Development of the scope of a Co-mediated O→C rearrangement reaction

Article abstract of DOI:10.1021/jo0517895

In this paper we describe an Al-promoted, Co-mediated O→C rearrangement reaction of cyclic enol ethers. This process delivers functionalized cyclohexanones with good to excellent levels of diastereocontrol, whereby the product stereochemistry is dependent

Full text of DOI:10.1021/jo0517895

Development of the Scope of a Co-Mediated OfC Rearrangement
Reaction
Simon J. Meek,† Fabienne Pradaux,† David R. Carbery,† Emmanuel H. Demont,‡ and
Joseph P. A. Harrity*,†
Department of Chemistry, University of Sheffield, Brook Hill, Sheffield, S3 7HF, UK, and
GlaxoSmithKline Research and Development, New Frontiers Science Park, Third Avenue,
Harlow, Essex, CM19 5AW, UK
j.harrity@sheffield.ac.uk
Received August 25, 2005
In this paper we describe an Al-promoted, Co-mediated OfC rearrangement reaction of cyclic enol
ethers. This process delivers functionalized cyclohexanones with good to excellent levels of
diastereocontrol, whereby the product stereochemistry is dependent on the E/Z-stereochemistry of
the starting enol ether. The rearrangement process also permits access to highly substituted
R-spirocyclic cyclohexanones as well as cyclopentanones. The latter rearrangement appears to
proceed via an unusual 5-(enolendo)-exo-trig cyclization process.
Introduction
(2) The stereoselectivity of the rearrangement reaction
was critically dependent on the nature and quality of
Lewis acid employed; while freshly distilled TiCl4 allowed
access to cis- and trans-stereoisomers, Bu2BOTf promoted
isomerization to the trans-product in all cases studied.
More recently, we have been endeavoring to simplify the
reaction protocol by reducing the number of steps to the
enol ethers and by uncovering a more general Lewis acid
for the OfC rearrangement reaction; we report our
results herein.
Our previously reported route to the requisite enol
ether substrates is summarized in Scheme 1. Addition
of the appropriate alkyne was carried out in the first step,
and the pyranylphosphonium salt was ultimately deliv-
ered after a series of functional group interconversions.
While this route required a number of synthetic steps, it
allowed significant quantitites of phosphonium salt to be
made available.
A significant drawback to our established route to the
phosphonium salts was that the alkyne unit is incorpo-
rated in step 1. Accordingly, the preparation of substrates
bearing various alkyne units by this procedure was
prohibitively time-consuming, and our studies were
limited to phenylacetylene- and 1-hexyne-based systems.
Accordingly, we opted to develop a more efficient route
to phosphonium salts that would allow a range of alkynes
to be prepared in a more convenient manner.
The stabilization of a cationic charge at a propargylic
center by a cobalt carbonyl cluster is now well-established
and allows efficient carbon-carbon bond formation to
take place, especially when π-nucleophiles are employed.1
We have recently exploited this chemistry in a Co-
mediated OfC rearrangement reaction that allowed the
stereoselective synthesis of functionalized cyclohexanones
to take place in good to excellent yields.2,3 Nonetheless,
these preliminary studies highlighted some limitations
associated with this methodology: (1) The substrate enol
ethers were prepared by a lengthy and linear procedure.
† University of Sheffield.
‡ GlaxoSmithKline Research and Development.
(1) (a) Nicholas, K. M. Acc. Chem. Res. 1987, 20, 207. (b) Caffyn, A.
J. M.; Nicholas, K. M. In Comprehensive Organometallic Chemistry
II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Hegedus, L. S., Eds.;
Pergamon: Oxford, 1995; Vol. 12, p 685. (c) Green, J. R. Curr. Org.
Chem. 2001, 5, 809. (d) Teobald, B. J. Tetrahedron 2002, 58, 4133.
(2) (a) Carbery, D. R.; Reignier, S.; Myatt, J. W.; Miller, N. D.;
Harrity; J. P. A. Angew. Chem., Int. Ed. 2002, 41, 2584. (b) Carbery,
D. R.; Miller, N. D.; Harrity, J. P. A. Chem. Commun. 2002, 1546. (c)
Carbery, D. R.; Reignier, S.; Miller, N. D.; Adams, H.; Harrity, J. P.
A. J. Org. Chem. 2003, 68, 4392.
(3) For other recent examples of OfC rearrangements, see: (a)
Smith, A. B., III; Verhoest, P. R.; Minbiole, K. P.; Lim, J. J. Org. Lett.
1999, 1, 909. (b) Smith, A. B., III; Minbiole, K. P.; Verhoest, P. R.;
Beauchamp, T. J. Org. Lett. 1999, 1, 913. (c) Sollogoub, M.; Mallet,
J.-M.; Sinay¨, P. Angew. Chem., Int. Ed. 2000, 39, 362. (d) Buffet, M.
F.; Dixon, D. J.; Edwards, G. L.; Ley, S. V.; Tate, E. W. J. Chem. Soc.,
Perkin Trans. 1 2000, 1815. (e) Zhang, Y.; Reynolds, N. T.; Manju, K.;
Rovis, T. J. Am. Chem. Soc. 2002, 124, 9720.
10.1021/jo0517895 CCC: $30.25 © 2005 American Chemical Society
Published on Web 10/18/2005
10046
J. Org. Chem. 2005, 70, 10046-10056

Scope of a Co-Mediated OfC Rearrangement Reaction
SCHEME 1
SCHEME 2a
TABLE 1. Alkyne Incorporation via Sulfone
Displacement
a Reagents and conditions: (a) PPh3‚HBF4, 4 Å molecular sieves,
MeCN, reflux, 48 h. (b) (i) BuLi, THF, -78 °C; PhCHO. (ii)
Co2(CO)8, CH2Cl2, rt, 1 h.
entry
R
product, % yielda
SCHEME 3
1
2
3
4
Ph
2, 89 (1:3.8)
3, 93 (1:3.2)
4, 87 (1:12.3)
5, 94 (1:6.4)
n-Bu
Me3Si
TBDPSOCH2
a Values in parentheses refer to cis:trans ratios.
Results and Discussion
We decided to use sulfone 1 as a convenient starting
material, as it can be prepared in multigram quantities
in a single step from commercial reagents.4 Literature
precedent suggested that alkynylmetal reagents could
substitute the sulfone group, and we therefore began our
investigations at this step. Our first attempts to displace
the sulfone with alkynylzinc reagents met with mixed
success. While phenylethynyl zinc chloride underwent
smooth substitution to generate the product in 64% yield
the procedure could not be reproduced with other alkyne
substrates.2c We were intrigued by a report from Ley and
co-workers in which an alkynylaluminum reagent suc-
cessfully displaced an activated sulfone in a key fragment
coupling toward the synthesis of okadaic acid.5 As
outlined in Table 1, we were pleased to find that addition
of the alkynyl diethyl aluminum reagent to 1 resulted in
a smooth and general protocol for sulfone displacement
that provided an effective means for installing various
alkyne substituents.
The conversion of the pyranyl ethers to the appropriate
rearrangement precursors was carried out under estab-
lished conditions, and the results are outlined in Scheme
2.6 Heating the acetals in the presence of Ph3P‚HBF4 and
molecular sieves provided the phosphonium salts in high
yield as hygroscopic, colorless powders that were con-
verted to Ph-substituted enol ethers after a Wittig
reaction. All complexes were isolated as 1:1 mixtures of
E:Z isomers, although isomers of complexes 10 and 12
were separable by column chromatography.7
While enol ether formation took place in acceptable
overall yield, we briefly investigated alternative condi-
tions for the Wittig reaction. Indeed, as outlined in
Scheme 3, we found that using t-BuOK in place of BuLi
in the formation of the ylide resulted in higher overall
yield in the two instanced examined.
With the enol ether complexes 10-13 in hand, we
turned our attention to the rearrangement reaction.
While previous work had shown that B- and Ti-based
Lewis acids successfully mediated the cyclohexanone
forming reaction, the quality of Lewis acid was critical
for efficient rearrangement, and careful experimentation
was required to achieve reproducibly high yields. In an
effort to develop a more robust and simpler set of reaction
conditions, we explored the use of alternative Lewis acid
promoters. Indeed, we found commercial diethylalumi-
num chloride to be a convenient reagent for the efficient
and reproducible conversion of enol ethers to the corre-
sponding cyclohexanone products; our results are out-
lined in Table 2.8 As we were able to isolate configura-
tionally pure E/Z-isomers of enol ethers 10 and 12, we
were in a position to study their rearrangement reactions
individually. We were pleased to find that these reactions
proceeded smoothly such that the Z-enol ethers were
transformed to the corresponding trans-disubstituted
ketones, whereas E-enol ethers furnished the cis-isomers
(entries 1-4). A similar trend was noted in cases where
E/Z-mixtures of starting complexes were employed (en-
(4) Brown, D. S.; Bruno, M.; Davenport, R. J.; Ley, S. V. Tetrahedron
1989, 45, 4293.
(8) The addition of Lewis acid to noncomplexed enol ether substrates
did not result in rearrangement to the corresponding ketones. A
mixture of recovered starting material and alkene isomerization
products were obtained instead. Additionally, significant substrate
conversions were only observed when >1.0 equiv of diethylaluminium
chloride was employed. Indeed, the Lewis acid character of dialkyla-
luminium chlorides has been found to be highly dependent on reaction
stoichiometry: (a) Evans, D. A.; Chapman, K. T.; Bisaha, J. J. Am.
Chem. Soc. 1988, 110, 1238. (b) Evans, D. A.; Allison, B. D.; Yang, M.
G. Tetrahedron Lett. 1999, 40, 4457. (c) Castellino, S.; Dwight, W. J.
J. Am. Chem. Soc. 1993, 115, 2986.
(5) Ley, S. V.; Humphries, A. C.; Eick, H.; Downham, R.; Ross, A.
R.; Boyce, R. J.; Pavey, J. B. J.; Pietruszka, J. J. Chem. Soc., Perkin
Trans. 1 1998, 3907.
(6) Ley, S. V.; Lygo, B.; Organ, H. M.; Wonnacott, A. Tetrahedron
1985, 41, 3825.
(7) The assignment of E- and Z-stereochemistry in complexes 10
and 11 has been described;2c in both cases, the olefinic CH signal for
the Z-isomer appears upfield in the 1H NMR spectrum. The stereo-
chemical assignments of complexes 12 and 13 were made by analogy.
J. Org. Chem, Vol. 70, No. 24, 2005 10047

Meek et al.
TABLE 2. Al-Mediated Stereoselective Rearrangement
Reaction
SCHEME 4
entrya R, starting material
E/Z
product, % yield (cis/trans)
1
2
3
4
5
6
Ph, 10
Z
14, 97 (0:100)
14, 63 (100:0)
15, 66 (0:100)
15, 80 (100:0)
16, 83 (1:1.5)
17, 89 (1:1)
Ph, 10
E
Me3Si, 12
Me3Si, 12
n-Bu, 11
Z
E
1:1.5
1:1
TBDPSOCH2, 13
a All reactions performed at -78 °C in CH2Cl2 with 1.5 equiv
of Lewis acid.
TABLE 3. Enol Ether Synthesisa
entry
R1
R2
conditionsb product, % yield (E/Z)
1
2
3
4
n-Bu E-CHdCHPh
A
A
B
B
18, 61 (1.1:1)
19, 53 (1.3:1)
20, 76 (100:0)
21, 73 (100:0)
5:1 mixture of cis:trans isomers. Finally, the rearrange-
ment of t-Bu enol ether substrate 21 under similar
conditions gave a new complex that was found to readily
undergo demetalation during chromatography. Accord-
ingly, we employed a mild decomplexation reaction with
TBAF10 upon workup and were pleased to find that the
cis-cyclohexanone 25 had been formed with high levels
of stereoselectivity and in good yield.11 Presumably, the
unusual instability of this complex is due to the proximity
of the bulky Co-alkyne cluster and t-Bu groups in this
compound (Scheme 4).
Accordingly, as described in Table 2 and Scheme 4, the
Et2AlCl-mediated rearrangement reaction provides good
to excellent levels of stereocontrol in the Co-mediated
rearrangement reaction, whereby cis-cyclohexanones are
generated from the corresponding E-enol ether substrates
while the trans-diastereomers are formed from the Z-
isomers (Figure 1). Furthermore, and in direct contrast
to our earlier studies involving Ti- and B-Lewis acids,
this trend is independent of the size of the enol ether
substituent, although the levels of stereochemical control
can be affected by the nature of the enol ether substitu-
ent.
