A new approach to enantiopure C3-symmetric molecules

Article abstract of DOI:10.1002/chem.200501031

Chiral base chemistry has been used to create three chiral centres in one pot on a C₃-symmetric substrate. The potential of this new approach to C₃-symmetric molecules is exemplified by the creation of an enantiopure C_3v-symmetric triol, triphosphane and tripyridine. A ruthenium complex of the last compound has been studied by X-ray crystallography.

Full text of DOI:10.1002/chem.200501031

DOI: 10.1002/chem.200501031
A New Approach to Enantiopure C3-Symmetric Molecules
M. Paola Castaldi,[a] Susan E. Gibson,*[a] Matthew Rudd,[a] and Andrew J. P. White[b]
Abstract: Chiral base chemistry has been used to create three chiral centres in one
pot on a C3-symmetric substrate. The potential of this new approach to C3-symmet-
ric molecules is exemplified by the creation of an enantiopure C3v-symmetric triol,
triphosphane and tripyridine. A ruthenium complex of the last compound has
been studied by X-ray crystallography.
Keywords: asymmetric synthesis ·
chiral bases chromium
ruthenium · structure elucidation
·
·
Introduction
kylation of aromatic aldehydes with diethylzinc.[9] Similarly
a titanium complex of the triol 9, constructed from benzene-
Recent widespread interest in molecules with twofold rota-
tional symmetry, and their successful application in several
areas of chemical research, has led, quite naturally, to a sig-
nificant interest in molecules with threefold rotational sym-
metry. Threefold symmetrical molecules are believed to
have significant potential in fields as diverse as nonlinear
optics, host–guest chemistry and catalysis.[1] For many of
these applications, nonracemic chiral molecules are re-
quired, and the synthesis of such molecules is often nontrivi-
al.
The success of the C2-symmetric diphosphane binap [2,2’-
bis(diphenylphosphino)-1,1’-binaphthalene], and the C2-
symmetric diol binol [1,1’-bi(2-naphthol)] in asymmetric cat-
alysis has led, not surprisingly, to interest in the synthesis of
C3-symmetric phosphanes and alcohols. Monophosphanes,
such as 1[2] and 2,[3] the tripodal triphosphanes 3[4] and 4,[5]
and the tetradentate ligand 5,[6] are representative of the
type of phosphanes that have been synthesised and, in some
cases, assayed in catalytic reactions. The catalytic activity of
complexes of triol 6 has been studied in some detail,[7]
whereas catalysis based on triol 7 has yet to be explored.[8]
The triol 8, built from axially chiral units, has recently been
shown to form a titanium complex that gives promising
yields (81–97%) and enantioselectivities (44–98%) in the al-
[a] M. P. Castaldi, Prof. S. E. Gibson, M. Rudd
Department of Chemistry, Imperial College London
South Kensington Campus, London SW7 2 AY (UK)
Fax: (+44)207-594-5804
E-mail: s.gibson@imperial.ac.uk
[b] Dr. A. J. P. White
Department of Chemical Crystallography
Imperial College London, South Kensington Campus
London SW7 2 AY (UK)
138
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Chem. Eur. J. 2006, 12, 138 – 148

FULL PAPER
mary and b-chiral ammonium ions that carry a b-substituent
which is a hydrogen-bond acceptor and can interact with
one of the tripod hydrogen bonds to form a bifurcated hy-
drogen bond.[12]
Having discovered a chiral-base-mediated reaction that
efficiently generates a single chiral centre,[13] we decided to
determine whether or not the reaction could be used to gen-
erate three stereocentres in one pot and thus provide a new
synthetic route to nonracemic, chiral C3-symmetric mole-
cules. Some of the results described herein have been pre-
sented in communication form.[14]
Results and Discussion
Tricarbonylchromium(0) complexes of alkyl benzyl ethers,
such as 12, react with n-butyllithium/chiral diamine 13 and
an electrophile to give the chiral ether complexes 14 in high
yield and enantiomeric excess (Scheme 1).[13] Working with
the (+)-R,S,S,R enantiomer of the diamine,[15] derived from
(R)-a-methylbenzylamine, gives the R configuration at the
new stereocentre, presumably because of the preference of
the base to abstract the pro-R benzylic proton.
1,3,5-tricarboxylic acid and (ꢀ)-(1R,2S)-2-amino-1,2-diphe-
nylethanol effects an enantioselective alkynylation of vari-
ous aldehydes in the presence of diethylzinc.[10]
C3-Symmetric tris(oxazolines) have been at the heart of
several particularly interesting recent studies. For example,
the tris(oxazoline) 10 binds to zinc to generate a complex
that is reminiscent of the tris(histidine)zinc binding site
found in many zinc-based peptidases. Indeed combining tris-
(oxazoline) 10 with zinc trifluoroacetate gave a catalyst that
Scheme 1.
In order to determine whether or not this reaction could
be used to create three chiral centres in a C3-symmetric ar-
rangement, the novel complex, tricarbonyl(1,3,5-trimethoxy-
methylbenzene)chromium(0) 19, was required. Esterifica-
tion of commercially available benzene-1,3,5-tricarboxylic
acid (15) with methanol gave the known triester 16[16a] in ex-
cellent yield (Scheme 2). Modification of the workup of a
literature procedure[16b] for the reduction of 16 with lithium
generated modest but significant enantioselectivities in the
kinetic resolution of various phenyl ester derivatives of N-
protected amino acids by transesterification with meth-
anol.[11] Studies using the tris(oxazoline) 11 have demon-
strated that it binds primary ammonium ions through tripod
hydrogen-bonding and cation–p interactions. The phenyl
substituents of 11 generate a C3-symmetric “screw-sense”
chiral environment that discriminates between a-chiral pri-
Scheme 2.
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139

S. E. Gibson et al.
aluminiumhydride gave triol 17, which on treatment with
four equivalents of sodium hydride followed by a slight
excess of iodomethane smoothly gave the triether 18.[17]
Heating 18 with a slight excess of hexacarbonylchromium(0)
in a 10:1 nBu2O/THFfor 24 h gave the required tricarbonyl-
chromium(0) complex 19 as an air-stable yellow crystalline
solid in 99% yield.
To deprotonate complex 19, diamine (+)-13 was treated
with n-butyllithium, and complex 19 was added to the result-
ing deep red solution of the diamide. After stirring the now
orange solution at ꢀ788C, iodomethane was added which
led to a colour change of the solution to yellow. After con-
siderable experimentation, which included varying the rela-
tive amounts of complex 19, diamine (+)-13 and n-butyl-
lithium, and a study of the effect of dilution on the product
distribution, it proved possible to identify conditions (19/
(+)-13/n-butyl lithium=1:3:6) that minimised the produc-
tion of mono- and dimethylated products and gave the tri-
methylated derivative 20 in an isolated yield of 85%
(Scheme 3).
Figure 1. View of the X-ray crystallographic structure of (+)-20 depicting
a) the molecular structure of the trimethylated complex, b) the C3-sym-
metric nature of the complex.
Scheme 3.
To assess the enantiomeric purity of (+)-20, its enantio-
mer (ꢀ)-20 was synthesised using the enantiomer of the di-
amine derived from (S)-a-methylbenzylamine, that is, (ꢀ)-
13. HPLC analysis of the two enantiomers revealed that the
ee of (+)- and (ꢀ)-20 was 95%.
An X-ray crystallographic analysis of the yellow crystals
(Figure 1a) confirmed that (+)-20 was the R,R,R stereo-
isomer. The orientation of the tricarbonylchromium(0)
“tripod” with respect to the trisubstituted aryl ring is such
that the carbonyl groups are staggered with respect to the
CH(Me)OMe substituents. Interestingly each of the
CH(Me)OMe substituents has adopted an orientation that
places the methoxy moiety “below” the aryl ring plane and
it is also noticeable that the methoxy carbon atom is in each
case oriented in a similar fashion, even though there is free
rotation about its bond to oxygen. Each of the
CH(Me)OMe substituents is oriented similarly with respect
to the central aryl ring, the Ar-C-H dihedral angles being
approximately 25, 19 and 188 for the three substituents.
Overall these conformations mean that the structure has ap-
proximate C3 symmetry, giving the molecule a propeller-like
conformation (Figure 1b).
The tricarbonylchromium(0) unit was subsequently re-
moved from (+)-20. Stirring (+)-20 in methanol in the pres-
ence of two equivalents of ceric ammonium nitrate at room
temperature for 15 min resulted in a 96% yield of analyti-
cally pure C3-symmetric triether (+)-21 (Scheme 3). As
there was no evidence for epimerisation and diastereoiso-
mer generation during this step, as judged by high-field
NMR spectroscopy, it was reasonably assumed that inver-
sion of stereochemistry at all three centres had not occurred
and that the enantiopurity of (+)-20 was uncompromised by
the decomplexation step.
