Verkade's Superbase as an Organocatalyst for the Strecker Reaction

Article abstract of DOI:10.1002/ejoc.201801170

Proazaphosphatranes -Verkade's superbases- proved to be efficient organocatalysts for the Strecker reaction between protected imines and trimethylsilyl cyanide (TMSCN). Excellent to quantitative yields were reached and, compared to other systems, only low

Full text of DOI:10.1002/ejoc.201801170

DOI: 10.1002/ejoc.201801170
Full Paper
Organocatalytic Mechanisms
Verkade's Superbase as an Organocatalyst for the Strecker
Reaction
Jian Yang,[a] Bastien Chatelet,[a] Fabio Ziarelli,[b] Véronique Dufaud,[c] Damien Hérault,[a] and
Alexandre Martinez*[a]
Abstract: Proazaphosphatranes -Verkade's superbases- proved A remarkable initial turnover frequency (TOF), close to 105 h–1,
to be efficient organocatalysts for the Strecker reaction be- was achieved, associated with an excellent selectivity since no
tween protected imines and trimethylsilyl cyanide (TMSCN). Ex- side reactions were observed. A reaction mechanism was pro-
cellent to quantitative yields were reached and, compared to posed and the key role played by the apical nitrogen in the
other systems, only low catalyst loading and short reaction proazaphosphatrane structure was demonstrated.
times were required for the reaction to proceed efficiently.
Introduction
confined in molecular cages or mesoporous silica leading to
unexpected behavior and reactivity.[8] Recently, proazaphos-
phatranes turned out to be remarkable catalysts for the reduc-
tive functionalization of CO2 into methylamines, in the presence
of hydroborane.[9] Moreover, Krempner et al. demonstrated that
Verkade's super-bases can be used to create intermolecular
frustrated Lewis pairs (FLP) when associated to a weak boron-
containing Lewis acid.[10] These “inverse” FLPs were able to
cleave dihydrogen leading to efficient hydrogenation catalysts.
The same group also reported the interactions and coordina-
tion properties of Verkade's superbases with strong Lewis acids
by reaction of proazaphosphatranes with various gallium-,
boron- and aluminium-containing Lewis acids.[11]
Proazaphosphatranes, also named Verkade's superbases, were
first described by J. G. Verkade in 1989.[1] In contrast to imino-
phosphine -phosphazenes- bases, the Verkade's superbases
protonate on the phosphorus atom: upon this proton transfer,
the apical nitrogen links to the positive phosphorus creating a
highly stable azaphosphatrane structure.[2] The remarkable sta-
bility of this conjugated acid renders the Verkade's superbase
highly basic (pKa = 32),[3] one of the most basic nonionic base
reported so far. Proazaphosphatranes have therefore attracted
considerable interests as highly efficient basic and nucleophilic
catalysts to promote a large number of reactions, such as trime-
rization of isocyanates,[4a] acylation of alcohols,[4b] dehydrohalo-
genations of alkyl halides,[4c] silylation of alcohols,[4d,4e] the
Henry reaction,[4f] transesterification of esters,[4g] and additions
of trimethylsilyl cyanide to aldehydes and ketones.[4h] The reac-
tion conditions are generally milder with the Verkade's super-
base than with other organocatalysts: lower temperatures and
shorter reaction times are usually used and the reactions are
often more selective.[4] Besides this remarkable activity as or-
ganocatalyst, new aspects of the chemistry of Verkade's super-
bases have recently been developed, i.e. they were found to act
as highly donor ligand for transition metal complexes,[5] leading
to very active organometallic catalysts, for Suzuki–Miyaura
cross-coupling reactions,[6] or Buchwald–Hartwig amination re-
actions of aryl chlorides.[7] Proazaphosphatranes have also been
Although these recent developments bring new insight into
the potentiality of such structure for new applications, the clas-
sical use of the Verkade's superbases as organocatalysts re-
mains attractive because of their high performance in term of
