Tungsten η1-five-membered oxygenated heterocycles derived from tungsten η1-propargyl compounds: Systematic syntheses, structural rearrangement, electrophilic alkylations, and oxidative demetalations

Article abstract of DOI:10.1021/ja9518888

In the presence of BF³?Et₂O, tungsten η¹-propargyl complexes reacted smoothly with aldehydes to give tungsten η¹-2,5-dihydro-3-furyl complexes 1-3. Treatment of 1-3 with Ph₃CBF₄ in CH₂Cl₂ (-60°C, 1 h) delivered tungsten η¹-3-furylidene complexes 4-6 which underwent skeletal rearrangement to η¹-furylidene 13-15 isomers when warmed to 5°C. Treatment of 4-6 with Et₃N at -60°C produced tungsten η¹-3-furyl complexes 7-9 which were isomerized to η¹-2-furyl isomers 10-12 by a strong Bronsted acid. Protonation of 10-12 by CF₃CO₂H yielded η¹-2-furylidene complexes 13-15. The two exceptional isomerizations were examined by in situ ¹H NMR studies. Further oxidation of η¹-2-furyl compounds 10-12 with m-chloroperbenzoic acid gave tungsten η¹-Δ³-butenolides 16-18. Tungsten η¹-3-furyl complexes 7 and 9 underwent alkylation with trimethoxymethane and aldehydes at -60°C to yield η¹-3-furylidene cationic precipitates that were subsequently reduced with NaBH₃CN to yield complex η¹-2,5-dihydro-3-furyl compounds in good diastereoselectivity; the stereochemical courses were distinct for 7 and 9. Tungsten η¹-2,5-dihydro-3-furyl, η¹-2-furyl, η¹-3-furyl, and η¹-Δ³-butenolide complexes were decomplexed with appropriate reagents to liberate 2,5-dihydrofurans, furans, and Δ³- and Δ²-butenolides in reasonable yields.

Full text of DOI:10.1021/ja9518888

530
J. Am. Chem. Soc. 1996, 118, 530-540
Tungsten η1-Five-Membered Oxygenated Heterocycles Derived
from Tungsten η1-Propargyl Compounds: Systematic
Syntheses, Structural Rearrangement, Electrophilic Alkylations,
and Oxidative Demetalations
Hsin-Guo Shu,† Lin-Hung Shiu,† Shin-Hwan Wang,† Sue-Lein Wang,†
Gene-Hsian Lee,‡ Shie-Ming Peng,‡ and Rai-Shung Liu*,†
Contribution from the Department of Chemistry, National Tsing-Hua UniVersity,
Hsinchu 30043, Taiwan, Republic of China, and Department of Chemistry,
National Taiwan UniVersity, Taipei 30002, Taipei, Republic of China
ReceiVed June 9, 1995X
Abstract: In the presence of BF3‚Et2O, tungsten η1-propargyl complexes reacted smoothly with aldehydes to give
tungsten η1-2,5-dihydro-3-furyl complexes 1-3. Treatment of 1-3 with Ph3CBF4 in CH2Cl2 (-60 °C, 1 h) delivered
tungsten η1-3-furylidene complexes 4-6 which underwent skeletal rearrangement to η1-2-furylidene 13-15 isomers
when warmed to 5 °C. Treatment of 4-6 with Et3N at -60 °C produced tungsten η1-3-furyl complexes 7-9 which
were isomerized to η1-2-furyl isomers 10-12 by a strong Bronsted acid. Protonation of 10-12 by CF3CO2H yielded
η1-2-furylidene complexes 13-15. The two exceptional isomerizations were examined by in situ 1H NMR studies.
Further oxidation of η1-2-furyl compounds 10-12 with m-chloroperbenzoic acid gave tungsten η1-∆3-butenolides
16-18. Tungsten η1-3-furyl complexes 7 and 9 underwent alkylation with trimethoxymethane and aldehydes at
-60 °C to yield η1-3-furylidene cationic precipitates that were subsequently reduced with NaBH3CN to yield complex
η1-2,5-dihydro-3-furyl compounds in good diastereoselectivity; the stereochemical courses were distinct for 7 and 9.
Tungsten η1-2,5-dihydro-3-furyl, η1-2-furyl, η1-3-furyl, and η1-∆3-butenolide complexes were decomplexed with
appropriate reagents to liberate 2,5-dihydrofurans, furans, and ∆3- and ∆2-butenolides in reasonable yields.
Introduction
Scheme 1
Condensation of metal η1-propargyl and η1-allenyl com-
plexes1-3 with aldehydes and ketones promoted by Lewis acid
is an important reaction in organic synthesis. In this reaction,
there often exits an equilibrium between η1-propargyl and η1-
allenyl species (typically two alcohols). The selectivity problem
can be circumvented by selecting metals of covalent type (M
) R3Si, R3Sn, R2B, CpTi(OR)2) where R1 and R2 are of suitable
sizes.1,2 Overwhelmingly, the products are either homopro-
† National Tsing-Hua University.
‡ National Taiwan University.
X Abstract published in AdVance ACS Abstracts, December 15, 1995.
(1) For the application of metal allenyl and propargyl compounds in
organic synthesis, see the review paper: (a) Yamamoto, H. In Compre-
hensiVe Organic Synthesis: Addition to C-X p bonds Part II; Trost, B. M.,
Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 2, Chapter 1.3, p
81. (b) Fleming, I. In ComprehensiVe Organic Synthesis: Addition to C-X
p bonds, Part I; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford,
1991; Vol. 2, Chapter 2.2, p 575. (c) Panek, J. S. In ComprehensiVe Organic
Synthesis: Addition to C-X p bonds Part II; Trost, B. M., Fleming, I., Eds.;
Pergamon Press: Oxford, 1991; Chapter 2.5, p 580. (d) Epsztein, R. In
ComprehensiVe Carbanion Chemistry; Buncel, E., Durst, T., Eds.; Elsevi-
er: Amsterdam, 1984; Part B, p 107.
(2) For main-group metal allenyl and propargyl compounds, see repre-
sentative examples: (a) Seyferth, D.; Son, D. Y.; Shah, S. Organometallics
1994, 13, 2105. (b) Brown, H. C.; Khire, U. R.; Racherla, U. S. Tetrahedron
Lett. 1993, 34, 15. (c) Brown, H. C.; Khire, U. R.; Narla, G.; Racherla, U.
S. J. Org. Chem. 1995, 60, 544. (d) Danheiser, R. L.; Carini, D. J. J. Org.
Chem. 1980, 45, 3925. (e) Boaretto, A.; Marton, D.; Tagliavini, G. J.
Organomet. Chem. 1985, 297, 149. (f) Marshall J. A.; Wang, X.-J. J. Org.
Chem. 1991, 56, 3212. (g) Marshall, J. A.; Wang, X. J. J. Org. Chem. 1991,
56, 6264.
pargyl or allenyl alcohols (Scheme 1, eq 1). Effective annulation
of these compounds with aldehydes to form a five-membered
heterocycle is rare and known only for (tert-butyldimethylsilyl)-
allene4 that furnishes 2,3-dihydrofurans in good yields (eq 2).
Lewis acid-promoted cyclizations of propargyltrimethylsilanes
with ketals or acetals are reported4d to yield 2,5-dihydrofurans
in 20-35% yields.
Five-membered oxygenated heterocycles including dihydro-
furans, furans, and butenolides are important structural units in
(4) (a) Danheiser, R. L.; Fink, D. M. Tetrahedron Lett. 1985, 26, 2513.
(b) Danheiser, R. L.; Kwasigroch, C. A.; Tsai, Y. M. J. Am. Chem. Soc.
1985, 107, 7233. (c) Danheiser, R. L.; Becker, D. A. Heterocycles 1987,
25, 277. (d) Pornet, J.; Miginiac, L.; Jaworski, K.; Randrianoelina, B.
Organometallics 1985, 4, 333.
(5) (a) Donnelly, D. M. X.; Meegan, M. J. In ComprehensiVe Heterocyclic
Chemistry; Katritzky, A. R., Reese, C. W., Eds.; Pergamon Press: Oxford,
1984; Vol. 4, Part 3, p 657. (b) Bolvin, T. L. B. Tetrahedron 1987, 43,
3309. (c) Katritzky, A. R. AdV. Heterocycl. Chem. 1982, 30, 167. (d)
Lipshutz, B. H. Chem. ReV. 1986, 86, 795. (e) Padwa, A.; Murphree, S. S.
Org. Prep. Proced. 1991, 23, 545.
(3) For chemistry of transition-metal propargyl and allenyl compounds,
see representative examples: (a) Bell, P. B.; Wojcicki, A. Inorg. Chem.
1981, 20, 1585. (b) Raghu, S.; Rosenblum, M. J. Am. Chem. Soc. 1973,
95, 3060. (c) Pu, J.; Peng, T. S.; Arif, A. M.; Gladysz, J. A. Organometallics
1992, 11, 3232. (d) Blosser, P. W.; Shimpff, D. G.; Gallucci, J. C.; Wojcicki,
A. Organometallics 1993, 12, 1393. (e) Benaim, J.; Merour, J.-Y.; Roustan,
J. L. C. R. Acad. Sci. Paris, Ser. C 1971, 272, 789.
0002-7863/96/1518-0530$12.00/0 © 1996 American Chemical Society

Tungsten η1-FiVe-Membered Oxygenated Heterocycles
J. Am. Chem. Soc., Vol. 118, No. 3, 1996 531
Scheme 2a
a
W ) CpW(CO)3. X ) BF4.
organic molecules.5,6 Numerous papers on metal-η1-propargyl
and η1-allenyl complexes are reported, yet none aim at the
systematic synthesis of these oxygenated heterocycles. We
hereby report7 an effective annulation of tungsten η1-propargyl
compounds with aldehydes to yield η1-2,5-dihydro-3-furyl
compounds that are subsequently transformed into η1-hetero-
cycles of various classes including η1-2-furyl, η1-3-furyl, η1-
2-furylidene, η1-3-furylidene, η1-∆3-butenolide and complex η1-
2,5-dihydro-3-furyl complexes. During the syntheses, we
enconter some unusual organometallic reactions of which the
mechanism will be discussed in details.
not operative because the corresponding intermediate is envis-
aged to be an unstable η2-allene cation of a five-membered
ring.11 Deprotonation of 4-6 with Et3N (2-3 equiv) in cold
CH2Cl2 (-60 °C, 0.5 h) afforded η1-3-furyl complexes 7-912,13
quantitatively (>95% yield).
Scheme 2 shows further syntheses of tungsten η1-2-furyl and
η1-2-furylidene compounds. In the presence of catalysts (ca. 5
mol %), 4-toluenesulfonic acid, or CF3CO2H, compounds 7-9
underwent a novel isomerization to η1-2-furyl isomers 10-12
at 23 °C and completely within 1 h. Compounds 7-9 and their
η1-2-furyl isomers 10-12 were easily distinguished by their 1H
and 13C NMR spectra in CDCl3. For 10-12, the loss of
aromaticity is achieved with a protonation reaction14 to give
Fischer-type carbenes. Slow addition of excess CF3CO2H (ca.
15 equiv) to 10-12 in anhydrous diethyl ether at 0 °C produced
red precipitates of η1-2-furylidenes 13-15; the yields exceeded
60% upon addition of excess hexane. Measurement of NMR
spectra of 13-15 was best performed on treatment of 10-12
with excess CF3CO2H (ca. 15 equiv) in an NMR tube (yields
> 96%, CD2Cl2, 0 °C). The reason is that these salts easily
lose one proton to regenerate η1-2-furyl compounds in the
absence of acid. The 2-furylidene structure of 10-12 is
supported by 1H and 13C NMR data; the WdCR carbon signals
Results
Syntheses of Tungsten η1-3-Furylidene, η1-3-Furyl, η1-2-
Furyl, and η1-2-Furylidene Compounds. As shown in
Scheme 2, treatment of CpW(CO)3(η1-3-R′-propargyl) (R′ )
Me, Ph) with aldehydes (2-3 equiv) in the presence of BF3‚
Et2O produced η1-2,5-dihydro-3-furyl complexes 1-3 in good
yields (>90%); the reaction mechanism followed a typical [3
+ 2] cyclization pathway8,9 involving an allene cationic
intermediate. Organic 2,3- and 2,5-dihydrofurans can be
oxidized to furans by 2,3-dichloro-5,6-dicyano-1,4-benzoqui-
none (DDQ);10 the reaction intermediate is proposed to be an
unstable 2-hydrofurylium cation. We have discovered that Ph3-
CBF4 effects the oxidation of 1-3 satisfactorily, and the
resulting cationic intermediates can be isolated and fully
characterized.
Treatment of 1-3 with Ph3CBF4 (0.98-1.00 equiv) in cold
CH2Cl2 (-60 °C, 1 h) followed by a slow addition of excess
cold pentane produced orange precipitates of η1-3-furylidenes
4-6; the yields exceeded 85%. Diagnostic for the η1-3-
furylidene structure are the 1H and 13C NMR spectra (-40 °C,
CD2Cl2) that show the absence of CδH hydrogen. In this
oxidation, hydride abstraction of the CRH2 protons of 1-3 is
appear at δ 270-280 (JWC ) 110-120 Hz). In the case of
R
13, the magnitude of the coupling constant JHCHMe ) 2.9 Hz
2
indicates that the site of protonation is the Cδ carbon.
