Asymmetric addition of aryloxy ethynyl lithium derivatives to N-sulfinyl imines

Article abstract of DOI:10.1007/s00706-012-0907-1

Aryloxy ethynyl lithium species can be generated in diethyl ether and efficiently added to aliphatic and aromatic N-sulfinyl imines in THF, affording aryloxypropargyl sulfinamides in good yield, and in most cases high diastereoselectivity. The diastereose

Full text of DOI:10.1007/s00706-012-0907-1

Monatsh Chem (2013) 144:455–460
DOI 10.1007/s00706-012-0907-1
ORIGINAL PAPER
Asymmetric addition of aryloxy ethynyl lithium derivatives
to N-sulfinyl imines
•
´
Charlie Verrier Sebastien Carret
Jean-Franc¸ois Poisson
•
Received: 17 October 2012 / Accepted: 16 December 2012 / Published online: 5 March 2013
Ó Springer-Verlag Wien 2013
Abstract Aryloxy ethynyl lithium species can be gener-
ated in diethyl ether and efficiently added to aliphatic and
aromatic N-sulfinyl imines in THF, affording aryloxy-
propargyl sulfinamides in good yield, and in most cases
high diastereoselectivity. The diastereoselectivity can be
reversed by precomplexation of the N-sulfinyl imine with
BF3ÁOEt2.
been little studied [22, 23]. We have recently reported the
diastereoselective addition of such lithiated ethynyl ethers
to chiral N-sulfinyl imines affording the alkoxypropargyl
sulfinamides in high yield and in most cases in very good
diastereoselectivity [24]. Remarkably, the selectivity could
be completely reversed by adding the strong Lewis acid
boron trifluoride. In this reaction, the best solvent was
THF, necessary for both the transformation of the dichlo-
roenol ether into the lithiated ynol ether, and to obtain high
diastereoselectivities. Aiming at bringing some diversity to
the substrates, we decided to explore the addition of aryl-
oxy ethynyl derivatives. We herein present the results of
this study.
Keywords Nucleophilic additions Á
Organometallic compounds Á Solvent effect Á
Asymmetric synthesis Á Ynol ethers
Introduction
Ynol ethers are valuable building blocks for synthesis; they
can afford esters by hydrolysis, enol ethers by partial
reduction, ethers by complete reduction, and they can also
undergo a variety of transition metal catalyzed transfor-
mations [1–3]. The ynol ethers can be synthesized from
esters [4], b-hydroxy ketones [5], gem-dibromoalkenes [6],
by oxidation of terminal alkynes [7–10] or from dichlo-
roenol ethers [11–17]. Among these available methods, the
synthesis of ethynyl ethers can be efficiently achieved
using the latter. Upon treatment with two equivalents of
n-butyllithium, dichloroenol ethers evolve to lithiated
ethynyl ethers, which can react in situ with electrophiles
[18–21]. However, the addition of these ethynyl ether
anions to carbonyl or imine derivatives has surprisingly
Results and discussion
We started by forming the p-methoxyphenyl dichloroenol
ether 1a [23] by treating the corresponding potassium
phenoxide with trichloroethylene. With no surprise, the
reaction was much slower compared to the reaction with an
alkoxide, requiring 24 h for completion. The second step
proved much more surprising: when the p-methoxyphenyl
dichloroenol ether 1a was reacted with n-butyllithium in
THF (-78 °C to -40 °C), and subsequently treated with
N-sulfinyl imine 2a, the starting dichloroenol ether 1a was
recovered intact accompanied by the product of addition of
n-butyllithium to the N-sulfinyl imine (3, Scheme 1). This
result showed that no lithiated ethynyl ether had been
formed under these reaction conditions, albeit standardly
used for alkoxy derivatives [24]. Repeating the experiment
without adding an electrophile, we could indeed notice that
no ynol ether was formed after hydrolysis, even upon
warming the reaction to 0 °C. We could secure the role of
the first equivalent of n-butyllithium by trapping the
C. Verrier Á S. Carret Á J.-F. Poisson (&)
´
Departement de Chimie Moleculaire (SERCO), UMR-5250,
ICMG FR-2607, CNRS, Universite Joseph Fourier, BP 53,
´
´
38041 Grenoble Cedex 9, France
e-mail: jean-francois.poisson@ujf-grenoble.fr
123

456
C. Verrier et al.
Scheme 1
OH
MeO
KH
Cl2CCHCl
68%
THF
1. n-BuLi (3.8 equiv)
THF, -78 °C -> -40 °C
Cl
SO-t-Bu
Cl
HN
PMPO
+
O
SO-t-Bu
Ph
Bu
2.
