Novel α-pinene-derived mono- and bisphosphinite ligands: Synthesis and application in catalytic hydrogenation

Article abstract of DOI:10.1016/j.ica.2011.01.020

Novel mono- and bisphosphinite (-)-pinane-based ligands have been synthesized from (-)-α-pinene. Mixed with [(COD)₂Rh] ⁺[BF₄]^-, these ligands displayed moderate up to high catalytic activity in hydrogenation of dimethyl itaconate with dihydrogen. It has been observed that the structure of the ligand, the reaction temperature and solvent are important to define productivity of the phosphinite-based Rh-catalysts. Bisphosphinite ligands in hydrogenation reactions suffered from an Arbuzov rearrangement, leading to fast deactivation of the hydrogenation catalyst. In contrast, monophosphinite-derived Rh-catalysts showed increased productivity as well as thermal stability. An almost quantitative conversion of dimethyl itaconate has been achieved at elevated temperatures in toluene. Alternatively, hydrogenation of dimethyl itaconate with monophosphinite ligands has been carried out in MeOH at room temperature or 40 °C and has led to a nearly quantitative conversion.

Full text of DOI:10.1016/j.ica.2011.01.020

Inorganica Chimica Acta 374 (2011) 94–103
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Novel
a
-pinene-derived mono- and bisphosphinite ligands: Synthesis
and application in catalytic hydrogenation
Dennis Hobuß a, Jens Hasenjäger b, Birgit Driessen-Hölscher b, , Angelika Baro a, Kirill V. Axenov a,
Sabine Laschat a, , Wolfgang Frey a
⇑
a Institut für Organische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany
b Department Chemie – Technische Chemie, Universität Paderborn, Warburgerstraße 100, D-33098 Paderborn, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 20 January 2011
Novel mono- and bisphosphinite (ꢀ)-pinane-based ligands have been synthesized from (ꢀ)-
a-pinene.
Mixed with [(COD)2Rh]+[BF4]ꢀ, these ligands displayed moderate up to high catalytic activity in hydroge-
nation of dimethyl itaconate with dihydrogen. It has been observed that the structure of the ligand, the
reaction temperature and solvent are important to define productivity of the phosphinite-based Rh-
catalysts. Bisphosphinite ligands in hydrogenation reactions suffered from an Arbuzov rearrangement,
leading to fast deactivation of the hydrogenation catalyst. In contrast, monophosphinite-derived Rh-
catalysts showed increased productivity as well as thermal stability. An almost quantitative conversion
of dimethyl itaconate has been achieved at elevated temperatures in toluene. Alternatively, hydrogena-
tion of dimethyl itaconate with monophosphinite ligands has been carried out in MeOH at room
temperature or 40 °C and has led to a nearly quantitative conversion.
Dedicated to Prof. Wolfgang Kaim on the
occasion of his 60th birthday.
Keywords:
Catalytic hydrogenation
Phosphinite ligands
Terpenes
Rhodium
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
phosphine and phosphinite ligands [35–39]. As one of the advanta-
ges, many terpene precursors are commercially available in both
Since a first synthetic application by Wilkinson and co-workers
[1], homogeneous catalytic hydrogenation became nowadays one
of the most important preparative methods in modern organic
chemistry [2]. At the end of 1960s, Schrock and Osborn have devel-
oped new types of Rh-catalysts for hydrogenation, where a
[(COD)Rh]+ core was connected with a mono- or bidentate phos-
phine ligand [3–5]. This structure could easily be modified by coor-
dination with chiral bidentate phosphines. The obtained chiral
catalysts are able to provide catalytic asymmetric hydrogenation
of olefinic double bonds [6–9]. For this purpose, chiral ligands
based on the BINAP core [10–12], bridged diphosphines [13–17],
ferrocene frameworks [18,19], and many others [20–22] have been
successfully employed. In addition to a broad diversity of reported
phosphine-based structures, phosphinite-derived ligands have also
attracted a considerable attention for catalytic hydrogenation [23–
29]. Recently, carbohydrates were reported as chiral building
blocks for phosphinite ligands [30–34]. Besides carbohydrates,
terpenes as well have extensively been used for synthesis of
enantiomeric forms and can be functionalized to a broad extent
[40,41]. Among a variety of terpenes, main efforts have so far been
directed to camphor-based mono- and bidentate phosphorus li-
gands, nowadays widely employed in asymmetric synthesis [42–
55]. In contrast, less attention has until now been spent on the
chemistry of pinane-derived phosphines and phosphinites [56–
63]. We have recently reported on the synthesis of cis-configurated
bisphosphinites 2 based on a dihydroxy-(ꢀ)-pinane framework
(Scheme 1) [64]. Having compounds 2 in hand, we were interested
to study their properties regarding to catalytic asymmetric hydro-
genation [65–72]. As a first step in this direction, we have planned
to expand the series of available (ꢀ)-pinane-derived ligands by a
modification of the dihydroxy-(ꢀ)-pinane core into monophosphi-
nite structures [73] and trans-configurated phosphinite ligands 3–
6 (Scheme 1). Börner [74] and Zhang [75] have shown that the
trans-isomers often display higher enantioselectivity in catalytic
asymmetric hydrogenation than the respective cis-analogs. In the
present work, we have intended to carry out Rh-catalyzed hydro-
genation of dimethyl itaconate as a benchmark substrate, employ-
ing a series of newly designed cis- and trans-phosphinites 2–6, then
to investigate the effect of reaction conditions, the structure of li-
gand, etc. on catalytic hydrogenation activity and to compare the
results with known phosphorus ligands.
⇑
Corresponding author. Tel.: +49 0 711 685 64565; fax: +49 0 711 685 64285.
E-mail address: sabine.laschat@oc.uni-stuttgart.de (S. Laschat).
Deceased 16.11.2004.
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.01.020

D. Hobuß et al. / Inorganica Chimica Acta 374 (2011) 94–103
95
previously published procedure [64] (Scheme 2). In order to access
trans-dihydroxy-(ꢀ)-pinane 11, we initially utilized the nucleo-
philic opening of the commercially available
a-pinene epoxide 8.
However, upon treatment of compound
8
with tris(trinitro-
cer(IV))paraperiodate (TTCPP) in water and acetonitrile under re-
flux, according to a procedure by Iranpoor [76,77], no formation
of the desired trans-diol 11 was observed. Instead, we isolated
the already known trans-sobrerol 9, resulting from a cationic rear-
rangement of the terpene skeleton [78,79]. In an alternative two-
step approach, (ꢀ)-a-pinene 1 was oxidized with KMnO4 in an ace-
tone/water mixture at subambient temperatures, following a pro-
cedure by Carlson and Pierce [80]. This reaction selectively gave
hydroxyketone 10 as a crystalline solid in a 52% yield. Subsequent
reduction of ketone 10 with NaBH4 in MeOH afforded desired
trans-diol 11 with an acceptable yield of 47%. The structure of
the ketone product 10 was investigated by single crystal X-ray
analysis [81]. In the compound 10 the hydroxyl group is oriented
exo to the (ꢀ)-pinane core (O2–C2: 1.433(3) Å, Fig. 1, Table 2).
The distance between C1 and O1 atoms has a length characteristic
for C@O carbonyl bonds (O1–C1: 1.210(4) Å).
Scheme 1.
According to our previously published procedure [64], deproto-
nation of cis-pinandiol 7 with nBuLi, followed by a treatment with
ClPPh2, led to the cis–bis(diphenylphosphinoxy)-(ꢀ)-pinane ligand
2a. In the present work, pinandiols 7 and 11 were deprotonated
with iPr2NEt or NEt3 in THF and treated with corresponding chlo-
rophosphanes under reflux. The subsequent protection of the
formed bisphosphinite ligands with BH3ꢁTHF [82] led to the borane
complexes 2bꢁBH3 (yield: 42%) and 3ꢁBH3 (yield: a, 39%, Ph2P–; b,
20%, iPr2P–), (Scheme 2).
2. Results and discussion
2.1. Bis(phosphinite)-(ꢀ)-pinane ligands
In our synthetic work, as the first goal, we were interested to
develop simple preparative methods, leading directly from cheap
The borane complex 2bꢁBH3 features three 1H NMR singlets of
(ꢀ)-pinane methyl groups at dH 0.94, 1.27, 1.33 (each rel. 3H
int.); multiple signals for CH2 and CH (ꢀ)-pinane protons at dH
1.46, 1.70, 1.94, 2.01, 2.19, 2.49, 4.62 (total rel. 7H int.) and a char-
and commercially available (ꢀ)-
a-pinene 1 to cis- and trans-dihy-
droxy-substituted (ꢀ)-pinanes, suited for subsequent synthesis of
phosphinite ligands 2–6 (Scheme 1). The transformation of (ꢀ)-
a
-pinene 1 into cis-pinandiol 7 was carried out according to our
Scheme 2.

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D. Hobuß et al. / Inorganica Chimica Acta 374 (2011) 94–103
Table 2
Selected structural parameters of compounds 10 and 5bꢁBH3.a
Compounds 10
5bꢁBH3
10
5bꢁBH3
C1–O1
C6–O2
C8-O1
C7–C1
C1–C6
B1–P1
O2–P1
C12–P1
C15–P1
1.433(3) 1.433(6) C10-C3–C11
1.210(4) 1.450(4) C1–C6–C5
107.9(3)
118.3(2)
111.9(2)
109.9(2)
–
–
–
–
107.0(4)
114.4(3)
110.2(4)
109.8(4)
116.5(5)
124.8(2)
116.90(19)
105.16(19)
–
1.442(6) C7–C1–C6
1.512(4) 1.521(6) O1–C1–C7
1.542(4) 1.556(5) C1–O1–C8
–
–
–
–
1.896(5) P1–O2–C6
1.590(2) B1–P1–O2
1.819(4) C12–P1–C15
1.815(4) O1–C1–C6–O2 ꢀ75.6(3) ꢀ25.1(4)
a
Bond lengths in Å, angles in deg, numeration according to 5bꢁBH3.