Ph
Ph
Ph
E-CHdCHPh
i-Pr
t-Bu
a Reagents and conditions: (a) (i) ylide formation (see footnote
b), (ii) R2CHO; (b) Co2(CO)8, pet. ether, rt. b Ylide formation:
conditions A, BuLi, THF, -78 °C; conditions B, t-BuOK, THF, -78
°C.
tries 5 and 6). Additionally, a propargylic silyl ether was
tolerated in the rearrangement process (13f17), dem-
onstrating the potential for regioselective Nicholas car-
bocation formation in these systems (entry 6).
We next decided to explore the efficiency and stereo-
selectivity of the rearrangement of substrates bearing
alternative substituents at the enol ether moiety. In
particular, our preliminary reports on the Ti-mediated
rearrangement reaction of E-enol ethers bearing i-Pr and
t-Bu-groups were all found to be highly trans-selective.
Notably, this stereochemical trend is in contrast to that
of enol ethers bearing sterically smaller substituents,
whereby E-enol ethers provide cis-diastereomers with
high levels of stereocontrol.2c Representative substrates
were prepared from the corresponding phosphonium salts
as before (Table 3).9
We first examined the rearrangement of complexes 18
and 19 in an effort to establish the regioselectivity of ring
closure of the intermediate dienolates. In the event,
treatment of these complexes with 1.5 equiv of the Al-
Lewis acid resulted in selective formation of the cyclo-
hexanone products 22 and 23 in moderate to excellent
yield. We next turned our attention to the i-Pr-substi-
tuted enol ether 20. The rearrangement of this substrate
was relatively slow and required elevated temperatures
and long reaction times to provide high yields of the
corresponding product (-30 °C for 24 h). Nonetheless,
these conditions provided ketone 24 in 84% yield as a
(10) Jones, G. B.; Wright, J. M.; Rush, T. M.; Plourde, G. W., II;
Kelton, T. F.; Mathews, J. E.; Huber, R. S.; Davidson, J. P. J. Org.
Chem. 1997, 62, 9379.
(11) The relative stereochemistry was proved by demetalation of
authentic Co-complexed trans-252c
: To a 0.1 M solution of trans-
dicobalthexacarbonyl-2-tert-butyl-3-(2-phenylethynyl)cyclohexanone (28
mg, 0.052 mmol, 1.0 equiv) in THF at room temperature was added
TBAF (1 M in THF, 78 µL, 1.5 equiv). The reaction was stirred for 1.5
h and filtered through a plug of alumina, and the plug was washed
with Et2O (2 × 10 mL) Et2O. The resulting ethereal solution was
shaken with water (10 mL), dried over MgSO4, and filtered through a
pad of Celite. Concentration in vacuo and purification by flash
chromatography (10:1, pet. ether:ether) afforded trans-ketone 25 (13.3
mg, 100%) as a clear oil: 1H NMR (250 MHz, CDCl3) δ 1.07 (9H, s),
1.77-2.53 (7H, m), 3.25-3.33 (1H, m), 7.22-7.30 (3H, m), 7.30-7.39
(2H, m); 13C NMR (62.9 MHz, CDCl3) δ 22.6, 28.7, 29.4, 31.0, 33.8,
41.8, 64.9, 82.6, 92.8, 123.5, 127.8, 128.2, 131.5, 212.5; FTIR (film, υmax
cm-1) 3056, 2960, 2870, 1700, 1598, 1490, 1476, 1443, 1369, 1314 1216;
HRMS (ES) m/z (M++ Na) calcd for C18H22ONa 277.1568, found
277.1556.
(9) The identity of the major isomers of 18 and 19 was not
elucidated.
10048 J. Org. Chem., Vol. 70, No. 24, 2005

Scope of a Co-Mediated OfC Rearrangement Reaction
TABLE 5. Rearrangement toward Spirocyclic Ketones
entry
R
X
product, % yield
1
2
3
4
5
6
7
8
Ph
CH2
CH2
CH2
CH2
NTs
NTs
NTs
34, 91
35, 82
36, 88
37, 97
38, 87
39, 85
40, 94
41, 70
n-Bu
FIGURE 1. Stereochemical rationale of the rearrangement
Me3Si
reaction.
CH2OTBDPS
Ph
TABLE 4. Enol Ether Synthesisa
Me3Si
CH2OTBDPS
CH2OTBDPS
C[(OCH2)2]
SCHEME 5
entry
R
X
product, % yield
1
2
3
4
5
6
7
8
Ph
CH2
CH2
CH2
CH2
NTs
NTs
NTs
26, 35
27, 48
28, 46
29, 54
30, 31
31, 25
32, 47
33, 50
n-Bu
Me3Si
CH2OTBDPS
Ph
Me3Si
CH2OTBDPS
CH2OTBDPS
C[(OCH2)2]
a Reagents and conditions: (a) BuLi, THF, -78 °C; ketone; (b)
Co2(CO)8, CH2Cl2, rt.
We next opted to exploit this technique for the syn-
thesis of more heavily substituted cyclohexanones. Specif-
ically, we were intrigued by the opportunity to prepare
R-spirocyclic systems via the rearrangement of cycloalky-
lidene enol ethers. These substrates were once again
accessed from the phosphonium salts by Wittig olefina-
tion procedures, as outlined in Table 4.12
SCHEME 6a
Not surprisingly, the rearrangement reaction of these
substrates was found to be rather sluggish, however, the
employment of 3 equiv of the Lewis acid followed by
warming the reaction mixture to -30 °C and strirring
overnight provided the R-spirocyclic products in good to
excellent yield. Remarkably, even in these hindered
pyranyl enol ether substrates, we were pleased to find
that the desired Nicholas carbocation could be generated
in the presence of a propargyl ether (entries 4, 7, 8 in
Table 5).
Having demonstrated the effectiveness of Et2AlCl in
the formation of cyclohexanone systems, we decided to
establish the potential of this technique for the formation
of cyclopentanones. Our earlier work with Ti- and B-
based Lewis acids failed to provide cyclopentanone
products by this approach. Our rationale for the failure
of the five-membered ring systems to rearrange was
based on the requirement for a 5-(enolendo)-exo-trig ring
closure reaction on to the Nicholas cation, which is
disfavored on stereoelectronic grounds (Scheme 5).13
Nonetheless, related ring closures are known,14 and we
therefore decided to investigate whether the Al-based
Lewis acid would provide the corresponding cyclopen-
tanone products.
a Reagents and conditions: (a) RCCAlEt2. (b) PPh3‚HBF4, 4 Å
molecular sieves, MeCN, reflux, 48 h. (c) (i) t-BuOK, THF, -78
°C; PhCHO. (ii) Co2(CO)8, CH2Cl2, rt, 1 h.
To establish the feasibility of this transformation, we
decided to prepare a furanyl-based enol ether, and we
employed an analogous procedure to that described in
Scheme 6. Treatment of sulfone 4215 with the alkynyla-
luminum reagent provided 43 and 44 in excellent yield.
Conversion of 43 and 44 to the phosphonium salt and
t-BuOK-mediated Wittig olefination proceeded smoothly
to furnish 47 and 48 after complexation. The complexes
(13) Baldwin, J. E.; Lusch, M. J. Tetrahedron 1982, 38, 2939.
(14) (a) Trost, B. M.; Runge, T. A. J. Am. Chem. Soc. 1981, 103,
2485. (b) Trost, B. M.; Runge, T. A. J. Am. Chem. Soc. 1981, 103, 7559.
(15) Brown, D. S.; Bruno, M.; Davenport, R. J.; Ley, S. V. Tetrahe-
dron 1989, 45, 4293.
(12) Surprisingly, the Wittig reaction was only successful for cyclo-
hexanone derivatives and failed to provide enol ether products when
ketones of other ring sizes were employed.
J. Org. Chem, Vol. 70, No. 24, 2005 10049

Meek et al.
13C NMR (62.5 MHz, CDCl3) δ 98.7, 85.0, 79.4, 60.4, 54.9, 32.2,
30.7, 29.4, 21.9, 18.4, 17.9, 13.5; FTIR (film, υmax cm-1) 2954
(s), 2871 (m), 1457 (m), 1440 (m), 1372 (m), 1196 (m), 1123
(s), 1022 (s); HRMS (EI) m/z (M+) calcd for C12H20O2 196.146330,
found 196.146622.
were isolated as an inseparable 2:1 mixture of E:Z
isomers16 that were used directly in the rearrangement
reaction. Pleasingly, utilizing 3 equiv of Et2AlCl resulted
in conversion of the E/Z mixture of enol ethers 47 and
48 into the corresponding trans-cyclopentanone com-
plexes in 47% and 57% yield, respectively.
(2-(6-Methoxytetrahydro-2H-pyran-2-yl)ethynyl)tri-
methylsilane (4). Reaction of 2-(benzenesulfonyl)tetrahydro-
6-methoxy-2H-pyran (5.0 g, 19.5 mmol) with the alkynylalu-
minum reagent prepared from trimethylsilylacetylene gave
compound 4 (3.6 g, 87%) isolated as a colorless oil containing
an inseparable mixture of diastereomers (cis:trans 1:12.3)
(chromatography, 15:1 petroleum ether/EtOAc). Trans-iso-
mer: 1H NMR (250 MHz, CDCl3) δ 0.00 (9H, s), 1.34-1.72 (6H,
m), 3.23 (3H, s), 4.36 (1H, dd, J ) 10, 3 Hz), 4.56 (1H, m); 13
C
NMR (62.5 MHz, CDCl3) δ 105.0, 98.8, 88.9, 60.6, 55.2, 31.9,
29.4, 17.9, 0.0; FTIR (film, υmax cm-1) 2955 (m), 1441 (w), 1371
(w), 1250 (m), 1196 (m), 1124 (m), 1082 (m), 1061 (m), 1023
(s); HRMS (ES) m/z (M+ + Na) calcd for C11H20O2SiNa
235.1130, found 235.1123.
In conclusion, we have developed a modified protocol
for the OfC rearrangement of Co-alkyne-containing
cyclic enol ethers that uses Et2AlCl. This reagent can be
used as supplied without need for purification and
mediates the rearrangement of a wide range of substrates
in good yield. Additionally, this Lewis acid provides a
consistent stereoselective reaction in the case of cyclo-
hexanone formation such that E-enol ethers furnish cis-
2,3-disubstituted ketones while Z-enol ethers provide the
trans-products. Finally, our observations also suggest
that cyclopentanones can be accessed by this strategy,
albeit in modest yield, via a formally disfavored 5-(eno-
lendo)-exo-trig cyclization.
tert-Butyl(3-(6-methoxytetrahydro-2H-pyran-2-yl)prop-
2-ynyloxy)diphenylsilane (5). Reaction of 2-(benzenesulfo-
nyl)tetrahydro-6-methoxy-2H-pyran (2.86 g, 11.0 mmol) with
the alkynylaluminum reagent prepared from (1,1-dimethyl-
ethyl)diphenyl(2-propyn-1-yloxy)silane gave compound 5 (4.30
g, 94%) isolated as a colorless oil containing an inseparable
mixture of diastereomers (cis:trans 1:5.6) (chromatography,
20:1 petroleum ether/EtOAc). Trans-isomer: 1H NMR (250
MHz, CDCl3) δ 1.05 (9H, s), 1.42-1.91 (6H, m), 3.38 (3H, s),
4.36 (2H, d, J ) 1.5 Hz), 4.53 (1H, d, J ) 9 Hz), 4.69-4.74
(1H, m), 7.33-7.48 (6H, m), 7.66-7.75 (4H, m); 13C NMR (62.5
MHz, CDCl3) δ 135.7, 133.2, 129.8, 127.7, 98.7, 84.3, 82.9, 60.5,
55.1, 52.7, 31.4, 29.4, 26.7, 19.2, 17.9; FTIR (film, υmax cm-1
)
3071 (w), 3049 (w), 2932 (s), 2895 (m), 2858 (s), 1961 (w), 1891
(w), 1825 (w), 1589 (w), 1473 (m), 1428 (m), 1372 (m), 1113
(s), 1079 (s), 1023 (s); HRMS (ES) m/z (M+ + Na) calcd for
C25H32O3SiNa 431.2018, found 431.2029.
Experimental Section
General Procedure for the 2-Substitution of Cyclic
Ethers 1 and 42 with Alkynylaluminum Reagents for
Synthesis of Compounds 2-5, 43, and 44. To a stirred 0.2
M solution of the alkyne (1.2 equiv) in toluene at -78 °C was
added n-BuLi (1.2 equiv) in a dropwise fashion. After 10 min
the reaction was warmed to 0 °C and stirred for a further 15
min. Et2AlCl (1.2 equiv) was added to the reaction. After 30
min at 0 °C the reaction was cooled to -78 °C and the cyclic
sulfone added dropwise via cannula as a solution in DCM (1.5
mL/g). The reaction was slowly warmed to room temperature,
stirred for 16-20 h, and quenched at room temperature by
addition of an equivalent volume of H2O. The mixture was
poured into water and extracted three times with EtOAc. The
combined organic layers were washed with saturated K2CO3
and brine, dried (MgSO4), and concentrated in vacuo. Chro-
matography with silica gel, eluting with an ethyl acetate/
petroleum ether system of appropriate polarity, yielded the
title compounds.