activity and selectivity.[12] Among the base-catalyzed transfor-
mations, the Strecker reaction is an appealing target reaction
since it leads to the synthesis of α-aminonitriles which are im-
portant and versatile building blocks in organic synthesis as
well as in biologically active products.[13] Consequently, numer-
ous catalysts have been developed to perform this reaction.[14]
One can cite the use of Lewis acids such as BiCl3,[15] InI3,[16]
RuCl3,[17] NiCl2,[18] La(NO3)3·6H2O,[19] Yb(OTf)3,[20] Sc(OTf)3,[21]
Cu(OTf)2.[22] Generally, in those reactions, the aqueous workup
is tedious and a large amount of toxic metal waste is generated
inevitably. A few organocatalysts have also been reported to
catalyze Strecker type reactions. N-heterocyclic carbenes were
shown to catalyze the addition of trimethylsilyl cyanide to
imines with excellent yields in the presence of 5 mol-% catalyst
loading at 0 °C, but substrates were limited to tosyl protected
imines, and, in most cases, long reaction times were needed (5–
6 hours).[23] Heydari et al. showed that guanidine hydrochloride
could act as catalyst for Strecker type reactions using aliphatic,
aromatic, heterocyclic conjugated aldehydes, and primary, sec-
[a] Aix Marseille Univ, CNRS, Centrale Marseille, iSm2, Marseille, France
E-mail: alexandre.martinez@centrale-marseille.fr
[b] Aix-Marseille Université, Centrale Marseille, CNRS, Fédération des Sciences
Chimiques de Marseille (FR 1739), 13397 Marseille, France
[c] Laboratoire de Chimie, Catalyse, Polymères, Procédés CNRS, UMR 5265,
Université Claude Bernard Lyon 1,
CPE Lyon, 43 Bd du 11 novembre 1918, 69616, Villeurbanne cedex, France
Supporting information and ORCID(s) from the author(s) for this article are
available on the WWW under https://doi.org/10.1002/ejoc.201801170.
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ondary amines as substrates.[24] However, only moderate activ-
ity could be achieved with TON around 33 at 40 °C in 1 hour.
Thiourea also performed well as catalyst with moderate to high
yields in the presence of 5 mol-% catalyst loading at 0 °C, using
primary amines and a range of aldehydes as substrates, in the
presence of acyl cyanides as cyanide source. However, extended
reaction times were required (1.5–2 days) for the reaction to
proceed.[25] Besides, aqueous formic acid has proven to be an
environment-friendly organocatalyst for the Strecker reaction
between aniline, aromatic aldehydes and TMSCN at room tem-
perature in 5–72 min, but a higher catalyst loading was neces-
sary (20 mol-%) to achieve sufficient activity.[26] Recently, an
ionic liquid was reported to be an efficient organocatalyst for
the strecker reaction with TOF reaching 10 000 000 h–1.[27] Al-
though significant progress has been made, these methodolo-
gies are far from ideal from a sustainability viewpoint and
greener organocatalysts able to function under milder reaction
conditions while exhibiting high turnover numbers (TONs) and
initial turnover frequencies (TOFs) still need to be developed.
Herein, we report on the use of differently substituted
proazaphosphatranes 1a–d (Figure 1) as catalysts for the
Strecker reaction using Ts-, N-Boc-, and Bn- protected imines as
substrates and TMSCN as cyanide source. These catalysts
proved to be highly efficient under very mild reaction condi-
tions providing at 0 °C high TOFs around 105 h–1 and TONs up
to 104. Besides, a mechanism is proposed for the cyanation of
imines catalyzed by proazaphosphatranes.
Table 1. Optimization of catalyst loading and reaction time for proazaphos-
phatrane 1a catalyzed cyanation of imines.[a]
Entry
1a (mol-%)
Time
Yield [%][b]
1
2
3
4
5
6
7
8
1
1
20 min
2 min
20 min
2 min
20 min
2 min
12 h
>99
97
99
83
58
31
99
<1
0.1
0.1
0.01
0.01
0.01
–
12 h
[a] Reaction conditions: N-Tosyl-benzaldimine (0.5 mmol), TMSCN
(0.75 mmol), 1.5 mL of THF, under argon, then 3 mL of H2O. [b] Isolated yields
are given.
