Synthesis of polyfunctional unsaturated amines by the addition of functionalized organomagnesium reagents to unsaturated imminium ions

Article abstract of DOI:10.1055/s-2002-34369

The reaction of propargylic and allylic aminals with trifluoromethanesulfonic anhydride at low temperature produces imminium salts, which react in the presence of N-methylpyrrolidinone (NMP) with functionalized arylmagnesium compounds, providing polyfunct

Full text of DOI:10.1055/s-2002-34369

PAPER
2143
Synthesis of Polyfunctional Unsaturated Amines by the Addition of Functiona-
lized Organomagnesium Reagents to Unsaturated Imminium Ions
S
ynthesis of Polyf
i
unction
n
a
l
U
nsaturat
a
e
d
A
mine
s
Gommermann, Christopher Koradin, Paul Knochel*
Department Chemie, Ludwig-Maximilians-Universität München, Butenandtstr. 5-13, Haus F, 81377 München, Germany
Fax +49(89)21807680; E-mail: paul.knochel@cup.uni-muenchen.de
Received 18 July 2002
Dedicated to Prof. Dieter Seebach on the occasion of his 65th birthday.
Abstract: The reaction of propargylic and allylic aminals with tri-
fluoromethanesulfonic anhydride at low temperature produces im-
minium salts, which react in the presence of N-methylpyrrolidinone
(NMP) with functionalized arylmagnesium compounds, providing
polyfunctional propargylic and allylic amines in satisfactory yields.
Key words: functionalized organomagnesium reagents, imminium
salts, propargylic amines, allylic amines, aminals
The preparation of polyfunctional organic molecules
without the use of protecting groups is an important syn-
thetic task. Polyfunctional organometallics are particular-
ly well suited for achieving this goal.1 It is well known
that functionalized organozinc compounds2 are compati-
ble with many functional groups, and it has also been
shown that polyfunctional organomagnesium reagents
can be readily obtained by an iodine- or a bromine-mag-
nesium exchange.3 The preparation of functionalized un-
saturated amines is especially important, since many
polyfunctional amino compounds are of interest due to
their biological activity.4 Herein, we wish to report the re-
action of the unsaturated aminals 1a b5,6 and 27 with func-
tionalized arylmagnesium species of type 3, leading after
treatment with trifluoromethanesulfonic anhydride to
amines 4 and 5. Thus, trifluoromethanesulfonic anhydride
reacts with the aminals 1,2, furnishing the corresponding
imminium triflates 6a b and 7, which react rapidly with
Scheme 1
Grignard reagents8 (see Scheme 1, Tables 1 and 2).
A range of different functionalized arylmagnesium re-
agents can be used. Thus, several para-substituted aryl-
magnesium species like 3a,b react well with the alkynyl
aminals 1a and 1b leading to the corresponding propargyl
amine derivatives (4a,b and 4h,i; entries 1, 2, 8 and 9 of
Table 1). Sterically hindered ortho-substituted arylmag-
nesium compounds 3c–f bearing carbethoxy, bromine, ni-
tro or trialkylsilyloxy groups react with 1a–b forming
products 4c–f in good yields (55 79%, entries 3 6 of
Table 1). The reactions involve treatment of aminals 1a,b
with Tf2O at –65 °C or –78 °C respectively, leading to an
intensely yellow solution of the imminium salts 6a,b. A
precipitate forms after a few minutes and redissolves after
the addition of N-methylpyrrolidinone (NMP; 5 equiv). A
THF solution of the Grignard reagent of type 3 (1.5 equiv)
is added and the addition reaction is complete after 0.5 to
1.0 hours. A heterocyclic magnesium reagent such as 5-
carbethoxyfurylmagnesium bromide (3g), obtained by a
bromine-magnesium exchange,9 reacts with 1a,b under
our standard conditions, furnishing the furans 4g and 4m
in 65% and 52% yield respectively (entries 7 and 13 of
Table 1). Interestingly, alkyl-, alkenyl- or alkynyl magne-
sium halides, such as octylmagnesium bromide (3i), vi-
nylmagnesium chloride (3j) and ethynylmagnesium
bromide (3k) react with 1a,b under typical conditions in
satisfactory yields, showing the generality of our proce-
dure.
Synthesis 2002, No. 14, Print: 07 10 2002.
Art Id.1437-210X,E;2002,0,14,2143,2149,ftx,en;C04402SS.pdf.
© Georg Thieme Verlag Stuttgart · New York
ISSN 0039-7881

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N. Gommermann et al.
PAPER
Table 1 Functionalized Propargylic Amines 4a–p Obtained by the Reaction of Funtionalized Arylmagnesium Reagents 3 with Unsaturated
Aminals 1a,b
Entry
Aminal
Grignard-Reagent
Product of Type 4
Yield (%)a
1
2
1a
1a
3a R = OMe
4a R = OMe
67
70
3b R = CO2Me
4b R = CO2Me
3
4
5
6
7
1a
1a
1a
1a
1a
3c R = CO2Et
3d R = Br
4c R = CO2Et
4d R = Br
79
60
68
55
65
3e R = NO2
3f R = OTIPS
4e R = NO2
4f R = OTIPS
3g
4g
8
9
1b
1b
3a
4h: R = OMe
4i R = CO2Et
76
80
3h R = CO2Et
10
11
12
13
1b
1b
1b
1b
3c
3d
3e
4j R = CO2Et
4k R = Br
72
69
79
52
4l R = NO2
3g
4m
4n
4o
14
15
16
1a
1a
1a
3i OctMgBr
80
56
67
3j CH2=CHMgCl
3k HC C MgBr
4p
a Yield of analytically pure product.
Synthesis 2002, No. 14, 2143–2149 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Synthesis of Polyfunctional Unsaturated Amines
2145
As can be seen in Table 2, the unsaturated aminal 2 reacts
similarly with arylmagnesium compounds. In this case,
the addition of Tf2O at –65 °C produces an orange precip-
itate, which redissolves upon addition of NMP (5 equiv).
The reactions with the Grignard reagents 3 are complete
within 1 hour (Scheme 1 and Table 2). The functionalized
allylic amines 5a–d are obtained in 50 81% yield.