2-Methoxy-6-(2-phenylethynyl)tetrahydro-2H-pyran (2).
Reaction of 2-(benzenesulfonyl)tetrahydro-6-methoxy-2H-py-
ran (5.0 g, 19.5 mmol) with the alkynylaluminum reagent
prepared from phenyl acetylene gave compound 2 (3.77 g, 89%)
isolated as a colorless oil containing an inseparable mixture
of diastereomers (cis:trans 1:3.8) (chromatography, 10:1 pe-
troleum ether/EtOAc). The physical and spectral data were
identical to those previously reported for this compound.2
2-Hex-1-ynyl-6-methoxytetrahydro-2H-pyran (3). Reac-
tion of 2-(benzenesulfonyl)tetrahydro-6-methoxy-2H-pyran (500
mg, 1.3 mmol) with the alkynylaluminum reagent prepared
from 1-hexyne gave compound 3 (227 mg, 93%) isolated as a
colorless oil containing an inseparable mixture of diastereo-
mers (cis:trans 1:3.2) (chromatography, 10:1 petroleum ether/
EtOAc). Trans-isomer: 1H NMR (250 MHz, CDCl3) δ 0.89 (3H,
t, J ) 7 Hz), 1.29-1.90 (10H, m), 2.21 (2H, dt, J ) 7, 2 Hz),
3.39 (3H, s), 4.50 (1H, dd, J ) 9.5, 1.5 Hz), 4.70-4.77 (1H, m);
General Procedure for the Formation of Phospho-
nium Wittig Salts 6-9, 45, and 46. To a round-bottom flask
fitted with a water-jacketed reflux condenser and containing
activated 4 Å molecular sieves was added HPPh3BF4 (2 equiv,
0.4 M in MeCN) followed by the cyclic acetal (1 equiv, 0.2 M
in MeCN). The mixture was heated to reflux (82 °C) and stirred
until complete consumption of the starting material was
observed by TLC (16-18 h). The reaction was cooled to room
temperature, diluted with DCM, and filtered through a Celite
pad under reduced pressure. Concentration of the filtrate in
vacuo afforded a crude residue, which was dissolved in DCM,
refiltered over Celite, and concentrated. To the resulting
residue taken up in DCM (2-5 mL) was added a 1:1 mixture
diethyl ether/hexane (50-100 mL) and the mixture was
subjected to a vigorous agitation for 10 min until the cloudy
suspension became clear. The solvent was decanted to leave a
gummy residue. The previous operation was repeated until
the addition of diethyl ether/hexane no longer gave a cloudy
suspension. The residue was then dissolved in DCM, filtered
through a pad of Celite, and concentrated to yield the corre-
sponding Wittig salt as a solid.
Triphenyl(6-(2-phenylethynyl)tetrahydro-2H-pyran-2-
yl)phosphonium tetrafluoroborate (6) was prepared as
described above using pyranyl ether 2 (3.77 g, 17.4 mmol) and
isolated as a pale yellow solid containing an inseparable 1.1:1
mixture of diastereomers (8.40 g, 90%). The physical and
spectral data were identical to those previously reported for
this compound.2
(6-Hex-1-ynyltetrahydro-2H-pyran-2-yl)triphenylphos-
phonium tetrafluoroborate (7) was prepared as described
above using cyclic acetal 3 (82 mg, 0.418 mmol) and isolated
as a pale yellow solid containing an inseparable 1.3:1 mixture
of diastereomers (205 mg, 95%). The physical and spectral data
were identical to those previously reported for this compound.2
Triphenyl(6-(2-(trimethylsilyl)ethynyl)tetrahydro-2H-
pyran-2-yl)phosphon ium tetrafluoroborate (8) was pre-
(16) The identity of the major isomer was not elucidated.
10050 J. Org. Chem., Vol. 70, No. 24, 2005

Scope of a Co-Mediated OfC Rearrangement Reaction
pared as described above using pyranyl ether 4 (3.6 g, 16.97
mmol) and isolated as a white powder containing an insepa-
rable 1.4:1 mixture of diastereomers (8.24 g, 92%): 1H NMR
(250 MHz, CDCl3) δ 0.00 (9H, s), 0.13 (9H, s), 1.39-2.01 (12H,
m), 4.53 (1H, d. J ) 10 Hz), 4.79-4.85 (1H, m), 5.42-5.52 (1H,
m), 5.64-5.75 (1H, m), 7.50-7.79 (30H, m); 13C NMR (62.5
MHz, CDCl3) see Supporting Information; FTIR (film, υmax
cm-1) 3646 (w), 3559 (w), 3065 (w), 2958 (m), 2262 (w), 1823
(w), 1588 (w), 1485 (w), 1440 (s), 1251 (m), 1195 (m), 1111 (s),
1058 (s); HRMS (FAB) m/z (M+ - BF4) calcd for C28H32OSiP
443.1960, found 443.1976.
E/Z-Dicobalthexacarbonyl-2-benzylidene-6-(phenyl-
ethynyl)tetrahydro-2H-pyran (10) (Wittig method A) was
isolated as a dark red oil (280 mg, 69% from 6) containing a
separable 1:1 mixture of stereoisomers (E)-10 (122 mg, 30%)
and (Z)-10 (129 mg, 32%) as dark red oils (chromatography,
100:1 petroleum ether/Et3N). The physical and spectral data
were identical to those previously reported for this compound.
2
E/Z-Dicobalthexacarbonyl-2-benzylidene-6-hex-1-yn-
yltetrahydro-2H-pyran (11) (Wittig method A) was isolated
as a dark red oil (125 mg, 59% from 7) containing an insep-
arable 1:1 mixture of (E)- and (Z)-stereoisomers (chromatog-
raphy, 100:1:1 petroleum ether/Et3N/Et2O). The physical and
spectral data were identical to those previously reported for
this compound.2
(6-(3-tert-Butyldiphenylsilyloxy)prop-1-ynyl)tetrahy-
dro-2H-pyran-2-yl)triphenylphosphonium tetrafluoro-
borate (9) was prepared as described above using pyranyl
ether 5 (5.36 g, 13.13 mmol) and isolated as a pale yellow solid
containing an inseparable 1:1 mixture of diastereomers (8.44
g, 88%): 1H NMR (250 MHz, CDCl3) δ 1.00 (9H, s), 1.02 (9H,
s), 1.44-2.13 (12H, m), 4.25-4.32 (2H, m), 4.50-5.56 (2H, m),
4.63 (1H, br d, J ) 10.5 Hz), 4.87-4.95 (1H, m), 5.39-5.53
(1H, m), 5.73-5.87 (1H, m), 7.24-7.91 (50H, m); 13C NMR
(62.5 MHz, CDCl3) see Supporting Information; FTIR (film,
υmax cm-1) 3644 (w), 3552 (w), 3070 (m), 2957 (m), 2858 (m),
2263 (w), 1976 (w), 1903 (w), 1826 (w), 1588 (m), 1440 (s), 1112
(s) 1061 (s); HRMS (FAB) m/z (M+ - BF4) calcd for C42H44O2-
SiP 639.2848, found 639.2817.
E/Z-Dicobalthexacarbonyl-((6-benzylidenetetrahydro-
2H-pyran-2-yl)ethynyl)trimethylsilane (12) (Wittig method
A) was isolated as a dark red oil (162 mg, 59% from 8)
containing a separable 1:1 mixture of stereoisomers (E)-12 (82
mg, 30%) and (Z)-12 (80 mg, 32%) as dark red oils (chroma-
tography, 100:1:1 petroleum ether/Et3N/Et2O). (Z)-12: 1H
NMR (250 MHz, CDCl3) δ 0.32 (9H, s), 1.65-2.17 (4H, m),
2.30-2.45 (2H, m), 4.93 (1H, br d, J ) 10.5 Hz), 5.48 (1H, s),
7.07-7.33 (3H, m), 7.56-7.67 (2H, m); 13C NMR (62.9 MHz,
CDCl3) δ 200.1, 154.0, 135.8, 128.4, 127.9, 125.7, 110.4, 108.2,
107.5, 79.1, 78.3, 35.3, 30.9, 23.4, 0.9; FTIR (film, υmax cm-1
)
3057 (w), 2955 (m), 2866 (w), 2090 (s), 2049 (s), 2022 (s), 1729
(w), 1657 (m), 1576 (w), 1446 (w), 1364 (w), 1250 (m), 1164
(w), 1132 (w), 1066 (w), 1036 (w); HRMS (ES) m/z (M+ + H)
calculated for C23H23O7SiCo2 556.9877, found 556.9861. (E)-
12: 1H NMR (250 MHz, CDCl3) δ 0.33 (9H, s), 1.61-2.39 (5H,
m), 2.86 (1H, br d, J ) 13.5 Hz), 4.78 (1H, br d, J ) 7.5 Hz),
6.12 (1H, s), 7.11-7.37 (5H, m); 13C NMR (62.9 MHz, CDCl3)
δ 200.5, 155.7, 136.8, 129.1, 128.5, 126.0, 111.3, 110.3, 80.0,
78.4, 34.4, 25.2, 23.0, 1.1; FTIR (film, υmax cm-1) 3025 (w), 2955
(m), 2090 (s), 2049 (s), 2023 (s), 1657 (m), 1574 (w), 1446 (w),
1365 (w), 1250 (m), 1164 (w), 1132 (w), 1066 (w), 1136 (w);
HRMS (ES) m/z (M+ + H) calculated for C23H23O7SiCo2
556.9877, found 556.9874.
General Procedure for the Conversion of Wittig Salts
into Cyclic Enol Ether Complexes for Compounds 10-
13, 18-21, 26-33, 47, and 48. Method A. The appropriate
amount of n-BuLi (1.1 equiv) was added dropwise to a 0.1 M
solution of the phosphonium salt (1 equiv) in THF at -78 °C.
The deep red solution was stirred for a further 5 min prior to
addition of the neat aldehyde or ketone (1.1 equiv). The
reaction was stirred for 2 h at -78 °C, unless stated otherwise,
warmed to room temperature, and quenched by addition of
water. The mixture was poured into water and extracted three
times with Et2O. The combined organic layers were washed
with water and brine, dried (MgSO4), filtered through a pad
of Celite, and concentrated in vacuo. The crude enol ether was
dissolved in 1 mL of ether and treated with 20 mL of petroleum
ether before cooling to -78 °C and decanting the organic
extracts from the formed precipitates through a pad of Celite,
and the solvent was removed in vacuo. The crude enol ether
in DCM (0.2 M) was added via cannula to a 0.2 M solution of
octacarbonyldicobalt (1.1 equiv) in DCM at room temperature.
After stirring for 1 h the mixture was filtered through a pad
of Celite, concentrated, and purified by silica gel chromatog-
raphy.
E/Z-Dicobalthexacarbonyl-[3-(6-benzylidenetetrahy-
dro-2H-pyran-2-yl)prop-2-ynyloxy]tert-butyldiphenylsi-
lane (13) (Wittig method A) was isolated as a dark orange oil
(132 mg, 64% from 9) containing a separable 1:1 mixture of
stereoisomers (E)-13 (66 mg, 32%) and (Z)-13 (66 mg, 32%) as
orange oils (chromatography, 100:1:1 petroleum ether/Et3N/
Et2O). (Z)-13: 1H NMR (250 MHz, CDCl3) δ 1.09 (9H, s), 1.64-
2.14 (4H, m), 2.28-2.37 (2H, m), 4.80 (1H, dd, J ) 10.5, 2.5
Hz), 4.83 (1H, d, J ) 14 Hz), 4.92 (1H, d, J ) 14 Hz), 5.42
(1H, s), 6.89-7.02 (3H, m), 7.35-7.52 (8H, m), 7.69-7.79 (4H,
m); 13C NMR (62.5 MHz, CDCl3) δ 199.5 (br), 154.2, 135.8,
135.6, 132.9, 129.9, 128.1, 127.9 (×2), 125.6, 107.9, 96.4, 95.0,
78.6, 64.7, 33.4, 30.5, 26.6, 23.0, 19.2; FTIR (film, υmax cm-1
)
Method B. To a 0.2 M solution of KOtBu (1.2 equiv) in THF
at -78 °C was added via cannula the phosphonium salt (1
equiv, 0.2 M in THF). After 1 h the neat aldehyde (1.2 equiv)
was added to the red mixture and the reaction slowly warmed
to room temperature. The reaction was stirred for a further
16 h and quenched by the addition of water. The mixture was
poured into water and the organics extracted three times with
Et2O. The combined organic layers were washed with water
and brine, dried (MgSO4), and filtered through a pad of Celite
and concentrated. The crude mixture was taken up in 1 mL
of Et2O or DCM and treated with 20 mL of petroleum ether.