NMR Studies on Isomerizations of Tungsten η1-3-Fu-
rylidene and Tungsten η1-2-Furyl Compounds. The tungsten
alkylidene cation15 CpW(CO)3(dCH2)+ decomposes quickly to
ethylene at 23 °C. On the contrary, η1-3-furylidene cations 4-6
(11) Stable metal η2-allene compounds of six- and seven-membered rings
are reported; see the representative examples: (a) Oons, S. M.; Jones, W.
M. Organometallics 1988, 7, 2172. (b) Yin, J.; Abboud, K. A.; Jones, W.
A. J. Am. Chem. Soc. 1993, 115, 3810.
(12) For transition-metal η1-furyl compounds, see: (a) Jones, W. D.;
Dong, L.; Myers, A. W. Organometallics 1995, 14, 855. (b) Selnau, H. E.;
Merola, J. S. Organometallics 1993, 12, 1583. (c) Selnau, H. E.; Merola,
J. S. Organometallics 1993, 12, 3800. (d) Pannell, K. H.; Cea-Olivares,
R.; Toscano, R. A.; Kapoor, R. N. Organometallics 1987, 6, 1821.
(13) Only one example of transition-metal η1-3-furyl compounds was
reported; see ref 12a.
(6) For metal-mediated synthesis of furans and butenolides, see repre-
sentative examples: (a) Davies, Hwu M. L.; Romines, K. R. Tetrahedron
1988, 44, 3343. (b) Padwa, A.; Kinder, F. R. J. Org. Chem. 1993, 58, 21.
(c) Wulff, W. D.; Gilberstson, S. R.; Springer, J. P. J. Am. Chem. Soc.
1986, 108, 520. (d) Danheiser, R. L.; Stoner, E. J.; Koyama, H.; Yamashita,
D. S.; Klade, C. A. J. Am. Chem. Soc. 1989, 111, 4407.
(7) Preliminary results of this paper: Wang, S.-H.; Shiu, L.-H.; Shu,
H.-G.; Liao, Y.-L.; Wang, S.-L.; Lee, G.-H.; Peng, S.-M.; Liu, R.-S. J.
Am. Chem. Soc. 1994, 116, 5967.
(8) (a) Welker, M. E. Chem. ReV. 1992, 92, 97. (b) Rosenblum, M.;
Watkins, J. C. J. Am. Chem. Soc. 1990, 112, 6316.
(9) Jiang, S.; Turros, E. Organometallics 1993, 12, 4280.
(10) Anderson, J. C.; Lindsay, D. G.; Reese, C. B. Tetrahedron 1964,
2091.
(14) For transition-metal η1-pyrrolyl and η1-thienyl compounds, see: (a)
Johnson, T. D.; Arif, A. M.; Gladysz, J. A. Organometallics 1993, 12, 4728.
(b) Robertson, M. J.; White, C. J.; Angelici, R. J. J. Am. Chem. Soc. 1994,
116, 5190. (c) Dong, L.; Duckett, S. B.; Ohman, K. F.; Jones, W. D. J.
Am. Chem. Soc. 1992, 114, 151. (d) Ng, M. M. P.; Roper, W. R.; Wright,
L. J. Organometallics 1994, 13, 2563. (e) Erker, G.; Petrenz, R.; Kruger,
C.; Lutz, F.; Weiss, A.; Werner, S. Organometallics 1992, 11, 1646.
(15) Kegley, S. E.; Brookhart, M.; Husk, G. R. Organometallics 1982,
1, 760.

532 J. Am. Chem. Soc., Vol. 118, No. 3, 1996
Shu et al.
Scheme 3a
Scheme 5
a
W ) CpW(CO)3. X ) BF4.
Scheme 4a
Scheme 6a
a
W ) CpW(CO)3. X ) CF3CO2.
undergo an irreversible transformation to their η1-2-furylidene
isomers 13-15 above 0 °C as shown in Scheme 2. When an
NMR sample of 6 (BF4 salt, CD2Cl2, -40 °C) was immediately
warmed to 5 °C, the 1H NMR spectra of solution species were
recorded for a period of 20 min, 45 min, and 4 h. These
spectra16 clearly indicated that compound 6 underwent a steady
isomerization to its 2-furylidene isomer 15 at 5 °C without
formation of any detectable intermediate. Only NMR signals
of 15 were observed after a long period (5 °C, t ) 4 h); the
yield was quantitative (>96%) based on the internal CD2Cl2
standard.
W ) CpW(CO)3. X- ) Sn(OMe)Cl4-. (i) CH(OMe)3/SnCl4, -60
°C; (ii) Et3N, -60 °C; (iii) NaBH4CN, -60 °C; (vi) RCHO/BF3‚Et2O,
-60 °C.
a
To assist understanding this structural rearrangement, we
prepared a deuterated sample of 6 in which one of the CRH2
protons was completely deuterated. Measurements of the rate
constants of isomerization for 6 and its deuterated sample showd
Câ-H proton of 12 gradually decreased until a 50% proton
content (a statistical distribution) was attained. A decreasing
proton content here is attributed to an exchange between D+
and the Câ-H proton of 12 that is slower than η1-3-furyl
isomerization.
a kinetic isotopic effect, kCH/kCD ) 6.0 (kCH ) 2.6 × 10-4 s-1
,
kCD ) 4.3 × 10-5 s-1, 23 °C). As depicted in Scheme 3, 4 h
after isomerization of the deuterated sample 6, a mixture of
deuterated species including 6, η1-2-furylidene 15, and η1-2-
furyl complex 12 was obtained with the molar ratio 1.45:1.25:
1, respectively; in this case, the proton NMR intensity ratio of
CâH, CδH, and CHH′Me of 15 was 0.40:0.65:1, respectively.
Here, the CδH/CâH ) 1.60 value of 15 is near an equilibrium
ratio (CδH/CâH ) 1.50) determined by a separate NMR
experiment.17
m-CPBA Oxidation of η1-2-Furyl Complexes. Scheme 5
shows the oxidation of 10-12 with m-chloroperbenzoic acid
(m-CPBA, 1.2 equiv) in hexane (5 °C, 1 h) over a HOAc/NaOAc
mixture, yielding the products 16-18 in 65-70% yields.
Spectral data reveal that 16-18 are related to 10-12 by
incorporation of an oxygen atom to form a η1-lactone species
(ν(CO) 1775-1765 cm-1). The ORTEP drawing19 of 18
confirms the η1-∆3-butenolide structure with a 1,2-shift of CpW-
(CO)3 to the Câ carbon. The oxidation mechanism here is
straightforward;20 m-CPBA preferentially oxidizes the furyl
WCRdCâ double bond due to the electron-donating ability of
the CpW(CO)3 fragment. Rearrangement of the epoxide
intermediate is expected to give the η1-∆3-butenolide compound.
1,4-Addition Reactions on η1-3-Furyl Compounds. Shown
in Scheme 6 is the reaction between 9 and a mixture of HC-
(OMe)3 (2.0 equiv) and SnCl4 (1.0 equiv) in cold CH2Cl2 (-60
°C), yielding a precipitate (I) that upon deprotonation with Et3N
gave tetrasubstituted η1-furyl complex 19 in good yield (83%);
one important feature here is the isolation of an η1-3-furylidene
precipitate (I). Reduction of this salt (I) with NaBH3CN at -60
°C led to hydride addition rather than deprotonation, yielding
η1-cis-2,5-dihydro-3-furyl complex 20 as one single diastereo-
mer in 86% yield; the ORTEP drawing of 20 appears in Figure
1a.
We further examined the isomerization of η1-3-furyl complex
9 with CF3CO2D by low-temperature 1H NMR spectra.18 The
results are briefly summarized in Scheme 4. Shortly after 9
was treated with CF3CO2D (1.0 equiv, 0.055 M) in CD2Cl2 at
1
-40 °C (t ) 3 min), the H NMR spectra revealed that η1-2-
furyl complex 12 was the dominant solution species (ca. 78%)
in addition to unreacted 9 (ca. 12%), η1-2-furylidene 15 (ca.
11%), and a trace of 3-furylidene 6 (<1%). On the basis of
the NMR integral, the CâH of newly generated 12 has a proton
content exceeding 95%; the complex 15 here is likely produced
from further protonation (D+) of 12.17 When the same NMR
sample was warmed to 23 °C for 4 h, the NMR signal of the
(16) Variable-temperature spectra showing the isomerization of 6 to 15
were prepared as supporting information.
(17) When a NMR sample of η1-2-furyl complex 12 was treated with
CF3CO2D (1.0 equiv, 0.22 M) in CD2Cl2 at -40 °C, after a brief period (t
) 10 min), the solution species consisted of 12 (86%) and η1-2-furylidene
15 (14%); in this case the CâH of 12 retained one unit of proton intensity,
whereas the CâH and CδH positions of 15 were scrambled with deuterium
with CδH/CâH ) 1.50 (CδH + CâH ) 1 H) like those in Scheme 3. After
the temperature was raised to 23 °C for 24 h, the proton content of CâH of
12 was decreased to 50%, whereas the proton (deuterium) distribution of
15 remained unaltered; a new equilibrium, [12]/[15] ) 30, was attained.
(18) 1H NMR spectra monitoring the isomerization of 9 with CF3CO2D
(1.0 equiv) in CD2Cl2 were prepared was supporting information.
Alkylation of 9 with a mixture of RCHO/BF3‚Et2O (R ) Me,
iBu, iPr) in cold toluene (-40 °C) likewise led to a 3-furylidene
(19) The ORTEP drawing and related structural parameters of compound
21 were prepared as supporting information.
(20) (a) Kuwajima, I.; Urabe, H. Tetrahedron Lett. 1981, 22, 5191. (b)
Takeda, K.; Minato, H.; Ishikawa, M.; Miyawaki, M. Tetrahedron 1964,
20, 2655.

Tungsten η1-FiVe-Membered Oxygenated Heterocycles
J. Am. Chem. Soc., Vol. 118, No. 3, 1996 533
five-membered oxygenated heterocycles of types that can be
produced from tungsten η1-propargyl complexes. Treatment of
2 and 3 with (NH4)2Ce(NO3)6 in CH2Cl2/MeOH mixture under
flowing CO (1 atm) produced only one organic component, 29
and 30, in 60-63% yields. Ce(IV) oxidation of 11 and 12
generated 31 and 32 in 54-59% yields, analyzed as ∆2-
butenolide21 according to NMR and mass spectral data. The
generation of 31 and 32 from 11 and 12 involves a four-electron
oxidation; it is not difficult to deduce the mechanism.22,23 Under
nitrogen, demetalation of 11 and 12 by I2 in CH2Cl2/CH3OH
afforded 33 and 34 in 60-63% yields in addition to byproducts
31 and 32 (8-10% yields). η1-∆3-Butenolides 17 and 18 were
demetalated with Me3NO (4.0 equiv, 30 °C, 2 h) in CH2Cl2 to
give 35 and 36 in 53-58% yields together with η3-∆-butenolide
compounds 37 and 38 in small yields (20-21%). The molecular
structure of 38 was determined by X-ray diffraction study; an
ORTEP drawing appears in Figure 2b. Ce(IV) oxidation of 21a
in CH2Cl2 under flowing CO led to an intramolecular lacton-
ization to give bicyclic lactone 39 as a single diastereomer
(40%). Ce(IV) oxidation of 28b under the same conditions gave
40 in 46% yield.
Figure 1. (a) ORTEP drawing of compound 20. Selected bond lengths
(Å): W-C(4) ) 2.264(4), C(4)-C(5) ) 1.327(5), C(5)-C(12) )
1.512(5), C(12)-O(4) ) 1.430(5), C(15)-O(4) ) 1.440(5), and C(4)-
C(15) ) 1.534(5). (b) ORTEP drawing of compound 21a. Selected
bond lengths (Å): W-C(4) ) 2.259(6), C(4)-C(7) ) 1.329(9), C(4)-
C(5) ) 1.530(7), C(5)-O(4) ) 1.438(8), and C(6)-O(4) ) 1.423(7).
precipitate (II) that was subsequently reduced with NaBH3CN
(3.0 equiv) to yield 2,5-dihydro-3-furyl complexes 21-23.
Although this reaction simultaneously created three asymmetric
carbon centers, the reactions proceeded diastereoselectively such
that only one diastereomer was found for 22 and 23, whereas
two diastereomers (a/b ) 2.5:1) were isolated for 21. The
stereochemistry of the dominant isomer was determined to be
the cis configuration at the ring structure and the syn configu-
ration at the CH(OH) and CR carbons according to an X-ray
diffraction study of 21a; an ORTEP drawing of 21a appears in
Figure 1b. The minor isomer 21b also adopts a cis configuration
according to 2D NOESY correlation spectra; hence, we assign
an anti-cis structure to 21b.
The stereochemical chemistry in 1,4-addition reactions of
compound 7 is summarized in Scheme 7; the outcome is distinct
from those observed for 9. Treatment of 7 with CH(OMe)3/
SnCl4 in cold CH2Cl2 at -60 °C followed by deprotonation
with Et3N gave 24 in 75% yield. Reduction of the same salts
(III) with NaBH3CN delivered 25 as a single isomer in 88%,
which has a trans configuration according to proton NOE
difference spectra. With the same procedure, the reaction
between 7 and RCHO/BF3‚Et2O (R ) Me, iBu) followed by
NaBH3CN reduction afforded 26 and 27, respectively. Three
diastereomers were formed for each of 26 and 27, separable on
a silica gel column; the respective isolated yields are depicted
in Scheme 7. The crystal quality of major diastereomers 26c
and 27c was poor; hence, the two compounds were converted
to their acetyl derivatives 28a,b in 86-88% yields. The ORTEP
drawing of 28a in Figure 2a reveals that the molecule adopts
an anti-trans structure.
