Iron-Catalyzed Asymmetric Nitro-Mannich Reaction

Article abstract of DOI:10.1021/acs.joc.7b01786

The first enantioselective addition of nitroalkanes to imines (nitro-Mannich reaction), mediated by an iron(II) catalyst assembled by a hindered hydroxyethyl-pybox ligand, is described. This valuable carbon-carbon bond-forming reaction proceeds smoothly at room temperature to afford enantioenriched β-nitro amines in good yields and high enantioselectivity, up to 98% with unprecedentedly low iron catalyst loading (5 mol %).

Full text of DOI:10.1021/acs.joc.7b01786

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Note
Iron-Catalyzed Asymmetric Nitro-Mannich Reaction
Agata Dudek, and Jacek Mlynarski
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The Journal of Organic Chemistry
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Iron-Catalyzed Asymmetric Nitro-Mannich Reaction
Agata Dudek and Jacek Mlynarski*a,b
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a Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Krakow, Poland
b Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, Warsaw, Poland
KEYWORDS iron catalyst, imines, asymmetric catalysis, nitro-Mannich reaction, amines
ABSTRACT: The first enantioselective addition of nitroalkanes to imines (nitro-Mannich reaction), mediated by an
iron(II) catalyst assembled by a hindered hydroxyethyl-pybox (he-pybox) ligand, is described. This valuable carbon-
carbon bond forming reaction proceeds smoothly at room temperature affording enantioenriched β-nitro amines in good
yields and high enantioselectivity, up to 98% with unprecedentedly low iron catalyst loading (5 mol%).
and Jacobsen9 featuring however some important re-
Catalytic asymmetric nitro-Mannich (or aza-Henry) reac-
strictions regarding the substrate scope.
tion involving nucleophilic addition of nitroalkanes to
imines and related compounds is one of the most funda-
mental reaction for the synthesis of optically active organ-
ic compounds bearing two vicinal nitrogenated function-
alities.1 The resulting β-nitro amines are versatile building
blocks for the transformation into biologically active
compounds such as diamines, β-amino alcohols and α-
amino acids.
The first example of catalytic enantioselective nitro-
Mannich reactions, between N-phosphinoyl imines and
nitromethane were reported by Shibasaki in 1999.2 The
use of binaphthoxide(binol)-based heterobimetallic com-
plexes of ytterbium and aluminum designed by Shibasaki
opened the way for broad application of hetero- and ho-
mobimetalic catalysts3 for the activation of various types
of imine-substrates. Example of an addition to N-Boc-
imines promoted by Trost catalyst (C2)3 is presented at
Scheme 1. Alternatively, Jørgensen and co-workers used
copper bis(oxazoline) complexes to catalyze the reaction
of silyl nitronates with α-imino esters (Scheme 1).4
In 2006, Palomo showed that cooperative activation of
nitro compounds and N-Boc aryl imines towards the aza-
Henry reaction can be effected by combination of zinc
triflate (30 mol%) coordinated by optically pure N-
methylephedrine (45 mol%) and a tertiary amine (30
mol%).5 This finding oriented new research towards es-
Scheme 1. Examples of nitro-Mannich reaction promoted
tablishing the validity of this activation model in related
reactions but also toward the application of more sustain-
able reaction conditions and catalysts for this reaction.
However, all above mentioned examples require a high
catalyst (20 or even 30 mol%) and chiral ligand (20-45%)
loading, while the substrate scope was limited with re-
gards to one or both of the reaction partners. The alterna-
tive organocatalytic asymmetric nitro-Mannich reactions
have been also reported by Johnston,6 Takemoto,7 Zhou8
by Zn- and Cu-based catalysts.
While previous works of Trost3 and Palomo5 addressed
the application of environmentally benign zinc-based
catalysts, nothing is known about more demanding but
also more desirable iron-based catalytic enantioselective
aza-Henry reaction. In spite of the recent statement that
“iron catalysis is potentially capable of covering almost
the entire range of organic synthesis”10a to the best of our
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knowledge this fundamental asymmetric transformation Table 1. Initial screening of iron salt and ligands in asym-
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has never been reported by using chiral iron catalysts. In
this communication we present the first example of
asymmetric nitro-Mannich reaction driven by chiral Fe(II)
complex thus providing new application of this metal in
asymmetric synthesis. Presented concept of substrate
activation requires small catalytic amount of metal salt
and chiral ligand and is superior to previously published
protocols in terms of reaction efficiency.
metric nitro-Mannich reactions of series of N-protected
imines.
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Previously, we showed that iron(II) chloride in a combi-
nation with chiral pybox ligand can control enantioselec-
tive carbon-carbon bond formation in asymmetric Mukai-
yama reaction.11 Assuming that iron complexes can also
control the addition to imine group, we started extensive
investigation for practical and efficient catalyst capable of
activating reagents in nitro-Mannich reaction. Our new
finding is that only 5 mol% of Fe(OTf)2 coordinated by
hindered pybox ligand (L7) can effect highly enantioselec-
tive aza-Henry reactions (Scheme 1) of nitromethane and
imines, thus providing a new and extremely practical
entry to enantioenriched diamines. Moreover, while the
wide range of transition metals complexes with pybox-
type ligands12 have been incorporated for series of catalyt-
ic stereoselective transformations13-16 this commonly used
ligand has not been investigated in the nitro-Mannich
reaction.
cat.
mol
%
Lewis
acid
yield
ee
imine
ligand
[%][a] [%][b]
1
1a
1b
1c
1c
1c
1c
1c
1c
1c
1c
1c
1c
1c
1c
1c
1c
1c
1c
1c
Fe(OTf)2
Fe(OTf)2
Fe(OTf)2
Fe(OTf)2
Fe(OTf)2
Fe(OTf)2
Fe(OTf)2
Fe(OTf)2
Fe(OTf)2
Fe(OTf)2
Fe(OTf)2
Fe(OTf)2
Fe(OTf)2
Fe(OTf)2
Fe(OTf)2
FeCl2
10
10
10
10
10
5
L1
L1
74
0
rac.