The resulting solution was cooled to -78 °C, the organic
extracts were decanted from the formed precipitates through
a pad of Celite, and the solvent was removed in vacuo. To a
solution of octacarbonyldicobalt (1.1 equiv) in either DCM or
petroleum ether (0.2 M) at room temperature was added a 0.2
M solution of the crude enol ether in the same solvent. After
stirring for 1 h the mixture was filtered through a pad of Celite,
concentrated, and purified by silica gel chromatography.
3073 (w), 2934 (m), 2860 (m), 2094 (s), 2053 (s), 2030 (s), 1659
(w), 1600 (w), 1429 (w), 1352 (w), 1301 (w), 1166 (w), 1113
(m), 1062 (m), 1030 m); HRMS (ES) m/z (M+ + H) calcd for
C37H35O8SiCo2 753.0765, found 753.0740. (E)-13: 1H NMR (250
MHz, CDCl3) δ 1.08 (9H, s), 1.55-1.90 (3H, m), 1.96-2.08 (1H,
m), 2.19-2.37 (1H, m), 2.78 (1H, dt, J ) 14.5, 3.5 Hz), 4.76
(1H, dd, J ) 10, 2.5 Hz), 4.83 (2H, s), 6.07 (1H, s), 7.10-7.20
(3H, m), 7.22-7.33 (2H, m), 7.35-7.51 (6H, m), 7.68-7.78 (4H,
m); 13C NMR (100 MHz, CDCl3) δ 199.6 (br), 155.1, 136.4,
135.6, 132.9, 129.8, 128.7, 128.1, 127.8, 125.6, 110.0, 95.8, 95.2,
79.3, 64.6, 33.0, 26.6, 24.8, 22.2, 19.1; FTIR (film, υmax cm-1
)
3073 (w), 2934 (m), 2860 (m), 2094 (s), 2053 (s), 2030 (s), 1656
(w), 1600 (w), 1473 (w), 1429 (w), 1232 (w), 1113 (m), 1065
(m), 1039 (m); HRMS (ES) m/z (M+ + H) calcd for C37H35O8-
SiCo2 753.0765, found 753.0754.
General Procedure for Et2AlCl-Promoted Rearrange-
ment of Cyclic Enol Ethers 10-13 and 18-20 to Cyclo-
hexanones. To a solution of the complex (1 equiv) in DCM
(0.02 M) at -78 °C was added diethylaluminum chloride (1.5
equiv, 1 M in hexanes). The reaction was stirred for the
J. Org. Chem, Vol. 70, No. 24, 2005 10051

Meek et al.
indicated amount of time at the stated temperature, quenched
by addition of water, and then warmed to ambient tempera-
ture. The mixture was poured into water and extracted three
times with Et2O. The combined organic layers were washed
with brine, dried over MgSO4, and concentrated in vacuo. The
crude reaction mixture was then chromatographed on silica
gel, eluting with petroleum ether/Et2O (10:1).
cis-Dicobalthexacarbonyl-2-phenyl-3-(2-phenylethynyl)-
cyclohexanone (cis-14) was isolated from (E)-10 (25 mg,
0.046 mmol) following the general procedure with a reaction
time of 2 h at -78 °C, as a single diastereomer and as a dark
red oil (16 mg, 63%). The physical and spectral data were
identical to those previously reported for this compound.2
trans-Dicobalthexacarbonyl-2-phenyl-3-(2-phenylethy-
nyl)cyclohexanone (trans-14) was isolated from (Z)-10 (13
mg, 0.024 mmol) following the general procedure with a
reaction time of 2 h at -78 °C, as a single diastereomer and
as a dark red solid (12 mg, 97%). The physical and spectral
data were identical to those previously reported for this
compound.2
2.42-2.63 (3H, m), 2.89 (1H, d, J ) 15.0 Hz), 3.31-3.48 (2H,
m), 3.53 (1H, d, J ) 15.0 Hz), 6.52-6.62 (1H, m), 6.72-6.88
1
(4H, m), 7.45-7.63 (10H,m); H NMR (250 MHz, benzene-d6)
δ 1.12 (9H, s), 1.28-1.44 (1H, m), 1.46-1.60 (1H, m), 1.67-
2.06 (2H, m), 2.13-2.28 (2H, m), 3.09 (1H, d, J ) 15.0 Hz),
3.12 (1H, d, J ) 12.0 Hz), 3.19 (1H, ddd, J ) 22.5, 12.0, 3.5
Hz), 3.69 (1H, d, J ) 15.0 Hz), 6.44-6.52 (1H, m), 6.64-6.80
(4H, m), 7.21-7.30 (6H, m), 7.61-7.69 (4H, m); 13C NMR (100
MHz, CDCl3) δ 207.9, 199.9 (br), 136.1, 135.6, 135.5, 132.8,
129.6, 129.5, 129.0, 128.5, 127.6, 127.5, 100.0, 99.4, 64.0, 62.9,
47.4, 41.5, 34.9, 26.5, 24.9, 18.9; FTIR (film, υmax cm-1) 3071
(w), 2933 (m), 2859 (m), 2089 (s), 2049 (s), 2029 (s), 1719 (m),
1605 (w), 1428 (m), 1354 (w), 1112 (m), 1057 (m); HRMS (ES)
m/z (M+ + H) calcd for C37H35O8SiCo2 753.0765, found 753.0771.
(E/Z)-Dicobalthexacarbonyl-2-hex-1-ynyl-6-((E)-3-phen-
ylallylidene)tetrahydro-2H-pyran (18) (Wittig method A)
was isolated as a dark red oil (258 mg, 61% from 7) containing
an inseparable 1.1:1 mixture of (E)-18 and (Z)-18 stereoisomers
(chromatography, 100:1:1 petroleum ether/Et3N/Et2O). (E/Z)-
18: 1H NMR (250 MHz, CDCl3) δ 0.98 (6H, t, J ) 7.0 Hz),
1.44-2.44 (19H, m), 2.75-2.91 (5H, m), 4.76-4.86 (2H, m),
5.41 (1H, d, J ) 11.0 Hz), 5.86 (1H, br d, J ) 12.5 Hz), 6.37
(1H, d, J ) 16.0 Hz), 6.42 (1H, d, J ) 15.5), 6.86 (1H, dd, J )
15.0, 11.0 Hz), 7.15-7.20 (1H, m), 7.23-7.38 (10H, m); 13C
NMR (62.5 MHz, CDCl3) δ 200.0 (br), 156.4, 154.7, 138.3,
138.2, 128.5 (×2), 128.4 (×2), 127.8, 126.7, 126.6, 125.9 (×2),
125.8 (×2), 123.9, 122.9, 110.3, 109.2, 98.7, 96.6, 79.4, 79.0,
34.1, 34.0, 33.5, 33.2, 33.1, 29.3, 24.4, 22.8, 22.7, 22.6, 22.1,
13.9 (×2); FTIR (film, υmax cm-1) 2934 (m), 2837 (m), 2090 (s),
2048 (s), 1647 (m), 1595 (m), 1448 (w), 1298 (m), 1031 (m);
HRMS (ES) m/z (M+) calcd for C26H24O7Co2 566.01860, found
566.01908.
(E/Z)-Dicobalthexacarbonyl-2-((E)-3-phenylallylidene)-
6-(2-phenylethynyl)tetrahydro-2H-pyran (19) (Wittig
method A) was isolated as a dark red oil (134 mg, 53% from
6) containing an inseparable 1.3:1 mixture of (E)-19 and (Z)-
19 stereoisomers (chromatography, 100:1:1 petroleum ether/
Et3N/Et2O). (E/Z)-19: 1H NMR (250 MHz, CDCl3) δ 1.79-2.06
(6H, m), 2.18-2.42 (4H, m), 2.82-2.92 (1H, m), 4.99 (1H, dd,
J ) 10.5, 2.5 Hz), 5.09 (1H, dd, J ) 10.5, 2.5 Hz), 5.45 (1H,
app d, J ) 10.5 Hz), 5.95 (1H, dd, J ) 11.5, 1.5 Hz), 6.38 (1H,
d, J ) 16.0 Hz), 6.45 (1H, d, J ) 16.5 Hz), 6.85 (1H, dd, J )
15.5, 11.0 Hz), 7.15-7.40 (17H, m), 7.58-7.63 (5H, m); 13C
NMR (62.5 MHz, CDCl3) δ 199.3 (br), 156.4, 154.6, 138.2,
137.7, 129.8 (×2), 129.6, 128.9, 128.8 (×2), 128.7, 128.5, 128.4
(×2), 128.0, 127.9, 127.8, 126.7, 126.6, 126.0, 125.8 (×2), 123.8,
122.8, 110.4, 109.3, 96.5, 90.0, 79.5, 78.9, 33.3, 33.2, 29.3, 24.4,
22.7, 22.3; FTIR (film, υmax cm-1) 3029 (m), 2949 (m), 2868 (m),
2091 (s), 2053 (s), 1645 (m), 1595 (m), 1484 (m), 1442 (m), 1264
(m), 1200 (m), 1164 (m), 1128 (m), 1030 (m); HRMS (ES) m/z
(M+) calcd for C28H20O7Co2 585.98730, found 585.98501.
(E)-Dicobalthexacarbonyl-2-isobutylene-6-(phenylethy-
nyl)tetrahydro-2H-pyran (20) (Wittig method B) was iso-
lated following complexation in petroleum ether (40-60) as a
dark red oil (301 mg, 76% from 6) and as a single stereoisomer
(chromatography, 100:1:10 petroleum ether/Et3N/Et2O). The
physical and spectral data were identical to those previously
reported for this compound.2
(E)-Dicobalthexacarbonyl-2-(2,2-dimethylpropylidene)-
6-(phenylethynyl)tetrahydro-2H-pyran (21) (Wittig method
B) was isolated following complexation in petroleum ether (40-
60), as a dark red oil (178 mg, 73% from 6) and as a single
stereoisomer (chromatography, 100:1:10 petroleum ether/Et3N/
Et2O). The physical and spectral data were identical to those
previously reported for this compound.2
cis/trans-Dicobalthexacarbonyl-3-hex-1-ynyl-2-((E)-
styryl)cyclohexanone (22) was isolated from E/Z-18 (59 mg,
0.10 mmol, E/Z 1.1:1) according to the general procedure with
a reaction time of 1 h at -78 °C, as a dark red oil containing
a 1.1:1 (cis:trans) mixture of diastereomers (32 mg, 54%)
(chromatography, 10:1 petroleum ether/Et2O). For the pur-
poses of characterization, the diastereomers were partially
cis-Dicobalthexacarbonyl-2-phenyl-3-(2-(trimethylsi-
lyl)ethynyl)cyclohexanone (cis-15) was isolated from (E)-
12 (52 mg, 0.093 mmol) following the general procedure with
a reaction time of 1.1 h at -78 °C, as a single diastereomer
and as a brown-red oil (41 mg, 80%). 1H NMR (400 MHz,
CDCl3) δ 0.19 (9H, s), 1.85-2.01 (1H, m), 2.14-2.40 (3H, m),
2.64 (1H, td, J ) 13.5, 4.0 Hz), 2.79 (1H, td, J ) 14.5, 6.5 Hz),
3.64 (1H, app dt, J ) 13.0, 5.0 Hz), 4.00 (1H, d, J ) 5.5 Hz),
7.17-7.37 (3H, m), 7.46-7.58 (2H, m); 13C NMR (100 MHz,
CDCl3) δ 209.1, 200.4, (br), 135.6, 130.4, 129.0, 127.8, 110.7,
80.1, 63.7, 48.5, 36.4, 31.3, 25.2, 0.9; FTIR (film, υmax cm-1
)
3062 (w), 3031 (w), 2958 (m), 2085 (s), 2045 (s), 2015 (s), 1714
(s), 1602 (w), 1496 (w), 1452 (w), 1249 (m); HRMS (ES) m/z
(M+ + H) calcd for C23H23O7SiCo2 556.9877, found 556.9884.