Dicussion
Proposed Mechanism for Isomerization of η1-3-Fu-
rylidene. Isomerization of the two furylidene cations is
unprecedented in transition-metal carbene chemistry;24 it in-
volves a switch of three atom positions. In this isomerization,
a large value of kinetic isotopic effect (kCH/kCD ) 6.0) for the
50% deuterated η1-3-furylidene sample 6 implies that a hydrogen
shift is important for the reaction mechanism. The oxonium
resonance of η1-3-furylidene represented by A in Scheme 8
resembles a metalated cyclopentadiene group in which a 1,2-
shift of hydrogen or metal is known to be feasible.25 We
propose a mechanism that the isomerization is initiated with a
1,2-shift of CRH2 hydrogen of A to give B that subsequently
undergoes a 1,2-tungsten shift to bring the CpW(CO)3 fragment
away from the CγR′ substituent, yielding η1-2-furyl oxonium
species C. For the state B, a 1,2-hydrogen shift of CâH to the
Cγ carbon is considered less important because the forming
intermediate suffers steric hindrance between R′ and neighboring
CpW(CO)3. Formation of η1-2-furylidene can be accomplished
by a consecutive 1,2-hydrogen shift of C via intermediates D
and E. All these elementary processes are reversible, but
thermodynamic equilibrium favors η1-2-furylidene complex.
According to this process, the CâD/CδD content ratio of η1-2-
furylidene 15 derived from 50% deuterated η1-3-furylidene 6
is expected to be near the equilibrium value 1.50 because of
Further structural assignment of the other two minor diaster-
(21) Binger, P.; Weintz, H. J. Chem. Ber. 1984, 117, 654.
(22) We propose that η1-2-furyl complexes 11 and 12 undergo one-
electron oxidation to give a cationic radical (I) that reacts with MeOH to
give a radical species (J).25,26 Further oxidation of J by Ce(IV) oxidation
produces 2-furylidene species K that subsequently loses two electrons to
the precursor L of ∆2-butenolide.
eomers relies on comparison of proton NMR spectra.
A
common feature of the two minor isomers 27a,b is the CH(OH)
proton that appears as a dd pattern (d ) doublet; JHCHH′ ) 10.5
Hz, JHC H ) 4.5 Hz, JHCHH′ ) 0 Hz), in contrast with a doublet
R
pattern (JHCHH′ ) 10.7 Hz, JHC H ) JHCHH′ ) 0 Hz) for the
R
corresponding proton of the major isomer 27c. We therefore
conclude that 27a,b have identical syn configurations for the
two asymmetric CRH and RCH(OH) carbons. In 2D NOESY
correlation spectra, the CRH and CδH protons of 27a show a
pronounced NOE relationship, whereas the CRH proton of 27b
shows no NOE correlation with the CδH proton but with the
methyl group of the isopropyl substituent. These data indicate
that 27a has a cis configuration whereas 27b has a trans
configuration.
(23) (a) Weinberg, N. L.; Weinberg, H. R. Chem. ReV. 1968, 68, 449.
(b) Elming, N. AdV. Org. Chem. 1960, 2, 67.
(24) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles
and Application of Organotransition Metal Chemistry; University Science
Books: Mill Valley, CA, 1987; Chapter 16, p 784.
Applications to Five-Membered Oxygenated Hetrocycles.
It is imperative to demetalate the η1-heterocycles chemoselec-
tively to substantiate organic syntheses. Chart 1 summarizes
(25) Mann, B. E. In CompresensiVe Organometallics Chemistry; Wilk-
enson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon Press: Oxford,
1982; Vol. 3, Chapter 20, p 173.

534 J. Am. Chem. Soc., Vol. 118, No. 3, 1996
Shu et al.
Scheme 7a
W ) CpW(CO)3. X- ) Sn(OMe)Cl4-. (i) CH(OMe)3/SnCl4, -60 °C; (ii) Et3N, -60 °C; (iii) NaBH4CN, -60 °C; (iv) RCHO/BF3‚Et2O, -60
°C; (v) Ac2O/DMAP, 0 °C.
a
Chart 1. Yields and Products for Oxidative Demetalation of
η1-Heterocyclesa
Figure 2. (a) ORTEP drawing of compound 28a. Selected bond lengths
(Å): W-C(4) ) 2.289(5), C(4)-C(7) ) 1.516(7), C(7)-O(4) )1.447-
(6), C(6)-O(4) ) 1.427(6), C(5)-C(6) ) 1.517(7), and C(4)-C(5) )
1.317(7). (b) ORTEP drawing of compound 38. Selected bond distances
(Å): W-C(3) ) 2.286(6), W-C(4) ) 2.239(5), W-C(5) ) 2.292(6),
C(3)-C(4) ) 1.443(8), C(4)-C(5) ) 1.463(8), C(5)-O(3) ) 1.454-
(7), C(8)-O(3) ) 1.368(7), and C(8)-O(4) ) 1.216(7).
multiple reversible steps, consistent with our isotopic result CâD/
CδD ) 1.60.
Proposed Mechanism for Isomerization of η1-3-Furyl
Complex. Several η1-3-metalated aromatic heterocycles are
known,12a,13,14b most of which have two methyl groups at the
heterocyclic 2,5-carbons. Treatment of these compounds with
strong Bronsted acid cleaves the metal-carbon σ bond.
Isomerization of η1-3-furyl compounds to their η1-2-furyl
isomers deserves special attention because the mechanism is
atypical. In the isomerization of 9 with CF3CO2D, the NMR
results in Scheme 4 reveal two important features. (i) The Câ-H
proton of newly generated η1-2-furyl complex 12 is virtually
all protonated rather deuterated, indicative of a 1,2-mutual switch
of CR-H and CpW(CO)3 positions during the isomerization
reaction. (ii) Only a trace of η1-3-furylidene 6 was detected
even though it was shown to be a stable species at this
temperature and in the presence of excess CF3CO2H (4-5
equiv). The latter information indicates that the isomerization
does not proceed Via the expected 3-furylidene f 2-furylidene
pathway. We propose a plausible mechanism which involves
a ring-opening process through protonation at the furan oxygen
as depicted in Scheme 9; the driving force for this process is
the formation of a tungsten η2-alkyne cationic species (F) that
a W ) CpW(CO)3, W′ ) CpW(CO)2. (i) (NH4)2Ce(NO3)6 (3.0
equiv), CO (1 atm), MeOH/CH2Cl2, -78 f 23 °C, 3 h; (ii)
(NH4)2Ce(NO3)6 (5.0 equiv), MeOH/CH2Cl2, -78 f 23 °C, CO (1
atm); (iii) I2 (2.0 equiv), MeOH/CH2Cl2, -78 f 23 °C, 3 h; (iv) Me3NO
(4.0 equiv), H2O (2.0 equiv), 30 °C, 4 h; (v) (NH4)2Ce(NO3)6 (3.0
equiv), CO (1 atm), CH2Cl2, -78 f 23 °C.
Scheme 8
subsequently undergoes a known facile η2-alkyne f η1-allene
rearrangement26,27 to yield G. Further attack of the enol group
of G on the allenylidene WdCRdC carbon results in ring
closure to yield η1-2-furyl isomer as the primary product.29b,c
(26) (a) Bruce, M. I. Chem. ReV. 1991, 91, 197. (b) Pombeiro, A. J. L.;
Richards, R. L. Coord. Chem. ReV. 1990, 104, 13. (c) Bullock, R. M. J.
Chem. Soc., Chem. Commun. 1989, 165. (d) Werner, H. Angew. Chem.,
Int. Ed. Engl. 1990, 29, 1077.

Tungsten η1-FiVe-Membered Oxygenated Heterocycles
J. Am. Chem. Soc., Vol. 118, No. 3, 1996 535
Scheme 9a
isopropyl groups. While in I and II, the bulky phenyl group is
envisaged to be quite nonplanar with the furylidene ring,
particularly as W-CR becomes a double bond to enhance steric
hindrance between CpW(CO)3 and the phenyl group. In this
manner, limited space is available for the hydride addition from
the same side as the CR-alkylated substituent; this kinetic effect
favors the cis product.
Scheme 10 shows models to rationalize the stereochemistry
in the aldehyde reaction.1ab,32-36 In an open transition-state
mechanism,1a,b,32-36 antiperiplanar (V) and synclinal (VI) states
are considered the most important among six possible confor-
mations because of less steric hindrance. Syn selectivity of 9
represents a more common case as for most allylsilanes32,33 and
allylstannanes32,33 including 3-alkoxyallyl compounds;34 this
stereoselection commonly arises from antiperiplanar conforma-
tion with a staggered conformation between the CdC and CdO
double bonds. The anti selectivity of 7 is exceptional because
few such cases36 are reported in an open transition-state
mechanism. The fact that 7 behaves distinctly from 9 leads us
to consider the roles of Cδ substituents of the two η1-3-furyl
complexes, i.e., ethyl versus isopropyl; the Cγ substituents are
too remote from the reaction center. In the case of 7, the
isopropyl group is considerably larger than the ethyl substituent,
in this case synclinal conformation VI becomes important to
yield anti stereoselection because antiperiplanar V suffers steric
interactions between the coordinated BF3 and isopropyl groups.
a
W ) CpW(CO)3.
One major concern with this mechanism is a possible enol
G-ketone H tautomerization. Very likely, this enolization rate
is slower than the intramolecular annulation of G because the
former requires protonation at the enol CγR carbon of G to
break its stable conjugated structure, yielding ketone species
H. Acid-catalyzed ketone-enol tautomerization is known to
be a slow step according to halogenation of ketones.28
The thermodynamic equilibriums in the two isomerizations
strongly favor η1-2-metalated species. Electronic effects are
certainly important because the furan oxygen of 2-metalated
isomers can stabilize the electron-deficient WCR carbon center.29
We believe that a steric effect is equally important because
3-metalated isomers suffer additional steric hindrance between
the neighboring CpW(CO)3 and Cγ-R substituents.
Conclusions
Stereochemical Course in 1,4-Addition Reactions on η1-
3-Furyl Compounds. No electrophilic alkylations have been
reported for any transition-metal η1-aromatic heterocycle includ-
ing furyl,11 thienyl,14 or pyrrolyl14 compounds. η1-3-Furyl
complexes in our system are capable of undergoing 1,4-addition
reactions, Via electrophilic alkylation and sequential reduction;
the intermediate involves an alkylated η1-3-furylidene cation.
This process represents a breakthrough in organic furan
chemistry because furans only undergo electrophilic substitu-
tion.30,31 The results in Schemes 6 and 7 clearly show the
different stereochemical outcomes for addition of aldehydes to
the two η1-3-furyl compounds 7 and 9, and sequential NaBH3-
CN reduction of the two furylidene intermediates proceeds in
different stereochemistry. We first rationalize the issue in
hydride addition. For intermediates III and IV derived from
7, the methyl group is too small to be a stereotemplate; NaBH3-
CN addition at the Cδ carbons occurs equally from the same or
other side with the CR-alkylated substituent. Therefore, the
stereoselectivity in this case favors trans products because the
cis form suffers the steric hindrance between CH(OBF3)R and
In this work, we elaborated tungsten η1-propargyl compounds
for systematic syntheses of tungsten η1-oxygenated heterocycles
including 2,5-dihydrofuryl, η1-2-furyl, η1-3-furyl, η1-2-fu-
rylidene, η1-3-furylidene, and η1-∆3-butenolide complexes.
During syntheses of these compounds, we discovered atypical
organometallic reactions involving skeletal rearrangement of η1-
3-furylidene to η1-2-furylidene and of η1-3-furyl to η1-2-furyl
compounds. The η1-3-furyl complexes in this system underwent
diastereoselective 1,4-addition reactions to yield complex η1-
2,5-dihydrofuryl compounds; this process greatly enhances
organic furan chemistry. Oxidative demetalations of representa-
tive η1-heterocyclic compounds were performed to yield useful
2,5-dihydrofurans, furans, ∆3-butenolides, ∆3-butenolides, and
complex 2,5-dihydrofurans.
Experimental Section
All operations were carried out under argon in a Schlenk apparatus
or glove box. The solvents benzene, diethyl ether, tetrahydrofuran,
and hexane were dried with sodium benzophenone and distilled before
use. Dichloromethane was dried over calcium hydride and distilled.
Ph3CBF4 was crystallized from CH2Cl2 and hexane at -40 °C before
use; tungsten hexacarbonyl, BF3‚Et2O, dicyclopentadiene, 3-phenylpro-
(27) (a) Kowalczyk, J. J.; Arif, A. M.; Gladysz, J. A. Organometallics
1991, 10, 1079. (b) Trost, B. M.; Dyker, G.; Kulawiec, R. J. J. Am. Chem.
Soc. 1990, 112, 7809. (c) Trost, B. M.; Martinez, J. A.; Kulawiec, R. J.;
Indolese, A. F. J. Am. Chem. Soc. 1993, 115, 10402.