-
2
3
L1
55
71
65
87
92
90
83
82
70
93
96
-
4
L2
L3
L3
L4
L5
L6
L7
L7
L7
L8
L9
L10
L7
L7
L7
L7
5
77
87
67
84
76
80
83
trace
87
31
6
7
10
10
10
10
5
8
Our initial aim was to identify the best-suited iron com-
plex in terms of both reaction conversion and enantiose-
lection. For this purpose, we initiated work by evaluating
reaction of N-Boc-imine (1a) with nitrometane under the
conditions reported previously by Palomo5 by replacing
zinc into iron salt. Unfortunately, the application of
iron(II) salts with various bidentate ligands, including (-)-
N-methylephedrine for the reaction of N-Boc-protected
aldimine was entirely unsuccessful. More promising re-
sults were gained after exchanging amine ligand for
commercial (S,S)-iPr-pybox (L1) in an in situ combination
with iron triflate (Table 1). However, observed reaction
yield and enantoselectivity highly depends on the imine
substrate (Table 1, entries 1-3). During the study, we found
that the most important objective was to identify the
best-suited N-protecting group in the imine component.
Thus series of N-protected aldimines (1a-c) were reacted
with nitromethane in the presence of 10 mol% of
Fe(OTf)2, ligand L1 and triethylamine in THF. Encourag-
ing outcomes were observed when N-Boc-imine (1a) or N-
phosphinoylimine (1c) were applied in the reaction,
whereas N-benzhydryl group (1b) turned out to be unre-
active under reaction conditions. Interestingly, while the
reaction of N-Boc-imine (1a) led to racemic product 2a,
addition of nitrometane to 1c resulted in synthesis of
desired amine with good level of enantioselectivity (Table
1, entry 3). These observation verified that the presence of
phosphinoyl moiety is a key for success, but there was still
much room for the improvement in terms of reaction
enantioselectivity.
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1
10
10
10
10
10
5
79
58
75
-
82
0
Zn(OTf)2
Zn(OTf)2
Cu(OTf)2
81
84
65
47
90
21
10
Reaction conditions: Imine (0.4 mmol), Lewis acid (5-10
mol%), pybox-type ligand (5-10 mol%), NO2Me (10
equiv.), TEA (0.5 equiv.), 0.5 mL THF, 2 h, rt. [a] Isolated
yields after column chromatography. [b] Determined by
HPLC.
Having the best type of imine in hand, we start to investi-
gate reaction enantioselectivity under control of structur-
ally-modified pybox ligands collected in Figure 1. As the
results in Table 1 show, the Ph-pybox (L2) and Inda-pybox
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The Journal of Organic Chemistry
ing in comparison to iron-based catalyst (Table 1, entry
(L3) in a combination with Fe(OTf)2 were superior to
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5
6
7
8
commercially available ligands. The highest enantioselec-
tivity (92%) was obtained in the reaction with L3, which
furnishes the corresponding product in 77% yield (Table 1,
entry 5). To our delight, catalyst loading could also be
reduced from 10 mol% to 5 mol%. Thus application of the
same iron catalyst with ligand L3 in 10- and 5 mol% gave
selectivities 92% and 90%, while reaction yield was even
better by using lower amount of catalyst (Table 1, entry 5
vs. 6). It is important to mention that all reactions pro-
ceeded at room temperature without any detrimental
effect in the reaction outcome.
17).
To test the reaction scope, a representative selection of
N-phosphinoyl-protected aryl imines was subjected to the
optimized reaction conditions (5 mol% of Fe(OTf)2-TPS-
he-pybox catalyst, at room temperature). As presented in
Figure 2, the proposed system allowed the formation of β-
nitro amines with very good yields and excellent enanti-
oselectivities in all tested cases.
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Fe(OTf)2 (5 mol%) ,
P(O)Ph2
(R,R)-TPS-he-pybox (5 mol%)
HN
P(O)Ph2
TEA 0.5 equiv.
N
R2
NO2
R1NO2
R
R
THF, rt, 2 h
1c, 3a-j
2c, 4a-n
NHP(O)Ph2
NO2
NHP(O)Ph2
NO2
NHP(O)Ph2
NO2
O
4b: 58%, 94% ee
2c: 83%, 96% ee
4a: 52%, 94% ee
NHP(O)Ph2
NHP(O)Ph2
NO2
NHP(O)Ph2
Figure 1. Series of pybox ligands tested in nitro-Mannich
reactions
.
NO2
NO2
O2N
Cl
F3C
Considering further improvement of the reaction enanti-
oselectivity a series of modified pybox ligands (L4-10) was
evaluated in association with Fe(OTf)2 to identify the
most enantioselective and reliable system. Ligands pre-
pared from serine (L4-6) and more hindered ones incor-
porating threonine moieties (L7-10) were tested in the
nitro-Mannich reaction (Table 1, entries 7-15).
4e: 74%, 96% ee
4c: 74%, 94% ee
4d: 84%, 94% ee
NHP(O)Ph2
NO2 NHP(O)Ph2
NO2
NHP(O)Ph2
O
O2N
NO2
NO2
4g: 61%, 97% ee
4f: 91%, 89% ee
4h: 77%, 90%
ee
Although in all cases the reaction proceeded smoothly to
give β-nitro amine product 2c in good yields, observed
enantioselectivities varied with the ligand structure. The
best results in terms of ee (93%) and high yield was re-
ported in the presence of tert-butyldiphenylsilyl-
protected hydroxyethyl-pybox (TPS-he-pybox) L7 (Table 1,
entry 10).
NHP(O)Ph2
NHP(O)Ph2
NHP(O)Ph2
*
NO2
NO2
NO2
4i: 72%, 98% eea
4j: 74%, 96% ee
4k: 61%, dr 1:1,
90%/89% ee
Conspicuously, bulky group attached to oxygen atom play
a crucial role in asymmetric induction and reaction effi-
ciency. In this case, decreasing of the catalyst loading to 5
mol% have progressive effect on the reactivity and enan-
tioselectivity of the reaction in hand (Table 1, entry 11).
Further decreasing of the catalyst loadings to 1 or 2 mol%
was not promising (Table 1, entry 12). Accordingly, the
best reaction conditions: 5 mol% of Fe(OTf)2 and TPS-he-
pybox ligand (L7) furnished the formation of β-nitro
amine 2c in 83% yield and with 96% ee in 2 h at room
temperature (Table 1, entry 11). Application of iron(II)
chloride (Table 1, entry 16) as well as iron (III) salts was
not promising.
NHP(O)Ph2
NHP(O)Ph2
NHP(O)Ph2
TBS
O
*
OH
*
NO2
NO2
NO2
O
4n: 50%, dr 1:1,
-/89% ee
4l: 40%, dr 1:1,
88%/90% ee
4m: 0%, - ee
Figure 2. Asymmetric nitro-Mannich reaction catalyzed by
iron(II)-TPS-he-pybox complex. [a] 10 mol% of catalyst.
