P-chiral 1-phosphanorbornenes: From asymmetric phospha-Diels-Alder reactions towards ligand design and functionalisation

Article abstract of DOI:10.1039/c5dt02564h

The principle of stereotopic face differentiation was successfully applied to 2H-phospholes which undergo a very efficient and highly stereoselective Diels-Alder reaction giving phosphorus-chiral 1-phosphanorbornenes with up to 87% yield. The observed reaction pathway has been supported by theoretical calculations showing that the cycloaddition reaction between 2H-phosphole 3a and the dienophile (5R)-(-)-menthyloxy-2(5H)-furanone (8) is of normal electron demand. Optically pure phosphanes were obtained by separation of the single diastereomers and subsequent desulfurisation of the sulfur-protected phosphorus atom. Finally, divergent ligand synthesis is feasible by reduction of the chiral auxiliary, subsequent stereospecific intramolecular Michael addition, and various functionalisations of the obtained key compound 13a. Furthermore, the unique structural properties of phospanorbornenes are presented and compared to those of phosphanorbornanes.

Full text of DOI:10.1039/c5dt02564h

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P-chiral 1-phosphanorbornenes: From asymmetric Phospha-Diels–
Alder reactions towards ligand design and functionalisation
Received 00th July 2015,
Accepted 00th July 2015
Tobias Möller, Peter Wonneberger, Menyhárt B. Sárosi, Peter Coburger, Evamarie Hey-Hawkins*
DOI: 10.1039/x0xx00000x
Abstract: The principle of stereotopic face differentiation was successfully applied to 2H-phospholes which undergo a very
efficient and highly stereoselective Diels–Alder reaction giving phosphorus-chiral 1-phospha-norbornenes with up to 87%
yield. The observed reaction pathway has been supported by theoretical calculations showing that the cycloaddition
reaction between 2H-phosphole 3a and the dienophile (5R)-(–)-menthyloxy-2(5H)-furanone (8) is of normal electron
demand. Optically pure phosphanes were obtained by separation of the single diastereomers and subsequent
desulfurisation of the sulfur-protected phosphorus atom. Finally, divergent ligand synthesis is feasible by reduction of the
chiral auxiliary, subsequent stereospecific intramolecular Michael addition, and various functionalisations of the obtained
key compound 13a. Furthermore, the unique structural properties of phospanorbornenes are presented and compared to
those of phosphanorbornanes.
www.rsc.org/
Dedicated to Professor Manfred
Scheer on the occasion of his 60th
birthday
compounds (phosphaalkenes, singlet phosphinidenes) are often not
stable or difficult to synthesise.4 Therefore, kinetic (sterically
Introduction
In the beginnings of enantioselective catalysis, ligands in which a
chiral coordinating phosphorus atom bears the optical information
were used.1 Today, the most widely applied ligands in asymmetric
transition metal catalysis carry their optical information in the chiral
backbone of the ligand.2 Because of the easy access to this type of
molecules, C-chiral ligands have dominated the field of
enantioselective catalysis until today. Nevertheless, tremendous
efforts in recent years have furnished novel synthetic pathways
towards P-chiral phosphanes and triggered a comeback of this class
of ligands.3 Most of these synthetic pathways are based on
resolution of racemates or diastereomers, kinetic and dynamic–
kinetic resolution, and desymmetrisation.3 These methods have one
common feature: they start from a phosphorus atom with
tetrahedral or trigonal-pyramidal coordination. This is in contrast to
the main method applied in the generation of C chirality – the
principle of stereotopic face differentiation – which starts from a
carbon atom with trigonal-planar coordination. Differences in the
applied methods are due to different stabilities and accessibilities of
the starting materials. Compounds with carbon or phosphorus in a
tetrahedral or trigonal-pyramidal environment are stable and
readily available, as are trigonal-planar carbon compounds (alkenes,
ketones, singlet carbenes), whereas the corresponding phosphorus
demanding groups) or thermodynamic stabilisation (delocalisation
or coordination to a metal atom) is necessary to obtain such low-
coordinate phosphorus species. The resulting compounds are often
expensive and not readily available. Furthermore, their substitution
pattern is less suitable for stereoselective synthesis. As a result,
there have been only two examples in which the principle of
stereotopic face differentiation has been applied. In both cases a
chiral substituent at the trigonal-planar phosphorus atom was
necessary to obtain optical induction.5 Recently, we contributed to
this hardly explored field by applying a diastereoselective Diels–
Alder reaction to 2H-phospholes.6 Even though these compounds
with a planar-coordinated phosphorus atom in a five-membered
ring are generated in situ, they are readily accessible and their
chemistry is well understood.7 Herein, we present our detailed
investigations on the diastereoselective Diels–Alder reaction of 2H-
phospholes and further functionalisation of the obtained
1-phosphanorbornenes for divergent ligand design.
Results and Discussion
The asymmetric Diels–Alder reaction of 2H-phospholes
In a first attempt to facilitate a Diels–Alder reaction of a 2H-
phosphole, phospholide 1 was protonated in situ and the 2H-
phosphole 3a trapped with the chiral dienophile 4 at low
temperature to ensure good stereoselectivity (Scheme 1). Usually a
dienophile like crotonic acid amide 4 is applied together with a
Lewis acid to activate the dienophile and connect it with the chiral
auxiliary.8
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H
[1,5]
[2+4]
Me3Si
P
P
P
Li
1
P
H
P
3a
P
P
SiMe3
SiMe3
Me3Si
7
2b
2a
3b
O
O
time
RT
7
7
28 minutes
N
O
1. Michael
addition
at 50 °C
7
7
2b 2b/7 = 31:69
[4+2]
21 minutes
at 50 °C
7
7
2b 2b/7 = 34:66
2b 2b/7 = 38:62
2b 2b/7 = 43:57
2. S8 (excess)
15 minutes
at 50 °C
7
7
4
9 minutes
at 50 °C
7
7
6 minutes
at 20 °C
7
7
7
2b 2b/7 = 44:56
19 minutes
at 40 °C
O
P
S
O
O
N
7
2b 2b/7 = 28:72
O
13 minutes
at 40 °C
N
O
7
7
2b 2b/7 = 33:67
2b 2b/7 = 40:60
P
8 minutes
at 40 °C
7
7
Bn
5 (87%)
O
Bn
6
10
0
10
20
30
40
50
60
70 ppm
Scheme 1 Protonation of phospholide 1 and subsequent reaction
with 4.
Figure 1. Temperature dependence of the equilibrium between 1H-
phosphole 2b and the corresponding 2H-phosphole dimer 7 with
SiMe3 as migrating group.
As a Lewis acid would also interact with the phosphorus atom,
deactivating the diene for cycloaddition reactions, the Diels–Alder
reaction was performed without adding a Lewis acid. When acetic
acid, sulfuric acid, or water were used as protonating reagent, an
inseparable product mixture was obtained; using propan-2-ol gave
the diastereomerically pure compound 5 (absolute configuration
was not determined). Other products or isomers could not be
isolated; hence, the de of the crude product could not be
determined. Obviously, a Michael addition occurred, probably base-
catalysed by the generated lithium isopropanolate. Thus, the
synthetic route via protonation of 1 did not seem to furnish the
targeted 1-phosphanorbornene 6.
We, therefore, switched to SiMe3, as this group is known to migrate
in a [1,5]-sigmatropic shift at low temperatures as well.7a,9 31P{1H}
NMR spetcroscopic investigations in which the temperature was
varied over time revealed that an equilibrium between monomeric
1H-phosphole (−51.5 ppm, s) 2b and only one dimer 7 exists at low
temperature (Figure 1). Monomeric 1H-phosphole 2b rearranges by
a [1,5]-sigmatropic shift to 2H-phosphole 3b, which cannot be
−30 °C, 30 min equilibration, addition of 4, 16 h at −30 °C) and
subsequent filtration over silica gave 5 (characterised by 31P{1H}
NMR spectroscopy). Therefore, direct trapping of a 2H-phosphole,
generated from the corresponding protonated or silylated 1H-
phosphole, with 4 did not yield the desired 1-phosphanorbornene.
Generating 2H-phosphole 3a in situ from its corresponding dimer
required a chiral dienophile that offers good stereoselectivity at the
high temperatures needed for the cycloreversion of the dimer of
3a. These requirements are met by (5R)-(–)-menthyloxy-2(5H)-
furanone (8). Owing to its rigid cyclic structure and fixed chiral
centre, which is close to the C=C bond, it has shown high
selectivities in cycloaddition reactions.10
As shown previously, this approach resulted in the desired products
9 and 10.6 The yields and selectivities were good to high and the
absolute configuration of the obtained isomers was completely
determined by NOE NMR spectroscopy and X-ray crystallography
(Table 1). The sulfurisation of the phosphorus atom made the
separation of the single isomers feasible. The molecular structure of
endo-9b is shown in Figure 2. However, the synthesis of C2-
symmetric bis-phosphanes starting from bis-phospholes11 was not
successful.6
observed in NMR experiments due to its fast dimerisation to give 7.
1
Only one isomer of the dimer (–49.6 ppm, −26.2 ppm, d, JP,P
=
202.6 Hz) is formed, and the coupling constant suggests a P–P
7d
bond.7b,
Increasing the temperature shifts the equilibrium
towards 2b. At room temperature a different isomer of the dimer is
formed, and this suggests a kinetically favoured isomer at low
temperatures. This system seemed to be suitable for
stereoselective Diels–Alder reactions for two reasons: the fast
equilibrium between 2b and 7 provides the intermediate 2H-
phosphole 3b, which is then available for an additional
cycloaddition reaction. Furthermore, 3b seems to react in a highly
stereoselective manner in cycloaddition reactions, since only one of
its dimers is formed at low temperatures. However, treating 2b/3b
with 4 at −30 °C (addition of SiMe3Cl to a solution of 1 in THF at
Furthermore, a detailed explanation of the observed selectivities
was given which was supported by DFT-calculations. The observed
cycloaddition reaction is a Diels–Alder reaction with normal
electron demand.6 A closer look at the energetic profile of the
reaction (Figure 3) gave further insight into the course of the
reaction. Under both conditions (THF at 60 °C and xylenes at
140 °C), endo-11a is slightly more thermodynamically stable than
exo-11a, and the activation enthalpy is smaller for the endo
transition state, which is in agreement with the observed
selectivities. Since the activation enthalpies are very similar under
2 | Dalton Trans., 2015, 00, 1-3
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both conditions,
temperatures.
a cycloreversion is more likely at higher
Table 1. Conditions, stereoselectivities,a and yields for compounds
9/10a,c,d.6
Figure 3. Energetic profile of the cycloaddition between 3a and 8.
Deprotection of P-chiral 1-phosphanorbornenes 9a,c,d
After an efficient method to create P-chiral 1-phosphanorbornenes
in a stereoselective manner had been established, we focused on
their functionalisation. In this context the application in transition
metal catalysis is an important aspect. Consequently,
desulfurisation of the diastereomerically pure compounds 9a,c,d to
yield their trivalent derivatives 11a,c,d was performed with Raney
nickel or electron-rich phosphanes like triethylphosphane, which –
unlike hydridic reagents such as LiAlH4 or BH3(THF) – tolerate a
number of functional groups and selectively reduce the P=S bond
(Scheme 2). The 31P{1H} NMR spectra of the reaction mixture of
triethylphosphane and diastereomerically pure 1-phospha-
norbornenes 9a,c,d revealed a mixture of products containing endo
regio-
isomers exo
endo:
diastereo-
mers:
siC=C:reC=C
T
Solvent
THF
Yieldb
9:10
98:2
97:3
97:3
(9, siC=C
)
a
60 °C
93:7
98:2
92:8
91:9
87%
84%
83%
c
d
140 °C xylenes
140 °C xylenes
70:30
73:27
and exo diastereomers of 11a,c,d. This suggests that
a
a) determined by 1H NMR spectroscopy; b) sum of yields of
separated diastereomers
cycloreversion reaction takes place, in agreement with the
computational results. In this regard, heating only
diastereomerically pure 9a,c,d in xylenes at 130 °C for 16 h did not
result in transformation into the other diastereomer. Thus,
cycloreversion only takes place for the trivalent derivatives 11a,c,d
and not for pentavalent 9a,c,d. In the case of endo-11d, only traces
of the exo diastereomer were observed in the reaction mixture, and
pure endo-11d was isolated in high yield. For endo-9a, 9c, exo-9c,
and exo-9d, Raney nickel is the reagent of choice and gives the
corresponding trivalent compounds 11a,c,d in moderate to good
yields. However, it is important to perform the desulfurisation with
Raney nickel at room temperature to avoid transformation into the
other diastereomer.