Ph
N
Cl
1a
Cl
MeO
2 : 1
2a
3
1a
H
(2 equiv)
Cl
O
1. n-BuLi (1 equiv) THF, -78 °C
Me
Cl
quant.
2. MeI, -78 °C
MeO
1. n-BuLi
O
S
2. 2a, Et2O
(3.8 equiv)
Et2O,
-78 °C -> -40°C
HN
32%
2. 2a, THF
OPMP
4a
dr = 86:14
79%
resulting vinyl anion with methyl iodide, forming the
methyl dichloroenol ether in quantitative yield
1H NMR spectrum, by the relative integration of the
propargylic proton of each diastereoisomer. The assign-
ment of the stereochemistry of the major isomer as SS,S
was reasonably attributed based on our previous studies
[24].
a
(Scheme 1). The fact that this intermediate vinyl lithium,
obtained by deprotonation of the aryloxy dichloroenol
ether, does not evolve to the ynol derivative by b-elimi-
nation is very surprising. Greene had previously reported
the formation of naphthyl ethynyl ether in THF [17].
However, Hashmi had used diethyl ether in his experiments
involving the formation of aryloxy ethynyl ethers [23].
Performing the deprotonation in diethyl ether indeed led to
the lithiated ethynyl ether, as evidenced by the formation of
30 % of the phenoxypropargyl sulfinamide 4a after addi-
tion of the N-sulfinyl imine 2a (Scheme 1). This difference
of behavior of the intermediate vinyl lithium species gen-
erated in THF or in diethyl ether is very surprising and no
satisfying explanation has been found so far. During our
previous study of addition of alkoxy ethynyl lithium
derivatives to N-sulfinyl imines, we had observed that the
presence of THF was crucial for good yields, and that the
best diastereoselectivity required the exclusive use of THF
[24]. As diethyl ether is compulsory for the formation of
the aryloxy ethynyl lithium derivative, we decided to add
the ethereal ethynyl lithium solution to a THF solution of
N-sulfinyl imine 2a (with a final Et2O/THF ratio of 1/2).
This procedure proved rewarding as the p-methoxyphen-
oxypropargyl sulfinamide 4a was isolated this time in 79 %
yield as a 86:14 mixture of diastereoisomers. The diaste-
reoselectivity of the reaction was determined on the crude
This procedure was next applied to a variety of N-sul-
finyl imines 2a–2g. With the p-methoxyphenyl N-sulfinyl
imine 2b, the yield was enhanced to 90 % and the diaste-
reoselectivity increased to 91:9. The procedure is
compatible with benzylic protons as the o-tolyl derivative
4c could be obtained in high yield. Nevertheless, with the
1-naphthyl N-sulfinyl imine 2d, the yield dropped to 67 %,
with the formation of two diastereoisomers 4d and 5d, in
nearly equal amount. With an electron poor aromatic
derivative, the 4-bromophenyl N-sulfinyl imine 2e, the
alkoxypropargyl sulfinamide 4e was obtained with a high
diastereoselectivity, whereas the furyl derivative 4g was
formed with a slightly lower efficiency. Finally, the tert-
butyl derivative 4f was also formed in good yield and
reasonable selectivity (Scheme 2).
We had also shown with alkoxy ethynyl lithium that
precomplexing the N-sulfinyl imine with BF3ÁOEt2 resulted
in a complete inversion of diastereoselectivity [24–26]. We
therefore next investigated this procedure with aryloxy
ethynyl lithium species. Precomplexing the N-sulfinyl
imine 2a with BF3ÁOEt2 in THF, followed by addition of
the ethereal solution of the lithiated ethynyl ether, afforded
the diastereoisomer 5a in very good yield (84 %), with a
123

Asymmetric addition of aryloxy ethynyl lithium derivatives to N-sulfinyl imines
457
Scheme 2
O
S
1. n-BuLi
Et2O, -78 °C -> -40 °C
MeO
O
Cl
HN
OMe
R
SO-t-Bu
Cl
2.
N
,THF
1a
O
4a-4g
2a-2g
(2 equiv)
R
H
O
O
S
O
S
S
HN
HN
HN
OPMP
OPMP
OPMP
O
4a
4b
4c
79%
(86:14)
90%
(91:9)
88%
(87:13)
O
S
O
S
HN
HN
OPMP
OPMP
HN
Br
4d
67%
(55:45)
4e
83%
O
O
S
(70:30)
S
HN
O
OPMP
OPMP
4f
66%
(92:8)
4g
90%
(85:15)
complete inversion and greater selectivity (dr = 2:98).