produced a 31 % yield in only 2 minutes which corresponds to
a TOF of 9.3 104 h–1, a remarkable activity value for an organo-
catalyst for the Strecker reaction (entry 6, Table 1). Prolonging
the reaction time at this very low catalyst loading resulted in
additional activity improvement with yields attaining 58 % in
20 minutes and up to 99 % after 12 hours, affording a total TON
around 104 (entries 5 and 7, Table 1). It is noteworthy that no
reaction occurred without catalyst (entry 8, Table 1), even after
12 hours, and that Et3N failed to catalyze this reaction when
used in the same reaction conditions as in entry 3 (0.1 mol-%,
20 min, 0 °C, <1 % yield). Thus, it appears that the Verkade's
superbase is a powerful catalyst for the Strecker reaction dis-
playing remarkable initial TOFs and TONs under mild condi-
tions, underlining both its high catalytic activity and stability. It
is worth mentioning that J. G. Verkade demonstrated in a previ-
ous report that an azaphosphatrane nitrate salt could catalyze
the three-component Strecker reaction, however 20 mol-% of
catalyst loading and long reaction times ranging from 15 to 35
hours were needed.[28]
Figure 1. Proazaphosphatranes 1a–1d used in this study.
We then chose to use the following reaction conditions to
further screen the reaction parameters and catalyst structural
pattern: 0.1 mol-% of catalyst loading at 0 °C for 20 minutes, as
they allow for the reaction to proceed in high yield and in rela-
tively short reaction timeframe. We first examined the influence
of the solvent on catalytic performance. As shown from Table 2,
high conversion levels were achieved in all the cases with yields
of 93 % for DCM and up to 99 % for both THF and toluene
(entries 1, 2, and 3, Table 2). The influence of the stereoelec-
tronic properties and basicity of the proazaphosphatranes 1a–d
on catalytic activity was then investigated using THF as solvent
(Table 2). In the presence of 0.1 mol-% catalyst within 20 min-
utes, all four proazaphosphatranes displayed excellent catalytic
activity with yields approaching 100 % (entries 3, 4, 5 and 6,
Results and Discussion
The cyanation of imines was first investigated in the presence of
proazaphosphatrane 1a as catalyst using the addition of TMSCN
(1.5 equiv.) to N-Tosyl-benzaldimine (1.0 equiv.) as a benchmark
reaction (Table 1). We were pleased to observe that, in the pres-
ence of 1 mol-% of proazaphosphatrane 1a in 20 minutes and
at 0 °C, more than 99 % yield was reached (entry 1, Table 1),
and even in very short reaction time (2 minutes), yield as high
as 97 % could be achieved (entry 2, Table 1), highlighting the
high efficiency of the Verkade's superbase as organocatalyst for
this reaction. In addition, 1a proved to be very selective leading
to α-aminonitriles as the sole products, in line wih the results
previously reported by J. G. Verkade for other transformations.[4]
Motivated by these results, we then decided to decrease the Table 2). In order to further discriminate catalytic activity
catalyst loading to explore further the performance scope of 1a: among the proazaphosphatranes 1a–d, a lower catalyst loading
with 0.1 mol-% loading, 83 % and 99 % yields were obtained in of 0.001 mol-% was used within the same reaction period. The
2 and 20 minutes respectively (entries 3 and 4 respectively, results indicated that catalytic activity was correlated to the ba-
Table 1). Decreasing further the amount of 1a to 0.01 mol-% sicity of proazaphosphatranes: stronger basicity resulted in
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higher yield (entries 3–6, Table 2). Indeed, the catalytic activity
follows the same trend (1a < 1d < 1b < 1c) as the basicity
order of proazaphosphatranes (1a < 1d < 1b < 1c).
Table 3. Substrate scope of proazaphosphatrane 1a-catalyzed cyanation of
imines.[a]
Table 2. Influence of solvent and stereoelectronic properties of proazaphos-
phatranes on catalytic activity.[a]
Entry
Imine
R1
R2
PG
Product
Yield [%][b]
1
2
3
4
5
6
7
8
9
10
2a
2b
2c
2d
2e
2f
2g
2h
2i
Ph
H
H
H
H
H
H
H
H
Tosyl
Tosyl
Tosyl
Tosyl
Tosyl
Tosyl
N-Boc
Bn
3a
3b
3c
3d
3e
3f
3g
3h
3i
quant.
quant.
quant.
quant.
quant.