A
transition metal complex, namely,
[W(CO)5(endo-11a)], has been obtained previously.6
Figure 2. Molecular structure of endo-9d. Ellipsoid level at 50%.
Hydrogen atoms are omitted for clarity. Selected bond lengths (in
pm) and angles (in °): P(1)–S(1) 192.93(3), P(1)–C(1) 185.02(9),
P(1)–C(5) 181.1(1), P(1)–C(6) 180.1(1), C(4)– C(5) 135.5(1), C(6)–
P(1)–S(1) 125.85(3), C(1)–P(1)–S(1) 119.09(3), C(6)–P(1)–C(1)
91.64(5).
Scheme 2. Desulfurisation of P-chiral 1-phosphanorbornenes; yields
and conditions: endo-11a: 55%, Raney nickel; endo-11c: 75%, Raney
nickel; exo-11c: 87%, Raney nickel; endo-11d: 93%, PEt3; exo-11d:
71%, Raney nickel.
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Functionalisation of 1-phosphanorbornenes
Functionalisation of the 1-phosphanorbornenes should facilitate an
efficient ligand design. As an improved synthesis compared to the
reported one6 afforded endo-9a on a multigram scale, this
derivative was studied first. In general, the different functional
groups in endo-9a allow various modifications. However, when
introduction of
a
second donor group is considered,
Scheme 4. Intramolecular Michael addition of diol 12c.
functionalisation of the C=C bond employing hydroboration or
epoxidation followed by ring opening would result in regioisomers
with uncontrollable regioselectivity. Furthermore, introducing
another donor group at the α position of the carbonyl group via the
enolate would result in an anti position to the phosphorus atom
and thus the resulting compound could not act as a chelating ligand.
We, therefore, focused on functionalisation of the menthyloxy-
furanone ring. Reductive cleavage of the chiral auxiliary gave diol
12a (Scheme 3). For further modifications, sulfur protection was
necessary due to a higher tolerance of the P=S group towards
various reagents (see further discussion). A selective chemical
transformation of only one of the two OH groups in diol 12a seems
challenging. However, treatment of 12a with a strong base resulted
in a Michael addition of the OH group in the 4-position relative to
the phosphorus atom. The overall yield of 13a over a two-step
process is good. The intramolecular Michael addition is regio- and
stereospecific, since only the OH group in 4-position to the
phosphorus atom can attack the C=C bond; the attack proceeds anti
to the bridge of the 1-phosphanorbornene. Consequently this
transformation is restricted to the endo isomers. This simple and
facile derivatisation of endo-9a prompted us to expand this
synthetic strategy to endo-9c and endo-9d. The additional challenge
in these two cases is the generation of a second stereogenic centre
in α position to the phosphorus atom, which does not proceed in a
stereospecific manner (Scheme 4). Reduction of endo-9c gives diol
12c in moderate yield due to low solubility of 12c in common
organic solvents (see Exp. Section). The subsequent intramolecular
Michael addition is an equilibrium reaction. Full conversion of 12c
could not be observed. Furthermore, when the pure isomer (S)-13c
(obtained by fractional crystallisation) was treated with KOtBu in
THF, the formation of 12c and (R)-13c was observed by 31P{1H} NMR
spectroscopy; after 20 h at room temperature an equilibrium was
reached showing the ratio 12c:(R)-13c:(S)-13c = 2:33:66.
M06-2X/MG3S calculations showed that the difference in energy
between the two diastereomers is very small (3.5 kJ·mol–1), and
thus thermodynamic control of the reaction is impossible, in
agreement with the observed selectivities. Varying the base or
temperature gave neither full conversion of 12c nor improved
stereoselectivity, so that kinetic control of the reaction is impossible
as well. Therefore, functionalisation by reduction and subsequent
Michael addition is only applicable to endo-9a.
Crystals of both diols (12a and 12c) and all three alcohols (13a, (R)-
13c and (S)-13c) suitable for crystal structure analysis were
obtained, and thus the absolute configurations of (R)-13c and (S)-
13c could be deduced (Figures 4 and 5). Comparing the molecular
structures of 12a and 13a reveals the unique structural features of a
1-phosphanorbornene in contrast to a 1-phosphanorbornane
(Figure 4). The biggest difference between the two structures is
observed for the σ bonds in the six-membered ring. In 12a, the
P(1)–C(5) and C(3)–C(4) bonds are shorter than in 13a; in contrast,
the P(1)–C(1) and C(2)–C(3) bonds are longer. This is caused by the
hyperconjugation of the π* orbital of the C(4)–C(5) double bond
with σ orbitals of the P(1)–C(1) and C(2)–C(3) bonds, resulting in a
delocalisation of the C=C bond over the 1-phosphanorbornene
system.12 These lengthenings and shortenings of the bonds are
considered to be a preliminary stage of a retro-Diels–Alder
reaction.12a,13 Due to the backbonding of all three P–C σ* orbitals
with the nonbonding orbitals of the sulfur atom, the P=S bond in
12a is included in the delocalisation and also shortened.
Figure 4. Molecular structures of 12a (left) and 13a (right); Ellipsoid
level at 50%. Hydrogen atoms except H(6A) and H(6B) are omitted.
Selected bonds lengths (in pm): 12a: S(1)–P(1) 194.47(4), P(1)–C(1)
184.5(1), P(1)–C(5) 179.3(1), P(1)–C(6) 180.4(1), C(1)–C(2) 156.6(1),
C(2)–C(3) 158.2(1), C(3)–C(4) 153.1(1), C(3)–C(6) 154.3(2), C(4)–C(5)
133.8(1), C(2)–C(7) 151.8(1); 13a: S(1)–P(1) 195.11(3), P(1)–C(1)
183.0(1), P(1)–C(5) 181.4(1), P(1)–C(6) 180.98(9), C(1)–C(2)
156.1(2), C(2)–C(3) 156.2(2), C(3)–C(4) 156.6(1), C(3)–C(6) 153.6(1),
C(4)–C(5) 155.5 (2), C(2)–C(7) 151.4(2).
Scheme 3. Reductive cleavage of the chiral auxiliary.
4 | Dalton Trans., 2015, 00, 1-3
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but seems unlikely due to the orientation of the corresponding
orbitals.12b However, on looking at the torsion angles C(4)–C(3)–
C(6)–H(6A) (167(1)° for 12a and 13a) und C(2)–C(3)–C(6)–H(6B)
(178(1)° for 12a and 173(1)° for 13a), the fixed antiperiplanar
orientation of these bonds is distinctive. Hence, an efficient
hyperconjugation between these bonds and therefore indirectly
with the π bond could cause a delocalisation of the double bond
over the whole 1-phosphanorbornene system. The same
conclusions can be drawn from the molecular structures of 12c and
(R)-13c and (S)-13c (see Figure 5).
Compound 13a represents a key molecule for divergent ligand
synthesis, as the unaltered OH group in 3-position to the
phosphorus atom facilitates the introduction of various functional
and coordinating groups to afford chelating ligands. First,
nucleophilic attack of the OH group at diarylchlorophosphanes was
conducted, initially without protecting the exocyclic phosphorus
atom. However, hydrolysis of the P–O bond was observed during
purification of the resulting phosphinites by column
chromatography (silica or alumina). An alternative purification by
recrystallisation did not yield a pure product. When the second
phosphorus atom was also protected with sulfur, compounds 14a,b
(Scheme 5) could be easily separated by column chromatography,
crystallised, and structurally characterised (Figure 6). Unfortunately,
a subsequent sulfur deprotection of 14a,b was not successful with
the methods described in Scheme 2. 31P{1H} NMR spectroscopic
studies showed that only the endocyclic phosphorus atom and not
the exocyclic one is desulfurised
Figure 5. Molecular structures of 12c (top), (R)-13c (centre), (S)-13c
(bottom); Ellipsoid level at 50%. Hydrogen atoms are omitted for
clarity. Selected bond lengths (in pm) and angles (in °): 12c: S(1)–
P(1) 193.8(1), P(1)–C(1) 184.5(1), P(1)–C(5) 181.3(2), P(1)–C(6)
180.0(2), C(1)–C(2) 156.7(2), C(2)–C(3) 158.1(2), C(3)–C(4) 153.5(2),
C(4)–C(5) 135.1(2), O(2)–C(8) 142.7(2), C(4)–C(3)–C(2) 109.4(1),
C(5)–P(1)–C(1) 101.14(6); (R)-13c: S(1)–P(1) 195.08(8), P(1)–C(1)
181.4(2), P(1)–C(5) 182.6(2), P(1)–C(6) 181.0(2), C(1)–C(2) 155.4(2),
C(2)–C(3) 155.7(2), C(3)–C(4) 157.0(2), C(4)–C(5) 157.8(2), O(2)–C(8)
142.9(2), C(4)–C(3)–C(2) 99.3(1), C(5)–P(1)–C(1) 105.95(7); (S)-13c:
S(1)–P(1) 194.25(9), P(1)–C(1) 182.6(1), P(1)–C(5) 183.9(2), P(1)–
C(6) 182.1(1), C(1)–C(2) 155.5(2), C(2)–C(3) 156.0(2), C(3)–C(4)
156.2(2), C(4)–C(5) 158.9(2), O(2)–C(8) 142.3(2); C(4)–C(3)–C(2)
99.68(9), C(5)–P(1)–C(1) 102.14(6).
Scheme 5. Synthesis of phosphinites 14.
A well-known effect in norbornene or norbornadiene systems is the
strong NMR deshielding of the bridge atom. Even though it is
known that the reason for this observation is the delocalisation of
the double bond as well, the way in which the bridge is involved is
not completely understood. Some theories suggest a direct
hyperconjugation of the π orbitals with the exocyclic σ orbitals of
the bridge.12,14a An interaction between the σ orbitals of the
endocyclic bond of the bridge and the π* orbitals is also discussed,
Figure 6. Molecular structures of 14a (left) and 14b (right); ellipsoid
level at 50%. Hydrogen atoms are omitted for clarity. Selected
bonds lengths (in pm): 14a: S(1)–P(1) 194.71(6), S(2)–P(2) 193.50(6),
C(1)–C(8) 150.1(3), O(2)–C(8) 145.7(2); 14b: S(1)–P(1) 194.60(7),
S(2)–P(2) 193.68(7), C(1)–C(8) 151.3(2), O(2)–C(8) 144.9(2).
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Since preparation of the phosphane–phosphinite ligands
(deprotected 14a,b) was not successful, another approach was
pursued to obtain bis-phosphanes having only P–C bonds
(Scheme 6). Bromination of 13a with Br2PPh3 gave bromide 15 in
excellent yield. However, the following nucleophilic substitution
turned out to be challenging. Treating 15 with LiPPh2 resulted in
elimination of HBr giving 16; apparently, the exocyclic proton in α
position is rather acidic. Nevertheless, applying the less basic
lithium phospholide 1 followed by sulfur protection afforded the
desired product 17 in excellent yield. The thiophosphole group of
17 can now be employed in other asymmetric Diels–Alder
reactions.15 The basicity of lithium phosphanides like LiPPh2 can be
reduced by coordination to borane. Accordingly, LiP(BH3)Ph2 gave
access to 18 in good yield. Compound 18 was fully characterised,
also by X-ray crystallography (Figure 7). Since no reducible groups,
such as the P–O bond in 14a,b are present, sulfur deprotection was
performed under very mild conditions with LiAlH4. The
corresponding bis-phosphane was isolated as bis-borane adduct 19
in good yield. 31P{1H} NMR studies showed that its trivalent species
20 can be generated quantitatively in situ with morpholine;
however, 20 was not isolated.