Table 3
31P NMR shifts of ligands 2–6.a
Ligands
31P NMR, dP [ppm]
Fig. 1. Structure of hydroxyketone 10 in the solid state.
BH3-protected
free
2a
2b
3a
3b
95.1
108.2
64.0
89.6
115.9
53.0
Table 1
51.9
50.9
Catalytic hydrogenation of dimethyl itaconate 12 in the presence of cis- and trans-
109.3
107.3
64.4
52.3
109.2
94.9
106.9
115.3
51.3
49.9
105.8
90.2
bisphosphinites 2 and 3 in MeOH at 40 °C.a
Entry
Ligand
R
Configuration of ligand
Conversion (%)b
1
2
3
4
2a
3a
2b
3b
Ph
Ph
iPr
iPr
cis
trans
cis
78
7
19
6
4a
5a
5b
6a
62.8
106.3
55.7
101.2
trans
a
1 mol% of [Rh(COD)2]+[BF4]ꢀ, 2 mol% of phosphinite ligand, 0.50 mmol of sub-
a
C6D6, external standart: P(OEt)3.
strate, 5 ml of toluene, 15 bar of H2, 40 °C, 2 h.
b
Determined by capillary GC (undecane as an internal standard).
acteristic 1:1:1:1 broad quadruplet for the BH3 moiety
(1JBH = 95 Hz) at dH 0.43. Due to an asymmetry of the (ꢀ)-pinane
core, methyl groups of two chemically different iPr2P– substituents
(
31P NMR: dP 51.9, 64.0) become diastereotopic and feature four 1H
NMR doublets of doublets at dH 1.22, 1.22, 1.25, 1.26 (3JPH = 14.7–
Scheme 3.
3
18.7 Hz, JHH = 7.1 Hz). Respectively, the compound 2bꢁBH3 shows
four 13C NMR resonances for CH3 groups at dC 16.1, 16.2, 16.5,
tuted ligand 2a conversion of the substrate 12 was achieved 78%
(Table 1).
iPr
16.6 (each d, JPC = 10.4 Hz/17.0 Hz) and two 13C NMR doublets
2
for CHiPr carbons at dC 26.2, 26.3 (1JPC = 37 Hz). The complexes
3aꢁBH3, 3bꢁBH3 display analogous to 2bꢁBH3 spectral features,
and the trans-isomer 3bꢁBH3 in its 1H and 13C NMR spectra is also
revealing signals of diastereotopic methyl groups from two chem-
ically nonequivalent iPr2P– substituents (see Section 4 and Supple-
mentary Material).
The cis- and trans-bisphosphinites 2ꢁBH3 and 3ꢁBH3 were tested
in Rh-catalyzed hydrogenation of dimethyl itaconate 12. The bor-
ane–phosphinite complexes were deprotected prior the hydroge-
nation experiments by heating in HNEt2 at 65 °C to give free
phosphinite ligands 2 and 3. Deprotection was monitored by 31P
NMR, which indicated complete removal of the borane groups
and formation of free phosphinites 2 and 3 without any concomi-
tant oxidation (Table 3).
In a typical hydrogenation setup, the substrate 12 was mixed in
MeOH with 1 mol% of [(COD)2Rh]+[BF4]ꢀ and 2 mol% of ligands 2 or
3. The reaction mixture was then stirred for 2 h at 40 °C under
15 bar of H2 (Scheme 3). Phosphinites 3 with trans-orientation of
phosphinoxy substituents showed a poor conversion in hydrogena-
tion of dimethyl itaconate 12. Conversely, cis-isomers 2 were much
more active in the hydrogenation reaction than their trans-analogs
3. As an example, with the cis-bis(diphenylphosphinoxy)-substi-
Dimethyl itaconate 12 is one of the benchmark substrates used
to estimate the activity of the investigated ligand in the catalytic
hydrogenation reaction. With the diphosphino-based Rh-((R,R)-
Et-DuPhos) catalyst the compound 12 was reduced with >98 ee%
[13]. Catalytic hydrogenation of 12 with Josiphos and 1 mol% of
[Rh(NBD)2]+BF4ꢀ (1 bar of H2/MeOH/r.t.) led to a quantitative yield
and 98–99 ee% of the hydrogenated product [18]. Enantioselectivi-
ty of diphosphinite ligands depends on the substitution pattern
around phosphorus atoms. Diphosphinites, based on the cyclic
dianhydro-D-mannitol framework, which carried unsubstituted
aryloxy groups, showed moderate ee values (up to 49.3 ee%) in cat-
alytic hydrogenation of 12 [31]. Much lower selectivity (5.2 ee%)
have been obtained, using very extremely bulky tetra-t-
butyl(biphenyl)-dioxy substituents. Conversely, ligands, having
chiral binaphthyl-dioxy groups around phosphorus atoms or bear-
ing moderately bulky biphenyl-dioxy groups, gave the hydroge-
nated product with a high enantiomeric excess (98–99 ee%) [31].
With chiral bicyclic bis(phosphoramidites), bearing binaphthol
substituents, in hydrogenation of 12 (1.3 bar of H2, 1.3 mol% of li-
gand/[(COD)2Rh]+[BF4]ꢀ, CH2Cl2, r.t., 12 h) high yields of the prod-
uct and high enantioselectivity have been achieved (up to 90 ee%)
[83].

D. Hobuß et al. / Inorganica Chimica Acta 374 (2011) 94–103
97
Scheme 4.
Scheme 5.
Due to a cis-orientation of bulky phosphinoxy substituents in 2,
a considerable degree of steric tension for the cis-isomers could be
proposed, and this should not be the case for trans-phosphinites.
On the other hand, assuming that bisphosphinites 2 and 3 behave
as bidentate ligands for the Rh-catalyst precursor, a newly formed
seven-membered chelate ring in trans-isomers [3ꢁRh(COD)]+
would adopt an energetically unfavorable twisted trans-geometry.
Consequently, cis-phosphinites 2 should form more stable cis-
[2ꢁRh(COD)]+ species than their trans-oriented analogs 3, which
might be an explanation of higher hydrogenation activity of the
cis-phosphinites 2 as compared to the trans-isomers 3 (Table 1).
In order to get more information about the hydrogenation reaction,
the crude mixtures, obtained after hydrogenation with ligand 2a,
have been investigated by 31P NMR. Surprisingly, the absence of
the ligand 2a in these mixtures was observed. The 31P NMR signals
of two chemically different Ph2P– groups at dP 89.6 and 115.9, cor-
responding to the compound 2a (Table 3), completely disappeared
and two new 31P NMR resonances at dP 24.5 and 30.5 were de-
tected. The shift of 31P NMR signals to a high field is a clear indica-
tion that a phosphinoxide species has been formed from the ligand
2a during the hydrogenation process. One possible way from phos-
phinites to phosphinoxides in the absence of oxidants (in a reduc-
tive hydrogen atmosphere) could be the well-known Arbuzov
rearrangement [84,85]. It seems that the coordination of the
[(COD)Rh]+ cation, derived from the [(COD)2Rh]+[BF4]ꢀ catalyst
precursor, causes not only hydrogenation of the C@C double bond
in the substrate 12, but also a catalytic rearrangement of the phos-
phinite groups in a (ꢀ)-pinane ligand into phosphinoxides [86].
Additionally, an increased tendency of (ꢀ)-pinane-derived bis-
phosphinites 2 and 3 to undergo an Arbuzov rearrangement maybe
due to a neighbor group effect of the nearby placed two phosphi-
nite units. For the previously described monophosphinite cam-
phane ligands such problems were not encountered, and the
camphane ligands showed high conversion values in hydrogena-
tion reactions [54,55]. Dialkylphosphito-substituted camphanes
displayed a high conversion in catalytic hydrogenation of methyl
(Z)-(N)-acetamido cynnamates, but rather low enantioselectivity
in a range of 29–34 ee%. The modification of the camphane frame-
work by the introduction of diarylphosphinito groups led to a
quantitative conversion of the cynnamate substrates with achieved
high enantioselectivity up to 89 ee% [55].
2.2. Mono(phosphinite)-(ꢀ)-pinane Ligands
In order to improve productivity of our (ꢀ)-pinane-based
catalytic hydrogenation system, further modifications of the

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D. Hobuß et al. / Inorganica Chimica Acta 374 (2011) 94–103
dihydroxy-(ꢀ)-pinane core to monophosphinite bidentate ligands
have been carried out. From a variety of possible structures, the
2- and 3-methoxy-substituted (ꢀ)-pinane frameworks 4–6
(Scheme 1) have been selected as target compounds for the further
synthesis. For the preparation of 3-methoxy-substituted phosphi-
nites 4,
a-hydroxyketone 10 was treated with trim-
ethylsilylimidazol at 50 °C to give trimethylsilylether 14 in a 78%
yield. Reduction of the carbonyl group in 14 with NaBH4 in EtOH
proceeded exclusively from the Re face, yielding trans-alcohol 15
in 42%. After deprotonation with nBuLi, quenching with MeI in
THF and the final cleavage of the trimethylsilylether group with
TBAF, the trans-3-methoxy-derivative 17 was obtained with a high
overall yield (Scheme 4). The compound 17 was converted into the
monophosphinite ligand 4a via deprotonation with nBuLi, followed
by the reaction with Ph2PCl. The subsequent in situ protection of
the ligand 4a with BH3ꢁTHF adduct under typical conditions
(25 °C, THF, 2 h) afforded the corresponding complex 4aꢁBH3 in a
moderate yield.
2-Methoxy-substituted phosphinites 5 and 6 were obtained
from hydroxyketone 10, employing the similar synthetic approach
as used for the preparation of monophosphinite 4a. The compound
10 was converted into 2-methoxyketone 18 by a treatment with
dimethylsulfate in the presence of Ba(OH)2 and BaO. Subsequent
reduction of 18 with NaBH4 gave a mixture of diastereomeric 2-
methoxyalcohols 19 and 20, separated by flash chromatography
on silica gel and isolated in a 62% and 27% yield, respectively
(Scheme 5). The conversion to borane-protected phosphinites
5ꢁBH3, 6ꢁBH3 proceeded via a typical procedure (see above and
Scheme 5) and provided these products in clean state with high
yields.
