Diamidophosphites with remote P*-stereocentres and their performance in Pd-catalyzed enantioselective reactions

Article abstract of DOI:10.1016/j.tetasy.2014.06.010

Diamidophosphite ligands based on 1,1′-bis(hydroxymethyl)ferrocene or N¹,N²-bis((S)-1-hydroxy-3,3-dimethylbutan-2-yl)oxalamide and bearing 1,3,2-diazaphospholidine rings with stereogenic phosphorus atoms were obtained. The use of the

Full text of DOI:10.1016/j.tetasy.2014.06.010

Tetrahedron: Asymmetry 25 (2014) 1116–1121
Contents lists available at ScienceDirect
Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
Diamidophosphites with remote P⁄-stereocentres and their
performance in Pd-catalyzed enantioselective reactions
a
a
a
Konstantin N. Gavrilov a, , Sergey V. Zheglov , Vladislav K. Gavrilov , Ilya V. Chuchelkin ,
⇑
Ivan M. Novikov a, Alexei A. Shiryaev a, Alexandr N. Volov b, Ilya A. Zamilatskov b
a Department of Chemistry, Ryazan State University, 46 Svoboda Street, 390000 Ryazan, Russian Federation
b A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninskiy prospekt 31, 119071 Moscow, Russian Federation
a r t i c l e i n f o
a b s t r a c t
Diamidophosphite ligands based on 1,10-bis(hydroxymethyl)ferrocene or N1,N2-bis((S)-1-hydroxy-3,3-
dimethylbutan-2-yl)oxalamide and bearing 1,3,2-diazaphospholidine rings with stereogenic phosphorus
atoms were obtained. The use of these ligands provides up to 96% ee in Pd-catalyzed asymmetric
allylations of (E)-1,3-diphenylallyl acetate, up to 70% ee in Pd-catalyzed desymmetrizations of N,N0-
ditosyl-meso-cyclopent-4-ene-1,3-diol bis-carbamate and up to 80% ee in Pd-catalyzed allylic alkylations
Article history:
Received 15 May 2014
Accepted 16 June 2014
of cinnamyl acetate with ethyl 2-oxocyclohexane-1-carboxylate. Results obtained with
a diam-
idophosphite containing an oxalamide framework show the considerable potential of such ligands in
enantioselective catalysis.
Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction
Among the phosphite-type chiral ligands, diamidophosphites
(one PAO bond and two PAN bonds) are a relatively small but very
Despite impressive advances in the preparation and application
of asymmetric transition-metal catalysis of large libraries of
different phosphorus-based chiral ligands,1–16 the development of
efficient enantioselective catalytic systems based on novel inexpen-
sive phosphorus-containing stereoselectors easily synthesized from
available enantiopure synthons remains a challenge.16–18 The
overwhelming majority of known ligands in the composition of
the corresponding metal complexes are able to catalyze (with differ-
ent enantioselectivities) either a certain type of chemical transfor-
mation, or one certain reaction. There are very few versatile (the
so-called ‘privileged’) ligands, and their high cost significantly limits
their wide application.16,19
promising group.1,36–42 It should be noted that these compounds
have different properties from more common phosphites (three
PAO bonds) or phosphoramidites (two PAO bonds and one PAN
bond). For example, nitrogen substituents create more steric bulk
around the phosphorus than the oxygen atom, since nitrogen sub-
stitution may be greater. Furthermore, replacing the oxygen atom
in the first coordination sphere of the phosphorus with a nitrogen
atom increases the electron density on the phosphorus center.1,42
The P,P-bidentate diamidophosphites LA–D (Fig. 1) have been suc-
cessfully applied in asymmetric Pd-catalyzed cycloadditions and
Rh-catalyzed hydrogenations.42–45
Diamidophosphites with 1,3,2-diazaphospholidine rings and
asymmetric phosphorus atoms have emerged as efficient stereoin-
ducers.46–48 In particular, these compounds display balanced
From a practical point of view, air-stable, inexpensive, and
easily accessible ligands are highly desirable.20 Optically active
phosphite-type compounds satisfy these criteria, since they are
favorably distinguished by stability to oxidation, pronounced
electronic characteristics since they are both good
(due to the accessibility of low-lying p⁄PN orbitals) as well as good
-donors. The inclusion of the phosphorus atom in the five-mem-
p-acceptors
p-acidity, and are inexpensive. It should also be noted that they
r
can be easily obtained by simple condensation processes, including
those involving parallel and solid-phase synthetic proce-
dures.8,12,18,21–35
bered ring enhances the resistance of the ligands to oxidation and
hydrolysis, and the possibility of varying the nature of the substit-
uents at the nitrogen and phosphorus atoms allows control over
the steric and electronic parameters. Their modular nature also
allows a facile systematic variation of the configuration at the
P⁄- and C⁄-stereocenters in the phospholidine rings.48,49 The pres-
ence of a stereogenic donor phosphorus atom significantly pro-
motes successful asymmetric induction in the key step of the
⇑
Corresponding author. Tel.: +7 4912 280580; fax: +7 4912 281435.
E-mail addresses: k.gavrilov@rsu.edu.ru (K.N. Gavrilov), joz@mail.ru
(I.A. Zamilatskov).
http://dx.doi.org/10.1016/j.tetasy.2014.06.010
0957-4166/Ó 2014 Elsevier Ltd. All rights reserved.

K. N. Gavrilov et al. / Tetrahedron: Asymmetry 25 (2014) 1116–1121
Ph
1117
Ph
Ph
Ph
Ph
Ph
Ph
N
N
N
N
O
P
O
P
P
O
P
O
N
N
N
N
Ph
Ph
Ph
Ph
Ph
(S,S)- and (R,R)-LB
LA
R
R
N
N
N
N
N
O
P
P
O
O
P
P
O
N
N
N
R
R
R = Me, Bn
LC
(Sa,Sa)- and (Ra,Ra)-LD
Figure 1. P,P-Bidentate diamidophosphite ligands.