(28) Carey, F. A.; Sundberg, R. J. AdVanced Organic Chemistry, Part
A: Structure and Mechanisms; Plenum Press: New York, 1990; Chapter
7, p 416.
(29) Hegedus, L. S. Transition Metals in the Synthesis of Complex
Organic Molecules; University Science Books: Mill Valley, CA, 1994;
Chapter 6, p 151.
(30) Bird, C. W.; Cheeseman, G. W. H. In ComprehensiVe Heterocyclic
Chemistry; Katritzky, A. R., Reese, C. W., Eds.; Pergamon Press: Oxford,
1984; Vol. 4, Part 3, p 39.
(31) Sargent, M. V.; Dean, F. M. In ComprehensiVe Heterocyclic
Chemistry; Katritzky, A. R., Reese, C. W., Eds.; Pergamon Press: Oxford,
1984; Vol. 4, Part 3, p 599.
(32) For discussion concerning the mechanism and stereochemistry of
antiperiplanar and synclinal transition states in organic reactions, see refs
1a,b and (a) Yamamoto, Y.; Asao, N. Chem. ReV. 1993, 93, 2207. (b) Roush,
W. R. In ComprehensiVe Organic Synthesis: Addition to C-X p bonds, Part
II; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Chapter
1.1, p 1. (c) Denmark, S. E.; Weber, E. J.; Wilison, T. M. Tetrahedron
1989, 45, 1053.
(33) (a) Denmark, S. E.; Weber, E. J. J. Am. Chem. Soc. 1984, 106,
7970. (b) Denmark, S. E.; Henke, B. R.; Weber, E. J. Am. Chem. Soc.
1987, 109, 2512. (c) Marshall, J. A.; Wang, X.-J. J. Org. Chem. 1991, 56,
3211. (d) Marshall, J. A.; Crooks, S. L.; DeHoff, B. S. J. Org. Chem. 1988,
53, 1616. (e) Panek, J. S.; Cirillo, P. F. J. Org. Chem. 1993, 59, 999. (f)
Panek, J. S.; Beresis, R. J. Org. Chem. 1993, 58, 809. (g) Reetz, M. T.
Angew. Chem., Int. Ed. Engl. 1984, 23, 556.
(34) (a) Korreda, M.; Tanaka, Y. Tetrahedron Lett. 1987, 28, 143. (b)
Keck, G. E.; Abbot, D. E.; Wiley, M. R. Tetrahedron Lett. 1987, 28, 139.
(35) Denmark, S. E.; Almstead, N. G. J. Org. Chem. 1994, 59, 5130.
(36) Only a few cases of anti selectivity are observed for allylation of
aldehydes in an open transition-state mechanism.34,35 For tributyltin allyl
compounds, several cases of anti selectivity derive from a closed transition-
state mechanism without catalysts or with SnCl4 or MgCl2 as catalyst; see
representative examples: (a) Keck, G. E.; Abbott, D. A. Tetrahedron Lett.
1984, 25, 1883. (b) Mikami, K.; Kawamoto, K.; Loh, T.-P.; Nakai, T. J.
Chem. Soc., Chem. Commun. 1990, 1359. (c) Hull, C.; Mortlock, S. V.;
Thomas, E. J. Tetrahedron 1989, 45, 1007. (d) Koreeda, M.; Tanaka, Y.
Chem. Lett. 1982, 1299.

536 J. Am. Chem. Soc., Vol. 118, No. 3, 1996
Shu et al.
Scheme 10
pargyl alcohol, 2-butyn-1-ol, aldehydes, and trimethoxymethane were
obtained commercially and used without purification. CpW(CO)3(η1-
3-phenylpropargyl) and CpW(CO)3(η1-3-methylpropargyl) were pre-
pared according to the procedures described in the literature.3a
All 1H NMR (400 and 300 MHz) and 13C NMR (100 and 75 MHz)
spectra were obtained on either a Bruker AM-400 or a Varian Gemini-
300 spectrometer; the chemical shifts of 1H and 13C NMR are reported
relative to tetramethylsilane (δ ) 0 ppm). Elemental analyses were
performed at National Cheng Kung University, Tainan; solid samples
of 10-15 were kept at -20 °C until analyses. Infrared spectra were
recorded on a Perkin-Elmer 781 spectrometer. High-resolution mass
spectra were recorded on a JEOL HX 110 spectrometer.
Synthesis of CpW(CO)3(η1-4-methyl-5-isopropyl-2,5-dihydro-3-
furyl) (1). To a CH2Cl2 solution (40 mL) of CpW(CO)3(η1-3-
methylpropargyl) (4.00 g, 10.4 mmol) at -40 °C were added BF3‚Et2O
(1.38 mL, 11.0 mmol) and iPrCHO (1.49 g, 20.7 mmol), and the mixture
was stirred for 2 h at the same temperature before addition of a saturated
NaHCO3 solution (15 mL). The organic layer was separated, washed
with water (2 × 10 mL), dried over MgSO4, and evaporated under
vacuum. The residue was eluted through a silica gel column (diethyl
ether/hexane ) 1/1) to produce a yellow band (Rf ) 0.50) that
yielded 1 as a yellow solid (4.43 g, 9.67 mmol, 93%). IR (Nujol, cm-1):
ν(CO) 2005 (s), 1934 (s), ν(CdC) 1630 (w). 1H NMR (400 MHz,
CDCl3): δ 5.51 (5H, s, Cp), 4.37 (3H, m, CRHH′ + CδH), 1.81 (1H,
m, J ) 6.9, 1.1 Hz, CH), 1.58 (3H, s, Me), 0.95 and 0.63 (6H, d, d, J
) 6.9 Hz, 2 Me). 13C NMR (100 MHz, CDCl3): δ 227.7, 215.3, 214.9,
144.5, 108.9, 93.1, 90.6, 89.1, 31.8, 20.0, 15.7, 14.4. MS (75 eV,
m/e): 458 (M+). Anal. Calcd for C16H18WO4: C, 41.94; H, 3.96.
Found: C, 41.76; H, 4.20.
in vacuo at -30 °C. The sample (2.10 g, 3.86 mmol, 88%) was kept
at -30 °C before spectral measurement and elemental analysis. IR
(Nujol, cm-1): ν(CO) 2054 (vs), 1991 (vs). 1H NMR (400 MHz, CD2-
Cl2, -40 °C): δ 6.01 (5H, s, Cp), 5.93 (2H, s, CRH), 3.21 (1H, hept,
J ) 7.1 Hz, CH), 2.14 (3H, s, Me), 1.29 (6H, d, J ) 7.1 Hz, Me). 13
C
NMR (100 MHz, CD2Cl2, -40 °C): δ 235.0 (WdCâ, JWC ) 110 Hz),
220.1, 212.9, 203.4, 143.5, 98.6, 94.6, 30.6, 18.8, 18.7, 14.3. Anal.
Calcd for C16H17O4WBF4: C, 35.33; H, 3.15. Found: C, 34.96; H,
3.40.
Synthesis of [CpW(CO)3(η1-4-phenyl-5-methyl-3-furylidene)]BF4
(5). This compound was similarly prepared from 2 and Ph3CBF4 (1.0
equiv) in cold CH2Cl2; the yield was 91%. IR (Nujol): ν(CO) 2054
(vs), 1990 (vs). 1H NMR (400 MHz, CD2Cl2, -40 °C): δ 7.20-7.60
(5H, m, Ph), 6.18 (2H, s, CRH2), 5.80 (5H, s, Cp), 2.51 (3H, s, Me).
13C NMR (100 MHz, CD2Cl2, -40 °C): δ 231.1 (WdCâ, JWC ) 112
Hz), 216.1, 211.5, 196.0, 149.1, 128.5, 128.2, 127.1, 126.6, 96.7, 90.8,
22.3. Anal. Calcd for C19H15WO4BF4: C, 39.48; H, 2.62. Found:
C, 39.04; H, 2.88.
Synthesis of [CpW(CO)3(η1-4-phenyl-5-ethyl-3-furylidene)]BF4
(6). This compound was similarly prepared from 3 and Ph3CBF4 (1.0
equiv) in cold CH2Cl2; the yield was 90%. IR (Nujol, cm-1): ν(CO)
2056 (vs), 1992 (vs). 1H NMR (400 MHz, CD2Cl2, -40 °C): δ 7.20-
7.60 (5H, m, Ph), 6.19 (2H, s, CRH2), 5.82 (5H, s, Cp), 2.81 (2H, q, J
) 7.2 Hz, CH2), 1.28 (3H, q, J ) 7.2 Hz, Me). 13C NMR (100 MHz,
CD2Cl2, -40 °C): δ 231.3 (WdCâ, JWC ) 119 Hz), 218.7, 214.6, 201.6,
150.8, 130.7, 129.0, 128.5, 128.3, 99.0, 93.1, 24.3, 7.8. Anal. Calcd
for C20H17WO4BF4: C, 40.58; H, 2.89. Found: 40.08; H, 3.12.
Synthesis of CpW(CO)3(η1-4-methyl-5-isopropyl-3-furyl) (7).
Et3N (1.10 g, 11.0 mmol) was added to 4 (2.00 g, 3.68 mmol) in CH2-
Cl2 (8 mL) at -60 °C, and the resulting yellow solution was stirred
for 20 min before it was warmed to 23 °C. After addition of water
(20 mL), the organic layer was extracted with diethyl ether (2 × 10
mL), washed with water, and dried in vacuo to give 7 as a yellow
solid (1.51 g, 3.31 mmol, 90%). IR (Nujol, cm-1): ν(CO) 2019 (s),
1918 (s), ν(CdC) 1617 (w). 1H NMR (400 MHz, C6D6): δ 7.11 (1H,
s, CâH), 4.62 (5H, s, Cp), 3.08 (1H, m, CH), 2.01 (3H, s, Me), 1.41
(6H, d, J ) 7.0 Hz, 2 Me). 13C NMR (100 MHz, C6D6): δ 229.5,
216.3, 155.9, 147.2, 129.9, 122.1, 90.4, 26.9, 21.7, 27.6, 12.8. MS
(12 eV, m/e): 456 (M+). Anal. Calcd for C16H16WO4: C, 42.13; H,
3.54. Found: C, 41.23; H, 3.53.
Synthesis of CpW(CO)3(η1-4-phenyl-5-methyl-2,5-dihydro-3-fu-
ryl) (2). This compound was similarly prepared from CpW(CO)3(η1-
3-phenylpropargyl), acetaldehyde, and BF3‚Et2O in cold CH2Cl2; the
yield was 90%. IR (Nujol, cm-1): ν(CO) 2012 (s), 1910 (s), ν(CdC)
1610 (w). 1H NMR (300 MHz, CDCl3): δ 7.10-7.42 (5H, m, Ph),
5.28 (5H, s, Cp), 5.00 (1H, m, CδH), 4.70 (1H, dd, J ) 6.9, 2.2 Hz,
CRHH′), 4.70 (1H, dd, J ) 6.9, 3.2 Hz, CRHH′), 1.07 (3H, d, J ) 6.2
Hz, Me). 13C NMR (75 MHz, CDCl3): δ 227.0, 217.3, 216.3, 153.0,
139.6, 129.2, 128.0 and 126.6, 111.4, 90.7, 89.8, 85.9, 20.9 (Me). MS
(75 eV, m/e): 492 (M+). Anal. Calcd for C19H16WO4: C, 46.37; H,
3.28. Found: C, 46.39; H, 3.37.
Synthesis of CpW(CO)3(η1-4-phenyl-5-methyl-3-furyl) (8). This
compound was similarly prepared from 5 and Et3N (2.5 equiv) in cold
CH2Cl2; the yield was 93%. IR (Nujol, cm-1): ν(CO) 2018 (s), 1917
(s), ν(CdC) 1618 (w). 1H NMR (300 MHz, CDCl3): δ 7.20-7.50
Synthesis of CpW(CO)3(η1-4-phenyl-5-ethyl-2,5-dihydro-3-furyl)
(3). This compound was similarly prepared from CpW(CO)3(η1-3-
phenylpropargyl), propionaldehyde, and BF3‚Et2O in cold CH2Cl2; the
yield was 94%. IR (Nujol, cm-1): ν(CO) 2009 (s), 1914 (s), ν(CdC)
1615 (w). 1H NMR (300 MHz, CDCl3): δ 7.20-7.50 (5H, m, Ph),
5.25 (5H, s, Cp), 4.99 (1H, m, CδH), 4.78 (1H, dd, J ) 14.3, 4.3 Hz,
CRHH′), 4.72 (1H, dd, J ) 14.3, 3.3 Hz, CRHH′), 1.55 (1H, m, CHH′),
1.35 (1H, m, CHH′), 0.84 (3H, t, J ) 6.5 Hz, Me). 13C NMR (75
MHz, CDCl3): δ 227.2, 217.5, 216.3, 151.1, 139.7, 129.1, 128.1, 126.6,
115.1, 90.7, 90.5, 77.2, 27.6, 8.4. MS (75 eV, m/e): 506 (M+). Anal.
Calcd for C20H18WO4: C, 47.42; H, 3.58. Found: C, 47.64; H, 3.64.
Synthesis of [CpW(CO)3(η1-4-methyl-5-isopropyl-3-furylidene)]-
BF4 (4). To a CH2Cl2 (10 mL) solution of 1 (2.00 g, 4.37 mmol) was
slowly added Ph3CBF4 (1.41 g, 4.30 mmol) in CH2Cl2 (3 mL) at -60
°C during a period of 30 min; the mixture was stirred for 20 min. At
-60 °C, cold pentane (ca. 100 mL) was slowly added to yield an orange
precipitate, and the solution layer was removed. The precipitate was
redissolved in cold CH2Cl2 (5 mL, -60 °C) and reprecipitated with
pentane (55 mL), and the organic layer was discarded again to leave 4
(5H, m, Ph), 6.92 (1H, s, CRH), 5.18 (5H, s, Cp), 2.12 (3H, s, Me). 13
C
NMR (75 MHz, CDCl3): δ 228.1, 216.1, 149.1, 147.1, 138.1, 132.1,
131.2, 128.1, 126.3, 91.3, 12.3. MS (75 eV, m/e): 490 (M+). Anal.
Calcd for C19H14WO4: C, 46.56; H, 2.88. Found: C, 46.32; H, 3.14.
Synthesis of CpW(CO)3(η1-4-phenyl-5-ethyl-3-furyl) (9). This
compound was similarly prepared from 6 and Et3N (3.0 equiv) in cold
CH2Cl2; the yield was 93%. IR (Nujol, cm-1): ν(CO) 2017 (s), 1910
(s), ν(CdC) 1614 (w). 1H NMR (300 MHz, CDCl3): δ 7.20-7.40
(5H, m, Ph), 6.89 (1H, s, CRH), 5.13 (5H, s, Cp), 2.40 (2H, q, J ) 7.4
Hz, CH2), 1.07 (3H, t, J ) 7.4 Hz, CH3). 13C NMR (75 MHz,
CDCl3): δ 228.5, 216.0, 154.0, 147.0, 143.8, 138.1, 131.7, 131.2, 127.6,
126.6, 91.2, 20.1, 13.3. MS (75 eV, m/e): 504 (M+). Anal. Calcd
for C20H18WO4: C, 47.61; H, 3.20. Found: C, 47.51; H, 3.15.
Synthesis of CpW(CO)3(η1-4-methyl-5-isopropyl-2-furyl) (10).
To a CH2Cl2 (20 mL) solution of 7 (1.66 g, 3.64 mmol) was added

Tungsten η1-FiVe-Membered Oxygenated Heterocycles
J. Am. Chem. Soc., Vol. 118, No. 3, 1996 537
p-TSA (31 mg, 0.18 mmol) in CH2Cl2 (3 mL) at 23 °C; the solution
was stirred for 1 h before the reaction was quenched with a saturated
NaHCO3 solution. The organic layer was separated, dried over MgSO4,
and evaporated to dryness under vacuum. The residue was eluted
through a silica gel column under nitrogen to produce a yellow band
(diethyl ether/hexane ) 1/1, Rf ) 0.87) that yielded 10 as a yellow oil
(1.58 g, 3.49 mmol, 96%). IR (Nujol, cm-1): ν(CO) 2011 (s), 1910
(s), ν(CdC) 1605 (w). 1H NMR (400 MHz, CDCl3): δ 6.25 (1H, s,
CâH), 5.49 (5H, s, Cp), 2.93 (1H, m, J ) 6.9 Hz, CH), 1.19 (6H, d, d,
J ) 6.9 Hz, 2 Me). 13C NMR (100 MHz, CDCl3): δ 228.3, 215.6,
163.3, 133.3, 132.8, 114.4, 91.6, 26.6, 21.8, 9.6. MS (75 eV, m/e):
456 (M+). Anal. Calcd for C16H16WO4: C, 42.13; H, 3.54. Found:
C, 42.24; H, 3.66.
CO3 solution, and the organic layer was extracted with diethyl ether,
washed with NaHCO3 (5 mL), and dried in vacuo. The residues were
chromatographed through a silica gel column (diethyl ether/hexane )
1/1) to yield an orange band of 16 (Rf ) 0.25; orange solid, 0.55 g,
1.17 mmol, 67%). IR (Nujol, cm-1): ν(CO) 2012 (s), 1914 (s), 1768
(s), ν(CdC) 1640 (w). 1H NMR (300 MHz, CDCl3): δ 5.44 (5H, s,
Cp), 3.80 (1H, s, CâH), 2.73 (1H, hept, J ) 6.9 Hz, CH), 1.67 (3H, s,
Me), 1.13, 1.10 (6H, d, d, J ) 6.9 Hz, 2 Me). 13C NMR (75 MHz,
CDCl3): δ 227.7, 218.1, 188.2, 145.8, 117.8, 92.9, 29.5, 21.3, 20.1,
12.1, 8.7. MS (12 eV, m/e): 472 (M+). Anal. Calcd for C16H16WO5:
C, 40.70; H, 3.42. Found: C, 40.54; H, 3.49.
Synthesis of CpW(CO)3(η1-2(3H)-oxo-4-phenyl-5-methylfuran-
3-yl) (17). This compound was similarly prepared from 11 and
m-CPBA over a HOAc/NaOAc mixture; the yield of 17 was 69% after
Synthesis of CpW(CO)3(η1-4-phenyl-5-methyl-2-furyl) (11). This
compound was prepared from 8 and p-TSA (5.0 mol %) in CH2Cl2 at
23 °C; the yield was 94%. IR (Nujol, cm-1): ν(CO) 2007 (s), 1911
(s), ν(CdC) 1607 (w). 1H NMR (300 MHz, CDCl3): δ 7.20-7.40
chromatographic elution (SiO
2, diethyl ether/hexane ) 1/1, Rf ) 0.26).
IR (Nujol, cm-1
): ν(CO) 2016 (s), 1915 (s), 1775 (s), ν(CdC) 1638
(w).
1H NMR (300 MHz, CDCl3): δ 7.00-7.40 (5H, m, Ph), 5.41
(5H, m, Ph), 6.64 (1H, s, CâH), 5.56 (5H, s, Cp), 2.48 (3H, s, Me). 13
C
(5H, s, Cp), 4.23 (1H, s, C
âH), 1.99 (3H, s, Me). 13C NMR (75 MHz,
NMR (75 MHz, CDCl3): δ 227.7, 215.8, 155.2, 135.9, 134.9, 131.4,
131.3, 128.4, 127.3, 125.6, 91.8, 13.5. MS (75 eV, m/e): 490 (M+).
Anal. Calcd for C19H14WO4: C, 46.56; H, 2.88. Found: C, 46.77; H,
2.89.
CDCl3): δ 227.7, 217.7, 217.2, 187.3, 138.7, 134.3, 129.1, 128.0, 127.3,
126.4, 92.5, 11.5, 8.1. MS (75 eV, m/e): 506 (M+
). Anal. Calcd for
19H14WO5: C, 45.05; H, 2.79. Found: C, 45.03; H, 2.81.
Synthesis of CpW(CO)3(η1-2(3H)-oxo-4-phenyl-5-ethylfuran-3-
C
Synthesis of CpW(CO)3(η1-4-phenyl-5-ethyl-2-furyl) (12). This
compound was similarly prepared from 9 and p-TSA (5.0 mol %) in
CH2Cl2 at 0 °C; the yield was 93%. IR (Nujol, cm-1): ν(CO) 2007
(s), 1911 (s), ν(CdC) 1607 (w). 1H NMR (300 MHz, CDCl3): δ 7.30-
7.40 (5H, m, Ph), 6.59 (1H, s, CâH), 5.54 (5H, s, Cp), 2.80 (1H, q, J
) 7.2 Hz, CH2CH3), 1.25 (1H, t, J ) 7.2 Hz, Me). 13C NMR (75
MHz, CDCl3): δ 227.8, 215.7, 160.4, 135.2, 135.1, 131.3, 131.2, 128.4,
127.3, 125.7, 91.7, 20.9, 13.4. MS (75 eV, m/e): 504 (M+). Anal.
Calcd for C20H16WO4: C, 47.64; H, 3.20. Found: C, 47.87; H, 3.33.
Synthesis of [CpW(CO)3(η1-4-methyl-5-isopropyl-2-furylidene)]-
CF3CO2 (13). To 10 (0.20 g, 0.44 mmol) in diethyl ether (3 mL) at
0 °C was slowly added CF3CO2H (0.70 g, 6.6 mmol) to yield a red
precipitate. The solution was concentrated to ca. 1.5 mL; then hexane
(2 mL) was added to yield further solid. The solvent was removed to
leave 13 as a red solid (0.17 g, 0.29 mmol, 67%). IR (Nujol, cm-1):
ν(CO) 2060 (s), 1988 (s), ν(CdC) 1607 (w). 1H NMR (400 MHz,
CD2Cl2, 0 °C): δ 7.32 (1H, s, CâH), 6.02 (5H, s, Cp), 5.67 (1H, d, J
) 2.9 Hz, CδH), 2.52 (1H, m, J ) 6.9, 2.9 Hz, CH), 2.43 (3H, s, Me),
1.47 and 0.68 (d, d, J ) 6.9 Hz, 2 Me). 13C NMR (100 MHz, CD2Cl2,
0 °C): δ 278.4 (WdCR, JWC ) 114 Hz), 213.6, 212.6, 179.0, 163.0
(q, JCF ) 43.7 Hz), 130.1, 115.0 (q, JCF ) 284.0 Hz), 110.1, 95.8,
38.2, 30.4, 21.4, 14.2. Anal. Calcd for C18H17WO6F3: C, 37.92; H,
3.01. Found: C, 37.77; H, 3.23.
Synthesis of [CpW(CO)3(η1-4-phenyl-5-methyl-2-furylidene)]-
CF3CO2 (14). This compound was similarly prepared from 11 and
CF3CO2H (15 equiv) in diethyl ether; the yield was 70%. IR (Nujol,
cm-1): ν(CO) 2068 (s), 1988 (s), ν(CdC) 1610 (w). 1H NMR (400
MHz, CD2Cl2, 0 °C): δ 7.74 (1H, s, CâH), 7.50-7.70 (5H, m, Ph),
6.40 (1H, q, J ) 7.1 Hz, CδH), 6.06 (5H, s, Cp), 1.80 (3H, d, J ) 7.1
Hz, Me). 13C NMR (75 MHz, CD2Cl2, 0 °C): δ 273.3 (WdCR, JWC
) 118 Hz), 213.7, 212.6, 176.0, 163.0 (q, JCF ) 43.7 Hz), 139.3, 130.4,
129.0, 128.9, 128.7, 115.0 (q, JCF ) 284.0 Hz), 101.1, 95.8, 20.9. Anal.
Calcd for C21H15WO6F3: C, 41.75; H, 2.50. Found: C, 41.66; H, 2.77.
Synthesis of [CpW(CO)3(η1-4-phenyl-5-ethyl-2-furylidene)]CF3CO2
(15). This compound was prepared from 12 and CF3CO2H (15 equiv)
in diethyl ether; the yield was 65%. IR (Nujol, cm-1): ν(CO) 2069
(s), 1996 (s), ν(CdC) 1610 (w). 1H NMR (400 MHz, CDCl3, 0 °C):
δ 7.78 (1H, s, CâH), 7.60-7.70 (5H, m, Ph), 6.43 (1H, dd, J ) 5.0,
3.6 Hz, CδH), 6.08 (5H, s, Cp), 2.57 (1H, ddq, J ) 20.1, 7.2, 3.6 Hz,
CHH′), 1.97 (1H, ddq, J ) 20.1, 7.2, 5.0 Hz, CHH′), 0.91 (3H, t, J )
7.2 Hz, Me). 13C NMR (100 MHz, CD2Cl2, 0 °C): δ 273.5 (WdCR,
JWC ) 110 Hz), 213.9, 212.7, 176.3, 163.0 (q, JCF ) 43.7 Hz), 140.3,
133.4, 129.1, 128.8, 128.6, 115.0 (q, JCF ) 284.0 Hz), 106.1, 95.1,
27.9, 8.3. Anal. Calcd for C22H17WO6F3: C, 42.74; H, 2.77. Found:
C, 42.88; H, 2.88.
yl) (18). This compound was similarly prepared from 12 and m-CPBA
over a HOAc/NaOAc mixture; the yield of 18 was 70% after
chromatographic elution (SiO2, diethyl ether/hexane ) 1/1, Rf ) 0.27).
IR (Nujol, cm-1): ν(CO) 2018 (s), 1914 (s), 1768 (s), ν(CdC) 1640
w); IR (Nujol, cm-1): ν(CO) 2027 (s), 1932 (s), 1770 (s), ν(CdC)
1618 (w). 1H NMR (300 MHz, CDCl3): δ 7.00-7.30 (5H, m, Ph),
4.69 (5H, s, Cp), 4.15 (1H, s, CâH), 2.28 (1H, dq, J ) 11.4, 7.4 Hz,
CHH′), 2.16 (1H, dq, J ) 11.4, 7.4 Hz, CHH′), 1.11 (3H, t, J ) 7.4
Hz, CH3). 13C NMR (75 MHz, CDCl3): δ 229.4, 218.9, 217.7, 186.3,
144.2, 135.0, 128.9, 128.4, 128.3, 126.2, 92.6, 19.7, 12.9, 8.4. MS
(75 eV, m/e): 520 (M+). Anal. Calcd for C20H16WO5: C, 46.15; H,
3.10. Found: C, 46.13; H, 3.12.
Synthesis of CpW(CO)3[η1-2-(dimethoxymethyl)-4-phenyl-5-
ethyl-3-furyl] (19). To 9 (0.20 g, 0.40 mmol) in CH2Cl2 (10 mL) at
-40 °C were added trimethoxymethane (80 mg, 0.80 mmol) and then
SnCl4 (1.0 M in heptane, 0.48 mL); the mixture was stirred for 1 h
before addition of Et3N (0.12 g, 1.20 mmol). The solution was warmed
to 23 °C and added with H2O (10 mL). The mixture was extracted
with diethyl ether (2 × 10 mL). The organic layer was washed with
water (2 × 10 mL), dried over MgSO4, and evaporated under vacuum
to give a yellow solid. Crystallization of this solid from a saturated
diethyl ether/hexane solution at -40 °C yielded 19 as a yellow
crystalline material (0.15 g, 0.26 mmol, 65%). A second crystallization
of the mother liquor gave 19 in 18% yield (40 mg, 0.070 mmol). IR
(Nujol, cm-1): ν(CO) 2014 (s), 1915 (s), ν(CdC) 1612 (w). 1H NMR
(300 MHz, toluene-d8): δ 7.25-7.44 (5H, m, Ph), 5.77 (1H, s, CH),
4.98 (5H, s, Cp), 3.61 (3H, s, OMe), 2.63 (2H, q, J ) 7.6 Hz, CH2),
1.27 (3H, t, J ) 7.6 Hz, Me). 13C NMR (75 MHz, toluene-d8): δ
228.5, 217.4, 157.0, 156.4, 141.2, 142.3, 135.4, 131.5, 129.1, 128.0,
103.5, 94.2, 56.1, 23.2, 18.1. MS (12 eV): 578 (M+). Anal. Calcd
for C23H22WO6: C, 47.77; H, 3.83. Found: C, 47.69; H, 3.82.
Synthesis of CpW(CO)3[η1-2-(dimethoxymethyl)-4-phenyl-5-
ethyl-cis-2,5-dihydro-3-furyl] (20). This compound was prepared from
9, CH(OMe)3, and SnCl4 in cold CH2Cl2 except that NaBH3CN replaced
Et3N; the yield of 20 (yellow solid) was 86% after elution through a
silica gel column (diethyl ether/hexane ) 1/1, Rf ) 0.20). IR (Nujol,
cm-1): ν(CO) 2011 (s), 1911 (s), ν(CdC) 1618 (w). 1H NMR (300
MHz, toluene-d8): δ 7.22-7.51 (5H, m, Ph), 5.49 (1H, br d, J ) 3.8
Hz, CRH), 5.19 (1H, br t, J ) 6.8 Hz, CδH), 4.84 (5H, s, Cp), 4.67
(1H, d, J ) 3.8 Hz, CH), 3.63 (3H, s, OMe), 3.60 (3H, s, OMe), 1.75
(1H, m, CHH′), 1.62 (1H, m, CHH′), 1.21 (3H, t, J ) 7.3 Hz, Me).
13C NMR (75 MHz, toluene-d8): δ 228.0, 216.8, 158.1, 143.5, 132.8,
131.1, 129.3, 117.4, 109.0, 101.8, 95.0, 94.4, 56.9, 56.8, 31.7, 13.7.
MS (12 eV): 580 (M+). Anal. Calcd for C23H24WO6: C, 47.61; H,
4.17. Found: C, 47.55; H, 4.12
Synthesis of CpW(CO)3(η1-2(3H)-oxo-4-methyl-5-isopropylfuran-
3-yl) (16). To a hexane solution (5 mL) of 10 (0.80 g, 1.76 mmol)
was added NaOAc (0.20 g, 2.4 mmol) and HOAc (0.20 mL, 3.5 mmol);
to this stirred mixture was added dropwise m-CPBA (0.34 g, 1.95 mmol)
at 0 °C. After stirring for 20 min, the solution was treated with a Na2-
Synthesis of CpW(CO)3[η1-2-(1′-hydroxyethyl)-4-phenyl-5-ethyl-
cis-2,5-dihydro-3-furyl] (21a,b). To 9 (0.30 g, 0.60 mmol) in toluene
(10 mL) at -40 °C were added CH3CHO (40 mg, 0.89 mmol) and
then BF3‚Et2O (0.09 mL, 0.71 mmol). A red oil was gradually
deposited when the solution was stirred for 1 h at -40 °C; to this

538 J. Am. Chem. Soc., Vol. 118, No. 3, 1996
Shu et al.
mixture was added a CH3CN solution (5 mL) of NaBH3CN (0.19 g,
2.95 mmol) that caused immediate disappearance of the oil. After
stirring for 1 h, a saturated NaHCO3 solution was added to the resulting
yellow solution; the organic layer was extracted with diethyl ether (2
× 15 mL), washed with H2O, and then dried in vacuo. Elution of
residues through a silica gel column (diethyl ether/hexane ) 1/1)
produced two yellow bands of 21a (Rf ) 0.80; yellow solid, 0.15 g,
0.28 mmol, 46.4%) and 21b (Rf ) 0.21; yellow solid, 60 mg, 0.11
mmol, 18.6%).
Spectral Data for 21a. IR (Nujol, cm-1): ν(CO) 2015 (s), 1910
(s), ν(CdC) 1610 (w). 1H NMR (400 MHz, toluene-d8): δ 7.36-7.12
(5H, m, Ph), 5.12 (1H, br s, CRH), 5.07 (1H, br t, J ) 4.7 Hz, CδH),
4.73 (5H, s, Cp), 4.39 (1H, q, J ) 4.2 Hz, CH(OH)), 1.62 (3H, d, J )
4.2 Hz, Me), 1.52 (1H, m, CHH′), 1.44 (1H, m, CHH′), 1.04 (3H, t, J
) 7.8 Hz, Me). 13C NMR (100 MHz, toluene-d8): δ 228.1, 218.7,
157.0, 141.6, 130.6, 128.8, 126.3, 117.9, 102.7, 92.5, 92.2, 68.6, 30.3,
22.9, 11.6. MS (12 eV): 550 (M+). Anal. Calcd for C22H22WO5: C,
48.02; H, 4.03. Found: C, 48.27; H, 4.15.
Spectral Data for 21b. IR (Nujol, cm-1): ν(CO) 2018 (s), 1911
(s), ν(CdC) 1605 (w). 1H NMR (300 MHz, C6D6): δ 6.82-7.01 (5H,
m, Ph), 5.15 (1H, br d, J ) 3.4 Hz, CRH), 4.85 (1H, br t, J ) 4.6 Hz,
CδH), 4.16 (5H, s, Cp), 4.04 (1H, dq, J ) 6.3, 3.4 Hz, CH(OH)), 1.22
(2H, m, CHH′), 1.13 (3H, d, J ) 6.3 Hz, Me), 0.79 (3H, t, J ) 7.4 Hz,
Me). 13C NMR (75 MHz, CDCl3): δ 227.8, 219.9, 154.0, 139.9, 129.1,
128.4, 126.8, 114.8, 103.5, 91.4, 91.2, 69.7, 28.3, 17.4, 10.7. MS (12
eV): 550 (M+). Anal. Calcd for C22H22WO5: C, 48.02; H, 4.03.
Found: C, 48.22; H, 4.14.
Synthesis of CpW(CO)3[η1-2-(syn-1′-hydroxy-4′-methylbutyl)-4-
phenyl-5-ethyl-cis-2,5-dihydro-3-furyl] (22a). This compound was
similarly prepared from 9, isovaleraldehyde, and BF3‚Et2O in cold
toluene followed by NaBH3CN reduction; the yield of 22a was 60%
after elution through a silica gel column (yellow solid; diethyl ether/
hexane ) 1/1, Rf ) 0.82). IR (Nujol, cm-1): ν(CO) 2014 (s), 1910
(s), ν(CdC) 1605 (w). 1H NMR (300 MHz, CDCl3): δ 7.17-7.36
(5H, m, Ph), 5.20 (5H, s, Cp), 4.85 (1H, d, J ) 3.5 Hz, CRH), 4.80
(1H, dt, J ) 4.1, 3.5 Hz, CδH), 3.95 (1H, d, J ) 8.4 Hz, CH(OH)),
1.70 (2H, m, CHH′), 1.64 (2H, m, CHH′), 1.65 (1H, m, CH), 1.30,
1.24 (2H, m, CHH′), 0.92 and 0.95 (6H, d, d, J ) 6.8 Hz, 2 Me), 0.83
(3H, t, J ) 7.4 Hz, Me). 13C NMR (75 MHz, CDCl3): δ 228.2, 218.9,
155.1, 140.1, 129.3, 128.3, 127.3, 117.3, 101.5, 91.6, 91.1, 69.4, 28.8,
24.6, 23.8, 21.8, 10.4. MS: 592 (M+). Anal. Calcd for C25H28WO5:
C, 50.69; H, 4.76. Found: C, 50.55; H, 4.88.
(Nujol, cm-1): ν(CO) 2016 (s), 1918 (s), ν(CdC) 1645 (w). 1H NMR
(300 MHz, toluene-d8): δ 5.12 (5H, s, Cp), 4.99 (1H, dd, J ) 3.8, 2.8
Hz, CRH), 4.68 (1H, d, J ) 2.8 Hz, CδH), 4.52 (1H, d, J ) 3.8 Hz,
CH), 3.47 (3H, s, OMe), 3.45 (3H, s, OMe), 2.06 (1H, m, CH), 1.91
(Me), 1.39 and 1.11 (6H, d, d, J ) 7.0 Hz, 2 Me). 13C NMR (75
MHz, toluene-d8): δ 228.5, 217.8, 151.5, 112.8, 99.4, 96.0, 94.2, 57.6,
57.4, 34.7, 22.8, 20.0, 18.8. MS: 532 (M+). Anal. Calcd for C19H24-
WO6: C, 42.88; H, 4.55. Found: C, 42.89; H, 4.50.
Synthesis of CpW(CO)3[η1-2-(1′-hydroxyethyl)-4-methyl-5-iso-
propyl-2,5-dihydro-3-furyl] (26a-c). These compounds were simi-
larly prepared from 7, acetaldehyde, and BF3‚Et2O in cold CH2Cl2
before NaBH3CN reduction; the three diastereomers were separated
on a silica gel column (diethyl ether/hexane ) 1/1) with the following
Rf values and yields: 26a (Rf ) 0.50; yellow solid, 0.08 g, 0.17 mmol,
15%), 26b (Rf ) 0.20; yellow solid, 30 mg, 0.060 mmol, 5%), and 26c
(Rf ) 0.12; yellow solid, 0.27 g, 0.55 mmol, 50%).
Spectral Data for 26a (syn-cis). IR (Nujol, cm-1): ν(CO) 2014
(s), 1911 (s), ν(CdC) 1610 (w). 1H NMR (300 MHz, C6D6): δ 4.84
(5H, s, Cp), 4.63 (1H, d, J ) 3.8 Hz, CRH), 4.43 (1H, d, J ) 3.8 Hz,
CδH), 4.37 (1H, q, J ) 6.5 Hz, CH), 1.80 (1H, hept, J ) 6.8 Hz, CH),
1.58 (3H, s, Me), 1.52 (3H, d, J ) 6.5 Hz, Me), 1.10 and 0.76 (6H, d,
d, J ) 6.8 Hz, 2 Me). MS (75 eV, m/e): 502 (M+). Anal. Calcd for
C18H22WO5: C, 43.05; H, 4.42. Found: C, 43.32; H, 4.40.
Spectral Data for 26b (syn-trans). IR (Nujol, cm-1): ν(CO) 2014
(s), 1910 (s), ν(CdC) 1638 (w). 1H NMR (300 MHz, CDCl3): δ 5.50
(5H, s, Cp), 4.52 (1H, d, J ) 5.3 Hz, CRH), 4.43 (1H, d, J ) 5.3 Hz,
CδH), 4.03 (1H, q, J ) 6.5 Hz, CH(OH)), 1.78 (1H, hept, J ) 6.8Hz,
CH), 1.76 (3H, s, Me), 1.27 (3H, d, J ) 6.5 Hz, Me), 0.98, 0.62 (3H,
3H, d, d, J ) 6.8 Hz, 2 Me). 13C NMR (75 MHz, CDCl3): δ 228.4,
217.5, 142.8, 109.2, 100.4, 94.4, 91.5, 69.5, 32.5, 21.5, 19.8, 17.0, 14.5.
MS (12 eV, m/e): 502 (M+). Anal. Calcd for C18H22WO5: C, 43.05;
H, 4.42. Found: C, 43.33; H, 4.51.
Spectral Data for 26c (anti-trans). IR (Nujol, cm-1): ν(CO) 1948
(s), 1850 (s), ν(CdC) 1645 (w). 1H NMR (300 MHz, CDCl3): δ 5.06
(5H, s, Cp), 4.98 (1H, d, J ) 3.3 Hz, CRH), 4.61 (1H, d, J ) 3.3 Hz,
CδH), 4.15 (1H, q, J ) 6.5 Hz, CH(OH)), 2.00 (1H, hept, J ) 7.0 Hz,
CH), 1.75 (3H, s, Me), 1.32 (3H, d, J ) 6.5 Hz, Me), 1.30, 1.01 (3H,
3H, d, d, J ) 7.0 Hz, CH). 13C NMR (75 MHz, CDCl3): δ 229.3,
217.5, 148.1, 112.5, 103.1, 94.7, 92.3, 71.6, 33.2, 21.3, 18.3, 17.4, 15.7.
