7.3, 14.6 Hz, H10), 1.05 (3H, t, J ) 7.3, 14.6 Hz,
H11). 13C NMR (CDCl3, ambient temperature, 300 MHz, δ): 211.2
(C9), 161.5 (C2), 160.3 (C6), 141.1 (C5), 114.0 (C3), 99.8 (C4),
53.5 (C12), 53.2 (C13), 41.8 (C8), 36.0 (C7), 23.6 (C10), 7.73
(C11). HRMS (UIUC) (m/z, obsd (%), calcd (%), error (ppm)):
224.1277 (100%), 224.1287 (100%), 4.46; 225.1323 (17.6%),
225.1319 (13.6%), 1.77.
4.6 Hz, H10). 13C NMR (CDCl3, ambient temperature, 300 MHz,
δ): 166.3 (C2), 149.7 (Tp d), 142.7 (Tp d), 140.2 (Tp, d), 136.4
(Tp d), 135.4 (Tp d), 134.2 (Tp d), 106.1 (Tp t), 105.5 (Tp t), 104.9
(Tp t), 100.5 (C6), 72.4 (C9), 54.04 (C5), 53.9 (d, J ) 15.6 Hz,
C4), 53.3 (C11), 49.2 (C12), 45.8 (C8), 40.4 (C3), 36.1 (C7), 21.7
(C10), 13.6 (d, J ) 27.8 Hz, PMe3). IR: ν (NO) ) 1561 cm-1
(vs), ν(imidate) ) 1650 cm-1(s), ν(OH) ) 3480 cm-1 (b). CV:
Ep,a +0.62 V. HRMS (UIUC) (m/z obsd (%), calcd (%), error
(ppm)): 713.2261 (82.53), 713.2263 (83.3), 0.3; 714.2286 (80.35),
714.2287 (80.3), 0.1; 715.2285 (100), 715.2279 (100), 0.8; 716.2325
(44.98), 716.2319 (44.3), 0.8; 717.2318 (83.84), 717.2318 (83.6),
0.0.
[TpW(NO)(PMe3)(4,5-η2-(1,3-dimethoxy-2-azabicyclo[2.2.2]octa-
2,5-dien-7-yl)methanol)] (21). A sample containing 0.034 g of exo
8B dissolved with 1.561 mL of DME (dried over basic alumina)
was prepared and added to a vial containing 0.004 g of LiAlH4
(9.27 × 10-5 mol, 2 equiv). The dark, heterogeneous solution was
allowed to stir at room temperature for 3 h. The resulting reaction
mixture was diluted with 8 mL of CH2Cl2 and 1.5 mL of Rochelle’s
salt. The organic layer was extracted, while the aqueous layer was
rewashed with 5 mL of CH2Cl2 and H2O. Again, the organic layer
was extracted, dried with MgSO4, and filtered over a 30 mL fine
fritted glass disk. The resulting filtrate was dried to a residue and
taken up in CDCl3. Overall yield was 75% with a dr <2:1. 1H
NMR (CDCl3, ambient temperature, 300 MHz, δ): 8.81 (1H, d, J
) 1.6 Hz, Tp), 8.14 (1H, d, J ) 1.6 Hz, Tp), 7.70 (1H, d, J ) 2.2
Hz, Tp), 7.68 (1H, d, J ) 2.0 Hz, Tp), 7.48 (1H, d, J ) 2.0 Hz,
Tp), 7.25 (1H, Tp), 6.28 (1H, t, J ) 2.0, 4.1 Hz, Tp), 6.15 (1H, t,
J ) 2.0, 4.1 Hz, Tp), 6.10 (1H, t, J ) 2.0, 4.1 Hz, Tp), 3.90 (1H,
H9), 3.83 (3H, s, H11), 3.67 (3H, s, H12), 3.64 (1H, buried, H9′),
2.97 (1H, m, H3), 2.40 (1H, m, H8), 2.21 (1H, ddd, J ) 2.6, 10.4,
13.0 Hz, H4), 2.04 (1H, ddd, J ) 2.6, 12.3 Hz, H7′) 1.77 (1H, dd,
J ) 2.5, 10.4 Hz, H5), 1.23 (9H, d, J ) 8.2 Hz, PMe3), 1.07 (1H,
ddd, J ) 2.2, 4.1, 11.0 Hz, H7). 13C NMR (CDCl3, ambient
temperature, 300 MHz, δ): 166.3 (C2), 149.1 (Tp d), 142.7 (Tp d),
140.1 (Tp, d), 136.5 (Tp d), 135.4 (Tp d), 134.3 (Tp d), 106.2 (Tp
t), 105.5 (Tp t), 104.9 (Tp t), 100.0 (C6), 67.1 (C9), 53.8 (C5),
53.7 (d, J ) 12.2 Hz, C4), 53.3 (C11), 49.2 (C12), 40.5 (C8), 40.1
(C3), 34.7 (C7), 13.6 (d, J ) 27.8 Hz, PMe3). IR: ν(NO) ) 1561
cm-1 (vs), ν(imidate) ) 1650 cm-1(s), ν OH ) 3410 cm-1 (b).
