Nonafluorobutanesulfonyl azide: A shelf-stable diazo transfer reagent for the synthesis of azides from primary amines

Article abstract of DOI:10.1002/adsc.201000417

Nonafluorobutanesulfonyl azide is an efficient, shelf-stable and cost-effective diazo transfer reagent for the synthesis of azides from primary amines. The reagent can also be successfully applied to the one-pot regioselective synthesis of 1,2,3-triazoles from primary amines by a sequential diazo transfer and azide-alkyne 1,3-dipolar cycloaddition process catalyzed by copper. The cycloaddition step can be conducted in an inter- or intramolecular way to afford 1,4- or 1,5-disubstituted triazoles, respectively. The atypical 1,5-regioselectivity under copper catalysis is a consequence of geometrical constraints of the amino-alkyne substrates used in the intramolecular version. Nonafluorobutanesulfonyl azide offers an advantageous alternative to the better known and most commonly used trifluoromethanesulfonyl azide.

Full text of DOI:10.1002/adsc.201000417

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DOI: 10.1002/adsc.201000417
Nonafluorobutanesulfonyl Azide: A Shelf-Stable Diazo Transfer
Reagent for the Synthesis of Azides from Primary Amines
Josꢀ Ramꢁn Suꢂrez,a Beatriz Trastoy,a M. Eugenia Pꢀrez-Ojeda,b
Rubꢀn Marꢃn-Barrios,a and Jose Luis Chiaraa,*
a
Instituto de Quꢃmica Orgꢂnica General, C.S.I.C., Juan de la Cierva 3, 28006 Madrid, Spain
Fax : (+34)-9-1564-4853; e-mail: jl.chiara@iqog.csic.es
Instituto de Quꢃmica-Fꢃsica “Rocasolano”, C.S.I.C., Serrano 119, 28006 Madrid, Spain
b
Received: May 28, 2010; Published online: September 30, 2010
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/adsc.201000417.
Abstract: Nonafluorobutanesulfonyl azide is an effi- tively. The atypical 1,5-regioselectivity under copper
cient, shelf-stable and cost-effective diazo transfer catalysis is a consequence of geometrical constraints
reagent for the synthesis of azides from primary of the amino-alkyne substrates used in the intramo-
amines. The reagent can also be successfully applied lecular version. Nonafluorobutanesulfonyl azide
to the one-pot regioselective synthesis of 1,2,3-tri- offers an advantageous alternative to the better
ACHTUNGTRENNUNGazoles from primary amines by a sequential diazo known and most commonly used trifluoromethane-
transfer and azide–alkyne 1,3-dipolar cycloaddition sulfonyl azide.
process catalyzed by copper. The cycloaddition step
can be conducted in an inter- or intramolecular way Keywords: amines; azides; click chemistry; copper;
to afford 1,4- or 1,5-disubstituted triazoles, respec- diazo transfer
Introduction
of the starting amine and has wide functional group
compatibility. The method was originally described by
Organic azides have found many important applica- Cavender and Shiner[5] in 1972 and was applied to
tions in organic synthesis,[1] chemical biology,[2] and amino acids nine years later,[10] but it did not found
materials science[3] thanks to their versatile chemistry. wider use until the early 1990s, when Vasella et al.[6]
Thus, azides are readily reduced to amines, amides or introduced it into carbohydrate chemistry. Over the
carbamates, act as precursors for nitrenes and as radi- years, the original experimental procedure has experi-
cal traps, and undergo a variety of named reactions enced some improvements, including the introduction
including 1,3-dipolar cycloadditions and rearrange- of transition metal catalysts[7] and the substitution of
ment processes.[1] From a practical point of view, in dichloromethane with other solvents in the prepara-
addition to their widely recognized utility for the syn- tion of the TfN3 reagent to avoid the adventitious for-
thesis of 1,2,3-triazoles,[4] azides are convenient and mation of potentially explosive azidochloromethane
atom-economic protecting groups for primary and diazidomethane.[11] In spite of these develop-
amines[5,6,7] and have found use as photoaffinity re- ments, the use of TfN3 as a diazo transfer reagent still
agents for biomolecules[8] and as bioorthogonal chem- suffers from several serious drawbacks. First, neat
ical reporters in biological systems.[2,9] Although TfN3 is an unstable and explosive compound that has
azides are most commonly prepared by nucleophilic to be prepared prior to use and should always be han-
substitution of an appropriate leaving group by the dled in solution.[5] In addition, the reagent is obtained
azide anion, this approach is sometimes compromised from the rather costly trifluoromethanesulfonic anhy-
by competing elimination processes or by poor stereo- dride and sodium azide[5] in variable yields and, ac-
chemical control. An alternative and widely used ap- cordingly, it is usually employed in large excess since
proach is the diazo transfer reaction of primary it is cumbersome to determine its exact concentration
amines with trifluoromethanesulfonyl azide (triflyl in the crude solution.