Imines, which bear electron-withdrawing substituents
(4c-g) were more reactive than those with electron-
donating groups (4a-b) however the product were formed
with the same control of enantioselectivity. What is more,
the obtained results for aromatic imine substrates pos-
sessing groups placed in ortho, meta and para position
(4f-h) suggest that electronic perturbations are not signif-
It is also noteworthy that zinc triflate with the same L7-
ligand in a combination with trimethylamine was also
found reactive, yet the reaction outcome was less promis-
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icant for yields and ee values. Moreover, the proposed Preparation of silylated bis-(hydroxymethyl)pyridine (L4–
1
2
3
4
5
6
7
8
catalytic system was suitable for asymmetric nitro-
Mannich reaction of heteroaromatic, bicyclic and α,β-
unsaturated substrates (4h-j) afforded desired product
with good yields and ee, up to 98%. Finally, the proposed
iron-based catalytic system was applied for higher-order
nitroalkanes. All the tested substrates but nitroethanol
(4m) gave products with acceptable yield and high level
of enantioselectivity ranging 90% (4k-l, n).
L6): To a to suspension of bis-(hydroxymethyl)pyridine
(0.5 mmol, 1 equiv.) in methylene chloride 2 mL was add-
ed imidazole (22.9 mmol, 4.6 equiv.) at rt followed by
addition of silyl chloride (1,5 mmol, 3 equiv.) in one por-
tion. The resulting mixture was stirred for 15 h at rt. The
white suspension was purified by column chromatog-
raphy on silica gel (EA-Hx, 1:1) to give desired silylated
ligands L4–L6.
9
In summary, we have demonstrated a new strategy for
asymmetric nitro-Mannich (aza-Henry) reaction of al-
dimines using iron(II)-TPS-he-pybox complex. The appli-
cation of only 5 mol% of this in-situ-formed chiral cata-
lyst for a broad scope of substrates resulted in formation
of corresponding β-nitro amines with high yields and
excellent enantioselectivities, surpassing results obtained
for commercially available ligands. It is noteworthy that
the reaction proceeded at room temperature without any
detrimental effect in the reaction outcome while high
catalyst activity and enantioselectivity remains at high
level. Elaborated methodology requires small catalytic
amount of metal salt and chiral ligand surpassing previ-
ously published protocols in terms of reaction efficiency
and sustainability.
TPS-me-pybox (L4):18 Compound was obtained as a white
solid 240 mg, yield 88%; purified by column chromatog-
raphy with EA-Hx, 1:1, [α]D25 = +122.8 (c = 1.0, CHCl3); Lit.18
[α]D25 = +117.0 (c = 1.0, CH2Cl2); 1H NMR (600 MHz, CDCl3)
δ 8.12 (d, J = 7.8 Hz, 2H), 7.82 (t, J = 7.6 Hz, 1H), 7.67 –
7.65 (m, 8H), 7.42 – 7.34 (m, 12H), 4.62 – 4.56 (m, 4H),
4.52 – 4.47 (m, 2H), 3.95 (dd, J = 9.8, 3.4 Hz, 2H), 3.76 (dd,
J = 10.2, 3.6 Hz, 2H), 1.02 (s, 18H) ppm; 13C NMR (151 MHz,
CDCl3) δ 163.8, 147.0, 137.3, 135.8, 135.7, 133.6, 133.4, 129.9,
127.9, 127.8, 125.9, 71.3, 68.6, 65.8, 26.9, 19.4 ppm.
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TBS-me-pybox (L5):17 Compound was obtained as a white
solid, 197 mg, yield 78%; purified by column chromatog-
raphy with EA-Hx , 1:1, [α]D25 = +76.2 (c = 1.0, CHCl3); Lit:17
18.5
1
[α]D
= +105.9 (c = 1.0, CH2Cl2); H NMR (600 MHz,
CDCl3) δ 8.16 (d, J = 7.8 Hz, 2H), 7.86 (t, J = 7.6 Hz, 1H),
4.56 (dt, J = 9.2, 7.9 Hz, 2H), 4.49 – 4.43 (m, 4H), 3.93 (dd,
J = 10.2, 3.9 Hz, 2H), 3.65 (dd, J = 5.7, 4.3 Hz, 2H), 0.86 (s,
18H), 0.07 (d, J = 15.8 Hz, 12H) ppm; 13C NMR (151 MHz,
CDCl3) δ 163.7, 147.0, 137.4, 125.9, 71.4, 68.6, 65.2, 26.0, 18.4
ppm.
Experimental section
General Information.
All starting materials and reagents were purchased from
commercial sources and used without purification. Dry
THF was distilled from potassium to prior to use. All
catalytic reactions were performed under inert atmos-
phere. Reactions were controlled using analytical thin-
layer chromatographies (TLC) using Merck Silica Gel 60
F254 precoated plates. All reagents and solvents were
purified and dried according to common methods. All
organic solutions were dried over anhydrous magnesium
sulfate (MgSO4). Reaction products were purified
by normal phase flash chromatography, in air, using silica
gel 60 (230–400 mesh) with n-Hx (Hx) and ethyl acetate
TIPS-me-pybox (L6):18 Compound was obtained as a white
solid, 182 mg, yield 62%; purified by column chromatog-
raphy with EA-Hx, 1:1, [α]D25 = +82.7 (c = 1.0, CHCl3); Lit:18
[α]D23 = +66.8 (c = 1.0, CH2Cl2); 1H NMR (600 MHz, CDCl3)
δ 8.16 (d, J = 7.3 Hz, 1H), 7.85 (t, J = 7.7, 2H), 4.59 – 4.54
(m, 4H), 4.50 – 4.45 (m, 2H), 4.04 (dd, J = 9.8, 4.0 Hz,
2H), 3.72 (dd, J = 9.8, 7.4 Hz, 2H), 1.14 – 1.04 (m, 42H)
ppm; 13C NMR (151 MHz, CDCl3) δ 163.8, 147.0, 137.3, 125.9,
71.5, 68.7, 65.6, 18.1, 12.1 ppm.