Hence, with or without Lewis acid, the diastereoselectivity
can again be reversed to obtain both diastereoisomers in
very high yield (Scheme 3).
influence of the solvent, and the nature of the aromatic are
very surprising, and further work is ongoing to understand
the origin of such a difference in behavior in the formation of
lithiated alkyl or aryl ethynyl ethers.
We also synthesized other aryloxy dichloroenol ethers
derivatives: the phenyl and the 3,5-dimethyl-4-chlor-
ophenyl dichloroenol ethers. Whereas these dichloroenol
ethers 1b, 1c were formed efficiently using the condensa-
tion of their potassium phenoxide with trichlorethylene, the
subsequent reaction was unproductive. With the phenyl
derivative 1b, the formation of the intermediate ynol ether
is incomplete in diethyl ether and the crude product is
obtained as a mixture of the expected sulfinamide 4h and
an unidentified, inseparable by-product in an estimated
70:30 ratio. The same result was unfortunately obtained
with dichloroenol ether 1c (Scheme 4).
Experimental
Reactions were carried out under argon in oven-dried
glassware. Standard inert atmosphere techniques were used
in handling all air and moisture sensitive reagents. Com-
mercial reagents were used without any further purification
unless otherwise stated. Dry THF and diethyl ether were
distilled from sodium/benzophenone. Thin-layer chroma-
tography was performed on 0.2 mm silica sheets, which
were visualized under ultraviolet light and by heating the
plate after treatment, generally with phosphomolybdic acid
in ethanol. Silica gel (0.040–0.063 mm) was employed for
flash column chromatography. A Fourier transform infra-
As a conclusion, we have found that p-methoxyphenyloxy
ethynyl lithium species, generated from the corresponding
dichloroenol ether using diethyl ether as a solvent, can sub-
sequently react stereoselectively with N-sulfinyl imines in
THF. This solvent combination is crucial for the outcome of
the reaction. With other aromatic substituents, the formation
of the lithiated ethynyl ether is incomplete. Both the
1
red spectrometer was used to record IR spectra. H NMR
and 13C NMR spectra were recorded on either an AV 300,
1
400, or 500 MHz apparatus. All shifts for H spectra were
referenced to the residual solvent peak and are reported in
123

458
C. Verrier et al.
Scheme 3
O
S
1. n-BuLi
Et2O, -78 °C -> -40 °C
MeO
O
Cl
HN
Ph
OMe
.
2. 2a, BF3 OEt2
Cl
THF
O
1a
5a
84%
(> 98:2)
Scheme 4
O
1. n-BuLi
Et2O, -78 °C -> -40 °C
S
ArO
Cl
Cl
KH
Cl2CCHCl
HN
ArOH
2. 2a, THF
Ph
OA
<70% purity
1b, Ar = Ph, 68%
1c, Ar = 3,5-Me-4-Cl-Ph, 62%
(s, 3H), 3.67 (d, J = 6.6 Hz, 1H), 1.23 (s, 9H) ppm; 13C
NMR (100 MHz, CDCl3): d = 156.8, 150.2, 140.3, 129.0,
128.6, 128.0, 116.3, 115.1, 90.3, 56.7, 56.1, 51.2, 43.7,
ppm. When ambiguous, proton and carbon assignments
were established through COSY, HMQC, and/or DEPT
experiments. Mass spectra were recorded by using ESI
techniques. HRMS were recorded on an Orbitrap apparatus
(ESI).
22.9 ppm; IR (neat): m = 2,280, 3,117 cm-1; MS (ESI):
ꢀ
m/z = 358.3 (M ? H)?; HRMS calcd for C20H24NO3S
358.147141, found 358.147181.
General procedure for the diastereoselective addition
of lithium aryloxy acetylide to N-tert-butyl sulfinyl
imines
(S*S)-N-[(S*)-3-(4-Methoxyphenoxy)-1-(4-methoxy-
phenyl)prop-2-yn-1-yl]-2-methylpropane-2-sulfinamide
(4b, C21H25NO4S)
Sulfinylimine 2b (75.5 mg, 0.316 mmol) and enol ether 1a
afforded 110.6 mg of sulfinamide 4b (90 %, dr = 91:9). A
diastereopure sample of 4b could be isolated as a pale
Preparation of a 0.25 M solution of lithiated ynol ether in
Et2O/hexane (4/1): to the dichloroenol ether 1a at -80 °C
in diethyl ether was slowly added a solution of n-BuLi
(2.5 M/hexane, 1.9 equiv). This solution was allowed
to warm to -40 °C, stirred for 90 min, and cooled down to
-80 °C.