Fig. 2. Structure of complex 5bꢁBH3 in the solid state.
angle between C6–O2 and O2–P1 bonds amounts to 124.8(2)°.
The phosphorus center adopts a pseudo-tetrahedral configuration
(B1–P1–O2: 116.90(19)°; C12–P1–C15: 105.16(19)°). The in-
creased values of C6–O2–P1 and B1–P1–O2 angles could be an
indication of a pronounced p –d interaction between the sp2-
p
p
hybridized oxygen atom and the phosphorus center. The B1–P1
distance has a typical length of 1.896(5) Å.
Known monodentate phosphorus ligands display diverse results
in asymmetric catalytic hydrogenation of the benchmark substrate,
dimethyl itaconate 12. Monodentate phosphinites, derived from a
chiral binaphthyl-dioxo core, provided a quantitative conversion
and optical yields in a range of 89.2–97.6 ee% (1.3 bar of H2,
0.1 mol% of ligand/[(COD)2Rh]+[BF4]ꢀ, CH2Cl2, r.t., 20 h). However,
the use of excessively bulky substituents lowers both the conver-
sion (up to 8%) and enantioselectivity (up to 28.6 ee%) [26]. Selec-
tivity as well as productivity of the Rh-catalysts, based on
monodentate phosphoramidite-binaphthyl ligands, is low, when
EtOAc is used as a solvent. However, in hydrogenation of itaconic
acid, a high conversion and optical yields (up to 97 ee%) were ob-
tained regardless of the solvent [87]. Bidentate phosphine–phos-
phinite ligands in a combination with the [(COD)2Rh]+[BF4]ꢀ
precursor show a high activity, but enantioselectivity varies from
52 ee% to 79 ee% [88].
The phosphinite-borane complexes 4ꢁBH3, 5ꢁBH3, 6ꢁBH3 feature
a 1H NMR signal pattern, typical for a methoxy-substituted mono-
phosphinite (ꢀ)-pinane core: dH 0.78–1.31 (pinane Me groups), dH
0.99–2.49 (pinane CH and CH2 protons, rel. int. 6H), dH 4.56–5.04
(3-H). A 1H NMR singlet of methoxy protons has been found in a
range of dH 3.02–3.27 (corresponding 13C NMR resonances at dC
50.9–57.1). The characteristic broad quadruplet of BH3 protons
has been observed in a range of dH 1.01–1.16 (1JBH ꢂ90 Hz). Due
to an asymmetric structure, Ph and iPr substituents at phosphorus
centers in 2- and 3-methoxy-(ꢀ)-pinane phosphinites 4ꢁBH3,
5ꢁBH3, 6ꢁBH3 are chemically nonequivalent to each other (addition-
iPr
ally, CH3 groups appeared to be diastereotopic). Consequently,
the compounds 4aꢁBH3, 5aꢁBH3, 6aꢁBH3 feature two sets of 1H
and 13C NMR resonances, corresponding to two chemically differ-
ent phenyl groups in the –OPPh2 moiety. The complex 5bꢁBH3,
bearing –OPiPr2 substituents, shows two 1H and 13C NMR signals
for chemically different CHiPr groups and four 1H doublets of dou-
Synthesized monodentate phosphinite complexes 4ꢁBH3–6ꢁBH3
were tested in Rh-catalyzed hydrogenation of dimethyl itaconate
12. First, the compounds 4ꢁBH3–6ꢁBH3 were deprotected via heat-
ing at 65 °C in Et2NH, leading to free ligands 4–6. The process
was monitored by 31P NMR and afforded selectively free mono-
phosphinites 4–6 (Table 3).
blets and 13C NMR doublets for diastereotopic CH3 groups (see
iPr
Section 4 and Supplementary Material). The 31P NMR resonances
of the trans-configurated complexes 4aꢁBH3, 6aꢁBH3 are shifted
into a low field, compared with 31P NMR of 5aꢁBH3 having a cis-
orientation of the phosphinite and 2-methoxy substituents (dP
109.2, 4aꢁBH3; 106.5, 6aꢁBH3 versus dP 94.9, 5aꢁBH3).
Typical reaction settings and amounts of reagents have been
used in hydrogenation experiments (see above and Tables 1 and
4). Employed solvent media and reaction temperatures were varied
in order to find optimal hydrogenation conditions. It was found
that these factors, the reaction solvent and temperature, appeared
to be essential to achieve high productivity of the Rh-catalysts, de-
rived from the monophosphite (ꢀ)-pinane ligands 4–6 (Table 4). At
room temperature, when CH2Cl2 or toluene were used as solvents,
only low up to moderate catalytic activity was observed. In MeOH,
conversely, hydrogenation was running at room temperature with
a high conversion of 12 in a range of 40–100%, depending on the
used phosphinite ligand. The catalytic activity in MeOH was signif-
icantly improved by an increase of reaction temperature to 40 °C,
giving almost quantitative conversions of 12 in a range of 83–
100%. A similar positive temperature effect was observed for
hydrogenation carried out in toluene. An increase of the reaction
Single crystals of the compound 5bꢁBH3, suitable for X-ray crys-
tal structure analysis, were obtained from a toluene solution [81].
The 2-methoxy-3-phosphinite complex 5bꢁBH3 features a (ꢀ)-pi-
nane core, substituted in the C1 position with the methoxy group
(C1–O1: 1.433(6) Å) and in the C6 position with the –OPiPr2ꢁBH3
phosphinite moiety (C6–O2: 1.450(4) Å, Table 2). The phosphinoxy
and methoxy groups are oriented cis to each other with an absolute
configuration around the C1 and C6 centers R and S, respectively
(enantiopol parameter ꢀ0.02(4), Fig. 2). The large –OPiPr2ꢁBH3
moiety (O2–P1: 1.590(2) Å) is moved away from the bulky (ꢀ)-pi-
nane framework. Due to steric repulsion, the methyl group from
the 2-methoxy substituent and the –PiPr2 phosphino moiety are
placed into opposite lateral sectors of the (ꢀ)-pinane core. The

D. Hobuß et al. / Inorganica Chimica Acta 374 (2011) 94–103
99
Table 4
Hydrogenation of dimethyl itaconate 12 at various conditions with [(COD)2Rh]+[BF4]ꢀ and ligands 4–6.a
Entry
Ligand
R
Configuration of ligand
Solvent
Temperature (°C)
Conversion (%)b
1
2
3
4
5
6
7
8
4a
4a
4a
4a
4a
5a
5a
5a
5a
5a
5b
5b
5b
5b
6a
6a
6a
6a
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
i-Pr
i-Pr
i-Pr
i-Pr
Ph
Ph
Ph
Ph
trans
trans
trans
trans
trans
cis
cis
cis
cis
cis
cis
cis
cis
cis
trans
trans
trans
trans
CH2Cl2
MeOH
MeOH
toluene
toluene
CH2Cl2
MeOH
MeOH
toluene
toluene
CH2Cl2
MeOH
toluene
toluene
CH2Cl2
MeOH
toluene
toluene
r.t.
r.t.
40
r.t.
40
r.t.
r.t.
40
r.t.
60
r.t.
40
40
60
r.t.
40
r.t.
60
25
100
98
86
94
42
79
99
8
9
10
11
12
13
14
15
16
17
18
67
2
96
62
97
24
83
8
99
a
1 mol% of [Rh(COD)2]+[BF4]ꢀ, 2 mol% of phosphinite ligand, 0.50 mmol of substrate, 5 ml of toluene, 1 atm of H2 and 20 h.
Determined by capillary GC (undecane as an internal standard).
b
temperature from r.t. to 60 °C led to enhanced catalytic activity
and high conversion values (compare, for example, runs 4 and 5,
9 and 10, 17 and 18 in Table 4). Overall, elevated temperature leads
to an almost quantitative conversion. At room temperature in
CH2Cl2, the trans-configurated ligands 4a and 6a, mixed with the
Rh-precursor, displayed much lower degree of conversion in
hydrogenation of 12 than the cis-isomer 5a (compare runs 1 and
15 with 6 in Table 4). Under the same conditions, the Rh-catalyst,
derived from i-Pr substituted cis-phosphinite 5b, was chemically
too labile and almost inactive in the hydrogenation reaction.
With the (ꢀ)-pinane-derived bisphosphinite ligands 2 and 3 a
maximum conversion of 12 achieved 78% at the reaction tempera-
ture of 40 °C in MeOH (see above). Under the same reaction condi-
tions, productivity of the monophosphinite ligands 4–6 was
considerably higher, ranging from 83% up to 99% conversion,
regardless of the configuration of 4–6. The monophosphinite li-
gands 4–6 displayed increased thermal stability, as high hydroge-
nation activity was observed at 60 °C in toluene. It seems that in
the temperature range of 40–60 °C, in toluene or MeOH used as
the reaction solvents, hydrogenation with the ligands 4–6 proceeds
considerably faster than a parallel Arbuzov rearrangement. Conse-
quently, most of the substrate 12 appeared under such conditions
hydrogenated before complete deactivation of the catalyst oc-
curred from a concurrent Arbuzov rearrangement. At room tem-
perature in all solvents, the rate of an Arbuzov rearrangement is
presumably higher than the rate of hydrogenation, leading at these
conditions to a rather low catalytic activity and fast deactivation of
the Rh-based catalytic species. We also followed stereoselectivity
of hydrogenation. At high temperatures, enantioselectivity was
low and we obtained almost racemic mixtures of the isomers 13.