Figure 7. Molecular structure of 18; ellipsoid level at 50%. Hydrogen
atoms are omitted for clarity. Bond lengths (in pm) and angles (in °):
S(1)–P(1) 194.4(1), P(1)–C(1) 181.9(3), P(1)–C(5) 180.8(3), P(1)–C(6)
180.7(3), C(1)–C(2) 157.2(4), C(2)–C(3) 155.7(4), C(3)–C(4) 156.0(4),
C(4)–C(5) 155.3(4), P(2)–B(1) 192.1(3); C(6)–P(1)–C(5) 93.1(2), C(6)–
P(1)–S(1) 125.5(1), C(5)–P(1)–S(1) 119.9(1), C(8)–P(2)–B(1) 113.3(2),
C(11)–P(2)–B(1) 112.5(2), C(11)–P(2)–C(8) 105.9(1).
Scheme 6. Bromination of 13a and subsequent nucleophilic
substitution at 15.
6 | Dalton Trans., 2015, 00, 1-3
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DOI: 10.1039/C5DT02564H
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ARTICLE
were synthesised according to the literature. All other compounds
are commercially available.
Conclusions
A diastereoselective synthetic route towards P-chiral 1-phospha-
norbornenes has been established by using the principle of
stereotopic face differentiation. The observed reaction pathway
was supported by theoretical calculations showing that the
cycloaddition reaction between 2H-phosphole 3a and dienophile 8
is of normal electron demand. The phosphorus atom in the
Synthesis of 5. Isopropanol was added at −30 °C to a 0.11 M stock
solution of 1-lithium-3,4-dimethyl phosphole (see synthesis of 9a) in
THF (5.0 ml, 0.55 mmol). The solution was stirred at this
temperature for one hour; then crotonic acid amide 4 (0.13 g,
0.54 mmol) was added. After 72 hours at −30 °C, the solution was
obtained Diels–Alder products 9a,c,d was easily desulfurised to give warmed to room temperature, sulfur (0.018 g, 0.56 mmol) and
the
corresponding
trivalent
species
11a,c,d.
Further
three drops of triethylamine were added and the solution was
stirred for 16 hours at room temperature. Chromatographic workup
(hexanes/diethyl ether = 1:3 to 1:2, v/v) of the crude product gave 5
as a white solid. Yield: 0.18 g, 87%. Rf (hexanes/diethyl ether = 1:3,
functionalisation yielded alcohol 13a as a key compound for
divergent ligand synthesis. A subsequent electrophilic substitution
at the OH group gave phosphinites which are sensitive towards
hydrolysis. This problem was overcome by sulfur protection (14a,b).
Finally, bromination of 13a afforded bromide 15, which underwent
v/v) = 0.22 – UV light, iodine. m.p.: 58–60 °C.
25 = +37.9° (c = 2.35
[α ]
D
elimination of HBr in the presence of a strong base with formation in toluene). 1H NMR (300 MHz): = 1.27 (3H, dd, 3JH,P = 18.7 Hz, 3JH,H
δ
of 16. By using less basic nucleophiles, this elimination reaction
could be suppressed and the desired nucleophilic substitution
products (17 and 18) were obtained. The phosphanes presented in
this work are expected to be very useful as ligands in asymmetric
transition metal catalysis.
= 7.1 Hz), 2.08 (6H, s), 2.60–2.84 (2H, m), 2.94–3.13 (1H, m), 3.24–
3.54 (2H, m), 4.12–4.27 (2H, m), 4.62–4.75 (1H, m), 6.03 (2H, d, 2JH,P
= 30.4 Hz), 7.18–7.26 (2H, m), 7.26–7.40 (3H, m) ppm. 13C{1H} NMR
(76 MHz):
δ
= 15.2 (s), 17.4 (d, 3JC,P = 3.3 Hz), 17.6 (d, 3JC,P = 3.3 Hz)
1
31.1 (d, JC,P = 51.8 Hz), 37.1 (s), 37.9 (s), 55.3 (s), 66.4 (s), 122.1–
123.5 (m), 123.1–123.6 (m), 127.4 (s), 129.0 (s), 129.4 (s), 135.1 (s),
Experimental
3
153.3 (s), 153.8–154.5 (m), 171.0 (d, JC,P = 13.4 Hz) ppm. 31P{1H}
NMR (162 MHz):
δ = 61.5 ppm. IR (KBr): ν̃ = 3453 (s), 2963 (m, νC–
General Methods: All reactions were carried out under dry high
purity nitrogen using standard Schlenk techniques. Experiments
including elemental lithium were carried out under dry high purity
argon. THF was degassed and distilled from potassium. The NMR
spectra were recorded with a Bruker Avance DRX 400 spectrometer
(1H NMR 400.13 MHz, 13C NMR 100.63 MHz, 31P NMR 161.98 MHz)
or a Bruker Fourier 300 spectrometer (1H NMR 300.23 MHz, 13C
NMR 75.50 MHz). 13C{1H} NMR spectra were recorded as APT
spectra. Assignment of the chemical shifts and configurations was
done using COSY, HMQC, HSQC HMBC and selective NOE
techniques. If not mentioned otherwise, CDCl3 was used as
deuterated solvent. TMS was used as the internal standard in the 1H
NMR spectra and all other nuclei spectra were referenced to TMS
using the Ξ-scale.16 A detailed assignment of all NMR data for all
compounds is given in the ESI. Mass spectra (ESI) were measured
using a Bruker Daltonics Esquire 3000 Plus spectrometer. High-
resolution mass spectra (HRMS; ESI) were measured using a Bruker
Daltonics APEX II FT-ICR spectrometer. IR spectra were obtained
with an FTIR spectrometer (Genesis ATI Mattson/Unicam or Perkin-
Elmer Spectrum 2000 FT-IR) in the range of 400–4000 cm−1 in KBr.
The melting points were determined in glass capillaries sealed
under nitrogen using a Gallenkamp apparatus and are uncorrected.
Column chromatography was performed using silica 60 (0.015–
0.040 mm) purchased from Merck. UV light (389 nm),
phosphomolybdic acid (12 g phosphomolybdic acid in 100 ml), para-
anisaldehyde (140 ml ethanol, 5 ml sulfuric acid (conc.), 1.5 ml
glacial acetic acid, 4 ml para-anisaldehyde) and iodine (saturated
atmosphere) were used as staining reagents.
H), 2345 (w), 1179 (s), 1699 (s), 1631 (m), 1543 (w), 1456 (m), 1387
(m), 1262 (m), 1217 (m), 1102 (m), 1121 (w), 802 (m), 763 (w), 685
(w), 658 (w), 633 (w), 597 (w), 502 (w), 457 (w), 442 (w), 417 (w)
cm−1. MS (ESI): m/z: calculated for C20H24NO3PS [M+Na]+: 412.1;
found: 412.2. C20H24NO3PS (389.45): calculated: C 61.68%, H 6.21%;
found: C 61.63%, H 6.19%.
In situ generation of 2b and 7. A 0.11 M stock solution of 1-lithium-
3,4-dimethyl phosphole (see synthesis of 9a) in THF (0.6 ml,
0.07 mmol) in an NMR tube was frozen in liquid nitrogen.
Afterwards ClSiMe3 (2–3 fold excess) was added and the sample
was equilibrated in the NMR machine at the given temperature.
31P{1H} NMR (162 MHz, no deuterated solvent): see Fig. 1.
Synthesis of endo-9a: endo-9a was synthesised by a modified
method reported before.6
A
mixture of 3,4-dimethyl-1-
phenylphosphole (2b) (7.05 g, 37.5 mmol) and pieces of lithium
(excess) in 200 ml THF was stirred at room temperature for 3-
4 hours (conversion was monitored by TLC, with phosphomolybdic
acid). The deep brown solution was filtered, cooled to −80 °C and
oxygen-free water (4.05 ml, 225 mmol) was added dropwise. After
complete addition, the solution was kept at −80 °C for 5 minutes
and then warmed to room temperature over 30 minutes.
Afterwards, the solution was dried over MgSO4, filtered and added
to a flask containing (5R)-(L-menthyloxy)-2(5H)-furanone (8) (7.44 g,
31.2 mmol). The pale yellow solution was heated at 63 °C for
24 hours. Sulfur (1.25 g, 39.2 mmol) and two drops of triethylamine
were added and the solution was kept at 40 °C for 18 hours. After
cooling to rt, the solvent was removed in vacuum and the crude
product was purified by recrystallisation (isopropanol/hexanes =
3:5, v/v) to give the main diastereomer endo-9a as a white solid.
The compounds 3,4-dimethyl-1-phenylphosphole (2c),17 3,4-
dimethyl-1-(2-pyridyl)phosphole
(2d),18
4,19
9c,d,6
benzyldiphenylphosphane,20 and dibromotriphenylphosphane21
This journal is © The Royal Society of Chemistry 2015
Dalton Trans., 2015, 00, 1-3 | 7
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ARTICLE
Dalton Transactions
3
3
2
Compound 10 could not be isolated. Yield: 9.66 g, 81%. Rf (1H, dd, JH,P = 8.1 Hz, JH,H = 1.4 Hz), 5.87 (1H, d, JH,P = 45.0 Hz)
ppm. 13C{1H} NMR (76 MHz):
δ = 15.7 (s), 18.3 (s), 19.2 (s), 20.9 (s),
(hexanes/diethyl ether = 1:1, v/v) = 0.33 – para-anisaldehyde. m.p.:
1
1
116–118 °C. 25 = −65.4° (c = 1.62 in toluene). H NMR (400 MHz):
22.2 (s), 23.2 (s), 25.4 (s), 31.4 (s), 34.3 (s), 40.0 (s), 46.3 (d, JC,P
=
α
[ ]
D
2
19.6 Hz), 47.7 (s), 51.8 (d, JC,P = 1.8 Hz), 53.2 (d, 1JC,P = 4.9 Hz), 62.9
δ
= 0.75 (3H, d, 3JH,H = 6.9 Hz), 0.81–0.91 (1H, m), 0.84 (3H, d, 3JH,H
=
2
2
1
3
(d, JC,P = 6.1 Hz), 77.2 (s), 101.9 (d, JC,P = 11.4 Hz), 124.0 (d, JC,P
=
7.1 Hz), 0.91–1.04 (m, 2H), 0.93 (3H, d, JH,H = 6.5 Hz), 1.19–1.29
(1H, m), 1.30–1.40 (1H, m), 1.63 (3H, s), 1.61–1.68 (2H, m), 1.94
(3H, s), 1.91–1.97 (1H, m), 2.02–2.08 (2H, m), 2.11–2.18 (1H, m),
2
24.2 Hz), 163.8 (d, JC,P = 4.3 Hz), 175.5 (s) ppm. 31P{1H} NMR
(162 MHz): = −30.0 ppm. IR (KBr): ν = 3458 (s), 2950 (m, νC–H),
δ
̃
3
2867 (m, νC–H), 1760 (s, νO–C=O), 1636 (w), 1584 (w), 1564 (w),
1460 (m), 1432 (w), 1358 (w), 1262 (w), 1205 (w), 1180 (m), 1114
(s), 988 (w), 944 (s), 801 (w), 777 (w), 751 (w), 681 (w), 646 (w), 548
(w), 490 (w), 469 (w), 414 (w), 428 (w), 417 (w) cm−1. MS (ESI,
DCM/MeOH): m/z: calculated for C20H31O3P [M+Na]+: 373.2; found:
373.2. C20H31O3P (350.43): calculated: C 68.6%, H 8.9%; found: C
68.5%, H 8.89%.