catalytic cycle. Since this atom is directly bonded to the central
metal atom (ion), it is positioned very close to the coordinated sub-
strate. This factor suppresses any potential inefficient secondary
transfer of chirality from the ligand framework and provides a
more efficient chiral environment at the site where the enantiose-
lection originates.4,19,49,50 Along these lines, we have reported on
an asymmetric Pd-catalyzed allylation and Rh-catalyzed hydroge-
nation and addition using some P⁄,P⁄-bidentate diamidophosphites
containing 1,3,2-diazaphospholidine rings.51–54
Herein we have dedicated our efforts to synthesizing novel
ligands containing remote diamidophosphite moieties and their
exploration in Pd-catalyzed asymmetric allylation and desymmetri-
zation reactions. The Pd-catalyzed allylic substitution is a powerful
and well-established synthetic tool, which is tolerant of various
functional groups in the substrate and which operates with a wide
range of C-, N-, O-, S-, and P-nucleophiles. As a consequence, Pd-cat-
alyzed allylic substitution is a versatile process that is widely used
in the total synthesis of useful enantiomerically pure natural and
unnatural compounds.2,5,50,55–61 This is a common benchmark test
for initial ligand screening and the enantiomeric excesses obtained
are the simplest scale for evaluating new chiral ligands.2,20,60 It
should be noted that the Pd-catalyzed enantioselective synthesis
of a quaternary carbon center is a formidable challenge.62 The
Pd-catalyzed desymmetrization of N,N0-ditosyl-meso-cyclopent-4-
ene-1,3-diol bis-carbamate has been successfully used as a key step
in the synthesis of mannostatin A and (ꢀ)-swainsonine.5,56
2. Results and discussion
As shown in Scheme 1, diamidophosphites 4 and 5 were synthe-
sized in one step from the suitable diols 2 or 3 and phosphorylating
reagent 1. The reactions were performed in the presence of excess
Et3N as a HCl scavenger in toluene. Ligands 4 and 5 were purified
by flash chromatography on Al2O3 or by crystallization and obtained
in reasonable yields as an orange oil and white solid, respectively.
The new stereoselectors could be prepared on a gram scale. They
can be stored under dry conditions at room temperature for at least
a few months with minimal degradation. Ligand 4 readily forms a
solvate with toluene. Therefore, lengthy high vacuum drying is
required for the preparation of analytically pure material. The ele-
mental analyses, 1H, 13C, and 31P NMR spectra and MALDI TOF/TOF
mass spectra, were consistent withthe expectation for these ligands.
Thus, during the phosphorylation, the exclusive formation of stereo-
specific diamidophosphites 4 and 5 with an (R)-configuration at the
P⁄-stereocentres occurred. The 31P NMR spectra of their solutions in
CDCl3 exhibited narrow singlets at dP 121.9 and 124.0, respectively.
The 13C NMR spectra of these compounds were characterized by
large spin–spin coupling constants 2JC(8),P (38.7 and 38.3 Hz, see Sec-
tion 4), which are indicative of the syn-orientation of the phosphorus
lone pair with respect to the C(8) atom. The pseudoequatorial exocy-
clic substituent at the phosphorus atom and the –(CH2)3– part of the
pyrrolidine fragment of the phosphabicyclic skeleton are in the anti-
arrangement (Fig. 2).46–48,51–54,63,64
N
Cl
4
P
2
N
5
6
8
7
1
O
O
OH
N
N
O
O
P
Fe
+
+
NH HN
O
OH
NH HN
OH
HO
2
3
Fe
4 Et3N, PhCH3
- 2 Et3N.HCl
O
N
O
O
N
P
P
P
N
N
N
N
5
4
Scheme 1. Synthesis of diamidophosphites 4 and 5.

1118
K. N. Gavrilov et al. / Tetrahedron: Asymmetry 25 (2014) 1116–1121
Table 3
H
Pd-catalyzed allylic amination of (E)-1,3-diphenylallyl acetate 6 with pyrrolidinea
(S)
..
8
N
N
P (R)
OAc
Ph
N
*
HN(CH2)4, cat
solvents
X
Ph
Ph
Ph
7c
6
Figure 2. Stereochemistry of the phosphabicyclic part in ligands 4 and 5 (X = exo-
cyclic substituent).
Entry
Ligand
L/Pd
Solvent
Conversion (%)
eeb (%)
1
2
3
4
5
6
7
8
4
4
4
4
5
5
5
5
1
2
1
2
1
2
1
2
CH2Cl2
CH2Cl2
THF
100
100
100
100
100
100
95
87 (R)
87 (R)
85 (R)
79 (R)
62 (R)
27 (R)
85 (R)
96 (R)
In order to explore the application of the new stereoinducers 4
and 5 in Pd-catalyzed asymmetric allylic substitutions, we evalu-
ated the interaction of (E)-1,3-diphenylallyl acetate 6 with various
nucleophiles. As stated above, compound 6 was chosen as a sub-
strate because this model process is very convenient for the direct
comparison of the efficiency of different stereoselectors. These
reactions were carried out at room temperature in the presence
of catalysts formed from [Pd(allyl)Cl]2 as a palladium source.
Results are summarized in Tables 1–3.
THF
CH2Cl2
CH2Cl2
THF
THF
85
a
All reactions were carried out with 2 mol % of [Pd(allyl)Cl]2 at room tempera-
ture for 48 h.
b
The conversion of substrate 6 and enantiomeric excess of 7c were determined
In a first set of experiments, we tested the new diamidophosph-
ites in the allylic sulfonylation of 6 with sodium para-toluene sulf-
inate as the S-nucleophile in THF as the solvent (Table 1). The
by HPLC (Daicel Chiralcel OD-H, C6H14/i-PrOH/HN(Et)2 = 200:1:0.1, 0.9 mL/min,
254 nm, t(R) = 5.0 min, t(S) = 6.1 min).
reaction product (R)-7a was obtained with good enantioselectivity
(up to 86% ee) when diamidophosphite 5 was employed as the chi-
ral auxiliary; the molar ratio L/Pd = 1 is undoubtedly preferable
(Table 1, entries 3 and 4). At the same time, ligand 4 afforded sul-
fone (S)-7a with a lower enantiomeric purity (up to 77% ee, Table 1,
entries 1 and 2), but with higher yields.