Due to a slowdown of the reaction rate at room temperature, selec-
tivity of hydrogenation has been improved and moderate ee values
up to 33 ee% were obtained.
provide chemically stable catalytic Rh-species upon complexation
with [(COD)2Rh]+[BF4]ꢀ, possibly due to a twisted chelate geome-
try in the formed Rh-species. Monophosphinite ligands give much
more active Rh catalysts compared with their bisphosphinite ana-
logs. Unfortunately, bis- and monophosphinite-derived Rh-cata-
lysts suffer from a concurrent Arbuzov rearrangement, leading to
deactivation of the catalyst. Nonetheless, mixed with
[(COD)2Rh]+[BF4]ꢀ, monophosphinite ligands at 40 °C (or even at
room temperature) are able to hydrogenate dimethyl itaconate
12 with a nearly quantitative conversion. Higher catalytic activity
of monophosphinites versus bulky bisphosphinites might result
from better coordination accessibility of the Rh center in the steri-
cally less hindered monophosphinite-derived catalysts. Presum-
ably, the monophosphinite ligand geometry is the best choice for
the dihydroxy-(ꢀ)-pinane-based Rh hydrogenation catalysts. A
next step in our work will be a modification of phosphinite and
methoxy substituents at the (ꢀ)-pinane core [26,89–92] in order
to keep high catalytic activity and improve enantioselectivity of
the hydrogenation process.
4. Experimental
4.1. General information
All reactions were carried out under a nitrogen atmosphere
with Schlenk-type glassware. Solvents were dried and distilled un-
der nitrogen prior to use. Reaction progress and purity were mon-
itored by GC with a Hewlett Packard HP 6890 equipped with a HP-
5MS column (30 m ꢃ 0.32 mm) or with a Thermo-Finnigan Trace
GC Ultra equipped with a Optima-5MS column (30 m ꢃ 0.25 mm)
using different temperature programs. Hydrogen was used as a
carrier gas. Enantioselectivities were determined by GC on chiral
stationary phases with a Fisons HRGC MEGA 8560 or a Thermo-
Finnigan Trace GC Ultra. The enantiomers are stated as major
and minor with their exact retention times. Flash chromatography
3. Conclusions
was performed on silica gel, grain size 40–63
Nagel).
lm (Macherey–
Cis/trans-bis(phosphinite)-(ꢀ)-pinane ligands can be readily
synthesized from cheap and commercially available
a-pinene.
The following instruments were used for physical characteriza-
tion of the compounds. Elemental analyses: Carlo Erba Strument-
azione Elemental Analyzer, Modell 1106. NMR: Bruker AC 250 F
(1H, 250 MHz; 13C, 63 MHz), Bruker ARX-500 (1H, 500 MHz; 13C,
126 MHz), Bruker ARX-400 (31P, 162 MHz), temperature 296 K.
Assignments of the resonances are supported by 2D experiments
Mixed with [(COD)2Rh]+[BF4]ꢀ, these ligands show moderate up
to high catalytic activity in hydrogenation of dimethyl itaconate
12. In this process, cis-configuration of a bisphosphinite ligand is
prerequisite in order to achieve high conversion of dimethyl itaco-
nate 12. Perhaps, trans-bisphosphinite ligands are not suitable to

100
D. Hobuß et al. / Inorganica Chimica Acta 374 (2011) 94–103
and chemical shift calculations. 1H and 13C NMR spectra were ref-
erenced to an internal Me4Si standart, 31P NMR spectra were refer-
enced to an external P(OEt)3 sample in C6D6 (dP = 138.0). IR: Bruker
22 FT-IR Spectrometer with golden-gate single-reflection Diamant
ATR system. MS: Finnigan MAT 95 Spectrometer (CI) with methane
as a carrier gas, Varian MAT711 (EI, 70 eV). Optical rotation: Per-
kin-Elmer 241LC Polarimeter (20 °C, 589 nm).
X-ray diffraction: data sets were collected with a Nicolet P3 or Sie-
mens P4 Diffractometers. Programs used, data collection: Siemens
P3/PC Data Collection System or Bruker XSCANS 2.31; data reduction:
(1.08 mL, 1.32 g, 6.00 mmol) in the presence of NEt3 (0.84 mL,
0.618 g, 6.00 mol) under reflux for 3.5 h and the subsequent stir-
ring at room temperature for 13 h, followed by the treatment with
a solution of BH3ꢁTHF (1 M, 6.00 mL, 6.00 mmol) in THF, gave after
flash chromatography (eluent: EtOAc/PE, 1:10, silica gel; Rf
(3aꢁBH3) = 0.16) the complex 3aꢁBH3 as a colorless viscous oil
(664 mg, 39%). Anal. Calc. for C34H42B2O2P2: C, 72.12; H, 7.48.
Found: C, 71.87; H, 8.16%.
1H NMR (250 MHz, CDCl3) d = 0.99 (s, 3H, 9-H), 1.07 (m, 3H,
BH3), 1.24, 1.40 (each s, each 3H, 8-H and 80-H), 1.43 (d,
2JHH = 10.7 Hz, 1H, 7-Hax), 1.81 (m, 1H, 4-Hax), 1.85 (m, 1H, 5-H),
SHELXTL-plus, XDISK or Bruker XSCANS 2.31; structure solution: SHELXS
-
3
97; structure refinement: SHELXS-97; graphics: SHELXTL-plus, XP.
1.93 (t, JHH = 5.9 Hz, 1H, 1-H), 2.13 (m, 1H, 7-Heq), 2.30 (ddd,
3
3
2JHH = 13.2 Hz, JHH-trans = 12.4 Hz, JHH = 4.5 Hz, 1H, 4-Heq), 4.74
3
3
3
4.2. General procedure (1) for preparation of cis- and trans-
bisphosphinite complexes 2bꢁBH3, 3aꢁBH3, 3bꢁBH3
(ddd, JPH = 13.0 Hz, JHH-trans=12.4 Hz, JHH-cis = 6.0 Hz, 1H, 3-H),
7.47 (m, 12H, m,p-PhA and m,p-PhB), 7.76 (m, 8H, o-PhA and o-PhB).
13C{1H} NMR (63 MHz, CDCl3) d = 22.9 (C-9), 25.4 (C-7), 26.1,
27.2 (C-8 and C-80), 34.6 (C-6), 38.7 (C-4), 39.8 (C-5), 53.7 (C-1),
Chlorodialkylphosphine (4.40 mmol) was added at ꢀ78 °C to a
solution of an amine base (4.00 mmol) and cis- or trans-pinandiol
(2.00 mmol) in THF (15 mL). The reaction was allowed to warm
up to room temperature and heated under reflux for a certain time.
The resulting mixture was filtered trough Celite, and the BH3ꢁTHF
complex (6.00 mmol) was added at 0 °C to the filtrate. The reaction
was stirred at room temperature for 1 h. After evaporation under
reduced pressure, the residue was purified via flash chromatogra-
phy on silica gel.
2
2
77.9 (d, JPC = 3.6 Hz, C-2), 81.3 (d, JPC = 3.2 Hz, C-3), 128.6 (d,
3JPC = 10.6 Hz, m-PhA and m-PhB), 131.2, 131.7 (each d,
2JPC = 11.2 Hz, o-PhA and o-PhB), 131.8, 132.0 (d, JPC = 2.3 Hz, p-
4
PhA and p-PhB), 132.2, 132.5 (each d, JPC = 61 Hz, i-PhA and i-PhB).
1
31P{1H} NMR (162 MHz, C6D6) d = 107.3, 109.3.
~
m
IR (film):
= 3648, 3529 (br), 3146, 3078, 3058, 2993, 2972,
2915 (s), 2870, 2378 (s), 2344, 2257, 1481, 1456, 1436, 1385,
1368, 1112, 1062, 1005, 980, 925, 876, 733, 691, 625, 611 cmꢀ1
.
MS (CI): m/z (%) = 554 (10), 553 (27), 417 (4), 367 (3), 365 (8),
355 (37), 349 (34), 337 (19), 308 (5), 281 (3), 241 (3), 231 (9), 215
(13), 203 (100), 185 (32), 165 (5), 109 (4), 108 (5), 93 (9), 71 (4).
4.2.1. (1R,2R,3S,5R)–cis-2,3-Bis(boronatodiisopropylphosphinoxy)-
pinane (2bꢁBH3)
According to the general procedure (1), the reaction of cis-
pinandiol 7 (340 mg, 2.00 mmol) with di(i-propyl)chlorophosphine
(0.70 mL, 671 mg, 4.40 mmol) in the presence of i-Pr2NEt (0.73 mL,
568 mg, 4.40 mmol) under reflux for 24 h and the subsequent
treatment with a solution of BH3ꢁTHF (1 M, 5.00 mL, 5.00 mmol)
in THF gave after flash chromatography (eluent: EtOAc/toluene,
1:10, silica gel; Rf (2bꢁBH3) = 0.43) the complex 2bꢁBH3 as a color-
less viscous oil (360 mg, 42%). Anal. Calc. for C22H50B2O2P2: C,
61.42; H, 11.71. Found: C, 61.97; H, 10.22%.
½
a 2D0
ꢄ
¼+24.7° (c = 1, CH2Cl2).
4.2.3. (1R,2R,3R,5R)-trans-2,3-Bis(boronatodiisopropylphosphinoxy)-
pinane (3bꢁBH3)
According to the general procedure (1), the reaction of trans-
pinandiol 11 (0.51 g, 3.00 mmol) with di(i-propyl)chlorophosphine
(1.1 mL, 1.00 g, 6.60 mmol) in the presence of i-Pr2NEt (0.85 g,
6.60 mmol)) under reflux for 17 h and the subsequent treatment
with a solution of BH3ꢁTHF (1 M, 7.50 mL, 7.50 mmol) in THF gave
after flash chromatography (eluent: EtOAc/toluene, 1:20, silica gel;
Rf (3bꢁBH3) = 0.30) the complex 3bꢁBH3 as a colorless viscous oil
(260 mg, 20%). Anal. Calc. for C22H50B2O2P2: C, 61.42; H, 11.71.
Found: C, 62.19; H, 10.55%.