3.13–3.20 (1H, m), 3.25–3.31 (1H, m), 3.50 (1H, ddd, JH,H = 10.7 Hz,
3
3
3JH,H = 10.7 Hz, JH,H = 2.4 Hz), 5.49 (1H, d, JH,P = 13.0 Hz), 5.90 (1H,
d, 2JH,P = 26.3 Hz) ppm. 13C{1H} NMR (101 MHz):
δ
= 15.7 (s), 18.6 (d,
3
3JC,P = 14.2 Hz), 19.3 (d, JC,P = 16.2 Hz), 20.9 (s), 22.2 (s), 23.1 (s),
1
25.4 (s), 31.5 (s), 34.2 (s), 40.0 (s), 47.5 (s), 48.6 (d, JC,P = 46.6 Hz),
2
1
50.9 (d, JC,P = 21.7 Hz), 53.5 (s), 56.5 (d, JC,P = 57.6 Hz), 78.7 (s),
2
1
2
99.5 (d, JC,P = 5.9 Hz), 121.1 (d, JC,P = 69.3 Hz), 165.5 (d, JC,P
=
=
7.2 Hz, 173.6 (d, JC,P = 3.0 Hz) ppm. 31P{1H} NMR (162 MHz):
δ
3
Synthesis of endo-11c. A suspension of freshly prepared Raney
nickel (2.02 g, excess) and endo-9c (0.310 g, 0.676 mmol) in 15 ml of
THF was stirred for 30 hours at room temperature. The solution was
filtered and the black solid was washed three times with 15 ml of
THF. Chromatographic workup (toluene) gave endo-11c as white
solid. Yield: 0.216 g, 75%. Rf (toluene) = 0.40 – UV light, para-
48.7 ppm. IR (KBr): ν
̃
= 3455 (m), 2953 (s, νC–H), 2925 (s, νC–H),
2870 (s, νC–H), 1766 (s, νO–C=O), 1633 (w), 1580 (m), 1456 (m),
1436 (m), 1414 (m), 1385 (m), 1371 (m), 1346 (m), 1303 (w), 1244
(m), 1231 (m), 1203 (w), 1178 (s), 1166 (s), 1119 (s), 1074 (m), 1038
(m), 1010 (m), 989 (s), 975 (m), 942 (s), 902 (m), 890 (m), 858 (m),
848 (w), 833 (m), 819 (m), 776 (m), 740 (m), 723 (s), 708 (m), 678
(s), 631 (w), 420 (s) cm−1. HRMS (ESI): m/z: calculated for C20H31O3PS
[M+Na]+: 405.16237; found: 405.16229. C20H31O3PS (382.50):
calculated: C 62.8%, H 8.17%; found: C 63.4%, H 8.23%.
anisaldehyde. m.p.: 128–130 °C.
25 = +260° (c = 1.27 in toluene).
[α]
D
1H NMR (300 MHz):
δ
= 0.74 (3H, d, JH,H = 6.9 Hz), 0.64–1.03 (9H,
3
m), 1.06–1.20 (1H, m), 1.20–1.32 (1H, m), 1.35–1.49 (1H, m), 1.50–
1.74 (3H, m), 1.70 (3H, s), 1.76–1.84 (1H, m), 1.94 (3H, s), 1.99–2.13
3
3
(1H, m), 3.00–3.24 (2H, m), 3.36 (1H, ddd, JH,H = 10.4 Hz, JH,H
General procedure for the activation of Raney nickel:
3
3
= 10.4 Hz, JH,H = 4.1 Hz), 5.06 (1H, d, JH,P = 7.1 Hz), 7.20–7.41 (5H,
m) ppm. 13C{1H} NMR (76 MHz):
δ = 15.0 (s), 15.7 (s), 20.2 (s), 20.8
In a Schlenk flask under nitrogen atmosphere solid NaOH was
added to a vigorously stirred suspension of an aluminium-nickel
alloy (Raney type) in 20 ml of water portion wise in such a manner
that the gas evolution was kept under control (caution: initiation
time required, solution warms up!). In this process, the greyish
metal alloy turned into a dark black solid. After the gas evolution
had ceased, the reaction mixture was stirred at 80 °C for one hour.
The clear solution was decanted and the black metal was washed
with 15 ml portions of water under vigorous stirring until a pH of 8–
9 was accomplished (usually 6–8 washing steps). Afterward, the
Raney nickel was washed three times with 15 ml of ethanol and two
times with 15 ml of THF. After desulfurisation was completed, the
nickel waste was destroyed by addition of diluted HCl and
subsequently concentrated HCl.
(s), 22.1 (s), 23.1 (s), 25.4 (s), 31.3 (s), 34.2 (s), 39.8 (s), 46.8 (d, 1JC,P
2
= 21.3 Hz), 47.6 (s), 51.0–51.2 (m), 64.5 (d, JC,P = 6.3 Hz), 77.1 (s),
3
101.0 (d, 2JC,P = 10.6 Hz), 127.0 (s), 128.4 (s), 129.0 (d, JC,P = 6.8 Hz),
136.8–139.3 (m), 153.9 (s), 175.6 (s) ppm. 31P{1H} NMR (162 MHz):
δ
= −14.5 ppm. IR (KBr): ν̃ = 3445 (s), 2963 (s, νC–H), 2922 (s, νC–H),
2868 (m, νC–H), 1754 (m, νO–C=O), 1631 (w), 1558 (w), 1506 (w),
1489 (w), 1456 (m), 1442 (w), 1386 (m), 1379 (m), 1351 (s), 1331
(m), 1298 (w), 1262 (w), 1246 (w), 1200 (m), 1168 (s), 1129 (m),
1106 (s), 1074 (m), 1038 (w), 1007 (w), 987 (m), 973 (w), 938 (s),
879 (w), 847 (w), 813 (w), 790 (w), 754 (w), 703 (m), 671 (w), 633
(w), 611 (w), 541 (w), 514 (w), 492 (w), 475 (w), 448 (w), 439 (w),
417 (w), 408 (w) cm−1. MS (ESI, MeOH): m/z: calculated for
C26H35O3P [M+Na]+: 449.2; found: 449.3. C26H35O3P (426.53):
calculated: C 73.2%, H 8.27%; found: C 73.3%, H 8.14%.
Synthesis of endo-11a. A suspension of freshly prepared Raney
nickel (2.20 g, excess) and endo-9a (0.420 g, 1.10 mmol) in 15 ml of
THF was stirred for 40 hours at room temperature. The solution was
filtered and the black solid was washed three times with 15 ml of
THF. Chromatographic workup (toluene) gave endo-11a as white
solid. Yield: 0.213 g, 55%. Rf (toluene) = 0.34 – para-anisaldehyde.
Synthesis of exo-11c. A suspension of freshly prepared Raney nickel
(2.01 g, excess) and exo-9c (0.329 g, 0.717 mmol) in 15 ml of THF
was stirred for 30 hours at room temperature. The solution was
filtered and the black solid was washed three times with 15 ml of
THF. Chromatographic workup (toluene) gave exo-11c as white
m.p.: 130–132 °C.
25 = +231° (c = 1.52 in toluene). 1H NMR
[α ]
D
solid. Yield: 0.267 g, 87%. Rf (toluene) = 0.42 – UV light, para-
= 0.75 (3H, d, 3JH,H = 6.9 Hz), 0.87 (3H, d, 3JH,H = 7.1 Hz),
1
anisaldehyde. m.p.: 55–57 °C.
25 = −148° (c = 3.60 in toluene). H
(300 MHz):
δ
[α]
D
3
3
3
0.65–1.13 (3H, m), 0.93 (3H, d, JH,H = 6.5 Hz), 1.15–1.27 (1H, m),
1.28–1.46 (2H, m), 1.52 (1H, dd, J = 11.5 Hz, J = 8.9 Hz), 1.63 (3H, s),
1.57–1.70 (2H, m), 1.88 (3H, s), 1.96–2.16 (2H, m), 2.97–3.07 (2H,
m), 3.42 (1H, ddd, 3JH,H = 10.7 Hz, 3JH,H = 10.7 Hz, 3JH,H = 4.2 Hz), 5.04
NMR (300 MHz): δ = 0.80 (3H, d, JH,H = 6.9 Hz), 0.87 (3H, d, JH,H
3
= 7.0 Hz), 0.71–1.08 (3H, m), 0.94 (3H, d, JH,H = 6.5 Hz), 1.14–1.42
(3H, m), 1.51 (1H, dd, J = 12.9 Hz, J = 8.0 Hz), 1.60–1.73 (2H, m), 1.64
(3H, s), 1.87 (3H, s), 2.02–2.20 (2H, m), 2.57–2.66 (2H, m), 3.55 (1H,
8 | Dalton Trans., 2015, 00, 1-3
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ddd, 3JH,H = 10.7 Hz, 3JH,H = 10.7 Hz, 3JH,H = 4.2 Hz), 5.51 (1H, d, 3JH,P
View Article Online
DOI: 10.1039/C5DT02564H
ARTICLE
=
60 °C.
25 = −170° (c = 2.27 in toluene). 1H NMR (300 MHz):
δ =
[α ]
D
8.8 Hz), 7.30–7.15 (3H, m), 7.30–7.38 (2H, m) ppm. 13C{1H} NMR
0.70 (3H, d, 3JH,H = 6.9 Hz), 0.77 (3H, d, 3JH,H = 7.0 Hz), 0.57–0.99 (3H,
m), 0.86 (3H, d, 3JH,H = 6.4 Hz), 1.01–1.32 (3H, m), 1.33–1.47 (1H, m),
1.48–1.64 (2H, m), 1.57 (3H, s), 1.93 (3H, s), 1.96–2.03 (1H, m),
2.03–2.11 (1H, m), 2.51–2.59 (1H, m), 2.61–2.73 (1H, m), 3.46 (1H,
(76 MHz): = 13.0 (s), 15.7 (s), 17.8 (s), 20.9 (s), 22.2 (s), 23.2 (s),
δ
1
25.4 (s), 31.4 (s), 34.3 (s), 39.9 (s), 42.3 (d, JC,P = 7.1 Hz), 47.8 (s),
48.7 (d, 2JC,P = 2.4 Hz), 49.5 (d, 1JC,P = 19.0 Hz), 63.9 (d, JC,P = 6.4 Hz)
2
2
3
ddd, 3JH,H = 10.6 Hz, 3JH,H = 10.6 Hz, 3JH,H = 4.1 Hz), 5.48 (1H, d, 3JH,P
=
76.9 (s), 101.3 (d, JC,P = 29.2 Hz), 126.9 (s), 128.1 (d, JC,P = 7.3 Hz),
2
1
3
3
3
128.3 (s), 137.6 (d, JC,P = 20.5 Hz), 142.2 (d, JC,P = 16.5 Hz), 154.2
(s), 174.8 (s) ppm. 31P{1H} NMR (162 MHz):
= −10.1 ppm. IR (KBr):
= 3424 (s), 2956 (s, νC–H), 2925 (s, νC–H), 2866 (m, νC–H), 2346
9.0 Hz), 7.04 (1H, dd, JH,H = 7.7 Hz, JH,H = 4.8 Hz), 7.19 (1H, d, JH,H
= 7.7 Hz), 7.57 (1H, dd, 3JH,H = 7.7 Hz, 3JH,H = 7.7 Hz), 8.51 (1H, d, 3JH,H
δ
= 4.8 Hz) ppm. 13C{1H} NMR (76 MHz):
δ = 13.4 (s), 15.7 (s), 17.7 (s),
ν̃
(w), 1769 (s, νO–C=O), 1630 (w), 1558 (w), 1506 (w), 1491 (w), 1456
(m), 1385 (w), 1370 (w), 1346 (m), 1243 (m), 1157 (s), 1104 (s),
1049 (m), 1010 (w), 976 (m), 944 (s), 921 (m), 868 (w), 848 (w), 797
(w), 756 (m), 698 (m), 674 (w), 640 (w), 591 (w), 549 (w), 518 (w),
493 (w), 467 (w), 453 (w), 441 (w), 422 (w), 416 (w) cm–1. MS (ESI,
MeOH): m/z: calculated for C26H35O3P [M+Na]+: 449.2; found: 449.3.
C26H35O3P (426.53): calculated: C 73.2%, H 8.27%, found: C 73.4%, H
8.04%.
20.8 (s), 22.2 (s), 23.2 (s), 25.4 (s), 31.3 (s), 34.3 (s), 39.7 (s), 41.7 (d,
1
1JC,P = 7.2 Hz), 47.7 (s), 48.8 (s), 49.3 (d, JC,P = 19.2 Hz), 64.3 (d, 2JC,P
= 6.6 Hz), 76.4 (s), 101.1 (d, 2JC,P = 29.9 Hz), 121.3 (s), 122.8 (d, 3JC,P
=
=
=
2
6.7 Hz), 135.9 (s), 142.8 (d, 1JC,P = 14.8 Hz), 149.4 (s), 156.5 (d, JC,P
19.8 Hz), 157.8 (s), 174.7 (s) ppm. 31P{1H} NMR (162 MHz):
δ
−12.1 ppm. IR (KBr): ν
̃
= 3440 (s), 2961 (s, νC–H), 2925 (s, νC–H)
2868 (m, νC–H), 1767 (s, νO–C=O), 1717 (w), 1608 (m), 1584 (m),
1564 (w), 1527 (w), 1506 (w), 1464 (m), 1432 (w), 1386 (w), 1348
(w), 1261 (m), 1160 (m), 1097 (s), 1050 (m), 978 (w), 943 (m), 921
(w), 868 (w), 802 (w), 747 (w), 681 (w), 647 (w), 542 (w), 521 (w),
469 (w), 440 (w), 429 (w), 409 (w) cm−1. MS (ESI, MeOH): m/z:
calculated for C25H34NO3P [M+Na]+: 450.2; found: 450.3. C25H34NO3P
(427.52): calculated: C 70.2%, H 8.02%; found: C 70.1%, H 8.13%.