CV: Ep,a +0.61 V. HRMS (m/z obsd (%), calcd (%), error (ppm)):
699.2104 (82.61), 699.2111 (83.9), 1.0; 700.2130 (80.00), 700.2136
(80.1), 0.9; 701.2128 (100), 701.2132 (100), 0.6; 702.2169 (44.35),
702.2188 (43.6), 2.7; 703.2161 (83.91), 703.2167 (83.8), 0.9.
[TpW(NO)(PMe3)(4,5-η2-(1,3-dimethoxy-7-(prop-1-en-2-yl)-2-
azabicyclo[2.2.2]octa-2,5-diene))] (19). A 0.0994 g sample of 4B
was dissolved in 2 mL of THF (dried with basic alumina). The
yellow, homogeneous solution was added to 0.143 g (2.513 × 10-4
mol, 2 equiv) of 0.5 M Tebbe’s solution in toluene. The red-yellow
reaction mixture was allowed to stir at room temperature for 12 h.
The reaction was quenched with 20 drops of 1 M NaOH and diluted
with 8 mL of CH2Cl2. The organic layer was extracted, dried with
MgSO4, and filtered over a 30 mL fine fritted glass disk. The filtrate
was evaporated to a residue and redissolved with 1 mL of dry THF.
The THF solution was added to a 125 mL flask containing 60 mL
of pentanes. A tan precipitate was isolated from the pentanes
solution over a 30 mL fine fritted glass disk, and the yellow filtrate
was evaporated to a residue. The residue was resolvated with 1
mL of CH2Cl2 and purified with silica gel chromatography (Rf of
0.15, 10% acetone/Et2O,). Overall yield was 25%. 1H NMR (CDCl3,
ambient temperature, 300 MHz, δ): 8.79 (1H, Tp), 8.12 (1H, Tp),
7.69 (1H, J ) 2.1 Hz, Tp), 7.64 (1H, J ) 1.8 Hz Tp), 7.43 (1H, d,
J ) 1.8 Hz, Tp), 7.22 (1H, Tp), 6.27 (1H, t, Tp), 6.13 (1H, t, Tp),
6.07 (1H, t, Tp), 4.97 (1H, H11), 4.85 (1H, H12), 3.82 (3H, s,
H14), 3.62 (3H, s, H15), 3.04 (1H, m, H3), 2.87 (1H, dd, J ) 5.3,
10.4 Hz, H8), 2.36 (1H, ddd, J ) 2.6, 10.2, 13.3 Hz, H4), 2.13
(1H, m, H7′), 1.85 (3H, s, H13), 1.82 (1H, dd, J ) 2.3 Hz, 10.2
Hz, H5), 1.72 (1H, ddd, J ) 1.0, 5.3, 12.1 Hz, H7) 1.26 (9H, d, J
) 8.1 Hz, PMe3). 13C NMR (CDCl3, ambient temperature, 300
MHz, δ): 166.3 (C2), 149.0 (Tp d), 146.8 (C9), 142.8 (Tp,d) 139.9
(Tp d), 136.2 (Tp d), 135.4 (Tp d), 134.1 (Tp d), 112.8 (C10),
106.1 (Tp t), 105.5 (Tp t), 105.1 (Tp t), 99.6 (C6), 77.0 (CDCl3, t),
55.1 (C5), 55.0 (d, J ) 15.3 Hz, C4), 53.1 (C14), 49.2 (C15), 48.5
(C8), 41.1 (C3), 37.7 (C7), 23.2 (C13), 13.6 (d, J ) 27.8 Hz, PMe3).
IR: ν(NO) ) 1562 cm-1 (vs), ν(imidate) ) 1650 cm-1 (s). CV:
Ep,a +0.59 V.