1
1H NMR (250 MHz, CDCl3) d = 0.43 (1:1:1:1 q, JBH = 95 Hz, 3H,
BH3), 0.94 (s, 3H, 9-H), 1.22, 1.22, 1.25, 1.26 (each dd,
3
iPr(A)
3JPH = 14.7 Hz/17.0 Hz/18.7 Hz, JHH = 7.1 Hz, each 6H, CH3
iPr(B)
and CH3
of 2-OP(iPr)2 and 3-OP(iPr)2, tentative assignment),
2
1
1.27, 1.33 (each s, each 3H, 8-H and 80-H), 1.46 (d, JHH = 10.5 Hz,
1H NMR (250 MHz, CDCl3) d = 0.47 (1:1:1:1 q, JBH = 95 Hz, 3H,
1H, 7-Hax), 1.70 (ddd, JHH = 13.8 Hz, JHH-cis = 5.8 Hz, JHH = 2.3 Hz,
BH3), 0.93 (s, 3H, 9-H), 1.21, 1.22, 1.22, 1.29 (each dd,
2
3
3
3
iPr(A)
iPr(B)
1H, 4-Hax), 1.94 (m, 1H, 5-H), 1.98, 2.18 (each m, each 2H, CHiPr),
3JPH = 14 Hz/15 Hz, JHH = 7.1 Hz, each 6H, CH3
and CH3
of
2.01 (t, JHH = 5.9 Hz, 1H, 1-H), 2.19 (m, 1H, 7-Heq), 2.49 (m, 1H,
2-OP(iPr)2 and 3-OP(iPr)2, tentative assignment), 1.24, 1.36 (each
3
3
3
3
2
4-Heq), 4.62 (ddd, JPH = 9.9 Hz, JHH-trans = 9.5 Hz, JHH-cis = 5.8 Hz,
s, each 3H, 8-H and 80-H), 1.45 (d, JHH = 10.6 Hz, 1H, 7-Hax), 1.71
2
3
1H, 3-H).
(ddm, JHH = 14.0 Hz, JHH-cis = 6.3 Hz, 1H, 4-Hax), 1.91 (m, 1H, 5-
3
13C{1H} NMR (63 MHz, CDCl3) d = 16.1, 16.2 (each d,
H), 1.92 (t, JHH = 5.8 Hz, 1H, 1-H), 2.05, 2.13 (each m, each 2H,
2JPC = 10.4 Hz), 16.5, 16.6 (each d, JPC = 17.0 Hz, CH3
and
CHiPr), 2.17 (m, 1H, 7-Heq), 2.54 (ddd, JHH = 14.0 Hz, JHH-
2
iPr(A)
2
3
iPr(B)
3
3
CH3
of 2-OP(iPr)2 and 3-OP(iPr)2), 24.3 (C-9), 27.9 (C-7), 26.2,
trans = 10.5 Hz, JHH = 3.7 Hz, 1H, 4-Heq), 4.57 (ddd, JPH = 11.1 Hz,
26.3 (each d, JPC = 37 Hz, CHiPr of 2-OP(iPr)2 and 3-OP(iPr)2),
3JHH-trans = 10.5 Hz, JHH-cis = 6.3 Hz, 1H, 3-H).
1
3
28.6, 29.8 (C-8 and C-80), 37.4 (C-4), 38.5 (C-6), 40.6 (C-5), 54.3
13C{1H} NMR (63 MHz, CDCl3) d = 15.9, 16.0 (each d,
2
2
2
iPr(A)
(C-1), 74.1 (d, JPC = 4.7 Hz, C-2), 76.6 (d, JPC = 4.2 Hz, C-3).
2JPC = 11.0 Hz), 16.5, 16.6 (each d, JPC = 6.0 Hz) (CH3
and
31P{1H} NMR (162 MHz, C6D6) d = 51.9 (s), 64.0 (s).
CH3
of 2-OP(iPr)2 and 3-OP(iPr)2), 22.8 (C-9), 25.3 (C-7), 25.8,
iPr(B)
1
~
m
IR (film):
= 3577 (w), 2966 (s), 2932 (s), 2874 (s), 2374 (s),
27.2 (C-8 and C-80), 25.9, 26.3 (each d, JPC = 38 Hz, CHiPr of 2-
OP(iPr)2 and 3-OP(iPr)2), 34.6 (d, JPC = 1.3 Hz, C-4), 38.8 (C-6),
3
2340, 2278 (w), 1464 (s), 1387, 1368, 1334, 1270, 1163, 1123,
2
1043, 1005, 993, 945, 928, 872, 788, 760, 687, 635, 590 cmꢀ1
.
39.9 (C-5), 54.4 (C-1), 78.2 (d, JPC = 4.0 Hz, C-2), 80.9 (d,
MS (DCI): m/z (%) = 447 (2), 435 (25), 417 (2), 375 (1), 299 (52),
281 (55), 269 (43), 229 (1), 201 (2), 173 (1), 163 (12), 135 (100),
117 (34), 93 (9), 75 (5), 55 (3).
2JPC = 4.9 Hz, C-3).
31P{1H} NMR (162 MHz, C6D6) d = 52.3 (s), 64.4 (s).
~
m
IR (film):
= 3523 (br), 2964 (s), 2934 (s), 2874, 2375 (s), 1461
½
a 2D0
ꢄ
¼ +4.5° (c = 1, CH2Cl2).
(s), 1386, 1368, 1137, 1069, 1050, 1005, 983, 925, 883, 869, 834,
795, 755, 688, 647, 582 cmꢀ1
.
4.2.2. (1R,2R,3R,5R)-trans-2,3-Bis(boronatodiphenylphosphinoxy)-
pinane (3aꢁBH3)
MS (CI): m/z (%) = 435 (1), 417 (5), 297 (6), 287 (18), 281 (42),
269 (11), 239 (3), 198 (1), 173 (1), 163 (14), 147 (48), 135 (100),
117 (74), 92 (23), 75 (8), 63 (3), 55 (2).
According to the general procedure (1), the reaction of trans-
pinandiol 11 (0.51 g, 3.00 mmol) with diphenylchlorophosphine
½
a 2D0
ꢄ
¼ ꢀ29.1° (c = 1, CH2Cl2).

D. Hobuß et al. / Inorganica Chimica Acta 374 (2011) 94–103
101
4.3. General procedure (2) for preparation of cis- and trans-
monophosphinite complexes 4aꢁBH3, 5aꢁBH3, 5bꢁBH3 and 6aꢁBH3
as a colorless crystalline solid (768 mg, 80%). m.p. 55 °C. Anal. Calc.
for C23H32BO2P: C, 72.26; H, 8.44. Found: C, 72.27; H, 8.47%.
1H NMR (500 MHz, CDCl3) d = 1.01 (s, 3H, 9-H), 1.09 (1:1:1:1 q,
3H, BH3), 1.14, 1.28 (each s, each 3H, 8-H and 80-H), 1.57 (d,
2JHH = 10.0 Hz, 1H, 7-Hax), 1.80 (ddd, 2JHH = 13.4 Hz, 3JHH-cis = 8.0 Hz,
A solution of methoxypinanol 17, 19 or 20 (461 mg, 2.50 mmol)
in THF (10 mL) was treated with a solution of nBuLi in hexane
(1.6 M, 1.72 mL, 2.75 mmol) at ꢀ78 °C. After stirring for 30 min
chlorodialkylphosphine (2.75 mmol) was added dropwise. After
warming to room temperature and stirring for 18 h, the resulting
mixture was treated with a solution of the BH3ꢁTHF complex in
THF (1 M, 2.50 mL, 2.5 mmol) at 0 °C. The reaction was stirred at
room temperature for 2 h then neutralized with water (50 mL).
After an extraction with EtOAc (4 ꢃ 50 mL), combined organic
phases were washed with brine (50 mL), dried over magnesium
sulfate and evaporated under reduced pressure. The residue was
purified via flash chromatography on silica gel.
3
JHH = 1.8 Hz, 1H, 4-Hax), 1.91 (m, 1H, 5-H), 2.11 (t, 3JHH = 5.9 Hz, 1H,
2
3
3
1-H), 2.16 (dtd, JHH = 10.0 Hz, JHH = 5.9 Hz, JHH = 2.3 Hz, 1H, 7-
Heq), 2.29 (dddd, JHH = 13.4 Hz, JHH-trans = 9.2 Hz, JHH = 4.3 Hz,
2
3
3
3JHH = 2.2 Hz, 1H, 4-Heq), 3.10 (s, 3H, OCH3), 5.04 (ddd,
3JPH = 12.6 Hz, JHH-trans = 9.2 Hz, JHH-cis = 8.0 Hz, 1H, 3-H), 7.40,
3
3
7.45 (each m, each 2H, m-PhA and m-PhB), 7.47, 7.49 (each m, each
1H, p-PhA and p-PhB), 7.73, 7.84 (each ddm, JPH = 11.0 Hz,
3
3JHH = 7.5 Hz, each 2H, o-PhA and o-PhB).
13C{1H} NMR (126 MHz, CDCl3) d = 22.6 (C-9), 24.1 (C-7), 28.5,
3
28.9 (C-8 and C-80), 36.4 (d, JPC = 2.0 Hz, C-4), 38.3 (C-6), 40.5 (C-
3
5), 48.8 (C-1), 51.7 (OCH3), 77.7 (d, JPC = 4.4 Hz, C-2), 78.0 (d,
2JPC = 1.7 Hz, C-3), 128.3, 128.3 (each d, JPC = 10.6 Hz, m-PhA and
3
4.3.1. (1R,2R,3S,5R)-trans-2-(Boronatodiphenylphosphinoxy)-3-
methoxy-pinane (4aꢁBH3)
m-PhB), 131.6, 131.6 (each d, JPC = 8.6 Hz, o-PhA and o-PhB),
2
131.4, 131.6 (each d, JPC = 2.2 Hz, p-PhA and p-PhB), 132.8, 133.7
4
According to the general procedure (2), the reaction of trans-
methoxypinanol 17 (461 mg, 2.5 mmol) with a solution of nBuLi
(1.6 M, 1.7 mL, 2.8 mmol) in hexane, followed by the treatment
with diphenylchlorophosphine (0.5 mL, 607 mg, 2.8 mmol), and
the subsequent reaction with a solution of BH3ꢁTHF (1 M, 2.5 mL,
2.5 mmol) in THF gave after flash chromatography (eluent:
EtOAc/PE, 1:10, silica gel; Rf (4aꢁBH3) = 0.37) the complex 4aꢁBH3
as soft colorless crystals (265 mg, 28%). Anal. Calc. for
(each d, JPC = 65 Hz / 67 Hz, i-PhA and i-PhB).