Table 2 Functionalized Allylic Amines 5a–d Obtained by the Re-
action of Functionalized Arylmagnesium Reagents 3 with the Unsat-
urated Aminal 2
Entry Grignard-Reagent Product of Type 5
Yield (%)a
Scheme 2 Reagents and conditions: (a) diallylamine (excess),
110 °C, 8 h (b) (CF3CO)2O (1.1 equiv), –60 °C, 15 min (c) NMP (5
equiv).
1
2
3
3a
3h
3c
5a: R = OMe
81
80
50
5b: R = CO2Et
5c
4
3g
61
Scheme 3.
5d
corded using a GC/MS-combination of the type HP 6890/MSD
5973 fitted with a HP-5 column (30 m 0.25 mm 0.25 m). High-
resolution mass spectra were recorded on a Finnigan-MAT 95Q
spectrometer (electron impact, 70 eV). Column chromatographical
purifications were carried out using Silicagel 60 (0.063 0.200 mm,
purchased from Merck, Darmstadt).
Aminals 1a b were prepared according to known methods.5,6 The
aminal 2 was obtained by condensation of cinnamaldehyde with di-
ethylamine. The crude product was used without further purifica-
tion.
a Yield of analytically pure product.
The preparation of primary propargylic amines can be
achieved starting from the aminal 1a. Its treatment with
excess diallylamine at 110 °C for 8 h produces the corre-
sponding tetraallylated aminal 8 in 71% yield.10 The reac-
tion of 8 with Tf2O leads, after the addition of an
organomagnesium reagent, to extensive decomposition.
However, the addition of trifluoroacetic anhydride cleanly
provides the imminium trifluoroacetate 9 at –60 ºC, which
after the addition of NMP (5 equiv) reacts with the aryl-
magnesium compounds 3a and 3h, furnishing the desired
proparylic amines 10a,b in 66–76% yield (Scheme 2).
Grignard Reagents 3a h; General procedure3
To a stirred soln of the aromatic halide (1.0 equiv, 1.0 to 0.5 mol/L
in THF) at –40 –20 °C, a soln of i-PrMgBr (1.05 to 1.1 equiv, 0.5
mol/L in THF) was added dropwise. The halogen-magnesium ex-
change was followed by GC/MS.
The allyl substituent can be readily removed by using the
method of Guibé.11 Thus, the reaction of 10a with 1,3-
dimethylbarbituric acid (6 equiv) in the presence of
Pd(PPh3)4 (5 mol%) in CH2Cl2 at 25 °C leads in 30 min-
utes to the propargylic amine 11 in 71% yield (Scheme 3).
Addition of Grignard Reagents 3 to Aminals 1a b, 2; General
Procedure for 4 and 5
To a stirred soln of the aminal 1a b or 2 (1.0 mmol) in THF (2 mL)
at –60 to –78 °C, Tf2O (310 mg, 1.1 mmol) was added dropwise.
After 10 min, NMP (0.5 mL, 5 mmol) was added. To this soln of the
imminium triflate, the soln of the Grignard reagent 3 (1.5 mmol)
In conclusion, we have described conditions allowing the was added dropwise. After 0.5–1 h, the reaction was complete ac-
cording to GC/MS-analysis and was quenched with aq NH4Cl soln
addition of a range of functionalized Grignard reagents to
(10 mL). The aq layer was extracted with Et2O (3 20 mL), the
alkynyl and alkenyl aminals, leading to functionalized
combined organic layers were washed with brine (30 mL), dried
propargylic and allylic amines, respectively.
(MgSO4), filtered and evaporated under reduced pressure. Purifica-
tion by column chromatography with pentane CH2Cl2 MeOH as
eluent gave the corresponding products 4 or 5.
Commercially available starting materials with a purity >97% were
used without further purification. Solvents were dried and distilled
before use.
NMR-spectra were recorded in CDCl3 at 300 MHz for 1H NMR and
75 MHz for 13C NMR (Varian XL 300). Chemical shifts are report-
ed in ppm relative to TMS. IR-spectra were recorded on a Perkin-
Elmar FT-IR Spectrum 1000. Low-resolution mass spectra were re-
1-(4-Methoxyphenyl)-N,N-dimethyl-3-phenyl-2-propyn-1-
amine (4a)
Column chromatographic purification using CH2Cl2–MeOH
(100:0 99:1) as eluent yielded 4a (177 mg, 0.67 mmol, 67%) as a
brown oil.
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N. Gommermann et al.
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IR (film): 2934 (m), 2858 (w), 2822 (w), 2777 (w), 1610 (m), 1510
(vs), 1490 (m), 1249 (vs), 1173 (s), 1037 (s), 806 (w), 956 (s), 692
(m) cm .
1H NMR (300 MHz, CDCl3): = 7.54–7.51 (m, 4 H), 7.35–7.32 (m,
3 H), 6.90 (d, J = 8.4 Hz, 2 H), 4.78 (s, 1 H), 3.82 (s, 3 H), 2.32 (s,
6 H).
MS: m/z (%) = 315 (13), 314 (11) [M+], 313 (13), 272 (12), 271
(68), 270 (12), 269 (70), 234 (15),
190 (13), 189 (68), 188 (11), 187 (11), 159 (13), 158 (100), 115
(17).
1
HRMS: m/z calcd for C17H16BrN, 313.0466; found, 313.0462.
N,N-Dimethyl-1-(2-nitrophenyl)-3-phenyl-2-propyn-1-amine
(4e)
Column chromatographic purification using CH2Cl2–pentane
(1:4 1:0) as eluent yielded 4e (192 mg, 0.68 mmol, 68%) as a
brown solid, mp 75 °C.
13C NMR (75 MHz, CDCl3): = 159.1, 131.8, 130.9, 129.6, 128.3,
128.1, 123.2, 113.5, 88.1, 85.1, 61.6, 55.3, 41.5.
MS: m/z (%) = 265 (7) [M+], 222 (19), 221 (100), 178 (11).
HRMS: m/z calcd for C18H19NO, 265.1467; found, 265.1480.
IR (KBr): 2822 (m), 1540 (vs), 1489 (m), 1359 (s), 1016 (m), 784
(m), 756 (s), 732 (m), 691 (m) cm .
1
4-[1-(Dimethylamino)-3-phenyl-2-propynyl]benzoic Acid
Methyl Ester (4b)
Column chromatographic purification using CH2Cl2–MeOH
(100:0 99:1) as eluent yielded 4b (205 mg, 0.70 mmol, 70%) as a
brown oil.