1
(EA) as eluents, unless otherwise stated. H and 13C NMR
L-Threonine-based ligands L7–L10 were obtained accord-
spectra were recorded with 600 MHz (1H) and referenced
relative to tetramethylsilane (δ = 0 ppm) for 1H NMR, and
ing to the literature procedure:11
13
TPS-he-pybox (L7):11 White solid, 1006 mg, yield 77%,
CDCl3 (δ = 77.16 ppm) for C NMR. Data are reported as
25
follows: chemical shift, multiplicity (br s = broad singlet, s
= singlet, d = doublet, t = triplet, q =quartet, qui = quintet,
m = multiplet) and integration. High resolution mass
spectra (HRMS) were recorded with an electrospray ioni-
zation time-of-flight (ESI-TOF) mass spectrometer. Infra-
red (IR) spectra were recorded with a Fourier transform
infrared (FT-IR) spectrometer and are reported in wave
numbers (cm–1).Optical rotations were measured at room
temperature with a digital polarimeter. HPLC analysis
were performed using OD-H and OZ-H columns with UV
detection at 220 nm.
purified by column chromatography with EA; [α]D = –
57.0 (c = 1.0, CHCl3); Lit:11 [α]D= – 45.1 (c = 1.05, CHCl3); 1H
NMR (600 MHz, CDCl3) δ 8.10 (d, J = 7.9 Hz, 2H), 7.80 (t,
J = 7.80 Hz, 1H), 7.69 – 7.66 (m, 8H), 7.44 – 7.40 (m, 4H),
7.37 – 7.35 (m, 8H), 4.65 – 4.62 (m, 2H), 4.50 – 4.42 (m,
4H), 4.28 – 4.24 (m, 2H), 1.05 (s, 19H), 1.03 (d, J = 6.3 Hz,
6H) ppm; 13C NMR (151 MHz, CDCl3) δ 163.4, 147.0, 137.3,
136.0, 135.9, 134.3, 134.0, 129.9, 129.8, 127.8, 127.7, 125.9, 71.6,
70.0, 69.2, 27.1, 19.4, 17.7 ppm.
TBS-he-pybox (L8):19 Light yellow solid, 166mg, yield 42%,
purified by column chromatography with Hx:EA (2:1);
25
1
L-Serine-based ligands L4–L6 were synthetized by accord-
[α]D = –57.0 (c = 1.0, CHCl3); H NMR (600 MHz, CDCl3)
ing to the literature procedure:11,17
δ 8.18 (d, J = 7.8 Hz, 2H), 7.86 (t, J = 7.6 Hz, 1H), 4.65 –
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The Journal of Organic Chemistry
N-(3-nitrobenzylidene)-P,P-diphenylphosphine
4.62 (m, 2H), 4.50 – 4.54 (m, 2H), 4.48 – 4.43 (m, 4H),
amide
1
2
3
4
5
6
7
8
4.22 – 4.17 (m, 2H), 1.1 (d, J = 6.1 Hz, 6H), 0.87 (s, 18H),
0.08 (d, J = 4.0 Hz, 12H) ppm; 13C NMR (151 MHz, CDCl3) δ
163.4, 147.0, 137.4, 125.9, 72.0, 69.2, 69.0, 25.9, 18.2, 18.02, –
4.4, –4.7 ppm.
(3f): yellow solid, 820 mg, overall yield 35%; 1H NMR (600
MHz, CDCl3) δ 9.41 (d, J = 30.4 Hz, 1H), 8.89 (t, J = 1.7 Hz,
1H), 8.42 (ddd, J = 8.2, 2.3, 1.1 Hz, 1H), 8.26 (dt, J = 7.6, 1.3
Hz, 1H), 7.98 – 7.94 (m, 4H), 7.72 (t, J = 7.9 Hz, 1H), 7.54 –
7.52 (m, 2H), 7.50 – 7.47 (m, 4H) ppm; 13C NMR (151 MHz,
CDCl3) δ 171.2, 148.9, 137.4, 137.3, 136.3, 132.6, 132.3 (d, J =
1.4 Hz), 131.8, 131.7 (d, J = 9.2 Hz ), 130.3, 128.8 (d, J = 12.7
Hz), 127.7, 123.9 ppm; FT-IR: 3075, 2924, 2854, 1622, 1528,
MeO-he-pybox (L9): White solid, 210 mg, yield 25%; puri-
fied by column chromatography with DCM:EtOH 50:1;
[α]D26 = –110.0 (c = 1.0, CHCl3); 1H NMR (600 MHz, CDCl3)
δ 8.21 (d, J = 7.9 Hz, 2H), 7.86 (t, J = 7.8 Hz, 1H), 4.59 –
4.55 (m, 2H), 4.52 – 4.49 (m, 2H), 4.44,(t, J = 8.3 Hz, 2H)
3.66 – 3.62 (m, 2H), 3.40 (s, 6H), 1.17 (s, 6H) ppm; 13C NMR
(151 MHz, CDCl3) δ 163.5, 146.9, 137.933, 126.1, 77.5, 70.1,
69.4, 57.0, 14.3 ppm; FT-IR: 3411, 2989, 2935, 2850, 1681,
1350, 1211 818 cm–1, mp = 173 C; HRMS (ESI-TOF): calcd.
o
9
for C19H15N2O3PNa [M+Na]+: 373.0718 found 373.0718.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
N-(2-nitrobenzylidene)-P,P-diphenylphosphine
amide
(3g): light brown solid, 873 mg, overall yield 25%; 1H NMR
(600 MHz, CDCl3) δ 9.62 (d, J = 30.6 Hz, 1H), 8.16 (dd, J =
7.7, 1.4 Hz, 1H), 8.01 (dd, J = 8.0, 1.1 Hz, 1H), 7.96 – 7.91 (m,
4H), 7.75 (dt, J = 7.5, 0.9 Hz, 1H), 7.70 (dt, J = 7.8, 1.5Hz,
1H), 7.54 – 7.52 (m, 2H), 7.40 – 7.47 (m, 4H) ppm; 13C NMR
(151 MHz, CDCl3) δ 169.6, 149.9, 133.4, 133.2, 132.8, 132.4,
132.2 (d, J = 1.7 Hz), 131.8 (d, J = 9.3 Hz), 131.6, 130.8, 130.5,
130.3, 128.8 (d, J = 12.7 Hz), 124.6 ppm; FT-IR: 3061, 2917,
1573, mp
=
105 oC; HRMS (ESI-TOF): calcd. for
C17H23N3O4Na [M+Na]+: 356.1586 found 356.1568.