trans-Dicobalthexacarbonyl-2-phenyl-3-(2-(trimethyl-
silyl)ethynyl)cyclohexanone (trans-15) was isolated from
(Z)-12 (60 mg, 0.11 mmol) following the general procedure with
a reaction time of 4.5 h at -78 °C, as a single diastereomer
1
and as a brown-red solid (40 mg, 66%): mp 101-102 °C; H
NMR (400 MHz, CDCl3) δ 0.20 (9H, s), 1.85-2.04 (2H, m),
2.13-2.22 (1H, m), 2.36-2.52 (2H, m), 2.57-2.66 (1H, m), 3.56
(1H, d, J ) 9.5 Hz), 3.81 (1H, td, J ) 9.5, 4.0 Hz), 7.17-7.22
(2H, m), 7.25-7.38 (3H, m); 13C NMR (100 MHz, CDCl3) δ
208.9, 200.3 (br), 136.5, 129.2, 128.8, 127.6, 114.8, 80.8, 63.9,
46.0, 40.3, 35.4, 23.7, 1.0; FTIR (film, υmax cm-1) 3033 (w), 2957
(w), 2086 (s), 2046 (s), 2015 (s), 1716 (m), 1576 (w), 1538 (w),
1498 (w), 1449 (w), 1249 (m); HRMS (ES) m/z (M+ + Na) calcd
for C23H22O7SiCo2Na 578.9696, found 578.9703.
cis/trans-Dicobalthexacarbonyl-3-hex-1-ynyl-2-phen-
ylcyclohexanone (16) was isolated from (E/Z)-11 (36 mg,
0.066 mmol, E/Z 1:1.5) following the general procedure with
a reaction time of 15 min at -78 °C, as a dark red oil
containing an inseparable 1.5:1 (cis:trans) mixture of diaster-
eomers (30 mg, 83%). The physical and spectral data were
identical to those previously reported for this compound.2
cis/trans-Dicobalthexacarbonyl-3-(3-(tert-butyldiphen-
ylsilyloxy)prop-1-ynyl)-2-phenylcyclohexanone (17) was
isolated from (E/Z)-13 (292 mg, 0.39 mmol, E/Z 1:1) following
the general procedure with a reaction time of 15 min at -78
°C, as a dark red oil containing a 1:1 (cis:trans) mixture of
diastereomers (261 mg, 89%). cis-17: 1H NMR (250 MHz,
CDCl3) δ 1.00 (9H, s), 1.81-2.04 (1H, m), 2.10-2.55 (4H, m),
2.66-2.84 (1H, m), 3.50-3.70 (2H, m), 3.89 (1H, app d, J )
5.5 Hz), 4.08 (1H, d, J ) 14.0 Hz), 6.78-6.98 (3H, m), 7.25-
7.68 (12H, m); 13C NMR (100 MHz, CDCl3) δ 208.9, 199.7 (br),
135.9, 135.6, 135.5, 132.9, 132.7, 129.7, 128.9, 127.7, 97.9, 95.8,
63.8, 62.7, 48.3, 36.7, 31.5, 26.5, 25.0, 19.0; FTIR (film, υmax
cm-1) 3071 (w), 2933 (m), 2859 (m), 2089 (s), 2047 (s), 2025
(s), 1713 (m), 1590 (w), 1428 (m), 1362 (m), 1111 (m), 1059
(m); HRMS (ES) m/z (M+ + H) calcd for C37H35O8SiCo2
753.0765, found 753.0760. trans-17: 1H NMR (250 MHz,
CDCl3) δ 0.96 (9H, s), 1.85-2.07 (2H, m), 2.20-2.39 (1H, m),
10052 J. Org. Chem., Vol. 70, No. 24, 2005

Scope of a Co-Mediated OfC Rearrangement Reaction
separated by careful chromatography. cis-22: 1H NMR (250
MHz, CDCl3) δ 0.85 (3H, t, J ) 7.0 Hz), 1.21-1.36 (2H, m),
1.40-1.70 (3H, m), 1.80-1.92 (1H, m), 2.08-2.27 (2H, m),
2.34-2.39 (1H, m), 2.58 (1H, dd, J ) 14.0, 6.0 Hz), 2.74-2.76
(2H, m), 3.29-3.41 (1H, m), 3.53-3.61 (1H, m), 6.40 (1H, dd,
J ) 16.0, 8.5 Hz), 6.58 (1H, d, J ) 16.0 Hz), 7.21-7.38 (5H,
m); 13C NMR (125 MHz, CDCl3) δ 208.6, 200.1 (br), 136.3,
135.6, 128.6, 128.1, 126.3, 121.9, 100.7, 97.8, 61.2, 47.8, 38.5,
34.0 (×2), 30.1, 25.4, 22.6, 13.7; FTIR (film, υmax cm-1) 3028
(w), 2959 (m), 2933 (m), 2873 (m), 2086 (s), 2016 (s), 1716 (s),
1600 (w), 1450 (w); HRMS (ES) m/z (M+ + Na) calcd for C26
H24O7NaCo2 589.0084, found 589.0110. trans-22: 1H NMR (250
MHz, CDCl3) δ 0.74 (3H, t, J ) 7.0 Hz), 0.89-1.09 (3H, m),
1.22-1.53 (2H, m), 1.83-1.96 (2H, m), 2.17-2.36 (2H, m),
2.46-2.61 (3H, m), 3.03-3.23 (2H, m), 6.19 (1H, dd, J ) 16.0,
8.5 Hz), 6.50 (1H, d, J ) 16.0 Hz), 7.23-7.40 (5H, m); 13C NMR
(125 MHz, CDCl3) δ 209.2, 200.2 (br), 136.6, 134.8, 128.6,
127.8, 126.3 (×2), 101.9, 101.5, 61.9, 48.1, 41.4, 34.8, 34.0, 33.9,
24.9, 22.4, 13.7; FTIR (film, υmax cm-1) 3028 (w), 2933 (m), 2872
(m), 2006 (s), 2016 (s), 1715 (s), 1601 (w), 1449 (w), 1248 (w),
1165 (w), 1030 (w); HRMS (ES) m/z (M+ + Na) calcd for C26
H24O7NaCo2 589.0084, found 589.0110.
(0.02 M) at -78 °C was slowly added Et2AlCl (2 equiv). The
reaction was stirred for 5 min at -78 °C, warmed to -30 °C,
and stirred for 24 h. The reaction was quenched at -30 °C
with H2O, warmed to ambient temperature, and extracted
twice with Et2O. The organic layer was washed with water
and brine, dried over MgSO4, and concentrated in vacuo to
yield the crude ketone. The crude residue was taken up in THF
(0.1 M), treated with TBAF (1 M in THF, 157 µL, 0.157 mmol,
1.0 equiv), and stirred for 2 h at room temperature. The
solution was filtered through a plug of alumina and the plug
washed with Et2O (2 × 10 mL). The resulting ethereal solution
was washed with water (10 mL), dried over MgSO4, filtered
through a pad of Celite, and concentrated in vacuo. Purification
by flash chromatography (10:1 petroleum ether/Et2O) afforded
ketone 25 (27 mg, 67%) as a clear oil and as an inseparable
mixture of stereoisomers (cis/trans; 15:1). cis-25: 1H NMR (250
MHz, CDCl3) δ 1.14 (9H, s), 1.85-2.43 (7H, m), 3.53-3.60 (1H,
m), 7.22-7.29 (3H), 7.30-7.38 (2H, m); 13C NMR (62.5 MHz,
CDCl3) δ 209.7, 131.4, 128.2, 127.8, 123.5, 89.9, 85.8, 63.0, 43.8,
33.0, 32.8, 32.7, 28.5, 24.0; FTIR (film, υmax cm-1) 3057 (w),
2954 (s), 2867 (m), 1715 (s), 1598 (w), 1490 (m), 1444 (w), 1362
(m), 1117 (m); HRMS (EI) m/z (M+) calcd for C18H22O 254.1671,
found 254.1682.
cis/trans-Dicobalthexacarbonyl-3-(phenylethynyl)-2-
((E)-styryl)cyclohexanone (23) was isolated from E/Z-19 (38
mg, 0.065 mmol, E/Z 1.3:1) according to the general procedure
with a reaction time of 1 h at -78 °C, as a dark red oil con-
taining a 1.5:1 (cis:trans) mixture of diastereomers (32 mg,
84%) (chromatography, 10:1 petroleum ether/Et2O). For the
purposes of characterization, the diastereomers were partially
separated by careful chromatography. cis-23: 1H NMR (500
MHz, CDCl3) δ 1.82-1.94 (1H, m), 2.20-2.40 (4H, m), 2.60
(1H, td, J ) 14.0, 6.0 Hz), 3.55 (1H, dt, J ) 12.0, 4.0 Hz), 3.58-
3.62 (1H, m), 6.21 (1H, dd, J ) 16.0, 8.0 Hz), 6.35 (1H, d, J )
16.0 Hz), 6.89-6.94 (2H, m), 7.10-7.20 (3H, m), 7.30-7.35
(3H, m), 7.40-7.44 (2H, m); 13C NMR (125 MHz, CDCl3) δ
208.7, 199.4 (br), 138.2, 136.2, 135.7, 129.2, 129.0, 128.3, 127.7,
127.5, 126.3, 121.8, 99.1, 93.1, 60.8, 47.4, 38.4, 30.1, 25.5; (film,
υmax cm-1) 2928 (w), 2088 (s), 2049 (s), 2019 (s), 1714 (m), 1442
(w), 1177 (w); HRMS (ES) m/z (M+ + Na) calcd for C28H20O7-
Co2Na 608.9771, found 608.9761. trans-23: 1H NMR (500
MHz, CDCl3) δ 1.91-2.08 (2H, m), 2.20-2.32 (1H, m), 2.38-
2.42 (1H, m), 2.43-2.52 (1H, m), 2.54-2.61 (1H, m), 3.13 (1H,
app t, J ) 9.0 Hz), 3.50 (1H, td, J ) 11.0, 4.0 Hz), 5.91 (1H,
dd, J ) 16.0, 9.0 Hz), 6.15 (1H, d, J ) 16.0 Hz), 6.82-6.84
(2H, m), 7.05-7.12 (3H, m), 7.13-7.21 (3H, m), 7.22-7.33 (2H,
m); 13C NMR (125 MHz, CDCl3) δ 209.1, 199.6 (br), 138.2,
136.3, 135.3, 128.8, 128.7, 128.0, 127.2, 127.1, 126.2, 125.7,
Dicobalthexacarbonyl-2-cyclohexylidene-6-(phenyl-
ethynyl)tetrahydro-2H-pyran (26) (Wittig method A) was
prepared using freshly distilled cyclohexanone and phospho-
nium salt 6 (2.034 g, 3.81 mmol). Following complexation in
petroleum ether (40-60) and chromatography (100:1 petro-
leum ether/Et3N), complex 26 (741 mg, 35% from 6) was
1
isolated as a deep red solid: mp 119-120 °C; H NMR (250
MHz, CDCl3) δ 1.37-1.60 (6H, m), 1.62-1.84 (2H, m), 1.89-
2.30 (6H, m), 2.32-2.45 (1H, m), 2.57-2.70 (1H, m), 4.76 (1H,
dd, J ) 10.5, 2.5 Hz), 7.27-7.38 (3H, m), 7.50-7.61 (2H, m);
13C NMR (62.5 MHz, CDCl3) δ 199.6 (br), 144.0, 138.0, 129.7,
128.8, 127.7, 119.9, 97.9, 89.6, 79.6, 34.3, 29.0, 28.3, 27.7, 27.0,
26.6, 24.4 (×2); FTIR (film, υmax cm-1) 2926 (w), 2853 (w), 2091
(s), 2051 (s), 2022 (s), 1682 (w); HRMS (EI) m/z (M+) calcd for
C25H22O7Co2 552.0029, found 552.0036.
Dicobalthexacarbonyl-2-cyclohexylidene-6-hex-1-yn-
yltetrahydro-2H-pyran (27) (Wittig method A) was prepared
using freshly distilled cyclohexanone and phosphonium salt 7
(681 mg, 1.32 mmol). Following complexation in DCM and
chromatography (100:1 petroleum ether/Et3N) complex 27 (335
mg, 48% from 7) was isolated as a deep red oil. 1H NMR (250
MHz, CDCl3) δ 0.96 (3H, t, J ) 7.0 Hz), 1.38-1.56 (8H, m),
1.56-1.70 (4H, m), 1.86-2.01 (3H, m), 2.02-2.17 (2H, m),
2.18-2.40 (2H, m), 2.52-2.64 (1H, m), 2.77-2.87 (2H, m), 4.51
(1H, dd, J ) 10.5, 2.5 Hz); 13C NMR (62.5 MHz, CDCl3) δ 200.1
(br), 144.0, 119.6, 98.5, 97.9, 79.4, 34.0 (×2), 33.6, 28.9, 28.2,
102.2, 94.1, 62.1, 53.4, 41.3, 34.3, 25.0; FTIR (film, υmax cm-1
)
2948 (w), 2088 (s), 2048 (s), 2019 (s), 1714 (s), 1442 (m); HRMS
(ES) m/z (M+ + Na) calcd for C28H20O7Co2Na 608.9771, found
608.9793.