1
31P{1H} NMR (162 MHz, C6D6) d = 94.9 (s).
~
m
IR (film):
= 3059 (w), 2976, 2929, 2826, 2383 (s), 1590 (w),
1437, 1367, 1334, 1309, 1277, 1255, 1243, 1183, 1159, 1111,
1093, 1064, 1009, 994, 951, 928, 879, 851, 797, 734 cmꢀ1
.
MS (EI): m/z (%) = 382 (1) [M+], 369 (3), 368 (13), 337 (2), 297
(1), 269 (2), 242 (3), 234 (14), 233 (100), 204 (5), 203 (36), 185
(43), 141 (6), 140 (32), 113 (25), 93 (45), 41 (13).
C
34H42B2O2P2: C, 77.12; H, 7.48. Found C, 77.43; H, 8.32%.
½
a 2D0
ꢄ
¼ ꢀ19.6° (c = 1, CH2Cl2).
1H NMR (500 MHz, CDCl3) d = 0.78 (s, 3H, 9-H), 0.86, 0.96 (each
s, each 3H, 8-H and 80-H), 0.99 (dd, 2JHH = 13.7 Hz, 3JHH = 3.6 Hz, 1H,
4.3.3. (1R,2R,3S,5R)-cis-2-Methoxy-3-(boronatodi
(i-propyl)phosphinoxy)-pinane (5bꢁBH3)
7-Hax), 1.01 (1:1:1:1 br q, JBH = 93 Hz, 3H, BH3), 1.72 (t,
1
3JHH = 4.4 Hz, 1H, 1-H), 1.78 (m, 1H, 4-Hax), 1.80 (m, 1H, 5-H),
2.17 (m, 1H, 7-Heq), 3.27 (s, 3H, OCH3), 3.88 (m, 1H, 3-H), 4.56
(m, 1H, 4-Heq), 7.45 (m, 4H, m-PhA and m-PhB), 7.50 (m, 2H, p-
According to the general procedure (2), the reaction of cis-meth-
oxypinanol 19 (461 mg, 2.5 mmol) with a solution of nBuLi (1.6 M,
1.7 mL, 2.8 mmol) in hexane, followed by the treatment with di-
(i-propyl)chlorophosphine (0.44 mL, 420 mg, 2.8 mmol), and the
subsequent reaction with a solution of BH3ꢁTHF (1 M, 2.5 mL,
2.5 mmol) in THF gave after flash chromatography (eluent:
EtOAc/PE, 1:3, silica gel; Rf (5bꢁBH3) = 0.64) the complex 5bꢁBH3
as a colorless crystalline solid (440 mg, 56%). m.p. 63–64 °C. Anal.
Calc. for C17H36BO2P: C, 64.97; H, 11.55. Found: C, 65.12; H, 11.47%.
1H NMR (250 MHz, CDCl3) d = 0.99 (s, 3H, 9-H), 1.09 (1:1:1:1 q,
1JBH = 92 Hz, 3H, BH3), 1.19, 1.19, 1.20, 1.29 (each dd, 3JPH = 12.5 Hz/
PhA and p-PhB), 7.70, 7.73 (each ddm, JPH = 9.6 Hz, JHH = 7.6 Hz,
3
3
each 2H, o-PhA and o-PhB); admixture of nBuPPh2ꢁBH3 (33 mol%):
3
d = 0.89 (t, JHH = 7.3 Hz, CH3), 1.40, 1.49 (each m, each 2H, CH2),
2.19 (m, 2H, CH2P), 7.45 (m, 4H, m-Ph), 7.47 (m, 2H, p-Ph), 7.67
3
3
(ddm, JPH = 10.3 Hz, JHH = 7.5 Hz, 4H, o-Ph).
13C{1H} NMR (126 MHz, CDCl3) d = 9.7 (C-9), 19.6, 21.2 (C-8 and
C-80), 36.9 (C-7), 38.2 (C-4), 44.6 (C-5), 47.6 (C-6), 54.1 (d,
3JPC = 5.1 Hz, C-1), 57.1 (OCH3), 80.4 (C-3), 82.9 (d, JPC = 2.5 Hz, C-
2
2), 128.5, 128.5 (each d, JPC = 10.5 Hz, m-PhA and m-PhB), 131.2,
3
3
iPr(A)
14.3 Hz/15.5 Hz, JHH = 7.1 Hz, each 3H, CH3
and CH3iPr(B), ten-
131.5 (each d, JPC = 11.4 Hz, o-PhA and o-PhB), 131.6, 131.8 (each
2
tative assignment), 1.29, 1.30 (each s, each 3H, 8-H and 80-H),
d, 4JPC = 2.2 Hz, p-PhA and p-PhB), 132.6, 133.1 (each d, 1JPC = 62 Hz,
i-PhA and i-PhB);admixture of nBuPPh2ꢁBH3 (33 mol%): d = 13.6
(CH3), 24.3 (d, 3JPC = 13.7 Hz, CH2), 25.02 (CH2), 25.4 (d, 1JPC = 36 Hz,
1.49 (d, JHH = 8.9 Hz, 1H, 7-Hax), 1.80 (ddd, JHH = 13.2 Hz,
2
2
3
3JHH-cis = 7.8 Hz, JHH = 1.7 Hz, 1H, 4-Hax), 1.95 (m, 1H, 5-H), 2.02
(m, 1H, 7-Heq), 2.10 (t, JHH = 5.6 Hz, 1H, 1-H), 2.15 (m, 2H, CHiPr(A)
3
3
1
CH2P), 128.8 (d, JPC = 9.9 Hz, m-Ph), 129.7 (d, JPC = 55 Hz, i-Ph),
and CHiPr(B)), 2.39 (dddd, 2JHH = 13.2 Hz, 3JHH-trans = 9.0 Hz,
4
2
131.1 (d, each JPC = 2.2 Hz, p-Ph), 132.1 (d, JPC = 8.9 Hz, o-
3JHH = 4.2 Hz, JHH = 2.0 Hz, 1H, 4-Heq), 3.09 (s, 3H, OCH3), 4.75
3
Ph).31P{1H} NMR (162 MHz, C6D6) d = 109.2.
3
3
3
(ddd, JPH = 11.8 Hz, JHH-trans = 9.0 Hz, JHH-cis = 7.8 Hz, 1H, 3-H).
~
m
IR (film):
= 3058 (w), 2975, 2920, 2825, 2380 (s), 2340, 2251,
13C{1H} NMR (63 MHz, CDCl3) d = 16.2 (two d, JPC = 4.6 Hz),
2
1587, 1366, 1333, 1307, 1277, 1240, 1180, 1160, 1110, 1090, 1060,
2
iPr(A)
16.6 (two d, JPC = 13.1 Hz) (CH3
and CH3iPr(B)), 22.9 (C-9),
1010, 993, 953, 930, 851 cmꢀ1
.
24.1 (C-7), 26.2, 26.4 (each d, JPC = 40 Hz / 37 Hz, CHiPr(A) and
1
MS (EI): m/z (%) = 382 (1) [M+], 368 (2), 269 (5), 234 (21), 233
CHiPr(B)), 28.3, 28.7 (C-8 and C-80), 37.1 (d, JPC = 1.7 Hz, C-4), 38.2
3
(90), 203 (100), 184 (55), 140 (33), 113 (26), 93 (40), 40 (12).
(C-6), 40.5 (C-5), 48.5 (C-1), 51.6 (OCH3), n.o (C-2), 77.8 (d,
½
a 2D0
ꢄ
¼ ꢀ54.9° (c = 1, CH2Cl2).
2JPC = 3.6 Hz, C-3).31P{1H} NMR (162 MHz, C6D6) d = 62.8 (s).
~
m
IR (film):
= 3003 (w), 2966, 2925 (s), 2873, 2824, 2374 (s),
4.3.2. (1R,2R,3S,5R)-cis-2-Methoxy-3-
(boronatodiphenylphosphinoxy)-pinane (5aꢁBH3)
2345, 1465, 1385, 1369, 1336, 1279, 1245, 1226, 1183, 1161,
1138, 1115, 1094, 1066, 1045, 1008, 992, 950, 885, 852 cmꢀ1
.
According to the general procedure (2), the reaction of cis-meth-
oxypinanol 19 (461 mg, 2.5 mmol) with a solution of nBuLi (1.6 M,
1.7 mL, 2.8 mmol) in hexane, followed by the treatment with
diphenylchlorophosphine (0.5 mL, 607 mg, 2.8 mmol), and the
subsequent reaction with a solution of BH3ꢁTHF (1 M, 2.5 mL,
2.5 mmol) in THF gave after flash chromatography (eluent:
EtOAc/PE, 1:3, silica gel; Rf (5aꢁBH3) = 0.59) the complex 5aꢁBH3
MS (EI): m/z (%) = 314 (1) [M+], 313 (3), 300 (10), 281 (4), 257
(8), 229 (3), 201 (4), 177 (5), 166 (14), 165 (43), 141 (9), 140
(66), 135 (100), 117 (33), 93 (64), 81 (28), 55 (18), 43 (41), 28 (25).
½
a 2D0
ꢄ
¼ ꢀ37.1° (c = 1, CHCl3).