MS (12 eV): 502 (M+). Anal. Calcd for C18H22WO5: C, 43.05; H,
4.42. Found: C, 43.24; H, 4.55.
Synthesis of CpW(CO)3[η1-2-(1′-hydroxy-3′-methylpropyl)-4-
ethyl-5-isopropyl-2,5-dihydro-3-furyl] (27a-c). This compound was
similarly prepared from 7, isovaleraldehyde, and BF3‚Et2O and
sequential NaBH3CN reduction in cold CH2Cl2; three diastereomers
were separated on a silica gel column (diethyl ether/hexane ) 1/1)
with the following Rf values and yields: 27a (Rf ) 0.50; yellow solid,
15%), 27b (Rf ) 0.20; yellow solid, 8%), and 27c (Rf ) 0.12; yellow
solid, 55%).
Synthesis of CpW(CO)3[η1-2-(syn-1′-hydroxy-3′-methylpropyl)-
4-phenyl-5-ethyl-cis-2,5-dihydro-3-furyl] (23a). This compound was
similarly prepared from 9, isobutyraldehyde, and BF3‚Et2O in cold
toluene followed by NaBH3CN reduction; the yield of 23a was 50%
after elution through a silica gel column (yellow solid; diethyl ether/
hexane ) 1/1, Rf ) 0.82). IR (Nujol, cm-1): ν(CO) 2011 (s), 1918
(s), ν(CdC) 1605 (w). 1H NMR (300 MHz, toluene-d8): δ 7.26-
7.39 (5H, m, Ph), 5.48 (1H, d, J ) 2.9 Hz, CRH), 5.10 (1H, m, CδH),
4.82 (5H, s, Cp), 3.89 (1H, d, J ) 7.7 Hz, CH(OH)), 2.36 (1H, m,
CH), 1.58 (1H, m, CHH′), 1.28 (1H, m, CHH′), 1.48 and 1.43 (6H, d,
d, J ) 5.0 Hz, 2 Me), 1.10 (3H, t, J ) 5.5 Hz, Me). 13C NMR (75
MHz, toluene-d8): δ 229.2, 218.7, 157.1, 142.0, 130.8, 129.7, 128.5,
118.7, 99.93, 91.8, 92.5, 77.9, 34.6, 30.5, 21.4, 21.1, 11.6. MS (12
eV, m/e): 578 (M+). Anal. Calcd for C24H26WO5: C, 49.85; H, 4.53.
Found: C, 49.66; H, 4.47.
Spectral Data for 27a (syn-cis). IR (Nujol, cm-1): ν(CO) 2010
(s), 1911 (s), ν(CdC) 1640 (w). 1H NMR (300 MHz, toluene-d8): δ
5.07 (5H, s, Cp), 4.71 (1H, dd, J ) 4.8, 2.3 Hz, CRH), 4.55 (1H, d, J
) 2.3 Hz, CδH), 4.39 (1H, dd, J ) 10.0, 4.8 Hz, CHOH), 2.26 (1H, m,
CH), 2.08 (1H, m, CHH′), 1.58 (1H, m, CHH′), 2.00 (1H, m, CH),
1.79 (3H, s, Me), 1.29, 1.21 (3H, 3H, d, d, J ) 6.6 Hz, 2 Me), 1.29,
0.92 (6H, d, d, J ) 6.9 Hz, 2 Me). 13C NMR (75 MHz, toluene-d8):
δ 228.9, 214.0, 150.8, 114.2, 99.0, 93.1, 91.6, 71.3, 46.6, 32.2, 26.1,
25.0, 23.1, 21.6, 18.1, 17.0. MS (12 eV, m/e): 544 (M+). Anal. Calcd
for C21H28WO5: C, 46.34; H, 5.19. Found: C, 46.68; H, 5.23.
Spectral Data for 27b (syn-trans). IR (Nujol, cm-1): ν(CO) 2010
(s), 1911 (s), ν(CdC) 1640 (w). 1H NMR (300 MHz, toluene-d8): δ
5.07 (5H, s, Cp), 4.91 (1H, dd, J ) 4.4, 3.5 Hz, CRH), 4.60 (1H, dd,
J ) 6.4, 3.5 Hz, CδH), 4.23 (1H, dd, J ) 10.3, 4.4 Hz, CHOH), 2.23
(1H, m, CHMe2), 2.10 (1H, m, CHH′), 1.97 (1H, m, CHMe2), 1.79
(3H, s, CγMe), 1.54 (1H, m, CHH′), 1.34, 0.98 (6H, d, d, J ) 6.6 Hz,
CδCHMe2), 1.26, 1.22 (6H, d, d, J ) 6.9 Hz, CHMe2). 13C NMR (75
MHz, toluene-d8): δ 228.4, 219.7, 150.7, 111.8, 101.9, 95.8, 92.5, 71.5,
46.5, 34.0, 26.0, 25.1, 22.7, 21.3, 18.0, 15.7. MS (12 eV, m/e): 544
(M+). Anal. Calcd for C21H28WO5: C, 46.34; H, 5.19. Found: C,
46.47; H, 5.34.
Synthesis of CpW(CO)3(η1-2-formyl-4-methyl-5-isopropyl-3-fu-
ryl) (24). This compound was similarly prepared from 16, CH(OMe)3,
and SnCl4 in cold CH2Cl2 followed by Et3N deprotonation; the yield
of 24 was 75% after crystallization from diethyl ether/hexane. IR
(Nujol, cm-1): ν(CO) 2012 (s), 1918 (s), ν(CdC) 1615 (w). 1H NMR
(300 MHz, toluene-d8): δ 10.05 (1H, s, CHO), 4.96 (5H, s, Cp), 3.07
(1H, m, CH), 2.15 (3H, s, Me), 1.09 (6H, d, d, J ) 6.5 Hz, 2 Me). 13
C
NMR (75 MHz, toluene-d8): δ 228.4, 217.6, 182.3, 164.1, 159.9, 149.9,
132.7, 94.7, 29.7, 23.2, 23.3, 17.3. MS (12 eV, m/e): 484 (M+). Anal.
Calcd for C17H16WO5: C, 42.26; H, 3.13. Found: C, 42.30; H, 3.11.
Synthesis of CpW(CO)3[η1-2-(dimethoxymethyl)-4-methyl-5-iso-
propyl-trans-2,5-dihydro-3-furyl] (25). This compound was similarly
prepared from 7, CH(OMe)3, and SnCl4 in cold CH2Cl2 followed by
NaBH3CN reduction; the yield was 85% after elution from a silica gel
column (yellow solid; Rf ) 0.20, diethyl ether/hexane ) 1/1). IR
Spectral Data for 27c (anti-trans). IR (Nujol, cm-1): ν(CO) 2014
(s), 1915 (s), ν(CdC) 1645 (w). 1H NMR (300 MHz, toluene-d8): δ

Tungsten η1-FiVe-Membered Oxygenated Heterocycles
J. Am. Chem. Soc., Vol. 118, No. 3, 1996 539
5.05 (5H, s, Cp), 4.97 (1H, d, J ) 2.5 Hz, CRH), 4.63 (1H, d, J ) 2.5
Hz, CδH), 3.85 (1H, d, J ) 10.7 Hz, CHOH), 2.23 (1H, m, CHH′),
2.20 (1H, m, CH), 1.73 (1H, m, CH), 1.76 (3H, s, Me), 1.39 (1H, m,
CHH′), 1.34, 1.04 (6H, d, d, J ) 6.7 Hz, 2 Me), 1.24, 1.22 (6H, d, d,
J ) 6.5 Hz, 2 Me). 13C NMR (75 MHz, toluene-d8): δ 229.4, 217.8,
146.4, 111.4, 102.3, 93.1, 90.7, 72.6, 39.2, 31.8, 24.6, 24.1, 21.6, 20.0,
15.9, 14.4. MS (12 eV, m/e): 544 (M+). Anal. Calcd for C21H28-
WO5: C, 46.34; H, 5.19. Found: C, 46.55; H, 5.34.
Synthesis of CpW(CO)3[η1-2-(anti-1′-acetoxyethyl)-4-methyl-5-
isopropyl-trans-2,5-dihydro-3-furyl] (28a). To 26c (0.27 g, 0.54
mmol) in CH2Cl2 (4 mL) and DMAP (0.11 g, 0.92 mmol) was added
acetic anhydride (0.080 mL, 0.81 mmol), and the mixture was stirred
for 2 h before addition of a saturated NH4Cl solution. The organic
layer was extracted with diethyl ether (2 × 15 mL), washed with water,
and dried in vacuo. The residue was chromatographed through a silica
gel column (diethyl ether/hexane ) 1/1) to develop a yellow band of
28a (Rf ) 0.55; yellow solid, 0.25 g, 0.46 mmol, 86%). IR (Nujol,
cm-1): ν(CO) 2015 (s), 1811 (s), 1710 (s), ν(CdC) 1637 (w). 1H
NMR (300 MHz, toluene-d8): δ 5.35 (1H, q, J ) 6.3 Hz, CH(OAc)),
5.15 (5H, s, Cp), 4.98 (1H, d, J ) 3.3 Hz, CRH), 4.68 (1H, d, J ) 3.3
Hz, CδH), 2.03 (1H, m, CδCHMe2), 1.99 (3H, s, COMe), 1.83 (3H, s,
CγMe), 1.48 (3H, d, J ) 6.3 Hz, (OAc)CHMe), 1.35, 1.05 (6H, d, d,
J ) 6.8, CHMe2). 13C NMR (75 MHz, toluene-d8): δ 229.5, 217.3,
171.7, 149.0, 112.4, 99.9, 95.3, 92.2, 74.8, 33.1, 24.0, 20.8, 17.6, 15.2,
14.1. MS (12 eV, m/e): 546 (M+). Anal. Calcd for C20H26WO6: C,
43.97; H, 4.80. Found: C, 43.89; H, 4.75.
Synthesis of CpW(CO)3[η1-1-(anti-1′-acetoxy-3′-methylpropyl)-
4-ethyl-5-isopropyl-trans-2,5-dihydro-3-furyl] (28b). This compound
was similarly prepared from 27c, acetyl anhydride, and DMAP; the
yield of 28b (yellow solid) was 88% after chromatographic elution
(Rf ) 0.58, silica gel, diethyl ether/hexane ) 1/1). IR (Nujol, cm-1):
ν(CO) 2014 (s), 1914 (s), 1712 (s), ν(CdC) 1640 (w). 1H NMR (300
MHz, toluene-d8): δ 5.37 (1H, dd, J ) 11.2, 1.8 Hz, CHOAc), 5.30
(5H, s, Cp), 4.94 (1H, dd, J ) 4.8, 1.8 Hz, CRH), 4.71 (1H, d, J ) 4.8
Hz, CδH), 2.21 (1H, m, CHH′), 1.57 (1H, m, CHH′), 2.05 (1H, m,
CH), 1.97 (3H, s, Me), 1.92 (1H, m, CH), 1.86 (3H, s, Me), 1.35, 1.07
(6H, d, d, J ) 6.7 Hz, 2 Me), 1.20, 1.05 (6H, d, d, J ) 6.5 Hz, 2 Me).
13C NMR (75 MHz, toluene-d8): δ 229.7, 218.3, 172.3, 148.6, 112.8,
100.4, 95.0, 92.3, 77.2, 36.6, 33.3, 26.1, 25.0, 22.8, 21.4, 21.0, 17.7,
15.7. MS (12 eV, m/e): 558 (M+). Anal. Calcd for C23H30WO6: C,
47.12; H, 5.16. Found: C, 47.24; H, 5.14.
Synthesis of 3-Carbomethoxy-4-phenyl-5-methyl-2,5-dihydrofu-
ran (29). Carbon monoxide was bubbled through a solution (5 mL)
of 2 (0.20 g, 0.41 mmol) in CH2Cl2/CH3OH (1/1) at -78 °C for 20
min, and (NH4)2Ce(NO3)6 (0.67 g, 1.23 mmol) in CH3OH (1 mL) was
added dropwise. The solution was stirred at -78 °C for 1 h before it
was warmed to 23 °C, and the solution was kept stirring for 1 h. The
dark red mixture was filtered through a short silica gel bed, and the
residue was eluted on a preparative silica gel TLC plate to produce an
organic component (Rf ) 0.44, diethyl ether/hexane ) 1/1; 50 mg,
0.25 mmol, 60%). IR (Nujol, cm-1): ν(CO) 1720 (s), ν(CdC) 1618
(w). 1H NMR (300 MHz, CDCl3): δ 7.20-7.40 (m, 5H, Ph), 5.31
(1H, m, CδH), 4.94 (1H, dd, J ) 16.9, 3.7 Hz, CRHH′), 4.86 (1H, dd,
J ) 16.9, 3.2 Hz, CRHH′), 3.63 (1H, s, OMe), 1.22 (3H, d, J ) 6.4
Hz, Me). 13C NMR (75 MHz, CDCl3): δ 163.3, 154.0, 132.4, 128.7,
128.5, 128.1, 128.0, 86.1, 75.1, 51.3, 20.1. MS (75 eV, m/e): 218
(M+). HRMS: calcd for C13H14O3, 218.0943; found, 218.0946.