1H NMR (300 MHz, CDCl3): = 7.96 (d, J = 7.5 Hz, 1 H), 7.73 (dd,
J = 8.0, 1.3 Hz, 1 H), 7.59–7.53 (m, 3 H), 7.40 (td, J = 7.6, 1.4 Hz,
1 H), 7.38–7.35 (m, 3 H), 5.66 (s, 1 H), 2.21 (s, 6 H).
13C NMR (75 MHz, CDCl3): = 149.7, 133.3, 131.9, 131.6, 129.9,
128.6, 128.5, 128.4, 124.4, 122.7, 90.2, 82.2, 57.9, 41.4.
MS: m/z (%) = 280 (2) [M+], 264 (10), 263 (100), 246 (14), 145
(18), 233 (17), 232 (73), 218 (17), 190 (20), 189 (40), 158 (17), 118
(17), 115 (24), 105 (14), 77 (14).
IR (film): 2949 (m), 2861 (w), 2824 (w), 2781 (w), 1723 (vs), 1611
(m), 1435 (s), 1279 (vs), 1112 (s), 1104 (s), 757 (s), 692 (m) cm .
1H NMR (300 MHz, CDCl3): = 8.04 (d, J = 8.4 Hz, 2 H), 7.71 (d,
J = 8.4 Hz, 2 H), 7.69–7.52 (m,
2 H), 7.36–7.33 (m, 3 H), 4.86 (s, 1 H), 3.92 (s, 3 H), 2.33 (s, 6 H).
1
HRMS: m/z calcd for C17H16N2O2, 280.1212; found, 280.1203.
13C NMR (75 MHz, CDCl3): = 166.9, 143.9, 131.8, 129.5, 128.4,
128.3, 128.2, 122.9, 115.3, 88.9, 83.9, 62.0, 52.1, 41.6.
MS: m/z (%) = 293 (19) [M+], 250 (19), 249 (100), 190 (17), 189
N,N-Dimethyl-3-phenyl-1-{2-[(trisisopropylsilyl)oxy]-phenyl}-
2-propyn-1-amine (4f)
Column chromatographic purification using CH2Cl2–pentane
(1:1 1:0) as eluent yielded 4f (226 mg, 0.55 mmol, 55%) as a
brown oil.
(25), 158 (53).
HRMS: m/z calcd for C19H19NO2, 293.1416; found, 293.1400.
2-[1-(Dimethylamino)-3-phenyl-2-propynyl]benzoic Acid Ethyl
Ester (4c)
Column chromatographic purification using CH2Cl2–pentane
(1:1 1:0) as eluent yielded 4c (244 mg, 0.79 mmol, 79%) as a
brown solid, mp 72 °C.
IR (film): 2945 (m), 2867 (m), 1490 (s), 1452 (m), 1282 (m), 1266
(m), 920 (m), 756 (s), 690 (m) cm .
1
1H NMR (300 MHz, CDCl3): = 7.63 (dd, J = 7.9, 2.2 Hz, 1 H),
7.50–7.45 (m, 2 H), 7.32–7.28 (m,
3 H), 7.15 (td, J = 8.1, 1.8 Hz, 1 H), 6.95 (td, J = 7.5, 1.3 Hz, 1 H),
6.84 (dd, J = 8.1, 1.3 Hz, 1 H), 5.16 (s, 1 H), 2.32 (s, 6 H), 1.36
(sept., J = 7.2 Hz, 3 H), 1.15 (t, J = 7.1 Hz, 18 H).
13C NMR (75 MHz, CDCl3): = 153.8, 131.7, 130.4, 128.8, 128.6,
128.2, 127.8, 123.5, 120.3, 118.5, 86.7, 86.5, 55.8, 41.9, 18.1, 13.1.
MS: m/z (%) = 407 (32) [M+], 393 (33), 392 (100), 351 (15), 350
(49), 319 (29), 249 (17), 235 (16),
IR (KBr): 2977 (m), 1723 (vs), 1489 (m), 1443 (m), 1310 (m), 1292
(s), 1262 (s), 1128 (s), 1087 (m), 1045 (m), 1015 (m), 758 (s), 744
1
(s), 694 (m) cm .
1H NMR (300 MHz, CDCl3): = 7.79 (dd, J = 8.2, 0.8 Hz, 1 H),
7.60 (dd, J = 7.5, 1.7 Hz, 1 H), 7.49–7.46 (m, 3 H), 7.38 (td, J = 7.5,
1.5 Hz,1 H), 7.29–7.24 (m, 3 H), 5.59 (s, 1 H), 4.30 (qd, J = 7.1,
3.4 Hz, 2 H), 2.16 (s, 6 H), 1.32 (t, J = 7.1 Hz, 3 H).
13C NMR (75 MHz, CDCl3): = 169.0, 138.8, 132.1, 131.8, 130.3,
129.3, 128.7, 128.3, 128.1, 127.5, 123.2, 89.3, 84.0, 60.9, 58.7,
41.1, 14.2.
MS: m/z (%) = 307 (17) [M+], 292 (48), 278 (100), 262 (24), 260
(66), 246 /76), 235 (23), 234 (88), 219 (35), 218 (23), 189 (51), 184
(35), 162 (20), 158 (21), 133 (54).
189 (17), 149 816), 125 (16), 115 (20).
HRMS: m/z calcd for C26H37NOSi, 407.2644; found, 407.2641.
5-[1-(Dimethylamino)-3-phenyl-2-propynyl]-2-furan-carboxyl-
ic Acid Ethyl Ester (4g)
Column chromatographic purification using CH2Cl2–pentane
(1:2) CH2Cl2–MeOH (99:1) as eluent yielded 4g (192 mg, 0.65
mmol, 65%) as an orange oil.
HRMS: m/z calcd for C20H21NO2, 307.1572; found, 307.1541.
IR (film): 2979 (m), 2944 (m), 1729 (vs), 1519 (m), 1490 (m), 1298
(vs), 1214 (s), 1136 (vs), 1016 (s), 759 (s), 692 (m) cm .
1
1-(2-Bromophenyl)-N,N-dimethyl-3-phenyl-2-propyn-1-amine
(4d)
Column chromatographic purification using CH2Cl2–pentane
(1:1 1:0) as eluent yielded 4d (188 mg, 0.60 mmol, 60%) as a
brown oil.
1H NMR (300 MHz, CDCl3): = 7.43–7.40 (m, 2 H), 7.27–7.24 (m,
3 H), 7.06 (d, J = 3.6 Hz, 1 H), 6.53 (dd, J = 3.5, 0.9 Hz, 1 H), 4.84
(s, 1 H), 4.27 (qd, J = 7.1, 3.1 Hz, 2 H), 2.27 (s, 6 H), 1.28
(t, J = 7.0 Hz, 3 H).
13C NMR (75 MHz, CDCl3): = 158.6, 156.1, 144.8, 131.8, 128.3,
123.1, 122.5, 118.2, 111.1, 87.3, 82.0, 60.9, 56.2, 41.4, 14.3.
IR (film): 2943 (m), 2821 (m), 2777 (m), 1490 (s), 1469 (s), 1440
(s), 1028 (s), 753 (vs), 691 (s),
1
596 (m) cm .
MS: m/z (%) = 297 (9) [M+], 282 (12), 254 (18), 253 (100), 225
(39).
1H NMR (300 MHz, CDCl3): = 7.76 (dd, J = 7.6, 1.8 Hz, 1 H),
7.60 (dd, J = 7.9, 1.4 Hz, 1 H), 7.54–7.50 (m, 2 H), 7.35–7.32 (m, 4
H), 7.17 (td, J = 7.9, 1.8 Hz, 1 H), 5.13 (s, 1 H), 2.37 (s, 6 H).
HRMS: m/z calcd for C18H19NO3, 297.1365; found, 297.1394.
13C NMR (75 MHz, CDCl3): = 138.0, 133.2, 131.8, 130.5, 129.7,
128.3, 128.2, 126.9, 125.1, 123.0, 88.5, 84.4, 61.5, 41.5.
Synthesis 2002, No. 14, 2143–2149 ISSN 0039-7881 © Thieme Stuttgart · New York

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Synthesis of Polyfunctional Unsaturated Amines
2147
1-(4-Methoxyphenyl)-N,N-dimethyl-2-heptyn-1-amine (4h)
Column chromatographic purification using CH2Cl2–pentane
(1:1) CH2Cl2–MeOH (99:1) as eluent yielded 4h (189 mg, 0.77
mmol, 77%) as an orange oil.
1H NMR (300 MHz, CDCl3): = 7.66 (dd, J = 7.4, 1.8 Hz, 1 H),
7.55 (dd, J = 7.9, 1.3 Hz, 1 H), 7.29 (td, J = 7.9, 1.2 Hz, 1 H), 7.13
(td, J = 7.4, 1.8 Hz, 1 H), 4.86 (t, J = 2.3 Hz, 1 H), 2.32 (td, J = 7.0,
2.3 Hz, 2 H), 2.26 (s, 6 H), 1.62–1.41 (m, 4 H), 0.94 (t, J = 7.6 Hz,
3 H).
13C NMR (75 MHz, CDCl3): = 138.6, 133.0, 130.5, 129.0, 126.8,
125.1, 88.7, 74.5, 61.0, 41.4, 31.1, 22.0, 18.4, 13.6.
IR (film): 2957 (s), 2934 (s), 2860 (m), 1611 (m), 1510 (s), 1464
(m), 1248 (vs), 1174 (m),
1
1038 (m) cm .
1H NMR (300 MHz, CDCl3): = 7.44 (d, J = 8.5 Hz, 2 H), 6.86 (d,
J = 8.9 Hz, 2 H), 4.51 (s, 1 H), 3.80 (t, J = 1.7 Hz, 3 H), 2.32 (td,
J = 6.7, 1.9 Hz, 2 H), 2.21 (s, 6 H), 1.70–1.40 (m, 4 H), 0.94 (t,
J = 7.1 Hz, 3 H).
MS: m/z (%) = 294 (4) [M+], 171 (11), 169 (11), 155 (11), 139 (14),
138 (100), 128 (18).
HRMS: m/z calcd for C15H20BrN, 293.0979; found, 293.0973.
13C NMR (75 MHz, CDCl3): = 158.9, 131.5, 129.5, 113.3, 88.2,
75.2, 61.2, 55.2, 41.3, 31.2, 22.0, 18.4, 13.6.
MS: m/z (%) = 245 (6) [M+], 202 (17), 201 (100), 121 (17), 115
N,N-Dimethyl-1-(2-nitrophenyl)-2-heptyn-1-amine (4l)
Column chromatographic purification using CH2Cl2–pentane
(1:4 1:0) as eluent yielded 4l (205 mg, 0.79 mmol, 79%) as a red
oil.
(10).
IR (film): 2958 (s), 2937 (s), 2862 (m), 1533 (vs), 1456 (m), 1362
(s), 1015 (m), 730 (m) cm .
HRMS: m/z calcd for C16H23NO, 245.1780; found, 245.1783.
1
4-[1-(Dimethylamino)-2-heptynyl]-benzoic Acid Ethyl Ester
(4i)
Column chromatographic purification using CH2Cl2–pentane
(1:2) CH2Cl2–MeOH (99:1) as eluent yielded 4i (230 mg, 0.80
mmol, 80%) as an orange oil.
1H NMR (300 MHz, CDCl3): = 7.88 (d, J = 7.6 Hz, 1 H), 7.67 (dd,
J = 8.1, 1.3 Hz, 1 H), 7.52 (td, J = 8.0, 1.8 Hz, 1 H), 7.40 (td,
J = 7.6, 1.2 Hz, 1 H), 5.37 (t, J = 2.1 Hz, 1 H), 2.37 (td, J = 6.6, 2.1
Hz, 2 H), 2.10 (s, 6 H), 1.65–1.43 (m, 4 H), 0.96 (t, J = 7.2 Hz, 3 H).
13C NMR (75 MHz, CDCl3): = 149.7, 134.0, 131.4, 130.0, 128.3,
124.2, 90.5, 72.5, 57.4, 41.2, 31.1, 22.0, 18.4, 13.6.
IR (film): 2959 (s), 2936 (s), 2863 (m), 1721 (vs), 1275 (vs), 1101
1
(s), 1018 (m), 753 (m) cm .
MS: m/z (%) = 260 (4) [M+], 243 (83), 213 (20), 212 (100), 198
(23), 197 (63), 183 (36), 171 (21), 170 (40), 138 (20).
1H NMR (300 MHz, CDCl3): = 8.01 (d, J = 8.4 Hz, 2 H), 7.61 (d,
J = 8.0 Hz, 2 H), 4.59 (s, 1 H), 4.37 (q, J = 7.1 Hz, 2 H), 2.34 (td,
J = 7.0, 2.2 Hz, 2 H), 2.21 (s, 6 H), 1.63–1.44 (m, 4 H), 1.39
(t, J = 7.1 Hz, 3 H), 0.94 (t, J = 7.1 Hz, 3 H).
13C NMR (75 MHz, CDCl3): = 166.5, 144.5, 129.6, 129.3, 128.3,
89.1, 74.2, 61.6, 60.9, 41.5, 31.1, 22.0, 18.4, 14.3, 13.6.
HRMS: m/z calcd for C15H20N2O2, 260.1525; found, 260.1504.
5-[1-(Dimethylamino)-2-heptynyl]-2-furancarboxylic Acid Eth-
yl Ester (4m)
Column chromatographic purification using CH2Cl2–pentane
(1:4) CH2Cl2–MeOH (99:1) as eluent yielded 4m (143 mg, 0.52
mmol, 52%) as a brown oil.
MS: m/z (%) = 287 (12) [M+], 243 (12), 242 (10), 155 (10), 139
(12), 138 (100), 129 (11).
IR (film): 2937 (s), 2863 (s), 1732 (vs), 1531 (s), 1519 (s), 1456 (m),
1301 (vs), 1213(s), 1174 (m), 1136 (vs), 1015 (s), 762 (m) cm .
HRMS: m/z calcd for C18H25NO2, 287.2885; found, 287.2838.
1
2-[1-(Dimethylamino)-2-heptynyl]-benzoic Acid Ethyl Ester
(4j)
Column chromatographic purification using CH2Cl2–pentane
(1:2) CH2Cl2–MeOH (99:1) as eluent yielded 4j (208 mg, 0.72
mmol, 72%) as an orange oil.
1H NMR (300 MHz, CDCl3): = 7.10 (d, J = 3.2 Hz, 1 H), 6.50 (dd,
J = 3.2, 1.0 Hz, 1 H), 4.66 (t, J = 1.7 Hz, 1 H), 4.33 (qd, J = 7.1 Hz,
2.7 Hz, 2 H), 2.29 (td, J = 6.5, 1.8 Hz, 2 H), 2.25 (s, 6 H), 1.59–1.39
(m, 4 H), 1.35 (t, J = 7.1 Hz, 3 H), 0.93 (t, J = 7.1 Hz,. 3 H).
13C NMR (75 MHz, CDCl3): = 158.7, 157.0, 144.5, 118.2, 110.8,
87.7, 72.4, 60.8, 55.7, 41.3, 30.9, 21.9, 18.3, 14.3, 13.5.
IR (film): 2958 (s), 2936 (s), 2861 (s), 1723 (vs), 1448 (m), 1261
1
(vs), 1136 (s), 1077 (s), 1014 (m), 741 (s) cm .
MS: m/z (%) = 277 (15) [M+], 234 (17), 233 (100), 204 (37), 159
(12), 153 (12), 138 (15), 131 (20), 125 (31), 91 (11).
1H NMR (300 MHz, CDCl3): = 7.78 (d, J = 7.4 Hz, 1 H), 7.59 (dd,
J = 7.1, 1.2 Hz, 1 H), 7.41 (td, J = 7.9, 1.6 Hz, 1 H), 7.30 (td,
J = 7.5, 1.5 Hz, 1 H), 5.36 (t, J = 1.8 Hz, 1 H), 4.32 (dq, J = 29.1,
7.0 Hz, 2 H), 2.35 (td, J = 7.2, 2.2 Hz, 2 H), 2.12 (s, 6 H), 1.64–1.40
(m, 4 H), 1.36 (t, J = 7.0 Hz, 3 H), 0.95 (t, J = 7.5 Hz, 3 H).
13C NMR (75 MHz, CDCl3): = 169.1, 139.4, 132.2, 130.1, 129.0,
128.6, 127.3, 89.4, 73.9, 60.8, 58.2, 41.0, 31.2, 22.0, 18.5, 14.2,
13.6.
HRMS: m/z calcd for C16H23NO3, 277.1678; found, 277.1632.
N,N-Dimethyl-1-phenyl-1-undecyn-3-amine (4n)
Column chromatographic purification using pentane–Et2O (4:1) as
eluent yielded 4n (235 mg, 0.86 mmol, 86%) as an orange oil.
IR (film): 2927 (vs), 2956 (vs), 2823 (m), 2780 (m), 1490 (m), 1468
1
(m), 755 (s), 691 (s) cm .
MS: m/z (%) = 287 (3) [M+], 272 (42), 259 (26), 258 (95), 245 (76),
242 (27), 226 (24), 214 (31), 197 (15), 184 (67), 173 (19), 172
(100), 170 (18), 143 (15), 128 (17), 115 (18).
1H NMR (300 MHz, CDCl3): = 7.44–7.42 (m, 2 H), 7.30–7.24 (m,
3 H), 3.49 (t, J = 7.2 Hz, 1 H), 2.31 (s, 6 H), 1.71–1.61 (m, 2 H),
1.54–1.42 (m, 2 H), 1.35–1.26 (m, 10 H), 0.86 (t, J = 7.2 Hz,
3 H).
HRMS: m/z calcd for C18H25NO2, 287.1885; found, 287.1869.
13C NMR (75 MHz, CDCl3): = 131.7, 128.2, 127.8, 123.5, 87.1,
85.9, 58.2, 41.4, 34.0, 31.9, 29.5, 29.4, 29.3, 26.7, 22.7, 14.1.
1-(4-Bromophenyl)-N,N-dimethyl-2-heptyn-1-amine (4k)
Column chromatographic purification using CH2Cl2–pentane
(1:4 1:0) as eluent yielded 4k (202 mg, 0.69 mmol, 69%) as a
brown oil.
MS: m/z (%) = 159 (13), 158 (100), 115 (17).
HRMS: m/z calcd for C19H27N, 270.2222; found, 270.2230.
IR (film): 2957 (vs), 2934 (vs), 2860 (s), 2821 (m), 2777 (m), 1466
1
(s), 1440 (s), 1025 (s), 1012 (s), 750 (vs), 683 (m) cm .
Synthesis 2002, No. 14, 2143–2149 ISSN 0039-7881 © Thieme Stuttgart · New York

2148
N. Gommermann et al.
PAPER
N,N-Dimethyl-1-phenyl-1-penten-4-yn-3-amine (4o)
Column chromatographic purification using CH2Cl2 as eluent yield-
ed 4o (109 mg, 0.59 mmol, 59%) as a brown oil.
MS: m/z (%) = 337 (34) [M+], 336 (38), 265 (69), 246 (39), 192
(34), 191 (41), 189 (26), 188 (69), 115 (100), 91 (28).
HRMS: m/z calcd for C22H27NO2, 337.2042; found, 337.2005.
IR (film): 2942 (m), 2860 (m), 2780 (m), 1490 (s), 1031 (s), 993
1
(m), 928 (m), 756 (vs), 691 (s) cm .
2-[(2E)-1-(Diethylamino)]-3-phenyl-2-propenylbenzoic Acid
Ethyl Ester (5c)
Column chromatographic purification using CH2Cl2–pentane
(1:1 1:0) as eluent yielded 5c (169 mg, 0.50 mmol, 50%) as an or-
ange oil.
1H NMR (300 MHz, CDCl3): = 7.49–7.46 (m, 2 H), 7.33–7.29 (m,
3 H), 5.93 (ddd, J = 16.9, 10.3, 5.1 Hz, 1 H), 5.59 (dt, J = 17.4, 1.8
Hz, 1 H). 5.30 (dt, J = 9.9, 1.7 Hz, 1 H), 4.25 (dt, J = 4.8, 1.8 Hz,
1 H), 2.34 (s, 6 H).
IR (film): 2972 (s), 2934 (m), 1721 (vs), 1449 (m), 1268 (s), 1253
(s), 1132 (s), 1095 (s), 1074 (s),
146 (s), 695 (s) cm .
13C NMR (75 MHz, CDCl3): = 136.0, 131.7, 128.2, 128.1, 123.1,
117.7, 88.2, 83.9, 60.5, 41.5.
MS: m/z (%) = 185 (14) [M+], 159 (13), 158 (100), 141 (33), 115
1
1H NMR (300 MHz, CDCl3): = 7.65 (d, J = 7.8 Hz, 1 H), 7.61 (dd,
J = 7.6, 1.4 Hz, 1 H), 7.43 (dd, J = 7.7, 1.3 Hz, 1 H), 7.39–7.36 (m,
3 H), 7.32–7.17 (m, 3 H), 6.62 (d, J = 16.0 Hz, 1 H), 6.39 (dd,
J = 15.9, 9.1 Hz, 1 H), 5.08 (d, J = 9.0 Hz, 1 H), 4.37 (qd, J = 7.6,
1,7 Hz, 2 H), 2.60 (sept, J = 7.5 Hz, 4 H), 1.41 (t, J = 7.1 Hz, 3 H),
0.96 (t, J = 7.1 Hz, 6 H).
13C NMR (75 MHz, CDCl3): = 169.0, 143.5, 137.2, 131.8, 131.4,
130.8, 130.8, 129.5, 128.5, 128.4, 127.4, 126.5, 126.4, 64.6, 60.9,
43.1, 14.3, 11.3.
(56).
HRMS: m/z calcd for C13H15N, 185.1204; found, 185.1202.
N,N-Dimethyl-1-phenyl-1,4-pentadiyn-3-amine (4p)
Column chromatographic purification using CH2Cl2 as eluent yield-
ed 4p (122 mg, 0.67 mmol, 67%) as a brown oil.
IR (film): 3293 (m), 2947 (m), 2864 (m), 2827 (m), 2784 (m), 1490
1
(s), 1285 (m), 1038 (s), 757 (vs), 691 (s), 653 (m) cm .
1H NMR (300 MHz, CDCl3): = 7.43–7.39 (m, 2 H), 7.27–7.24 (m,
3 H), 4.50 (d, J = 2.6 Hz, 1 H), 2.37 (d, J = 2.6 Hz, 1 H), 2.36 (s, 6
H).
MS: m/z (%) = 337 (6) [M+], 309 (23), 308 (100), 265 (17), 264
(78), 246 (23), 219 (42), 204 (12), 191 (15), 189 (14), 188 (10), 130
(12), 15 (12), 91 (21).
13C NMR (75 MHz, CDCl3): = 131.8, 128.4, 128.2, 122.4, 84.5,
83.1, 77.9, 72.5, 49.3, 41.2.
HRMS: m/z calcd for C22H25NO2, 336.1965; found, 336.1964.
MS: m/z (%) = 183 (34) [M+], 182 (69), 168 (28), 167 (11), 140
(14), 139 (100).
5-[(2E)-1-(Diethylamino)-3-phenyl-2-propenyl]-2-furan-car-
boxylic Acid Ethyl Ester (5d)
Column chromatographic purification using CH2Cl2–pentane
(1:1) CH2Cl2–MeOH (99:1) as eluent yielded 5d (200 mg, 0.61
mmol, 61%) as an orange oil.
HRMS: m/z calcd for C13H13N, 183.1048; found, 183.1027.
(2E)-N,N-Diethyl-1-(4-methoxyphenyl)-3-phenyl-2-propen-1-
amine (5a)
Column chromatographic purification using CH2Cl2–pentane
(1:4) CH2Cl2–MeOH (99:1) as eluent yielded 5a (239 mg, 0.81
mmol, 81%) as an orange oil.
IR (film): 2971 (vs), 1725 (s), 1514 (m), 1450 (m), 1300 (s), 1214
1
(m), 1136 (s), 1017 (m), 762 (m), 699 (m) cm .
1H NMR (300 MHz, CDCl3): = 7.40–7.20 (m, 5 H), 7.14 (d,
J = 3.0 Hz, 1 H), 6.57 (d, J = 16.0 Hz, 1 H), 6.41–6.33 (m, 2 H),
4.59 (d, J = 7.5 Hz, 1 H), 4.34 (q, J = 7.0 Hz, 2 H), 2.73–2.51 (m, 4
H), 1.36 (t, J = 7.1 Hz, 3 H), 1.05 (t, J = 7.1 Hz, 6 H).
IR (film): 2968 (s), 2933 (m), 1609 (m), 1509 (vs), 1247 (vs), 1173
1
(s), 1036 (s), 969 (m), 831 (s), 741 (s), 693 (m) cm .
13C NMR (75 MHz, CDCl3): = 159.9, 158.8, 143.8, 136.7, 132,9,
128.5, 127.7, 127.5, 126.5, 118.7, 109.5, 61.6, 60.7, 44.0, 14.4,
12.5.
MS: m/z (%) = 327 (10) [M+], 256 (21), 255 (100), 227 (54), 209
(26), 181 (18), 153 (27), 152 (16),
115 (12).
1H NMR (300 MHz, CDCl3): = 7.31–7.10 (m, 6 H), 6.79 (d,
J = 8.9 Hz, 2 H), 6.43 (d, J = 15.4 Hz, 2 H), 6.27 (dd, J = 15.8, 8.7
Hz, 1 H), 4.18 (d, J = 8.5 Hz, 1 H), 3.72 (s, 3 H), 2.54 (qd, J = 7.2,
1.4 Hz, 4 H), 0.93 (t, J = 7.1 Hz, 6 H).
13C NMR (75 MHz, CDCl3): = 158.5, 137.2, 135.0, 131.8, 130.6,
128.9, 128.5, 127.2, 126.3, 113.7, 68.0, 55.2, 43.0, 11.6.
MS: m/z (%) = 295 (8) [M+], 224 (18), 223 (100), 145 (14), 115
HRMS: m/z calcd for C20H25NO3, 327.1834; found, 327.1831.
(23).
N,N,N ,N -Tetraallyl-3-phenyl-2-propin-1,1-diamine (8)
The aminal 8 was prepared according to a known method10 using
aminal 1a.
4-[(2E)-1-(Diethylamino)]-3-phenyl-2-propenylbenzoic Acid
Ethyl Ester (5b)
Column chromatographic purification using CH2Cl2–pentane
(1:1) CH2Cl2–MeOH (99:1) as eluent yielded 5b (268 mg, 0.80
mmol, 80%) as an orange oil.
Yield: 1.73 g (5.6 mmol, 71%) orange oil (after distillation at 1.5
10 1 mbar, bp 93–97 °C).
1H NMR (300 MHz, C6D6): = 7.40–7.37 (m, 2 H), 7.00–6.95 (m,
3 H), 5.98–5.85 (m, 4 H), 5.20 (dq, J = 17.2, 1.8 Hz, 4 H), 5.09–5.04
(m, 4 H), 4.55 (s, 1 H), 3.65 (ddt, J = 14.6, 5.7, 1.4 Hz, 4 H), 3.41
(dd, J = 14.1, 7.1 Hz, 4 H).
IR (film): 2971 (s), 2817 (m), 1717 (vs), 1609 (s), 1449 (m), 1368
(m), 1275 (vs), 1172 (m), 1104 (s), 1020 (m), 970 (m), 747 (s), 694
1
(s) cm .
1H NMR (300 MHz, CDCl3): = 7.96 (d, J = 8.3 Hz, 2 H), 7.49 (d,
J = 8.4 Hz, 2 H), 7.35–7.15 (m, 5 H), 6.52 (d, J = 16.0 Hz, 1 H),
6.27 (dd, J = 16.0, 8.9 Hz, 1 H), 4.33 (q, J = 7.0 Hz, 2 H), 4.31 (d,
J = 8.8 Hz, 1 H), 2.64–2.51 (m, 4 H), 1.34 (t, J = 7.1 Hz, 3 H), 0.97
(t, J = 7.1 Hz, 6 H).
13C NMR (75 MHz, C6D6): = 136.5, 132.1, 128.6, 128.4, 123.5,
117.1, 88.1, 85.3, 71.6, 52.5.
Addition of Grignard Reagents 3a h to Aminal 8: General Pro-
cedure for 10
13C NMR (75 MHz, CDCl3): = 166.6, 148.5, 136.8, 131.7, 130.5,
129.7, 129.1, 128.5, 127.8, 127.5, 126.4, 68.6, 60.8, 43.1, 14.3,
11.6.
To a stirred soln of the aminal 8 (306 mg, 1.0 mmol) in THF (2 mL)
at –60 °C, (CF3CO)2O (231 mg, 1.1 mmol) was added dropwise.
After 15 min, NMP (0.5 mL, 5 mmol) was added. To this soln, the
Synthesis 2002, No. 14, 2143–2149 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Synthesis of Polyfunctional Unsaturated Amines
2149
Grignard reagent 3 [1.5 mmol, dissolved in THF (3 mL)] was added
dropwise. After 0.5 to 1 h, the reaction was complete according to
GC/MS-analysis and quenched with sat. aq NH4Cl soln (10 mL).
The aq layer was extracted with Et2O (3 20 mL), the combined or-
ganic layers were washed with brine (30 mL), dried (MgSO4), fil-
tered and evaporated under reduced pressure. Purification by
column chromatography with pentane–CH2Cl2 as eluent gave the
corresponding products 10a,b.
pH 8 was reached. The aq phase was extracted with CH2Cl2 (6 25
mL), dried (MgSO4) and filtered. The solvent was removed under
reduced pressure to give the primary amine (47 mg, 0.20 mmol,
71%) as a brown oil.
IR (film): 3368 (w), 2959 (m), 2932 (m), 2836 (m), 1608 (s), 1511
(vs), 1490 (s), 1303 (s), 1250 (vs), 1174 (s), 1032 (s), 834 (s), 758
1
(s), 693 (s) cm .
1H NMR (300 MHz, CDCl3): = 7.52 (d, J = 8.7 Hz, 2 H), 7.47–
7.44 (m, 2 H), 7.32–7.29 (m, 3 H), 6.91 (d, J = 8.9 Hz, 2 H), 4.97 (s,
1 H), 3.82 (s, 3 H), 1.87 (br s, 2 H).
13C NMR (75 MHz, CDCl3): = 159.1, 134.5, 131.6, 128.2, 128.1,
128.0, 123.1, 113.9, 88.7, 84.1, 55.3, 46.8.
MS: m/z (%) = 237 (23) [M+], 236 (100), 222 (29), 221 (19), 206
(17), 193 (13), 178 (10), 129 (21),
128 (15).
N,N-Diallyl-N-[1-(4-methoxyphenyl)-3-phenyl-2-propynyl]-
amine (10a)
Column chromatographic purification using CH2Cl2–pentane
(1:4 1:2) as eluent yielded 10a (242 mg, 0.76 mmol, 76%) as an
orange oil.
IR (film): 2931 (w), 2835 (w), 2816 (w), 1610 (m), 1586 (m), 1510
(vs), 1490 (m), 1443 (m), 1249 (vs), 1171 (s), 1036 (m), 920 (m),
1
757 (s), 691 (m) cm .
1H NMR (300 MHz, CDCl3): = 7.58 (d, J = 8.9 Hz, 2 H), 7.55–
7.51 (m, 2 H), 7.35–7.33 (m, 3 H), 6.89 (d, J = 8.8 Hz, 2 H), 5.92–
5.79 (m, 2 H), 5.30–5.11 (m, 4 H), 5.04 (s, 1 H), 3.82 (s, 3H), 3.27
(ddt, J = 14.2, 4.0, 2.2 Hz, 2 H), 3.03 (dd, J = 14.2, 7.9 Hz, 2 H).
13C NMR (75 MHz, CDCl3): = 158.9, 136.6, 131.8, 131.4, 129.4,
128.3, 128.1, 123.3, 117.2, 113.4, 87.7, 85.7, 56.0, 55.3, 53.4.
Acknowledgments
We thank the BASF AG for a fellowship to C. K. and the Fonds der
Chemischen Industrie for financial support. We thank Chemetall
GmbH (Frankfurt a. M.) and BASF AG (Ludwigshafen) for the ge-
nerous gift of chemicals.
MS: m/z (%) = 317 (83) [M+], 222 (20), 221 (100), 178 (10).
References
HRMS: m/z calcd for C22H23NO, 317.1780; found, 317.1714.
(1) Boudier, A.; Bromm, L. O.; Lotz, M.; Knochel, P. Angew.
Chem. Int. Ed. 2000, 39, 4415.
(2) Knochel, P.; Millot, N.; Rodriguez, A. L.; Tucher, C. A.
Organic Reacions, 58; Overman, L. E., Ed.; Wiley & Sons
Ltd.: New York, 2001, 417.
4-[1-(Diallylamino)-3-phenyl-2-propynyl] Benzoic Acid Ethyl
Ester (10b)
Column chromatographic purification using CH2Cl2–pentane
(1:6 1:0) as eluent yielded 10b (239 mg, 0.66 mmol, 66%) as an
orange oil.
(3) (a) Boymond, L.; Rottländer, M.; Cahiez, G.; Knochel, P.
Angew. Chem.Int. Ed. 1998, 37, 1701. (b) Rottländer, M.;
Boymond, L.; Bérillon, L.; Leprêtre, A.; Varchi, G.; Avolio,
S.; Laaziri, H.; Queguiner, G.; Ricci, A.; Cahiez, G.;
Knochel, P. Chem.–Eur. J. 2000, 6, 767. (c) Varchi, G.;
Jensen, A. E.; Dohle, W.; Ricci, A.; Cahiez, G.; Knochel, P.
Synlett 2001, 477. (d) Sapountzis, I.; Knochel, P. Angew.
Chem. Int. Ed. 2002, 41, 1610.
(4) (a) Huffman, M. A.; Yasuda, N.; DeCamp, A. E.;
Grabowski, E. J. J. J. Org. Chem. 1995, 60, 1590.
(b) Koninski, M.; Okhuma, H.; Tsnuno, T.; Oki, T.; Van
Duyne, G. D.; Chardy, J. J. J. Am. Chem. Soc. 1990, 112,
3715.
(5) Weingarten, H. Tetrahedron 1968, 24, 2767.
(6) Bredereck, H.; Simchen, G.; Horn, P. Chem. Ber. 1970, 103,
210.
(7) (a) Sekiya, M.; Sakai, H. Chem. Pharm. Bull. 1969, 17, 32.
(b) Betschart, C.; Schmidt, B.; Seebach, D. Helv. Chim. Acta
1988, 71, 1999.
IR (film): 2980 (w), 2828 (w), 1719 (vs), 1275 (vs), 1104 (s), 1022
1
(m), 756 (s), 691 (m) cm .
1H NMR (300 MHz, CDCl3): = 8.03 (d, J = 8.4 Hz, 2 H), 7.77 (d,
J = 8.1 Hz, 2 H), 7.56–7.53 (m, 2 H), 7.38–7.33 (m, 3 H), 5.91–5.78
(m, 2 H), 5.28 (d, J = 17.3 Hz, 2 H), 5.14 (d, J = 12.4 Hz, 2 H), 5.12
(s, 1 H), 4.38 (q, J = 7.1 Hz, 2 H), 3.25 (ddt, J = 14.2, 4.5, 2.2 Hz,
2 H), 3.05 (dd, J = 14.1, 8.5 Hz,
2 H), 1.40 (t, J = 7.1 Hz, 3 H).
13C NMR (75 MHz, CDCl3): = 166.5, 144.7, 136.2, 131.8, 129.7,
129.4, 128.4, 128.3, 128.2, 123.0, 117.6, 88.3, 84.5, 60.9, 56.5,
53.7, 14.3.
MS: m/z (%) = 359 (11) [M+], 358 (17), 264 (23), 263 (100), 235
(41), 210 (51), 191 (13), 190 (19), 189 (31).
HRMS: m/z calcd for C24H24NO2, 358.1807; found, 358.1779.
1-(4-Methoxyphenyl)-3-phenyl-2-propynylamine (11)
To a stirred soln of Pd(PPh3)4 (16 mg, 0.014 mmol) and N,N-dime-
thylbarbituric acid (262 mg, 1.68 mmol) in CH2Cl2 (2 mL) was add-
ed a soln of 10a (88 mg, 0.28 mmol) in CH2Cl2 (3 mL). After
stirring for 30 min at r.t., the reaction was complete according to
GC/MS-analysis. The solvent was removed under vacuo and the
residue was redispersed in Et2O (15 mL). The organic layer was
washed with sat. Na2CO3 soln (2 30 mL) and extracted with 2
mol/L HCl (40 mL). The aq phase was washed with Et2O (2 50
mL) and treated with sat. Na2CO3 soln in the presence of Et2O until
(8) Millot, N.; Piazza, C.; Avorio, S.; Knochel, P. Synthesis
2000, 941.
(9) Abarbri, M.; Thibonnet, J.; Bérillon, L.; Dehmel, F.;
Rottländer, M.; Knochel, P. J. Org. Chem. 2000, 65, 4618.
(10) Kiesel, M.; Haug, E.; Kantlehner, W. J. Prakt. Chem. 1997,
339, 159.
(11) Garro-Helion, F.; Merzouk, A.; Guibé, F. J. Org. Chem.
1993, 58, 6109.
Synthesis 2002, No. 14, 2143–2149 ISSN 0039-7881 © Thieme Stuttgart · New York