85
p-MeC6H4
p-MeOC6H4
p-CNC6H4
2-naphthyl
tBu
Ph
Ph
2-furan
Ph
[b]
Entry
Catalyst
Solvent
pKa
Yield [%][c]
1
2
3
4
5
6
1a
1a
1a
1b
1c
1d
DCM
Toluene
THF
THF
THF
32.14
32.14
32.14
33.53
33.63
32.90
93
99
94
99 (15)[d]
99 (22)[d]
99 (28)[d]
99 (17)[d]
92
H
CH3
Tosyl
Tosyl
95[c]
2j
3j
93[c,d]
THF
[a] Reaction conditions: imines (0.5 mmol), TMSCN (0.75 mmol), 0.1 mol-%
1a, 1.5 mL of THF, 20 min, under argon, then 3 mL of H2O. [b] Isolated yields
are given. [c] 2 mol-% of catalyst was used. [d] The reaction was performed
for 2 h.
[a] Reaction conditions: N-Tosyl-benzaldimine (0.5 mmol), TMSCN
(0.75 mmol), 0.1 mol-% catalyst, 1.5 mL of solvent, under argon for 20 min,
then 3 mL of H2O. [b] pKa values of conjugate acids of proazaphosphatrane
bases in acetonitrile.[8c,3] [c] Isolated yields are given. [d] 0.001 mol-% catalyst
was used for 2 h.
With optimized conditions in hand, we then studied the
scope of substrates for the cyanation of imines on representa-
tive examples. Tosyl-protected imines bearing phenyl groups
differently substituted were first explored (entries 1–4, Table 3),
for which nearly quantitative isolated yields were obtained. In
addition to aromatic substituents, aliphatic analogue 2f also
proceeded well with 85 % yield (entry 6, Table 3). Furthermore,
N-Boc and Bn-protected imines were tested in our system. Re-
markably, excellent yields of 94 % and 92 % of corresponding
products were reached, respectively (entries 7 and 8, Table 3).
Clearly, different protecting groups are compatible with our
methodology, which provides an attractive alternative for some
specific low-reactive imines. Another key advantage is the use
of TMSCN as cyanide source, which is more convenient and
safer than typical cyanide salts such as NaCN, KCN or extremely
toxic ones like HCN. Cyanation of an imine bearing a hetero-
cyclic furan group was also successfully achieved in high yield
(95 %) after 2 hours (entry 9, Table 3). Using ketimine 2j as
substrate also provides the expected product 3j in 93 % yield
(entry 10, Table 3).
A possible reaction mechanism is depicted in Scheme 1. The
first step is the activation of TMSCN by attack of the superbase
to form a tetra-coordinated silicon complex A which was con-
firmed by solid-state CP MAS 29Si NMR: the appearance of a
new signal was observed at 7.8 ppm by mixing 1 equiv. of
TMSCN with 1 equiv. of 1a, in addition to the resonance at
–12.0 ppm for TMSCN, in agreement with the literature data
(Figures S47–48).[4h] Then, the nucleophilic anion CN– attacks
the imine substrate affording the key intermediate ion pair B.
Cleavage of the Si–P bond leads to the regeneration of the
catalyst 1a and the concomitant release of the TMS-protected
amine product C which is subsequently hydrolyzed to give the
desired amine product D.[29a,30]
Scheme 1. Proposed mechanism for the cyanation of imines catalyzed by
proazaphosphatrane.
ing N-Tosyl-benzaldimine and TMSCN as substrates in the pres-
ence of 20 mol-% of HMPT at 0 °C in THF for 24 h (Scheme 2).