Synthesis of endo-11d. A solution of endo-9d (0.35 g, 0.75 mmol)
and PEt3 (0.25 ml, 1.7 mmol) in 5 ml of xylenes was heated at 130 °C
for 5 hours. Chromatographic workup (hexanes/diethyl ether = 5:1
to 3:1, v/v) gave endo-11d as a white solid. Yield: 0.30 g, 93%. Rf
(hexanes/diethyl ether
=
2:1, v/v)
= 0.35 – UV light, para-
anisaldehyde. m.p.: 129–131 °C.
25 = −27.2° (c = 1.62 in toluene).
[α]
Synthesis of 12a. endo-9a (0.31 g, 0.81 mmol) was added to a
D
1H NMR (300 MHz):
δ = 0.67 (3H, d, JH,H = 6.9 Hz), 0.80 (3H, d, JH,H suspension of LiAlH4 (0.080 g, 2.1 mmol) in 10 ml of diethyl ether at
3
3
3
= 7.0 Hz), 0.59–0.99 (3H, m), 0.88 (3H, d, JH,H = 6.5 Hz), 1.10–1.30 0 °C. The cooling bath was removed and the solution was left to stir
(2H, m), 1.32–1.44 (1H, m), 1.50–1.62 (3H, m), 1.65 (3H, s), 1.95 for 90 minutes. The reaction was quenched by the addition of
(3H, s), 2.00–2.09 (1H, m), 2.09–2.18 (1H, m), 2.95–3.18 (2H, m), 0.45 ml water, stirred for 30 minutes and MgSO4 was added. The
3
3
3
3.31 (1H, ddd, JH,H = 10.6 Hz, JH,H = 10.6 Hz, JH,H = 4.1 Hz), 5.68 mixture was transferred onto
a D2 frit; and the solid was
3
(1H, d, JH,P = 8.3 Hz), 7.06–7.12 (1H, m), 7.16–7.27 (1H, m), 7.44– continuously extracted with a DCM/diethyl ether mixture (2:1, v/v)
7.75 (1H, m), 8.43–8.60 (1H, m) ppm. 13C{1H} NMR (76 MHz):
δ =
for 3 hours. Sulfur (0.03 g, 0.94 mmol) was added to the extract and
the solution was stirred for 16 hours. After chromatographic
workup (DCM/MeOH = 50:1 to 20:1, v/v) 12a was obtained as a
white solid. Crystals suitable for X-ray diffraction measurements
were obtained from chloroform. Yield: 0.16 g, 87%. Rf
15.0 (s), 15.8 (s), 20.1 (s), 20.9 (s), 22.4 (s), 23.2 (s), 25.5 (s), 31.5 (s),
1
1
34.4 (s), 40.1 (s), 46.3 (d, JC,P = 21.8 Hz), 47.6 (s), 50.9 (d, JC,P
=
=
=
2
2
5.6 Hz), 52.2 (s), 65.1 (d, JC,P = 6.7 Hz), 77.5 (s), 102.7 (d, JC,P
10.0 Hz), 121.3 (s), 123.1 (d, 3JC,P = 4.1 Hz), 135.8 (s), 140.6 (d, 1JC,P
18.1 Hz), 149.4 (s), 155.8 (s), 157.2 (d, 2JC,P = 17.3 Hz), 175.5 (s) ppm.
31P{1H} NMR (162 MHz):
= −13.6 ppm. IR (KBr): ν = 3424 (s), 2949
25
D
(DCM/methanol = 10:1, v/v) = 0.40 – iodine. m.p.: 145–147 °C.
α
[ ]
1
δ
̃
= −59.4° (c = 2.31 in chloroform). H NMR (400 MHz): δ = 1.45 (3H,
(s, νC–H), 2864 (m, νC–H), 1759 s (νO–C=O), 1603 (m), 1584 (s),
1563 (w), 1460 (s), 1433 (m), 1411 (w), 1386 (m), 1357 (m), 1281
(w), 1262 (w), 1245 (w), 1205 (m), 1180 (s), 1156 (m), 1128 (s), 1114
(s), 1040 (w), 1011 (m), 987 (m), 970 (w), 944 (s), 916 (m), 879 (w),
843 (w), 798 (w), 777 (m), 751 (w), 719 (w), 704 (w), 681 (m), 645
(w), 612 (w), 541 (w), 492 (w), 469 (w), 448 (w), 440 (w), 423 (w)
cm−1. MS (ESI, MeOH): m/z: calculated for C25H34NO3P [M+Na]+:
450.2; found: 450.3. C25H34NO3P (427.52): calculated: C 70.2%, H
8.02%; found: C 70.1%, H 8.08%.
s), 1.88 (3H, s), 1.89–2.01 (2H, m), 2.47–2.70 (1H, m), 2.72–2.90 (1H,
m), 3.36–3.48 (1H, m), 3.59–3.71 (1H, m), 3.71–3.81 (1H, m), 4.15–
2
4.26 (1H, m), 4.81 (2H, s (br)), 5.76 (1H, d, JH,P = 26.3 Hz) ppm.
3
3
13C{1H} NMR (101 MHz):
δ = 19.1 (d, JC,P = 15.0 Hz), 19.7 (d, JC,P =
1
2
17.0 Hz), 44.7 (d, JC,P = 42.4 Hz), 49.6 (d, JC,P = 24.2 Hz), 52.0 (s),
54.7 (d, 1JC,P = 56.3 Hz), 59.0 (d, 2JC,P = 6.2 Hz), 59.5 (d, 3JC,P = 3.4 Hz),
121.4 (d, JC,P = 68.8 Hz), 163.9 (d, JC,P = 7.4 Hz) ppm. 31P{1H} NMR
1
2
(162 MHz): = 48.2 ppm. IR (KBr): ν = 3470 (s), 2965 (m, νC–H),
δ
̃
2925 (m, νC–H), 2325. (w), 1625 (m), 1585 (m), 1475 (m), 1456 (m),
1433 (m), 1384 (m), 1314 (w), 1262 (w), 1159 (w), 1126 (s), 1043 (s),
1033 (s), 983 (w), 879 (w), 825 (w), 791 (m), 768 (m), 751 (w), 703
(s), 682 (s), 626 (w), 529 (w), 464 (w), 444 (w), 431 (w), 421 (w), 414
(w) cm−1. MS (ESI, DCM/MeOH): m/z: calculated for C10H17O2PS
[M+Na]+: 255.1; found: 255.0. C10H17O2PS (232.28): calculated: C
51.7%, H 7.38%; found: C 51.4%, H 7.38%.
Synthesis of exo-11d. A suspension of freshly prepared Raney nickel
(2.08 g, excess) and exo-9d (0.320 g, 0.696 mmol) in 15 ml of THF
was stirred for 43 hours at room temperature. The solution was
filtered and the black solid was washed three times with 10 ml of
THF. Chromatographic workup (hexanes/diethyl ether = 2:1, v/v)
gave exo-11d as white solid. Yield: 0.211 g, 71%. Rf (hexanes/diethyl
ether = 2:1, v/v) = 0.25 – UV light, para-anisaldehyde. m.p.: 58–
This journal is © The Royal Society of Chemistry 2015
Dalton Trans., 2015, 00, 1-3 | 9
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DOI: 10.1039/C5DT02564H
ARTICLE
Dalton Transactions
Synthesis of 13a. A solution of endo-9a (12.91 g, 33.8 mmol) in one hour. After chromatographic workup (DCM/MeOH = 60:1 to
150 ml THF was added at 0 °C over 5 minutes to a mixture of LiAlH4 10:1, v/v) 12c was obtained as a white solid. Crystals suitable for X-
(2.56 g, 67.5 mmol) in 50 ml THF. The cooling bath was removed ray diffraction measurements were obtained from DCM. Yield:
and the solution was left to stir for 20 hours. The reaction was 0.072 g, 45%. Rf (DCM/Methanol = 40:1, v/v) = 0.08 – iodine. m.p.:
quenched by slowly adding a solution of KOH (3.1 g in 10 ml 198–200 °C.
= 1.54 (3H, s), 1.94 (3H, d, 4JH,P = 2.7 Hz), 2.00–2.10 (2H, m),
degassed water) at 0 °C. The slurry was heated to 60 °C for one
MHz): δ
25 = −54.1° (c = 0.795 in DMSO). 1H NMR (400
[α ]
D
hour and then cooled to room temperature. The mixture was
filtered and the residue was washed with 200 ml of THF. The
combined filtrates were treated with sulfur (1.20 g, 37.4 mmol) and
0.50 ml of trimethylamine, and the solution was stirred at 55 °C for
16 hours. The solvent was removed under vacuum, the residue
transferred to a pad of silica and washed with a mixture of
hexanes/diethyl ether (1:1, v/v). Crude 12a was eluted by washing
the silica pad with a mixture of DCM/methanol (1:1, v/v). The
solvent was removed and the residue was dissolved in a solution of
NaOEt in 170 ml of ethanol (prepared by dissolving sodium (1.60 g,
69.6 mmol) in 170 ml of ethanol). The solution was left to stir at
room temperature for 4 days. The reaction was quenched by
addition of glacial acid (4.00 ml, 63.4 mmol) and the solvent was
removed in vacuum. The residue was taken up in a mixture of 60 ml
water and 50 ml brine, and the organic phase was extracted once
with 150 ml and three times with 75 ml of chloroform. After drying
the combined organic phases over MgSO4, the solvent was removed
2.61–2.72 (1H, m), 2.85–2.98 (1H, m), 3.54–3.63 (1H, m), 3.73–3.82
(1H, m), 3.83–3.91 (1H, m), 4.20–4.31 (1H, m), 7.26–7.30 (2H, m),
3
3
7.34 (1H, t, JH,H = 7.4 Hz), 7.42 (2H, t, JH,H = 7.4 Hz) ppm. 13C{1H}
NMR (101 MHz):
= 16.0 (d, 3JC,P = 11.6 Hz), 20.3 (d, 3JC,P = 16.9 Hz),
45.1 (d, JC,P = 41.6 Hz), 48.4 (d, 2JC,P = 22.8 Hz), 52.6 (s), 53.6 (d,
δ
1
1JC,P = 56.8 Hz), 59.5 (d, JC,P = 6.2 Hz), 59.8 (d, JC,P = 3.7 Hz), 127.8
2
3
5
3
2
(d, JC,P = 1.6 Hz), 128.3 (s), 129.5 (d, JC,P = 5.1 Hz), 132.1 (d, JC,P
=
1
2
9.5 Hz), 132.8 (d, JC,P = 64.3 Hz) , 154.6 (d, JC,P = 13.7 Hz) ppm.
31P{1H} NMR (162 MHz):
= 56.4 ppm. IR (KBr): ν = 3424 (s), 2969 (s,
δ
̃
νC–H), 2927 (s, νC–H), 1631 (m), 1606 (s), 1485 (m), 1456 (m), 1440
(s), 1385 (w), 1372 (w), 1344 (w), 1319 (w), 1261 (m), 1223 (w),
1151 (w), 1135 (m), 1106 (m), 1176 (m), 1037 (s), 938 (w), 902 (w),
883 (w), 802 (m), 793 (m), 785 (m), 763 (m), 734 (w), 708 (s), 638
(m), 563 (w), 502 (w), 495 (w), 449 (w) cm−1. MS (ESI, DCM/MeOH):
m/z: calculated for C16H21O2PS [M+Na]+: 331.1; found: 331.1.