X-ray crystal structure analysis of complex 5bꢁBH3 (s1335rc): CCDC
number: CCDC 791979, formula C17H36BO2P, colorless crystal
0.7 ꢃ 0.7 ꢃ 0.5 mm, M = 314.24, a = 7.0483(8) Å, b = 14.7491(11) Å,

102
D. Hobuß et al. / Inorganica Chimica Acta 374 (2011) 94–103
c = 19.404(2) Å, V = 2017.2(3) Å3,
q
calc = 1.035 g cmꢀ3
,
l
= 0.1206
dimethyl ester of 2-methylsuccinic acid 13 were defined by chro-
matography methods.
mmꢀ1
,
Z = 4, orthorhombic space group P212121 (No. 19),
k = 1.54178 Å, T = 293(2) K, 3273 reflections collected (ꢀ8 h 8,
ꢀ17 k 15, ꢀ23 l 20), [(sinh)/k] = 0.60 Åꢀ1
,
2832 independent
(I)], 191 refined
r(I)]), maximum (mini-
Acknowledgments
(Rint = 0.0312) and 2536 observed reflections [I 2
r
parameters, R1 = 0.0570, wR2 = 0.1534 ([I 2
Generous financial support by the Deutsche Forschungsgeme-
inschaft, the Ministerium für Wissenschaft, Forschung und Kunst
des Landes Baden-Württemberg and the Fonds der Chemischen
Industrie are gratefully acknowledged.
mum) residual electron density 0.240 (ꢀ0.304) e Åꢀ3, Flack param-
eter ꢀ0.02(4), data collection on a Siemens P4 diffractometer.
4.3.4. (1R,2R,3R,5R)-trans-2-methoxy-3-
(boronatodiphenylphosphinoxy)-pinane (6aꢁBH3)
Appendix A. Supplementary material
According to the general procedure (2), the reaction of trans-
methoxypinanol 20 (461 mg, 2.5 mmol) with a solution of nBuLi
(1.6 M, 1.7 mL, 2.8 mmol) in hexane, followed by the treatment
with diphenylchlorophosphine (0.5 mL, 607 mg, 2.8 mmol) and
the subsequent reaction with a solution of BH3ꢁTHF (1 M, 2.5 mL,
2.5 mmol) in THF gave after flash chromatography (eluent:
EtOAc/PE, 1:5, silica gel; Rf (6aꢁBH3) = 0.52) the complex 6aꢁBH3
as a colorless oil (671 mg, 70%). Anal. Calc. for C23H32BO2P: C,
72.26; H, 8.44. Found: C, 72.17; H, 8.43%.
CCDC 791978 and 791979 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.ica.2011.01.020.
References
1H NMR (250 MHz, CDCl3) d = 0.99 (s, 3H, 9-H), 1.16 (1:1:1:1 q,
3H, BH3), 1.23, 1.31 (each s, each 3H, 8-H and 80-H), 1.39 (d,
[1] J.A. Osborn, F.H. Jardine, J.F. Young, G. Wilkinson, J. Chem. Soc. A: Inorg. Phys.
Theor. (1966) 1711.
[2] A. Pfalz, S. Bell, in: J.G. de Vries, C.J. Elsevier (Eds.), The Handbook of
Homogeneous Hydrogenation, Wiley, Weinheim, 2008, pp. 1049–1072 (and
references therein).
2
3
2JHH = 9.4 Hz, 1H, 7-Hax), 1.65 (ddt, JHH = 14.3 Hz, JHH-cis = 5.4 Hz,
3JHH = 1.7 Hz, 1H, 4-Hax), 1.82 (m, 1H, 5-H), 2.02 (t, JHH = 5.3 Hz,
3
1H, 1-H), 2.08 (m, 1H, 7-Heq), 2.49 (ddd, JHH = 14.3 Hz, JHH-
2
3
trans = 10.4 Hz, JHH = 4.3 Hz, 1H, 4-Heq), 3.02 (s, 3H, OCH3), 4.78
3
[3] J.R. Shapley, R.R. Schrock, J.A. Osborn, J. Am. Chem. Soc. 91 (1969) 2816.
[4] R.R. Schrock, J.A. Osborn, J. Am. Chem. Soc. 93 (1971) 2397.
[5] R.R. Schrock, J.A. Osborn, J. Am. Chem. Soc. 98 (1976) 2134.
[6] Review: G. Erre, S. Enthaler, K. Junge, S. Gladiali, M. Beller, Coord. Chem. Rev.
252 (2008) 471 (and references therein).
[7] T.P. Dang, H.B. Kagan, J. Chem. Soc., Chem. Commun. (1971) 481.
[8] H.B. Kagan, T.P. Dang, J. Am. Chem. Soc. 94 (1972) 6429.
[9] M.T. Reetz, Angew. Chem., Int. Ed. 47 (2008) 2556 (and references therein).
[10] K. Tani, T. Yamagata, S. Akutagawa, H. Kumobayashi, T. Taketomi, H. Takaya, A.
Miyashita, R. Noyori, S. Otsuka, J. Am. Chem. Soc. 106 (1984) 5208.
[11] K. Tani, T. Yamagata, Y. Tatsuno, Y. Yamagata, K. Tomita, S. Akutagawa, H.
Kumobayashi, S. Otsuka, Angew. Chem., Int. Ed. Engl. 24 (1985) 217.
[12] Review: H. Shimizu, I. Nagasaki, K. Matsumura, N. Sayo, T. Saito, Acc. Chem.
Res. 40 (2007) 1385 (and references therein).
3
3
3
(ddd, JPH = 11.2 Hz, JHH-trans = 10.4 Hz, JHH-cis = 5.4 Hz, 1H, 3-H),
7.39–7.52 (m, 6H, m-PhA, m-PhB, p-PhA and p-PhB), 7.75, 7.79 (each
m, each 2H, o-PhA and o-PhB).
13C{1H} NMR (63 MHz, CDCl3) d = 19.8 (C-9), 22.9 (C-7), 25.2,
27.5 (C-8 and C-80), 35.2 (C-4), 38.2 (C-6), 39.8 (C-5), 48.9 (C-1),
2
3
50.9 (OCH3), 79.0 (d, JPC = 2.9 Hz, C-3), 82.4 (d, JPC = 6.0 Hz, C-2),
128.4, 128.5 (each d, JPC = 10.6 Hz, m-PhA and m-PhB), 131.3,
3
131.5 (each d, 2JPC = 9.0 Hz, o-PhA and o-PhB), 131.7 (d, 4JPC = 2.3 Hz,
p-PhA and p-PhB), 132.9, 133.4 (each d, JPC = 65 Hz, i-PhA and i-
1
PhB).31P{1H} NMR (162 MHz, C6D6) d = 106.3 (s).
[13] M.J. Burk, J. Am. Chem. Soc. 113 (1991) 8518.
~
m
IR (film):
= 3058 (w), 2919 (br), 2825, 2380 (s, br), 2343, 2255
[14] M.J. Burk, Y.M. Wang, J.R. Lee, J. Am. Chem. Soc. 118 (1996) 5142.
[15] M.J. Burk, C.S. Kalberg, A. Pizzano, J. Am. Chem. Soc. 120 (1998) 4345.
[16] M.J. Burk, Acc. Chem. Res. 33 (2000) 363.
[17] Review: W. Zhang, Y. Chi, X. Zhang, Acc. Chem. Res. 40 (2007) 1278 (and
references therein).
[18] A. Togni, C. Breutel, A. Schnyder, F. Spindler, H. Landert, A. Tijani, J. Am. Chem.
Soc. 116 (1994) 4062.
[19] Review: H.-U. Blaser, Nachr. Chem. 58 (2010) 864 (and references therein).
[20] A.J. Minnaard, B.L. Feringa, L. Lefort, J.G. de Vries, Acc. Chem. Res. 40 (2007)
1267 (and references therein).
(w), 1817 (w), 1738, 1589, 1481, 1455, 1437, 1384, 1369, 1337,
1311, 1282, 1242, 1215, 1182, 1159, 1112, 1085, 1060, 1019,
996, 977, 955, 914, 880, 846, 827 cmꢀ1
.
MS (EI): m/z (%) = 382 (1) [M+], 369 (3), 368 (14), 335 (3), 308
(4), 267 (3), 245 (4), 242 (9), 215 (8), 214 (16), 203 (100), 141
(8), 140 (49), 93 (30), 69 (10), 41 (14).
½
a 2D0
ꢄ
¼ ꢀ12.3° (c = 1, CHCl3).
[21] L. Eberhardt, D. Armspach, J. Harrowfield, D. Matt, Chem. Soc. Rev. 37 (2008)
839 (and references therein).
[22] J.F. Teichert, B.L. Feringa, Angew. Chem., Int. Ed. 49 (2010) 2486 (and
references therein).
[23] R.H. Grubbs, R.A. DeVries, Tetrahedron Lett. 18 (1977) 1879.
[24] J. Bakos, I. Tóth, L. Markó, J. Org. Chem. 46 (1981) 5427.
[25] A.S.C. Chan, W. Hu, C.-C. Pai, C.-P. Lau, Y. Jiang, A. Mi, M. Yan, J. Sun, R. Lou, J.
Deng, J. Am. Chem. Soc. 119 (1997) 9570.
[26] M.T. Reetz, G. Mehler, Angew. Chem., Int. Ed. 39 (2000) 3889.
[27] I.D. Kostas, K.A. Vallianatou, J. Holz, A. Börner, Appl. Organomet. Chem. 19
(2005) 1090.
[28] C. Darcel, D. Moulin, J.-C. Henry, M. Lagrelette, P. Richard, P.D. Harvey, S. Jugé,
Eur. J. Org. Chem. (2007) 2078.
[29] H. Fernández-Pérez, S.M.A. Donald, I.J. Munslow, J. Benet-Buchholz, F. Maseras,
A. Vidal-Ferran, Chem. Eur. J. 16 (2010) 6495 (and references therein).
[30] T.H. Johnson, G. Rangarajan, J. Org. Chem. 45 (1980) 62.
[31] M.T. Reetz, T. Neugebauer, Angew. Chem., Int. Ed. 38 (1999) 179.
[32] E. Guimet, M. Diéguez, A. Ruiz, C. Claver, Tetrahedron: Asymmetry 15 (2004)
2247.
[33] T. Minuth, M.M.K. Boysen, Org. Lett. 11 (2009) 4212.
[34] Review: M. Diéguez, O. Pàmies, C. Claver, Chem. Rev. 104 (2004) 3189 (and
references therein).
[35] H. Brunner, W. Zettelmeier, Handbook of Enantioselective Catalysis with
Transition Metals, first ed., vol. I and II, VCH, Weinheim, 1993.
[36] I. Ojima, Asymmetric Catalysis, VCH, Weinheim, 1993.
[37] D. Valentine Jr., K.K. Johnson, W. Priester, R.C. Sun, K. Toth, G. Saucy, J. Org.
Chem. 45 (1980) 3698.
4.3.5. General procedure (3) for catalytic hydrogenation of dimethyl
itaconate 12 with mixture of [Rh(COD)2]+[BF4]ꢀ and phosphinite
pinane-based ligands 2–6
Prior the hydrogenation reaction, the complexes 2ꢁBH3–6ꢁBH3
(0.06 mmol) were deprotected by heating in Et2NH (1.5 mL) at
65 °C for 20 h. After removal all volatiles and drying for 2 h under
vacuum, the residue (the deprotected ligand) was dissolved in tol-
uene (4.0 mL) and added in one portion to a suspension of
[Rh(COD)2]+[BF4]ꢀ (12.0 mg, 0.03 mmol) in toluene (2.0 mL). The
obtained suspension was homogenized in an ultrasonic bath and
the resulting stock solution of a catalyst (concentration of a cata-
lyst 0.005 mmol/mL) was used for subsequent hydrogenation reac-
tions. A flask with a solution of substrate 12 (0.07 mL, 80.0 mg,
0.50 mmol) in a solvent (4.0 mL) was charged with hydrogen
(pressure 1 atm). Subsequently, an aliquot of the stock solution
of
a catalyst (1.0 mL, 0.01 mmol of ligand, 0.005 mmol of
[Rh(COD)2]+[BF4]ꢀ) was added and the reaction mixture was stir-
red for 20 h (for ligands 2 and 3 at hydrogen pressure of 15 bar).
After filtration through silica gel, the filtrate was evaporated under
vacuum to give the product 13. The conversion and purity of
[38] J. Almena, A. Monsees, T. Riermeier, R. Kadyrov, Chim. Oggi 23 (2005) 48.

D. Hobuß et al. / Inorganica Chimica Acta 374 (2011) 94–103
103
[39] R. Zalubovskis, E. Hörmann, A. Pfaltz, C. Moberg, ARKIVOC 14 (2008) 58.
[40] K.Z. Ła˛czkowski, A. Kmieciak, A. Kozakiewicz, Tetrahedron: Asymmetry 20
(2009) 1487.
[41] K.Z. Ła˛czkowski, A. Baranowska, Eur. J. Org. Chem. (2009) 4600.
[42] B. Bogdanovic´, B. Henc, B. Meister, H. Pauling, G. Wilke, Angew. Chem., Int. Ed.
Engl. 11 (1972) 1023.
[43] J.D. Morrison, W.F. Masler, M.K. Neuberg, Adv. Catal. 25 (1976) 81.
[44] T.H. Johnson, D.K. Pretzer, S. Thomen, V.J.K. Chaffin, G. Rangarajan, J. Org.
Chem. 44 (1979) 1878.
[45] D.A. Knight, D.J. Cole-Hamilton, D.C. Cupertino, J. Chem. Soc., Dalton Trans.
(1990) 3051.
[46] E.U. Zhorov, K.N. Gavrilov, V.A. Pavlov, A.T. Teleshev, L.S. Gorshkova, E.E.
Nifantev, E.I. Klabunovskii, Russ. Chem. Bull. (1991) 871.
[47] A. Alexakis, J. Vastra, J. Burton, P. Mangeney, Tetrahedron: Asymmetry 8
(1997) 3193.
[67] W.S. Knowles, Angew. Chem., Int. Ed. 41 (2002) 1998.
[68] R. Noyori, Angew. Chem., Int. Ed. 41 (2002) 2008.
[69] W.S. Knowles, R. Noyori, Acc. Chem. Res. 40 (2007) 1238.
[70] I.D. Gridnev, T. Imamoto, Acc. Chem. Res. 37 (2004) 633.
[71] I.D. Gridnev, T. Imamoto, Chem. Commun. (2009) 7447.
[72] H. Shimizu, I. Nagasaki, K. Matsumura, N. Sayo, T. Saito, Acc. Chem. Res. 40
(2007) 1385.
[73] I.V. Komarov, A. Börner, Angew. Chem., Int. Ed. 40 (2001) 1197.
[74] V.I. Tararov, R. Kadyrov, T.H. Riermeier, J. Holz, A. Börner, Tetrahedron Lett. 41
(2000) 2351.
[75] G. Zhu, P. Cao, Q. Jiang, X. Zhang, J. Am. Chem. Soc. 119 (1997) 1799.
[76] H. Firouzabadi, N. Iranpoor, G. Hajipoor, J. Toofan, Synth. Commun. 14 (1984)
1033.
[77] N. Iranpoor, F.S. Zardaloo, Synth. Commun. 24 (1994) 1959.
[78] M.K. Lajunen, T. Maunula, A.M.P. Koskinen, Tetrahedron 56 (2000) 8167.
[79] B.A. Allal, L.E. Firdoussi, S. Allaoud, A. Karim, Y. Castanet, A. Mortreux, J. Mol.
Catal. A: Chem. 200 (2003) 177.
[48] X. Li, R. Lou, C.-H. Yeung, A.S.C. Chan, W.K. Wong, Tetrahedron: Asymmetry 11
(2000) 2077.
[49] I.V. Komarov, M.V. Gorichko, M.Y. Kornilov, Tetrahedron: Asymmetry 8 (1997)
435.
[50] I.V. Komarov, A. Monsees, R. Kadyrov, C. Fischer, U. Schmidt, A. Börner,
Tetrahedron: Asymmetry 13 (2002) 1615.
[51] I.V. Komarov, A. Monsees, A. Spannenberg, W. Baumann, U. Schmidt, C. Fischer,
A. Börner, Eur. J. Org. Chem. (2003) 138.
[52] R. Kadyrov, I.Z. Ilaldinov, J. Almena, A. Monsees, T.H. Riermeier, Tetrahedron
Lett. 46 (2005) 7397 (and references therein).
[53] A. Lledó, J. Solà, X. Verdaguer, A. Riera, M.A. Maestro, Adv. Synth. Catal. 349
(2007) 2121.
[54] T. Sell, S. Laschat, I. Dix, P.G. Jones, Eur. J. Org. Chem. (2000) 4119.
[55] A. Monsees, S. Laschat, Synlett (2002) 1011.
[56] F. Langer, P. Knochel, Tetrahedron Lett. 36 (1995) 4591.
[57] A. Longeau, F. Langer, P. Knochel, Tetrahedron Lett. 37 (1996) 2209.
[58] A. Gavryushin, K. Polborn, P. Knochel, Tetrahedron: Asymmetry 15 (2004)
2279.
[59] E.J. Bergner, G. Helmchen, Eur. J. Org. Chem. (2000) 419.
[60] K.W. Kottsieper, U. Kühner, O. Stelzer, Tetrahedron: Asymmetry 12 (2001)
1159.
[80] R.G. Carlson, J.K. Pierce, J. Org. Chem. 36 (1971) 2319.
[81] Crystallographic data (excluding structure factors) for the structures included
in this paper have been deposited with the Cambridge Crystallographic Data
Centre as supplementary publication nos. CCDC 791978 and 791979. Copies of
the data can be obtained free of charge on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (internet) +44(1223)336-033, E-mail:
deposit@ccdc.cam.ac.uk.
[82] M. Ohff, J. Holz, M. Quirmbach, A. Börner, Synthesis (1998) 1391.
[83] O. Huttenloch, J. Spieler, H. Waldmann, Chem. Eur. J. 7 (2001) 671.
[84] A. Arbuzov, K. Nikonorov, Rus. J. Gen. Chem. 18 (1948) 2008.
[85] Knochel has recently utilized the Arbuzov rearrangement for a transformation
of allylphosphinites to allylphosphine oxides. For details see Ref. [58].
[86] P.-Y. Renard, P. Vayron, E. Leclerc, A. Valleix, C. Mioskowski, Angew. Chem., Int.
Ed. 42 (2003) 2389.
[87] M. van der Berg, A.J. Minnaard, R.M. Haak, M. Leeman, E.P. Schudde, A.
Meetsma, B.L. Feringa, A.H.M. de Vries, C.E.P. Maljaars, C.E. Willans, D. Hyett,
J.A.F. Boogers, H.J.W. Henderickx, J.G. de Vries, Adv. Synth. Catal. 345 (2003)
308.
[88] M.T. Reetz, A. Gosberg, Tetrahedron: Asymmetry 10 (1999) 2129.
[61] X. Meng, X. Li, D. Xu, Tetrahedron: Asymmetry 20 (2009) 1402.
[89] For example, the methoxy substituent at the (ꢀ)-a-pinane core could be
´
[62] C.M. Binder, A. Bautista, M. Zaidlewicz, M.P. Krzeminski, A. Oliver, B. Singaram,
converted into a hydroxyl group, which is known to improve selectivity of a Rh
hydrogenation catalyst. See Refs. [90–92].
J. Org. Chem. 74 (2009) 2337.
[63] D. Wei, M. Tang, J. Zhao, L. Sun, W. Zhang, C. Zhao, S. Zhang, H. Wang,
Tetrahedron: Asymmetry 20 (2009) 1020.
[90] A. Börner, A. Kless, R. Kempe, D. Heller, J. Holz, W. Baumann, Chem. Ber. 128
(1995) 767.
[64] D. Hobuß, C. Thöne, S. Laschat, A. Baro, Synthesis (2003) 2053.
[65] J.M. Brown, in: E.N. Jacobsen, A. Pfaltz, H. Yamamoto (Eds.), Comprehensive
Asymmetric Catalysis, vol. 1, Springer Verlag, New York, 1999, pp. 1–62.
[66] K. Rossen, Angew. Chem., Int. Ed. 40 (2001) 4611.
[91] S. Borns, R. Kadyrov, D. Heller, W. Baumann, A. Spannenberg, R. Kempe, J. Holz,
A. Börner, Eur. J. Inorg. Chem. (1998) 1291.
[92] A. Börner, Eur. J. Inorg. Chem. (2001) 327.