Table 1
Pd-catalyzed allylic sulfonylation of (E)-1,3-diphenylallyl acetate 6 with sodium para-
toluene sulfinatea
In the Pd-catalyzed allylic alkylation of 6 with dimethyl malon-
ate as the C-nucleophile, diamidophosphites 4 and 5 were found to
be the equally efficient stereoinducers, providing up to 92% and
94% ee, respectively (Table 2, entries 1 and 8). It should be noted
that in all cases, the catalytic systems based on novel diam-
idophosphites led to product 7b with an (S)-configuration. When
the reaction was carried out using 4 as the ligand, the best ee val-
ues were observed in CH2Cl2, the L/Pd molar ratio had no effect on
the enantioselectivity in this medium. Ligand 4 provided quantita-
tive conversions of 6 in both solvents at the molar ratio L/Pd = 1
(Table 2, entries 1–4). It is noteworthy that for diamidophosphite
5, the nature of the solvent did not have a significant effect on
the reaction rate or the asymmetric induction, while an increase
in the L/Pd molar ratio led to a slight increase in enantioselectivity
(Table 2, entries 5–8).
OAc
O
S
*
O
NaSO2pTol, cat
Ph
Ph
THF
Ph
Ph
6
7a
Entry
Ligand
L/Pd
Yield (%)
eeb (%)
1
2
3
4
4
4
5
5
1
2
1
2
70
87
42
35
23 (S)
77 (S)
86 (R)
61 (R)
a
All reactions were carried out with 2 mol % of [Pd(allyl)Cl]2 in THF at room
temperature for 48 h.
b
Enantiomeric excess of 7a was determined by HPLC (Daicel Chiralcel OD-H,
C6H14/i-PrOH = 4:1, 0.5 mL/min, 254 nm, t(R) = 16.3 min, t(S) = 18.5 min).
We also investigated novel stereoinducers in the enantioselec-
tive Pd-catalyzed allylic amination of 6 with pyrrolidine. With
diamidophosphite 4, quantitative conversion of 6 and good enanti-
oselectivities (79–87%) were achieved (Table 3, entries 1–4).
Ligand 5 demonstrated higher asymmetric induction (up to 96%
ee), but the nature of the solvent and the L/Pd molar ratio were
found to have a significant effect on the reaction rate and enanti-
oselectivity. In particular, the reaction in THF was more enantiose-
lective, while a higher conversion was achieved in CH2Cl2 (Table 3,
entries 5–8). As shown in Table 3, the resulting amination product
7c proved to have the same (R)-configuration in all cases.
In the next step, stereoselectors 4 and 5 were studied in the
Pd-catalyzed desymmetrization of N,N0-ditosyl-meso-cyclopent-
Table 2
Pd-catalyzed allylic alkylation of (E)-1,3-diphenylallyl acetate
6 with dimethyl
malonatea
MeO2C
CO2Me
Ph
OAc
Ph
CH2(CO2Me)2, cat
Ph
Ph
*
solvents
6
7b
Entry
Ligand
L/Pd
Solvent
Conversion (%)
eeb (%)
1
2
3
4
5
6
7
8
4
4
4
4
5
5
5
5
1
2
1
2
1
2
1
2
CH2Cl2
CH2Cl2
THF
100
62
100
78
96
92
92 (S)
91 (S)
87 (S)
73 (S)
88 (S)
93 (S)
88 (S)
94 (S)
4-ene-1,3-diol bis-carbamate
9 (Table 4). The reaction was
THF
performed in THF in the presence of [Pd2(dba)3]ꢁCHCl3 as the cata-
lytic precursor. Catalytic compositions based on ligand 4 showed
mediocre yields and enantioselectivity (up to 46% ee, Table 4,
entries 1 and 2) irrespective of the L/Pd molar ratio. Compound 5
produced significantly better chemical yields and asymmetric
induction (up to 70% ee, Table 4, entries 3 and 4). In this case the
molar ratio L/Pd = 1 was optimal.
CH2Cl2
CH2Cl2
THF
90
99
THF
a
All reactions were carried out with 2 mol % of [Pd(allyl)Cl]2 at room tempera-
ture for 48 h (BSA, KOAc).
b
The conversion of substrate 6 and enantiomeric excess of 7b were determined
Finally the Pd-catalyzed allylic alkylation of cinnamyl acetate 11
with ethyl 2-oxocyclohexane-1-carboxylate 12 (Table 5) was inves-
by HPLC (Daicel Chiralcel OD-H, C6H14/i-PrOH = 99:1, 0.3 mL/min, 254 nm,
t(R) = 28.0 min, t(S) = 29.3 min).

K. N. Gavrilov et al. / Tetrahedron: Asymmetry 25 (2014) 1116–1121
1119
Table 4
3. Conclusion
Pd-catalyzed desymmetrization of N,N0-ditosyl-meso-cyclopent-4-ene-1,3-diol bis-
carbamate 9a
In summary, the following conclusions can be drawn: (i) we
have designed and synthesized some novel readily accessible phos-
phorus-containing stereoinducers. These ligands have the follow-
ing key advantages: the diamidophosphite nature of their remote
phosphite-type moieties, the P⁄-chirogenic phosphorus atoms
and the 1,3,2-diazaphospholidine rings with balanced electronic
characteristics; (ii) these ligands demonstrate moderate to high
levels of asymmetric induction in Pd-catalyzed enantioselective
allylations of (E)-1,3-diphenylallyl acetate, desymmetrizations of
N,N0-ditosyl-meso-cyclopent-4-ene-1,3-diol bis-carbamate and in
the asymmetric construction of quaternary carbon stereocenters;
(iii) overall, diamidophosphite 5 with an oxalamide backbone is a
more efficient stereoselector than its ferrocene-based analogue 4.
As a result, studies aimed at estimating the potential of the chiral
phosphite-type ligands based on bis(aminoalcohol)oxalamides in
asymmetric transition-metal catalysis are currently in progress.
Ts
Ts
HN
NH
O
O
HO
OH
TsNCO
THF
O
O
8
9
Ts
N
Ts
H
H
H
N
cat
O
O
+
THF, Et3N
O
O
H
- CO2, - TsNH2
(R,S)-10
(S,R)-10
Entry
Ligand
L/Pd
Yield (%)
eeb,c (%)
1
2
3
4
4
4
5
5
1
2
1
2
49
52
87
90
45 (II)
46 (II)
70 (II)
56 (II)
4. Experimental
4.1. General
a
All reactions were carried out with 5 mol % of [Pd2(dba)3]ꢁCHCl3 in THF at 35 °C
for 24 h.
b
The enantiomeric excess of 10 was determined by HPLC (Kromasil 5-CelluCoat,
31P, 13C and 1H NMR spectra were recorded on a Bruker AMX
400 (162.0 MHz for 31P, 100.6 MHz for 13C and 400.13 MHz for
1H) or a Bruker Avance III 600 (242.9 MHz for 31P, 150.9 MHz for
13C and 600.13 MHz for 1H) instrument. The complete assignment
of all of the resonances in the 1H and 13C NMR spectra was
achieved by the use of APT, DEPT, COSY, HSQC, and NOESY tech-
niques and published data.46,47,63 Chemical shifts (ppm) are given
C6H14/i-PrOH = 9:1, 2 mL/min, 219 nm, t(I) = 13 min, t(II) = 17 min).