C16H21O2PS (308.38): calculated: C 62.3%, H 6.86%; found: C 61.23%,
H 6.50%.
and the residue was recrystallised from
a
mixture of
isopropanol/hexanes (9:5, v/v) to give 13a as a white solid. Crystals
suitable for X-ray diffraction measurements were obtained from
DCM/hexanes at 4 °C. Yield: 6.11 g, 78%. Rf (DCM/Methanol = 10:1,
Synthesis of (R)-13c and (S)-13c. A solution of endo-9c (1.2 g,
2.6 mmol) in 5 ml THF was added to a suspension of LiAlH4 (0.19 g,
5.0 mmol) in 10 ml THF at 0 °C. The cooling bath was removed and
the solution was left to stir for 5 h. The reaction was quenched by
the addition of 4 ml of an aqueous sodium hydroxide solution
(32%). 15 ml of THF and MgSO4 were added, the suspension was
transferred onto a frit and the white solid was continuously
extracted with THF for 12 h. Sulfur (0.090 g, 2.8 mmol) and three
drops of triethylamine were added and the solution was left to stir
for 11 days. After chromatographic workup (DCM/MeOH = 50:1) a
mixture of (R)-13c and (S)-13c was obtained as a white solid (R)-
13c:(S)-13c = 1.3:1.0). Analytical amounts of the separated
diastereomers as well as crystals suitable for X-ray diffraction
measurements were obtained by recrystallisation from DCM.Yield:
0.37 g, 45%.
v/v) = 0.40 – iodine. m.p.: 124–126 °C.
chloroform). 1H NMR (300 MHz):
δ = 1.15 (3H, s), 1.21 (3H, s), 1.79–
25 = +17.2° (c = 2.04 in
α
[ ]
D
1.98 (2H, m), 1.99–2.13 (1H, m), 2.18–2.34 (1H, m), 2.39–2.67 (2H,
m), 3.05 (1H, s (br), 3.71–4.24 (4H, m) ppm. 13C{1H} NMR (76 MHz):
3
3
1
δ
= 18.2 (d, JC,P = 16.0 Hz), 23.9 (d, JC,P = 7.3 Hz), 39.9 (d, JC,P =
1
1
51.5 Hz), 41.4 (d, JC,P = 44.8 Hz), 44.0 (d, JC,P = 47.6 Hz), 47.2 (d,
2JC,P = 1.5 Hz), 51.6 (d, 2JC,P = 19.5 Hz), 57.9 (d, JC,P = 1.9 Hz), 66.1 (s),
86.2 (s) ppm. 31P{1H} NMR (162 MHz):
δ = 44.9 ppm. IR (KBr): ν̃ =
3484 (s), 2965 (m, νC–H), 2897 (m, νC–H), 2226. (w), 1631 (m),
1501 (w), 1459 (m), 1421 (m), 1385 (m), 1327 (m), 1298 (w), 1263
(m), 1204 (w), 1140 (m), 1082 (s), 1051 (m), 1043 (m), 1030 (m),
1006 (s), 959 (m), 935 (w), 889 (m), 862 (m), 788 (m), 776 (m), 751
(m), 679 (s), 654 (m), 585 (m), 557 (m), 504 (w), 444 (m), 417 (w),
407 (w) cm−1. MS (ESI, DCM/MeOH): m/z: calculated for C10H17O2PS
[M+Na]+: 255.1; found: 255.0. C10H17O2PS (232.28): calculated: C
51.7%, H 7.38%; found: C 51.5%, H 7.40%.
(S)-13c: Rf (DCM/methanol = 40:1, v/v) = 0.14 – iodine. m.p.: 167–
1
169 °C.
25 = 113° (c = 1.86 in CHCl3). H NMR (300 MHz):
δ
= 0.85
[α ]
D
(3H, s), 1,21 (3H, s), 2,26 (1H, ddd, 2JH,H = 13.4 Hz, 2JH,P = 9.9 Hz, 4JH,H
= 2.2 Hz), 2.37 (1H, dd, 2JH,H = 13.4 Hz, 2JH,P = 6.5 Hz), 2.52–2.67 (2H,
2
4
Synthesis of 12c. A solution of endo-12c (0.24 g, 0.62 mmol) in 5 ml
diethyl ether was added to a suspension of LiAlH4 (0.049 g,
1.3 mmol) in 10 ml of diethyl ether at 0 °C. The cooling bath was
removed and the solution was left to stir for 60 h. The reaction was
quenched by adding 0.13 ml water and stirred for 30 min. The
mixture was filtered, the solid was treated with 6 ml THF at 65 °C
for 30 min and the solution was filtered again. The solvent was
removed from the combined filtrates. The residue was taken up in
10 ml toluene, sulfur (0.050 g, 1.6 mmol) and three drops of
triethylamine were added and the solution was stirred at 110 °C for
m), 2.67–2.84 (1H, m), 3.55 (1H, dd, JH,P = 13.9 Hz, JH,H = 2.2 Hz),
3.99–4.19 (3H, m), 4.21–4.37 (1H, m), 7.17–7.42 (5H, m) ppm.
3
3
13C{1H} NMR (76 MHz):
δ = 18.8 (d, JC,P = 15.1 Hz), 20.9 (d, JC,P =
2.6 Hz), 40.7 (d, 1JC,P = 47.7 Hz), 45.1 (d, 1JC,P = 49.7 Hz), 46.9 (d, 2JC,P
2
1
= 2.3 Hz), 51.5 (d, JC,P = 17.6 Hz), 55.1 (d, JC,P = 42.1 Hz), 58.6 (s),
66.3 (s), 92.6 (d, 2JC,P = 7.1 Hz), 127.5 (s (br)), 128.6 (s (br)), 134.2 (d,
2JC,P = 2.9 Hz) ppm. 31P{1H} NMR (162 MHz):
δ = 50.5 ppm. IR (KBr): ν̃
= 3432 (s), 3092 (w, νC–H), 3027 (w, νC–H), 2998 (m, νC–H), 2986
(s, νC–H), 2967 (s, νC–H), 2932 (m, νC–H), 2891 (s, νC–H), 2822 (m,
νC–H), 2758 (w, νC–H), 1950 (w), 1800 (w), 1602 (w), 1498 (m),
10 | Dalton Trans., 2015, 00, 1-3
This journal is © The Royal Society of Chemistry 2015
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DOI: 10.1039/C5DT02564H
ARTICLE
1469 (m), 1444 (s), 1422 (m), 1387 (m), 1380 (m), 1366 (w), 1341 670 (s), 638 (s), 615 (w), 562 (w), 530 (s), 503 (m), 471 (w), 458 (w),
(s), 1287 (w), 1259 (m), 1234 (m), 1194 (w), 1174 (w), 1144 (m), 439 (w), 421 (w), 405 (w) cm−1. MS (ESI, DCM/MeOH): m/z:
1127 (s), 1114 (s), 1087 (s), 1061 (m), 1045 (s), 1034 (m), 1009 (s), calculated for C22H26O2P2S2 [M+Na]+: 471.1; found: 471.2.
990 (s), 953 (s), 920 (w), 877 (s), 864 (m), 841 (s), 811 (w), 789 (m), C22H26O2P2S2 (448.52): calculated: C 58.9%, H 5.84%; found: C
775 (s), 765 (s), 707 (s), 679 (m), 662 (w), 627 (m), 615 (m), 583 (m), 58.8%, H 5.86%.
566 (m), 499 (m), 459 (m), 426 (w) cm−1. MS (ESI, DCM/MeOH):
m/z: calculated for C16H21O2PS [M+Na]+: 331.1; found: 333.1.
Synthesis of 14b. Chlorodimesitylphosphane (0.81 g, 2.61 mmol)
was added to a solution of 13a (0.41 g, 1.8 mmol) and triethyl
C16H21O2PS (308.38): calculated: C 62.3%, H 6.86%; found: C 62.2%,
amine (0.74 ml, 5.3 mmol) in 20 ml DCM at 0 °C. After 15 min the
H 6.64%.
cooling bath was removed and the solution was stirred for another
(R)-13c: Rf (DCM/methanol = 40:1, v/v) = 0.16 – iodine. m.p.: 188– 30 min at room temperature. Subsequently, sulfur was added and
190 °C. Due to the small amount of pure (R)-13b, only NMR and MS the solution stirred for 16 h after which the reaction was quenched
with 100 μl of isopropanol. Chromatographic workup
data were obtained. 1H NMR (300 MHz):
δ = 1.34 (3H, s), 1.42 (3H,
4
2
2
(hexanes/diethyl ether = 2:1 to 1:1, v/v) gave 14b as a white solid.
d, JH,P = 1.8 Hz), 1.94 (1H, dd, JH,P = 6.9 Hz, JH,H = 13.0 Hz), 2.14
2
2
Crystals suitable for X-ray diffraction measurements were obtained
(1H, dd, JH,P = 8.2 Hz, JH,H = 13.0 Hz), 2.14 (1H, s (br)), 2.57–2.68
2
from DCM/hexanes at 4 °C. Yield: 0.28 g, 30%. Rf (hexanes/diethyl
(1H, m), 2.71–2.86 (1H, m), 3.17 (1H, d, JH,P = 19.8 Hz), 3.79–3.95
25
D
ether = 1:3, v/v) = 0.41 – UV light, iodine. m.p.: 88–90 °C.
=
(1H, m), 3.99–4.13 (3H, m), 7.27–7.38 (3H, m), 7.63–7.74 (2H, m)
[ ]
α
ppm. 13C{1H} NMR (76 MHz):
δ
= 19.2 (d, 3JC,P = 14.5 Hz), 24.2 (d, 3JC,P
−18.6° (c = 1.67 in chloroform). 1H NMR (300 MHz):
δ = 1.18 (3H, s),
1.23 (3H, s), 1.81–1.96 (2H, m), 1.97–2.25 (2H, m), 2.25 (6H, s),
= 8.8 Hz), 39.5 (d, 1JC,P = 54.3 Hz), 46.3 (d, JC,P = 43.0 Hz), 47.5 (d,
2JC,P = 2.1 Hz), 51.8 (d, 2JC,P = 17.9 Hz), 56.0 (d, 1JC,P = 42.0 MHz), 58.3
1
4
2.18–2.44 (1H, m), 2.37 (12H, d, JH,P = 9.0 Hz), 2.72–2.95 (1H, m),
2
2
5
2
3
2
(d, JC,P = 3.4 Hz), 65.8 (s), 86.7 (d, JC,P = 3.2 Hz), 127.3 (d, JC,P
=
3.82 (1H, dd, JH,H = 10.2 Hz, JH,H = 5.8 Hz), 4.13 (1H, d, JH,H
3
2
2.2 Hz), 128.2 (s), 130.3 (d, JC,P = 6.7 Hz), 132.2 (d, JC,P = 4.5 Hz)
= 10.2 Hz) 4.13–4.26 (1H, m), 4.38–4.50 (1H, m), 6.82 (4H, s) ppm.
ppm. 31P{1H} NMR (162 MHz):
δ = 51.0 ppm. MS (ESI, DCM/MeOH):
3
13C{1H} NMR (76 MHz):
δ
= 18.3 (d, JC,P = 16.1 Hz), 20.9 (s), 23.2–
m/z: calculated for C16H21O2PS (308.38): [M+Na]+: 331.1; found:
3
1
23.4 (m), 23.8 (d, JC,P = 7.1 Hz), 39.7–41.7 (m), 43.5 (dd, JC,P
45.5 Hz, 3JC,P = 8.2 Hz), 47.3 (s), 51.3 (d, 2JC,P = 18.8 Hz), 58.8 (dd, 2JC,P
=
333.1.