azide, TfN3). This reaction takes place under mild
In a recent project, we needed to prepare octa-
conditions, with complete retention of configuration kis(3-azidopropyl)octasilsesquioxane (2) starting from
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AHCTUNGTRENNUNG
Results and Discussion
We prepared NfN3 in ca. 20 to 40-gram batches fol-
lowing the described procedure.[18b,c] Although it has
been reported that NfN3 can be safely distilled under
vacuum,[18a,c] the crude product was pure enough for
our purposes as obtained, after drying over anhydrous
Na2SO4. This reagent can be kept at 48C for months
Scheme 1. Synthesis of octa-azide 2 using TfN3 and NfN3.
commercially available octakis(3-aminopropyl)octasil- without any observable decomposition. For the diazo
sesquioxane octa-hydrochloride (1) by employing a transfer reaction, a small excess (1.2–1.5 equivalents)
diazo transfer approach (Scheme 1).[12] We hoped that of NfN3 was added to a solution of the amine, a cata-
the mild conditions of the diazo transfer process lytic amount of CuSO4·5H2O (0.1 equivalent), and an
would prevent nucleophile-induced cage rearrange- excess of NaHCO3 (4 equivalent) in a homogeneous
ments[13] that were expected to occur in alternative Et2O/MeOH/H2O (1:3:1) solvent mixture at room
routes to 2 using nucleophilic substitution reactions temperature. The reactions were usually complete
with azide anion.[14] Compound 1, containing eight after 1–6 h as judged by TLC analysis. The azide was
amino groups, provided a stringent test for the effi- isolated by liquid-liquid extraction of the crude reac-
ciency of the diazo transfer process. The moderate tion mixture with CH2Cl2, followed by repeated wash-
and variable yields of 2 that we obtained using TfN3, ing (5ꢅ) of the organic phase with a saturated aque-
together with the hazards and high cost of the reagent ous solution of NaHCO3 to remove the nonafluorobu-
required for our gram-scale experiments prompted us tanesulfonamide by-product. Residual nonafluorobu-
to investigate safer and less costly options. In view of tanesulfonamide was completely removed by sublima-
the known empirical relationship between explosive- tion during the concentration of the crude material at
ness and nitrogen relative content of organic azi- reduced pressure. This simple work-up afforded in
des,[1b,c,15] we reasoned that higher molecular weight most cases analytically pure products that did not re-
polyfluoroalkylsulfonyl azides could be safer alterna- quired further purification. To facilitate isolation,
tives to TfN3 while holding a similar or even increased azides derived from d-glucosamine and neomycin
reactivity.[16] Among the commercially available poly- were peracetylated in situ by treating the concentrat-
fluoroalkylsulfonic acid derivatives, nonafluorobu- ed crude reaction mixture with an excess of acetic an-
ACHTUNGTRENNUNG
tanesulfonyl fluoride (nonaflyl fluoride, NfF)[17] is a hydride in pyridine (Table 1, entries 9 and 10). Isolat-
bulk product that is remarkably cheaper than ed yields of azides were good to excellent in all cases
common triflating reagents. Reacting NfF with and compared favorably to those reported in the liter-
sodium azide in MeOH readily affords nonaflyl azide ature for the same substrates using TfN3.
(NfN3) in good yield.[18] This reagent is a colorless
To further illustrate the versatility of NfN3 as an ef-
liquid with a characteristic pungent odor resembling ficient reagent for the preparation of azides, we also
that of TfN3 and is stable at room temperature as a assayed its performance in sequential one-pot diazo
neat reagent, with a reported decomposition tempera- transfer followed by intermolecular copper-catalyzed
ture of around 1208C.[18b] Zhu et al. have studied the azide–alkyne 1,3-dipolar cycloaddition, as recently de-
reactions of NfN3 with electron-rich alkenes,[19] aro- scribed for TfN3.[23] Both aliphatic (Table 2, entries 1–
matic compounds,[20] and nitrogen,[21] phosphorus,[18b,c] 3) and aromatic amines (Table 2, entries 4, 5) per-
and sulfur[18b,c] nucleophiles. However, at the onset of formed equally well in this transformation to give the
our work, there was only a single example reported in expected 1,4-disubstituted 1,2,3-triazole products re-
the literature on the use of NfN3 for the synthesis of gioselectively and in good overall yields. The method-
an organic azide from a primary amine.[22]
ology could also be applied to intramolecular Huisgen
In our previous work,[12] we found that NfN3 afford- cycloadditions (Scheme 2).[24] We selected two 2-
ed higher and more reproducible yields of 2 (60–73%, (prop-2-yn-1-yloxy)anilines 10a, b as substrates that
which accounts for >94% yield per amino group) could be readily prepared from the corresponding 2-
than TfN3, under otherwise similar reaction condi- nitrophenols. Due to geometrical constraints, the in-
tions (Scheme 1). In order to assess the efficiency and tramolecular 1,3-dipolar cycloaddition afforded only
general utility of NfN3 as an advantageous and safer the corresponding 1,5-disubstituted tricyclic triazoles
alternative to TfN3 for the preparation of organic 11a, b. We could not detect the presence of cyclic di-
1
azides, we have now extended this study to a diverse meric products or of higher oligomers in the H NMR
set of amines, including simple alkylamines, aryl- spectra of the crude reaction mixtures. Overall yields
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Nonafluorobutanesulfonyl Azide: A Shelf-Stable Diazo Transfer Reagent
Table 1. Synthesis of azides from primary amines with nonaflyl azide.
Entry
Substrate
Product
Yield [%][a]
1
2
3
3a
3b
3c
4a
4b
4c
91
88
97
4
5
3d
3e
4d
4e
94
86
6
3f
4f
89
7
8
3g
3h
4g
4h
90
85
9
3i
4i
74[b]
10
3j
4j
72[b]
[a]
Yield of pure product after simple extractive work-up (see text).
Overall yield after conventional acetylation of the crude azide with an excess of Ac2O in pyridine at room temperature
followed by column chromatography purification (see Supporting Information).
[b]
were ca. 20% higher in these two examples when the Conclusions
diazo transfer reaction was performed in the absence
of copper catalyst, which required an extended reac- In summary, we have shown that nonafluorobutane-
tion time, using CH2Cl2 instead of Et2O in the solvent sulfonyl azide is a shelf-stable and cost-effective diazo
mixture. When the diazo transfer was complete, addi- transfer reagent for the efficient synthesis of azides
tion of CuSO4/sodium ascorbate triggered the intra- from primary amines. In most cases, the resultant
molecular Huisgen cycloaddition at room tempera- azides can be readily isolated in pure form and in
ture, confirming that these were in fact Cu(I)-cata- good yield after a simple extractive work-up that
lyzed cycloadditions in spite of their atypical regiose- avoids chromatographic purification. The reagent has
lectivity.
also proven its utility in the one-pot regioselective
synthesis of 1,2,3-triazoles from primary amines by a
sequential diazo transfer and azide–alkyne 1,3-dipolar
cycloaddition process catalyzed by copper. This one-
pot procedure can be applied to amino-alkynes to
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Table 2. Synthesis of triazoles from primary amines by one-pot diazo transfer and intermolecular Huisgen 1,3-dipolar cyclo-
addition using nonaflyl azide.
Entry
1
R1NH2
R2
Product
Yield [%][a]
83
3a
(CH2)5CH3
5
2
3
p-Tol
6
7
77
62
3d
3e
Ph
4
(CH2)5CH3
8
9
80
66
5
Ph
[a]
Overall isolated yield.
Scheme 2. Synthesis of triazoles from primary amines by one-pot diazo transfer and intramolecular Huisgen 1,3-dipolar cy-
cloaddition using nonaflyl azide
afford the corresponding 1,5-disubstituted 1,2,3-tri- Experimental Section
ACHTUNGTRENNUNGazoles, due to geometrical constraints. Nonaflyl azide
is an advantageous alternative to the better known General Procedure for Diazo Transfer Reactions
and most commonly used triflyl azide. Together with
To a solution of the corresponding amine 3 (0.6 mmol) in
water (0.8 mL) was added in sequence MeOH (2.2 mL),
the recently described imidazole-1-sulfonyl azide,[25]
the nonaflyl analogue is an interesting addition to the
NaHCO3 (0.201 g, 2.4 mmol), a solution of nonafluorobu-
growing arsenal of efficient and shelf-stable diazo
transfer reagents. Investigations on other synthetic ap-
plications of this compound are currently underway in
our laboratory.
AHCTUNGTREGNUNtN anesulfonyl azide (0.295 g, 0.9 mmol) in Et2O (1.2 mL) and
CuSO4·5H2O (14 mg, 0.06 mmol). The reaction mixture was
stirred at room temperature for 6 h. The mixture was con-
centrated at reduced pressure, CH2Cl2 (15 mL) was added,
and the resultant solution was washed with a saturated
aqueous solution of NaHCO3 (5ꢅ10 mL). The organic layer
was separated, dried over anhydrous Na2SO4, and concen-
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Nonafluorobutanesulfonyl Azide: A Shelf-Stable Diazo Transfer Reagent
trated under reduced pressure. The corresponding azide 4
2005, 44, 5188; c) Organic Azides: Synthesis and Appli-
was obtained in pure form without any further purification.
cations, (Eds.: S. Brꢆse, K. Banert), John Wiley & Sons
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[2] a) M. Kçhn, R. Breinbauer, Angew. Chem. 2004, 116,
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General Procedure for One-Pot Diazo Transfer and
Intermolecular 1,3-Dipolar Huisgen Cycloaddition
Reactions
To a solution of the corresponding amine 3 (0.6 mmol) in
water (0.8 mL) was added in sequence MeOH (2.2 mL),
NaHCO3 (0.201 g, 2.4 mmol), a solution of nonafluorobu-
ACHTUNGTRENNUNGtanesulfonyl azide (0.295 g, 0.9 mmol) in Et2O (1.2 mL) and
CuSO4·5H2O (14 mg, 0.06 mmol). The reaction mixture was
stirred at room temperature for 6 h. Then, a terminal alkyne
(0.06 mL, 0.65 mmol) and sodium ascorbate (178 mg,
0.9 mmol) were added and the reaction mixture was stirred
at room temperature overnight. The mixture was concen-
trated under reduced pressure, CH2Cl2 (15 mL) was added,
and the resultant solution was washed with a saturated
aqueous solution of NaHCO3 (4ꢅ10 mL). The organic layer
was separated, dried over anhydrous Na2SO4, and concen-
trated under reduced pressure. The residue was purified by
flash column chromatography to afford the corresponding
triazole 5–9.
[4] a) R. Huisgen, R. Knorr, L. Moebius, G. Szeimies,
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General Procedure for One-Pot Diazo Transfer and
Intramolecular 1,3-Dipolar Huisgen Cycloaddition
Reactions
To a solution of the corresponding amine 10 (0.6 mmol) in
water (0.8 mL) was added in sequence MeOH (2.2 mL),
NaHCO3 (0.201 g, 2.4 mmol), a solution of nonafluorobu-
[5] C. J. Cavender, V. J. Shiner Jr, J. Org. Chem. 1972, 37,
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ACHTUNGTRENNUNGtanesulfonyl azide (0.295 g, 0.9 mmol) in CH2Cl2 (1.2 mL).
[6] A. Vasella, C. Witzig, J. L. Chiara, M. Martꢃn-Lomas,
Helv. Chim. Acta 1991, 74, 2073.
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K. M. Koeller, C.-H. Wong, J. Am. Chem. Soc. 2002,
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[8] S. A. Fleming, Tetrahedron 1995, 51, 12479.
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After stirring the reaction mixture at room temperature for
12 h, CuSO4·5H2O (14 mg, 0.06 mmol) and sodium ascor-
bate (178 mg, 0.9 mmol) were added and the reaction was
stirred at room temperature for 3 h. The mixture was con-
centrated under reduced pressure, CH2Cl2 (15 mL) was
added, and the resultant solution was washed with a saturat-
ed aqueous solution of NaHCO3 (4ꢅ10 mL). The organic
layer was separated, dried over Na2SO4, and concentrated
under reduced pressure. The residue was purified by flash
column chromatography to afford the corresponding tricy-
clic triazole 11.
[12] B. Trastoy, M. E. Pꢀrez-Ojeda, R. Sastre, J. L. Chiara,
Chem. Eur. J. 2010, 16, 3833.
[13] E. Rikowski, H. C. Marsmann, Polyhedron 1997, 16,
3357.
Acknowledgements
We thank the Spanish Ministerio de Ciencia e Innovaciꢀn
(projects CTQ-2006-15515-C02-02/BQU and CTQ2009-
14551-C02-02) and Comunidad de Madrid (project S2009/
PPQ-1634 “AVANCAT”) for financial support. We also
thank Ministerio de Ciencia e Innovaciꢀn for a FPU predoc-
toral fellowship to B. T. and C.S.I.C. for a JAE-Doc contract
to J. R. S., a JAE-Predoc fellowship to M. E. P.-O., and a
JAE-Intro fellowship to R. M.-B.
[14] For recent alternative routes to 2 via nucleophilic sub-
stitution with varying degrees of cage rearrangements,
see: a) Z. Ge, D. Wang, Y. Zhou, H. Liu, S. Liu, Macro-
molecules 2009, 42, 2903–2910; b) V. Ervithayasuporn,
X. Wang, Y. Kawakami, Chem. Commun. 2009, 5130;
c) S. Fabritz, D. Heyl, V. Bagutski, M. Empting, E. Ri-
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Schneider, O. Avrutina, H. Kolmar, Org. Biomol.
Chem. 2010, 8, 2212; d) D. Heyl, E. Rikowski, R. C.
Hoffmann, J. J. Schneider, W.-D. Fessner, Chem. Eur. J.
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