Only 23 % yield was reached, which can be compared to the
quantitative yield obtained with 0.1 mol-% of proazaphosphat-
rane 1a in only 20 minutes (entry 1, Table 3). As can be seen,
HMPT and 1a have similar structure except for the bridgehead
nitrogen in 1a, the transannulation between bridgehead nitro-
gen and phosphorus enhanced the basicity and nucleophilicity
of the phosphorus atom in 1a, which makes it more reactive
for activation of TMSCN in agreement with other reported pro-
azaphosphatrane-catalyzed transformations.[4h,29a,30]
Conclusions
In order to shed light on the nature of the high efficiency of In summary, we have presented a mild, convenient and highly
proazaphosphatranes, we carried out a control experiment us- efficient methodology for the synthesis of α-aminonitriles using
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116.3, 48.2, 21.7 ppm. HRMS (ESI-TOF) m/z: calcd. for C15H18N3O2S+
[M + NH4]+, 304.1114, found 304.1112.
N-[Cyano(p-tolyl)methyl]-4-methylbenzenesulfonamide (3b):[31]
Obtained as white solid, 151 mg (quant.) 1H NMR (400 MHz, CDCl3):
δ = 7.82 (d, J = 8.3 Hz, 2 H), 7.37 (d, J = 8.0 Hz, 2 H), 7.32 (d, J =
8.1 Hz, 2 H), 7.21 (d, J = 8.0 Hz, 2 H), 5.44 (d, J = 8.8 Hz, 1 H), 4.93
(d, J = 8.8 Hz, 1 H), 2.46 (s, 3 H), 2.36 (s, 3 H) ppm. 13C NMR
(101 MHz, CDCl3): δ = 144.68, 140.12, 136.11, 130.05, 129.15, 127.36,
126.99, 116.39, 48.04, 21.66, 21.16 ppm. HRMS (ESI-TOF) m/z: calcd.
for C16H20N3O2S+ [M + NH4]+, 318.1271, found 318.1272.
Scheme 2. Cyanation of imine in the presence of HMPT.
proazaphosphatranes 1a–d as catalysts. In general, our method
tolerates a variety of substrates, ranging from aromatic, hetero-
aromatic to aliphatic imines with different protecting groups
including Tosyl-, Bn-, and N-Boc. The very low catalyst loading,
safer cyanide source and excellent yield and selectivity make
1a–d outstanding among the best organocatalysts for the
Strecker reaction.
N-[Cyano(4-methoxyphenyl)methyl]-4-methylbenzenesulfon-
amide (3c):[31] Obtained as white solid, 158 mg (quant.). 1H NMR
(400 MHz, CDCl3): δ = 7.81 (d, J = 7.1 Hz, 2 H), 7.46–7.28 (m, 4 H),
6.90 (d, J = 7.4 Hz, 2 H), 5.42 (d, J = 8.5 Hz, 1 H), 5.00 (d, J = 8.2 Hz,
1 H), 3.81 (s, 3 H), 2.46 (s, 3 H) ppm. 13C NMR (101 MHz, CDCl3): δ =
160.72, 144.66, 136.12, 130.04, 128.54, 127.35, 124.03, 116.47,
114.74, 55.44, 47.78, 21.66 ppm. HRMS (ESI-TOF) m/z: calcd. for
C
16H20N3O3S+ [M + NH4]+, 334.1220, found 334.1221.
N-[Cyano(4-cyanophenyl)methyl]-4-methylbenzenesulfonamide
(3d):[31] Obtained as white solid, 156 mg (quant.). 1H NMR
(400 MHz, CDCl3): δ = 7.75 (d, J = 7.5 Hz, 2 H), 7.69–7.50 (m, 4 H),
7.34 (d, J = 7.1 Hz, 2 H), 5.95 (d, J = 9.3 Hz, 1 H), 5.50 (d, J = 9.4 Hz,
1 H), 2.45 (s, 3 H) ppm. 13C NMR (101 MHz, CDCl3): δ = 145.12,
137.14, 135.65, 133.02, 130.19, 127.95, 127.24, 117.76, 115.47,
113.73, 47.75, 21.69 ppm. HRMS (ESI-TOF) m/z: calcd. for
Experimental Section
All commercial reagents and starting materials were used directly as
received without further purification. Proazaphosphatrane 1a was
prepared using a reported procedure,[8d] 1b–d were purchased
from commercial sources. All dry solvents were purified prior to use
through standard procedures or obtained from a solvent drying
system (MB-SPS-800). All the reactions were carried out under an
atmosphere of argon, unless otherwise noted. Flash column chro-
matography was performed using silica gel 60 (230–400 mesh).