2
= 11.2 Hz, JC,P = 4.8 Hz), 66.0 (s), 86.3 (s), 129.1–130.9 (m), 131.1–
Synthesis of 14a. Chlorodiphenylphosphane (0.067 g, 0.30 mmol)
132.3 (m), 140.2–141.4 (m) ppm. 31P{1H} NMR (162 MHz):
δ = 43.5
was added to
a solution of 13a (0.048 g, 0.21 mmol) and
(s), 83.0 (s) ppm. IR (KBr): ν = 3431 (s), 2965 (s, νC–H), 2930 (s, νC–
̃
triethylamine (0.10 ml, 0.72 mmol) in 6 ml DCM at 0 °C. After 15
min the cooling bath was removed and the solution was stirred for
another 30 min at room temperature. Subsequently, sulfur (0.022 g,
0.67 mmol) was added and the solution stirred for 16 h. Then the
reaction was quenched with 20 μl of isopropanol. Chromatographic
workup (hexanes/diethyl ether = 1:1 to 1:3, v/v) gave 14a as a white
solid. Crystals suitable for X-ray diffraction measurements were
obtained from DCM/hexanes at 4 °C. Yield: 0.086 g, 93%. Rf
(hexanes/diethyl ether = 1:3, v/v) = 0.32 – UV light, iodine. m.p.:
H), 2346. (w), 2138 (w), 1605 (w), 1507 (w), 1451 (m), 1383 (m),
1262 (m), 1080 (s), 1021 (s), 888 (w), 851 (w), 802 (m), 726 (m), 687
(s), 641 (m), 556 (m), 465 (m), 439 (m), 431 (m), 422 (w), 416 (w)
cm−1. MS (ESI, DCM/MeOH): m/z: calculated for C28H38O2P2S2
[M+Na]+: 555.2; found: 555.3. C28H38O2P2S2 (532.68): calculated: C
63.1%, H 7.19%; found: C 63.6%, H 7.45%.
Synthesis of 15. Compound 13a (2.65 g, 11.4 mmol), dissolved in
40 ml DCM, was added to a solution of Br2PPh3 (7.37 g, 17.5 mmol)
in 40 ml of DCM at 0 °C. The solution was allowed to warm up to
184–186 °C.
25 = −9.63° (c = 1.77 in chloroform). 1H NMR (400
[α ]
D
MHz):
δ = 1.19 (3H, s), 1.24 (3H, s), 1.82–1.98 (2H, m), 2.00–2.12 room temperature overnight. The reaction was quenched by
(1H, m), 2.18–2.32 (1H, m), 2.45–2.58 (1H, m), 2.77–2.93 (1H, m), addition of 35 ml water and the phases were separated. The
2
3
2
3.93 (1H, dd, JH,H = 10.2 Hz, JH,H = 5.8 Hz), 4.19 (1H, d, JH,H aqueous layer was extracted two times with 20 ml DCM, the
= 10.2 Hz), 4.27–4.40 (1H, m), 4.40–4.50 (1H, m), 7.38–7.58 (6H, m), combined organic layers were washed with brine and dried over
3
7.81–7.99 (4H, m) ppm. 13C{1H} NMR (101 MHz):
δ
= 18.2 (d, JC,P
=
MgSO4. After chromatographic workup (hexanes/diethyl ether = 1:1
15.7 Hz), 23.9 (d, 3JC,P = 7.3 Hz), 40.3 (d, 1JC,P = 52.2 Hz), 41.6 (d, JC,P
1
to 1:2, v/v) 15 was obtained as a white solid. Yield: 3.27 g, 97%. Rf
1
3
2
(hexanes/diethyl ether = 1:2, v/v) = 0.44 – iodine. m.p.: 159–160 °C.
= 44.8 Hz), 43.1 (dd, JC,P = 46.5 Hz, JC,P = 9.1 Hz), 47.3 (d, JC,P
=
2.0 Hz), 51.5 (d, 2JC,P = 18.7 Hz), 60.3 (dd, 2JC,P = 5.3 Hz, 2JC,P = 5.3 Hz),
25 = +50.0° (c = 2.50 in toluene). 1H NMR (300 MHz):
δ = 1.24 (3H,
[α]
D
2
2
6
66.2 (s), 86.3 (d, JC,P = 1.4 Hz), 128.6 (dd, JC,P = 13.5 Hz, JC,P
=
=
s), 1.27 (3H, s), 1.83–2.26 (4H, m), 2.44–2.62 (1H, m), 2.66–2.91 (1H,
m), 3.26–3.56 (1H, m), 3.89–4.15 (3H, m) ppm. 13C{1H} NMR
3
7
4
2.5 Hz), 131.3 (dd, JC,P = 11.6 Hz, JC,P 5.7 Hz), 132.1 (d, JC,P
2.4 Hz), 133.6 (dd, JC,P = 109.8 Hz, JC,P = 6.2 Hz) ppm. 31P{1H} NMR
1
5
(76 MHz):
2JC,P = 6.0 Hz), 39.3–41.7 (m), 45.4 (d, JC,P = 41.5 Hz), 47.1 (d, JC,P
2.4 Hz), 51.2 (d, 2JC,P = 18.5 Hz), 65.7 (s), 86.4 (d, 2JC,P = 1.3 Hz) ppm.
31P{1H} NMR (162 MHz):
= 46.7 ppm. IR (KBr): ν = 3430 (s), 2987
δ
= 18.3 (d, 3JC,P = 16.2 Hz), 23.8 (d, 3JC,P = 7.4 Hz), 27.7 (d,
1
2
(162 MHz): = 44.2 (s), 83.0 (s) ppm. IR (KBr): ν = 3429 (s), 3056
δ
̃
=
(m), 2974 (m, νC–H), 2887 (m, νC–H), 2346. (w), 1631 (w), 1493 (w),
1479 (m), 1437 (s), 1405 (m), 1382 (m), 1314 (w), 1263 (w), 1199
(w), 1114 (s), 1080 (s), 1014 (s), 993 (s), 961 (m), 929 (w), 888 (m),
848 (m), 814 (m), 801 (m), 780 (m), 756 (m), 728 (s), 719 (s), 695 (s),
δ
̃
(m, νC–H), 2962 (m, νC–H), 2887 (m, νC–H), 2194. (w), 1631 (m),
1498 (w), 1436 (w), 1401 (m), 1386 (w), 1375 (w), 1314 (w), 1262
This journal is © The Royal Society of Chemistry 2015
Dalton Trans., 2015, 00, 1-3 | 11
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ARTICLE
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(m), 1239 (m), 1205 (w), 1185 (w), 1162 (m), 1134 (s), 1051 (s), Synthesis of 18. A 1.64 M solution of n-butyl lithium in n-hexane
1017 (m), 932 (w), 912 (w), 887 (w), 873 (m), 784 (s), 740 (m), 670 (0.990 ml, 1.62 mmol) was added to a solution of HP(BH3)Ph2
(s), 624 (m), 578 (m), 538 (w), 524 (w), 496 (w), 475 (w), 460 (w), (0.382 g, 1.92 mmol) in 8 ml of diethyl ether at 0 °C. After 5 min at
445 (w), 414 (w) cm−1. MS (ESI, MeOH): m/z: calculated for this temperature, the solution was added to a suspension of 15
C10H16BrOPS [M+Na]+: 317.0 (79Br), 319.0 (81Br); found: 317.0 (79Br), (0.435 g, 1.47 mmol) in 5 ml diethyl ether at 0 °C. The mixture was
319.0 (81Br). C10H16BrOPS (295.18): calculated: C 40.7%, H 5.46%; stirred for 18 h. Chromatographic workup of the crude product
found: C 41.0%, H 5.54%.
(hexanes/diethyl ether = 1:1, v/v) yielded 18 as a white solid. Yield:
0.520 g, 85%. Rf (hexanes/diethyl ether = 1:1, v/v) = 0.43 – iodine.
1
Characterisation of the side product 16. Product 16 was obtained
as a side product in small amounts during test reactions for the
nucleophilic substitution of 15. Hence, only NMR and MS data were
obtained. Rf (hexanes/diethyl ether = 2:1, v/v) = 0.44 – iodine. 1H
m.p.: 216–220 °C.
25 = −11.3° (c = 1.16 in toluene). H NMR (400
[ ]
α
D
MHz):
δ = 1.19 (3H, s), 1.23 (3H, s), 0.30–1.50 (3H, m, B–H), 1.79–
2.01 (3H, m), 2.06–2.42 (3H, m), 2.56–2.68 (1H, m), 3.11–3.26 (1H,
2
3
2
m), 3.94 (1H, dd, JH,H = 10.8 Hz, JH,H = 5.4 Hz), 4.10 (1H, d, JH,H
=
NMR (300 MHz): δ = 1.22 (3H, s), 1.32 (3H,s), 1.94–2.21 (4H, m),
10.8 Hz), 7.37–7.58 (6H, m), 7.60–7.72 (2H, m), 7.86–7.98 (2H, m)
2
2
2.82–2.95 (1H, m), 3.80 (1H, d, JH,H = 8.5 Hz), 4.20 (1H, dd, JH,H
3
ppm. 13C{1H} NMR (76 MHz):
δ = 18.6 (d, JC,P = 18.9 Hz), 19.0 (d,
= 8.5 Hz, 3JH,H = 5.7 Hz), 5.81 (1H, d, JH,P = 42.0 Hz), 6.03 (1H, d, 3JH,P
= 22.0 Hz) ppm. 13C{1H} NMR (76 MHz):
3
2JC,P = 35.3 Hz), 23.9 (d, JC,P= 7.5 Hz), 37.2 (d, JC,P = 46.9 Hz), 38.8
3
1
3
δ
= 17.9 (d, JC,P = 14.1 Hz),
(d, JC,P = 51.0 Hz), 41.0 (d,1JC,P = 44.2 Hz), 47.8 (d, JC,P = 2.4 Hz),
1
2
3
1
1
24.0 (d, JC,P = 7.6 Hz), 40.5 (d, JC,P = 52.9 Hz), 43.4 (d, JC,P
=
51.5 (d, 2JC,P = 19.9 Hz), 67.0 (s), 86.2 (d, 2JC,P = 2.0 Hz), 126.5 (d, 1JC,P
2
2
48.3 Hz), 50.5 (d, JC,P = 14.6 Hz), 52.7 (d, JC,P = 15.6 Hz), 73.0 (s),
1
= 55.5 Hz), 128.6–129.7 (m), 130.3 (d, JC,P = 55.6 Hz), 131.3–132.3
(m), 133.0 (d, J = 9.2 Hz) ppm. 31P{1H} NMR (162 MHz):
2
1
86.6 (s), 124.0 (d, JC,P = 8.2 Hz), 148.5 (d, JC,P = 68.1 Hz) ppm.
δ
= 15.1–
31P{1H} NMR (162 MHz):
δ = 37.8 ppm. MS (ESI, DCM/MeOH): m/z:
3
16.8 (m (br)), 51.8 (d, JP,P = 47.3 Hz) ppm. IR (KBr): ν
̃ = 3438 (m),
calculated for C10H15OPS [M+Na]+: 237.1; found: 237.0.
3061 (w), 2989 (w, νC–H), 2969 (m, νC–H), 2932 (m, νC–H), 2888
(w, νC–H), 2383 (s, νB–H), 1637 (w), 1437 (m), 1421 (w), 1411 (w),
1400 (w), 1381 (w), 1262 (w), 1198 (w), 1161 (w), 1131 (m), 1107
(m), 1064 (s), 1046 (s), 1013 (w), 984 (w), 866 (w), 783 (m), 769 (m),
751 (m), 737 (s), 719 (w), 705 (s), 695 (m), 667 (m), 655 (s), 595 (w),
501 (w), 467 (w) cm−1. MS (ESI, DCM/MeOH): m/z: calculated for
C22H29BOP2S [M+Na]+: 437.1; found: 437.3. C22H29BOP2S (414.29):
calculated: C 63.78%, H 7.06%; found: C 63.20%, H 7.04%.
Synthesis of 17. A mixture of 3,4-dimethyl-1-phenylphosphole
(0.21 g, 1.1 mmol) and pieces of lithium (excess) in 10 ml THF was
stirred at room temperature for 3–4 hours (conversion was
monitored by TLC, with phosphomolybdic acid). The deep brown
solution was filtered, tert-butyl chloride (0.16 ml, 1.5 mmol) was
added and the solution was stirred at 65 °C for one hour.