tBuO-he-pybox (L10): White solid, 320 mg, yield 52%;
24
purified by column chromatography with EA; [α]D = –
65,5 (c = 1.0, CHCl3); 1H NMR (600 MHz, CDCl3) δ 8.19 (d,
J = 7.8 Hz, 2H), 7.85 (t, J = 7.8 Hz, 1H), 4.61 – 4.55 (m, 2H),
4.51 – 4.46 (m, 4H), 4.10 – 4.03 (m, 2H), 1.21 (s, 18H), 1.05
(d, J = 6.4 Hz, 6H) ppm; 13C NMR (151 MHz, CDCl3) δ 163.3,
147.1, 137.3, 125.9, 74.1, 71.5, 69.3, 67.7, 28.5, 17.0 ppm. FT-
IR: 3254, 3067, 2974, 2921, 1633 1380, 1197 1089 cm–1; mp =
161 oC; HRMS (ESI-TOF): calcd. for C23H35N3O4Na
[M+Na]+: 440.2525 found 440.2538.
o
1620, 1526, 1437, 1350, 1206, 1125, 820 cm–1; mp = 100 C;
HRMS (ESI-TOF): calcd. for C19H15N2O3PNa [M+Na]+:
373.0718 found 373.0719.
General Procedure for the nitro-Mannich reaction: In
typical procedure, Fe(OTf)2 (7.1mg, 0.02 mmol ) and TPS-
he-pybox L7 (16 mg, 0,02 mmol) were dissolved in dry and
deoxygenated THF (0.5 mL) under a argon atmosphere
and stirred at room temperature for 30 min. Nitroalkane
(0.214 mL, 4 mmol) was then added and deer-purple mix-
ture was stirred for an additional 30 min. Then corre-
sponding N-phosphinoylimine (0.4 mmol) was added
followed by TEA (0.28 mL, 0.2 mmol) and reaction was
stirred at room temperature for 2 h. After this time reac-
tion mixture was directly poured onto a silica gel column
and eluted by chloroform-acetone (10:1) to yield to desire
adduct.
Preparation of aldoximes: N-phosphinylimines were syn-
thesized from the corresponding oximes by the modifica-
tion of the literature procedure.20 Suspension of hydroxyl-
amine hydrochloride (1.6 equiv), and NaOAc (2.0 equiv.)
in 80% aqueous EtOH (20.0 mL) was stirred at rt for 30
min. After this time aldehyde (1.0 equiv.) was added and
the reaction mixture was heated gently to reflux for 30
min. Following cooling to rt, the solvent was evaporated
under vacuum and the residue purified by column chro-
matography with Hx:EA (9:1) as eluent, to provide crystal-
line oxime with quantitative yield.
(R)-(-)-N-(2-nitro-1-phenylethyl)-diphenylphosphine
amide (2c):26 white solid, 122 mg, yield 83%; ee 96% by
HPLC Chiralcel OD-H Hx:2-Propanol (90:10), flow 1.0
mL/min, UV=220 nm, 35 oC, tS = 17.8 min. (minor) (S), tR =
Preparation of N-phosphinylimines.21 In the round bottle
flask under inert atmosphere oxime (1.0 equiv.) was dis-
solved in mixture of dry DCM/ Hx (1:1) and cooled to –40
°C. To the reaction mixture TEA (1.1 equiv.) was added
dropwise followed (after 10 min.) by addition of Ph2PCl
(1.1 equiv). After adding was finished, reaction mixture
was gradually warmed to room temperature and stirred
overnight. When reaction was completed, content of the
flask was poured over ice and the aqueous phase was
extracted with DCM (3×15mL). The combined organic
layers were washed with water, brine and dried under
anhydrous Na2SO4.The solvents were evaporated under
reduced pressure affords the crude aldimine, which was
purified by column chromatography on silica gel with
DCM-Acetone (9:1) as eluent.
31.7 min. (major) (R); [α]D = –53.8 (c = 1.0, CHCl3); Lit.26
25
28
1
[α]D = +33.2 (for enantiomer S, c=0.9, CHCl3). H NMR
(600 MHz, CDCl3): δ = 7.85 – 7.81 (m, 4H), 7.55 – 7.50 (m,
2H), 7.47 – 7.41 (m, 4H), 7.37 – 7.29 (m, 5H), 4.95 – 4.92
(m, 3H), 4.04 – 4.01 (m, 1H) ppm; 13C NMR (151 MHz,
CDCl3): δ = 137.9 (d, J = 5.9 Hz), 132.6 – 132.4 (m), 132.3,
131.9, 131.8 (d, J = 9.8 Hz), 131.5, 130.8, 129.3, 128.9 – 128.7
(m), 126.4, 81.0, 55.4, ppm.
(R)-(-)-N-(2-nitro-1-(4-methylphenyl)ethyl)-
diphenylphosphine amide (4a):26 white solid, 79 mg, yield
52%; ee 94% by HPLC Chiralcel OD-H Hx:2-Propanol
(90:10), flow 1.0 mL/min, UV=220 nm, 21 oC, tS = 20.5 min.
The spectral characteristics of N-phosphinylimines 1c,22
3a,22 3b,22 3c,22 3d,22 3e,23 3h,24 3i,23 3j25 were consistent
with those reported previously in the literature.
25
(minor, S), tR = 28.9 min. (major, R); [α]D = – 63.6 (c =
1.0, CHCl3); Lit.26 [α]D = +87.3 (for enantiomer S, c = 1.12,
30
1
CHCl3). H NMR (600 MHz, DMSO): δ = 7.70 – 7.63 (m,
4H), 7.57 – 7.48 (m, 4H), 7.44 – 7.41 (m, 2H), 7.21 (d, J = 8.1
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Hz, 2H), 7.11(d, J = 7.8 Hz, 2H), 6.28 (dd, J = 11.1, 8.9 Hz
Page 6 of 9
128.9 (m), 127.7, 124.4, 80.4 (d, J = 3.0 Hz), 52.9 ppm; FT-
IR:3107, 2906, 1552, 1519, 1347, 1179 cm–1; mp = 172 oC;
HRMS (ESI-TOF): calcd. for C20H18N3O5PNa [M+Na]+:
434.0882 found 434.0857.