Thin-layer chromatography was per-formed on aluminum-coated
plates with silica gel 60 F254 and was visualized with a UV lamp or
by staining with potassium permanganate. 1H NMR spectra were
recorded at either 300 or 400 MHz on BRUKER Avance III nanobay
spectrometers. 13C NMR spectra were recorded at either 101 or
126 MHz and reported in ppm relative to CDCl3 (δ = 77.4 ppm),
unless otherwise noted. Single Pulse Magic Angle Spinning (CP
MAS) 29Si Solid State NMR spectra were obtained with a Bruker
Avance 400 MHz WB spectrometer at the 29Si resonance frequency
of 79.5 MHz. Chemical shifts were referenced to tetramethylsilane,
whose resonance was set to 0 ppm. High-resolution mass spectra
(HRMS) were performed at Spectropole Analysis Service of Aix Mar-
seille University.
C
16H13N3O2SNa+ [M + Na]+, 334.0621, found 334.0621.
N-[Cyano(naphthalen-2-yl)methyl]-4-methylbenzenesulfon-
amide (3e):[32] Obtained as white solid, 170 mg (quant.). 1H NMR
(400 MHz, CDCl3): δ = 7.97–7.78 (m, 6 H), 7.56 (d, J = 4.5 Hz, 2 H),
7.47 (d, J = 8.7 Hz, 1 H), 7.36 (d, J = 8.0 Hz, 2 H), 5.65 (d, J = 8.8 Hz,
1 H), 5.12 (d, J = 9.1 Hz, 1 H), 2.45 (s, 3 H) ppm. 13C NMR (101 MHz,
CDCl3): δ = 144.77, 136.08, 133.54, 132.87, 130.08, 129.70, 129.18,
128.24, 127.78, 127.49, 127.37, 127.17, 126.66, 123.91, 116.26, 48.47,
21.66 ppm. HRMS (ESI-TOF) m/z: calcd. for C19H20N3O2S+ [M + NH4]+,
354.1271, found 354.1270.
N-(1-Cyano-2,2-dimethylpropyl)-4-methylbenzenesulfonamide
1
(3f):[33] Obtained as white solid, 133 mg (85 %). H NMR (400 MHz,
CDCl3): δ = 7.79 (d, J = 8.1 Hz, 2 H), 7.35 (d, J = 7.8 Hz, 2 H), 5.68
(d, J = 10.2 Hz, 1 H), 3.88 (d, J = 10.3 Hz, 1 H), 2.43 (s, 3 H), 1.04 (s,
9 H) ppm. 13C NMR (101 MHz, CDCl3): δ = 144.49, 136.02, 130.04,
127.23, 116.68, 54.69, 35.30, 25.66, 21.63 ppm. HRMS (ESI-TOF) m/z:
calcd. for C13H22N3O2S+ [M + NH4]+, 284.1427, found 284.1422.
General Procedure for Proazaphosphatrane-catalyzed Cyan-
ation of Imines: To a solution of pro-azaphosphatrane (0.1 %mmol)
and TMSCN (94 μL, 0.75 mmol) in THF (1.5 mL) was added imine
(0.5 mmol) under an atmosphere of argon. The mixture was stirred
at 0 °C for 20 minutes, upon completion monitored by TLC, 3 mL
of H2O was added and the mixture was stirred for another 30 min-
utes. The reaction mixture was then extracted with ethyl acetate
(3 × 50 mL). The organic phase was collected, dried with anhydrous
Na2SO4, filtered, and concentrated under vacuum. The crude prod-
uct was purified by flash column chromatography using petroleum
ether and ethyl acetate (10:1) as eluent to give products 3a–j. All
tert-Butyl [Cyano(phenyl)methyl]carbamate (3g):[24] Obtained as
white solid, 110 mg (94 %). 1H NMR (400 MHz, CDCl3): δ = 7.60–
7.30 (m, 5 H), 5.80 (s, 1 H), 5.16 (s, 1 H), 1.48 (s, 9 H) ppm. 13C NMR
(101 MHz, CDCl3): δ = 154.17, 133.49, 129.50, 129.32, 126.89, 117.74,
81.60, 46.13, 28.24 ppm. HRMS (ESI-TOF) m/z: calcd. for
C13H16N2O2Na+ [M + Na]+, 255.1104, found 255.1104.