Afterwards, a solution of 15 (0.16 g, 0.56 mmol) in 20 ml THF was
added at 0 °C over five minutes and the mixture was stirred for
another 10 min at room temperature. The reaction was quenched
by addition of 50 μl water, stirred for ten minutes, treated with
MgSO4 and filtered. Sulfur (0.054 g, 1.7 mmol) and three drops of
triethylamine were added and the reaction mixture was stirred for
13 h. Chromatographic workup of the crude product (DCM/diethyl
ether = 40:1 to 15:1, v/v) yielded 17 as a white solid. Yield: 0.20 g,
98%. Rf (DCM/diethyl ether = 20:1, v/v) = 0.25 – iodine. m.p.: 208–
Synthesis of 19. LiAlH4 (0.040 g, 1.1 mmol) was added to a solution
of 18 (0.055 g, 0.13 mmol) in 3 ml of THF and the suspension was
stirred for 20 h at 60 °C. The reaction was cooled to 0 °C and
quenched by addition of 0.3 ml of an aqueous KOH solution (20%).
The mixture was diluted with 3 ml of diethyl ether, dried over
MgSO4, filtered and the residue was washed three times with 3 ml
diethyl ether. From the combined organic layers the solvent was
removed in vacuum and the residue was dissolved in 2 ml THF. A
1 M solution of borane in THF (0.65 ml, 0.65 mmol) was added and
the solution was stirred for 18 h. Chromatographic workup of the
crude product (hexanes/diethyl ether = 3:2 v/v) yielded 19 as a
210 °C.
25 = +16.9° (c = 1.42 in toluene). 1H NMR (300 MHz):
δ =
[α]
D
1.20–1.28 (6H, m), 1.79–2.31 (5H, m), 2.08 (6H, s), 2.62–2.75 (3H,
2
2
m), 3.87–4.12 (2H, m), 5.95 (1H, d, JH,P = 31.0 Hz), 6.09 (1H, d, JH,P
= 30.6 Hz) ppm. 13C{1H} NMR (76 MHz):
= 17.2–17.7 (m), 18.5 (dd,
3JC,P = 12.3 Hz, JC,P = 3.4 Hz), 23.7 (d, JC,P = 5.5 Hz), 23.9–25.7 (m),
δ
3
white solid. Yield: 0.041 g, 78%. Rf (hexanes/diethyl ether = 3:2, v/v)
6
25
D
= 0.46 – iodine. m.p.: 159–164 °C.
= −16.9° (c = 0.92 in
[ ]
α
2
5
37.0–39.3 (m), 38.1–42.1 (m), 47.2 (s), 51.5 (dd, JC,P = 15.2 Hz, JC,P
toluene). 1H NMR (300 MHz):
(6H, m, B-H), 1.55–1.79 (3H, m), 1.83–1.97 (1H, m), 2.10–2.42 (2H,
δ =1.19 (3H, s), 1.24 (3H, s), 0.00–2.10
= 4.1 Hz), 66.5 (s), 86.3 (s), 122.7–125.6 (m), 153.4–154.1 (m) ppm.
31P{1H} NMR (162 MHz):
δ = 50.5–51.6 (m) ppm. IR (KBr): ν̃ = 3452
2
m), 2.48–2.62 (1H, m), 2.80–3.00 (1H, m), 3.89 (1H, dd, JH,H
=
(s), 2965 (s, νC–H), 2873 (m, νC–H), 2345 (w), 2086 (w), 1631 (s),
1539 (w), 1450 (m), 1402 (w), 1386 (w), 1262 (m), 1137 (m), 1085
(s), 1048 (s), 865 (w), 801 (s), 741 (m), 674 (m), 643 (m), 587 (w),
502 (w), 482 (w), 473 (w), 456 (w), 444 (w), 430 (w), 417 (w), 405
(w) cm−1. MS (ESI, DCM/MeOH): m/z: calculated for C16H24OP2S2
[M+Na]+: 381.1; found: 381.1. C16H24OP2S2 (326.37): calculated: C
53.6%, H 6.75%; found: C 53.5%, H 6.67%.
3
2
10.8 Hz, JH,H = 5.0 Hz), 4.01 (1H, d, JH,H = 10.8 Hz), 7.37–7.68 (8H,
m), 7.81–7.91 (2H, m) ppm. 13C{1H} NMR (76 MHz): = 18.6 (d, 3JC,P
δ
1
3
= 10.0 Hz), 20.3 (d, JC,P = 35.4 Hz), 24.3 (d, JC,P = 4.3 Hz), 32.7 (d,
1JC,P = 28.8 Hz), 34.1 (d, 1JC,P = 33.2 Hz), 35.4 (d, 1JC,P = 27.2 Hz), 47.9
2
2
2
(d, JC,P = 3.6 Hz), 56.9 (d, JC,P = 4.5 Hz), 66.1 (s, 7), 86.6 (d, JC,P
=
=
1
1
4.2 Hz), 126.5 (d, JC,P = 56.6 Hz), 129.0–129.5 (m), 130.2 (d, JC,P
55.5 Hz), 131.7 (d, J = 9.4 Hz), 133.0 (d, J = 9.3 Hz) ppm. 31P{1H} NMR
(162 MHz):
δ
= 15.7–17.8 (m (br)), 28.8–30.0 (m (br)) ppm. IR (KBr):
This journal is © The Royal Society of Chemistry 2015
12 | Dalton Trans., 2015, 00, 1-3
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= 3422 (m), 3060 (w), 2967 (m, νC–H), 2384 (s, νB–H), 1637 (w),
View Article Online
DOI: 10.1039/C5DT02564H
ARTICLE
Silicon Relat. Elem. 2002, 177, 1827; f) M. Yoshifuji, J.
Organomet. Chem. 2000, 611, 210; g) A. Marinetti, S. Bauer,
ν̃
1489 (w), 1437 (m), 1419 (w), 1263 (m), 1136 (m), 1106 (m), 1062
(s), 1046 (s), 984 (w), 928 (w), 868 (w), 794 (m), 751 (m), 737 (m),
704 (m), 660 (w), 635 (w), 593 (w), 499 (w), 469 (w), 456 (w), 430
(w), 419 (w), 410 (w) cm-1. MS (ESI, DCM/MeCN): m/z: calculated
for C22H32B2OP2 [M+Na]+: 419.2; found: 419.4. C22H32B2OP2 (396.06):
calculated: C 66.72%, H 8.14%; found: C 66.13%, H 8.18%.
L. Ricard, F. Mathey, Organometallics 1990,
Mathey, Acc. Chem. Res. 1992, 25, 90; i) F. Mathey, A.
Marinetti, S. Bauer, P. Le Floch, Pure Appl. Chem. 1991, 63
9, 793; h) F.
,
855; j) F. Mathey, Angew. Chem. 2003, 115, 1616; k) M.
Regitz, O. J. Scherer, R. Appel, Multiple bonds and low
coordination in phosphorus chemistry, G. Thieme Verlag,
1990; l) K. B. Dillon, F. Mathey, J. F. Nixon, Phosphorus: the
carbon copy Wiley, 1998.
In situ deboranation of 19. A solution of 19 (0.010 g, 0.025 mmol)
and morpholine (20 μl, 0.23 mmol) in 0.7 ml of CDCl3 was heated at
60 °C. The reaction was monitored by 31P{1H} NMR spectroscopy. A
5
a) R. de Vaumas, A. Marinetti, L. Ricard, F. Mathey, J. Am.
Chem. Soc. 1992, 114, 261; b) X. Sava, A. Marinetti, L. Ricard,
F. Mathey, Eur. J. Inorg. Chem. 2002, 1657.
T. Möller, M. B. Sárosi, E. Hey-Hawkins, Chem. – Eur. J. 2012,
18, 16604.
a) F. Mathey, Acc. Chem. Res. 2004, 37, 954; b) C. Charrier, H.
Bonnard, G. de Lauzon, F. Mathey, J. Am. Chem. Soc. 1983,
105, 6871; c) F. Mercier, F. Mathey, J. Organomet. Chem.
1984, 263, 55; d) G. de Lauzon, C. Charrier, H. Bonnard, F.
Mathey, Tetrahedron Lett. 1982, 23, 511; e) P. le Goff, F.
Mathey, L. Ricard, J. Org. Chem. 1989, 54, 4754; f) F. Mathey,
F. Mercier, C. Charrier, J. Fischer, A. Mitschler, J. Am. Chem.
Soc. 1981, 103, 4595; g) F. Mercier, F. Mathey, J. Organomet.
Chem. 1993, 462, 103; h) G. de Lauzon, C. Charrier, H.
Bonnard, F. Mathey, J. Fischer, A. Mitschler, J. Chem. Soc.,
Chem. Commun. 1982, 1272.
6
7
full conversion to 20 was observed after
6
h. 31P{1H} NMR
3
3
(162 MHz) ):
ppm.
δ
= −36.9 (d, JP,P = 45.6 Hz), −18.3 (d, JP,P = 45.6 Hz)
Theoretical methods:
All calculations were carried out with the GAUSSIAN 09 program
package,25 at the M06-2X/MG3S level of theory.25 The polarisable
continuum model (PCM) using the integral equation formalism
variant, as implemented in GAUSSIAN 09, has been used to account
for solvent effects.
8
9
D. A. Evans, K. T. Chapman, J. Bisaha, J. Am. Chem. Soc. 1988,
110, 1238.
M. L. Sierra, N. Maigrot, C. Charrier, L. Ricard, F. Mathey,
Organometallics 1991, 10, 2835.
Acknowledgements
10 a) B. L. Feringa, J. C. de Jong, J. Org. Chem. 1988, 53, 1125; b)
J. F. G. A. Jansen, B. L. Feringa, Tetrahedron: Asymmetry
1990, 1, 719.
11 F. Mathey, F. Mercier, M. Spagnol, F. Robin, V. Mouries,
Rhodia Chimie, 1998.
12 a) S. N. Steinmann, P. Vogel, Y. Mo, C. Corminboeuf, Chem.
Commun. 2011, 47, 227; b) M. C. Holthausen, W. Koch, J.
Phys. Chem. 1993, 97, 10021.
This work was supported by the Saxon State Ministry of Science and
the Arts (doctoral fellowship for T.M. (Landesgraduierten-
stipendium)). Support from the Graduate School “Building with
Molecules and Nano-objects (BuildMoNa)“ and the EU-COST Action
CM0802 PhoSciNet is gratefully acknowledged.
13 a) B. R. Pool, J. M. White, Org. Lett. 2000, 2, 3505; b) D.
Birney, T. K. Lim, J. H. P. Koh, B. R. Pool, J. M. White, J. Am.
Chem. Soc. 2002, 124, 5091.
We thank Dr. P. Lönnecke (X-ray crystallography) and Dr. M.
Findeisen (NMR spectroscopy) for their support.
14 a) L. Nyulászi, P. von Ragué Schleyer, J. Am. Chem. Soc. 1999,
121, 6872; b) S. N. Steinmann, D. F. Jana, J. I. C. Wu, P. von
Ragué Schleyer, Y. Mo, C. Corminboeuf, Angew. Chem. Int.
Ed. 2009, 48, 9828.
Keywords: Asymmetric Reaction • Phospha-Diels–Alder •
Diastereotopic Face Differentiation • Chiral Phosphanes
15 T. Möller, P. Wonneberger, N. Kretzschmar, E. Hey-Hawkins,
Chem. Commun. 2014, 50, 5826.
16 R. K. Harris, E. D. Becker, S. M. Cabral De Menezes, R.
Notes and references
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17 A. Breque, F. Mathey, P. Savignac, Synthesis 1981, 983.
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1
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19 D. A. Evans, K. T. Chapman, J. Bisaha, J. Am. Chem. Soc. 1988,
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2
3
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a) M. Christmann (Hrsg.), S. Bräse (Hrsg.), Asymmetric
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25 a) M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M.
A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B.
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Dalton Transactions
View Article Online
DOI: 10.1039/C5DT02564H
P-chiral 1-phosphanorbornenes: From asymmetric Phospha-Diels–Alder reactions
towards ligand design and functionalisation
Tobias Möller, Peter Wonneberger, Menyhárt B. Sárosi, Peter Coburger, Evamarie Hey-Hawkins*
A building set for chiral phosphorus. The principle of stereotopic face differentiation is successfully applied to a P=C bond. The
synthetic approach features a very efficient and highly stereoselective Diels–Alder reaction. The observed reaction pathway could be
supported by theoretical calculations. Furthermore, a divergent-oriented ligand synthesis is feasible by reduction of the chiral
auxiliary, subsequent stereospecific intramolecular Michael addition, and various functionalisations of the obtained key compound.