(1-(1,3-Dimethoxy-2-azabicyclo[2.2.2]octa-2,5-dien-7-yl)etha-
nol) (22). A sample containing 0.142 g of 20 (1.988 × 10-4 mol)
was dissolved with 0.792 g of CDCl3 and added to preweighed
vial containing 0.068 g (3.396 × 10-4 mol, 2 equiv) of recrystal-
lized m-CPBA. The reaction turned orange-brown instantly and was
allowed to react for 14 h at room temperature. The resulting solution
was evaporated to dryness, and resolvated with 8 mL of CH2Cl2
and 2 mL of saturated NaHCO3. The organic layer was extracted,
while the aqueous layer was rewashed with 4 mL of CH2Cl2. The
organic solution was dried over MgSO4, filtered over a 30 mL fritted
glass disk, and evaporated to a residue. The resulting residue was
taken up in 1 mL of CH2Cl2 and purified via silica gel chroma-
tography (elution with 70% Et2O/hexanes). Overall yield was 31%.
1H NMR (CDCl3, ambient temperature, 300 MHz, δ): 6.52 (1H, d,
J ) 7.8 Hz, H5), 6.37 (1H, dd, J) 6.0, 7.8 Hz, H4), 3.71 (3H, s,
H11), 3.64 (3H, s, H12), 3.36 (3H, m, H3, H9, H9′), 2.10 (1H, m,
H8), 1.83 (1H, ddd, J ) 3.1, 9.6, 12.4 Hz, H7′), 0.62 (1H, ddd, J
) 2.1, 5.2, 12.0 Hz, H7). 13C NMR (CDCl3, ambient temperature,
300 MHz, δ): 171.4 (C2), 133.8 (C5), 130.5 (C4), 98.1 (C6), 66.5
(C9), 54.0 (C11), 52.1 (C12), 43.6 (C8), 38.2 (C3), 27.8 (C7: IR:
ν(imidate) ) 1643 cm-1 (s). HRMS (UIUC) (m/z obsd (%), calcd
(%), error (ppm)): 234.11045 (100), 234.11006 (100), 1.7; 235.10982
(11.8), 235.11329 (0.5), 14.8.
[TpW(NO)(PMe3)(4,5-η2-(1-(1,3-dimethoxy-2-azabicyclo[2.2.2]octa-
2,5-dien-7-yl)ethanol))] (20). A sample containing 0.112 g of 4B
dissolved with 1.561 mL of DME (dried over basic alumina) was
prepared and added to a vial containing 0.012 g of LiAlH4 (9.27 ×
10-5 mol, 2 equiv). The dark, heterogeneous solution was allowed
to stir at room temperature for 3 h. The resulting reaction mixture
was diluted with 8 mL of CH2Cl2 and 1.5 mL of Rochelle’s salt.
The organic layer was extracted, while the aqueous layer was
rewashed with 5 mL of CH2Cl2 and H2O. Again, the organic layer
was extracted, dried with MgSO4, and filtered over a 30 mL fine
fritted glass disk. The resulting filtrate was dried to a residue, taken
up in minimal CH2Cl2, and purified with a SiO2 column (Rf of 0.15,
10% acetone/Et2O). Isolated yield of exo 20B is 74% with a dr
>10:1. 1H NMR (CDCl3, ambient temperature, 300 MHz, δ): 8.81
(1H, d, J ) 1.8 Hz, Tp), 8.12 (1H, d, J ) 1.8 Hz, Tp), 7.70 (1H,
d, J ) 2.4 Hz, Tp), 7.64 (1H, d, J ) 2.3 Hz, Tp), 7.47 (1H, d, J )
2.4 Hz, Tp), 7.25 (1H, d, J ) 2.0 Hz, Tp), 6.27 (1H, t, J ) 2.1, 4.3
Hz, Tp), 6.10 (1H, t, J ) 2.3, 4.4 Hz, Tp), 6.07 (1H, t, J ) 2.3, 4.4
Hz, Tp), 5.38 (1H, s, H13), 3.89 (1H, m, H9), 3.81 (3H, s, H11),
3.68 (3H, s, H12), 2.96 (1H, m, H3), 2.24 (1H, ddd, J ) 2.7, 10.4,
13.0 Hz, H4), 2.07 (3H, m, H7, H7′, H8) 1.82 (1H, dd, J) 2.6,
10.4 Hz, H5), 1.22 (9H, d, J ) 8.2 Hz, PMe3), 1.20 (3H, d, J )

4522 Organometallics, Vol. 27, No. 17, 2008
Kosturko et al.