1
2
3
4
1H), 4.87 (dd, J = 12.3, 8.5 Hz, 1H), 4.80 (ddd, J = 12.3, 6.4,
1.0 Hz 1H), 4.67 – 4.61 (m, 1H), 2.27 (s, 3H) ppm; 13C NMR
(151 MHz, DMSO): δ = 137.0, 136.6 (d, J = 3.1 Hz), 133.7,
133.5, 132.8, 132.6, 131.8 – 131.6 (m), 129.0, 128.4 (t, J = 11.3
Hz), 126.7, 81.9 (d, J = 4.5 Hz), 53.3, 20.7 ppm.
5
(R)-(-)-N-(2-nitro-1-(3-nitrophenyl)-ethyl)-
6
7
8
9
diphenylphosphine amide (4f): light yellow solid, 150 mg,
yield 91%; ee 89% by HPLC Chiralcel OD-H Hx:2-
Propanol (80:20), flow 1.0 mL/min, UV=220 nm, 21 oC, tR =
(R)-(-)-N-(1-(4-methoxyphenyl)-2-nitro-ethyl)-
diphenylphosphine amide (4b):27 white solid, 92 mg, yield
58%; ee 94% by HPLC Chiralcel OZ-H Hx:2-Propanol
(80:20), flow 1.0 mL/min, UV=220 nm, 21 oC, tR = 28.1 min.
25
15.2 min. (major, R), tS = 20.2 min. (minor, S); [α]D = –
58.1 (c = 1.0, CHCl3); 1H NMR (600 MHz, CDCl3): δ = 7.79
– 7.84 (m, 4H), 7.60 – 7.62 (m, 2H), 7.48 – 7.57 (m, 2H),
7.40 – 7.43 (m, 6H), 4.87 – 4.92 (m, 3H), 4.22 (dd, J = 10.2,
6.2 1H) ppm; 13C NMR (151 MHz, CDCl3): δ = 141.9 (d, J =
5.4 Hz), 132.7, 132.4 (d, J = 9.7 Hz), 131.9 (d, J = 10.0 Hz),
131.5, 131.1 (d, J = 2.6 Hz), 130.8, 130.7, 129.0, 128.9 (d, J =
12.8 Hz), 127.0, 126.2 (d, J = 3.2 Hz), 124.8, 123.0, 80.6 (d, J =
2.5 Hz), 53.0 ppm; FT-IR: 3138, 2912, 1552, 1529, 1349, 1178
10
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13
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15
16
17
18
19
20
21
22
23
24
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26
27
28
29
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32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
25
(major, R), tS = 49.8 min. (minor, S); [α]D = – 67.5 (c =
1
1.0, CHCl3); H NMR (600 MHz, CDCl3): δ = 7.85 – 7.80
(m, 4H), 7.54 – 7.50 (m, 2H), 7.46 – 7.41 (m, 4H), 7.22 –
7.19 (m, 2H), 6.88 – 6.85 (m, 2H), 4.91 (dd, J = 12.6, 6.0 Hz,
1H), 4.85 (dd, J = 12.6, 5.9 Hz, 1H), 4.82 – 4.78 (m, 1H), 3.79
13
(s, 3H) ppm; C NMR (151 MHz, CDCl3) δ = 159.8, 132.6 –
132.5 (m), 131.9 – 131.8 (m), 131.6, 130.9, 129.9 (d, J = 6.1 Hz),
128.8 (dd, J = 12.7, 5.0 Hz), 127.7, 114.6, 81.0, 55.4 (d, J = 5.1
Hz), 53.0 ppm.
cm–1; mp
=
174 oC; HRMS (ESI-TOF): calcd. for
C20H18N3O5PNa [M+Na]+: 434.0882 found 434.0863.
(R)-(-)-N-(1-(4-chlorophenyl)-2-nitro-ethyl)-
(R)-(-)-N-(2-nitro-1-(2-nitrophenyl)-ethyl)-
diphenylphosphine amide (4c):26 white solid, 119 mg, yield
74%; ee 94% by HPLC Chiralcel OZ-H Hx:2-Propanol
(80:20), flow 1.0 mL/min, UV=220 nm, 21 oC, tR = 15.6 min.
(major, R), tS = 23.8 min. (minor, S); [α]D25 = – 71.7 (c = 1.0,
diphenylphosphine amide (4g): white solid, 97 mg, yield
61%; ee 97% by HPLC Chiralcel OZ-H Hx:2-Propanol
(80:20), flow 1.0 mL/min, UV=220 nm, 21 oC, tR = 12.8 min.
(major, R), tS = 21.6 min. (minor, S); [α]D25 = –53.5 (c = 1.0,
CHCl3); 1H NMR (600 MHz, DMSO) δ 8.04 (dd, J = 7.9, 0.9
Hz, 1H), 7.90 (dd, J = 8.2, 1.1 Hz, 1H), 7.79 (dt, J = 11.2, 1.0
Hz, 1H), 7.63 – 7.49 (m, 9H), 7.38 (dt, J = 7.7, 3.1 Hz, 2H),
6.66 (t, J = 10.1 Hz, 1H), 5.36 (ddd, J = 19.0, 10.1, 4.2 Hz, 1H),
4.92 (ddd, J = 12.6, 4.1, 2.2 Hz, 1H), 4.83 (dd, J = 12.7, 9.8
Hz, 1H) ppm; 13C NMR (151 MHz, DMSO) δ 147.2, 134.6,
134.0, 133.2, 132.6, 132.3, 132.0 – 131.4 (m), 129.8, 129.3, 128.4
(dd, J = 20.8, 12.3 Hz ), 124.3, 79.7 (d, J = 6.7 Hz), 48.7 (d, J
= 7.8 Hz) ppm; FT-IR: 3139, 2914, 1550, 1525, 1348, 1179 cm–
1; mp = 212 oC; HRMS (ESI-TOF): calcd. for C20H18N3O5PNa
[M+Na]+: 434.0882 found 434.0876.
29
CHCl3); Lit.26 [α]D = +46.6 (for enantiomer S, c = 1.01,
1
CHCl3 ); H NMR (600 MHz, CDCl3): δ = 7.82 – 7.78 (m,
4H), 7.55 – 7.50 (m, 2H), 7.47 – 7.40 (m, 4H), 7.32 – 7.30
(m, 2H), 7.25 – 7.22 (m, 2H), 4.90 – 4.78 (m, 3H), 4.17 (dd,
J = 10.8, 6.2 Hz, 1H) ppm; 13C NMR (151 MHz, CDCl3) δ
136.5 (d, J = 5.5 Hz), 134.7, 132.6 – 132.4 (m), 132.1, 131.9 (d, J
= 9.8 Hz), 131.6, 131.2, 130.8, 129.4, 128.9 (d, J = 12.7 Hz),
127.9, 80.7 (d, J = 1.7 Hz), 52.8 ppm.