Synthesis of 3-Carbomethoxy-4-phenyl-5-ethyl-2,5-dihydrofuran
(30). This compound was similarly prepared from 3 and (NH4)2Ce-
(NO3)6 under flowing CO in CH2Cl2/CH3OH (1/1, 3 mL); the yield of
30 was 63% as a colorless oil (Rf ) 0.46, diethyl ether/hexane ) 1/1).
IR (Nujol, cm-1): ν(CO) 1700 (s), ν(CdC) 1610 (w). 1H NMR (300
MHz, CDCl3): δ 5.27 (1H, dt, J ) 4.0, 3.3 Hz, CδH), 4.99 (1H, dd, J
) 16.3, 3.3 Hz, CRHH′), 4.93 (1H, dd, J ) 16.3, 3.3 Hz, CRHH′), 1.63
(1H, m, CHH′), 1.45 (1H, m, CHH′), 0.86 (3H, t, J ) 7.2 Hz, CH3).
13C NMR (75 MHz, CDCl3): δ 163.3, 152.6, 132.6, 128.7, 128.2, 128.1,
125.3, 90.8, 75.9, 51.5, 26.7, 8.6. MS (75 eV, m/e): 232 (M+).
HRMS: calcd for C14H16O3, 232.1099 (M+); found, 232.1094.
Synthesis of 2(5H)-4-Phenyl-5-methyl-5-methoxyfuranone (31).
This compound was similarly prepared from the reaction between 11
and (NH4)2Ce(NO3)6 (5.0 equiv) under flowing CO in CH2Cl2/CH3OH
(1/1); the yield was 54% as a colorless oil (Rf ) 0.45, diethyl ether/
hexane ) 1/1). IR (Nujol, cm-1): ν(CO) 1750, ν(CdC) 1618. 1H
NMR (300 MHz, CDCl3): δ 7.40-7.80 (5H, m, Ph), 6.39 (1H, s, CâH),
3.23 (3H, s, OMe), 1.75 (3H, s, Me). 13C NMR (75 MHz, CDCl3): δ
168.6, 163.5, 131.7, 129.2, 128.9, 127.7, 116.3, 109.4, 50.9, 24.8. MS
(75 eV, m/e): 204 (M+). HRMS: calcd for C12H12O3, 204.0786; found,
204.0788.
Synthesis of 2(5H)-4-Phenyl-5-ethyl-5-methoxyfuranone (32).
This compound was similarly prepared from 12 and (NH4)2Ce(NO3)6
under flowing CO; the yield was 59% as a colorless oil (Rf ) 0.49,
diethyl ether/hexane ) 1/1). IR (Nujol, cm-1): ν(CO) 1760 (s),
ν(CdC) 1617 (w). 1H NMR (300 MHz, CDCl3): δ 7.40-7.80 (5H,
m, Ph), 6.42 (1H, s, CâH), 3.25 (3H, s, OMe), 2.21 (1H, dq, J ) 18.0,
7.6 Hz, CHH′), 1.92 (1H, m, J ) 18.0, 7.6 Hz, CHH′), 0.81 (3H, t, J
) 7.6 Hz, CH3). 13C NMR (75 MHz, CDCl3): δ 169.7, 162.4, 131.7,
129.1, 127.5, 127.3, 117.3, 111.9, 50.8, 30.4, 7.2. MS (75 eV, m/e):
218 (M+). HRMS: calcd for C13H14O3, 218.0943; found, 218.0945.
Demetalation of 11 with I2. This reaction was conducted similarly
from the reaction between 11 and I2 (2.0 equiv) under a nitrogen
atmosphere according to the synthesis of 29 except that I2 replaced
(NH4)2Ce(NO3)6; the yields of 33 and 31 were 60% and 10%,
respectively.
Spectral Data for 33. IR (Nujol, cm-1): ν(CdC) 1618 (w). 1H
NMR (300 MHz, CDCl3): δ 7.20-7.40 (5H, m, Ph), 7.35 (1H, d, J )
2.0 Hz, CRH), 6.55 (1H, d, J ) 2.0 Hz, CâH), 2.47 (3H, s, Me). 13C
NMR (75 MHz, CDCl3): 144.2, 140.2, 134.5, 129.5, 128.5, 127.7,
126.3, 11.2, 20.4. MS (75 eV, m/e): 158 (M+). HRMS: calcd for
C11H10O, 158.0732; found, 158.0734.
Demetalation of 12 with I2. This reaction was conducted similarly
from the reaction between 12 and I2 (2.0 equiv); the yields of 34 and
32 were 63% and 8%, respectively.
Spectral Data for 34. IR (Nujol, cm-1): ν(CdC) 1600 (w). 1H
NMR (400 MHz, CDCl3): δ 7.28 (1H, d, J ) 2.3 CRH), 7.40-7.27
(5H, m, Ph), 6.50 (1H, d, J ) 2.3 Hz, CâH), 2.82 (2H, q, J ) 5.4 Hz,
CH2), 1.29 (3H, t, J ) 5.4 Hz, Me). 13C NMR (100 MHz, CDCl3): δ
144.0, 140.2, 134.5, 129.5, 128.5, 127.7, 126.3, 111.2, 20.4, 12.9. MS
(12 eV, m/e): 172 (M+). HRMS: calcd for C12H12O, 172.0888; found,
172.0892.
Demetalation of 17 with Me3NO. To a solution of 17 (0.20 g,
0.40 mmol) in CH2Cl2 (5 mL) were added anhydrous Me3NO (0.12 g,
1.60 mmol) and H2O (14.4 mg, 0.80 mmol), and the solution was stirred
at 28 °C for 2 h. The residue was treated with H2O (5 mL); the organic
layer was extracted with diethyl ether, dried in vacuo, and eluted through
a silica gel column (diethyl ether/hexane ) 1/1) to produce two bands
that gave 35 (Rf ) 0.49; 36 mg, 0.21 mmol) and 37 (Rf ) 0.33; 40 mg,
0.084 mmol) in 53% and 21% yields, respectively.
Spectral Data for 35. IR (Nujol, cm-1
): ν(CO) 1760 (s), ν(CdC)
1618 (w). 1H NMR (300 MHz, CDCl3): δ 7.20-7.50 (5H, m, Ph),
3.52 (2H, s, CâH2), 2.20 (3H, s, Me). 13C NMR (75 MHz, CDCl3): δ
174.9, 147.8, 132.4, 129.2, 128.7, 127.2, 126.8, 36.3, 13.0. MS (75
eV, m/e): 174 (M+). HRMS: calcd for C11H10O2, 174.0681 (M+);
found, 174.0689.
Spectral Data for 37. IR (Nujol, cm-1): ν(CO) 1987 (s), 1920
(s), 1730 (s), ν(CdC) 1618 (w). 1H NMR (300 MHz, CDCl3): δ 7.10-
7.50 (5H, m, Ph), 5.45 (5H, s, Cp), 3.83 (1H, s, CâH), 2.42 (3H, s,
Me). 13C NMR (75 MHz, CDCl3): δ 221.0, 219.1, 178.1, 137.5, 128.6,
128.5, 127.7, 125.5, 94.3, 92.4, 30.2, 22.9. MS (75 eV, m/e): 478
(M+). Anal. Calcd for C18H14WO4: C, 45.18; H, 2.95. Found: C,
44.87; H, 3.03.
Demetalation of 18 with Me3NO. This reaction was conducted
similarly from 18 and Me3NO in the presence of water; the yields of
36 and 38 were 58% and 20%, respectively.
Spectral Data for 36. IR (Nujol, cm-1): ν(CO) 1785 (s), ν(CdC)
1617 (w). 1H NMR (300 MHz, CDCl3): δ 7.30-7.60 (5H, m, Ph),
3.54 (2H, s, CâH2), 2.57 (2H, m, J ) 7.5 Hz, CH2), 1.22 (3H, t, J )
1.6, Me). 13C NMR (75 MHz, CDCl3): δ 174.5, 152.7, 131.3, 129.3,
128.7, 127.2, 126.8, 36.6, 20.3, 11.3. MS (75 eV, m/e): 188 (M+).
HRMS: calcd for C12H12O2, 188.0837; found, 188.0844.
Spectral Data for 38. IR (Nujol, cm-1): ν(CO) 1988 (s), 1921
(s), 1722 (s), ν(CdC) 1617 (w). 1H NMR (300 MHz, CDCl3): δ 7.10-
7.50 (5H, m, Ph), 5.48 (5H, s, Cp), 3.88 (1H, s, CâH), 2.78 (1H, m, J
) 18.5, 7.5 Hz, CHH′), 2.51 (1H, m, J ) 18.5, 7.5 Hz, CHH′), 1.13
(3H, t, J ) 7.5 Hz, CH3). 13C NMR (75 MHz, CDCl3): δ 221.3, 218.5,

540 J. Am. Chem. Soc., Vol. 118, No. 3, 1996
Shu et al.
178.7, 137.3, 130.0, 128.5, 127.6, 125.4, 99.8, 91.9, 30.0, 29.5, 13.1.
MS (75 eV, m/e): 492 (M+). Anal. Calcd for C19H16WO4: C, 46.37;
H, 3.28. Found: C, 46.17; H, 3.15.
radiation, and the structures were solved by the heavy atom method;
all data reduction and structural refinements were performed with the
NRCCSDP package. Data for 18 were collected on a Nicolet R3M/V
diffractometer using graphite-monochromated Mo KR radiation, and
the structure was solved by the Patterson superposition method; all
data reduction and structural refinement were performed with the
SHELXTL Plus package. Crystal data, details of data collection, and
structural analysis of these seven compounds are prepared as supporting
information. For all structures, all non-hydrogen atoms were refined
with anisotropic parameters, and all hydrogen atoms included in the
structure factor were placed in idealized positions.
Demetalation of 21a by Ce(IV) Salt. This reaction followed the
synthesis of 29 except that reactants 21a and (NH4)2Ce(NO3)6 were
treated in CH2Cl2 rather than in CH3OH/CH2Cl2; the yield of bicyclic
lactone 39 was 40%. IR (neat, cm -1): ν(CO) 1767 (s), ν(CdC) 1622
(m). 1H NMR (300 MHz, CDCl3): δ 7.62-7.23 (5H, m, Ph), 5.73
(1H, dq, J ) 7.9, 6.5Hz, CH), 5.65 (1H, dd, J ) 7.9, 5.1 Hz, CRH),
4.78 (1H, m, CδH), 1.98 (1H, m, CHH′), 1.72 (1H, m, CHH′), 1.35
(3H, d, J ) 6.5 Hz, Me), 0.96 (3H, t, J ) 7.3 Hz, Me). 13C NMR (75
MHz, CDCl3): δ 171.9, 149.8, 134.2, 130.0, 128.7, 128.0, 128.5, 96.0,
86.5, 77.7, 28.1, 15.0, 9.4. MS (12 eV, m/e): 244 (M+). HRMS: calcd
for C15H16O3, 244.1099; found, 244.1103.
Demetalation of 28b by Ce(IV) Salt. This reaction followed the
synthesis of 29 involving the use of CH2Cl2/CH3OH as solvent; the
yield of 40 was 46%. IR (neat, cm -1): ν(CO) 1712 (s), ν(CdC) 1615
(w). 1H NMR (300 MHz, CDCl3): δ 5.38 (1H, dd, J ) 11.2, 1.8 Hz,
CHOAc), 5.06 (1H, dd, J ) 4.0, 1.8 Hz, CRH), 4.66 (1H, d, J ) 4.0
Hz, CδH), 3.75 (3H, s, OMe), 2.06 (3H, s, Me), 2.02 (3H, s, Me), 1.88
(1H, m, CHH′), 1.54 (1H, m, CHH′), 1.62 (1H, m, CH), 1.09 (1H, m,
CH), 1.04, 0.72 (6H, d, d, J ) 6.7 Hz, 2 Me), 0.85, 0.79 (6H, d, d, J
) 6.5 Hz, CH). 13C NMR (75 MHz, toluene-d8): δ 170.6, 163.8, 154.7,
124.5, 94.0, 87.5, 74.1, 51.3, 36.7, 31.3, 24.4, 23.5, 21.5, 21.2, 19.6,
14.7, 12.3. MS (12 eV, m/e): 312 (M+). HRMS: calcd for C17H28O5,
312.1937; found, 312.1934.
Acknowledgment. The authors wish to thank the National
Science Council and National Institute of Health, Taiwan, for
financial support of this work; the authors also thank reviewers
of this manuscript for their valuable comments and suggestions.
Supporting Information Available: Variable-temperature
1H NMR spectra showing the isomerization of 6 to 15 in CD2-
1
Cl2, H NMR spectra monitoring the isomerization of 9 to 12
with CF3CO2D (1.0 equiv) in CD2Cl2 (-40 °C), tables of crystal
data, atomic coordinates, bond distances, bond angles, and
thermal parameters, and ORTEP drawings for 18, 20, 21a, 28a,
and 38 (39 pages). This material is contained in many libraries
on microfiche, immediately follows this article in the microfilm
version of the journal, and can be ordered from the ACS; see
any current masthead page for ordering information.
X-ray Diffraction Studies of 18, 20, 21a, 28a, and 38. Single
crystals of 18, 20, 21a, 28a, and 38 were sealed in glass capillaries
under an inert atmosphere. Data for 20, 21a, 28a, and 38 were collected
on a Nonius CAD 4 instrument using graphite-monochromated Mo KR
JA9518888