(1,3-Dimethoxy-2-azabicyclo[2.2.2]octa-2,5-dien-7-yl)metha-
nol)] (23). A sample containing 0.119 g of 21 (1.698 × 10-4 mol)
was dissolved with 0.792 g of CDCl3 and added to preweighed
vial containing 0.049 g (1.698 × 10-4 mol, 1 equiv) of cerric(IV)
ammonium nitrate. The reaction turned orange-brown instantly and
was allowed to react for 14 h at room temperature. The resulting
solution was evaporated to dryness and resolvated with 8 mL of
CH2Cl2 and 2 mL of saturated NaHCO3. The organic layer was
extracted, while the aqueous layer was rewashed with 4 mL of
CH2Cl2. The organic solution was dried over MgSO4, filtered over
a 30 mL fritted glass disk, and evaporated to a residue. The resulting
residue was taken up in 1 mL of CH2Cl2 and purified via silica gel
chromatography (elution with 70% Et2O/hexanes). Overall yield
was 51%, with a dr <2:1. 1H NMR (CDCl3, ambient temperature,
300 MHz, δ): 23 exo 6.52 (1H, d, J ) 7.8 Hz, H5), 6.37 (1H, dd,
J ) 6.0, 7.8 Hz, H4), 3.71 (3H, s, H11), 3.64 (3H, s, H12), 3.36
(3H, m, H3,H9, H9′), 2.10 (1H, m, H8), 1.83 (1H, ddd, J ) 3.1,
ature. The resulting brown, heterogeneous mixture was extracted
with 10 mL of CH2Cl2 and concentrated to a residue. The residue
was redissolved in 1 mL of CH2Cl2 and purified with SiO2
chromatography (Rf 0.71 in 75% Et2O/hexanes). The product is
also UV active at 354 nm. Overall yield was 33%. 1H NMR (CDCl3,
ambient temperature, 300 MHz, δ): 7.88 (1H, d, J ) 8.4 Hz, H5),
7.68 (1H, br, H9), 7.24 (1H, d, J ) 8.4 Hz, H6), 4.09 (3H, s, H12),
3.97 (3H, s, H10), 1.24 (hexanes). 13C NMR (CDCl3, ambient
temperature, 300 MHz, δ): 166.6 (C7 or C9), 165.7 (C7 or C9),
164.6 (C12), 160.7 (C1), 126.4 (C5), 124.2 (C4 and C2), 120.1
(C3), 115.8 (C6), 56.8 (C12), 53.2 (C10), 29.7 (hexanes). IR:
ν(phthalimide) ) 1762 cm-1 (m), ν(CO2Me) ) 1732 cm-1. LRMS
(ESI+): 236.1 (M + 1).
TpW(NO)(PMe3)(4,5-η2-6-Methylpyridine-2-carboxylic acid eth-
yl ester) (28). A solution of TpW(NO)(PMe3)(4,5-η2-2,6-lutidine)16
(49.7 mg, 0.0815 mmol) in DME (6 mL) was added to a test tube
and placed in a cold bath at -10 °C. Ethyl cyanoformate (45.0
mg, 0.454 mmol, 5 equiv) and DME (1 mL) were added to a second
test tube, which was also placed in the cold bath. After 5 min the
contents of the cyanoformate test tube were added to the one
containing TpW(NO)(PMe3)(4,5-η2-2,6-lutidine). The reaction was
then left at -10 °C for 3 days. The reaction mixture was then added
to pentane (50 mL), and the resulting precipitate was collected on
a medium-porosity glass filter and dried in Vacuo to yield 28 (23.4
9.6, 12.4 Hz, H7′), 0.62 (1H, ddd, J ) 2.1, 5.2, 12.1 Hz, H7). 13
C
NMR: 171.4 (C2), 133.8 (C5), 130.5 (C4), 98.1 (C6), 66.5 (C9),
54.0 (C11), 52.1 (C12), 43.6 (C8), 38.2 (C3), 27.8 (C7). IR:
ν(imidate) ) 1643 cm-1 (s).