Having established that three chiral centres may be instal-
led in one pot using the model electrophile iodomethane,
we started to consider the introduction of functional groups
that could be used directly or indirectly to bind to metals.
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Asymmetric Synthesis
FULL PAPER
We looked first at allyl bromide and propargyl bromide with
a view to using a hydroboration/oxidation sequence to gen-
erate a triol with the former, and to using click chemistry[18]
with the latter to generate heterocyclic donors in the form
of 1,2,3-triazoles. Reaction of the triether complex 19 with
the chiral diamine (+)-13/nBuLi followed by quenching
with allyl bromide indeed created three chiral centres to
produce (+)-22 in 77% yield and 98% ee (Scheme 4). In
Scheme 4.
contrast, addition of propargyl bromide resulted in the crea-
tion of just one chiral centre and the production of the
monoalkyne (+)-23 in modest enantiopurity (75% ee). Dis-
appointingly, all efforts to date to generate a triol from the
trialkene (+)-22 through hydroboration/oxidation generated
intractable mixtures.
Scheme 5.
alents of dilithium amide and six equivalents of butane. Ad-
dition of triether complex 19 could then lead either to the
formation of a monoanion followed by a sequential quench,
deprotonation, quench, deprotonation, quench sequence or
to the formation of a trianion followed by sequential
quenching of the three anions. In view of the successful use
of iodomethane and allyl bromide (added in excess, typically
nine equivalents), that is, electrophiles that should readily
react with and quench any dilithium amide present in the re-
action mixture, it is tentatively proposed that deprotonation
at the benzylic positions of the complex takes place before
the addition of the electrophile; that is, reaction of complex
19 with three equivalents of dilithium amide produces a tri-
anion represented here by structure 27 (Scheme 6), an
almost certainly over-simplified version of the true struc-
ture.
In view of the range of potential uses of C3-symmetric
triols, a second approach to these compounds was investigat-
ed. This initially involved quenching the reaction mixture
with the aldehyde methanal, and the ketones benzophenone
and propanone (Scheme 5). Whilst methanal delivered a
complex mixture of products, the ketone quenches led to
the isolation of monoalcohols (+)-24 and (+)-25 in high
yields but modest enantiopurity (76 and 78% respectively).
In contrast to the results obtained with benzophenone and
propanone, quenching with ethylene oxide led to the gener-
ation and isolation of triol (+)-26 in good yield (72%) and
acceptable enantiomeric excess (93%). It is anticipated that
this triol will not only be interesting to study as a C3-sym-
metric ligand for transition metals, but will also act as a
gateway to many other C3-symmetric molecules (e.g. esters,
aldehydes, imines).
Why does this proceed to react three times with iodo-
methane, allyl bromide and ethylene oxide but just once
with benzophenone, acetone and propargyl bromide? In-
spection of the putative species that react further and those
that do not reveal that in the former group a dilithium spe-
cies can be invoked (it has been assumed that the primary
The production of mono- and triadducts in the reactions
described above may be explained as follows. In a typical re-
action six equivalents of n-butyllithium are reacted with
three equivalents of diamine (+)-13 to generate three equiv-
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141

S. E. Gibson et al.
structure of (+)-28 is similar to
that of (+)-20, with the carbon-
yl groups staggered with respect
to the aryl substituents, the me-
thoxy groups oriented “below”
the aryl ring plane and the me-
thoxy groups all adopting simi-
lar conformations, with the
carbon atom in each case being
oriented “downwards”. Each of
the CH(PPh2)OMe substituents
is oriented similarly with re-
spect to the central aryl ring,
the Ar-C-H dihedral angles
being about 35, 39 and 408.
Overall the structure has ap-
proximate C3-symmetry and a
propeller-like conformation.
Attempts
to
oxidatively
remove the tricarbonylchromi-
um(0) unit and concomitantly
oxidize the phosphanes to phos-
phane oxides led to complex
mixtures of products. Treatment
with H3B·THFfollowed by
aerial oxidation, however, gave
an excellent yield of the chro-
mium-free triphosphane pro-
tected as its triborane deriva-
tive (+)-29. It is anticipated
that this novel phosphane will
find interesting applications in
asymmetric catalysis.
In a second attempt to intro-
duce heterocyclic donor atoms
onto the C3 scaffold, we investi-
Scheme 6.
alkoxide generated from ethylene oxide reacts with the tri-
fluoroborane present in the reaction mixture, a process that
is less facile for the tertiary alkoxides formed from benzo-
phenone and propanone), whilst in the second group a new
trilithium species can be envisaged. Why the dilithium com-
pounds proceed to react with more electrophile to generate
ultimately triadducts of high enantiomeric purity, whilst the
new trilithium compounds are resistant to further electro-
philic attack and generate monoadducts of modest enantio-
purity on work-up, is as yet unclear, but is probably a func-
tion of the properties of higher order species.
In view of the huge success enjoyed by phosphanes in
transition-metal chemistry in general and asymmetric cataly-
sis in particular, we next investigated the possibility of gen-
erating a nonracemic chiral triphosphane using the chiral-
base methodology. Treatment of 19 with (+)-13/n-butyllithi-
um followed by a chlorodiphenylphosphane quench indeed
gave the yellow crystalline triphosphane (+)-28 in accept-
able yield and high enantiopurity (Scheme 7).
An X-ray crystal structure of (+)-28 confirmed both its
structure and its absolute configuration (Figure 2). The
Scheme 7.
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Asymmetric Synthesis
FULL PAPER
Figure 2. The molecular structure of the triphosphane (+)-28.
gated the effectiveness of bromomethylpyridines as electro-
philes in the chiral base reaction. Although 4- and 2-bromo-
methylpyridine gave complex mixtures, 3-bromomethylpyri-
dine (which is less susceptible to deprotonation) reacted
smoothly to provide the tripyridine complex (+)-30 as a
yellow fluffy solid in good yield and excellent enantiomeric
excess (Scheme 8). Oxidative removal of the tricarbonyl-
chromium(0) unit by using ceric ammonium nitrate proceed-
ed smoothly to give the chromium-free tripyridine (+)-31 in
good yield.
In a first attempt to explore the transition-metal chemis-
try of a C3-symmetric compound synthesized by means of
our new approach, (+)-31 was treated with ruthenium(iii)
trichloride. Anion exchange with ammonium hexafluoro-
phosphate led to yellow crystals of a complex that was iden-
tified as (+)-[Ru{(+)-31}2](PF6)2, that is, complex (+)-32, by
X-ray crystallography.
The X-ray structure of (+)-32 (Figure 3a) shows the ge-
ometry at the ruthenium centre to be close to ideal octahe-
dral, the cis N-Ru-N angles ranging between 89.15(18) and
90.59(19)8 with the trans angles being no more that 18 away
Scheme 8.
the hydrogen atoms on the chiral centres that lie in the
same plane as the C6 ring, the oxygen atoms being oriented
away from the ruthenium centre. Despite these different
conformations, the Ru···A and Ru···B separations are only
slightly different, being approximately 5.62 and 5.59 Š, re-
spectively. In contrast the difference in conformations of the
two ligands does affect intermolecular cation···anion interac-
ꢀ
from linear; the Ru N coordination distances are in the
range 2.129(5)–2.142(5) Š. The two chiral tripyridine ligands
both coordinate to the metal centre in a facial manner and
it is noticeable that the trans-pyridyl units are nearly copla-
nar with each other. The coordination of each ligand is ap-
proximately threefold symmetric (Figure 3b) and these mo-
lecular C3 axes are almost colinear, the vectors between the
metal and the A and B aryl-ring centroids subtending an
angle of approximately 1798 at the ruthenium atom. It is evi-
dent from Figure 3a and b, however, that the two ligands do
not adopt similar conformations, there being marked differ-
ences in the torsion angles about the bonds linking the
chiral carbon centres to their parent C6 aromatic rings. For
the ligand based around ring A, the Ar-C-O torsion angles
are about 11, 11 and 108, whilst for the ring B ligands the
equivalent angles are approximately 59, 57 and 568; that is,
for the ring A ligand, the oxygen atoms are approximately
coplanar with the C6 ring, whilst for the ring B ligand it is
ꢀ
tions, each ligand being involved in a different pattern of C
H···Fcontacts. For the ring A ligand, each of the hydrogen
atoms on the chiral carbon centres links to a PF6 fluorine
ꢀ
atom, whilst for the ring B ligand the shortest C H···Fdis-
tances are for protons on the methyl groups of the methoxy
substituents on the chiral carbon centres (Figure 3c).