(R)-(-)-N-(1-(4-(trifluoromethyl)phenyl)-2-nitro-ethyl)-
diphenylphosphine amide (4d): white solid, 149 mg, yield
84%; ee 94% by HPLC Chiralcel OZ-H Hx:2-Propanol
(80:20), flow 1.0 mL/min, UV=220 nm, 21 oC, tR = 11.4 min.
(major, R), tS = 17.7 min. (minor, S); [α]D25 = – 55.8 (c = 1.0,
CHCl3); 1H NMR (600 MHz, DMSO) δ 7.72 – 7.67 (m, 6H),
7.65 – 7.58 (m, 3H), 7.54 – 7.48 (m, 3H), 7.42 (dt, J = 7.6,
3.0 Hz, 2H), 6.48 (dd, J = 10.7, 9.2 Hz, 1H), 4.97 – 4.87 (m,
2H), 4.86 – 4.76 (m, 1H) ppm; 13C NMR (151 MHz, DMSO)
δ 144.1 , 133.5, 133.1, 132.7, 132.2, 131.9 – 131.6 (m), 128.7 –
128.3 (m), 127.9, 125.3, 125.1, 123.2, 80.3 (d, J = 6.1 Hz) 53.09
(R)-(-)-N-(1-(furyl)-2-nitroethyl)-diphenylphosphine am-
ide (4h):26 light yellow solid, 110 mg, yield 77%; ee 90% by
HPLC Chiralcel OD-H Hx:2-Propanol (90:10), flow 1.0
o
mL/min, UV=220 nm, 21 C, tS = 9.1 min. (minor, S), tR =
25
15.8 min. (major, R); [α]D = –57.7 (c = 1.0, CHCl3); Lit.26
[α]D29 = +41.8 (for enantiomer S, c = 0.98, CHCl3); 1H NMR
(600 MHz, CDCl3) δ 7.91 – 7.88 (m, 2H), 7.84 – 7.80 (m,
2H), 7.56 – 7.52 (m, 2H), 7.48 – 7.44 (m 4H), 7.35 (dd, J =
1.8, 0.8 Hz, 1H), 6.33 (dd, J = 3.3, 1.8 Hz, 2H), 5.01 – 4.96
(m, 1H), 4.92 – 4.98 (m, 2H), 3.96 (dd, J = 10.7, 7.0 Hz, 1H)
ppm; 13C NMR (151 MHz, CDCl3) δ 150.7 (d, J = 7.4 Hz),
143.0, 132.5 (m), 132.1, 131.8 (d, J = 9.9 Hz), 131.6, 131.3, 130.7,
129.0, 128.9 (t, J = 12.0 Hz), 110.9, 108.3, 78.5 (d, J = 2.3 Hz),
47.9 ppm.
ppm; FT-IR: 3130, 2902, 1549, 1372, 1118 cm–1; mp = 175 C;
o
HRMS (ESI-TOF): calcd. for C21H18F3N2O3PNa [M+Na]+:
457.0905 found 457.0909.
(R)-(-)-N-(2-nitro-1-(4-nitrophenyl)-ethyl)-
diphenylphosphine amide (4e): light yellow solid, 122 mg,
yield 74%; ee 96% by HPLC Chiralcel OD-H Hx:2-
Propanol (80:20), flow 1.0 mL/min, UV=220 nm, 21 ºC, tR =
14.8 min. (major, R), tS = 27.9. (minor, S); [α]D25 = – 54.8 (c
= 1.0, CHCl3); 1H NMR (600 MHz, CDCl3) δ 8.20 – 8.19 (m,
2H), 7.83 – 7.77 (m, 4H), 7.58 – 7.43 (m, 8H), 4.96 – 4.92
(m, 3H), 4.46 – 4.41 (m, 1H) ppm; 13C NMR (151 MHz,
CDCl3) δ 148.0, 145.0 (d, J = 5.1 Hz), 132.8, 132.3 (d, J = 9.7
Hz), 131.9 (d, J = 9.8 Hz), 131.7, 131.4, 130.8, 130.6 129.1 –
(R)-(-)-N-(1-(2-naphtyl)-2-nitroethyl)-diphenylphosphine
amide (4i):26 white solid, 120mg, yield 72%; ee 98% by
HPLC Chiralcel OD-H Hx:2-Propanol (80:20), flow 1.0
o
mL/min, UV=220 nm, 21 C, tS = 16.8 min. (minor, S), tR =
25
22.4 min. (major, R); [α]D = – 97.3 (c = 1.0, CHCl3); Lit.26
30
1
[α]D = +56.6 (for enantiomer S, c = 0.47, MeOH); H
NMR (600 MHz, DMSO) δ 7.89 – 7.88 (m, 2H), 7.83 – 7.82
ACS Paragon Plus Environment

Page 7 of 9
The Journal of Organic Chemistry
= 9.8 Hz), 132.6, 132.5 – 132.1 (m), 131.9– 131.8 (m), 131.5,
(m, 1H), 7.77 (s, 1H), 7.73 – 7.66 (m, 4H), 7.60 (dd, J = 8.6,
1
2
3
4
5
6
7
8
1.8 Hz, 2H), 7.53 – 7.47 (m, 5H), 7.40 (td, J = 7.6, 3.0 Hz,
2H), 6.46 (dd, J = 10.9, 9.1 Hz, 1H), 5.02 – 4.94 (m, 2H),
4.91 – 4.85 (m, 1H) ppm; 13C NMR (151 MHz, DMSO) δ
137.0 (d, J = 2.3 Hz), 133.7, 133.4, 132.9, 132.6 – 132.5 (m),
131.8 – 131.6 (m), 128.5 – 128.2 (m), 127.9, 127.5, 126.3 (d, J =
15.4 Hz), 125.8 (d, J = 3.9 Hz), 124.8, 80.8 (d, J = 6.5 Hz),
53.7 ppm.
131.4, 131.0, 130.6 (d, J = 2.1 Hz), 129.5 (d, J = 4.4 Hz), 128.8 –
128.5 (m), 128.2, 128.0, 114.5, 114.3, 88.5 (d, J = 5.9 Hz), 87.8,
58.1, 57.9, 55.4 (d, J = 6.4 Hz), 17.2 (d, J = 3.2 Hz), 15.8 (d, J
= 3.0 Hz) ppm.