A portion of the above cold solution of lithiated ynol
ether (2 equiv/sulfinylimine) was added to the sulfinylim-
ine 2a–2g in THF (0.06 M) at -80 °C. The reaction
mixture was allowed to warm to -20 °C over 3 h. After
disappearance of the starting material (monitored by TLC,
eluent AcOEt/pentane 35:65), isopropanol was added and
the mixture transferred into a separatory funnel. The
organic phase was washed with water and brine, dried over
Na2SO4, filtered, and concentrated under reduced pressure.
The crude material was purified by flash chromatography
(SiO2/2.5% Et3N v/v) to afford the N-tert-butyl sulfinamide
4a–4g.
1
yellow oil. H NMR (400 MHz, CDCl3): d = 7.49–7.42
(m, 2H), 7.25–7.18 (m, 2H), 6.92–6.83 (m, 4H), 5.31
(d, J = 6.2 Hz, 1H), 3.81 (s, 3H), 3.78 (s, 3H), 3.61
(d, J = 6.2 Hz, 1H), 1.22 (s, 9H) ppm; 13C NMR
(100 MHz, CDCl3): d = 159.9, 156.7, 150.2, 132.3,
129.2, 116.3, 115.1, 114.3, 90.1, 56.5, 56.1, 55.6, 50.6, 43.9,
22.9 ppm; IR (neat): m = 2,274, 3,200 cm-1; MS (ESI):
ꢀ
m/z = 388.3 (M ? H)?; HRMS calcd for C21H26NO4S
388.157706, found 388.157746.
(S*S)-N-[(S*)-3-(4-Methoxyphenoxy)-1-(o-tolyl)prop-2-yn-
1-yl]-2-methylpropane-2-sulfinamide (4c, C21H25NO3S)
Sulfinylimine 2c (73.7 mg, 0.33 mmol) and enol ether 1a
afforded 108.9 mg of sulfinamide 4c (88 %, dr = 87:13).
A diastereopure sample of 4c could be isolated as a pale
1
yellow oil. H NMR (400 MHz, CDCl3): d = 7.68–7.61
(S*S)-N-[(S*)-3-(4-Methoxyphenoxy)-1-phenylprop-2-yn-1-
yl]-2-methylpropane-2-sulfinamide (4a, C20H23NO3S)
Sulfinylimine 2a (67.5 mg, 0.32 mmol) and dichoroenol
ether 1a afforded 87.7 mg of sulfinamide 4a (78 %,
dr = 86:14). A diastereopure sample of 4a could be
isolated as a pale yellow oil. 1H NMR (500 MHz, CDCl3):
d = 7.55 (d, J = 7.3 Hz, 2H), 7.42–7.28 (m, 3H), 7.23
(m, 2H), 6.90–6.82 (m, 2H), 5.36 (d, J = 6.6 Hz, 1H), 3.77
(m, 1H), 7.27–7.15 (m, 5H), 6.90–6.83 (m, 2H), 5.51
(d, J = 6.5 Hz, 1H), 3.77 (s, 3H), 3.53 (d, J = 6.5 Hz,
1H), 2.45 (s, 3H), 1.21 (s, 9H) ppm; 13C NMR (75 MHz,
CDCl3): d = 156.7, 150.2, 138.0, 136.3, 131.1, 128.6,
128.1, 126.7, 116.3, 115.0, 89.8, 56.6, 56.0, 48.5, 43.7,
22.9, 19.5 ppm; IR (neat): m = 2,273, 3,296 cm-1; MS
ꢀ
(ESI): m/z = 372.3 (M ? H)?; HRMS calcd for C21H26
NO3S 372.162791, found 372.163058.
123

Asymmetric addition of aryloxy ethynyl lithium derivatives to N-sulfinyl imines
459
(S*S)-N-[(S*)-3-(4-Methoxyphenoxy)-1-(naphthalen-1-
yl)prop-2-yn-1-yl]-2-methylpropane-2-sulfinamide
(4d, C24H25NO3S)
yellow oil. H NMR (400 MHz, CDCl3): d = 7.24–7.17
(m, 2H), 6.87–6.80 (m, 2H), 3.77 (d, J = 9.2 Hz, 1H), 3.74
(s, 3H), 3.17 (d, J = 9.2 Hz, 1H), 1.22 (s, 9H), 0.99 (s, 9H)
ppm; 13C NMR (100 MHz, CDCl3): d = 156.5, 150.3,
116.1, 114.9, 89.2, 58.6, 56.8, 55.9, 43.4, 36.6, 26.5,
1
Sulfinylimine 2d (91.2 mg, 0.35 mmol) and enol ether 1a
afforded 96.4 mg of sulfinamide 4d (67 %, dr = 55:45). A
diastereopure sample of 4d could be isolated as a yellow
oil. 1H NMR (400 MHz, CDCl3): d = 8.31 (d, J = 8.2 Hz,
1H), 7.92–7.82 (m, 3H), 7.59–7.44 (m, 3H), 7.30–7.18
(m, 2H), 6.87-6.82 (m, 2H), 6.02 (d, J = 6.7 Hz, 1H), 3.77
(s, 3H), 3.73 (d, J = 6.7 Hz, 1H), 1.18 (s, 9H) ppm; 13C
NMR (100 MHz, CDCl3): d = 156.7, 150.2, 135.0, 134.5,
130.8, 129.6, 129.2, 126.46, 126.43, 126.2, 125.6, 124.5,
116.3, 115.0, 90.6, 56.6, 56.0, 49.4, 43.7, 22.9 ppm; IR
23.0 ppm; IR (neat): m = 2,271, 3,212 cm-1; MS (ESI):
ꢀ
m/z = 338.3 (M ? H)?; HRMS calcd for C18H28NO3S
338.178441, found 338.178578.