Conclusion
A short and versatile route to enantiopure C3-symmetric
molecules, utilizing chiral-base methodology to install three
stereocentres in one pot has been devised and tested. Of the
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143

S. E. Gibson et al.
electrophiles examined, benzophenone, propanone, metha-
nal and propargyl bromide proved to be unsuitable, giving
either monoderivatives or an intractable product mixture,
but iodomethane, allyl bromide, ethylene oxide, chlorodi-
phenylphosphane and 3-bromomethylpyridine all gave good
to excellent yields of enantiopure triderivates. The straight-
forward synthesis of a ruthenium complex of a C3-symmetric
tripyridine generated in this study serves to demonstrate the
potential of our approach for generating new ligands for
transition-metal complexes.
ExperimentalSection
All reactions involving the use of organometallic compounds were per-
formed under an inert atmosphere of dry nitrogen using standard
Schlenk techniques.[19] Reactions involving the use of arene tricarbonyl-
chromium(0) complexes were protected from sunlight. Chiral diamine
(+)-13 was prepared by a literature procedure.[15] Tetrahydrofuran (THF)
was distilled from sodium benzophenone ketyl and used immediately. Di-
chloromethane (DCM) was distilled from calcium hydride and also used
immediately. Methanol (MeOH) was distilled from calcium hydride and
stored under an inert atmosphere over 3 Š molecular sieves. Chlorodi-
phenylphosphine was distilled prior to use and then stored under nitro-
gen. Acetone was purchased from the Aldrich Chemical Company (ACS
grade) and stored under nitrogen over 3 Š molecular sieves. All other re-
agents were used as purchased from commercial sources. The concentra-
tions of the alkyllithium compounds were determined by titration against
[20]
diphenylacetic acid in THF. Flash column chromatography was per-
formed with BDH silica gel (330–70 mm particle size). Thin-layer chroma-
tography (TLC) was performed on Merck TLC plates coated with Merck
silica gel 60. Melting points were recorded on a Buchi 510 melting point
apparatus in open capillaries and are uncorrected. Optical rotations were
recorded on a Perkin–Elmer 241 Polarimeter using a 1 dm path length
and with concentrations given as gmLꢀ1. IR spectra were recorded on a
Perkin–Elmer 1600 FT-IR spectrometer. NMR spectra were recorded at
room temperature on Bruker AC300FA360 and AM500 instruments;
J
values are reported in Hz and chemical shifts in ppm. Mass spectra were
recorded on Micromass Platform II and Micromass AutoSpec-Q spec-
trometers at Imperial College London or JEOL AX 505W spectrometer
at Kings College London. Elemental analyses were performed by the
London Metropolitan University microanalytical service. Analytical
HPLC was performed using a Unicam Crystal 200 pump, a Unicam 100
UV-Vis detector and Daicel Chiralcel OD-H and Chiralpak AD columns
(25”0.46 cm).
[16a]
Trimethylbenzene-1,3,5-tricarboxyalte (16)
:
A 500 mL flask was
charged with benzene-1,3,5-tricarboxylic acid (15; 10.00 g, 47.6 mmol),
MeOH (200 mL) and a magnetic stirrer. Sulfuric acid (2.5 mL) was
added carefully to the mixture and a reflux condenser was fitted. The re-
action mixture was stirred vigorously and heated at reflux for 24 h before
being allowed to cool to room temperature. A saturated solution of
sodium hydrogencarbonate (100 mL) was slowly added to neutralise the
mixture and the contents of the flask were transferred to a separating
funnel. The layers were partitioned and the aqueous layer extracted with
diethyl ether (3”100 mL). The organic layers were combined, dried
(MgSO4) and concentrated in vacuo to give 16 as a white solid (11.90 g,
99%). Rf =0.37 (silica gel; hexane/ethyl acetate 4:1); m.p. 144–1458C (lit.
m.p.[16] 145–1478C); IR (CH2Cl2): n˜max =1730 cmꢀ1 (C=O); 1H NMR
(300 MHz, CDCl3): d=4.00 (s, 9H; OCH3 ”3), 8.88 ppm (s, 3H; CArH”
3); 13C NMR (75 MHz, CDCl3): d=52.6 (OCH3 ”3), 131.2 (CArH”3),
134.6 (CAr ”3), 165.5 ppm (COOCH3 ”3); MS (EI): m/z (%): 252 (33)
[M+], 221 (100) [M+ꢀOCH3], 193 (18) [M+ꢀCO2CH3], 161 (11) [M+
ꢀCO2CH3ꢀCH3OH].
Figure 3. Views of the X-ray crystallographic structure of (+)-32 depict-
ing a) the molecular structure of the ruthenium dication in (+)-32, b) the
1,3,5-Tris(hydroxymethyl)benzene (17):[16b] A 500 mL flask containing a
magnetic stirrer was placed under an inert atmosphere and charged with
lithium aluminiumhydride (2.40 g, 63.0 mmol). THF(150 mL) was added
ꢀ
C3-symmetric nature of the two tripyridine ligands, and c) the C H···F
contacts.
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Asymmetric Synthesis
FULL PAPER
through a syringe. The suspension was vigorously stirred and then cooled
to 08C before a solution of triester 16 (6.00 g, 23.8 mmol) in THF
(150 mL) was introduced through a cannula over a period of 10 min.
After the addition was complete a condenser was fitted and the reaction
mixture heated at reflux for 24 h before being allowed to cool to room
temperature. Upon cooling, water (100 mL) was carefully added. The
mixture was then filtered through Celite pad and the filter cake was
washed thoroughly with CHCl3 (100 mL). The volatiles were removed in
vacuo to give 17 as a white solid (3.90 g, 99%). Rf =0.36 (silica gel;
chloroform/methanol 9:1); m.p. 75–768C (lit. m.p.[17] 778C); IR (CHCl3):
MeOH (3 mL) was added and the solvent removed in vacuo. Purification
of the residue by flash column chromatography (silica gel; hexane/ethyl
acetate 10:0!4:1) afforded (+)-20 as a fluffy yellow solid (0.770 g,
85%). Rf =0.32 (silica gel; hexane/ethyl acetate 4:1). Enantiomeric
excess was determined by HPLC analysis (Chiralpak AD, n-hexane/
propan-2-ol 99.5:0.5, 0.5 mLminꢀ1
, 330 nm); S,S,S enantiomer tr =
18.4 min (minor); R,R,R enantiomer tr =21.2 min (major): ꢂ95% ee;
[a]2D0 =+113 (c=0.0058 in CHCl3); m.p. 85–888C; IR (neat): n˜max =1960
(CꢁO) 1884 cmꢀ1 (CꢁO); 1H NMR (360 MHz, CDCl3): d=1.38 (d, J=
6.5 Hz, 9H; CHCH3 ”3), 3.41 (s, 9H; OCH3 ”3), 4.04 (q, J=6.5 Hz, 3H;
CHCH3 ”3), 5.40 ppm (s, 3H; CCrH”3); 13C NMR (90 MHz, CDCl3): d=
23.2 (CHCH3 ”3), 57.9 (OCH3 ”3), 77.3 (CHCH3 ”3), 89.3 (CCrH”3),
112.5 (CCr ”3), 233.1 ppm (CꢁO”3); MS (EI): m/z (%): 388 (37) [M+],
304 (64) [M+ꢀ3CO], 273 (32) [M+ꢀ3COꢀOCH3], 237 (100) [M+
ꢀCr(CO)3ꢀCH3]; elemental analysis calcd (%) for C18H24CrO6 (388.37):
C 55.66, H 6.23; found: C 55.80, H 6.22.
1
n˜max =3286 cmꢀ1 (OH); H NMR (300 MHz, D2O): d=4.53 (s, 6H; CH2 ”
3), 7.20 ppm (s, 3H; CArH”3); 13C NMR (75 MHz, D2O): d=63.6 (CH2 ”
3), 125.6 (CArH”3), 140.9 ppm (CAr ”3); MS (EI): m/z (%): 168 (100)
[M+], 150 (17) [M+ꢀH2O], 137 (78) [M+ꢀCH2OH], 119 (40) [M+
ꢀCH2OHꢀH2O], 104 (51) [M+ꢀ2CH3OH].