The absolute configuration of product 10 was not assigned.
c
tigated; this is a reaction where a quaternary stereogenic center is
generated in the nucleophile. The catalysts were generated from
the complex [Pd(allyl)Cl]2 and the corresponding ligand in CH2Cl2
and toluene as the medium. Enantioselection occurred when the
relative to Me4Si (1H and 13C) and 85% H3PO4 31P NMR). Data
(
p
-allyl-ligand complex differentiates between the prochiral faces
of the approaching reagent. In this mechanism, where the nucleo-
phile attacks on the face of the -allyl system opposite to that of
are represented as follows: chemical shift, multiplicity (br = broad,
s = singlet, d = doublet, t = triplet, m = multiplet); coupling con-
stants nJ in Hertz (Hz) integration, ‘n’ values are reported in the
case of their unambiguous determination. Mass spectra were
recorded on a Bruker Daltonics Ultraflex spectrometer (MALDI
TOF/TOF). Optical rotations were measured on an Atago AP-300
polarimeter. HPLC analyses were performed on Agilent 1100 and
Stayer instruments using ChiralcelÒ and KromasilÒ columns. Ele-
mental analyses were performed on a CHN-microanalyzer Carlo
Erba EA1108 CHNS-O.
p
the chirality inducing metal–ligand complex, the generation of
asymmetry appears to be relatively challenging.5 Ligand 5 is a rela-
tively good stereoselector, but 4 provided much lower asymmetric
induction: quaternary-substituted product (S)-13 was obtained in
80% and 37% ee, respectively (Table 5, entries 8 and 4). For diam-
idophosphite 5 toluene is the solvent of choice and L/Pd = 1:2 is
the preferred molar ratio (Table 5, entries 5–10).
All manipulations were carried out under a dry argon atmo-
sphere in flame-dried glassware and in freshly dried and distilled
solvents. For example, toluene and tetrahydrofuran were freshly
distilled from sodium benzophenone ketyl before use; dichloro-
methane was distilled from NaH. Triethylamine and pyrrolidine
were distilled over KOH and then over a small amount of LiAlH4
before use. Thin-layer chromatography was performed on E. Merck
pre-coated silica gel 60 F254 and Macherey-Nagel Alugram Alox N/
UV254 plates. Column chromatography was performed using silica
gel MN Kieselgel 60 (230–400 mesh) and MN-Aluminum oxide,
basic, Brockmann Activity 1. Phosphorylating reagent (5S)-2-
chloro-3-phenyl-1,3-diaza-2-phosphabicyclo[3.3.0]octane 1, 1,
10-bis(hydroxymethyl)ferrocene 2 and N1,N2-bis((S)-1-hydroxy-3,
3-dimethylbutan-2-yl)oxalamide 3 were prepared analogously to
known procedures.47,65–69 The [Pd(allyl)Cl]2, starting substrate 6,
and [Pd2(dba)3]ꢁCHCl3 were obtained as published.70,71 Pd-catalyzed
reactions: allylic sulfonylation of (E)-1,3-diphenylallyl acetate 6
with sodium para-toluene sulfinate, alkylation with dimethyl mal-
onate, amination with pyrrolidine; desymmetrization of N,N0-dito-
Table 5
Pd-catalyzed allylic alkylation of cinnamyl acetate 11 with ethyl 2-oxocyclohexane-1-
carboxylate 12a
EtO
O
O
O
Ph
OEt
cat
*
Ph
OAc
+
O
solvents
11
12
13
Entry
Ligand
L/Pd
Solvent
Conversion (%)
eeb (%)
1
2
3
4
5
6
7
8
9
4
4
4
4
5
5
5
5
5
5
1
2
1
2
CH2Cl2
CH2Cl2
PhCH3
PhCH3
CH2Cl2
CH2Cl2
CH2Cl2
PhCH3
PhCH3
PhCH3
77
84
82
63
99
28 (S)
25 (S)
33 (S)
37 (S)
58 (S)
57 (S)
16 (S)
80 (S)
73 (S)
21 (S)
1:2
1
100
95
2
1:2
1
83
85
syl-meso-cyclopent-4-ene-1,3-diol biscarbamate
9 and allylic
10
2
100
alkylation of cinnamyl acetate 11 with ethyl 2-oxocyclohexane-1-
carboxylate 12 were performed according to the literature
procedures.47,72,54,62
a
All reactions were carried out with 2 mol % of [Pd(allyl)Cl]2 at room tempera-
ture for 48 h (BSA, Zn(OAc)2).
b
The conversion of substrate 11 and enantiomeric excess of 13 were determined
Sodium para-toluene sulfinate, dimethyl malonate, BSA
(N,O-bis(trimethylsilyl)acetamide), meso-cyclopent-4-ene-1,3-diol
by HPLC (Kromasil 5-CelluCoat, C6H14/i-PrOH = 95:5, 0.4 mL/min, 254 nm,
t(R) = 14.3 min, t(S) = 16.4 min).

1120
K. N. Gavrilov et al. / Tetrahedron: Asymmetry 25 (2014) 1116–1121
8, tosyl isocyanate, cinnamyl acetate 11 and ethyl 2-oxocyclohex-
ane-1-carboxylate 12 were purchased from Aldrich and Acros
Organics and used without further purification.
(0.05 mL, 0.25 mmol) was added and the solution stirred for
15 min, then sodium para-toluene sulfinate (0.089 g, 0.5 mmol)
was added. The reaction mixture was stirred for a further 48 h,
quenched with brine (3 mL) and extracted with THF (3 ꢃ 2 mL).
The organic layer was washed with brine (2 ꢃ 2 mL) and dried over
MgSO4. The solvent was evaporated at reduced pressure (40 Torr).
Crystallization of the residue from EtOH, followed by desiccation in
a vacuum (10 Torr, 12 h), gave (E)-1,3-diphenyl-3-tosylprop-1-ene
7a as white crystals.73,74 The enantiomeric excess of 7a was deter-
mined by HPLC (Daicel Chiralcel OD-H column, C6H14/i-PrOH = 4:1,
0.5 mL/min, 254 nm, t(R) = 16.3 min, t(S) = 18.5 min).
4.2. General procedure for the preparation of ligands 4 and 5
To a vigorously stirred solution of phosphorylating reagent 1
(0.49 g, 2 mmol) and Et3N (0.56 mL, 4 mmol) in toluene (20 ml)
was added the relevant diol 2 or 3 (1 mmol) in one portion. The
mixture obtained was stirred for 24 h at 20 °C, then heated to
45 °C, and stirred at this temperature for 1 h, and then cooled to
20 °C. The resulting suspension was filtered through a short plug
of aluminum oxide, the column was washed twice with toluene
(5 mL), and the solvent was evaporated under reduced pressure
(40 Torr). The residue was dried in vacuo (1 Torr) for 1 h. Products
4 and 5 were purified by flash chromatography on aluminum oxide
(toluene) and by crystallization from heptane, respectively.
4.3.2. The Pd-catalyzed allylic alkylation of (E)-1,3-diphenylallyl
acetate 6 with dimethyl malonate
A solution of [Pd(allyl)Cl]2 (0.0019 g, 0.005 mmol) and the
appropriate ligand (0.01 mmol or 0.02 mmol) in the appropriate
solvent (1.5 mL) was stirred for 40 min. Next, (E)-1,3-diphenylallyl
acetate (0.05 mL, 0.25 mmol) was added and the solution stirred
for 15 min. after which dimethyl malonate (0.05 mL, 0.44 mmol),
BSA (0.11 mL, 0.44 mmol) and potassium acetate (0.002 g) were
added. The reaction mixture was then stirred for 48 h, diluted with
CH2Cl2 or THF (2 mL) and filtered through a thin layer of silica gel.
The filtrate was evaporated at reduced pressure (40 Torr) and dried
in vacuo (10 Torr, 12 h) to afford a residue containing (E)-dimethyl
2-(1,3-diphenylallyl)malonate 7b.75,76 In order to evaluate the ee
and conversion, the residue obtained was dissolved in an appropri-
ate eluent mixture (8 mL) and a sample was taken for HPLC analy-
sis (Daicel Chiralcel OD-H column, C6H14/i-PrOH = 99:1, 0.3 mL/
min, 254 nm, t(R) = 28.0 min, t(S) = 29.3 min).
4.2.1. 1,10-Bis[((2R,5S)-3-phenyl-1,3-diaza-2-phosphabicyclo
[3.3.0]octyloxy)methyl]ferrocene 4
Orange viscous oil (0.45 g, yield 68%). [
a
]
D
25 = ꢀ284.8 (c 1.0,
CHCl3). 1H NMR (400.13 MHz, CDCl3, 26 °C): d = 1.63–1.70 (m, 2H,
C(6)H2), 1.74–1.81 (m, 2H, C(7)H2), 1.83–1.91 (m, 2H, C(7)H2),
2.02–2.11 (m, 2H, C(6)H2), 3.15–3.24 (m, 4H, C(4)H2 and C(8)H2),
3.55–3.63 (m, 2H, C(8)H2), 3.76–3.80 (m, 2H, C(4)H2), 3.98–4.0
(m, 2H, CHFc), 4.01–4.03 (m, 2H, CHFc), 4.04–4.06 (m, 2H, CHFc),
4.10–4.12 (m, 2H, CHFc), 4.15–4.22 (m, 2H, C(5)H), 4.30 (dd,
J = 11.3 Hz, J = 6.0 Hz, 2H, CH2O), 4.49 (dd, J = 11.4 Hz, J = 6.5 Hz,
2H, CH2O), 6.85 (t, 3J = 7.4 Hz, 2H, CHPh), 7.04 (br d, 3J ꢂ 7.8 Hz,
4H, CHPh), 7.24 (t, 3J = 7.6 Hz, 4H, CHPh). 13C NMR (100.6 MHz,
CDCl3, 25 °C): d = 26.1 (d, 3J = 3.5 Hz, C(7)), 31.9 (s, C(6)), 48.7 (d,
2J = 38.7 Hz, C(8)), 54.9 (d, 2J = 6.5 Hz, C(4)), 60.1 (d, 2J = 3.1 Hz,
CH2O), 63.1 (d, 2J = 8.8 Hz, C(5)), 68.6 (s, CHFc), 68.7 (s, CHFc), 69.1
(s, CHFc), 69.2 (s, CHFc), 85.0 (s, CFc), 114.8 (d, 3J = 11.5 Hz, CHPh),
118.7 (s, CHPh), 129.0 (s, CHPh), 145.7 (d, 2J = 15.7 Hz, CPh). MS
(MALDI TOF/TOF): m/z (%) = 677 (15) [M+Na]+, 177 (100)
[C11H16N2+H]+. Anal. Calcd for C34H40FeN4O2P2: C, 62.39; H, 6.16;
N, 8.56. Found: C, 62.60; H, 6.22; N, 8.21.
4.3.3. The Pd-catalyzed allylic amination of (E)-1,3-diphenylallyl
acetate 6 with pyrrolidine
A solution of [Pd(allyl)Cl]2 (0.0019 g, 0.005 mmol) and the appro-
priate ligand (0.01 mmol or 0.02 mmol) in the appropriate solvent
(1.5 mL) was stirred for 40 min. Next, (E)-1,3-diphenylallyl acetate
(0.05 mL, 0.25 mmol) was added and the solution stirred for
15 min, after which freshly distilled pyrrolidine (0.06 mL, 0.75 mmol)
was added. The reaction mixture was stirred for 48 h, diluted with
CH2Cl2 or THF (2 mL) and filtered through a thin layer of silica gel.
The filtrate was evaporated at reduced pressure (40 Torr) and dried
in vacuo (10 Torr, 12 h) to afford a residue containing (E)-1-(1,3-
diphenylallyl)pyrrolidine 7c.77,78 In order to evaluate the ee and con-
version, the residue obtained was dissolved in an appropriate eluent
mixture (8 mL) and a sample was taken for HPLC analysis (Daicel Chi-
ralcel OD-H column, C6H14/i-PrOH/HN(Et)2 = 200:1:0.1, 0.9 mL/min,
254 nm, t(R) = 5.0 min, t(S) = 6.1 min).
4.2.2. N1,N2-Bis[(S)-1-((2R,5S)-3-phenyl-1,3-diaza-2-phospha-
bicyclo[3.3.0]octyloxy)-3,3-dimethylbutan-2-yl]oxalamide 5
White powder (0.53 g, yield 76%). [a]
25 = +208.5 (c 1.0, CHCl3).
D
1H NMR (400.13 MHz, CDCl3, 27 °C): d = 0.93 (s, 18H, CH3), 1.59–
1.66 (m, 2H, C(6)H2), 1.68–1.79 (m, 2H, C(7)H2), 1.82–1.90 (m,
2H, C(7)H2), 2.03–2.11 (m, 2H, C(6)H2), 3.15–3.24 (m, 4H, C(4)H2
and C(8)H2), 3.49–3.57 (m, 2H, C(8)H2), 3.63–3.71 (m, 2H, CH2O),
3.74 (t, J = 7.8 Hz, 2H, C(4)H2), 3.78–3.85 (m, 4H, CH2O and CHN),
4.11–4.18 (m, 2H, C(5)H), 6.84 (t, 3J = 7.4 Hz, 2H, CHPh), 7.01 (br
d, 3J ꢂ 8.1 Hz, 4H, CHPh), 7.24 (t, 3J = 8.0 Hz, 4H, CHPh), 7.61 (br d,
3J ꢂ 9.8 Hz, 2H, NH). 13C NMR (150.9 MHz, CDCl3, 25 °C): d = 26.2
(d, 3J = 3.8 Hz, C(7)), 26.9 (s, CH3), 32.1 (s, C(6)), 34.3 (s, C), 48.6
(d, 2J = 38.3 Hz, C(8)), 54.9 (d, 2J = 6.9 Hz, C(4)), 57.8 (d,
3J = 2.3 Hz, CHN), 61.2 (d, 2J = 4.1 Hz, CH2O), 63.3 (d, 2J = 8.8 Hz,
C(5)), 114.8 (d, 3J = 11.6 Hz, CHPh), 119.0 (s, CHPh), 129.1 (s, CHPh),
145.5 (d, 2J = 15.8 Hz, CPh), 159.8 (s, CO). MS (MALDI TOF/TOF):
m/z (%) = 719 (10) [M+Na]+, 177 (100) [C11H16N2+H]+. Anal. Calcd
for C36H54N6O4P2: C, 62.05; H, 7.81; N, 12.06. Found: C, 62.31; H,
8.02; N, 12.14.
4.3.4. The Pd-catalyzed desymmetrization of N,N0-ditosyl-meso-
cyclopent-4-ene-1,3-diol biscarbamate 9
A solution of [Pd2(dba)3]ꢁCHCl3 (0.005 g, 0.005 mmol) and the
appropriate ligand (0.01 mmol or 0.02 mmol) in THF (1 mL) was
stirred for 40 min. The resulting solution was brought to the
35 °C and a solution of N,N0-ditosyl-meso-cyclopent-4-ene-1,3-diol
biscarbamate 9 and Et3N (14 lL, 0.099 mmol) in THF (0.5 mL) was
added [compound 9 was prepared in situ as follows: to a solution
of the meso-cyclopent-4-ene-1,3-diol 8 (0.01 g, 0.099 mmol) in THF
(0.5 mL), tosyl isocyanate (35 lL, 0.232 mmol) was added; the mix-
ture was stirred at room temperature for 15 min, heated to 55 °C
for 1 h and cooled down to room temperature]. The reaction
mixture was then stirred for 24 h. The solvent was removed at
reduced pressure (40 Torr) and the residue was purified by flash
chromatography on a short pad of silica gel (EtOAc/hexane, 1:4)
and dried in vacuo (1 Torr) for 2 h to give the desired product 10
as a slightly brown solid.79 The enantiomeric excess of 10 was
determined by HPLC (Kromasil 5-CelluCoat column, C6H14/i-
PrOH = 9:1, 2 mL/min, 219 nm, t(I) = 13 min, t(II) = 17 min).
4.3. Catalytic reactions
4.3.1. The Pd-catalyzed allylic sulfonylation of (E)-1,3-diphenyl
allyl acetate 6 with sodium para-toluene sulfinate
A solution of [Pd(allyl)Cl]2 (0.0019 g, 0.005 mmol) and the
appropriate ligand (0.01 mmol or 0.02 mmol) in THF (1.5 mL)
was stirred for 40 min. Next, (E)-1,3-diphenylallyl acetate

K. N. Gavrilov et al. / Tetrahedron: Asymmetry 25 (2014) 1116–1121
1121
31. Mata, Y.; Pamies, O.; Dieguez, M. Chem. Eur. J. 2007, 13, 3296–3304.
32. Swennenhuis, B. H. G.; Chen, R.; van Leeuwen, P. W. N. M.; de Vries, J. G.;
Kamer, P. C. J. Org. Lett. 2008, 10, 989–992.
4.3.5. The Pd-catalyzed allylic alkylation of cinnamyl acetate 11
with ethyl 2-oxocyclohexane-1-carboxylate 12
A solution of [Pd(allyl)Cl]2 (0.0019 g, 0.005 mmol) and the appro-
priate ligand (0.01 mmol or 0.02 mmol) in the appropriate solvent
(1.5 mL) was stirred for 40 min. Next, cinnamyl acetate (0.04 mL,
0.25 mmol) was added and the solution stirred for 15 min. after
which ethyl 2-oxocyclohexane-1-carboxylate (0.06 mL, 0.375
mmol), BSA (0.25 mL, 1 mmol), and zinc acetate (0.005 g) were
added. The reaction mixture was stirred for 48 h, diluted with
CH2Cl2 or toluene (2 mL), and filtered through a thin layer of silica
gel. The filtrate was evaporated at reduced pressure (40 Torr) and
dried in vacuo (10 Torr, 12 h) to afford a residue containing ethyl
1-cinnamyl-2-oxocyclohexanecarboxylate 13.62 In order to evaluate
the ee and conversion, the residue obtained was dissolved in an
appropriate eluent mixture (8 mL) and a sample was taken for HPLC
analysis (Kromasil 5-CelluCoat, C6H14/i-PrOH = 95:5, 0.4 mL/min,
254 nm, t(R) = 14.3 min, t(S) = 16.4 min).