Methyl-3-acetyl-4-methoxybenzimidate (24). A sample contain-
ing 0.101 g of 14B (1.422 × 10-4 mol, 1 equiv) was added to a
preweighed vial containing 0.072 g (2.845 × 10-4, 2 equiv) of
AgOTf. The two solids were dissolved with 0.960 g of d6-acetone,
and the solution was stirred for 20 h at room temperature. The
resulting brown, heterogeneous mixture was extracted with 10 mL
of CH2Cl2 and concentrated to a residue. The residue was
redissolved in 1 mL of CH2Cl2 and purified with SiO2 chromatog-
raphy (Rf 0.45 in 50% ethyl acetate/Et2O). Isolated yield was 37%.
1H NMR (CDCl3, ambient temperature, 300 MHz, δ): 8.15 (1H, J
) 2.2 Hz, H3), 7.93 (1H, dd, J ) 2.2, 8.8 Hz, H5), 7.02 (1H, d, J
) 8.8 Hz, H6), 3.97 (3H, s, H8), 3.92 (3H, s, H10), 2.63 (3H, s,
H12), 1.28 (hexanes). 13C NMR (CDCl3, ambient temperature, 300
MHz, δ): 197.8 (C11), 172.2 (C7), 164.6 (C1), 135.4 (C5), 132.9
(C3), 129.0 (C4), 116.9 (C2), 113.1 (C6), 60.0 (C8), 56.9 (C10),
1
mg, 0.0350 mmol, 43%) as a yellow powder. H NMR (acetone-
d6, ambient temperature, 300 MHz, δ): 8.24 (1H, d, Tp), 8.02, (1H,
d, Tp), 7.98 (1H, d, Tp), 7.96 (1H, d, Tp), 7.80 (1H, d, Tp), 7.53
(1H, d, Tp), 6.37 (1H, t, Tp), 6.34 (1H, t, Tp), 6.19 (1H, t, Tp),
5.56 (1H, d (J ) 4.3), 3), 4.01 (2H, q (J ) 7.0), 7), 3.48 (1H, ddd
(J ) 4.3, 9.8, 13.7), 4), 2.21 (3H, s, 9), 1.75 (1H, d (J ) 9.8), 5),
1.26 (9H, d (J ) 8.5), PMe3), 1.16 (3H, t (J ) 7.0), 8). 13C NMR
(acetone-d6, ambient temperature, 300 MHz, δ): 144.4 (s, Tp), 143.6
(s, Tp), 140.8 (s, Tp), 137.0 (s,Tp), 136.5 (s, Tp), 136.0 (s, Tp),
106.8 (s, 3), 106.5 (s, Tp), 105.5 (s, Tp), 104.6 (s, Tp), 57.6 (d (J
) 10.9), 4), 57.0 (s, 7), 53.0 (s, 5), 17.3 (s, 9), 14.5 (s, 8), 12.4 (d
(J ) 9.2), PMe3).
31.9 (C11). IR: ν(CO) ) 1677 cm-1, ν(imidate) )1637 cm-1
LRMS: (ESI+) 208.1 (M + 1).
.
Acknowledgment is made to the NSF (CHE-0116492
(UR) and CHE-0320669 (UR)), the NIH (NIGMS: R01-
GM49236 (UVA)), and the PRF (47306-AC1) for financial
support of this work.
3-Acetyl-4-methoxybenzamide (25). 1H NMR (CDCl3, ambient
temperature, 300 MHz, δ): 8.12 (1H, s, H3), 8.11 (1H, dd, J )
2.2, 9.4 Hz, H5), 7.08 (1H, d, J ) 9.4 Hz, H6), 3.99 (3H, s, H8),
2.64 (3H, s, H10), 1.58 (H2O), 1.26 (m, hexanes), 0.88 (m, hexanes).
LRMS (ESI+): found 194.0 (M + 1).
Supporting Information Available: Crystallographic details for
compounds exo-5B, exo-6B, exo-7B, exo-8B, exo-11B, and endo-
12B and spectra for selected compounds. This material is available
free of charge via the Internet at http://pubs.acs.org.
Methyl 5-methoxy-1,3-dioxoisoindoline-4-carboxylate (26). A
sample containing 0.089 g (1.160 × 10-4 mol) of 13B was added
to a preweighed vial containing 0.059 g (2.320 × 10-4 mol, 2
equiv) of AgOTf. The two solids were dissolved with 0.882 g of
d6-acetone, and the solution was stirred for 20 h at room temper-
OM800430P