1,3,5-Tris(methoxymethyl)benzene (18):[17] Sodium hydride (3.40 g, 60%
dispersion in mineral oil, 71.4 mmol) previously washed with pentane,
was placed in a 250 mL flask. THF(60 mL) was added by means of a sy-
ringe and the suspension was cooled to 08C. Triol 17 (3.00 g, 17.9 mmol)
was added portion-wise to the reaction mixture over 10 min. A condenser
was fitted and the mixture heated at reflux for 2 h before being allowed
to cool to room temperature. Iodomethane (4.90 mL, 80.3 mmol) was
added through a syringe and the reaction mixture was stirred for 14 h
before a saturated ammonium chloride solution (50 mL) was carefully
added. The layers were separated, the aqueous layer was extracted with
dichloromethane (3”100 mL) and the combined organic layers washed
with brine (100 mL), dried (MgSO4) and concentrated in vacuo to give
18 as a colourless oil (3.70 g, 99%). Rf =0.33 (silica gel; hexane/ethyl ace-
(+)-(R,R,R)-1,3,5-Tris(1-methoxyethyl)benzene ((+)-21): Ceric ammoni-
um nitrate (0.317 g, 0.58 mmmol) was added to a solution of complex
(+)-20 (0.115 g, 0.29 mmol) in MeOH (6 mL). The resulting mixture was
stirred at room temperature for 15 min before being filtered through
Celite and evaporated. Purification of the crude product by flash column
chromatography (silica gel; hexane/ethyl acetate 100:0!95:5) afforded
(+)-21 as a white solid (0.070 g, 96%). Rf =0.32 (silica gel; hexane/ethyl
acetate 9:1); m.p. 238–2408C; [a]2D0 =+157 (c=0.019 in CHCl3); IR
(CH2Cl2): n˜max =3054 (=CH), 1114 cmꢀ1 (C-O-C); 1H NMR (300 MHz,
CDCl3): d=1.44 (d, J=6.5 Hz, 9H; CHCH3 ”3), 3.24 (s, 9H; OCH3 ”3),
4.31 (q, J=6.5 Hz, 3H; CHCH3 ”3), 7.16 ppm (s, 3H;
CArH”3);
13C NMR (75 MHz, CDCl3): d=23.7 (CHCH3 ”3), 56.4 (OCH3 ”3), 79.6
(CHCH3 ”3), 123.1 (CArH”3), 143.9 ppm (CAr ”3); MS (EI): m/z (%):
252 (7) [M+], 237 (100) [M+ꢀCH3]; elemental analysis calcd (%) for
C15H24O3 (252.34): C 71.39, H 9.58; found: C 71.31, H 9.57.
tate 4:1); IR (CH2Cl2): n˜max =1104 cmꢀ1 (C O); 1H NMR (360 MHz,
ꢀ
CDCl3): d=3.31 (s, 9H; OCH3 ”3), 4.38 (s, 6H; CH2 ”3), 7.16 ppm (s,
3H; CArH”3); 13C NMR (90 MHz, CDCl3): d=58.6 (OCH3 ”3), 74.8
(CH2 ”3), 126.6 (CArH”3), 139.0 ppm (CAr ”3); MS (EI): m/z (%): 210
(70) [M+], 178 (79) [M+ꢀOCH3], 165 (100) [M+ꢀOCH3ꢀCH3+H]; ele-
mental analysis calcd (%) for C12H18O3 (210.13): C 68.54, H 8.63; found:
C 68.46, H 8.69.
(+)-(R,R,R)-Tricarbonyl[1,3,5-tris(1-methoxybutyl-3-ene)benzene]chro-
mium(0) ((+)-22): n-Butyllithium (2.40 mL, 2.50m in hexanes, 6.0 mmol)
was added dropwise to a stirred solution of diamine (+)-13 (1.260 g,
3.00 mmol) in dry THF(24 mL) at ꢀ788C. The solution was allowed to
warm to room temperature over a period of 30 min and was then re-
cooled to ꢀ788C. A solution of heat-gun-dried lithium chloride (0.127 g,
3.00 mmol) in THF(8 mL) was added through a cannula and the reaction
mixture was stirred for a further 5 min before a precooled solution
(ꢀ788C) of complex 19 (0.346 g, 1.00 mmol) in THF(8 mL) was intro-
duced dropwise through a short cannula. Stirring was continued for
60 min before allyl bromide (0.78 mL, 9.0 mmol) was added in one por-
tion through a syringe. Stirring was then continued for a further 1.5 h at
ꢀ788C before MeOH (2 mL) was added and the solvent removed in
vacuo. Purification of the resulting residue by flash column chromatogra-
phy (silica gel; hexane/diethyl ether 99:1 ! 95:5) afforded (+)-22 as a
yellow solid (0.360 g, 77%). Rf =0.70 (silica gel; hexane/diethyl ether
2:1). Enantiomeric excess was determined by HPLC analysis (Chiralcel
OD-H, n-hexane/propan-2-ol 99:1, 0.5 mLminꢀ1, 330 nm); S,S,S enantio-
mer tr =8.4 min (minor); R,R,R enantiomer tr =10.2 min (major): 98% ee.
[a]2D0 =+75 (c=0.023 in CHCl3); m.p. 99–1018C; IR (CH2Cl2): n˜max =1962
Tricarbonyl[1,3,5-tris(methoxymethyl)benzene]chromium(0)
(19):
A
250 mL round-bottomed flask containing a stirrer bar and fitted with a
reflux condenser was placed under an inert atmosphere of nitrogen and
charged with compound 18 (3.60 g, 17.2 mmol), hexacarbonylchromi-
um(0) (4.20 g, 19.1 mmol), dry THF(18 mL) and dry di- n-butyl ether
(180 mL). The suspension was thoroughly saturated with nitrogen, before
it was heated to 1408C and maintained under an inert atmosphere at the
same temperature for 24 h. The yellow reaction mixture was then allowed
to cool to room temperature. Filtration of the crude product through
Celite followed by evaporation of the solvent afforded 19 as a yellow
crystalline solid (5.70 g, 99%). Rf =0.36 (silica gel; hexane/ethyl acetate
3:1); m.p. 90–928C; IR (neat): n˜max =1967 (CꢁO) 1891 cmꢀ1 (CꢁO);
1H NMR (360 MHz, CDCl3): d=3.39 (s, 9H; OCH3 ”3), 4.16 (s, 6H;
CH2 ”3), 5.25 ppm (s, 3H; CCrH”3); 13C NMR (90 MHz, CDCl3): d=
59.4 (OCH3 ”3), 73.1 (CH2 ”3), 90.0 (CCrH”3), 108.4 (CCr ”3), 232.3 ppm
(CꢁO”3); MS (EI): m/z (%): 346 (30) [M+], 262 (48) [M+ꢀ3CO], 231
(20) [M+ꢀ3COꢀOCH3], 172 (100) [M+ꢀ3COꢀ3OCH3]; elemental anal-
ysis calcd (%) for C15H18CrO6 (346.29): C 52.03, H 5.24; found: C 52.12,
H 5.33.
1
(CꢁO), 1884 cmꢀ1 (CꢁO); H NMR (500 MHz, CDCl3): d=2.42 (ddd, J=
6.3, 7.0, 20.7 Hz, 3H; CH(OCH3)CHH”3), 2.49 (ddd, J=4.0, 5.2,
20.7 Hz, 3H; CH(OCH3)CHH”3), 3.54 (s, 9H; OCH3 ”3), 4.04 (dd, J=
5.2, 6.3 Hz, 3H; CH(OCH3)CH2 ”3), 4.99 (dd, J=1.4, 17.1 Hz, 3H;
CH2CH=CHH (E)”3), 5.06 (dd, J=1.4, 10.1 Hz, 3H; CH2CH=CHH
(Z)”3), 5.40 (s, 3H; CCrH”3), 5.76 ppm (dddd, J=4.0, 7.0, 10.1, 17.1 Hz,
3H; CH2CH=CH2 ”3); 13C NMR (125 MHz, CDCl3): d=42.7
(CHCH2CH”3), 58.6 (OCH3 ”3), 80.5 (CH(OCH3)”3), 88.6 (CCrH”3),
109.7 (CCrCH”3), 118.3 (CH2CH=CH2 ”3), 133.1 (CH2CH=CH2 ”3),
233.2 ppm (CꢁO”3); MS (EI): m/z (%): 466 (42) [M+], 425 (20) [M+
ꢀC3H5], 382 (100) [M+ꢀ3CO], 350 (13) [M+ꢀ3COꢀCH3OH], 341 (19)
[M+ꢀ3COꢀC3H5], 318 (18) [M+ꢀ3COꢀ2CH3OH], 288 (77) [M+
ꢀ3COꢀ2OCH3ꢀCH3OH], 248 (20) [M+ꢀCr(CO)3ꢀ2C3H5]; elemental
analysis calcd (%) for C24H30CrO6 (466.49): C 61.79, H 6.48; found: C
61.94, H 6.41.