N-(3-(tert-butyldimethylsiloxy)-2-nitro-1-phenylpropyl)-
diphenylphosphine amide (4n): white solid, 35 mg, yield
50%; eemajor=89%, by HPLC major diasteromer: Chiralcel
OZ-H Hx:2-Propanol (80:20), flow 1.0 mL/min, UV=220
9
(R,E)-(-)-N-(1-nitro-4-phenylbut-3-en-2-yl)-
diphenylphosphine amide (4j):26 light cream solid, 116 mg,
yield 74%; ee 96% by HPLC Chiralcel OD-H Hx:2-
Propanol (90:10), flow 1.0 mL/min, UV=220 nm, 21 ºC, tS =
nm, 21 C, t1 = 6.6 min. (major), t2 = 9.5 min. (minor); H
NMR (600 MHz, CDCl3) δ 7.80 – 7.77 (m, 2H), 7.69 – 7.65
(m, 2H), 7.55 – 7.52 (m, 1H), 7.48 – 7.42 (m, 3H), 7.33 –
7.29 (m, 5H), 7.16 – 7.15 (m, 2H), 4.93 – 4.89 (m, 1H), 4.65
– 4.60 (m, 1H), 4.16 – 4.11 (m, 2H), 3.76 (dd, J = 7.7, 3.9 Hz,
o
1
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
25
20.5 min. (minor, S), tR = 28.9 min. (major, R); [α]D = –
90.2 (c = 1.0, CHCl3); Lit.26 [α]D31 = +39.1 (for enantiomer S,
1
13
c = 1.04, CHCl3); H NMR (600 MHz, CDCl3) δ 7.93 – 7.90
1H), 0.79 (s, 9H), −0.03 (d, J = 8.0 Hz, 6H) ppm; C NMR
(m, 2H), 7.87 – 7.84 (m, 2H), 7.54 – 7.51 (m, 4H), 7.47 –
7.44 (m. 4H), 7.30 (d, J = 4.4 Hz, 2H), 7.27 – 7.25 (m, 1H),
6.60 (dd, J = 15.9, 1.4 Hz, 1H), 6.18 (dd, J = 15.9, 6.3 Hz, 1H),
4.79 (dd, J = 12.8, 5.1 Hz, 1H), 4.73 (dd, J = 12.8, 5.2 Hz, 1H),
4.45 – 4.38 (m, 1H), 3.92 – 3.87 (m, 1H) ppm; 13C NMR (151
MHz, CDCl3) δ 135.7, 133.6, 132.6, 132.5, 131.9 (d, J = 9.9 Hz),
131.6, 131.1, 129.5, 129.0 – 128.7 (m), 128.5, 126.9, 125.5 (d, J =
5.8 Hz), 80.6, 51.7 ppm.
(151 MHz, CDCl3) δ 138.3 (d, J = 1.9 Hz), 132.4 – 132.0 (m),
131.4 (d, J = 5.2 Hz), 129.2, 128.8–128.5 (m), 126.5, 94.2 (d, J
= 5.5 Hz), 63.1, 55.0, 25.7, 18.1, –5.6 (d, J = 24.1 Hz) ppm;
FT-IR:3147, 30.62, 2928, 2856, 1554, 1437, 1187, 1125 cm–1;
mp = 159 oC, HRMS (ESI-TOF): calcd. for C27H35N2O4PSiNa
[M+Na]+: 533.2001 found 533.1996.
ASSOCIATED CONTENT
Supporting Information. Copy of NMR spectra and HPLC
data. This material is available free of charge via the Internet
at http://pubs.acs.org.
N-(2-nitro-1-phenylpropyl)-diphenylphosphine
amide
(4k):26 white solid, 92 mg, yield 61%; ee1D= 88%, ee2D= 90%
by HPLC Chiralcel OZ-H Hx:2-Propanol (80:20), flow 1.0
o
AUTHOR INFORMATION
mL/min, UV=220 nm, 21 C, major diastereomer :t1 = 11.4
min. (major), t2 = 24.7 min. (minor), minor diastereomer:
Corresponding Author
1
t1 = 20.8 min. (major), t2 = 47.6 min. (minor); H NMR
*jacek.mlynarski@gmail.com
(600 MHz, CDCl3) δ 7.82 – 7.76 (m, 2Hmajor, 2Hminor), 7.73 –
7.66 (m, 2Hmajor, 2Hminor), 7.55 – 7.41 (m, 4Hmajor, 4Hminor),
7.38 – 7.28 (m, 4Hmajor, 4Hminor), 7.15 (dd, J = 7.7, 1.5 Hz,
2H), 7.14 – 7.09 (m, 2H), 5.02 – 4.99 (m, 1Hmajor), 4.89 (qui,
J = 6.8 Hz, 1Hminor), 4.56 (td, J = 11.1, 5.4 Hz, 1Hmajor), 4.50 –
4.46 (td, J = 10.5, 3.2 Hz, 1Hminor), 4.22 (dd, J = 11.4, 7.4 Hz,
1Hmajor), 4.17 (dd, J = 11.1, 7.2 Hz, 1Hminor), 1.54 (d, J = 6.8 Hz,
3Hmajor), 1.51 (d, J = 6.7 Hz, 3Hminor) ppm. 13C NMR (151
MHz, CDCl3) δ 138.6 (d, J = 1.6 Hz), 137.5 (d, J = 4.2 Hz),
132.7 (d, J = 9.8 Hz), 132.5 -132.0 (m), 131.9 – 131.7 (m) 131.5,
131.4, 130.9, 129.1, 128.9 – 128.5 (m), 127.0, 126.8, 88.3 (d, J =
2.9 Hz), 87.6, 58.5, 58.4, 17.3, 15.6 ppm.
ACKNOWLEDGMENT
Financial support from the Polish National Science Centre
(grant number NCN 2012/07/B/ST5/00909) is gratefully
acknowledged.
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diphenylphosphine amide (4l):28 white solid, 64mg, yield
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,
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6.84 – 6.81 (m, 2Hmajor, 2Hminor), 5.02 – 4.97 (m, 1Hmajor),
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1.54 (d, J = 6.8 Hz,3Hmajor), 1.50 (d, J = 6.7 Hz, 3Hminor) ppm;
13C NMR (151 MHz, CDCl3) δ 159.7 (d, J = 8.7 Hz), 132.7 (d, J
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