27.7, 26.9, 26.5, 24.3 (×2), 22.7, 13.9; FTIR (film, υmax cm-1
)
2930 (s), 2855 (s), 2090 (s), 2047 (s), 2014 (s), 1681 (m), 1616
(m), 1450 (m), 1035 (s); HRMS (ES) m/z (M+ + H) calcd for
C23H27O7Co2 533.0421, found 533.0414.
cis trans-Dicobalthexacarbonyl-2-isopropyl-3-(2-phen-
ylethynyl)cyclohexanone (24) was isolated from (E)-20 (300
mg, 0.57 mmol) according to the general procedure with a
reaction time of 16 h at -30 °C, as a dark brown-red oil
containing a 5:1 (cis:trans) mixture of diastereomers (250 mg,
83%) (chromatography, 10:1 petroleum ether/Et2O). For the
purposes of characterization, the diastereomers were partially
separated by careful chromatography. The physical and spec-
tral data for trans-24 were identical to those previously
reported for this compound.2 cis-24: 1H NMR (400 MHz,
CDCl3) δ 0.74 (3H, d, J ) 7.0 Hz), 0.93 (3H, d, J ) 7.0 Hz),
1.88-2.05 (2H, m), 2.11-2.28 (3H, m), 2.34-2.53 (2H, m), 2.64
(1H, app t, J ) 6.5 Hz), 3.79-3.88 (1H, m), 7.25-7.40 (5H,
m); 13C NMR (100 MHz, CDCl3) δ 210.9, 199.4 (br), 138.8,
129.0, 128.6, 127.4, 98.3, 96.1, 61.6, 45.0, 42.5, 33.1, 25.5, 24.0,
21.8, 21.7; FTIR (film, υmax cm-1) 3078 (w), 2961 (m), 2872 (w),
2089 (s), 2049 (s), 2020 (s), 1715 (s), 1597 (w), 1480 (w), 1442
(w), 1371 (w), 1312 (w), 1217 (w); HRMS (ES) m/z (M+) calcd
for C23H20O7Co2 525.9873, found 525.9888.
Dicobalthexacarbonyl-((6-cyclohexylidenetetrahydro-
2H-pyran-2-yl)ethynyl)trimethylsilane (28) (Wittig method
A) was prepared using freshly distilled cyclohexanone and
phosphonium salt 8 (332 mg, 0.626 mmol). Following com-
plexation in DCM and chromatography (100:1 petroleum ether/
Et3N), complex 28 (159 mg, 46% from 8) was isolated as a deep
1
red solid: mp 54-55 °C; H NMR (250 MHz, CDCl3) δ 0.24
(9H, s), 1.31-1.72 (8H, m), 1.78-2.08 (5H, m), 2.12-2.35 (2H,
m), 2.48-2.59 (1H, m), 4.45 (1H, dd, J ) 11 Hz, 2.5 Hz); 13C
NMR (62.5 MHz, CDCl3) δ 200.4 (br), 144.0, 119.7, 111.9, 92.6,
79.6, 35.3, 29.0, 28.3, 27.7, 26.9, 26.6, 24.4, 24.4, 0.7; FTIR
(film, υmax cm-1) 2927 (s), 2854 (s), 2089 (s), 2014 (s), 1681 (m),
1580 (m), 1449 (m), 1250 (s), 1033 (m); HRMS (ES) m/z (M+
H) calcd for C22H27O7SiCo2 549.0190, found 549.0197.
+
Dicobalthexacarbonyl-tert-butyl-[3-(6-cyclohexylidene-
tetrahydro-2H-pyran-2-yl)prop-2-ynyloxy]diphenylsi-
lane (29) (Wittig method A) was prepared using freshly
distilled cyclohexanone and phosphonium salt 9 (470 mg, 0.648
mmol). Following complexation in DCM and chromatography
cis/trans-2-tert-butyl-3-(2-phenylethynyl)cyclohexa-
none (25). To a solution of (E)-21 (85 mg, 0.157 mmol) in DCM
J. Org. Chem, Vol. 70, No. 24, 2005 10053

Meek et al.
(100:1:1 petroleum ether/Et3N/Et2O), complex 29 (264 mg, 54%
1,4-cyclohexanedione monoethylene ketal and phosphonium
salt 9 (308 mg, 0.42 mmol). The reaction was stirred for 5 h
at -78 °C before warming to room temperature and quenching.
Following complexation in DCM and chromatography (100:1:
10 petroleum ether/Et3N/Et2O), complex 33 (170 mg, 50% from
9) was isolated as a orange-red oil: 1H NMR (250 MHz, CDCl3)
δ 1.08 (9H, s), 1.46-1.69 (6H, m), 1.78-2.01 (3H, m), 2.17-
2.27 (2H, m), 2.32-2.44 (2H, m), 2.50-2.63 (1H, m), 3.96 (4H,
s), 4.42-4.51 (1H, m), 4.80 (2H, s), 7.35-7.49 (6H, m), 7.67-
7.75 (4H, m); 13C NMR (62.5 MHz, CDCl3) δ 199.7 (br), 144.8,
135.6, 133.0, 129.8, 127.8, 116.6, 109.1, 96.5, 94.9, 79.4, 64.6,
64.3, 36.0, 35.3, 33.9, 26.6, 25.5, 24.3, 24.0, 23.1, 19.2; FTIR
(film, υmax cm-1) 3072 (w), 3051 (w), 2945 (m), 2888 (m), 2859
(m), 2093 (s), 2052 (s), 2030 (s), 1682 (w), 1615 (w), 1590 (w),
1473 (w), 1428 (m), 1364 (w), 1229 (w), 1138 (m), 1113 (m),
1094 (m), 1063 (m), 1034 (m); HRMS (ES) m/z (M+ + H) calcd
for C38H41O10SiCo2 803.1133, found 803.1146.
General Procedure for Et2AlCl-Promoted Rearrange-
ment of Cyclic Enol Ethers to R-Spirocyclohexanones
34-41 and R-Alkylcyclopentanones 49 and 50. To a
solution of the complex (1 equiv) in DCM (0.02 M) at -78 °C
was added diethylaluminum chloride (3.0 equiv, 1 M in
hexanes). The reaction was warmed to -30 °C and stirred for
the indicated amount of time, quenched by addition of water,
and then warmed to ambient temperature. The mixture was
poured into water and extracted three times with Et2O. The
combined organic layers were washed with brine, dried over
MgSO4, and concentrated in vacuo. The crude reaction mixture
was then chromatographed on silica gel, eluting with a
petroleum ether/Et2O system of appropriate polarity.
1
from 9) was isolated as a red-orange oil. H NMR (250 MHz,
CDCl3) δ 1.10 (9H, s), 1.41-1.80 (8H, m), 1.82-1.98 (3H, m),
2.00-2.14 (2H, m), 2.15-2.33 (2H, m), 2.57 (1H, br d, J ) 13
Hz), 4.46 (1H, dd, J ) 10.5 Hz, 2.5 Hz), 4.82 (2H, s), 7.38-
7.50 (6H, m), 7.71-7.77 (4H, m); 13C NMR (62.5 MHz, CDCl3)
δ 199.8 (br), 143.9, 135.6, 133.0, 129.8, 127.8, 119.6, 96.8, 95.0,
79.4, 64.6, 34.1, 28.9, 28.2, 27.6, 26.9, 26.6, 26.5, 24.2 (×2),
19.2; FTIR (film, υmax cm-1) 3073 (w), 2931 (s), 2858 (s), 2093
(s), 2051 (s), 2028 (s), 1674 (m), 1614 (m), 1473 (m), 1448 (m),
1429 (m), 1113 (s), 1063 (s), 1036 (s); HRMS (ES) m/z (M+
Na) calcd for C36H38O8SiCo2Na 767.0898, found 767.0892.
+
Dicobalthexacarbonyl-4-(6-(phenylethynyl)tetrahy-
dropyran-2-ylidene)-1-tosylpiperidine (30) (Wittig method
A) was prepared using N-tosylpiperidone and phosphonium
salt 6 (200 mg, 0.374 mmol). The reaction was stirred for 5 h
at -78 °C before warming to room temperature and quenching.
Following complexation in DCM and chromatography (100:1:
10 petroleum ether/Et3N/Et2O), complex 30 (81 mg, 31% from
1
6) was isolated as a red metallic solid: mp >300 °C dec; H
NMR (250 MHz, CDCl3) δ 1.58 (2H, m), 1.87-2.11 (3H, m),
2.30 (2H, app t, J ) 5.5 Hz), 2.36-2.57 (3H, m), 2.41 (3H, s),
2.81-3.14 (4H, m), 4.70 (1H, m), 7.26-7.34 (5H, m), 7.46-
7.52 (2H, m), 7.59-7.65 (2H, m); 13C NMR (100 MHz, CDCl3)
δ 199.3 (br), 146.3, 143.3, 137.7, 133.4, 129.6, 129.5, 128.8,
127.9, 127.6, 112.9, 97.0, 89.8, 79.4, 47.3, 47.0, 33.8, 27.6, 25.3,
24.3, 23.6, 21.5; FTIR (film, υmax cm-1) 2927 (s), 2846 (s), 2091
(s), 2051 (s), 2025 (s), 1684 (m), 1598 (m), 1442 (m), 1339 (s),
1165 (s); HRMS (ES) m/z (M+ + H) calcd for C31H28NO9SCo2
708.0149, found 708.0121.
Dicobalthexacarbonyl-5-(phenylethynyl)spiro[5.5]-
undecan-1-one (34) was isolated from 26 (17 mg, 0.031 mmol)
with a reaction time of 16 h as a dark red solid (16 mg, 93%)
(chromatography, 20:1 petroleum ether/Et2O): mp 118-120
°C; 1H NMR (250 MHz, CDCl3) δ 0.73-1.07 (2H, m), 1.24-
1.97 (8H, m), 2.02-2.35 (5H, m), 2.76 (1H, td, J ) 12.5, 6.0
Hz), 3.19 (1H, dd, J ) 11.0, 3.5 Hz), 7.23-7.42 (5H, m); 13C
NMR (100 MHz, CDCl3) δ 215.0, 199.9 (br), 138.8, 129.1, 128.7,
127.5, 99.3, 95.6, 55.8, 22.4, 53.0, 37.6, 32.0, 30.6, 29.0, 26.3,
25.3, 22.8; FTIR (film, υmax cm-1) 3077 (w), 2935 (w), 2858 (w),
2088 (s), 2049 (s), 2020 (s), 1707 (s), 1599 (w), 1442 (w); HRMS
(ES) m/z (M+ + H) calcd for C25H23O7Co2 553.0108, found
553.0110.
Dicobalthexacarbonyl-1-tosyl-4-(6-trimethylsilylethy-
nyl)tetrahydropyran-2-ylidene)piperidine (31) (Wittig
method A) was prepared using N-tosylpiperidone and phos-
phonium salt 8 (341 mg, 0.643 mmol). The reaction was stirred
for 5 h at -78 °C before warming to room temperature and
quenching. Following complexation in DCM and chromatog-
raphy (100:1:1 petroleum ether/Et3N/Et2O), complex 31 (111
mg, 25% from 8) was isolated as a red-brown metallic solid:
1
mp >300 °C dec; H NMR (250 MHz, CDCl3) δ 0.29 (9H, s),
1.52-1.71 (2H, m), 1.85-2.01 (3H, m), 2.25-2.34 (2H, m),
2.38-2.54 (2H, m), 2.42 (3H, s), 2.54-2.63 (1H, m), 2.85-3.12
(4H, m), 4.51 (1H, dd, J ) 10.5, 2.5 Hz), 7.27-7.36 (2H, m),
7.58-7.68 (2H, m); 13C NMR (100 MHz, CDCl3) δ 200.2 (br),
146.3, 143.3, 133.5, 129.6, 127.6, 112.8, 111.1, 79.5, 77.5, 47.3,
47.0, 34.9, 27.6, 25.4, 24.3, 23.6, 21.5, 0.8; FTIR (film, υmax
cm-1) 2951 (m), 2909 (m), 2847 (m), 2087 (s), 2027 (s), 1966
(m), 1683 (m), 1595 (m), 1339 (m), 1249 (m), 1164 (s); HRMS
(ES) m/z (M+ + Na) calcd for C28H31NO9SiSCo2Na 726.0050,
found 726.0026.
Dicobalthexacarbonyl-5-hex-1-ynylspiro[5.5]undecan-
1-one (35) was isolated from 27 (106 mg, 0.20 mmol) with a
reaction time of 15 h as a dark red oil (87 mg, 82%) (chroma-
tography, 10:1 petroleum ether/Et2O): 1H NMR (400 MHz,
CDCl3) δ 0.97 (3H, t, J ) 7 Hz), 1.02-1.22 (2H, m), 1.35-1.85
(11H, m), 1.95-2.33 (6H, m), 2.71 (1H, td, J ) 12.5, 6.5 Hz),
2.87 (1H, dd, J ) 16.5, 6.5 Hz), 2.77-3.00 (2H, m); 13C NMR
(100 MHz, CDCl3) δ 215.1, 200.1 (br), 101.1, 98.4, 55.6, 53.5,
37.7, 35.0, 33.9, 32.1, 30.7, 26.2, 29.6, 22.8, 22.7, 22.6, 13.9;
FTIR (film, υmax cm-1) 2948 (s), 2933 (s), 2859 (s), 2086 (s),
Dicobalthexacarbonyl-4-{6-[3-(tert-butyldiphenylsilyl-
oxy)prop-1-ynyl]tetrahydropyran-2-ylidene}-1-tosylpip-
eridine (32) (Wittig method A) was prepared using N-tosylpi-
peridone and phosphonium salt 9 (200 mg, 0.276 mmol). The
reaction was stirred for 5 h at -78 °C before warming to room
temperature and quenching. Following complexation in DCM
and chromatography (100:1:10 petroleum ether/Et3N/Et2O),
complex 32 (117 mg, 47% from 9) was isolated as a red metallic
solid: mp >300 °C dec; 1H NMR (250 MHz, CDCl3) δ 1.07 (9H,
s), 1.47-1.61 (2H, m), 1.78-1.95 (3H, m), 2.26 (2H, t, J ) 5.5
Hz), 2.39-2.63 (3H, m), 2.43 (3H, s), 2.76-3.12 (4H, m), 4.42
(1H, dd, J ) 10.5, 2.0 Hz), 4.76 (2H, s,), 7.28-7.34 (2H, m),
2044 (s), 2012 (s), 1965 (s), 1711 (s); HRMS (ES) m/z (M+
H) calcd for C23H27Co2O7 533.0421, found 533.0414.
+
Dicobalthexacarbonyl-5-(trimethylsilylethynyl)spiro-
[5.5]undecan-1-one (36) was isolated from 28 (46 mg, 0.084
mmol) with a reaction time of 15 h as a dark red solid (41 mg,
88%) (chromatography, 10:1 petroleum ether/Et2O): mp 91-
1
93 °C; H NMR (400 MHz, CDCl3) δ 0.37 (9H, s), 1.07-1.28
(2H, m), 1.54-1.81 (7H, m), 1.97 (1H, d, J ) 9.0 Hz), 2.11-
2.27 (4H, m), 2.31 (1H, dt, J )12.5, 4.5 Hz), 2.72 (1H, dt, J )
6.0, 2.5 Hz), 2.99 (1H, dd, J ) 8.0, 6.0 Hz); 13C NMR (100 MHz,
CDCl3) δ 215.0, 200.5 (br), 110.7, 81.5, 54.6, 54.3, 37.6, 32.1,
7.37-7.48 (6H, m), 7.59-7.66 (2H, m), 7.67-7.76 (4H, m); 13
C
NMR (62.5 MHz, CDCl3) δ 199.5 (br), 146.0, 143.2, 135.4,
133.3, 132.7, 129.8, 129.5, 127.7, 127.5, 112.5, 95.8, 94.9, 79.2,
64.5, 47.2, 46.9, 33.5, 27.4, 26.4, 25.0, 24.0, 23.3, 21.4, 19.0;
FTIR (film, υmax cm-1) 3073 (m), 2933 (s), 2860 (s), 2093 (s),
2051 (s), 1683 (m), 1599 (m), 1464 (m), 1429 (m), 1357 (m),
1340 (m), 1166 (s); HRMS (FAB) m/z (M+ + Na) calcd for
C42H43NO10SiSCo2Na 922.0939, found 922.0953.
31.2, 29.6, 26.1, 25.5, 22.7, 22.2, 1.5; FTIR (film, υmax cm-1
)
2934 (s), 2859 (m), 2084 (s), 2043 (s), 2014 (s), 1709 (s), 1568
(m), 1450 (m), 1250 (s); HRMS (ES) m/z (M+ + Na) calcd for
C22H26O7Co2SiNa 571.0009, found 571.0013.
Dicobalthexacarbonyl-5-[3-(tert-butyldiphenylsilyl-
oxy)prop-1-ynyl]spiro[5.5]undecan-1-one (37) was isolated
from 29 (64 mg, 0.086 mmol) with a reaction time of 19 h as
a orange-red oil (62 mg, 97%) (chromatography, 10:1 petroleum
Dicobalthexacarbonyl-tert-butyl-{3-[6-(1,4-dioxaspiro-
[4.5]dec-8-ylidene)tetrahydropyran-2-yl]prop-2-ynyloxy}-
diphenylsilane (33) (Wittig method A) was prepared using
10054 J. Org. Chem., Vol. 70, No. 24, 2005

Scope of a Co-Mediated OfC Rearrangement Reaction
ether/Et2O): 1H NMR (400 MHz, CDCl3) δ 0.73 (3H, m), 1.10
(9H, s), 1.27-1.81 (6H, m), 1.84-1.91 (1H, m), 1.93-2.21 (4H,
m), 2.27 (1H, dt, J ) 12.5, 4.5 Hz), 2.66 (1H, td, J ) 12.5, 6.0
Hz), 2.93 (1H, dd, J ) 10.5, 4.0 Hz), 4.79 (2H, s), 7.38-7.49
(6H, m), 7.70-7.75 (4H, m); 13C NMR (100 MHz, CDCl3) δ
214.7, 199.9 (br), 135.6, 132.7, 129.9, 127.8, 97.6, 97.0, 65.8,
55.0, 53.2, 37.6, 31.9, 31.0, 29.6, 26.6, 26.0, 25.6, 22.6, 22.4,
19.1; FTIR (film, υmax cm-1) 3072 (w), 2933 (s), 2859 (s), 2089
(s), 2048 (s), 2024 (s), 1707 (s), 1590 (w), 1448 (m), 1428 (s),
1106 (s), 1055 (s); HRMS (ES) m/z (M+ + Na) calcd for
C36H38O8SiCo2Na 767.0898, found 767.0873.
Dicobalthexacarbonyl-11-(phenylethynyl)-3-tosyl-3-
azaspiro[5.5]undecan-7-one (38) was isolated from 30 (168
mg, 0.237 mmol) with a reaction time of 24 h as a dark red-
brown oil (146 mg, 87%) (chromatography, 3:1 petroleum ether/
Et2O): 1H NMR (400 MHz, CDCl3) δ 1.72-1.90 (2H, m), 1.96-
2.44 (9H, m), 2.40 (3H, s), 2.53-2.63 (1H, m), 3.22-3.28 (1H,
m), 3.42-3.49 (1H, m), 3.57-3.65 (1H, m), 7.23-7.28 (2H, m),
7.30-7.41 (5H, m), 7.47-7.52 (2H, m); 13C NMR (100 MHz,
CDCl3) δ 213.4, 199.2 (br), 143.5, 138.0, 132.7, 129.6, 129.0,
128.7, 127.9, 127.5, 96.7, 95.5, 52.7, 51.4, 43.3, 43.0, 37.6, 31.2,
30.0, 28.3, 25.2, 21.5; FTIR (film, υmax cm-1) 3075 (w), 2956
(w), 2859 (w), 2090 (s), 2051 (s), 2023 (s), 1706 (m), 1598 (w),
1471 (w), 1342 (w), 1166 (m); HRMS (ES) m/z (M+ + H) calcd
for C31H28NO9SCo2 708.0149, found 708.0148.
2-Methoxy-5-(2-phenylethynyl)tetrahydrofuran (43).
Reaction of 2-methoxy-5-(phenylsulfonyl)tetrahydrofuran (4 g,
16.51 mmol) with the alkynlaluminum reagent prepared from
phenyl acetylene gave compound 43 (2.91 g, 87%) isolated as
a colorless oil containing an inseparable mixture of diastere-
omers (cis:trans 1:1, isomers not elucidated) (chromatography,
10:1 petroleum ether/EtOAc): 1H NMR (250 MHz, CDCl3) δ
1.88-2.46 (8H, m), 3.38 (3H, s), 3.43 (3H, s), 4.89-4.97 (2H,
m), 5.08 (1H, dd, J ) 5.0, 1.0 Hz), 5.15 (1H, dd, J ) 5.0, 1.5
Hz), 7.26-7.35 (6H, m), 7.40-7.48 (4H, m); 13C NMR (62.5
MHz, CDCl3) δ 131.7 (×2), 128.4, 128.2 (×3), 122.9, 122.6,
105.4, 105.3, 89.7, 88.1, 84.9, 84.1, 68.7, 67.6, 55.0, 54.6, 33.0,
32.2, 31.5, 31.3; FTIR (film, υmax cm-1) 3057 (w), 2989 (m), 2953
(m), 2829 (m), 1598 (w), 1490 (m), 1442 (m), 1356 (m), 1206
(m), 1100 (s), 1028 (s); HRMS (ES) m/z (M+) calcd for C13H14O2
202.0994, found 202.0992.
2-Hex-1-ynyl-5-methoxytetrahydrofuran (44). Reaction
of 2-methoxy-5-(phenylsulfonyl)tetrahydrofuran (1.74 g, 7.2
mmol) with the alkynlaluminum reagent prepared from 1-hex-
yne gave compound 44 (1.10 g, 84%) isolated as a colorless oil
containing an inseparable mixture of diastereomers (cis:trans
1:1, isomers not elucidated) (chromatography, 10:1 petroleum
ether/EtOAc): 1H NMR (250 MHz, CDCl3) δ 0.90 (6H, t, J )
7.0 Hz), 1.34-1.55 (8H, m), 1.80-2.26 (12H, m), 3.34 (3H, s),
3.38 (3H, s), 4.68 (2H, m), 5.00 (1H, app d, J ) 5.5 Hz), 5.06
(1H, app d, J ) 5.0 Hz); 13C NMR (125 MHz, CDCl3) δ 105.1
(×2), 85.8, 84.9, 80.5, 79.0, 68.7, 67.4, 54.8, 54.5, 32.9, 32.2,
31.6, 31.4, 30.6 (×2), 21.9, 21.8, 18.4 (×2) 13.5 (×2); FTIR (film,
υmax cm-1) 2932 (m), 2874 (s), 2830 (s), 1458 (m), 1356 (m),
1207 (s), 1161 (w), 1102 (s), 1033 (s); HRMS (ES) m/z (M+)
calcd for C11H18O2 182.1307, found 182.1302.
Triphenyl(5-(2-phenylethynyl)tetrahydrofuran-2-yl)-
phosphonium tetrafluoroborate (45) was prepared accord-
ing to the general procedure for Wittig salt formation as
described above using acetal 43 (2.91 g, 14.38 mmol) and
isolated as a pale yellow solid containing an inseparable 1.2:1
mixture of diastereomers (7.13 g, 95%): 1H NMR (250 MHz,
CDCl3) δ 1.75-1.92 (2H, m), 1.98-2.12 (1H, m), 2.14-2.39 (2H,
m), 2.48-2.64 (1H, m), 2.86-3.15 (2H, m), 4.57 (1H, app t, J
) 6.5 Hz), 5.10 (1H, dd, J ) 7.0, 5.0 Hz), 5.95-6.08 (2H, m),
7.19-7.88 (40H, m); 13C NMR (62.5 MHz, CDCl3) see Sup-
porting Information; FTIR (film, υmax cm-1) 3650 (w), 3554 (w),
3063 (m), 2954 (m), 1976 (w), 1905 (w), 1826 (w), 1690 (w),
1588 (m), 1490 (m), 1440 (s); HRMS (ES) m/z (M+ - BF4) calcd
for C30H26OP 433.1721, found 433.1719.
Dicobalthexacarbonyl-3-tosyl-11-(trimethylsilylethy-
nyl)-3-azaspiro[5.5]undecan-7-one (39) was isolated from
31 (190 mg, 0.27 mmol) with a reaction time of 20 h as a dark
red-brown solid (161 mg, 85%) (chromatography, 10:1 petro-
1
leum ether/Et2O): mp dec 189-190 °C; H NMR (400 MHz,
CDCl3) δ 0.43 (9H, s), 1.68-1.82 (1H, m), 1.89-2.31 (9H, m),
2.42 (3H, s), 2.49-2.61 (2H, m), 3.09 (1H, dd, J ) 10.5, 4.0
Hz), 3.67-3.76 (2H, m), 7.25-7.32 (2H, m), 7.55-7.61 (2H,
m); 13C NMR (100 MHz, CDCl3) δ 213.4, 200.2 (br), 143.6,
132.6, 129.7, 127.6, 109.5, 80.8, 54.2, 51.7, 43.3, 42.9, 37.8, 31.6,
30.7, 28.6, 25.6, 21.5, 1.6; FTIR (film, υmax cm-1) 2958 (w), 2871
(w), 2085 (s), 2045 (s), 2016 (s), 1706 (m), 1598 (w), 1560 (w),
1342 (w), 1250 (w), 1166 (m); HRMS (ES) m/z (M+ + H) calcd
for C28H32NO9SiSCo2 704.0231, found 704.0261.
Dicobalthexacarbonyl-11-[3-(tert-butyldiphenylsilyl-
oxy)prop-1-ynyl]-3-tosyl-3-azaspiro[5.5]undecan-7-one (40)
was isolated from 32 (92 mg, 0.102 mmol) with a reaction time
of 24 h as a dark red oil (86 mg, 94%) (chromatography, 10:1
petroleum ether/Et2O): 1H NMR (400 MHz, CDCl3) δ 1.11 (9H,
s), 1.71-1.88 (3H, m), 1.90-2.01 (1H, m), 2.05-2.24 (5H, m),
2.24-2.33 (1H, m), 2.41 (3H, s), 2.37-2.50 (2H, m), 2.96 (1H,
dd, J ) 9.0, 3.5 Hz), 3.52-3.61 (2H, m), 4.79 (1H, d, J ) 13.5
Hz), 4.84 (1H, d, J ) 14.0 Hz), 7.26 (2H, d, J ) 8.0 Hz), 7.41-
(5-(Hex-1-ynyl)tetrahydrofuran-2-yl)triphenylphos-
phonium tetrafluoroborate (46) was prepared according to
the general procedure for Wittig salt formation as described
above using cyclic acetal 44 (1.10 g, 5.99 mmol) and isolated
as a pale yellow solid containing an inseparable 1.2:1 mixture
7.50 (6H, m), 7.55 (2H, d, J ) 8.0 Hz), 7.71-7.76 (4H, m); 13
C
NMR (100 MHz, CDCl3) δ 213.2, 199.5 (br), 143.5, 135.6, 132.6,
132.5, 132.4, 130.0, 129.7, 127.9, 127.6, 98.5, 94.6, 65.2, 52.1,
43.3, 43.1, 37.7, 31.8, 30.2, 29.0, 26.8, 25.0, 21.5, 19.2; FTIR
(film, υmax cm-1) 3072 (w), 2933 (m), 2859 (m), 2090 (s), 2050
(s), 2025 (s), 1706 (s), 1598 (w), 1472 (m), 1429 (m), 1356 (m),
1343 (m), 1167 (s); HRMS (ES) m/z (M+ + Na) calcd for C42H43-
NO10NaSiSCo2 922.0939, found 922.0968.
1
of diastereomers (2.65 g, 89%). H NMR (500 MHz, CDCl3) δ
0.86 (3H, t, J ) 7.2 Hz), 0.88 (3H, t, J ) 7.3 Hz), 1.25-1.39
(6H, m), 1.43-1.49 (2H, m), 1.60-1.66 (2H, m), 1.89-1.95 (1H,
m), 2.01 (2H, tt, J ) 7.0, 2.0 Hz), 2.07-2.25 (4H, m), 2.38-
2.44 (1H, m), 2.83-3.01 (2H, m), 4.34 (1H, m), 4.83 (1H, m),
5.88-5.95 (2H, m), 7.65-7.83 (30H, m); 13C NMR (125 MHz,
CDCl3) see Supporting Information; FTIR (film, υmax cm-1
)
Dicobalthexacarbonyl-13-[3-(tert-butyldiphenylsilyl-
oxy)prop-1-ynyl]-1,4-dioxadispiro[4.2.5.2]pentadecan-9-
one (41) was isolated from 33 (54 mg, 0.070 mmol) with a
reaction time of 16 h as a dark orange-red oil (39 mg, 70%)
(chromatography, 5:1 petroleum ether/Et2O): 1H NMR (250
MHz, CDCl3) δ 1.08 (9H, s), 1.02-3.32 (13H, m), 2.69 (1H, td,
J ) 12.5, 5.5 Hz), 2.98 (1H, dd, J ) 11.0, 3.5 Hz), 3.07-3.21
(2H, m), 3.65-3.74 (2H, m), 4.90 (1H, d, J ) 14.5 Hz), 5.06
(1H, d, J ) 14.0 Hz), 7.34-7.48 (6H, m), 7.68-7.79 (4H, m);
13C NMR (62.5 MHz, CDCl3) δ 214.1, 199.9 (br), 135.6, 135.6,
133.0, 129.7, 127.7, 97.7, 96.4, 65.5, 64.2, 63.4, 54.0, 53.2, 37.4,
32.0, 31.5, 31.1, 29.4, 27.0, 26.6, 26.2, 19.1; FTIR (film, υmax
cm-1) 3073 (w), 2934 (m), 2860 (m), 2088 (s), 2047 (s), 2023
(s), 1706 (m), 1590 (w), 1473 (w), 1429 (w), 1111 (m), 1087 (m),
1049 (m); HRMS (ES) m/z (M+ + Na) calcd for C38H40O10-
NaSiCo2 825.0952, found 825.0912.
3064 (w), 2957 (m), 2872 (s), 1588 (s), 1440 (s), 1113 (s), 1057
(w); HRMS (ES) m/z (M+ - BF4) calcd for C28H30OP 413.2034,
found 413.2022.
(E/Z)-Dicobalthexacarbonyl-2-benzylidene-5-(2-phen-
ylethynyl)tetrahydrofuran (47) (Wittig method B) was
prepared using freshly distilled benzaldehyde and phospho-
nium salt 45 (200 mg, 0.38 mmol). Following complexation in
DCM and chromatography (10:1 petroleum ether/Et2O), com-
plex 47 (128 mg, 60% from 45) was isolated as a dark red oil
as an inseparable 2.3:1 mixture of isomers (E/Z-isomers not
elucidated): 1H NMR (250 MHz, CDCl3) δ 1.88-2.10 (2H, m),
2.46-2.68 (2H, m), 2.84-3.10 (4H, m), 5.21-5.26 (1H, m), 5.61
(1H, app t, J ) 7.0 Hz), 5.77 (1H, dd, J ) 8.0, 6.0 Hz), 5.90-
5.96 (1H, m), 6.95-7.60 (20H, m); 13C NMR (62.5 MHz, CDCl3)
δ 199.0 (br), 157.9, 156.0, 137.5, 137.4, 136.4, 129.8, 129.7 (×2),
J. Org. Chem, Vol. 70, No. 24, 2005 10055

Meek et al.
128.9 (×2), 128.4 (×2), 128.0 (×2), 127.3, 127.1(×2), 124.8, 99.9,
97.9, 95.5, 94.5, 91.4, 91.2, 84.0, 80.6, 33.1, 32.4, 31.6, 28.9;
FTIR (film, υmax cm-1) 3058 (w), 3024 (w), 2092 (s), 2054 (s),
2024 (s), 1668 (m), 1600 (w), 1484 (w), 1444 (w), 1224 (w), 1128
(m); HRMS (EI) m/z (M+) calcd for C25H16O7Co2 545.9560,
found 545.9543.
NMR (250 MHz, CDCl3) δ 1.82-2.04 (1H, m), 2.39-2.74 (3H,
m), 3.23 (1H, d, J ) 11.5 Hz), 4.04 (1H, td, J ) 11.5, 6.0 Hz),
7.01-7.35 (10H, m); 13C NMR (62.5 MHz, CDCl3) δ 215.5, 199.2
(br), 137.6, 136.7, 128.9 (×3), 128.6, 127.5 (×2), 99.7, 92.9, 64.2,
47.5, 38.4, 30.7; FTIR (film, υmax cm-1) 3062 (w), 3032 (w), 2970
(w), 2089 (s), 2049 (s), 2021 (s), 1748 (s), 1604 (w), 1498 (w),
(E/Z)-Dicobalthexacarbonyl-2-benzylidene-5-hex-1-yn-
yltetrahydrofuran (48) (Wittig method B) was prepared
using freshly distilled benzaldehyde and phosphonium salt 46
(200 mg, 0.40 mmol). Following complexation in DCM and
chromatography (100:1 petroleum ether/Et2O), complex 48 (73
mg, 35% from 46) was isolated as a dark red oil as an
inseparable 2:1 mixture of isomers (E/Z-isomers not eluci-
dated). 1H NMR (250 MHz, CDCl3) δ 0.92 (3H, t, J ) 7.2 Hz),
0.98 (3H, t, J ) 7.3 Hz), 1.43-1.55 (5H, m), 1.63-1.75 (4H,
m), 1.85-2.03 (2H, m), 2.24 (1H, m), 2.42-2.54 (2H, m), 2.83-
3.04 (6H, m), 5.27 (1H, s), 5.48 (1H, t, J ) 6.6 Hz), 5.63 (1H,
app dd, J ) 7.9, 6.4 Hz), 5.94 (1H, app s), 7.03-7.58 (10H, m);
13C NMR (125 MHz, CDCl3) (major isomer) δ 199.7 (br), 156.1,
136.5, 128.0 (×2), 127.3 (×2), 124.7, 97.7, 83.9, 34.0, 33.8, 32.2,
31.5, 22.8, 13.9; (minor isomer) δ 199.7 (br), 156.1, 136.5, 128.3
(×2), 128.2 (×2), 127.0, 99.7, 80.5, 32.9, 30.8, 30.5, 28.7, 18.5,
13.6; FTIR (film, υmax cm-1) 2960 (s), 2933 (s), 2874 (s), 2091
(s), 2858 (s), 2023 (s), 1674 (s), 1597 (w), 1493 (s), 1448 (m),
1364 (m), 1285 (m), 1132 (w), 1017 (w); HRMS (ES) m/z (M+
+ H) calcd for C23H21O7Co2 526.9951, found 526.9937.
trans-Dicobalthexacarbonyl-2-phenyl-3-(2-phenylethy-
nyl)cyclopentanone (trans-49). According to the general
procedure, with a reaction time of 3 h, the title compound was
prepared from 47 (23 mg, 0.042 mmol) as a dark red oil (10
mg, 47%) (chromatography, 10:1 petroleum ether/Et2O): 1H
1482 (w), 1454 (w), 1442 (w), 1129 (w); HRMS (ES) m/z (M+
+
Na) calcd for C25H16O7NaCo2 568.9458, found 568.9480.
trans-Dicobalthexacarbonyl-3-hex-1-ynyl-2-phenylcy-
clopentanone (trans-50). According to the general proce-
dure, with a reaction time of 4 h, the title compound was
prepared from 48 (31 mg, 0.058 mmol) as a dark red oil (16
mg, 57%) (chromatography, 50:1 petroleum ether/Et2O): 1H
NMR (250 MHz, CDCl3) δ 0.80 (3H, app t, J ) 7.2 Hz), 1.16-
1.25 (4H, m), 1.88-2.07 (1H, m), 2.26 (2H, m), 2.44-2.75 (3H,
m), 3.16 (1H, app d, J ) 11.3 Hz), 3.83 (1H, td, J ) 11.6, 5.2
Hz), 7.15-7.40 (5H, m); 13C NMR (125 MHz, CDCl3) δ 215.1,
200.0 (br), 136.5, 128.9 (×2), 127.7, 101.1, 99.4, 64.4, 47.3, 37.9,
33.8, 33.7, 29.9, 22.6, 13.7; FTIR (film, υmax cm-1) 2961 (s), 2960
(s), 2875 (s), 2087 (s), 2044 (s), 2015 (w), 1749 (s), 1604 (m),
1498 (s), 1453 (m), 1261 (m), 1099 (w); HRMS (ES) m/z (M+
Na) calcd for C23H20O7NaCo2 548.9771, found 548.9759.
+
Acknowledgment. We are grateful to the EPSRC
and GlaxoSmithKline for financial support.
Supporting Information Available: 1H and 13C NMR
spectra for selected compounds. This material is available free
of charge via the Internet at http://pubs.acs.org.
JO0517895
10056 J. Org. Chem., Vol. 70, No. 24, 2005