(+)-(R,R,R)-Tricarbonyl[1,3,5-tris(1-methoxyethyl)benzene]chromium(0)
((+)-20): n-Butyllithium (5.60 mL, 2.50m in hexanes, 13.9 mmol) was
added dropwise to
a stirred solution of diamine (+)-13 (2.915 g,
6.93 mmol) in dry THF(204 mL) at ꢀ788C under an inert atmosphere.
The solution was then allowed to warm to room temperature over a
period of 30 min. The resulting deep red solution was recooled to ꢀ788C
and a solution of heat-gun-dried lithium chloride (0.293 g, 6.93 mmol) in
THF(35 mL) was added dropwise through a cannula. The reaction mix-
ture was stirred for a further 5 min before a precooled (ꢀ788C) solution
of complex 19 (0.800 g, 2.31 mmol) in THF(10 mL) was introduced drop-
wise through a short cannula. After stirring the orange solution at ꢀ788C
for a period of 60 min, iodomethane (0.87 mL, 13.9 mmol) was added in
one portion, which resulted in a colour change of the solution to yellow.
The reaction mixture was then stirred for 60 min at ꢀ788C before
(+)-(R)-Tricarbonyl[1-(1-methoxybut-3-ynyl)-3,5-bis(methoxymethyl)-
benzene]chromium(0) ((+)-23): n-Butyllithium (2.64 mL, 2.27m in hex-
Chem. Eur. J. 2006, 12, 138 – 148
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
145

S. E. Gibson et al.
anes, 6.0 mmol) was added to diamine (+)-13 (1.260 g, 3.00 mmol) in
THF(40 mL) at ꢀ788C. The solution was allowed to warm to room tem-
perature (30 min) and was recooled to ꢀ788C. Heat-gun-dried lithium
chloride (0.127 g, 3.00 mmol) in THF(10 mL) was added through a can-
nula and the reaction mixture was stirred for 5 min before a solution of
complex 19 (0.346 g, 1.00 mmol) in THF(6 mL) was introduced. The re-
action mixture was stirred for 1 h, then propargyl bromide (1.01 mL,
80% in toluene, 9.0 mmol) was added through a syringe. Stirring was
continued for a further 1 h at ꢀ788C before MeOH (2 mL) was added
and the solvent removed in vacuo. Purification of the resulting residue by
flash column chromatography (silica gel; hexane/diethyl ether 9:1!5:5)
afforded (+)-23 as a yellow oil (0.345 g, 92%). Rf =0.18 (silica gel;
hexane/diethyl ether 4:1). Enantiomeric excess was determined by HPLC
2.27m in hexanes, 3.0 mmol) was added to diamine (+)-13 (0.630 g,
1.50 mmol) in THF(20 mL) at ꢀ788C. The solution was allowed to warm
to room temperature (30 min) and was recooled to ꢀ788C. Heat-gun-
dried lithium chloride (0.064 g, 1.50 mmol) in THF(5 mL) was added
through a cannula and the reaction mixture was stirred for 5 min before
a solution of complex 19 (0.176 g, 0.50 mmol) in THF(3 mL) was intro-
duced. The reaction mixture was stirred for 1 h, then acetone (0.33 mL,
4.5 mmol) was added followed immediately by BF3·OEt2 complex
(0.38 mL, 3.0 mmol). Stirring was continued for a further 1 h at ꢀ788C
before MeOH (2 mL) was added and the solvent removed in vacuo. Puri-
fication of the resulting residue by flash column chromatography (silica
gel; hexane/diethyl ether 9:1!1:1) afforded (+)-25 as
a yellow oil
(0.177 g, 88%). Rf =0.20 (silica gel; hexane/diethyl ether 1:2). Enantio-
meric excess was determined by HPLC analysis (Chiralcel OD-H, n-
analysis (Chiralcel OD-H, n-hexane/propan-2-ol 95:5, 0.5 mLminꢀ1
330 nm); R enantiomer tr =20.2 min (major); S enantiomer tr =22.3 min
(minor): 75% ee. [a]D20 =+26 (c=0.034 in CHCl3); IR (CH2Cl2): n˜max
,
hexane/propan-2-ol 90:10, 0.5 mLminꢀ1
, 330 nm); R enantiomer tr =
=
14.5 min (major); S enantiomer tr =16.3 min (minor): 78% ee. [a]2D0 =+38
(c=0.010 in CHCl3); IR (CH2Cl2): n˜max =1966 (CꢁO), 1890 cmꢀ1 (CꢁO);
1H NMR (300 MHz, CDCl3): d=1.17 (s, 3H; C(CH3)(CH3)OH), 1.22 [s,
3H; C(CH3)(CH3)OH], 2.21 (s, 1H; OH), 3.46 (s, 6H; CH2OCH3 ”2),
3.69 (s, 3H; CHOCH3), 3.71 (s, 1H; CHC(CH3)2OH), 4.08–4.27 (m, 4H;
CH2OCH3 ”2), 5.42 (s, 1H; CCrH), 5.58 (s, 1H; CCrH), 5.70 ppm (s, 1H;
1967 (CꢁO), 1890 cmꢀ1 (CꢁO); 1H NMR (300 MHz, CDCl3): d=2.07
(virt t, J=2.5 Hz, 1H; CHCH2CꢁCH), 2.65–2.70 (m, 2H; CHCH2Cꢁ
CH), 3.470 (s, 3H; OCH3) 3.474 (s, 3H; OCH3) 3.60 (s, 3H; OCH3), 4.11
(virt t, J=5.7 Hz, 1H; CHCH2CꢁCH), 4.17–4.28 (m, 4H; CH2OCH3 ”2),
5.35 (s, 1H; CCrH), 5.42 (s, 1H; CCrH), 5.58 ppm (s, 1H; CCrH); 13C NMR
(75 MHz, CDCl3): d=27.3 (CHCH2CꢁCH), 58.6 (CHOCH3), 59.0
(CH2OCH3 ”2), 71.6 (CHCH2CꢁCH), 72.7, 72.9 (CH2OCH3), 79.0
(CHCH2CꢁCH), 79.5 (CHCH2CꢁCH), 89.2, 89.3, 91.3 (CCrH), 106.6,
106.8 (CCrCH2), 111.1 (CCrCH), 232.5 ppm (CꢁO”3); MS (EI): m/z (%):
384 (24) [M+], 353 (4) [M+ꢀOCH3], 345 (18) [M+ꢀCH2CꢁCH], 300
(100) [M+ꢀ3CO], 269 (12) [M+ꢀ3COꢀOCH3], 261 (14) [M+
ꢀ3COꢀCH2CꢁCH], 240 (30) [M+ꢀ3COꢀ2OCH3+2H], 209 (67) [M+
ꢀ3COꢀ3OCH3+2H]; elemental analysis calcd (%) for C18H20CrO6
(384.34): C 56.25, H 5.24; found: C 56.34, H 5.25.
C
CrH); 13C NMR (90 MHz, CDCl3): d=25.4, 25.7 [C(CH3)2OH], 58.9
(CH2OCH3 ”2), 60.7 (CHOCH3), 73.7 (CH2 ”2), 74.6 (COH), 87.7
(CHCOH), 91.9, 93.1, 94.3 (CCrH), 104.1, 104.9, 106.4 (CCrC), 239.4 ppm
(CꢁO”3); MS (EI): m/z (%): 404 (72) [M+], 373 (13) [M+ꢀOCH3], 356
(3) [M+ꢀOCH3ꢀOH], 345 (5) [M+ꢀ(CH3)2COH], 320 (34) [M+ꢀ3CO],
289 (4) [M+ꢀ3COꢀOCH3], 258 (6) [M+ꢀ3COꢀ2OCH3], 228 (15) [M+
ꢀ3COꢀ2CH2OCH3ꢀ2H], 210 (27) [M+ꢀCr(CO)3ꢀ(CH3)2COH+H],
200 (12) [M+ꢀ3COꢀOCH3ꢀ(CH3)2COHꢀ2CH3], 178 (100) [M+
ꢀCr(CO)3ꢀ(CH3)2COHꢀOCH3]; elemental analysis calcd (%) for
C18H24CrO7 (404.09): C 53.46, H 5.98; found: C 53.40, H 6.06.