33. Qiao, X.-C.; Zhu, S.-F.; Zhou, Q.-L. Tetrahedron: Asymmetry 2009, 20, 1254–1261.
34. Gavrilov, K. N.; Zheglov, S. V.; Gavrilova, M. N.; Novikov, I. M.; Maksimova, M.
G.; Groshkin, N. N.; Rastorguev, E. A.; Davankov, V. A. Tetrahedron 2012, 68,
1581–1589.
35. Gavrilov, K. N.; Chuchelkin, I. V.; Zheglov, S. V.; Shiryaev, A. A.; Potapova, O. V.;
Novikov, I. M.; Rastorguev, E. A.; Petrovskii, P. V.; Davankov, V. A. Russ. Chem.
Bull., Int. Ed. 2012, 61, 1925–1932.
36. Hilgraf, R.; Pfaltz, A. Synlett 1999, 1814–1816.
37. Delapierre, G.; Brunel, J. M.; Constantieux, T.; Buono, G. Tetrahedron:
Asymmetry 2001, 12, 1345–1352.
38. Reetz, M. T.; Oka, H.; Goddard, R. Synthesis 2003, 12, 1809–1814.
39. Hilgraf, R.; Pfaltz, A. Adv. Synth. Catal. 2005, 347, 61–77.
40. Schonleber, M.; Hilgraf, R.; Pfaltz, A. Adv. Synth. Catal. 2008, 350, 2033–2038.
41. Markert, C.; Rosel, P.; Pfaltz, A. J. Am. Chem. Soc. 2008, 130, 3234–3235.
42. Trost, B. M.; Lam, T. M. J. Am. Chem. Soc. 2012, 134, 11319–11321.
43. Trost, B. M.; Lam, T. M.; Herbage, M. A. J. Am. Chem. Soc. 2013, 135, 2459–2461.
44. Trost, B. M.; Maruniak, A. Angew. Chem., Int. Ed. 2013, 52, 6262–6264.
45. Bravo, M. J.; Ceder, R. M.; Muller, G.; Rocamora, M. Organometallics 2013, 32,
2632–2642.
46. Brunel, J. M.; Constantieux, T.; Buono, G. J. Org. Chem. 1999, 64, 8940–8942.
47. Tsarev, V. N.; Lyubimov, S. E.; Shiryaev, A. A.; Zheglov, S. V.; Bondarev, O. G.;
Davankov, V. A.; Kabro, A. A.; Moiseev, S. K.; Kalinin, V. N.; Gavrilov, K. N. Eur. J.
Org. Chem. 2004, 2214–2222.
Acknowledgments
48. Buono, G.; Toselli, N.; Martin, D. In Phosphorus Ligands in Asymmetric Catalysis;
Börner, A., Ed.; Wiley-VCH: Weinheim, 2008; Vol. II, pp 529–546.
49. Gavrilov, K. N.; Shiryaev, A. A.; Zheglov, S. V.; Potapova, O. V.; Chuchelkin, I. V.;
Novikov, I. M.; Rastorguev, E. A.; Davankov, V. A. Tetrahedron: Asymmetry 2013,
24, 409–417.
50. Crepy, K. V. L.; Imamoto, T. Adv. Synth. Catal. 2003, 345, 79–101.
51. Gavrilov, K. N.; Zheglov, S. V.; Vologzhanin, P. A.; Maksimovaa, M. G.; Safronov,
A. S.; Lyubimov, S. E.; Davankov, V. A.; Schaffner, B.; Borner, A. Tetrahedron Lett.
2008, 49, 3120–3123.
The reported study was partially supported by Russion Founda-
tion for Basic Research, research Project No. 14-03-00396-a and
Ministry of Education and Science of the Russian Federation,
research Project No. 2014/378.
References
52. Gavrilov, K. N.; Zheglov, S. V.; Benetsky, E. B.; Safronov, A. S.; Rastorguev, E. A.;
Groshkin, N. N.; Davankov, V. A.; Schaffner, B.; Borner, A. Tetrahedron:
Asymmetry 2009, 20, 2490–2496.
1. Ayora, I.; Ceder, R. M.; Espinel, M.; Muller, G.; Rocamora, M.; Serrano, M.
Organometallics 2011, 30, 115–128.
2. Fernandez-Perez, H.; Etayo, P.; Panossian, A.; Vidal-Ferran, A. Chem. Rev. 2011,
111, 2119–2176.
3. Brown, J. M. In Comprehensive Asymmetric Catalysis; Jacobsen, E. N., Pfaltz, A.,
Yamamoto, H., Eds.; Springer: Berlin, 1999; Vol. I, pp 121–182.
4. Ohkuma, T.; Kitamura, M.; Noyori, R. In Catalytic Asymmetric Synthesis; Ojima,
I., Ed.; Wiley-VCH: New York, 2000; pp 1–110.
5. Trost, B. M.; Crawley, M. L. Chem. Rev. 2003, 103, 2921–2943.
6. Blaser, H.-U.; Schmidt, E. Asymmetric Catalysis on Industrial Scale; Wiley-VCH:
Weinheim, 2004.
7. Burk, M. J. Acc. Chem. Res. 2000, 33, 363–372.
8. van Leeuwen, P. W. N. M.; Kamer, P. C. J.; Claver, C.; Pamies, O.; Dieguez, M.
Chem. Rev. 2011, 111, 2077–2118.
9. Beletskaya, I. P.; Kustov, L. M. Russ. Chem. Rev. 2010, 79, 441–461.
10. Coll, M.; Ahlford, K.; Pamies, O.; Adolfsson, H.; Dieguez, M. Adv. Synth. Catal.
2012, 354, 415–427.
11. Hammerer, T.; Weisgerber, L.; Schenk, S.; Stelzer, O.; Englert, U.; Leitner, W.;
Francio, G. Tetrahedron: Asymmetry 2012, 23, 53–59.
12. Claver, C.; Pamies, O.; Dieguez, M. In Phosphorus Ligands in Asymmetric
Catalysis; Börner, A., Ed.; Wiley-VCH: Weinheim, 2008; Vol. II, pp 507–528.
13. Falciola, C. A.; Alexakis, A. Eur. J. Org. Chem. 2008, 3765–3780.
14. Hargaden, G. C.; Guiry, P. J. Chem. Rev. 2009, 109, 2505–2550.
15. Bini, L.; Muller, C.; Vogt, D. Chem. Commun. 2010, 8325–8334.
16. Tolstikov, A. G.; Khlebnikova, T. B.; Tolstikova, O. V.; Tolstikov, G. A. Russ. Chem.
Rev. 2003, 72, 803–822.
17. Dieguez, M.; Ruiz, A.; Claver, C. Dalton Trans. 2003, 2957–2963.
18. Teichert, J. F.; Feringa, B. L. Angew. Chem., Int. Ed. 2010, 49, 2486–2528.
19. Zhou, Q.-L. Privileged Chiral Ligands and Catalysts; Wiley-VCH: Weinheim, 2011.
20. Nemoto, T.; Hamada, Y. Tetrahedron 2011, 67, 667–687.
21. Ansell, J.; Wills, M. Chem. Soc. Rev. 2002, 31, 259–268.
22. Alexakis, A.; Benhaim, C. Eur. J. Org. Chem. 2002, 19, 3221–3236.
23. Molt, O.; Schrader, T. Synthesis 2002, 2633–2670.
24. Reetz, M. T.; Mehler, G.; Meiswinkel, A.; Sell, T. Tetrahedron Lett. 2002, 43,
7941–7943.
25. Dieguez, M.; Pamies, O.; Claver, C. Tetrahedron: Asymmetry 2004, 15, 2113–
2122.
26. Gavrilov, K. N.; Bondarev, O. G.; Polosukhin, A. I. Russ. Chem. Rev. 2004, 73, 671–
699.
27. Jerphagnon, T.; Renaud, J.-L.; Bruneau, C. Tetrahedron: Asymmetry 2004, 15,
2101–2111.
53. Gavrilov, K. N.; Zheglov, S. V.; Rastorguev, E. A.; Groshkin, N. N.; Maksimovaa,
M. G.; Benetsky, E. B.; Davankov, V. A.; Reetz, M. T. Adv. Synth. Catal. 2010, 352,
2599–2610.
54. Gavrilov, K. N.; Zheglov, S. V.; Shiryaev, A. A.; Groshkin, N. N.; Rastorguev, E. A.;
Benetskiy, E. B.; Davankov, V. A. Tetrahedron Lett. 2011, 52, 964–968.
55. McCarthy, M.; Guiry, P. J. Tetrahedron 2001, 57, 3809–3844.
56. Graening, T.; Schmalz, H.-G. Angew. Chem., Int. Ed. 2003, 42, 2580–2584.
57. Chapsal, B. D.; Ojima, I. Org. Lett. 2006, 8, 1395–1398.
58. Lu, Z.; Ma, S. Angew. Chem., Int. Ed. 2008, 47, 258–297.
59. Dieguez, M.; Pamies, O. Acc. Chem. Res. 2010, 43, 312–322.
60. Lam, F. L.; Kwong, F. Y.; Chan, A. S. C. Chem. Commun. 2010, 4649–4667.
61. Lafrance, D.; Bowles, P.; Leeman, K.; Rafka, R. Org. Lett. 2011, 13, 2322–2325.
62. Nemoto, T.; Matsumoto, T.; Masuda, T.; Hitomi, T.; Hatano, K.; Hamada, Y. J.
Am. Chem. Soc. 2004, 126, 3690–3691.
63. Barta, K.; Hölscher, M.; Franciò, G.; Leitner, W. Eur. J. Org. Chem. 2009, 4102–
4116.
64. Kimura, M.; Uozumi, Y. J. Org. Chem. 2007, 72, 707–714.
65. Carlstrom, A.-S.; Frejd, T. J. Org. Chem. 1990, 55, 4175–4180.
66. Muller, D.; Umbricht, G.; Weber, B.; Pfaltz, A. Helv. Chim. Acta 1991, 74, 232–
240.
67. Denmark, S. E.; Stavenger, R. A.; Faucher, A.-M.; Edwards, J. P. J. Org. Chem.
1997, 62, 3375–3389.
68. Gavrilov, K. N.; Polosukhin, A. I.; Bondarev, O. G.; Lyubimov, S. E.; Lyssenko, K.
A.; Petrovskii, P. V.; Davankov, V. A. J. Mol. Catal. A: Chem. 2003, 196, 39–53.
69. Sunkur, M.; Baris, D.; Hosgoren, H.; Togrul, M. J. Org. Chem. 2008, 73, 2570–
2575.
70. Auburn, P. R.; Mackenzie, P. B.; Bosnich, B. J. Am. Chem. Soc. 1985, 107, 2033–
2046.
71. Ukai, T.; Kawazura, H.; Ishii, Y.; Bonnet, J. J.; Ibers, J. A. J. Organomet. Chem.
1974, 65, 253–266.
72. Gavrilov, K. N.; Lyubimov, S. E.; Zheglov, S. V.; Benetsky, E. B.; Davankov, V. A. J.
Mol. Catal. A: Chem. 2005, 231, 255–260.
73. Seebach, D.; Devaquet, E.; Ernst, A.; Hayakawa, M.; Kuhnle, F. N. M.; Schweizer,
W. B.; Weber, B. Helv. Chim. Acta 1995, 78, 1636–1650.
74. Wolfe, J. A.; Hitchcock, S. R. Tetrahedron: Asymmetry 2010, 21, 2690–2695.
75. Breeden, S.; Wills, M. J. Org. Chem. 1999, 64, 9735–9738.
76. Mei, L.-Y.; Yuan, Z.-L.; Shi, M. Organometallics 2011, 30, 6466–6475.
77. Smyth, D.; Tye, H.; Eldred, C.; Alcock, N. W.; Wills, M. J. Chem. Soc., Perkin Trans.
1 2001, 2840–2849.
28. Reetz, M. T.; Mehler, G.; Bondarev, O. Chem. Commun. 2006, 2292–2294.
29. deVries, J. G.; Lefort, L. Chem. Eur. J. 2006, 12, 4722–4734.
30. Jagt, R. B. C.; Toullec, P. Y.; Geerdink, D.; de Vries, J. G.; Feringa, B. L.; Minnaard,
A. J. Angew. Chem., Int. Ed. 2006, 45, 2789–2791.
78. Chen, J.; Lang, F.; Li, D.; Cun, L.; Zhu, J.; Deng, J.; Liao, J. Tetrahedron: Asymmetry
2009, 20, 1953–1956.
79. Trost, B. M.; Van Vranken, D. L.; Binge1, C. J. Am. Chem. Soc. 1992, 114, 9327–
9343.