2-(Benzylamino)-2-phenylacetonitrile (3h):[33] Obtained as yellow
1
oil, 102 mg (92 %). H NMR (400 MHz, CDCl3): δ = 7.66–7.28 (m, 10
H), 4.77 (s, 1 H), 4.08 (d, J = 13.1 Hz, 1 H), 3.97 (d, J = 13.0 Hz, 1 H),
1.89 (s, 1 H) ppm. 13C NMR (101 MHz, CDCl3): δ = 138.17, 134.81,
129.05, 128.99, 128.67, 128.44, 127.67, 127.33, 118.78, 53.49, 51.29
1
compounds have been described elsewhere, therefore only H, 13C
ppm. HRMS (ESI-TOF) m/z: calcd. for C15H15N2 [M + H]+, 223.1230,
+
and mass spectra are given, which are consistent with reported
literatures.
found 223.1228.
N-[Cyano(phenyl)methyl]-4-methylbenzenesulfonamide (3a):[31]
Obtained as white solid, 143 mg (quant.). 1H NMR (400 MHz, CDCl3):
δ = 7.81 (d, J = 7.8 Hz, 2 H), 7.50–7.39 (m, 5 H), 7.37 (d, J = 7.8 Hz,
2 H), 5.48 (s, 1 H), 5.12 (s, 1 H), 2.46 (s, 3 H) ppm. 13C NMR (101 MHz,
CDCl3): δ = 144.7, 136.1, 132.1, 130.1, 129.9, 129.4, 127.3, 127.1,
N-[Cyano(furan-2-yl)methyl]-4-methylbenzenesulfonamide
(3i):[33] Obtained as colorless solid, 131 mg (95 %) 1H NMR
(400 MHz, CDCl3): δ = 7.76 (d, J = 8.1 Hz, 2 H), 7.39–7.35 (m, 1 H),
7.32 (d, J = 8.1 Hz, 2 H), 6.45 (d, J = 3.2 Hz, 1 H), 6.33 (t, J = 2.5 Hz,
1 H), 5.71 (d, J = 8.9 Hz, 1 H), 5.52 (d, J = 9.0 Hz, 1 H), 2.43 (s, 3 H)
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ppm. 13C NMR (75 MHz, CDCl3): δ = 144.63, 144.43, 144.14, 136.09,
129.97, 127.25, 114.68, 110.97, 110.36, 42.26, 21.60 ppm. HRMS (ESI-
TOF) m/z: calcd. for C13H16N3O3S+ [M + NH4]+, 294.0907, found
294.0907.
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2 H), 7.38–7.28 (m, 3 H), 7.26–7.18 (m, 2 H), 5.40 (s, 1 H), 2.42 (s, 3
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Keywords: Pro-Azaphophatranes · Verkade's superbase ·
Strecker reaction · Organocatalysis · Phosphorus
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Received: July 25, 2018
Eur. J. Org. Chem. 0000, 0–0
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
Organocatalytic Mechanisms
J. Yang, B. Chatelet,
F. Ziarelli, V. Dufaud, D. Hérault,
A. Martinez* ......................................... 1–6
Verkade's Superbase as an Organo-
catalyst for the Strecker Reaction
Verkade's superbases were found to in short reaction time and requiring
be efficient organocatalysts for the low catalyst loading.
Strecker reaction, leading to high yield,
DOI: 10.1002/ejoc.201801170
Eur. J. Org. Chem. 0000, 0–0
www.eurjoc.org
6
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim