First propargyl azides bearing strong acceptor substituents and their effective conversion into allenyl azides: Influence of the electronic effects of substituents on the reactivity of propargyl azides

Article abstract of DOI:10.1002/ejoc.200500135

We have succeeded in the synthesis of propargyl azides containing 1- or 3-phenylthio functionalities. The selective oxidation of their sulfur atoms to sulfoxides and sulfones allows access to the first propargyl azides bearing acceptor substituents. Inter

Full text of DOI:10.1002/ejoc.200500135

FULL PAPER
First Propargyl Azides Bearing Strong Acceptor Substituents and Their
Effective Conversion into Allenyl Azides: Influence of the Electronic Effects of
Substituents on the Reactivity of Propargyl Azides[‡]
Joseph Rodolph Fotsing[a] and Klaus Banert*[a,b]
Dedicated to Professor Harald Günther on the occasion of his 70th birthday
Keywords: Azides / Propargyl azides / Allenyl azides / Triazoles / Rearrangements
We have succeeded in the synthesis of propargyl azides con-
taining 1- or 3-phenylthio functionalities. The selective oxi-
dation of their sulfur atoms to sulfoxides and sulfones allows
access to the first propargyl azides bearing acceptor substitu-
ents. Interestingly, the prototropic rearrangement of the latter
propargyl azides leads to the formation of allenyl azides with
relatively high stabilities and with moderate to good yields.
Propargyl azides containing phenylthio functionalities react
in the presence of nucleophiles to afford the expected N-un-
substituted 1,2,3-triazoles via short-lived allenyl azides.
These results are entirely different from those of the corre-
sponding sulfoxides and sulfones, which react under the
analogous conditions either to produce the corresponding bis-
(triazolo)pyrazine derivatives or to yield newly substituted vi-
nyl azides. The latter compounds can successfully be used as
starting material providing access to azirines.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2005)
be trapped by nucleophiles to afford the triazoles 4 and 7,
respectively.[8] If 1 is generated in situ starting with propar-
gyl halides or sulfonates and sodium azide, the synthesis
of the heterocycles 4 and 7 can be performed in one-pot
procedures without isolation of dangerous azides.[9–11] Such
a reaction cascade is based on simple and cheap starting
materials to produce N-unsubstituted 1,2,3-triazoles bear-
ing a functional group in the side chain. Thus, different
groups have used this method successfully.[6–13]
In some special cases, allenyl azides can be directly char-
acterized by 1H and 13C NMR spectroscopy.[8] However,
isolation of these compounds is very difficult because the
proportions of these quasi-stationary intermediates are
rather low [2a ( Յ 3%), 2b ( Յ 1%), 2c ( Յ 3%), 2d ( Յ
7%), 2e ( Յ 8%), 2f ( Յ 11%), 2g ( Յ 0.32%), 2h ( Յ
0.13%)].[6–8] Moreover, any other attempts to isolate or to
observe azido allenes failed.[14–17] Investigations on the for-
mation of azido allenes 2a–h show that donor substituents
accelerate the rate of the [3,3] sigmatropic rearrangement of
1 to 2.[6–8] Unfortunately, the rate of the ring closure of 2
to 3 proved to be even more greatly increased by the donor
substituents. By contrast, the CH2Cl group (see 2d) which
can be regarded as a weak acceptor decreased the rate of
the ring closure of 2d to 3d. These observations as well as
the kinetic data of the transformations 2a–h Ǟ 3a–h led to
the postulate[6–8] that allenyl azides are better stabilized by
acceptor substituents than by sterically demanding alkyl
substituents acting as donors.
Introduction
Due to their synthetic versatile character, organic azides
are compounds of great interest.[1] Some organic azides can
be synthesized by addition of XN3 (X = H or halogen) to
unsaturated compounds.[2] In the case with X = halogen,
the latter azides can be converted to unsaturated derivatives
by elimination of an HX molecule. This method is mainly
used for the synthesis of vinyl azides.[2] Other methods to
prepare organic azides include the nucleophilic substitution
using the azide anion[3] as well as electrophilic azide trans-
fer[4] and stepwise formation of the azido group from
amines or diazo derivatives.[5]
Propargyl azides of type 1 are known to isomerize to
allenyl azides 2 and 5 by [3,3] sigmatropic migration of the
azido group (path A, Scheme 1) and by prototropic re-
arrangement (base-catalyzed path B, Scheme 1).[6–8] The
species 2 and 5 proved to be short-lived intermediates that
cyclized rapidly to the triazafulvenes 3 and 6, which could
[‡] Reactions of Unsaturated Azides, 16. Part 15: K. Banert, F.
Köhler, B. Meier, Tetrahedron Lett. 2003, 44, 3781–3783.
[a] Chemnitz University of Technology, Institute of Chemistry, Or-
ganic Chemistry,
Strasse der Nationen 62, 09111 Chemnitz, Germany
Fax: +493-715-311-839
[b] Chemnitz University of Technology, Institute of Chemistry, Or-
ganic Chemistry,
Strasse der Nationen 62, 09111 Chemnitz, Germany
E-mail: klaus.banert@chemie.tu-chemnitz.de
3704
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/ejoc.200500135
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Reactions of Propargyl Azides with Acceptor Substituents
FULL PAPER
Scheme 1.
During this work, we faced a triple challenge. First of vinyl azide 12 instead of the propargyl azide 16 (Scheme 2).
all, we were looking for an access to new propargyl azides The reaction of the analogous compound 9 with sodium
bearing electron-withdrawing groups. Due to the postulated azide follows the same pathway producing the vinyl azide
diminishing effect of the acceptor substituents on the rate 13 instead of the propargyl azide 17. Although a variety of
of the ring closure of azido allenes to triazafulvenes, we different reaction conditions were tested, access to 16 and
expected to produce long-lived azido allenes in good yields 17 was not possible by simple nucleophilic substitution. In
from these propargyl azides. However, whereas numerous fact, due to the presence of the acceptor substituent (EWG),
propargyl azides
1 bearing electron-donating groups which increases the acidity of the propargyl hydrogen, the
(ERG) are known,[8,18] their analogs bearing strongly prototropic isomerization of 8 to 10 and 9 to 11 was favored
electron-withdrawing groups (R1, R2 and/or R3 = EWG) under the basic reaction conditions. Obviously, the allene
are unknown to the best of our knowledge.[19,20] Moreover, intermediates 10 and 11 reacted under addition of hydra-
we wanted to perform a rational comparison between the zoic acid (HN3) to form the compounds 12 and 13, respec-
reactivity of the propargyl azides bearing acceptor tively, in 65% and 95% yield. The proof of the presence of
substituents with the reactivity of those propargyl azides only one azido group in the structure of 12 was performed
connected with electron-donating groups. Finally, we as- by its treatment with an excess of cyclooctyne to produce
sume that a convenient access to allenyl azides will open the triazole derivative 14 (82%). The structure of the vinyl
the door to long-sought[14–16] methylene-2H-azirines which azide 13 was proved not only by its spectroscopic data but
were unknown[21–23] until recently when they were also by its photochemical conversion into the 2H-azirine
generated by photolysis of allenyl azides[24,25] or other derivative 15 in 95% yield based on NMR spectroscopy.
azides.[26]
Moreover, Priebe has already shown that the reaction of
methyl 4-chlorobut-2-ynoate (a structural isomer of 9) with
sodium azide led to the formation of the Michael addition
product without substitution of the chloride at the propar-
gylic position.[28]
To overcome the problem described above, we prepared
the sulfur()-containing propargyl azides 19 (95%), 22a
Results and Discussion
Synthesis of Propargyl Azides Bearing Acceptor
Substituents
Our investigations showed that the synthesis of acceptor- (99%) and 22b (99%) by the reaction of the corresponding
substituted propargyl azides through direct substitution of propargyl chlorides 18,[27] 21a[29] and 21b, respectively, with
the propargyl precursors bearing a leaving group is not ap- TMGA (Scheme 3). The compounds 19, 22a and 22b offer
propriate. For example, the reaction of 8[27] with tetrameth- an elegant possibility to produce the corresponding ac-
ylguanidinium azide (TMGA) led to the formation of the ceptor-substituted propargyl azides by oxidation of the thio-
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J. R. Fotsing, K. Banert
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Scheme 2.
Scheme 3.
ethers to sulfoxides and sulfones. In this respect, treatment Et3N or DABCO led to polymerization via short-lived al-
of 22a and 22b in each case with one equivalent of m-chlo- lenyl azides and triazafulvenes without formation of any
roperbenzoic acid (m-CPBA) at –20 °C for 12 h led to the identifiable products, the oxidized derivatives 16, 23a, 24a
formation of the desired sulfoxides 23a and 23b (mixture of and 24b isomerized under the same reaction conditions to
diastereomers, 1.1:1) with good yields. All attempts to iso- afford the corresponding allenyl azides 20 (89%), 25a
late the sulfoxide derived from 19 failed. In order to get (40%), 26a (11%) and 26b (19%), respectively (Scheme 4).
also the sulfones derived from the propargyl azides 19, 22a
and 22b, treatment of each with two equivalents of m-
CPBA was performed. Whereas 22a and 22b were easily
oxidized to the sulfones 24a (95%) and 24b (90%), respec-
tively, oxidation of 19 led to the formation of unstable com-
pound 16 in only 23% yield after chromatography. In fact,
16 reacted especially during its purification on silica gel to
afford surprisingly the azido allene 20. The reaction of the
sulfoxides 23a and 23b with one equivalent of m-CPBA also
affords the sulfones 24a and 24b with 92% and 87% yield,
respectively.
Reactivity of Propargyl Azides with Bases of Weak
Nucleophilicity: Synthesis of Azido Allenes
Whereas the reaction of propargyl azides 19, 22a and
22b, bearing only electron-donating groups, with bases like Scheme 4.
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Reactions of Propargyl Azides with Acceptor Substituents
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These yields were based on isolation by chromatography; 26a that an azido allene is better stabilized when the azido
1
yields determined by H NMR were even higher. Due to group and the acceptor substituent are geminal to each
the stereocenter on the sulfur() atom and the chirality of other. No indication on the ring closure of the allenyl azides
the allene, 25a was obtained as a 9:10 mixture of diastereo- 20, 25a, 26a and 26b to the corresponding triazafulvenes of
isomers. The high yield (89%) of the azido allene 20 com- type 6 (Scheme 1) was obtained.
pared to those of 25a and 26a,b was favored by the great
Due to the unfavorable distance between the orbitals of
acidity of the propargyl hydrogen of 16 which is bound di- N-1 and C-5, simple vinyl azides 27 do not give triazoles of
rectly at the α-position of the sulfone group. Consequently, type 28 by intramolecular reaction,[31] whereas their anions
the time for isomerization is reduced to only 10 min. These 29 are known to cyclize to 30 rapidly (Scheme 5).[32] Con-
results show that azido allenes are stabilized by electron- sidering the proposed mechanism[6–8] of the ring closure of
withdrawing groups which prevent ring-closure to give tri- azido allenes 2 or 5 to triazafulvenes 3 or 6, we can say that
azafulvenes. However, the non-observation of azido allenes the perpendicular geometry of the p orbitals of the central
in the reaction of 19, 22a and 22b is probably not only carbon atoms of the allenes 20, 25a, 26a and 26b, which
caused by the very rapid cyclization of their allenyl azide may favor their ring closure to triazafulvenes, suffers from
derivatives, which are connected to electron-donating the decrease of the nucleophilicity of these central carbon
groups, but also by lower rates of prototropic rearrange- atoms through the acceptor substituents.
ment of these propargyl azides.
In a diluted CDCl3 solution, compound 26a decomposes
after one hour at room temperature to give a complex mix-
ture of products. Under the same conditions, compound
25a exhibits a longer life time (5 h). These observations
show that the acceptor substituents do not only prevent
cyclization to generate triazafulvenes, but also increase the
sensitivity of the allenes to other reactions. Nevertheless,
the latter effect of acceptor substituents is not surprising,
because it is also known for other allenyl compounds.[30]
When the hydrogen atom in the 3Ј-position of 26a was re-
placed with a methyl group, the corresponding allenyl azide
26b proved to be more stable. This can be rationalized by
the compensation of the effect of the acceptor substituent
by the electron-donating methyl group. The position of the
azido groups with regard to those of the electron-with-
drawing groups seems to play also an important role for the
lifetime of the allenyl azides. It turned out through com-
parison of the lifetimes of the diluted solutions of 20 and Scheme 5.
Scheme 6.
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Succeeding Products from Propargyl Azides in Methanol
with the strengthening of the acceptor character of the sul-
fur substituents, whereas an additional methyl group de-
creased the yield due to steric hindrance.
In methanol solutions, the propargyl azides 19, 22a and
22b bearing donor substituents reacted at room tempera-
ture or above through [3,3] sigmatropic rearrangement to
produce the 1,2,3-triazoles 33a (47%), 37a (68%) and 37b
(80%), respectively (Scheme 6, path A). When a very con-
centrated solution of 22a in methanol was used, a small
amount of the double [3+2] cycloaddition product 38a
(5.2%, Scheme 7) was found, together with 37a. Under sim-
ilar conditions, 22b afforded a mixture, in which only the
triazole 37b was identifiable.
Succeeding Products from Propargyl Azides in Methanol in
the Presence of a Base
In order to continue our investigation on the influence
of the electronic effect of substituents on the reactivity of
propargyl azides, both propargyl azides bearing donor sub-
stituents and those with acceptor substituents were treated
with methanol in the presence of base. When the methanol
solutions of the propargyl azides 19 and 22a were treated
with sodium hydroxide at room temperature, the 1,2,3-tri-
azoles 37a (35%) and 33a (20%), respectively, were ob-
tained (Scheme 6, path B). In the case of 22a, the formation
of by-product 34a (12%) was surprisingly observed. This
product can be explained probably by in situ formation of
thiophenol which then reacted with the intermediate 32a.
Under similar reaction conditions, 22b led to the formation
of 37b (path A) rather than 33b (path B). This can be ra-
tionalized by the weak acidity of the propargyl hydrogen of
22b, which is situated geminal to the methyl group and the
azido group, as well as the fact that an additional donor
substituent like a methyl group accelerates the rate of the
Scheme 7.
In contrast to the reactions of propargyl azides 19, 22a [3,3] sigmatropic rearrangement of propargyl azides.[6–8]
and 22b, the reactions of the analogous compounds 23a In contrast to the propargyl azides with donor substitu-
and 24a bearing acceptor substituents afforded in methanol ents 19, 22a and 22b, the analogous compounds 23a, 24a
solutions after fourteen days at room temperature only the and 24b react with methanol in the presence of base to af-
[3+2] cycloaddition products 39a and 40a in 23% and 57% ford the corresponding 1-azido-2-methoxyethenes. No evi-
yields, respectively (Scheme 7). Compound 39a was ob- dence of the formation of the N-unsubstituted triazoles an-
tained as a mixture of diastereomers (1:1). No evidence for alogs of type 33a,b or 37a,b was obtained. In fact, treatment
the formation of the N-unsubstituted triazoles analogous to of 23a, 24a and 24b with bases (NaOH, Et3N) in methanol
33a,b or 37a,b was obtained. Under similar conditions, 24b solution led to the formation of 41a (73%), 42a (77%) and
undergoes no significant reaction. However, when neat 24b 42b (77%), respectively (Scheme 8). Only the E-isomers of
was left standing at room temperature for two days the cor- 41a and 42a and in the case of 42b a 3:2-mixture of E- and
responding [3+2] cycloaddition product 40b was afforded in Z-isomers were found. This method provides an easy and
8% yield as a mixture of diastereomers (7:5). The structures efficient access to newly substituted vinyl azides. The posi-
of the heterocycles 38a, 39a, 40a and 40b were determined tion of the olefinic double bond in the structures of 41a,
by comparison of their NMR spectroscopic data with those 42a and 42b was determined by photochemical transforma-
of the parent compound.[33] As it is shown by these results, tion to the 2H-azirines 43a (like/unlike = 1:1), 44a and 44b,
the yield of the [3+2] cycloaddition products is increased respectively.
Scheme 8. [a] Yield of isolated product. [b] Yield determined by NMR.
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Reactions of Propargyl Azides with Acceptor Substituents
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Scheme 9.
How are 1-Azido-2-methoxyethenes Formed from Acceptor-
Substituted Propargyl Azides?
nor substituents react as expected[6–13] by [3,3] sigmatropic
rearrangement of the azido group or by prototropic isomer-
ization (base catalysis) to short-lived azido allenes that cy-
clized rapidly to triazafulvenes. These intermediates un-
dergo a nucleophilic addition to afford N-unsubstituted tri-
azoles. In methanol solution, the acceptor-substituted pro-
pargyl azides yield the corresponding bis(triazolo)pyrazines
by double [3+2] cycloaddition. Only two compounds con-
taining the bis(triazolo)pyrazines unit were until now men-
tioned in the literature.[33,34] By treatment with bases in
methanol solution, the title compounds produced 1-azido-
2-methoxyethenes. The latter method provides a simple and
efficient way to newly substituted vinyl azides.
The formation of the compounds 41a, 42a and 42b from
the corresponding propargyl azide precursors allows two
plausible mechanistic pathways (Scheme 9). In the first
pathway, the nucleophile may first attack the most electro-
philic carbon atom (C-2Ј) of the propargyl azides to form
compounds of type 45a or 46a,b, followed by a prototropic
rearrangement to afford the final products. To prove the
plausibility of this pathway, a diluted solution of 24a in
methanol was heated for 20 h under reflux producing the
bis(triazolo)pyrazine 40a (Scheme 7) and the expected com-
pound Z-46a (Scheme 9) in 12% yield after chromatog-
raphy; E-46a was not found. In the presence of Et3N, Z-
46a isomerizes to E-42a (40%) showing the possibility of
prototropic rearrangement. In the second pathway
(Scheme 9), the prototropic isomerization of the propargyl
azides takes place first to afford the corresponding azido
allenes, which then react with methanol to form the final
products. The first step of this pathway was already ob-
served (Scheme 4). The formation of 42a was also found
when methanol and Et3N was added to a CDCl3 solution
of 26a. Thus, the observed products 41a, 42a and 42b can
be plausibly formed by concurrent reaction pathways.
Experimental Section
1
General Remarks: H and 13C NMR spectra were recorded at 300
and 75 MHz, respectively, in CDCl3, unless otherwise noted.
Chemical shifts (δ) are reported in parts per million (ppm) down-
field from TMS. Coupling constants (J) are reported in Hertz (Hz),
and spin multiplicities are indicated by the following symbols: s
(singlet), d (doublet) t (triplet), q (quartet), m (multiplet). Infrared
spectra were recorded as solutions in CDCl3. TLC was performed
on Macherey–Nagel precoated silica gel Polygram Sil G/UV254
plates and viewed by UV. Chromatography refers to flash
chromatography,[35] carried out on Fluka silica gel 60. For the
HPLC, the HPLC-pump 64 from Knauer was used. The detection
ensued with a UV/Vis filter-photometer (λ = 254 nm) from Knauer.
The photolyses were performed with a 150-W-Hg high pressure
lamp (polychromatic) TQ 150 from Quarzlampen-Gesellschaft. For
the elemental analyses, Vario El (Elementar Analysensystem
GmbH) was employed. Mariner 5229 from Applied Biosystems was
used for (HR)-MS-spectra. The method applied was the Electro-
spray Ionisation. For unstable compounds such as 2H-azirines, no
elemental analyses could be measured.
Conclusion
In conclusion, we have developed an elegant and efficient
method giving access to acceptor-substituted propargyl
azides by selective oxidation of sulfur atoms of the corre-
sponding thioethers. The base-catalyzed prototropic re-
arrangement of these propargyl azides afforded the desired
allenyl azides in acceptable to very good yields. Propargyl
azides bearing electron-withdrawing groups and those with
electron-donating groups prove to undergo different reac-
tions in methanol with and without the presence of a base.
Warning: Elemental analyses of azides could not be performed be-
cause of explosive decomposition. Caution should be exercised dur-
ing isolation of azide which may be explosive. In the case of solu-
Under both reaction conditions, propargyl azides with do- tions of tetrabutylammonium azide in CH2Cl2, an explosion proba-
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J. R. Fotsing, K. Banert
FULL PAPER
bly caused by diazidomethane was reported.[36] Therefore, special
caution is also necessary in the case of tetramethylguanidinium az-
ide (TMGA) in CH2Cl2 although we never observed any incidence.
The known compounds 8,[27] 18[27] and 21a[29] were synthesized ac-
cording to the literature.
12). IR (CDCl ): ν = 3305 cm–1 (HCϵ), 2113 (N3). 1H NMR
˜
3
(CDCl3): δ = 2.87 (d, 4J = 2.1 Hz, 1 H, H-3Ј), 5.08 (d, 4J = 2.1 Hz,
1 H, H-1Ј), 7.35 (m, 3 H, Ph), 7.55 (m, 2 H, Ph) ppm. 13C NMR
(CDCl3): δ = 58.75 (d, C-1Ј), 75.83 (s, C-2Ј), 78.12 (d, C-3Ј), 129.17
(d, 2 C), 129.27 (d, p-Ph), 130.78 (s, i-Ph), 134.21 (d, 2 C) ppm.
(1-Azidoprop-2-ynylsulfonyl)benzene (16): Compound 19 (1.125 g,
5.95 mmol) was dissolved in CH2Cl2 (100 mL) and 70% m-chloro-
perbenzoic acid (m-CPBA, 4.37 g, 17.73 mmol) was added in small
portions while stirring at 0 °C. After stirring at this temperature
for additional 60 min, the mixture was washed three times with
cooled NaHSO3 solution, three times with cooled NaHCO3 solu-
tion and three times with cooled water. The organic phase was
dried with MgSO4, filtered, and the solvent was evaporated under
vacuum. The residue, which contained no 20 (yet), was separated
by flash chromatography on silica gel with Et2O/n-hexane (1:4).
The first fractions gave 16 (0.30 g, 1.36 mmol, 23%) as a yellow oil
whereas a mixture of 16 and the azido allene 20 (for the synthesis of
Methyl 2-Chlorobut-3-ynoate (9): This compound was synthesized
in 95% yield based on NMR by analogy with the procedure de-
scribed in the literature[37] starting with the corresponding alcohol
methyl 2-hydroxybut-3-ynoate[38] and thionyl chloride. IR (CCl4):
ν = 3300 cm–1 (HCϵ), 1740 (C=O). 1H NMR (CDCl3): δ = 2.76
˜
(d, 4J = 2.7 Hz, 1 H, HCϵ), 3.88 (s, 3 H, CH3), 5.01 (d, 4J =
2.7 Hz, 1 H, H-2) ppm.
(2-Azido-1-chloroprop-2-enylsulfonyl)benzene (12): To a stirred solu-
tion of 8[27] (0.73 g, 3.40 mmol) in CH2Cl2 (15 mL), was added a
solution of tetramethylguanidinium azide (TMGA, 2.50 g,
15.8 mmol) in CH2Cl2 (15 mL) at 0 °C within 60 min. After ad-
ditional stirring at this temperature for 30 min, the mixture was
partially evaporated, and the residue was filtered on silica gel with
Et2O. The obtained solution was evaporated under vacuum, and
the residue was crystallized from Et2O/n-hexane to give 12 (0.50 g,
20, see below) was obtained thereafter. IR (CDCl ): ν = 3302 cm–1
˜
3
1
(HCϵ), 2109 (N3), 1328 (SO2), 1138 (SO2). H NMR (CDCl3): δ
4
4
= 2.98 (d, J = 2.4 Hz, 1 H, H-3Ј), 4.82 (d, J = 2.4 Hz, 1 H, H-
1Ј), 7.58 (m, 2 H, m-Ph), 7.69 (m, 1 H, p-Ph), 7.94 (m, 2 H, o-Ph)
2
2
ppm. 13C NMR (CDCl3): δ = 70.11 (dd, JC,H = 50, JC,H = 9 Hz,
2.17 mmol, 65%) as a yellow solid; m.p. 108–110 °C. IR (CDCl3):
1
ν = 2127 cm–1 (N3), 1332 (SO2), 1156 (SO2). H NMR (CDCl3): δ
C-2Ј), 70.70 (dd, 1JC,H = 162, JC,H = 4 Hz, C-1Ј), 81.32 (dd, 1JC,H
= 258, JC,H = 4 Hz, C-3Ј), 129.13 (dm, 2 C), 129.70 (dm, 2 C),
3
˜
2
2
3
= 5.03 (s, 1 H, H-1Ј), 5.17 (d, J = 3.0 Hz, 1 H, H2C=), 5.35 (d, J
= 3.0 Hz, 1 H, H2C=), 7.60 (m, 2 H, Ph), 7.88 (m, 3 H, Ph) ppm.
13C NMR (CDCl3): δ = 68.66 (d, C-1Ј), 103.10 (t, C-3Ј), 121.00 (s,
C-2Ј), 124.57 (d, 2 C), 125.77 (d, 2 C), 130.44 (d, p-Ph), 133.53 (s,
i-Ph) ppm.
134.28 (m, i-Ph), 134.93 (dm, p-Ph) ppm.
(1-Azidopropa-1,2-dienylsulfonyl)benzene (20): Compound 16
(45.0 mg, 204 µmol) was dissolved in dry CDCl3 (0.50 mL) and
treated with Et3N (2.00 mg, 20.0 µmol). The reaction was moni-
tored by 1H NMR spectroscopy. After 10 min, the mixture was
filtered over silica gel (1 g, filled in a Pasteur pipette) with Et2O.
The obtained filtrate was evaporated under vacuum to give 20
Methyl (3-Azido-2-chlorobut-3-enoate (13): To a stirred solution of
NaN3 in a solvent mixture of water/CCl4 (3 mL:3.3 mL), was added
an etheric solution of 9 (2.5 mL, 0.75 mmol, 0.3 ). Stirring was
continued for 2 h at room temperature affording the compound 13
(40.0 mg, 181 µmol, 89 %) as a yellow oil. IR (CDCl ): ν =
˜
3
with 95% yield based on NMR spectroscopy. IR (CDCl ): ν =
2125 cm–1 (N3), 1332 (SO2), 1157 (SO2). 1H NMR (CDCl3): δ =
5.98 (s, 2 H, H-3), 7.57 (m, 2 H, m-Ph), 7.67 (m, 1 H, p-Ph), 7.93
(m, 2 H, o-Ph) ppm. 13C NMR (CDCl3): δ = 94.22 (t, C-3), 117.73
(s, C-1), 128.41 (d, 2 C), 129.25 (d, 2 C), 134.28 (d, p-Ph), 138.46
(s, i-Ph), 200.74 (s, C-2) ppm.
˜
3
2140 cm–1 (N3), 1740 (C=O). H NMR (CDCl3): δ = 3.84 (s, 3 H,
1
CH3), 4.77 (s, 1 H, H-2), 5.01 (d, 2J = 2.9 Hz, 1 H, H2C=), 5.27
2
(d, J = 2.9 Hz, 1 H, H2C=) ppm.
[1-(α-Chlorophenylsulfonylmethyl)ethenyl]-4,5,6,7,8,9-hexahydro-1H-
cyclooctatriazole (14): To a stirred solution of 12 (32.0 mg,
124 µmol) in CH2Cl2 (2 mL) was added cyclooctyne[39] (30.0 mg,
278 µmol). The mixture was stirred for 3 h at room temperature.
The solvent was evaporated under vacuum, and the unreacted cy-
clooctyne was removed at 10–3 Torr. The residue was purified by
flash chromatography on silica gel with Et2O/n-hexane (1:1) to give
the vinyl triazole 14 (37.0 mg, 101 µmol, 82%) as a yellowish oil.
1H NMR (CDCl3): δ = 1.51 (m, 4 H), 1.76 (m, 4 H), 2.86 (m, 4
H), 5.72 (d, J = 2.4 Hz, 1 H, H2C=), 6.13 (d, J = 2.4 Hz, 1 H,
H2C=), 6.18 (s, 1 H, HCCl), 7.56 (m, 2 H, m-Ph), 7.70 (m, 1 H, p-
Ph), 7.89 (m, 2 H, o-Ph). 13C NMR (CDCl3): δ = 22.36 (t), 24.28
(t), 24.97 (t), 25.58 (t), 27.18 (t), 27.89 (t), 71.73 (d, CCl), 118.62
(t, H2C=), 129.16 (d, 2 C, Ph), 129.63 (d, 2 C, Ph), 134.30 (s),
134.38 (s), 134.84 (d, p-Ph), 135.30 (s), 145.38 (s) ppm. MS (ESI):
m/z (%) = 366.00 (100) [M + H+, 35Cl]. C17H20ClN3O2S (365.89):
calcd. C 55.81, H 5.51, N 11.48, S 8.76; found C 55.79, H 5.54, N
11.50, S 8.95.
(3-Chlorobut-1-ynylsulfanyl)benzene (21b): Under argon, a solution
of 3-chlorobut-1-yne[40] (2.00 g, 22.6 mmol) in dry Et2O (30 mL)
was cooled to –80 °C. n-Butyllithium (9.10 mL, 2.50  in n-hexane)
was added dropwise while stirring at –80 °C. After additional stir-
ring at –80 °C for 45 min, PhSCl[41] (2.96 g, 20.5 mmol) was added
dropwise at the same temperature. The mixture was stirred for
20 min and then warmed to room temperature within 45 min.
Thereafter, the argon flow was stopped, and 35 mL of H2O was
added while stirring vigorously. The organic phase was separated
in a funnel, and the aqueous phase was extracted several times with
Et2O. The combined organic phases were dried with MgSO4 and
filtered. The solvent was removed to give 21b (3.99 g, 20.3 mmol,
99%) as a yellow oil. H NMR (CDCl3): δ = 1.85 (d, J = 6.9 Hz,
3 H, Me), 4.90 (q, 3J = 6.9 Hz, 1 H, H-3Ј), 7.26 (m, 1 H, p-Ph),
7.39 (m, 4 H) ppm. 13C NMR (CDCl3): δ = 26.39 (q, Me), 44.88
(d, C-3Ј), 73.20 (s, Csp), 97.36 (s, Csp), 126.35 (d, 2 C), 126.79 (d,
p-Ph), 129.28 (d, 2 C), 131.86 (s, i-Ph) ppm. HRMS (ESI): calcd.
for C10H9ClS [M + H+, 35Cl] 197.0139, found 197.0159.
1
3
Methyl (2H-Azirin-3-yl)chloroacetate (15): The photolysis of 13 in
CDCl3 afforded after 8 h at –50 °C the desired azirine in 95% yield
(3-Azidoprop-1-ynylsulfanyl)benzene (22a): A solution of TMGA
(5.00 g, 31.6 mmol) in CH2Cl2 (40 mL) was added dropwise to a
solution of 21a[29] (2.90 g, 15.9 mmol) in CH2Cl2 (40 mL) cooled
to 0 °C. The mixture was stirred at this temperature for 8 h and
kept overnight at 7 °C. After work-up (see synthesis of 12), 22a
1
based on NMR spectroscopy. H NMR (CDCl3): δ = 1.89 (s, 2 H,
N–CH2), 3.90 (s, 3 H, CH3), 5.55 (s, 1 H, Cl–CH) ppm.
(1-Azidoprop-2-ynylsulfanyl)benzene (19): The treatment of a solu-
tion of 18[27] (1.76 g, 9.64 mmol) in CH2Cl2 (25 mL) with a solution
of TMGA (3.70 g, 23.4 mmol) in CH2Cl2 (25 mL) afforded 19 (3.00 g, 15.8 mmol, 99%) was obtained as a yellow oil. IR (CDCl3):
(1.73 g, 9.15 mmol, 95%) as yellow oil (procedure: see synthesis of
ν =2124 cm–1 (N3). 1H NMR (CDCl3): δ = 4.17 (s, 2 H, H-3Ј), 7.28
˜
3710
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2005, 3704–3714

Reactions of Propargyl Azides with Acceptor Substituents
FULL PAPER
3
(m, 1 H, p-Ph), 7.37 (m, 2 H), 7.44 (m, 2 H) ppm. 13C NMR 4.29 (q, J = 6.9 Hz, 1 H, H-3Ј), 7.59 (m, 2 H, m-Ph), 7.71 (m, 1
(CDCl3): δ = 41.10 (t, C-3Ј), 74.99 (s, Csp), 90.72 (s, Csp), 126.59
(d, 2 C), 126.86 (d, p-Ph), 129.25 (d, 2 C), 131.58 (s, i-Ph) ppm.
H, p-Ph), 8.02 (m, 2 H, o-Ph) ppm. 13C NMR (CDCl3): δ = 19.82
(q, Me), 47.55 (d, C-3Ј), 82.30 (s, Csp), 90.48 (s, Csp), 127.52 (d, 2
C), 129.47 (d, 2 C), 134.57 (d, p-Ph), 141.00 (s, i-Ph) ppm.
(3-Azidobut-1-ynylsulfanyl)benzene (22b): Compound 21b (3.99 g,
20.3 mmol) was dissolved in CH2Cl2 (50 mL) and treated dropwise
with a solution of TMGA (9.00 g, 57 mmol) in CH2Cl2 (15 mL)
within 10 min while stirring at 0 °C. The mixture was kept for 4
days at 7–10 °C. After work-up (see synthesis of 12), 22b (4.07 g,
20.05 mmol, 99%) was obtained as a yellowish liquid. IR (CDCl3):
(3-Azidopropa-1,2-dienylsulfinyl)benzene (25a): Compound 23a
(0.40 g, 1.95 mmol) was dissolved in dry CH2Cl2 (5 mL) and
treated dropwise with Et3N (0.20 g, 1.95 mmol) over a period of
15 min while stirring at 0 °C. The mixture was stirred for additional
45 min at 0 °C, and then the solvent was partially removed under
cooling. The residue was chromatographed (column of Ø = 4 cm;
filed with 150 cm3 SiO2) rapidly with 2 L of Et2O/n-hexane (1:1).
Fractions of 20 mL each were collected. Unreacted 23a was col-
lected first and then the desired allene. Removal of the solvent was
performed under cooling affording a mixture of syn/anti-25a
(0.16 g, 0.78 mmol, 40%) as a yellowish solid, which decomposed
rapidly in contact with air. Diastereomeric ratio = 9:10. IR (CDCl3,
1
3
ν =2105 cm–1 (N3), 1227 (N3). H NMR (CDCl3): δ = 1.52 (d, J
˜
= 6.9 Hz, 3 H, Me), 4.42 (q, 3J = 6.9 Hz, 1 H, H-3Ј), 7.25 (m, 1 H,
p-Ph), 7.39 (m, 4 H) ppm. 13C NMR (CDCl3): δ = 21.34 (q, Me),
49.57 (d, C-3Ј), 73.56 (s, Csp), 95.00 (s, Csp), 126.47 (d, 2 C), 126.81
(d, p-Ph), 129.31 (d, 2 C), 131.81 (s, i-Ph) ppm.
(3-Azidoprop-1-ynylsulfinyl)benzene (23a): To a stirred solution of
22a (1.31 g, 6.93 mmol) in CHCl3 (25 mL), was added dropwise
at –10 °C a solution of 70% m-CPBA (1.70 g, 7.19 mmol) in CHCl3
(25 mL). The mixture was kept overnight at –23 °C. The unreacted
m-CPBA was filtered from the cooled mixture, and the liquid phase
was diluted with CHCl3 and washed three times with a saturated
Na2CO3 solution. The organic phase was dried with MgSO4. After
filtration, the solvent was removed under vacuum to give 23a
mixture): ν =2113 cm–1 (N3), 1942 (C=C=C), 1272 (N3), 1048 (SO).
˜
4
1H NMR (CDCl3, mixture): δ = 6.41 (br. d, J = 5.7 Hz, 1 H, H-
4
4
3Ј), 6.43 (br. d, J = 5.7 Hz, 1 H, H-3Ј), 6.61 (d, J = 5.7 Hz, 1 H,
4
H-1Ј), 6.62 (d, J = 5.7 Hz, 1 H, H-1Ј), 7.55 (m, 2×3 H), 7.68 (m,
2×2 H) ppm. 13C NMR (CDCl3, mixture): δ = 108.50 (d), 110.10
(d), 113.71 (d), 114.02 (d), 124.25 (d, 4 C), 129.54 (d, 4 C), 131.65
(d, 2 C, p-Ph), 143.30 (s, i-Ph), 143.84 (s, i-Ph), 196.73 (s, C-2Ј),
197.45 (s, C-2Ј) ppm.
(1.27 g, 6.20 mmol, 90 %) as a yellow oil. IR (CDCl ): ν =
˜
3
2129 cm–1 (N3), 1053 (SO). 1H NMR (CDCl3): δ = 4.08 (s, 2 H, H-
3Ј), 7.53 (m, 3 H), 7.79 (m, 2 H). 13C NMR (CDCl3): δ = 39.79 (t,
C-3Ј), 84.86 (s, Csp), 95.26 (s, Csp), 124.74 (d, 2 C), 129.54 (d, 2
C), 131.94 (d, p-Ph), 142.93 (s, i-Ph) ppm.
[(3-Azidopropa-1,2-dienyl)sulfonyl]benzene (26a): Compound 24a
(0.32 g, 1.44 mmol) was dissolved in dry benzene (5 mL) and
treated dropwise with Et3N (10 mg, 0.10 mmol) at 0 °C. The mix-
ture was stirred for 30 min at 0 °C and filtered on silica gel with
Et2O. The solvent was removed under cooling and the residue di-
luted with dichloromethane (2 mL). The obtained solution was
purified by HPLC [20 cm×2 cm Ø LiChrosphor Si 60 (5 µ)] with
cooled CH2Cl2. Removal of the solvent under cooling afforded the
allene 26a (35 mg, 1.58 mmol, 11%) as a yellowish solid. The pure
solid decomposed rapidly at room temperature to give a complex
mixture of products. A small amount of the unreacted starting ma-
(3-Azidobut-1-ynylsulfinyl)benzene (23b): The oxidation of 22b
(0.90 g, 4.43 mmol) in CH2Cl2 (25 mL) with 70% m-CPBA (0.80 g,
4.64 mmol) in CH2Cl2 (20 mL) afforded the mixture of the dia-
stereomers (1.1:1) of 23b (0.80 g, 3.65 mmol, 82%) as a yellow oil
(procedure: see synthesis of 23a). IR (CDCl , mixture): ν =
˜
3
2104 cm–1 (N3), 1232 (N3), 1054 (SO). 1H NMR (CDCl3, mixture):
3
3
δ = 1.46 (d, J = 7.2 Hz, 3 H, Me), 1.48 (d, J = 7.2 Hz, 3 H, Me),
3
3
4.33 (q, J = 7.2 Hz, 1 H, H-3Ј), 4.34 (q, J = 7.2 Hz, 1 H, H-3Ј),
7.55 (m, 2×3 H), 7.81 (m, 2×2 H) ppm. 13C NMR (CDCl3, mix-
ture): δ = 20.23 (q, 2 C, Me), 48.18 (d, 2 C, C-3Ј), 83.73 (s, 2 C,
Csp), 99.21 (s, 2 C, Csp), 124.89 (d, 4 C), 129.62 (d, 4 C), 131.99
(d, 2 C, p-Ph), 143.17 (s, 2 C, i-Ph) ppm.
terial 24a was also isolated from other fractions. IR (CDCl ): ν =
˜
3
2117 cm–1 (N3), 1324 (SO2), 1153 (SO2). 1H NMR (CDCl3): δ =
4
4
6.44 (br. d, J = 5.7 Hz, 1 H, H-3Ј), 6.76 (d, J = 5.7 Hz, 1 H, H-
1Ј), 7.59 (m, 2 H, m-Ph), 7.68 (m, 1 H, p-Ph), 7.94 (m, 2 H, o-Ph)
ppm. 13C NMR (CDCl3): δ = 109.19 (d), 110.44 (d), 128.02 (d, 2
C), 129.32 (d, 2 C), 134.06 (d, p-Ph), 145.44 (s, i-Ph), 201.98 (s, C-
2Ј) ppm.
(3-Azidoprop-1-ynylsulfonyl)benzene (24a): Compound 22a (0.73 g,
3.86 mmol) was dissolved in CH2Cl2 (15 mL) and treated dropwise
with a cooled solution (0 °C) of 70% m-CPBA (2.50 g, 10.6 mmol)
in CH2Cl2. The mixture was kept overnight at about 6 °C, then
it was diluted with CH2Cl2 (50 mL) and washed three times with
saturated Na2CO3 solution. The organic phase was dried with
MgSO4 and filtered. The solvent was removed to give 24a (0.81 g,
3.67 mmol, 95 %) as a yellow oil. Starting from 23a (0.50 g,
2.44 mmol) and m-CPBA (0.71 g, 3.00 mmol), 24a (0.49 g,
[(3-Azidobuta-1,2-dienyl)sulfonyl]benzene (26b): Compound 24b
(0.30 g, 1.28 mmol) was dissolved in dry CHCl3 (15 mL) and
treated in small portions with 1,4-diazabicyclo[2.2.2]octane
(DABCO, 0.21 g, 1.91 mmol) while stirring at room temperature.
After additional stirring for 1 h, the solvent was partially removed
and the residue chromatographed on silica gel (150 g) with Et2O.
The fractions containing the major product were collected and
evaporated to give 100 mg residue, which was dissolved in cooled
Et2O. This solution was used for HPLC [20 cm×2 cm Ø LiCh-
rosphor Si 60 (5 µ)] using Et2O/n-hexane (1:1) to give 26b (ca.
2.24 mmol, 92%) was also obtained. IR (CDCl ): ν = 2112 cm–1
˜
3
1
(N3), 1333 (SO2), 1166 (SO2). H NMR (CDCl3): δ = 4.06 (s, 2 H,
H-3Ј), 7.59 (m, 2 H, m-Ph), 7.70 (m, 1 H, p-Ph), 8.00 (m, 2 H, o-
Ph) ppm. 13C NMR (CDCl3): δ = 39.24 (t, C-3Ј), 83.18 (s, Csp),
86.86 (s, Csp), 127.43 (d, 2 C), 129.43 (d, 2 C), 134.60 (d, p-Ph),
140.71 (s, i-Ph) ppm.
56.0 mg, 238 µmol, 19 %) as a yellowish oil. IR (CDCl ): ν =
˜
3
2125 cm–1 (N3), 1332 (SO2), 1157 (SO2). 1H NMR (CDCl3): δ =
5
5
1.86 (d, J = 2.7 Hz, 3 H, Me), 6.61 (q, J = 2.7 Hz, 1 H, H-1Ј),
7.51 (m, 3 H), 7.91 (m, 2 H, o-Ph) PPM. 13C NMR (CDCl3): δ =
17.07 (q, Me), 108.40 (d, C-1Ј), 119.92 (s, C-3Ј), 127.95 (d, 2 C),
129.27 (d, 2 C), 133.85 (d, p-ph), 139.95 (s, i-Ph), 199.94 (s, C-2Ј)
ppm.
(3-Azidobut-1-ynylsulfonyl)benzene (24b): For the oxidation of 22b
(0.81 g, 3.99 mmol) in CH2Cl2 (25 mL) with 70% m-CPBA (2.50 g,
10.6 mmol) in CH2Cl2 (15 mL) to yield 24b (0.84 g, 3.57 mmol,
90%), see synthesis of 24a. Starting from 23b (0.71 g, 3.24 mmol)
in CH2Cl2 (20 mL) and m-CPBA (1.00 g, 4.06 mmol) in CH2Cl2
(15 mL), 24b (0.66 g, 2.81 mmol, 87%) was also obtained as a yel- 4-[Methoxy(phenylsulfanyl)methyl]-1H-1,2,3-triazole (33a) from 19:
low oil. IR (CDCl ): ν = 2105 cm–1 (N3), 1232 (N3), 1331 (SO2), Compound 19 (298 mg, 1.58 mmol) was dissolved in MeOH
˜
3
1159 (SO2). 1H NMR (CDCl3): δ = 1.47 (d, 3J = 6.9 Hz, 3 H, Me),
(25 mL) and stirred for 36 h at room temperature. Methanol was
Eur. J. Org. Chem. 2005, 3704–3714
www.eurjoc.org
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3711

J. R. Fotsing, K. Banert
FULL PAPER
removed under vacuum and the residue chromatographed on silica
s), 147.96 (br. s) ppm. C11H13N3OS (235.31): calcd. C 56.15, H
gel with Et2O/n-hexane (1:1) to give 33a (165 mg, 0.75 mmol, 47%) 5.57, N 17.86, S 13.63; found C 56.43, H 5.45, N 17.89, S 13.88.
as a yellow oil. IR (CDCl ): ν = 3439 cm–1 (NH). 1H NMR
(CDCl3): δ = 3.62 (s, 3 H, MeO), 5.99 (s, 1 H, MeOHC), 7.26 (m,
˜
3
3,8-Bis(phenylsulfanyl)-4H,9H-bis[1,2,3]triazolo[1,5-a:1Ј,5Ј-d]pyraz-
ine (38a): A solution of 22a (250 mg, 1.32 mmol) in methanol
(1 mL) was heated at 50 °C for 6 days with occasional addition of
a few drops of methanol. The mixture was diluted with methanol
3 H, Ph), 7.36 (m, 2 H, Ph), 7.43 (s, 1 H, H-5), 12.20 (br. s, 1 H,
NH) ppm. 13C NMR (CDCl3): δ = 55.76 (q, MeO), 83.71 (d,
MeOHC), 128.15 (d), 128.65 (d, 2 C, Ph), 129.36 (s, i-Ph), 131.34
(5 mL) and filtered. The precipitate was washed several times with
(d), 133.95 (d, 2 C, Ph), 145.51 (s, C-4) ppm. MS (ESI): m/z (%)
small amounts of methanol to give 38a (13.0 mg, 34.4 µmol, 5.2%)
= 222.08 (42) [M + H+], 190.05 (100). HRMS (ESI): calcd. for
as a white powder; m.p. (MeOH) Ͼ 300 °C. 1H NMR ([D6]-
C10H11N3OS [M + H+] 222.0701, found 222.0724.
DMSO): δ = 5.79 (s, 4 H, CH2), 7.63 (m, 10 H, Ph) ppm. 13C NMR
([D6]DMSO): δ = 43.13 (t, 2 C, CH2), 126.71 (d, 2 C, p-Ph), 127.89
(d, 4 C), 129.32 (d, 4 C), 130.68 (s, 2 C), 133.08 (s, 2 C), 134.46 (s,
2 C) ppm. C18H14N6S2 (378.48): calcd. C 57.12, H 3.73, N 22.20,
S 16.94; found C 56.81, H 3.94, N 21.92, S 17.54.
4-[Methoxy(phenylsulfanyl)methyl]-1H-1,2,3-triazole (33a) and 4-
[Bis(phenylsulfanyl)methyl]-1H-1,2,3-triazole (34a) from 22a: To a
stirred solution of NaOH (0.26 g, 6.50 mmol) in MeOH (50 mL)
was added 22a (0.50 g, 2.65 mmol). Stirring was continued for 60 h
at room temperature. Methanol was removed under vacuum, and
the residue was dissolved in H2O (40 mL). The obtained mixture
was washed with Et2O, and the aqueous layer was adjusted in ice
bad with diluted (20%) H2SO4 to pH = 5–6. The mixture was ex-
tracted 5 to 6 times with Et2O. After drying with MgSO4, the sol-
vent was removed under vacuum and the residue chromatographed
on silica gel with Et2O/n-hexane (1:1) to give 33a (116 mg,
3,8-Bis(phenylsulfinyl)-4H,9H-bis[1,2,3]triazolo[1,5-a:1Ј,5Ј-d]pyraz-
ine (39a): Compound 23a (220 mg, 1.07 mmol) was dissolved in
MeOH (1 mL) and stirred at room temperature for 14 days with
occasional addition of a few drops of MeOH. The yellowish pow-
der formed was washed several times with small amounts of MeOH
to give 39a (50.1 mg, 122 µmol, 23%) as a diastereomeric mixture
(meso/rac = 1:1); m.p. (MeOH, mixture) Ͼ 300 °C. 1H NMR ([D6]
2
DMSO, mixture): δ = 5.57 (d, J = 16.5 Hz, 2 H, CH2), 5.62 (d, 2J
525 µmol, 20%) and 34a (45.0 mg, 151 µmol, 12%) as a yellow oil.
1
IR (CDCl ): ν = 3438 cm–1 (NH). H NMR (CDCl3): δ = 5.79 (s,
2
2
˜
= 15.3 Hz, 2 H, CH2), 5.88 (d, J = 15.3, 2 H, CH2), 5.90 (d, J =
16.5 Hz, 2 H, CH2) 7.59 (m, 2×6 H, Ph), 7.78 (m, 2×4 H, Ph)
ppm. 13C NMR ([D6]DMSO, mixture): δ = 43.00 (t, 4 C, CH2),
124.76 (d, 8 C, Ph), 129.64 (d, 8 C, Ph), 129.86 (s, 4 C), 131.75 (d,
4 C, p-Ph), 142.55 (s, 4 C), 143.83 (s, 4 C) ppm. C18H14N6O2S2
(410.48): calcd. C 52.67, H 3.44, N 20.47, S 15.62; found C 52.50,
H 3.40, N 20.17, S 16.05.
3
1 H, HC–S), 7.27 (m, 2×3 H, Ph), 7.48 (m, 2×2 H, Ph), 7.58 (s, 1
H, H-5), 9.20 (br. s, 1 H, NH) ppm. 13C NMR (CDCl3): δ = 50.76
(d, HC–S), 128.38 (d, 2×1C), 129.00 (d, 2×2 C), 130.63 (d), 132.98
(s, 2×1 C), 133.09 (d, 2×2 C), 146.53 (s, C-4) ppm. MS (ESI):
m/z (%) = 300.02 (45) [M + H+], 190.01 (100). C15H13N3S2
(299.42): calcd. C 60.17, H 4.38, N 14.03, S 21.42; found C 59.73,
H 4.39, N 13.61, S 21.03.
3,8-Bis(phenylsulfonyl)-4H,9H-bis[1,2,3]triazolo-[1,5-a:1Ј,5Ј-d]pyraz-
ine (40a): A solution of 24a (220 mg, 995 µmol) in MeOH (1 mL)
was treated as in the case of 23a Ǟ 39a to give 40a (125 mg,
283 µmol, 57%) as a white powder; m.p. (MeOH) Ͼ 300 °C. 1H
NMR ([D6]DMSO): δ = 6.11 (s, 4 H, H2C), 7.63 (m, 4 H, m-Ph),
7.74 (m, 2 H, p-Ph), 8.07 (m, 4 H, o-Ph) ppm. 13C NMR ([D6]
DMSO): δ = 43.91 (t, 2 C, H2C), 127.51 (d, 4 C), 129.74 (d, 4 C),
131.79 (s, 2 C), 134.75 (d, 2 C, p-Ph), 139.85 (s, 2 C), 141.14 (s, 2
C) ppm. C18H14N6O4S2 (442.47): calcd. C 48.86, H 3.19, N 18.99,
S 14.49; found C 48.44, H 3.47, N 18.50, S 14.66.
4-Methoxymethyl-5-phenylsulfanyl-1H-1,2,3-triazole (37a) from
22a: A solution of 22a (500 mg, 2.65 mmol) in methanol (50 mL)
was stirred for 60 h under reflux. The mixture, which contained
traces of solid formed, was filtered. This solid proved to be 38a
[(2.0 mg, 5.25 µmol, 0.40%), for the synthesis of 38a see below].
Removal of the solvent from the liquid phase afforded a residue,
which was purified on silica gel with Et2O/n-hexane (1:1) yielding
37a (400 mg, 1.81 mmol, 68%) as a yellow oil and the unreacted
starting material 22a (45.0 mg, 238 µmol, 9%). IR (CDCl ): ν =
˜
3
3427 cm–1 (NH). H NMR (CDCl3): δ = 3.34 (s, 3 H, MeO), 4.55
1
4,9-Dimethyl-3,8-bis(phenylsulfonyl)-4H,9H-bis[1,2,3]triazolo[1,5-
a:1Ј,5Ј-d]pyrazine (40b): Compound 24b (300 mg, 1.28 mmol) was
kept at room temperature for two days without solvent. The pro-
duct was washed three times with CH2Cl2 and two times with
MeOH to give a diastereomeric mixture (7:5) of 40b (25.5 mg,
(s, 2 H, MeOCH2), 7.24 (m, 5 H, Ph), 13.25 (br. s, 1 H, NH) ppm.
13C NMR (CDCl3): δ = 58.59 (q, MeO), 63.95 (t, MeOCH2),
126.87 (d, p-Ph), 129.03 (d, 2 C), 129.06 (d, 2 C), 134.16 (s, i-Ph),
137.02 (s), 144.53 (s) ppm. MS (ESI); m/z (%): 222.08 (57) [M +
H+], 190.03 (100). C10H11N3OS (221.28): calcd. C 54.23, H 5.01,
N 18.99, S 14.49; found C 54.01, H 4.71, N 18.54, S 14.15.
1
53 µmol, 8.3%) as a whitish powder; m.p. (mixture) Ͼ 300 °C. H
NMR ([D6]DMSO): δ = 2.00 (d, 3J = 6.6 Hz, 2×6 H, Me), 6.46
[q, 3J = 6.6 Hz, 2 H, Me(H)C, major isomer], 6.53 [q, 3J = 6.6 Hz,
2 H, Me(H)C, minor isomer], 7.70 (m, 2×6 H), 8.06 (m, 2×4 H,
o-Ph). 13C NMR ([D6]DMSO): δ = 22.12 (q, 2 C, Me), 23.63 (q, 2
C, Me), 51.62 (d, 2 C, Me(H)C), 52.14 (d, 2 C, Me(H)C), 127.53
(d, 4 C), 127.71 (d, 4 C), 129.71 (d, 4 C), 129.77 (d, 4 C), 134.56
(d, 4 C, p-Ph), 134.98 (s, 2 C), 139.62 (s, 2 C), 139.76 (s), 141.35
(s). Some signals could not be separated. C20H18N6O4S2 (470.52):
calcd. C 51.05, H 3.86, N 17.86, S 13.63; found C 50.96, H 4.01,
N 17.79, S 14.04.
4-Methoxymethyl-5-phenylsulfanyl-1H-1,2,3-triazole (37a) from 19:
Starting from 19 (0.26 g. 1.38 mmol) and NaOH (0.13 g.
3.25 mmol) in methanol (50 mL), the mixture was stirred at 40 °C
for 20 h. The work-up was done as in the synthesis of 33a/34a to
give 37a (0.11 g, 0.50 mmol, 36%).
4-(1-Methoxyethyl)-5-phenylsulfanyl-1H-1,2,3-triazole (37b): A
solution of 22b (1.00 g, 4.93 mmol) in 75 mL of MeOH was heated
at 60 °C for 3 days. After removal of the solvent under vacuum,
the residue was purified on silica gel with Et2O/n-hexane (11:9) to
give the triazole 37b (0.93 g, 3.96 mmol, 81%) as a yellow oil. IR
(E)-(3-Azido-2-methoxyprop-2-enylsulfinyl)benzene (E-41a): To a
solution of 23a (50 mg, 244 µmol) in methanol (2 mL) was added
Et3N (50 µL). The mixture was stirred at room temperature for 1 h,
then it was chromatographed on silica gel with Et2O to give E-41a
(42.0 mg, 177 µmol, 73%) as a yellow oil. E-41a was also obtained
1
3
(CDCl ): ν =3425 cm–1 (NH). H NMR (CDCl3): δ = 1.46 (d, J
˜
3
3
= 6.6 Hz, 3 H, Me(H)C), 3.17 (s, 3 H, MeO), 4.67 [q, J = 6.6 Hz,
1 H, Me(H)C], 7.19 (m, 5 H, Ph) ppm. 13C NMR (CDCl3): δ =
20.51 [q, Me(H)C], 56.63 (q, MeO), 70.48 [d, Me(H)C], 126.66 (d, with lower yield using NaOH as base. IR (CDCl ): ν = 2111 cm–1
˜
3
1
p-Ph), 128.72 (d, 2 C), 129.97 (d, 2 C), 134.72 (s, i-Ph), 135.58 (br. (N3), 1048 (SO). H NMR (CDCl3): δ = 3.50 (s, 3 H, MeO), 3.52
3712
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2005, 3704–3714

Reactions of Propargyl Azides with Acceptor Substituents
FULL PAPER
(d, 2J = 12.6 Hz, 1 H, CH2), 3.78 (d, 2J = 12.6 Hz, 1 H, CH2), 5.75
(s, 1 H, H-3Ј), 7.50 (m, 3 H, Ph), 7.64 (m, 2 H, Ph) ppm. 13C NMR
(CDCl3): 55.61 (q, MeO), 57.90 (t, C-1Ј), 106.43 (d, C-3Ј), 124.16
(d, 2 C), 128.90 (d, 2 C), 131.29 (d, p-Ph), 142.55 (s), 143.52 (s)
ppm. The stereochemistry of 41a was determined by 1H NMR
NOE difference spectra.
2-Methoxy-3-methyl-2-phenylsulfonylmethyl-2H-azirine (44b): Irra-
diation of E/Z-42b at –50 °C for 50 min. IR (CDCl ): ν = 1742 cm–1
˜
3
1
(C=N), 1319 (SO2), 1145 (SO2). H NMR (CDCl3): δ = 2.54 (s, 3
H, MeC), 2.86 (s, 3 H, MeO), 2.88 (d, 2J = 14.4 Hz, 1 H, CH2),
2
4.18 (d, J = 14.4 Hz, 1 H, CH2), 7.56 (m, 2 H, m-Ph), 7.64 (m, 1
H, p-Ph), 7.92 (m, 2 H, o-Ph) ppm. 13C NMR (CDCl3): δ = 14.61
(q, MeC), 51.74 (q, MeO), 62.90 (t, CH2), 64.72 (s, C-2) 127.87 (d,
2 C), 129.03 (d, 2 C), 133.75 (d, p-Ph), 139.33 (s, i-Ph), 177.24 (s,
C-3) ppm.
(E)-(3-Azido-2-methoxyprop-2-enylsulfonyl)benzene (E-42a): The
sulfone 24a (0.32 g, 1.45 mmol) was dissolved in methanol (20 mL)
and treated at room temperature with NaOH (1.00 mg, 25.0 µmol).
The mixture was stirred for 30 min, evaporated and purified on
silica gel with Et2O/n-hexane (1:1) to give E-42a (0.28 g, 1.11 mmol,
(Z)-(3-Azido-2-methoxyprop-1-enylsulfonyl)benzene (Z-46a): A
solution of 24a (500 mg, 2.26 mmol) in dry MeOH (500 mL) was
heated for 20 h under reflux. The solid formed was filtered and
proved to be 40a (Ϸ 5 mg). The liquid phase was then concentrated
and chromatographed on silica gel with Et2O/n-hexane (4:1) to give
77%) as yellow oil. IR (CDCl ): ν = 2113 cm–1 (N3), 1321 (SO2),
˜
3
1
1158 (SO2). H NMR (CDCl3): δ = 3.48 (s, 3 H, MeO), 4.00 (s, 2
H, H-1Ј), 5.71 (s, 1 H, H-3Ј), 7.56 (m, 2 H, m-Ph), 7.66 (m, 1 H,
p-Ph), 7.91 (m, 2 H, o-Ph) ppm. 13C NMR (CDCl3): δ = 55.91 (q,
MeO), 56.68 (t, C-1Ј), 107.38 (d, C-3Ј), 128.51 (d, 2 C), 128.77 (d,
2 C), 133.83 (d, p-Ph), 139.03 (s), 140.93 (s) ppm. The stereochemis-
try of 42a was determined by NOE.
Z-46a (70.0 mg, 277 µmol, 12%) as a yellow oil. IR (CDCl ): ν =
˜
3
2112 cm–1 (N3), 1307 (SO2), 1152 (SO2). 1H NMR (CDCl3): δ =
3.77 (s, 3 H, MeO), 3.90 (br. s, 2 H, H-3Ј), 5.88 (s, 1 H, H-1Ј), 7.55
(m, 3 H), 7.96 (m, 2 H, o-Ph) ppm. 13C NMR (CDCl3): δ = 49.72
(t, C-3Ј), 57.00 (q, MeO), 110.75 (d, C-1Ј), 127.57 (d, 2 C), 128.70
(d, 2 C), 133.02 (d, p-Ph), 142.33 (s, i-Ph), 160.60 (s, C-2Ј) ppm.
(E/Z)-(3-Azido-2-methoxybut-2-enylsulfonyl)benzene (E/Z-42b): To
a stirred solution of 24b (230 mg, 979 µmol) in methanol (15 mL)
was added NaOH (1.00 mg, 25.0 µmol). After stirring for 2 h, the
mixture was evaporated and chromatographed on silica gel with
Et2O/n-hexane (2:3) to give E-42b (105 mg, 393 µmol, 40%, yellow
oil), Z-42b (66.0 mg, 247 µmol, 25%, yellow oil) and a mixture of
E- and Z-42b (30.0 mg, 112 µmol, 11%); overall yield 77%. E-42b:
Acknowledgments
J. R. F. gratefully thanks the German Academic Exchange Service
(DAAD) for a generous fellowship. The research was supported by
the Fonds der Chemischen Industrie. We also wish to thank Dyna-
mit Nobel GmbH, Leverkusen, for providing chemicals. Finally, we
acknowledge assistance with some of the syntheses performed by
Mr. Kai Vrobel.
IR (CDCl ): ν = 2116 cm–1 (N3), 1309 (SO2), 1265 (N3), 1154
˜
3
(SO2). 1H NMR (CDCl3): δ = 1.84 (s, 3 H, MeC), 3.51 (s, 3 H,
MeO), 4.05 (2 H, H-1Ј), 7.55 (m, 2 H, m-Ph), 7.64 (m, 1 H, p-Ph),
7.90 (m, 2 H, o-Ph) ppm. 13C NMR (CDCl3): δ = 11.06 (q, MeC),
53.45 (t, C-1Ј), 57.85 (q, MeO), 125.98 (s), 128.53 (d, 4 C), 133.76
(d, p-Ph), 133.88 (s), 138.68 (s) ppm. Z-42b: IR (CDCl ): ν =
˜
3
2113 cm–1 (N3), 1309 (SO2), 1148 (SO2). 1H NMR (CDCl3): δ =
1.62 (s, 3 H, MeC), 3.49 (s, 3 H, MeO), 3.94 (s, 2 H, H-1Ј), 7.57
(m, 2 H, m-Ph), 7.67 (m, 1 H, p-Ph), 7.91 (m, 2 H, o-Ph) ppm. 13C
NMR (CDCl3): δ = 14.25 (q, MeC), 57.20 (t, C-1Ј), 58.71 (q, MeO),
124.63 (s), 128.36 (d, 2 C), 129.19 (d, 2 C), 133.36 (s), 133.97 (d,
p-Ph), 138.68 (s) ppm. The stereochemistry of the isomers of 42b
was determined by NOE.
[1] a) D. V. Banthorpe, in: The Chemistry of the Azido Group (Ed.:
S. Patai), Wiley, New York, 1971, pp. 397–440; b) (Ed.: E. F. V.
Scriven), Azides and Nitrenes: Reactivity and Utility, Academic
Press, Orlando, 1984; c) E. F. V. Scriven, K. Turnbull, Chem.
Rev. 1988, 88, 297–368; d) A. Hassner, in: Houben-Weyl, vol.
E 16a, part 2 (Ed.: D. Klamann), Thieme, Stuttgart, 1990, pp.
1243–1290; e) S. Bräse, C. Gil, K. Knepper, V. Zimmermann,
Angew. Chem. 2005, in press.
[2] K. Banert, in: Houben-Weyl, vol. E 15 (Eds.: H. Kropf, E.
Schaumann), Thieme, Stuttgart, 1993, pp. 818–875.
[3] a) M. E. C. Biffin, J. Miller, D. B. Paul, in: The Chemistry of
the Azido Group (Ed.: S. Patai), Wiley, New York, 1971, pp.
57–190; b) W. Lwowski, in: The Chemistry of the Azido Group
(Ed.: S. Patai), Wiley, New York, 1971, pp. 503–554.
[4] a) D. A. Evans, T. C. Britton, J. Am. Chem. Soc. 1987, 109,
6881–6883; b) D. A. Evans, T. C. Britton, J. A. Ellman, R. L.
Dorow, J. Am. Chem. Soc. 1990, 112, 4011–4030.
Photolysis of E-41a, E-42a and E/Z-42b (General Procedure): In
order to determine the position of the olefinic double bonds, the
compounds E-41a (20 mg, 84.4 µmol), E-42a (30.0 mg, 119 µmol)
or E/Z-42b (30.0 mg, 112 µmol) were dissolved in CDCl3 and irra-
diated at low temperature. The measurement of the NMR spectro-
scopic data was performed at 19 °C. Due to the decomposition,
only a few signals of both diastereomers of 43a (Ϸ 30%) could be
assigned. The azirines 44a (from E-42a) and 44b (from E/Z-42b)
were obtained with 95% and 80% yields (based on NMR), respec-
tively.
[5] M. E. C. Biffin, J. Miller, D. B. Paul, in: The Chemistry of the
Azido Group (Ed.: S. Patai), Wiley, New York, 1971, pp. 147–
176.
2-Methoxy-2-phenylsulfinylmethyl-2H-azirine (like/unlike-43a): Ir-
radiation of E-41a at –50 °C for 45 min. 1H NMR (CDCl3): δ =
2.92 (s, 3 H, MeO), 3.13 (s, 3 H, MeO), 2.60–3.80 (CH2), 7.54 (m,
10 H, Ph), 10.34 (s, 1 H, H-3), 10.63 (s, 1 H, H-3) ppm. 13C NMR
(CDCl3): 175.15 (d, C-3), 175.63 (d, C-3) ppm.
[6] K. Banert, Liebigs Ann./Recueil 1997, 2005–2018.
[7] K. Banert, Targets in Heterocyclic Systems 2000, 3, pp. 1–32.
[8] K. Banert, M. Hagedorn, Angew. Chem. 1989, 101, 1710–1711;
Angew. Chem. Int. Ed. Engl. 1989, 28, 1675–1676.
[9] K. Banert, Chem. Ber. 1989, 122, 911–918.
[10] K. Banert, Chem. Ber. 1989, 122, 1963–1967.
2-Methoxy-2-phenylsulfonylmethyl-2H-azirine (44a): Irradiation of
[11] K. Banert, Chem. Ber. 1989, 122, 1175–1178.
E-42a at –55 °C for 45 min. IR (CDCl ): ν = 1713 cm–1 (C=N),
˜
3
[12] T. Harrison, A. P. Owens, B. J. Williams, C. J. Swain, A. Wil-
liams, E. J. Carlson, W. Rycroft, D. Tattersall, M. A. Cascieri,
G. G. Chicchi, S. Sadowski, N. M. Rupniak, R. J. Hargreaves,
J. Med. Chem. 2001, 44, 4296–4299.
1321 (SO2), 1151 (SO2). 1H NMR (CDCl3): δ = 2.88 (s, 3 H, MeO),
2.95 (d, 2J = 14.6 Hz, 1 H, CH2), 4.16 (d, 2J = 14.6 Hz, 1 H, CH2),
7.59 (m, 2 H, m-Ph), 7.67 (m, 1 H, p-Ph), 7.96 (m, 2 H, o-Ph),
10.48 (s, 1 H, H-3) ppm. 13C NMR (CDCl3): δ = 52.11 (q, MeO),
61.96 (s, C-2), 62.62 (t, CH2), 128.05 (d, 2 C), 129.27 (d, 2 C),
134.01 (d, p-Ph), 139.40 (s, i-Ph), 172.99 (d, C-3) ppm.
[13] J. C. Loren, K. B. Sharpless, Synthesis 2005, 1514–1520.
[14] G. LЈAbbé, M. Bollyon, G. Germain, G. Scheefer, Bull. Soc.
Chim. Belg. 1983, 92, 881–891.
Eur. J. Org. Chem. 2005, 3704–3714
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© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3713

J. R. Fotsing, K. Banert
FULL PAPER
[15] G. LЈAbbé, Bull. Soc. Chim. Belg. 1984, 93, 579–592.
[16] A. Hassner, J. Keogh, J. Org. Chem. 1986, 51, 2767–2770.
[17] a) The 1H NMR spectroscopic data mentioned in the literatur;
were not, as the authors presumed, those of the 1-azido-3-
methyl-1,2-butadiene; compare with ref.[9]; b) V. J. Shiner, J. S.
Humphrey, J. Am. Chem. Soc. 1967, 89, 622–630.
[26] S. V. Chapyshev, H. Tomioka, Bull. Chem. Soc., Jpn. 2003, 76,
2075–2089.
[27] F. G. Bordwell, T. G. Mecca, J. Am. Chem. Soc. 1972, 94, 5829–
5837.
[28] H. Priebe, Acta Chem. Scand. B 1987, 640–645.
[29] H. Maruyama, M. Shiozaki, S. Oida, T. Hiraoka, Tetrahedron
Lett. 1985, 26, 4521–4522.
[18] a) K. Banert, Tetrahedron Lett. 1985, 26, 5261–5264; b) K.
Banert, Chem. Ber. 1987, 120, 1891–1896; c) K. Banert, M. [30] K. Banert, J. Lehman, in: Modern Allene Chemistry (Eds.: N.
Hagedorn, A. Müller, Eur. J. Org. Chem. 2001, 1089–1103; d)
A. Koziara, A. Zwierzak, Synthesis 1992, 1063–1065; e) P.
Wipf, L. Rahman, S. R. Rector, J. Org. Chem. 1998, 63, 7132–
7133; f) A. Saito, K. Saito, A. Tanaka, T. Oritani, Tetrahedron
Lett. 1997, 38, 3955–3958; g) S. Knapp, J. J. Hale, M. Bastos,
A. Molina, K. Y. Chen, J. Org. Chem. 1992, 57, 6239–6256; h)
B. Alcaide, P. Almendros, J. M. Alonso, J. Org. Chem. 2004,
69, 993–996; i) L. He, H.-S. Byun, R. Bittman, J. Org. Chem.
2000, 65, 7627–7633; j) H. Takahara, T. Takamatsu, T. Yama-
zaki, J. Org. Chem. 1989, 54, 4812–4822; k) F. E. McDonald,
M. M. Gleson, J. Am. Chem. Soc. 1996, 118, 6648–6659.
[19] Well-known[20] propynoyl azides are not classified as propargyl
azides bearing electron-withdrawing groups because of their
completely different chemistry.
Krause, A. S. K. Hashmi), Wiley-VCH, Weinheim, 2004, pp.
359–424.
[31] R. Huisgen, Angew. Chem. 1980, 92, 979–1005; Angew. Chem.
Int. Ed. Engl. 1980, 19, 947–973.
[32] a) J. S. Meek, J. S. Fowler, J. Am. Chem. Soc. 1967, 89, 1967;
b) J. S. Meek, J. S. Fowler, J. Org. Chem. 1968, 33, 985–991.
[33] H. Priebe, Acta Chem. Scand. B 1984, 38, 623–626.
[34] E. M. Burgess, J. P. Sanchez, J. Org. Chem. 1973, 38, 176–178.
[35] W. C. Still, M. Kahn, A. Mitra, J. Org. Chem. 1978, 43, 2923–
2925.
[36] a) R. Dharanipragada, K. VanHulle, A. Bannister, S. Bear, L.
Kennedy, V. J. Hruby, Tetrahedron 1992, 48, 4733–4748; b) V. J.
Hruby, L. Boteju, G. Li, Chem. Eng. News 1993, 71, 2.
[37] R. Rambaud, R. Vessiere, M. Verny, Compt. Rend. 1963, 257,
1619–1621.
[20] R. Herges, D. Geuenich, G. Bucher, C. Tönshoff, Chem. Eur.
J. 2000, 6, 1224–1228.
[38] M. N. T. Chang, C. T. Walsh, J. Am. Chem. Soc. 1981, 103,
[21] An alleged 2-methylene-2H-azirine[22] proved to be a structur-
4921–4927.
ally isomeric product[23]
.
[39] L. F. Tietze, T. Eicher, Reaktionen und Synthesen im organisch-
chemischen Praktikum und Forschungslaboratorium, Thieme,
Stuttgart, 1991, p. 39.
[22] R. K. M. R. Kallury, P. S. U. Devi, Tetrahedron Lett. 1977,
3655–3658.
[23] a) D. J. Anderson, J. Org. Chem. 1986, 51, 945–947; b) K.
Ashok, G. Sridevi, Y. Umadevi, Synthesis 1993, 623–626.
[24] K. Banert, M. Hagedorn, Angew. Chem. 1990, 102, 90–92; An-
gew. Chem. Int. Ed. Engl. 1990, 29, 103–105.
[25] K. Banert, M. Hagedorn, E. Knözinger, A. Becker, E.-U.
Würthwein, J. Am. Chem. Soc. 1994, 116, 60–62.
[40] L. Brandsma, Preparative Acetylenic Chemistry, Elsevier, 2nd
ed., Amsterdam, 1992.
[41] G. M. Barrett, D. Dhanak, G. G. Graboski, S. J. Taylor, Org.
Synth. 1990, 68, 8–12.
Received: February 24, 2005
Published Online: July 20, 2005
3714
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2005, 3704–3714