N-phosphino-p-tolylsulfinamide ligands: Synthesis, stability, and application to the intermolecular Pauson-Khand reaction

Article abstract of DOI:10.1021/jo800710n

(Chemical Equation Presented) Here we synthesized a family of racemic and optically pure N-phosphino-p-tolylsulfinamide (PNSO) ligands. Their stability and coordination behavior toward dicobalt-alkyne complexes was evaluated. Selectivities of up to 3:1 we

Full text of DOI:10.1021/jo800710n

N-Phosphino-p-tolylsulfinamide Ligands: Synthesis, Stability, and
Application to the Intermolecular Pauson-Khand Reaction
Marc Reve´s, Thierry Achard, Jordi Sola`, Antoni Riera,* and Xavier Verdaguer*
Unitat de Recerca en S´ıntesi Asime`trica (URSA-PCB), Institute for Research in Biomedicine (IRB
Barcelona), and Departament de Qu´ımica Orga`nica, UniVersitat de Barcelona, c/Baldiri Reixac 10,
E-08028 Barcelona, Spain
xaVier.Verdaguer@irbbarcelona.org
ReceiVed April 3, 2008
Here we synthesized a family of racemic and optically pure N-phosphino-p-tolylsulfinamide (PNSO)
ligands. Their stability and coordination behavior toward dicobalt-alkyne complexes was evaluated.
Selectivities of up to 3:1 were achieved in the ligand exchange process with (µ-TMSC2H)Co2(CO)6. The
resulting optically pure major complexes were tested in the asymmetric intermolecular Pauson-Khand
reaction and yielded up to 94% ee. X-ray studies of the major complex 18a indicated that the presence
of an aryl group on the sulfinamide reduces the hemilabile character of the PNSO ligands.
Introduction
Interest in the preparation of chiral sulfur compounds in
general and chiral sulfoxides and sulfinamides in particular has
increased considerably since the beginning of the 1980s. This
growth is attributed to the fact that chiral sulfoxides and
sulfinamides are efficient chiral auxiliaries that can induce
relevant asymmetric transformations.1–3 Ligands that contain
only sulfur as donor atom are of limited use in metal catalysis
due to their poor coordination capacity with respect to phos-
phines and phosphites. This limitation has been addressed by
preparing phosphine-sulfoxide or phosphine-sulfinamide ligands
FIGURE 1. Phosphine-sulfinamide ligands.
in which the phosphorus atom provides metal affinity while the
sulfur moiety is the source of chirality (Figure 1). Only a few
P,SdO ligands have been described in the literature. This lack
of information is probably due to the low stability of these
ligands as a result of sulfur-to-phosphorus oxygen migration.4–6
In the context of our project in the asymmetric Pauson-Khand
reaction,7–9 we recently provided the first report of the synthesis
of N-phosphino-tert-butylsulfinamide ligands (I), which were
found to be highly efficient in the intermolecular Pauson-Khand
reaction.10 Ligands of type I were synthesized in high yield
and were stable toward oxygen migration in solution and solid
form. A closely related family of ligands would arise from
switching the tert-butyl group for an aryl group. We consider
(1) Ferna´ndez, I.; Khiar, N. Chem. ReV. 2003, 103, 3651–3706.
(2) Pellissier, H. Tetrahedron 2006, 62, 5559–5601.
(3) Senanayake, C. H.; Krishnamurthy, D.; Lu, Z.; Han, Z.; Gallou, I.
Aldrichim. Acta 2005, 38, 93–104.
(4) Alcock, N. W.; Brown, J. M.; Evans, P. L. J. Organomet. Chem. 1988,
356, 233–247.
(5) Hiroi, K.; Suzuki, Y.; Kawagishi, R. Tetrahedron Lett. 1999, 40, 715–
718.
(6) Before the present report, Wenschuch and co-workers described the
synthesis of racemic 8. Along with 8, N-trimethylsilyl-N-diphenylphosphino-p-
tolylsulfinamide was also described. Products were characterized only by
elemental analysis. Oxygen migration was not studied; however, the authors
report that the products are water sensitive. See: Wenschuh, E.; Fritzsche, B. J.
Prakt. Chem 1970, 312, 29–134.
(7) Verdaguer, X.; Lledo´, A.; Lo´pez-Mosquera, C.; Maestro, M. A.; Perica`s,
M. A.; Riera, A. J. Org. Chem. 2004, 69, 8053–8061.
(8) Verdaguer, X.; Perica`s, M. A.; Riera, A.; Maestro, M. A.; Mah´ıa, J.
Organometallics 2003, 22, 1868–1877.
(9) Verdaguer, X.; Moyano, A.; Perica`s, M. A.; Riera, A.; Maestro, M. A.;
Mah´ıa, J. J. Am. Chem. Soc. 2000, 122, 10242–10243.
(10) Sola`, J.; Reve´s, M.; Riera, A.; Verdaguer, X. Angew. Chem., Int. Ed.
2007, 46, 5020–5023.
(11) Backes, B. J.; Dragoli, D. R.; Ellman, J. A. J. Org. Chem. 1999, 64,
5472–5478.
(12) Ellman, J. A. Pure Appl. Chem. 2003, 75, 39–46.
7080 J. Org. Chem. 2008, 73, 7080–7087
10.1021/jo800710n CCC: $40.75 2008 American Chemical Society
Published on Web 08/26/2008

N-Phosphino-p-tolylsulfinamide Ligand
TABLE 1. Synthesis of Racemic PNSO Ligands
SCHEME 1. Synthesis of PNSO Ligand 8 without Borane
Protection
followed by the addition of borane as a phosphine-protecting
group afforded 11 examples of borane-protected PNSO ligands
in good to moderate yields (Table 1). Most intriguingly,
isopropyl amine-derived compound 8 was isolated as a mixture
of protected and deprotected ligands. Interestingly the depro-
tected fraction of 8 displayed no oxygen migration from sulfur
to phosphorus.
Stability Evaluation of Free PNSO Ligands. N-Phosphino-
sulfinamides show a complex functionality that allows multiple
decomposition pathways. First, sulfinamides can be easily
hydrolyzed in acidic medium to provide the free amine. This is
a desired property in asymmetric reductive amination with
optically pure tert-butylsulfinamide and p-tolylsulfinamide,
which allows the convenient isolation of the free primary
amine.12–14 Second, PNSO ligands bear a phosphinamide group
that can also be hydrolyzed.15 Finally, another undesired process
for the use of these molecules as metal ligands is the
aforementioned migration of the oxygen atom from sulfur to
phosphorus.16 Our previous studies on type I ligands bearing a
tert-butylsulfinamide fragment indicated that protection by
borane provided the stability required for purification after the
introduction of the phosphinamide group. Once the borane-
protected ligand was isolated, removal of borane with an amine
(DABCO) was performed, with no decomposition of the
molecule. At this point, the ligands were stable to oxygen
migration and hydrolysis provided they were not exposed to
acidic conditions, and thus they were shelf-stable solids.
Following our previous procedure, deprotection of 1-BH3,
bearing a benzyl group on nitrogen, was first examined.
Treatment of 1-BH3 with DABCO in toluene provided a
mixture of compounds from which no free ligand could be
isolated by flash chromatography on SiO2. However, a closer
look at the deprotection step showed that product decomposi-
a C2O2Cl2, toluene, rt, 1 h. b RNH2, Et3N, toluene, 0 °C. c BuLi or
LiHMDS, THF, -78 °C, PPh2Cl, then BH3–SMe2 at -30 °C. d Yield
refers to crude material that was used without further purification in the
next step. e Isolated as a 1/1.5 mixture of borane- and borane-free
ligand.
that N-phosphino-tolylsulfinamide ligands (II) would show
different electronic and structural properties of interest with
respect to type I ligands. Thus here we addressed the synthesis
of racemic and optically pure N-phosphino-tolylsulfinamide
ligands (II), their coordination behavior toward terminal
alkyne-dicobalt carbonyl complexes, and their application in
the intermolecular asymmetric Pauson-Khand reaction.
Results and Discussion
1
tion occurred during the purification procedure on SiO2. H
Synthesis of PNSO Ligands. We synthesized borane-
protected N-phosphino-p-tolylsulfinamide ligands 1-11 follow-
ing the scheme in Table 1. To prevent oxygen migration during
the synthesis, the borane protection strategy reported for type I
ligands was used.10 Racemic PNSO ligands were prepared
efficiently from sodium p-toluenesulfinate by conversion to the
sulfinyl chloride with oxalyl chloride followed by aminolysis
with several amines in toluene.11 At this point, using parallel-
chemistry techniques, a number of amines were used to yield
up to 11 distinct sulfinamides (III). Benzylic amines (Table 1,
entries 1-6) as well as aliphatic amines (Table 1, entries 7 and
8) provided good yields of the corresponding sulfinamide
intermediates. In contrast, anilines provided a clear pattern in
which electron-withdrawing groups on the aromatic ring sta-
bilized the sulfinamide functional group while electron-releasing
groups caused the opposite effect. Thus, while p-chloro-,
p-fluoro-, and p-CF3-anilines provided the corresponding sul-
finamides with good yields, the use of p-methoxyaniline (Table
1, entry 12) led only to decomposition products, probably
because of enhanced hydrolysis of the sulfinamide functionality.
Finally, sulfinamide deprotonation with either n-BuLi or
LiHMDS at low temperature and subsequent addition of Ph2PCl,
NMR monitoring indicated that the free ligand was stable in
solution under the deprotection conditions used (DABCO,
toluene, 25-65 °C). These results suggest that decomposition
is due to acidic hydrolysis on silica, rather than to oxygen
migration. We next turned our attention to the N-isopropyl
ligand 8-BH3 isolated as a 1:1.5 mixture of borane-containing
and borane-free ligands. When this mixture was treated with
DABCO, the corresponding borane-free ligand 8 was isolated
as a sole product after filtration on SiO2. This result indicates
that ligand 8 is robust to hydrolytic decomposition and
oxygen migration. To check whether the phosphine protection
step was required in this case, the synthesis of 8 was repeated
without the protection step. In this case, the free ligand 8
was isolated after flash chromatography with an improved
88% yield (Scheme 1).6 The thermal stability of 8 was further
(13) Liu, G.; Cogan, D. A.; Ellman, J. A. J. Am. Chem. Soc. 1997, 119,
9913–9914.
(14) Fanelli, D. L.; Szewczyk, J. M.; Zhang, Y.; Reddy, G. V.; Burns, D. M.;
Davis, F. A. Org. Synth. 2000, 77, 50–63.
(15) Koizumi, T.; Haake, P. J. Am. Chem. Soc. 1973, 95, 8073–8079.
(16) Vedejs, E.; Meier, G. P.; Powell, D. W.; Mastalerz, H. J. Org. Chem.
1981, 46, 5253–5254.
J. Org. Chem. Vol. 73, No. 18, 2008 7081

Reve´s et al.
TABLE 2. Coordination of Racemic PNSO Ligands to a
Dicobaltalkyne Complex
examined by heating a solution of the ligand at 65 °C in dry
toluene under nitrogen atmosphere for 24 h. Under these
conditions no substantial decomposition or oxygen transfer
occurred since 93% of the ligand remained unaltered (1H
NMR). The robustness of ligand 8 appears to be related to
the right steric bulk of the isopropyl group on nitrogen. Thus,
neither the N-benzylic ligands (1-6), the N-isobutyl (7), nor
the N-phenyl ligands (9-11) were isolated as borane-free
ligands. These results indicate that N-phosphino-p-tolylsul-
finamides are more prone to hydrolysis than their corre-
sponding tert-butylsulfinamide counterparts. However, in-
creasing the steric bulk on nitrogen provided enough stability
against hydrolysis and oxygen transfer for isolation of the
free PNSO ligands.
Reactions with (µ-Alkyne)Co2(CO)6 Complexes. Given that
most of the PNSO ligands could not be isolated in their borane-
free form, deprotection and ligand exchange reaction were
performed in situ in the same reaction flask. Thus, cobalt
complexes were prepared by treatment of trimethylsilylacetylene
dicobaltcarbonyl with the corresponding borane-protected ra-
cemic PNSO ligands in the presence of 1.5 equiv of DABCO
at 65 °C for 2 h (Table 2). This procedure afforded the
corresponding diastereomeric mixture of complexes in good
yield except for the N-phenyl ligands 9-11, which produced
consistently lower yields (16-32%), probably as a result of
ligand decomposition on heating. No selectivity was observed
for most of the ligand exchange reactions, even when extended
reaction times and continued heating at 80 °C were used. The
exception to this behavior were ligands 7 and 8 bearing an
N-isobutyl and N-isopropyl fragment, which afforded a 2:1 and
3:1 mixture of diastereomeric complexes, respectively (Table
2, entries 6 and 7). To check whether this diastereoselectivity
could be improved, the initial 2:1 mixture of 18a/18b was
subjected to thermodynamic equilibration in three experimental
conditions: extended heating in toluene (65 °C, 18 h), heating
in CO atmosphere (1 bar, 65 °C, 18 h), and heating in the
presence of 0.1 equiv of dibenzyl sulfide (65 °C, 18 h). Both
CO and sulfide should enhance equilibration through open
nonbridged phosphine complexes.17–19 Experimentally, heating
alone resulted in no equilibration of the initial mixture; however,
the use of CO or sulfide produced equilibration toward a 1:1
mixture of complexes 18a/18b. These results suggest that
tolylsulfinamide PNSO ligands equilibrate slowly compared to
tert-butylsulfinamide ligands (I), and that the selectivity ob-
served for ligands 7 and 8 is due to a kinetic control during the
ligand exchange process rather than to thermodynamic equili-
bration of the final tetracarbonyl complexes.
a
As determined by H NMR spectroscopy. b The borane-free ligand 8
1
was used; therefore DABCO was not employed in this case.
TABLE 3. Synthesis of Chiral PNSO Ligandsa
a Reagents and conditions: (a) Ti(OEt)4, CH2Cl2, ∆, 1.5 h with 1.3
equiv of one of the following: benzaldehyde (entry 1), isobutyraldehyde
(entry 2), or acetone (entry 3). (b) NaBH4, EtOH, rt, overnight. (c)
BuLi, THF, -78 °C, Ph2PCl, then BH3–SMe2 at -30°C. (d) BuLi, THF,
-78 °C, Ph2PCl. b Product 8 was isolated as borane-free ligand.
Chiral N-Phosphino-p-tolylsulfinamide Ligands. After
studying the coordination behavior of racemic PNSO ligands,
we undertook the synthesis of the optically pure ligands 1, 7,
and 8 (Table 3). Condensation of commercially available S-(+)-
p-tolylsulfinamide 23 with the corresponding aldehyde/ketone
reagent with Ti(OEt)4 as a Lewis acid and water scavenger
followed by in situ reduction with NaBH4 afforded the corre-
sponding sulfinamides in 87-58% yield.20 Phosphinylation
reaction and protection with borane provided the chiral ligands
(-)-1-BH3 and (-)-7-BH3 in good yields. Alternatively, (-)-8
was isolated as a stable borane-free ligand.
With these optically pure ligands in our hands, the
corresponding tetracarbonyl dicobalt complexes of TMSC2H,
PhC2H, and HO(CH3)2CC2H were prepared (Table 4). For
trimethylsilylacetilene complexes analogous yields and se-
lectivity as observed for the racemic series were obtained
(Table 4, entries 1-3). Reaction of ligands 7 and 8 with
phenylacetylene and 2-methyl-3-butyn-2-ol dicobalt com-
plexes provided the corresponding complexes with excellent
yields but almost no selectivity (Table 4, entries 4-7). Most
notably, optically pure diastereomeric complexes 18a, 19a,
24b, and 25a could be crystallized from hexane/toluene
(17) Sola`, J.; Riera, A.; Verdaguer, X.; Maestro, M. A. Organometallics 2006,
25, 5795–5799.
(18) Hay, A. M.; Kerr, W. J.; Kirk, G. G.; Middlemiss, D. Organometallics
1995, 14, 4986–4988.
(19) Sun, H.; Gu, J.; Zhang, Z.; Lin, H.; Ding, F.; Wang, Q. Angew. Chem.,
Int. Ed. 2007, 46, 7498–7500.
(20) Tanuwidjaja, J.; Peltier, H. M.; Ellman, J. A. J. Org. Chem. 2007, 72,
626–629.
7082 J. Org. Chem. Vol. 73, No. 18, 2008

N-Phosphino-p-tolylsulfinamide Ligand
TABLE 4. Ligand Exchange Reaction with Optically Pure PNSO
Ligands and Dicobaltalkyne Complexes
TABLE 5. Pauson-Khand Reaction of Optically Pure Complexes
with Norbornadiene
a Yield of isolated product after purification by flash chromatography.
b Enantiomeric excess determined by either chiral GC or HPLC.
a
As determined by H NMR spectroscopy. b The borane-free ligand 8
1
was used; therefore DABCO was not employed in this case.
on the basis of higher backbonding within the metal and
sulfur centers in the case of arylsulfinamide ligands, and is
indicative of increased bond strength. Consequently, aryl-
sulfinamide PNSO ligands are less hemilabile than their tert-
butyl counterparts. This fact could explain why thermody-
namic equilibration between the two diastereomeric complexes
requires stronger reaction conditions (i.e., CO pressure, sulfur
additive).
Finally, we tested the diastereomerically and optically pure
tetracarbonyl complexes obtained in the asymmetric thermal
intermolecular Pauson-Khand reaction with norbornadiene
at 70 °C (Table 5). Complexes 18a and 19a produced (-)-
cyclopentenone 28 in 82% ee and 50% ee, respectively (Table
5, entries 1 and 2). When a phenyl group is attached to the
dicobalt-alkyne core, better selectivities were obtained with
94% and 89% ee (Table 5, entries 3 and 4). Finally, the
complexes derived from 2-methyl-3-butyn-2-ol, a much more
difficult substrate, provided selectivities between 11 and 28%
ee (Table 5, entries 5 and 6). From the stereochemical point
of view it is important to mention, that complexes of the Xa
series always provided levorotatory products, while Xb
complexes provided the (+) enantiomer. As previously
determined, alkene reaction at the Pro-R cobalt atom provides
levorotary products, while alkene reaction at the Pro-S center
provides dextrorotatory products.8,22 The levorotatory cy-
clopentenone produced from 18a entail that norbornadiene
reacts mainly at the Pro-R metal center where the sulfinamide
was attached (see the X-ray, Figure 2). All the experiments
described in Table 5 are in agreement with the stereochemical
outcome observed for 18a. Thus, diastereomers 18a, 19a,
25a, 26a, and 27a (S bonded to Pro-R Co) provided
levorotatory products, while 24b and 26b (S bonded to Pro-S
Co) provided dextrorotatory ones.
FIGURE 2. ORTEP plot for crystal structure of 18a. The sulfur atom
is bonded to the Pro-R cobalt atom (Co1).
mixtures.21 Alternatively, diastereomeric mixtures 26a/26b
and 27a/27b derived from 2-methyl-3-butyn-2-ol could be
separated by flash chromatography.
The structure of the major isomer 18a was firmly estab-
lished by X-ray analysis (Figure 2). In a similar fashion as
type I ligands, N-phosphino-p-tolylsulfinamides work as P,S
bridged ligands. In the present case, the phosphorus was
attached to cobalt Pro-S, while the sulfur atom was linked
to the Pro-R center. The ligand and the alkyne substituent
adopted an anti conformation to minimize steric interactions.
The Co-S bond observed for 18a (Figure 2) was shorter
(2.17Å) than the same bond in tert-butylsulfinamide com-
plexes (2.19 Å).10 This shorter distance may be rationalized
With this in mind, two mechanistic scenarios are possible:
either the N-phosphino-p-tolylsulfinamides operate as hemilabile
(21) Diastereomeric complexes can be distinguished from one another by
1H NMR by means of the terminal alkyne resonance (5.53-6.25 ppm). The Xa
series of diastereomers display 2-8 Hz coupling constant to phosphorus, while
the Xb series display a coupling constant between 9 and 12 Hz.
´
(22) Castro, J.; Moyano, A.; Perica`s, M. A.; Riera, A.; Alvarez-Larena, A.;
Piniella, J. F. J. Am. Chem. Soc. 2000, 122, 7944–7952.
J. Org. Chem. Vol. 73, No. 18, 2008 7083

Reve´s et al.
(CH3), 29.1 (CH), 48.7 (CH2), 126.0 (CH), 129.5 (CH), 141.1 (C),
141.2 (C) ppm; MS (CI-NH3) m/z 212 [(M + H)+, 100%]. HRMS
(ESI) calcd for C11H17NOS + H 212.1103, found 212.1111.
(S)-(+)-N-Isopropyl-p-tolylsulfinamide. Following the general
procedure, 1 g of S-(+)-p-tolylsulfinamide (6.443 mmol), 0.583
mL of dry acetone (8.376 mmol), 6.76 mL of Ti(OEt)4 (32.241
mmol), and 293 mg of NaBH4 (3.86 mmol) were used. Chroma-
tography on silica gel (90:10 hexane/EtOAc) afforded 735 mg
(58%) of (S)-(+)-N-isopropyl-p-tolylsulfinamide as a white solid.
Mp 77-78 °C. [R]D +96 (c 0.108, CHCl3); IR (KBr) νmax 3171,
1490, 1445, 1382, 1364, 1139, 1127, 1085, 1050, 1031, 1017, 989
cm-1; 1H NMR (400 MHz, CDCl3) δ 1.15 (d, J ) 6 Hz, 3H), 1.29
(d, J ) 6 Hz, 3H), 2.41 (s, 3H), 3.60 (oc, J ) 6 Hz, 1H), 3.78 (d,
J ) 6 Hz, 1H), 7.29 (d, J ) 8 Hz, 2H), 7.59 (d, J ) 8 Hz, 2H)
ppm; 13C NMR (100 MHz, CDCl3) δ 21.5 (CH3), 24.7 (CH3), 25.1
(CH3), 46.2 (CH), 125.9 (CH), 129.7 (CH), 141.3 (C), 142.5 (C)
ppm; MS (ESI, H2O:CH3CN (1:1) 1% formic) m/z 417 [(2 M +
Na)+, 2%], 395 [(2 M + H)+, 2%], 336 [6%], 220 [(M + Na)+,
4%], 198 [(M + H)+, 56%], 181 [(M - O)+, 12%], 139 [(M -
C3H8N)+, 100%]; HRMS (ESI) calcd for C10H15NOS + H
198.0947, found 198.0946.
General Procedure for the Synthesis of (S)-N-Phosphino-p-
tolylsulfinamide Borane Complexes. An oven-dried, 100 mL, one-
necked, round-bottomed flask, equipped with a magnetic stirring
bar, was charged with the corresponding sulfinamide (1.89 mmol)
under a N2 purge. Anhydrous THF (20 mL) was added and the
solution was cooled to -78 °C. n-BuLi 2.5 M (0.83 mL, 2.08 mmol)
was added dropwise via a syringe, which resulted in the solution
turning red. After the solution was stirred for 15 min at -78 °C,
ClPPh2 (2.08 mmol) was added via a syringe and the reaction
mixture turned yellow. The solution was stirred for 1 h, during
which time the temperature was warmed to -30 °C. At this point,
0.27 mL of BH3-SMe2 (2.83 mmol) was added. The solution was
then allowed to warm to 0 °C. Et2O (20 mL) and H2O (10 mL)
were carefully added in this order. The organic layer was dried
over anhydrous magnesium sulfate, filtered, and concentrated under
vacuum. The crude product was purified on silica gel (90:10 hexane/
EtOAc), affording the desired borane-protected (S)-N-phosphino-
p-tolylsulfinamides.
ligands, or alternatively the ligand functions as a solid bridged
ligand while the alkene reaction occurs through a labilized
CO ligand in the same metal center. The increased S-Co
strength observed in the crystal structure of 18a supports the
second mechanistic hypothesis and could explain the lower
selectivities observed for N-phosphino-p-tolylsulfinamides ligands
(II) in the Pauson-Khand reaction compared to their tert-butyl
PNSO analogues (I).
Conclusions
We have synthesized a family of racemic and optically pure
borane-protected N-phosphino-p-tolylsulfinamide ligands. Our
results have shown that these ligands are stable in solution under
the deprotection conditions (DABCO, 65 °C). The steric bulk
on nitrogen is of major relevance and determines the final
stability of the PNSO ligands. Thus, we have identified
N-phosphino-N-isopropyl-p-tolylsulfinamide as the stable bo-
rane-free PNSO ligand. Coordination of this type of ligands with
alkyne-dicobalt complexes provided, in general, low diaste-
reoselectivities. The following experimental findings (a) ham-
pered equilibration of diastereomeric complexes and (b) reduced
the S-Co bond length with respect tert-butyl PNSO complexes,
indicating that the presence of a tolyl group on sulfur reduces
the hemilabile character of the PNSO ligands, which is
detrimental for selectivity in the Pauson-Khand reaction.
However, the alkene reaction still occurs predominantly at the
metal center where the sulfinamide is bonded, as deduced from
the absolute configuration of the resulting Pauson-Khand
product.
Experimental Section
General Procedure for the Preparation of (S)-N-Alkyl-p-tolyl-
sulfinamides. A 100 mL, two-necked, round-bottomed flask,
equipped with a magnetic stirring bar and rubber septum, was
charged with 3.22 mmol of S-(+)-p-tolylsulfinamide under a N2
purge. Thirty milliliters of CH2Cl2 and 4.19 mmol of aldehyde were
added. Immediately, 3.40 mL of Ti(OEt)4 (16.1 mmol) was added
via a syringe. The reaction mixture was heated to reflux during
1.5 h. The mixture was concentrated under vacuum and a yellow
oil was obtained. This oil was then dissolved in 20 mL of EtOH
and 3.86 mmol of NaBH4 was added. The reaction mixture was
kept at room temperature for 15 h. The resulting suspension was
filtered through Celite and the solution was concentrated under
vacuum. Flash chromatography on SiO2 (80:20 hexane/EtOAc)
afforded the desired (S)-N-alkyl-p-tolylsulfinamides.
(S)-(-)-N-Benzyl-N-diphenylphosphino-p-tolylsulfinamide Bo-
rane Complex, (-)-1-BH3. Following the general procedure, 500
mg of (S)-(+)-N-Benzyl-p-tolylsulfinamide (2.04 mmol), 0.90 mL
of BuLi 2.5 M (2.24 mmol), 0.40 mL of ClPPh2 (2.24 mmol), and
0.29 mL of BH3-SMe2 (3.06 mmol) were used. Chromatography
on silica gel (90:10 hexane/EtOAc) afforded 768 mg (85%) of (-)-
1-BH3 as a white foam. [R]D -59.0 (c 0.50, CHCl3); IR (film) νmax
1
3058, 2961, 2871, 2389, 2347, 1437 cm-1; H NMR (400 MHz,
CDCl3) δ 0.90-1.89 (br, 3H, BH3), 2.28 (s, 3H), 4.36 (dd, J ) 16
and 16 Hz, 1H), 4.64 (dd, J ) 16 and 8 Hz, 1H), 6.91-6.98 (m,
5H), 7.06 (m, 2H), 7.25 (m, 2H), 7.40-7.51 (m, 6H), 7.79 (m,
4H) ppm; 13C NMR (100 MHz, CDCl3) δ 21.4 (CH3), 46.8 (d, JP
) 4 Hz, CH2), 125.9 (CH), 126.7 (CH), 127.6 (CH), 128.6 (d, JP
) 59 Hz, C), 128.8 (d, JP ) 11 Hz, CH), 128.9 (CH), 129.0 (d,
JP ) 11 Hz, CH), 129.6 (CH), 129.9 (d, JP ) 60 Hz, C), 131.9 (d,
JP ) 2 Hz, CH), 132.3 (d, JP ) 2 Hz, CH), 133.0 (d, JP ) 11 Hz,
CH), 133.3 (d, JP ) 11 Hz, CH), 136.6 (C), 139.6 (d, JP ) 5 Hz,
C), 142.1 (C) ppm; 31P NMR (121 MHz, CDCl3) 76.5 ppm; MS
(QI, NH3) m/z 430 [(M - BH3)+, 74%], 442 [(M - H)+, 61%],
444 [(M + H)+, 25%], 461 [(M + NH4)+, 11%]; HRMS (ESI)
calcd for C26H27BNOPS-H 442.1566, found 442.1558.
(S)-(+)-N-Benzyl-p-tolylsulfinamide.23 Following the general
procedure, 500 mg of S-(+)-p-tolylsulfinamide (3.22 mmol), 0.42
mL of benzaldehyde (4.19 mmol), 3.36 mL of Ti(OEt)4 (16.10
mmol), and 146 mg of NaBH4 (3.86 mmol) were used. Chroma-
tography on SiO2 (80:20 hexane/EtOAc) afforded 650 mg (82%)
1
of (S)-(+)-N-benzyl-p-tolylsulfinamide. Mp 84-86 °C. H NMR
(400 MHz, CDCl3) δ 2.42 (s, 3H), 3.91 (dd, J ) 15 and 8 Hz,
1H), 4.25 (m, 2H), 7.28-7.34 (m, 7H), 7.66 (m, 2H) ppm.
(S)-(+)-N-Isobutyl-p-tolylsulfinamide. Following the general
procedure, 500 mg of S-(+)-p-tolylsulfinamide (3.22 mmol), 0.38
mL of isobutyraldehyde (4.19 mmol), 3.36 mL of Ti(OEt)4 (16.10
mmol), and 146 mg of NaBH4 (3.86 mmol) were used. Chroma-
tography on SiO2 (80:20 hexane/EtOAc) afforded 584 mg (87%)
of (S)-(+)-N-isobutyl-p-tolylsulfinamide as a colorless oil. [R]D
+143.5 (c 1.00, CHCl3); IR (film) νmax 3214, 2956, 2870, 1087,
1057 cm-1; 1H NMR (400 MHz, CDCl3) δ 0.88 (d, J ) 7 Hz, 3H),
0.90 (d, J ) 7 Hz, 3H), 1.72 (m, 1H), 2.41 (s, 3H), 2.64 (m, 1H),
2.93 (m, 1H), 4.12 (br, 1H), 7.30 (d, J ) 8 Hz, 2H), 7.58 (d, J )
8 Hz, 2H) ppm; 13C NMR (100 MHz, CDCl3) δ 20.2 (2CH3), 21.4
(S)-(-)-N-Isobutyl-N-diphenylphosphino-p-tolylsulfinamide
Borane Complex, (-)-7-BH3. Following the general procedure,
400 mg of (S)-(+)-N-Isobutyl-p-tolylsulfinamide (1.89 mmol), 0.83
mL of BuLi (2.5 M, 2.08 mmol), 0.37 mL of ClPPh2 (2.08 mmol),
and 0.27 mL of BH3-SMe2 (2.83 mmol) were used. Chromatog-
raphy on silica gel (90:10 hexane/EtOAc) afforded 569 mg (74%)
of (-)-7-BH3 as a white foam. [R]D -161.7 (c 0.94, CHCl3); IR
1
(film) νmax 3057, 2960, 2926, 2870, 2389, 2347, 1437 cm-1; H
NMR (400 MHz, CDCl3) δ 0.60 (d, J ) 7 Hz, 3H), 0.66 (d, J )
7084 J. Org. Chem. Vol. 73, No. 18, 2008

N-Phosphino-p-tolylsulfinamide Ligand
7 Hz, 3H), 0.90-1.87 (br, 3H, BH3), 1.66 (m, 1H), 2.39 (s, 3H),
2.78 (ddd, J ) 15, 15, and 8 Hz, 1H), 3.40 (ddd, J ) 15, 9, and 6
Hz, 1H), 7.20 (m, 4H), 7.54 (m, 6H), 7.81 (m, 2H), 7.98 (m, 2H)
ppm; 13C NMR (100 MHz, CDCl3): δ 20.2 (CH3), 20.4 (CH3), 21.5
(CH3), 28.4 (CH), 52.7 (d, JP ) 6 Hz, CH2), 125.8 (CH), 128.9 (d,
JP ) 3 Hz, CH), 129.0 (d, JP ) 4 Hz, CH), 129.5 (d, JP ) 60 Hz,
C), 129.9 (CH), 131.0 (d, JP ) 63 Hz, C), 132.0 (d, JP ) 2 Hz,
CH), 132.3 (d, JP ) 2 Hz, CH), 132.9 (d, JP ) 10 Hz, CH), 133.4
dicobalt complex (0.80 mmol) were used. Chromatography on silica
gel (95:5 hexane/EtOAc) afforded 464 mg (88%) of 18a/18b (2:1)
as a red solid. Then 120 mg (23%) of major diastereomer 18a was
isolated by simple crystallization in a hexane/toluene solvent
1
mixture. IR (film) νmax 2960, 2034, 2002, 1978 cm-1; H NMR
(400 MHz, C6D6) δ 0.03 (d, J ) 6 Hz, 3H), 0.07 (d, J ) 6 Hz,
3H), 0.37 (s, 9H), 0.98 (m, 1H), 1.90 (s, 3H), 2.54 (m, 1H), 3.39
(ddd, J ) 15, 5, and 2 Hz, 1H), 5.98 (d, J ) 8 Hz, 1H), 6.86 (d,
J ) 8 Hz, 2H), 7.01-7.14 (m, 6H), 7.81 (m, 4H), 7.90 (d, J ) 8.0
Hz, 2H) ppm; 13C NMR (100 MHz, C6D6) δ 0.9 (3CH3), 19.1 (CH3),
20.1 (CH3), 21.1 (CH3), 26.5 (CH), 54.7 (d, JP ) 5 Hz, CH2), 86.1
(CH), 94.1 (C), 125.6 (CH), 128.7 (d, JP ) 10 Hz, CH), 129.1 (d,
JP ) 10 Hz, CH), 129.5 (CH), 129.9 (CH), 130.7 (d, JP ) 13 Hz,
CH), 131.3 (CH), 133.9 (d, JP ) 14 Hz, CH), 135.9 (d, JP ) 39
Hz, C), 138.5 (d, JP ) 35 Hz, C), 141.7 (C), 149.4 (d, JP ) 12 Hz,
C) ppm; 31P NMR (121 MHz, C6D6) 116.1 ppm; MS (ESI, H2O:
CH3CN (1:1) 1% formic) m/z 612 [(M + H - 4CO)+, 38%], 640
[(M + H - 3CO)+, 25%], 668 [(M + H - 2CO)+, 12%], 696 [(M
+ H - CO)+, 42%], 724 [(M + H)+, 62%]; HRMS (ESI) calcd
for C32H36Co2NO5PSSi + H 724.0558, found 724.0577.
(d, JP ) 11 Hz, CH), 139.8 (d, JP ) 5 Hz, C), 142.2 (C) ppm; 31
P
NMR (121 MHz, CDCl3) 74.6 ppm; MS (ESI, H2O:CH3CN (1:1)
1% formic) m/z 256 [(C11H19BNOPS + H)+, 16%], 408 [(M -
H)+, 100%], 409 [(M)+, 22%], 410 [(M + H)+, 10%]; HRMS (ESI)
calcd for C23H29BNOPS-H 408.1716, found 408.1721.
(S)-(-)-N-Isopropyl-N-diphenylphosphino-p-tolylsulfina-
mide, (-)-8. Following the general procedure, 630 mg of (S)-(+)-
N-isopropyl-p-tolylsulfinamide (3.19 mmol), 3.51 mL of LiHMDS
(1.0 M, 3.51 mmol), and 0.70 mL of ClPPh2 (2.24 mmol) were
used. No borane was required to stabilize the ligand in this case.
Chromatography on silica gel (80:20 hexane/EtOAc) afforded 785
mg (65%) of (-)-8 as a white foam. [R]D -171.8 (c 0.1, CHCl3);
IR (film) νmax 3053, 2996, 1481, 1433, 1381, 1132, 1087, 1067,
991 cm-1; 1H NMR (400 MHz, CDCl3) δ 0.95 (d, J ) 7 Hz, 3H),
1.36 (d, J ) 7 Hz, 3H), 2.32 (s, 3H), 3.84 (non, J ) 7 Hz, 1H),
6.88 (d, J ) 8 Hz, 2H), 7.08 (d, J ) 8 Hz, 2H), 7.42 (m, 6H), 7.62
Co2(µ-TMSC2H)(CO)4(µ-C22H24NOPS), 19a. Following the
general procedure, 200 mg (0.524 mmol) of (-)-8 and 211 mg
(0.577 mmol) of trimethylsilylacetylene dicobalt complex were
used. No DABCO was used in this case. The reaction mixture was
kept at 65 °C for 7 h. Flash chromatography on silica gel (95:5
hexane/EtOAc) afforded 346 mg (92%) of a 19a/19b mixture
(3:1) as a red solid. Crystallization in a mixture of hexane and
toluene provided 227 mg (60%) of the major diastereomer 19a. IR
(td, J ) 2 and 8 Hz, 2H), 7.70 (td, J ) 1 and 8 Hz, 2H) ppm; 13
C
NMR (100 MHz, CDCl3) δ 21.3 (CH3), 23.4 (d, JP ) 10 Hz, CH3),
24.8 (d, JP ) 10 Hz, CH3), 46.8 (d, JP ) 20 Hz, CH), 125.6 (CH),
128.5 (CH), 128.6 (d, JP ) 5 Hz, CH), 128.8 (d, JP ) 8 Hz, CH),
129.7(CH), 130.3 (CH), 131.3 (d, JP ) 19 Hz, CH), 134.7 (d, JP )
24 Hz, CH), 137.7 (d, JP ) 11 Hz, C), 138.8 (d, JP ) 13 Hz, C),
140.9 (C), 141.7 (C). ppm; 31P NMR (121 MHz, CDCl3) 39.1 ppm;
MS (ESI, H2O:CH3CN (1:1) 1% formic) m/z 260 [33%], 382 [(M
+ H)+, 12%], 519 [(2[iPrNP(O)Ph2] + H)+, 100%], 541 [8%], 584
[7%], 800 [(3[iPrNP(O)Ph2] + Na)+, 11%]; HRMS (ESI) calcd
for C22H24NOPS + H 382.1389, found 382.1376.
1
(KBr) νmax 2031, 1996, 1969, 1978 cm-1; H NMR (400 MHz,
C6D6) δ 0.17 (d, J ) 7 Hz, 3H), 0.36 (s, 3H), 0.99 (d, J ) 7 Hz,
3H), 1.91 (s, 3H), 3.69 (hep, J ) 6 Hz, 1H), 6.04 (d, J ) 8 Hz,
1H), 6.85 (d, J ) 8 Hz, 2H), 7.10 (m, overloap with solvent peak,
6H), 7.91 (t, J ) 8 Hz, 4H), 7.98 (d, J ) 9.2 Hz, 4H) ppm; 13C
NMR (100 MHz, C6D6) δ 0.9 (d, J ) 2 Hz, 3CH3), 21.1 (CH3),
23.5 (CH3), 23.6 (CH3), 58.3 (d, JP ) 5 Hz, CH), 85.5 (d, JP ) 11
Hz, CH), 93.4 (C), 126.3 (CH), 128.7 (d, JP ) 10 Hz, CH), 129.1
(d, JP ) 10 H, CH), 129.3 (CH), 129.8 (CH), 130.4 (d, JP ) 13 H,
CH), 131.1 (CH), 133.6 (d, JP ) 14 Hz, CH), 136.4 (d, JP ) 38
Hz, C), 139.1 (d, JP ) 36 Hz, C), 141.6 (C), 149.7 (d, JP ) 12 Hz,
C) ppm; 31P NMR (121 MHz, C6D6) 114.5 ppm; MS (ESI, H2O:
CH3CN (1:1) 1% formic) m/z 121 [100%], 282 [42%], 598 [(M +
H - 4CO)+, 79%], 626 [(M + H - 3CO)+, 46%], 654 [(M + H
- 2CO)+, 20%], 682 [(M + H - CO)+, 58%], 710 [(M + H)+,
48%], 1436 [(2 M + NH4)+, 4%]; HRMS (ESI) calcd for
C31H34Co2NO5PSSi+H 710.0401, found 710.0393.
Dicobalt-Tetracarbonyl Complexes of Optically Pure
PNSO Ligands: General Procedure. A Schlenk tube equipped
with a magnetic stirring bar was charged with 0.73 mmol of
corresponding borane-protected PNSO ligand, 1.09 mmol of
DABCO, and 0.80 mmol of trimethylsilylacetylene dicobalt com-
plex. The reaction mixture was purged with N2 and 10 mL of
toluene was added. The mixture was kept at 65 °C for 2 h. The
crude product was concentrated under vacuum and purified on silica
gel(95:5hexane/EtOAc),therebyobtainingPNSOdicobalt-tetracarbonyl
complexes as red solids.
Co2(µ-PhC2H)(CO)4(µ-C23H26NOPS), 24b. Following the gen-
eral procedure, 200 mg of (-)-7-BH3 (0.49 mmol), 82 mg of
DABCO (0.73 mmol), and 227 mg of phenylacetylene dicobalt
complex (0.59 mmol) were used. Chromatography on silica gel
(95:5 hexane/EtOAc) afforded 330 mg (93%) of 24a/24b (1:1) as
a red solid. This mixture was crystallized twice in hexane/toluene
solvent mixtures to afford 60 mg of diastereomer 24b. IR (film)
Co2(µ-TMSC2H)(CO)4(µ-C26H24NOPS), 13a/13b. Following
the general procedure, 196 mg of (-)-1-BH3 (0.44 mmol), 74 mg
of DABCO (0.66 mmol), and 185 mg of trimethylsilylacetylene
dicobalt complex (0.37 mmol) were used. Chromatography on silica
gel (95:5 hexane/EtOAc) afforded 283 mg (85%) of 13a/13b (1:1)
1
as a red solid. IR (film) νmax 2961, 2035, 2002, 1978 cm-1; H
NMR (400 MHz, C6D6) δ 0.35/0.39 (2s, 9H), 1.75/1.77 (2s, 3H),
4.11 (m, 1H), 4.75 (m, 1H), 5.92 (m, 1H), 6.03-6.13 (m, 2H),
6.48-6.55 (m, 4H), 7.01-7.14 (m, 7H), 7.63 (m, 2H), 7.63-7.84
(m, 3H), 7.94 (m, 1H) ppm; 13C NMR (100 MHz, C6D6) δ 0.8/0.9
(d, JP ) 2 Hz, 3CH3), 20.8/20.9 (CH3), 48.5/49.6 (d, JP ) 5 Hz,
CH2), 85.4/86.5 (d, JP ) 12 Hz, CH), 93.7/95.1 (C), 125.9 (CH),
127.7 (m, CH), 127.9 (m, CH), 128.6 (br, CH), 128.6-129.1 (m,
CH), 129.5/129.6 (CH) 130.3/131.3 (d, JP ) 15 Hz, CH), 130.9/
131.0 (CH), 133.6/134.0 (d, JP ) 15 Hz, CH), 135.9/136.8 (m, C),
138.0 (d, JP ) 35 Hz, C), 141.2/141.4 (C), 147.3/147.5 (d, JP )
10 Hz, C) ppm; 31P NMR (121 MHz, C6D6) 115.9/118.5 ppm; MS
(ESI, H2O:CH3CN (1:1) 1% formic) m/z 646 [(M - 4CO)+, 100%],
674 [(M - 3CO)+, 71%], 702 [(M - 2CO)+, 44%], 730 [(M -
CO)+, 44%], 758 [(M + H)+, 26%]; HRMS (ESI) calcd for
C35H34Co2NO5PSSi + H 758.0401, found 758.0365.
1
νmax 2038, 2007, 1982 cm-1; H NMR (400 MHz, C6D6) δ 0.01
(d, J ) 7 Hz, 3H), 0.12 (d, J ) 7 Hz, 3H), 1.13 (m, 1H), 1.87 (s,
3H), 2.64 (m, 1H), 3.44 (ddd, J ) 15, 6, and 3 Hz, 1H), 5.99 (d,
J ) 10 Hz, 1H), 6.83 (d, J ) 8 Hz, 2H), 6.96-7.16 (m, overloap
with solvent peak, 9H), 7.70 (d, J ) 8 Hz, 2H), 7.78 (m, 2H),
7.87-7.95 (m, 4H) ppm; 13C NMR (100 MHz, C6D6) δ 19.2 (CH3),
20.1 (CH3), 21.0 (CH3), 26.9 (CH), 54.6 (d, JP ) 5 Hz, CH2), 73.0
(d, JP ) 12 Hz, CH), 103.8 (d, JP ) 19 Hz, C), 125.7 (CH), 127.5
(CH), 128.7 (CH), 128.8 (CH), 128.9 (CH), 129.6 (CH), 130.1 (CH),
130.3 (d, JP ) 4 Hz, CH), 131.2 (CH), 131.6 (d, JP ) 12 Hz, CH),
133.4 (d, JP ) 15 Hz, CH), 136.5 (d, JP ) 37 Hz, C), 137.1 (d, JP
) 36 Hz, C), 141.0 (C), 142.0 (C), 148.8 (d, JP ) 10 Hz, C) ppm;
31P NMR (121 MHz, C6D6) 114.1 ppm; MS (ESI, H2O:CH3CN
(1:1) 1% formic) m/z 616 [(M - 4CO)+, 66%], 644 [(M - 3CO)+,
31%], 672 [(M - 2CO)+, 24%], 700 [(M - CO)+, 12%], 1477 [(2
M + Na)+, 100%]; HRMS (ESI) calcd for C35H32Co2NO5PS +
Na 750.0295, found 750.0290.
Co2(µ-TMSC2H)(CO)4(µ-C23H26NOPS), 18a. Following the
general procedure, 300 mg of (-)-7-BH3 (0.73 mmol), 123 mg of
DABCO (1.09 mmol), and 310 mg of trimethylsilylacetylene
J. Org. Chem. Vol. 73, No. 18, 2008 7085

Reve´s et al.
Co2(µ-PhC2H)(CO)4(µ-C22H24NOPS), 25a. Following the gen-
eral procedure, 200 mg (0.52 mmol) of (-)-8 and 223 mg (0.58
mmol) of phenylacetylene dicobalt complex were used. The reaction
mixture was kept at 65 °C for 2.5 h. Flash chromatography on silica
gel (EtOAc) afforded 310 mg (83%) of a 1:1 mixture of diaster-
omers 25a and 25b. Crystallization in toluene/hexane mixtures
provided pure 25a (62 mg) as a red/brown solid. IR (KBr) νmax
(m, 1H), 5.72 (d, J ) 2 Hz, 1H), 6.85 (d, J ) 8 Hz, 2H), 7.07 (m,
3H), 7.15 (overlaps with solvent peak, 3H), 7.86 (t, J ) 10 Hz,
4H), 7.96 (d, J ) 8 Hz, 2H), 8.05 (t, J ) 10 Hz, 2H) ppm; 13C
NMR (100 MHz, C6D6) δ 21.1 (CH3), 23.6 (2CH3), 33.0 (CH3),
34.3 (CH3), 58.5 (d, JP ) 5 Hz, CH), 73.4 (CH), 76.3 (C), 126.2
(CH), 128.7 (d, JP ) 10 Hz, CH), 128.9 (d, JP ) 10 Hz, CH),
130.3(CH), 130.9 (CH), 131.8 (d, JP ) 13 Hz, CH), 132.7 (d, JP )
14 Hz, CH), 137.1 (d, JP ) 38 Hz, C), 138.0 (d, JP ) 35 Hz, C),
141.9 (C), 148.7 (d, JP ) 12 Hz, C) ppm; 31P NMR (121 MHz,
C6D6) 114.5 ppm; MS (ESI, H2O:CH3CN (1:1) 1% formic) m/z
678 [(M - OH)+, 100%], 718 [(M + Na)+, 67%], 1413 [(2 M +
Na)+, 23%]; HRMS (ESI) calcd for C31H32Co2NO6PSNa 718.0244,
found 718.0248.
1
2035, 2005, 1984, 1971 cm-1; H NMR (400 MHz, C6D6) δ 0.24
(d, J ) 7 Hz, 3H), 0.98 (d, J ) 7 Hz, 3H), 1.92 (s, 3H), 3.75 (m,
1H), 5.90 (d, J ) 7 Hz, 1H), 6.87 (d, J ) 8 Hz, 2H), 7.06 (m, 6H),
7.16 (overlaps with solvent peak, 3H), 7.79 (d, J ) 8 Hz, 2H),
7.89 (m, 5H), 7.99 (d, J ) 8 Hz, 2H) ppm; 13C NMR (100 MHz,
C6D6) δ 21.1 (CH3), 23.5 (CH3), 23.6 (CH3), 57.9 (d, JP ) 5 Hz,
CH), 73.1 (CH), 102.0 (C), 126.3 (CH), 127.2 (CH), 128.3 (CH),
128.7 (d, JP ) 10 Hz, CH), 128.9 (CH), 129.1 (d, JP ) 9 Hz, CH),
129.3 (CH), 129.9 (CH), 130.1 (d, JP ) 4 Hz, CH), 130.7 (d, JP )
13 Hz, CH), 131.1 (CH), 133.4 (d, JP ) 14 Hz, C), 136.4 (d, JP )
37 Hz, C), 138.8 (d, JP ) 37 Hz, C), 141.7 (C), 149.5 (d, JP ) 13
Hz, C) ppm; 31P RMN (121 MHz, C6D6) 114.0 ppm; MS (ESI,
H2O:CH3CN (1:1) 1% formic) m/z 304 [100%], 602 [(M + H -
4CO)+, 90%], 630 [(M + H - 3CO)+, 7%], 658 [(M + H -
2CO)+, 34%], 736 [(M + Na)+, 31%], 1398 [(2 M - 2CO)+, 27%],
4-(Trimethylsilyl)tricyclo[5.2.1.02,6]decadien-4,8-dien-3-one,
28.7 From 18a: Optically pure tetracarbonyl complex 18a (55 mg,
0.07 mmol), 76 µL of norbornadiene (0.75 mmol), and 2 mL of
toluene were charged in a Schlenk flask under nitrogen and the
reaction was stirred at 70 °C. The reaction was completed after
22 h. Purification by flash chromatography on SiO2 (95:5 hexane/
EtOAc) yielded 12 mg (75%) of (-)-28 as a white solid (82% ee).
From 19a: Optically pure tetracarbonyl complex 19a (50 mg,
0.07 mmol), 70 µL of norbornadiene (0.70 mmol), and 2 mL of
toluene were charged in a Schlenk flask under nitrogen and the
reaction was stirred at 70 °C. The reaction was stopped after 28 h.
Purification by flash chromatography on SiO2 (95:5 hexane/EtOAc)
yielded 9 mg (60%) of (-)-28 as a white solid (50% ee).
GC analysis: Beta-DEX, 160 °C, tR (-) isomer ) 16.8 min. tR
(+) isomer ) 17.6 min.
1449 [(2
M +
Na)+, 37%]; HRMS (ESI) calcd for
C34H30Co2NO5PSNa 736.0138, found 736.0137.
Co2(µ-HO(CH3)2CC2H)(CO)4(µ-C23H26NOPS), 26a and 26b.
Following the general procedure, 200 mg of (-)-7-BH3 (0.49
mmol), 82 mg of DABCO (0.73 mmol), and 216 mg of 2-methyl-
3-butyn-2-ol dicobalt complex (0.59 mmol) were used. This
afforded 298 mg (86%) of 26a/26b (1:1). Chromatography on silica
gel (95:5 hexane/EtOAc) afforded 103 mg of pure 26a and 80 mg
of pure 26b as red solids. 26a: IR (film) νmax 2973, 2037, 2005,
4-Phenyltricyclo[5.2.1.02,6]deca-4,8-dien-3-one, 29.22 From
24b: Optically pure tetracarbonyl complex 24b (55 mg, 0.07 mmol),
76 µL of norbornadiene (0.75 mmol), and 2 mL of toluene were
charged in a Schlenk flask under nitrogen and the reaction was
stirred at 70 °C. The reaction was completed after 2 h. Purification
by flash chromatography on SiO2 (97:3 hexane/EtOAc) yielded 16
mg (97%) of (+)-29 as a white solid (94% ee).
From 25a: Optically pure tetracarbonyl complex 25a (40 mg,
0.06 mmol), 57 µL of norbornadiene (0.56 mmol), and 2 mL of
toluene were charged in a Schlenk flask under nitrogen and the
reaction was stirred at 70 °C. The reaction was completed after
2 h. Purification by flash chromatography on SiO2 (97:3 hexane/
EtOAc) yielded 11 mg (88%) of (-)-29 as a white solid (89% ee).
HPLC analysis: CHIRALCEL OD (25 cm), 2% IPA-98%
heptane, 0.5 mL/min, λ ) 254 nm. tR (+) isomer ) 16.4 min. tR
(-) isomer ) 20.7 min.
1
1979 cm-1; H NMR (400 MHz, C6D6) δ 0.07 (s, 3H), 0.09 (s,
3H), 1.32 (m, 1H), 1.75 (s, 3H), 1.79 (s, 3H), 1.91 (s, 3H), 2.61
(m, 1H), 3.13 (m, 1H), 3.54 (br, 1H), 5.80 (d, J ) 2 Hz, 1H), 6.88
(d, J ) 8 Hz, 2H), 7.05-7.16 (m, overlap with solvent peak, 6H),
7.71 (m, 2H), 7.96 (d, J ) 8 Hz, 2H), 8.03 (m, 2H); 13C NMR
(100 MHz, C6D6) δ 19.8 (2CH3), 21.0 (CH3), 27.1 (CH), 33.2 (CH3),
34.7 (CH3), 56.0 (CH2), 73.4 (CH), 78.6 (C), 110.0 (C), 126.1 (CH),
128.7 (d, JP ) 9 Hz, CH), 128.9 (d, JP ) 10 Hz, CH), 129.7 (CH),
130.6 (CH), 130.7 (CH), 132.3 (d, JP ) 13 Hz, CH), 132.6 (d, JP
) 14 Hz, CH), 137.3 (d, JP ) 36 Hz, C), 137.4 (d, JP ) 40 Hz, C),
142.2 (C), 147.1 (d, JP ) 11 Hz, C) ppm; 31P NMR (121 MHz,
C6D6) 114.8 ppm; MS (ESI, H2O:CH3CN (1:1) 1% formic) m/z
580 [(M - OH - 4CO)+, 5%], 608 [(M - OH - 3CO)+, 6%],
636 [(M - OH - 2CO)+, 8%], 664 [(M - OH - CO)+, 11%],
692 [(M - OH)+, 100%]; HRMS (ESI) calcd for C32H34Co2NO6PS-
OH 692.0475, found 692.0484. 26b: 1H NMR (400 MHz, C6D6) δ
-0.02 (d, J ) 6 Hz, 3H), 0.11 (d, J ) 6 Hz, 3H), 1.11 (m, 1H),
1.50 (s, 3H), 1.51 (s, 3H), 1.87 (s, 3H), 2.60 (m, 1H), 3.42 (m,
1H), 5.53 (d, J ) 10 Hz, 1H), 6.84 (d, J ) 8 Hz, 2H), 7.03-7.16
(m, overlap with solvent peak, 6H), 7.74 (m, 2H), 7.86-7.93 (m,
4H); 13C NMR (100 MHz, C6D6) δ 19.1 (CH3), 20.1 (CH3), 21.1
(CH3), 26.8 (CH), 32.7 (d, JP ) 3 Hz, CH3), 32.8 (d, JP ) 2 Hz,
CH3), 54.7 (d, JP ) 6 Hz, CH2), 71.6 (d, JP ) 11 Hz, C), 72.9
(CH), 121.0 (d, JP ) 17 Hz, C), 125.7 (CH), 128.7 (d, JP ) 9 Hz,
CH), 128.9 (d, JP ) 10 Hz, CH), 129.6 (CH), 130.2 (CH), 131.2
(CH), 131.6 (d, JP ) 12 Hz, CH), 133.3 (d, JP ) 15 Hz, CH),
136.4 (d, JP ) 37 Hz, C), 136.9 (d, JP ) 36 Hz, C), 142.1 (C),
148.7 (d, JP ) 11 Hz, C) ppm; 31P NMR (121 MHz, C6D6) 113.4
ppm.
4-(1-Hydroxy-1-methylethyl)tricyclo[5.2.1.02,6]deca-4,
8-dien-3-one, 30. From 26a: Optically pure tetracarbonyl complex
26a (41 mg, 0.06 mmol), 57 µL of norbornadiene (0.57 mmol), and
2 mL of toluene were charged in a Schlenk flask under nitrogen and
the reaction was stirred at 70 °C. The reaction was completed after
18 h. Purification by flash chromatography on SiO2 (90:10 hexane/
EtOAc) yielded 11 mg (95%) of (-)-30 as a white solid (21% ee).
From 26b: Optically pure tetracarbonyl complex 26b (49 mg,
0.07 mmol), 70 µL of norbornadiene (0.69 mmol), and 2 mL of
toluene were charged in a Schlenk flask under nitrogen and the
reaction was stirred at 70 °C. The reaction was completed after
18 h. Purification by flash chromatography on SiO2 (90:10 hexane/
EtOAc) yielded 12 mg (89%) of (+)-30 as a white solid (28% ee).
From 27a: Optically pure tetracarbonyl complex 27a (50 mg,
0.07 mmol), 72 µL of norbornadiene (0.71 mmol), and 2 mL of
toluene were charged in a Schlenk flask under nitrogen and the
reaction was stirred at 70 °C. The reaction was completed after
21 h. Purification by flash chromatography on SiO2 (90:10 hexane/
EtOAc) yielded 13 mg (90%) of (-)-30 as a white solid (11% ee).
HPLC analysis: CHIRALCEL OD (25 cm), 5% IPA-95%
heptane, 1.0 mL/min, λ ) 254 nm. tR (-) isomer ) 6.3 min. tR
(+) isomer ) 7.0 min.
Co2(µ-HO(CH3)2CC2H)(CO)4(µ-C22H24NOPS), 27a. Following
the general procedure, 200 mg (0.524 mmol) of (-)-8 and 213 mg
(0.577 mmol) of 2-methyl-3-butyn-2-ol dicobalt complex were used.
The reaction mixture was kept at 65 °C for 5.5 h. This afforded
297 mg (81%) of 27a/27b mixture (1.3:1). Flash chromatography
on silica gel (95:5 hexane/EtOAc) afforded 137 mg of diasteromer
27a as a red/brown solid. IR (KBr) νmax 2035, 2002, 1974, 1959
1
cm-1; H NMR (400 MHz, C6D6) δ 0.19 (d, J ) 7 Hz, 3H), 0.98
(23) Garc´ıa-Ruano, J. L.; Alonso, R.; Zarzuelo, M. M.; Noheda, P. Tetra-
hedron: Asymmetry 1995, 6, 1133–1142.
(d, J ) 7 Hz, 3H), 1.69 (s, 6H), 1.91 (s, 3H), 3.10 (br, 1H), 3.70
7086 J. Org. Chem. Vol. 73, No. 18, 2008

N-Phosphino-p-tolylsulfinamide Ligand
Acknowledgment. This work was supported by a MEC grant
(CTQ2005-623). M.R. thanks MEC for a fellowship.
X-ray refinement parameters and crystal data with a complete
numbering scheme, atomic distances, and angles for 18a. This
material is available free of charge via the Internet at
http://pubs.acs.org.
Supporting Information Available: General methods,
procedures, and spectroscopic data for racemic ligands and
complexes, copy of NMR spectra for new compounds, and
JO800710N
J. Org. Chem. Vol. 73, No. 18, 2008 7087