(S*S)-N-[(R*)-3-(4-Methoxyphenoxy)-1-phenylprop-2-yn-1-
yl]-2-methylpropane-2-sulfinamide (5a, C20H23NO3S)
Imine 2a was precomplexed with BF3ÁEt2O (1.1 eq) at
room temperature in THF before the addition of the
lithiated ynol ether at -80 °C. The reaction was quenched
with a saturated solution of NaHCO3 instead of isopropa-
nol. Sulfinylimine 2a (84.0 mg, 0.40 mmol) and enol ether
1a afforded 119.7 mg of sulfinamide 5a (84 %, dr [ 2:98).
A diastereopure sample of 5a could be isolated as a pale
(neat): m = 2,272, 3,189 cm-1; MS (ESI): m/z = 408.3
ꢀ
(M ? H)?; HRMS calcd for C24H26NO3S 408.162791,
found 408.162963.
(S*S)-N-[(S*)-1-(4-Bromophenyl)-3-(4-methoxyphen-
oxy)prop-2-yn-1-yl]-2-methylpropane-2-sulfinamide
(4e, C20H22BrNO3S)
1
yellow oil. H NMR (400 MHz, CDCl3): d = 7.61–7.49
(m, 2H), 7.43–7.29 (m, 3H), 7.23–7.16 (m, 2H), 6.89–6.82
(m, 2H), 5.43 (d, J = 3.5 Hz, 1H), 3.77 (s, 3H), 3.57 (d,
J = 3.5 Hz, 1H), 1.23 (s, 9H) ppm; 13C NMR (100 MHz,
CDCl3): d = 156.7, 150.1, 140.3, 129.1, 128.7, 127.9,
116.1, 115.0, 90.3, 56.1, 56.0, 50.9, 42.9, 22.9 ppm; IR
Sulfinylimine 2e (86.3 mg, 0.30 mmol) and enol ether 1a
afforded 108.0 mg of sulfinamide 4e (83 %, dr = 70:30).
A diastereopure sample of 4e could be isolated as a pale
1
yellow oil. H NMR (400 MHz, CDCl3): d = 7.54–7.46
(neat): m = 2,273, 3,188 cm-1; MS (ESI): m/z = 358.3
ꢀ
(m, 2H), 7.44–7.37 (m, 2H), 7.23–7.16 (m, 2H), 6.91–6.82
(m, 2H), 5.31 (d, J = 6.2 Hz, 1H), 3.78 (s, 3H), 3.62
(d, J = 6.2 Hz, 1H), 1.22 (s, 9H) ppm; 13C NMR (75 MHz,
CDCl3): d = 156.8, 150.0, 139.3, 132.1, 129.7, 122.6,
116.2, 115.1, 90.4, 56.7, 56.0, 50.5, 43.1, 22.9 ppm; IR
(M ? H)?; HRMS calcd for C20H24NO3S 358.147141,
found 358.147396.
Acknowledgments We thank the CNRS, the University Joseph
Fourier, and the ANR (Project Lycomet ANR-11-JS-07-006-01) for
`
financial support. C.V. acknowledges the Ministere de la Recherche
for a PhD fellowship.
(neat): m = 2,272, 3,183 cm-1; MS (ESI): m/z = 438.2
ꢀ
(M ? H)? (81Br); HRMS calcd for C20H23BrNO3S
436.057653, found 436.057732.
(S*S)-N-[(R*)-1-(Furan-2-yl)-3-(4-methoxyphenoxy)prop-2-
yn-1-yl]-2-methylpropane-2-sulfinamide
(4f, C18H21NO4S)
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1
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