(+)-(R)-Tricarbonyl[1-(2-hydroxy-1-methoxy-2,2-diphenylethyl)-3,5-bis-
(methoxymethyl)benzene]chromium(0)
((+)-24):
n-Butyllithium
(+)-(R,R,R)-Tricarbonyl[1,3,5-tris(1-methoxy-3-hydroxy-propyl)ben-
zene]chromium(0) (+)-26: n-Butyllithium (2.40 mL, 2.50m in hexanes,
6.0 mmol) was added dropwise to a stirred solution of diamine (+)-13
(1.260 g, 3.00 mmol) in dry THF(24 mL) at ꢀ788C. The solution was al-
lowed to warm to room temperature over a period of 30 min and then re-
cooled to ꢀ788C before a solution of heat-gun-dried lithium chloride
(0.127 g, 3.00 mmol) in THF(8 mL) was added through a cannula. The
reaction mixture was stirred for a further 5 min, then a precooled solu-
tion (ꢀ788C) of complex 19 (0.346 g, 1.00 mmol) in THF(8 mL) was in-
troduced dropwise through a short cannula. Stirring was continued for a
period of 60 min before a cooled solution (ꢀ788C) of ethylene oxide
(2.5 mL, 50.0 mmol) in THF(2.5 mL) was added through a short cannula.
Immediately after the addition of epoxide, BF3·OEt2 complex (0.76 mL,
6.0 mmol) was added in one portion leading to a colour change of solu-
tion from red to yellow. The reaction mixture was then stirred for 1.5 h at
ꢀ788C, MeOH (2 mL) was then added and the solvent was removed in
vacuo. Purification of the residue by flash column chromatography (silica
gel; ethyl acetate/methanol 99:1!95:5) afforded (+)-26 as a yellow oil
which solidified upon standing (0.330 g, 69%). Rf =0.50 (silica gel; ethyl
acetate/methanol 9:1). Enantiomeric excess was determined by HPLC
(0.72 mL, 2.50m in hexanes, 1.8 mmol) was added dropwise to a stirred
solution of diamine (+)-13 (0.378 g, 0.90 mmol) in THF(10 mL) at
ꢀ788C. The solution was allowed to warm to room temperature over a
period of 30 min and was recooled to ꢀ788C. A solution of heat-gun-
dried lithium chloride (0.038 g, 0.90 mmol) in THF(5 mL) was added
through a cannula and the reaction mixture was stirred for a further
5 min before a precooled solution (ꢀ788C) of complex 19 (0.104 g,
0.30 mmol) in THF(5 mL) was introduced dropwise through a short can-
nula. Stirring was continued for 60 min, then benzophenone (0.492 g,
2.70 mmol) in THF(2 mL) was added in one portion through a cannula
followed immediately by BF3·OEt2 complex (0.23 mL, 1.8 mmol). The re-
action mixture was stirred for a further 1 h at ꢀ788C before MeOH
(1 mL) was added and the solvent removed in vacuo. Purification of the
resulting residue by flash column chromatography (silica gel; hexane/di-
ethyl ether 9:1!7:3) afforded (+)-24 as a yellow oil, which solidified
upon standing (0.154 g, 97%). Rf =0.45 (silica gel; hexane/diethyl ether
1:1). Enantiomeric excess was determined by HPLC analysis (Chiralcel
OD-H, n-hexane/propan-2-ol 90:10, 0.5 mLminꢀ1, 330 nm); R enantiomer
tr =14.8 min (major); S enantiomer tr =31.4 min (minor): 76% ee. [a]20
=
+9 (c=0.009 in CHCl3); m.p. 99–1018C; IR (CH2Cl2): n˜max =1964 (CꢁDO),
1888 cmꢀ1 (CꢁO); 1H NMR (500 MHz, CDCl3): d=3.04 (s, 1H; OH),
3.20 (s, 3H; OCH3), 3.43 (s, 3H; OCH3), 3.66 (s, 3H; OCH3), 3.69 (d, J=
12.2 Hz, 1H; CHH(OCH3)), 3.90 (d, J=12.2 Hz, 1H; CHH(OCH3)), 4.12
(d, J=12.1 Hz, 1H; CHH(OCH3)), 4.21 (d, J=12.1 Hz, 1H; CHH-
(OCH3)), 4.45 (s, 1H; CHC(OH)Ph2), 4.80 (s, 1H; CCrH), 5.49 (s, 1H;
CCrH), 5.70 (s, 1H; CCrH), 7.20–7.55 ppm (m, 10H; CArH); 13C NMR
(90 MHz, CDCl3): d=58.5, 58.6, 59.6 (OCH3), 72.1, 72.7 (CH2), 81.4
(CPh2(OH)), 84.7 (CHCPh2(OH)), 93.0, 93.2, 94.0 (CCrH), 104.8, 104.6,
104.7 (CCrC), 127.0, 127.2, 127.4, 128.0, 128.2 (CArH), 142.6, 144.8 (CArC),
232.8 ppm (CꢁO”3); MS (EI): m/z (%): 528 (47) [M+], 497 (9) [M+
ꢀOCH3], 444 (49) [M+ꢀ3CO], 344 (11) [M+ꢀCr(CO)3ꢀOCH3ꢀOH],
281 (6) [M+ꢀCr(CO)3ꢀ3OCH3ꢀH2O], 209 (100) [M+ꢀCr(CO)3ꢀPh2-
COH], 178 (99) [M+ꢀCr(CO)3ꢀPh2COHꢀOCH3]; elemental analysis
calcd (%) for C24H30CrO6 (528.12): C 63.63, H 5.35; found: C 63.59, H
5.38.
analysis (Chiralpak AD, n-hexane/propan-2-ol 80:20, 0.5 mLminꢀ1
,
330 nm); S,S,S enantiomer tr =20.6 min (minor); R,R,R enantiomer tr =
23.0 min (major): 93% ee. [a]2D0 =+96 (c=0.018 in CHCl3); m.p. 112–
1148C; IR (CH2Cl2): n˜max =3250 (OH) 1963 (CꢁO), 1887 cmꢀ1 (CꢁO);
1H NMR (500 MHz, CDCl3): d=1.90–1.93 (m, 3H; CHHCH2OH”3),
1.96–1.99 (m, 3H; CHHCH2OH”3), 2.36 (s, 3H; OH”3), 3.60 (s, 9H;
OCH3 ”3), 3.79 (s, 6H, CHHCH2OH”3), 4.25–4.29 (m, 3H;
CHCH2CH2OH”3), 5.55 ppm (s, 3H; CCrH”3); 13C NMR (125 MHz,
CDCl3): d=41.3 (CH2CH2OH”3), 58.9 (OCH3 ”3), 59.7 (CH2OH”3),
79.9 (CHOCH3 ”3), 89.7 (CCrH”3), 109.2 (CCrCH”3), 232.8 ppm (CꢁO”
3); MS (EI): m/z (%): 478 (2) [M+], 402 (6) [M+ꢀCH2CH2OHꢀOCH3],
332 (13) [M+ꢀ2COꢀ2CH2CH2OH], 310 (7) [M+ꢀCH3OCH2CH2-
CH2OHꢀCH3CH2OHꢀCH3OH], 297 (100) [M+ꢀ2CH3OCH2CH2-
CH2OHꢀH], 270 (27) [M+ꢀCOꢀ2CH3OCH2CH2CH2OH], 265 (38) [M+
ꢀ2CH3OCH2CH2CH2OHꢀCH3OHꢀH]; HRMS (EI): m/z calcd for
C21H30CrO9: 478.1295; found: 478.1276.
(+)-(R)-Tricarbonyl[1-(2-hydroxy-1-methoxy-2-methylpropyl)-3,5-bis-
(methoxymethyl)benzene]chromium(0) (+)-25: n-Butyllithium (1.32 mL,
(+)-(R,R,R)-Tricarbonyl[1,3,5-tris(1-diphenylphosphino-1-methoxymeth-
yl)benzene]chromium(0) ((+)-28): n-Butyllithium (1.49 mL, 2.50m in
146
www.chemeurj.org
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2006, 12, 138 – 148

Asymmetric Synthesis
FULL PAPER
hexanes, 3.7 mmol) was added dropwise to a stirred solution of diamine
(+)-13 (0.208 g, 1.86 mmol) in dry THF(100 mL) at ꢀ788C. The reaction
mixture was allowed to warm to room temperature over 30 min and was
recooled to ꢀ788C before a solution of heat-gun-dried lithium chloride
(0.080 g, 1.86 mmol) in THF(10 mL) was added through a cannula. The
reaction mixture was stirred for a further 5 min, then a precooled solu-
tion (ꢀ788C) of complex 19 (0.208 g, 0.60 mmol) in THF(10 mL) was in-
troduced dropwise through a short cannula. Stirring was continued for a
period of 60 min before chlorodiphenylphosphine (0.99 mL, 5.4 mmol)
was added in one portion. The reaction mixture was then stirred for 1 h
at ꢀ788C followed by a further 2 h at ꢀ408C; MeOH (2 mL) was then
added and the solvent was removed in vacuo. Purification of the resulting
residue by flash column chromatography (silica gel; hexane/diethyl ether
99:1!90:10) afforded (+)-28 as a yellow solid (0.253 g, 47%). Rf =0.40
(silica gel; hexane/diethyl ether 9:1). Enantiomeric excess was deter-
mined by HPLC analysis (Chiralcel OD-H, n-hexane/propan-2-ol
99.6:0.4, 1.0 mLminꢀ1, 330 nm); S,S,S enantiomer tr =12.5 min (minor);
R,R,R enantiomer tr =20.6 min (major):=95% ee. [a]2D0 =+227 (c=
0.0067 in CHCl3); m.p. 155–1578C; IR (CH2Cl2): nmax =1967 (CꢁO),
1882 cmꢀ1 (CꢁO); 1H NMR (500 MHz, CDCl3): d=3.43 (s, 9H; OCH3 ”
3), 4.75 (d, J=4.7 Hz, 3H; CHPPh2 ”3), 5.54 (s, 3H; CCrH”3), 7.28–7.40
solution was then allowed to cool to room temperature over a period of
40 min.
Preparation of complex (+)-30: n-Butyllithium (2.08 mL, 2.50m in hex-
anes, 5.2 mmol) was added dropwise to a stirred solution of diamine (+)-
13 (1.186 g, 2.82 mmol) in dry THF(50 mL) at ꢀ788C under an inert at-
mosphere of nitrogen. The solution was then allowed to warm to room
temperature over a period of 30 min. The resulting deep red solution was
recooled to ꢀ788C and a solution of heat-gun-dried lithium chloride
(0.110 g, 2.60 mmol) in THF(16 mL) was added dropwise through a can-
nula. The reaction mixture was stirred for a further 5 min, then a pre-
cooled (ꢀ788C) solution of complex 19 (0.300 g, 0.87 mmol) in THF
(10 mL) was introduced dropwise through a short cannula. After stirring
the orange solution at ꢀ788C for a period of 60 min, 3-(bromomethyl)-
pyridine (prepared as above) was added through a cannula and the re-
sulting yellow solution was stirred for 2 h at ꢀ788C. MeOH (3 mL) was
then added and the solvent removed in vacuo. Purification of the residue
by flash column chromatography (silica gel; ethyl acetate/methanol 4:1
and then silica gel; chloroform/methanol 9:1) afforded (+)-30 as a yellow
solid (0.45 g, 84%). Rf =0.38 (silica gel; ethyl acetate/methanol 4:1);
[a]2D0 =+36 (c=0.0067 in CHCl3); m.p. 104–1068C; IR (CH2Cl2): nmax
=
1965 (CꢁO), 1889 (CꢁO), 1592 (C=N), 1575 cmꢀ1 (C=N); 1H NMR
(300 MHz, CDCl3): d=2.74 (dd, J=6.5, 14.0 Hz, 3H; CHCHHPy”3),
2.89 (dd, J=4.0, 14.0 Hz, 3H; CHCHHPy”3), 3.46 (s, 9H; OCH3 ”3),
4.08 (dd, J=4.0, 6.5 Hz, 3H; CHCH2Py”3), 5.13 (s, 3H; CCrH”3), 7.26
(dd, J=4.5, 7.5 Hz, 3H; CPyH”3), 7.47 (d, J=7.5 Hz, 3H; CPyH”3), 8.30
(d, J=1.5 Hz, 3H; CPyH”3), 8.49 ppm (dd, J=1.5, 4.5 Hz, 3H; CPyH”3);
13C NMR (75 MHz, CDCl3): d=41.5 (CHCH2 ”3), 58.7 (OCH3 ”3), 81.1
(m, 24H;
CArH”3), 7.46–7.51 ppm (m, 6H; C
ArH”3); 31P NMR
(202 MHz, CDCl3): d=13.38 ppm (PPh2 ”3); 13C NMR (125 MHz,
CDCl3): d=61.0 (OCH3 ”3), 83.6 (d, J=23.6 Hz, CHPPh2 ”3), 89.8 (d,
J=10.4 Hz, CCrH”3), 107.2 (d, J=19.4 Hz, CCrCH”3), 128.3–128.5 (m,
CAr), 128.9, 129.5 (CAr), 132.2 (d, J=15.3 Hz, CAr), 133.2 (d, J=19.4 Hz,
CAr), 135.2 (d, J=20.0 Hz, CAr), 135.9 (d, J=14.7 Hz, CAr), 233.6 ppm
(CꢁO”3); MS (FAB): m/z (%): 898 (72) [M+], 814 (100) [M+ꢀ3CO],
629 (38) [M+ꢀ3COꢀPPh2]; elemental analysis calcd (%) for
C51H45CrO6P3 (898.83): C 68.15, H 5.05; found: C 68.15, H 4.93.
(CHCH2 ”3), 88.5 (CCrH”3), 108.5 (CCr ”3), 123.2 (CPyH”3), 132.3 (CPy
”
3), 137.4, 148.1, 150.9 (CPyH”3), 232.5 ppm (CꢁO”3); MS (EI): m/z
(%): 619 (4) [M+], 535 (40) [M+ꢀ3CO], 483 (60) [M+ꢀ3COꢀCr], 391
(100) [M+ꢀ3COꢀCrꢀCH2Py]; elemental analysis calcd (%) for
C33H33CrN3O6 (619.18): C 63.97, H 5.37, N 6.78; found: C 63.98, H 5.31,
N 6.72.
(+)-(R,R,R)-1,3,5-Tris[1-(boronatodiphenylphosphino)-1-methoxymeth-
yl)]benzene ((+)-29): A BH3·THFcomplex (1.56 mL, 1.00 m solution in
THF, 1.6 mmol) was added dropwise, under an inert atmosphere, to a
stirred solution of triphosphine (+)-28 (0.350 g, 0.39 mmol) in THF
(30 mL). Stirring was continued for 1.5 h at room temperature and then
the solvent was removed in vacuo. The resulting residue was then redis-
solved in DCM (100 mL) before being stirred in an open vessel and in
the presence of air and light. After stirring for 18 h no more chromium-
containing species were detected (by TLC) and the green reaction mix-
ture was concentrated to give a residue which was purified by flash
column chromatography (silica gel; hexane/ethyl acetate 3:1) to afford
(+)-29 as a white solid (0.301 g, 97%). Rf =0.20 (silica gel; hexane/ethyl
(+)-(R,R,R)-1,3,5-Tris[1-methoxy-2-(3-pyridyl)ethyl]benzene
((+)-31):
Ceric ammonium nitrate (1.042 g, 1.90 mmol) was added to a solution of
complex (+)-30 (0.588 g, 0.95 mmol) in MeOH (15 mL). The resulting
mixture was stirred at room temperature for 1 h. The reaction mixture
was neutralized by addition of a saturated potassium carbonate solution
and extracted with dichloromethane (2”20 mL). The combined extracts
were washed with brine (2”10 mL), dried (MgSO4) and then concentrat-
ed in vacuo to afford the crude product. Purification of the crude product
by flash column chromatography (silica gel; ethyl acetate/acetone/tri-
ethylamine 6:3:1) afforded (+)-31 as a colourless oil (0.367 g, 76%); Rf =
0.35 (silica gel; ethyl acetate/acetone/triethylamine 6:3:1); [a]2D0 =+15
(c=0.002 in CH2Cl2); IR (KBr pellet): n˜max =1592 (C=N), 1575 cmꢀ1 (C=
N); 1H NMR (300 MHz, CDCl3): d=2.79 (dd, J=6.0, 14.0 Hz, 3H;
CHCHHPy”3), 3.01 (dd, J=7.0, 14.0 Hz, 3H; CHCHHPy”3), 3.15 (s,
9H; OCH3 ”3), 4.24 (t, J=6.5 Hz, 3H; CHCH2Py”3), 6.89 (s, 3H;
1
acetate 4:1). [a]2D0 =+109 (c=0.015 in CHCl3); m.p. 114–1168C; H NMR
(500 MHz, CDCl3): d=0.70 (s, 9H; BH3 ”3), 2.99 (s, 9H; OCH3 ”3), 4.90
(d, J=5.4 Hz, 3H; CHPPh2 ”3), 6.83 (d, J=1.6 Hz, 3H; CArH”3), 7.37–
7.49 (m, 18H;
CArH), 7.63–7.76 ppm (m, 12H; C
ArH); 31P NMR
(202 MHz, CDCl3): d=25.60 ppm (PPh2 ”3); 11B NMR (160 MHz,
CDCl3): d=ꢀ40.04 ppm (BH3 ”3); 13C NMR (125 MHz, CDCl3): d=58.5
(OCH3 ”3), 82.5 (d, J=43.5 Hz, CHPPh2 ”3), 125.3 (d, J=53.2 Hz, CAr),
128.3 (d, J=10.4 Hz, CArH), 128.5 (d, J=10.3 Hz, CArH), 128.6 (CAr),
130.9, 131.5 (CArH), 132.7 (d, J=8.6 Hz, CArH), 134.3 (CAr), 134.7 ppm
(d, J=8.7 Hz, CArH); MS (FAB): m/z (%): 804 (14) [M+(11B”3)], 803
(22) [M+(11B”2, 10B”1)], 789 (10) [M+ꢀBH3], 775 (4) [M+ꢀ2BH3], 745
(12) [M+ꢀ2BH3ꢀOCH3], 701 (13) [M+ꢀ3BH3ꢀOCH3ꢀ2CH3], 671 (6)
[M+ꢀ3BH3ꢀ3OCH3+H], 605 (8) [M+ꢀBH3ꢀPPh2], 591 [M+
ꢀ2BH3ꢀPPh2] (11), 577 (8) [M+ꢀ3BH3ꢀPPh2], 561 (8) [M+
ꢀ2BH3ꢀPPh2ꢀOCH3], 547 (29) [M+ꢀ3BH3ꢀPPh2ꢀOCH3]; elemental
analysis calcd (%) for C48H54B3O3P3 (804.36): C 71.68, H 6.77; found: C
71.65, H 6.73.
C
C
ArH”3), 7.16 (dd, J=4.5, 7.0 Hz, 3H; CPyH”3) 7.35 (d, J=7.0 Hz, 3H;
PyH”3), 8.24 (s, 3H; CPyH”3), 8.42 ppm (d, J=4.5 Hz, 3H; CPyH”3);
13C NMR (75 MHz, CDCl3): d=41.9 (CHCH2 ”3), 57.2 (OCH3 ”3), 84.3
(CHCH2 ”3), 122.9 (CPyH”3), 124.5 (CArH”3), 133.4 (CPy ”3), 137.4
(CPyH”3), 141.4 (CAr ”3), 148.1, 151.1 ppm (CPyH”3); MS (EI): m/z
(%): 484 (19) [M++H], 483 (67) [M+], 391 (100) [M+ꢀCH2Py]; elemen-
tal analysis calcd (%) for C30H33N3O6 (483.25): C 74.51, H 6.87, N 8.68;
found: C 74.50, H 7.00, N 8.69.
(+)-(R,R,R)-[1,3,5-Tris(1-methoxy-2-(3-pyridyl)ethyl)benzene]ruthenium
dihexafluorophosphate ((+)-32): A mixture of ligand (+)-31 (0.100 g,
0.21 mmol) and RuCl3 (0.215 g, 0.11 mmol) were refluxed in 5 mL of eth-
ylene glycol for 20 min. The solution was cooled to room temperature,
water added (5 mL) and a precipitate was formed upon addition of a con-
centrated aqueous NH4PF6 solution (2 mL). The green precipitate was fil-
tered off, washed with water (10 mL) and dried under reduced pressure.
The residue was purified via crystallization from dichloromethane/metha-
(+)-(R,R,R)-Tricarbonyl[1,3,5-tris(1-methoxy-2-(3-pyridyl)ethyl)ben-
zene]chromium(0) ((+)-30)
Preparation of 3-(bromomethyl)pyridine: A 250 mL flask containing a
stirrer bar and fitted with a reflux condenser was placed under an inert
atmosphere of nitrogen. The flask was charged with 3-(bromomethyl)pyr-
idine hydrobromide (3.26 g, 12.9 mmol), powdered potassium carbonate
(7.13 g, 51.6 mmol) and anhydrous toluene (78 mL). The reaction mixture
was stirred vigorously for 45 min at room temperature, 45 min at 408C,
45 min at 508C, 45 min at 658C, 45 min at 808C and 30 min at 908C. The
nol/hexane (1:0.25:3) to afford (+)-32 as
a yellow crystalline solid
(0.074 g, 46%). [a]2D0 =+26 (c=0.0047 in CHCl3); m.p. 2408C (decomp);
UV/Vis spectrum (CH3CN): lmax (e)=368 (67060), 246 nm (103063); IR
(KBr pellet): n˜max =1483 (C=N), 1430 cmꢀ1 (C=N); 1H NMR (500 MHz,
Chem. Eur. J. 2006, 12, 138 – 148
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
147

S. E. Gibson et al.
CD3CN): d=2.21 (t, J=13.0 Hz, 3H;
CHCHHPy”3 A), 2.30 (dd, J=4.0,
13.0 Hz, 3H; CHCHHPy”3 B), 3.09
(s, 9H; OCH3 ”3 A), 3.28 (dd, J=4.0,
13.0 Hz, 3H; CHCHHPy”3 A and B),
3.39 (s, 9H; OCH3 ”3 B), 4.23 (dd, J=
4.0, 13.0 Hz, 3H; CHCH2Py”3 A),
4.63 (t, J=4.0 Hz, 3H; CHCH2Py”
3 B), 6.35 (s, 6H; CPyH”3 A and B),
6.47 (s, 3H; CArH”3 B), 6.67 (s, 3H;
CArH”3 A), 7.18–7.27 (m, 12H;
Table 1. Crystal data, data collection and refinement parameter for compounds (+)-20, (+)-28 and (+)-32.
(+)-20
(+)-28
(+)-32
formula
Mr
colour/habit
T [K]
C18H24CrO6
388.37
yellow platy needles
293
C51H45CrO6P3
898.78
yellow plates
293
C60H66N6O6RuPF6·2CH2Cl2
1528.05
yellow shards
173
crystal system
space group
a [Š]
b [Š]
c [Š]
triclinic
P1 (no. 1)
7.176(2)
10.628(4)
13.043(4)
102.081(14)
91.33(3)
101.31(3)
951.7(5)
2
ortho-rhombic
P212121 (no 19)
11.497(5)
17.024(8)
23.651(10)
90
90
90
4629(3)
4
1.290
monoclinic
P21 (no. 4)
10.5334(5)
18.2106(8)
17.6404(9)
90
90.877(4)
90
3383.4(3)
2
C
PyH”6 A and B), 7.81 (d, J=7.0 Hz,
3H; CPyH”3 A or B), 7.92 ppm (d, J=
7.0 Hz, 3H; PyH”3 A or B);
a [8]
b [8]
C
13C NMR (125 MHz, CD3CN): d=39.7
(CHCH2 ”3 B), 41.6 (CHCH2 ”3 A),
56.6 (OCH3 ”3 A), 57.6 (OCH3 ”3 B),
81.0 (CHCH2 ”3 B), 85.0 (CHCH2 ”
3 A), 122.3 (CPyH”3 A and B), 127.1
(CArH”3 A and B), 127.7, 128.5
g [8]
V [Š3]
Z
1calcd [gcmꢀ3
]
1.355
1.500
radiation
CuKa
5.203
CuKa
3.403
MoKa
0.524
m [mmꢀ1
]
reflns measured
reflns observed [jFo j>4s(jFoj)]
2qmax [8]
3415
2719
128
4388
3294
130
21626
20273
66
(CPyH”3 A and B), 137.3, 138.0 (CPy
”
3 A and B), 140.5, 141.7 (CPyH”3 A
and B), 141.0, 141.6 (CAr ”3 A and B)
152.9, 153.1, 155.5 ppm (CPyH”3 A
and B); MS (FAB+): m/z (%): 1213
(19) [M+ꢀPF6], 1068 (22) [M+ꢀ2PF6],
584 (82) [M+ꢀ2PF6ꢀC30H33N3O3], 484
(12) [M+ꢀ2PF6ꢀC30H33N3O3], 73
(100) [C3H6OCH3+]; elemental analy-
sis calcd (%) for [C60H66N6O6Ru]-
(PF6)2·2CH2Cl2 (1528.05): C 48.72, H
4.61, N 5.49; found: C 48.81, H 4.64, N
5.48.
parameters
452
0.0694
0.0784
0.04(3)
0.96(3)
0.069/0.170
479
838
+
R1ꢀ
0.0601
0.0928
0.000(14)
n/a
0.1075
0.1091
0.11(4)
0.89(4)
0.108/0.182
R1
Flack parameter x+
Flack parameter xꢀ
R1/wR2
0.060/0.149
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Published online: November 9, 2005
148
www.chemeurj.org
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2006, 12, 138 – 148