The sequel to a carbocyclic nucleoside synthesis: A divergent access to both arenediazonium ions and aryl triflates

Article abstract of DOI:10.1016/j.tetlet.2004.01.147

Depending on the amount of acid used, treating aryl-dialkyl triazenes of general structure 3 with triflic acid resulted in the formation of either the corresponding arenediazonium triflates 4 or aryl triflates 8 apparently by two different pathways, the latter conversion being favoured at high acid concentration.

Full text of DOI:10.1016/j.tetlet.2004.01.147

Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 2579–2583
The sequel to a carbocyclic nucleoside synthesis: a divergent
access to both arenediazonium ions and aryl triflates
C. Picherit, F. Wagner and D. Uguen*
Laboratoire de Synthꢀese Organique, associꢁe au CNRS, Ecole Europꢁeenne de Chimie, Polymꢀeres et Matꢁeriaux,
Universitꢁe Louis Pasteur, 25, rue Becquerel, 67087 Strasbourg, France
Received 17 November 2003; revised 16 January 2004; accepted 30 January 2004
ꢁ
In memoriam, this Letter is dedicated to Dr. Patrick Leon, who passed away while this work was in progress
Abstract—Depending on the amount of acid used, treating aryl–dialkyl triazenes of general structure 3 with triflic acid resulted in
the formation of either the corresponding arenediazonium triflates 4 or aryl triflates 8 apparently by two different pathways, the
latter conversion being favoured at high acid concentration.
ꢀ 2004 Elsevier Ltd. All rights reserved.
€
As part of work aimed at synthesising 1a, a carbocyclic
adenosine derivative with promising cardioprotective
and antilipolytic properties,1 we faced the problem of
converting aristeromycin 1b into a corresponding six-
halo compound. Since 1b is accessible by fermentation,2
successful halo-deamination would have paved the way
for a straightforward access to 1a (Scheme 1).
presence of Hunigꢀs base followed by sequential treat-
ment of the resulting substitution product with TBAF,
MeI/t-BuOK and concd HCl afforded compound 1a,
with spectroscopic data corresponding to those in the
literature.1;6
Due to the limited solubility in halogenated solvents of
all the compounds in this series, the purification of crude
1e by column chromatography and re-crystallisation to
eliminate by-product hydroxy compounds was rather
tedious. With the aim of improving this halogenation
step, conversion of 1c into a triazene derivative was
considered.
As anticipated from results obtained with nucleosides,3
the use of classical, aqueous, Gatterman–Sandmeyer
conditions proved ineffective. Better results were
obtained by submitting the protected derivative 1c to
aprotic Sandmeyer conditions.
Reacting 1c with i-amyl nitrite and CuCl2 in aceto-
nitrile4a was unsuitable, as very stable complexes of the
chloride 1d thus formed with the copper species were
produced. The situation was improved by the use of
CCl4 as halogen donor,4b;c the pure chloride 1d being
then isolated in moderate yield (37%). Finally, treating
1c with excess i-amyl nitrite in hot CH2I2, with the
addition of iodine,4d afforded the iodide 1e in a satisfy-
ing 66% yield after purification.5 Subsequently, con-
densation of 1e with the amine 2 in EtOH and in the
It has been reported that adding triflic acid (TfOH) to a
benzene solution of the triazene 3a results in the pre-
cipitation of p-tolyldiazonium triflate 4a as a crystalline
solid.7 Our hope was that diazotising 1c and then adding
a lipophilic secondary amine to the resulting mixture
would furnish a triazene having an appreciable solubility
in organic solvents. In the event, treatment with TfOH
as above would deliver the corresponding diazonium
triflate.8
Unexpectedly, reacting 1c with i-amyl nitrite and
TMSCl, followed by N,N-dibenzylamine afforded in low
yield (7%) a coloured pasty solid to which the structure
1f was tentatively assigned (NMR). Moreover, treat-
ment of this product with TfOH failed to give a diazo-
nium derivative and therefore this approach was
abandoned.
Keywords: Carbocyclic nucleosides; Diazotisation; Diazonium triflate;
Triazene; Aryl triflate; Diazo coupling.
* Corresponding author. Tel.: +33-3-90-24-27-63; fax: +33-3-90-24-26-
12; e-mail: uguen@chimie.u-strasbg.fr
0040-4039/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2004.01.147

2580
C. Picherit et al. / Tetrahedron Letters 45 (2004) 2579–2583
X
N
H
N
N
N
H2N
N
N
N
N
R1O
N
N
N
CF3
N
N
CF3
MeO
2
R2O
OR2
HO
OH
1b R1=R2=H; X=NH2 aristeromycin
1c R1=TBDMS; R2,R2=CMe2; X=NH2
1d R1=TBDMS; R2,R2=CMe2; X=Cl
1e R1=TBDMS; R2,R2=CMe2; X=I
1a RPR 118749
1f R1=TBDMS; R2,R2=CMe2; X=N=N-NBn2
C-6
NH2
I
N
N
N
a, b
N
c
N
N
1a
HO
TBDMSO
N
N
HO
OH
O
O
Aristeromycin 1b
1e
Scheme 1. Reagents and conditions: (a) (i) 2,2-Dimethoxypropane (2 equiv), MeSO3H (1 equiv), acetone (8 mL/mmol); )10 ꢁC to rt, 14 h (85%); (ii)
TBDMSCl (1.5 equiv), imidazole (3 equiv), DMF (1 mL/mmol); rt, 15 h (86%); (b) i-amyl nitrite (19 equiv), KI (3.3 equiv), I2 (3 equiv), CH2I2 (6 mL/
ꢁ
ꢁ
€
mmol); 85 C, 3 h, then 0.25 M (in CH2I2) i-amyl nitrite (13 equiv), 85 C, 2.5 h (66%); (c) (i) 2 (1.2 equiv), Hunigꢀs base (3 equiv), EtOH (5 mL/mmol);
reflux, 1 d (75%); (ii) 1 M (in THF) TBAFÆ3H2O (1.1 equiv); rt, 4 h (87%); (iii) t-BuOK (1 equiv), methyl triflate (1 equiv) THF (3 mL/mmol); )78 ꢁC,
1.5 h, then t-BuOK (0.5 equiv), methyl triflate (0.5 equiv), )78 ꢁC, 1 h (59%); (iv) 37% HCl (7 equiv), MeOH (30 mL/mmol); rt, 5 h (79%).
Our interest then returned to the aforementioned 3a–4a
conversion. Unlike more commonly encountered diazo-
nium salts,9 no general procedure for preparing arene-
diazonium triflates from triazenes has been disclosed to
date. This prompted us to re-examine this result and to
this end a series of triazenes was prepared (Scheme 2).
ethyltriazene 3e with TfOH resulted in the separation of
an oil, which by trituration in ether afforded crystals
identified as N,N-diethylammonium triflate (NMR).
After extensive experimentation, we found that slowly
adding TfOH (2 equiv) to a cold AcOEt (or CH2Cl2)
solution of 3a then diluting the reaction mixture with
ether resulted in the precipitation of pure (NMR) 4a,
subsequently isolated in fair yield (47%) after re-crys-
tallisation.11a Comparable results were obtained with
triazenes 3b–d (Table 1).
First, the triazene 3a was reacted with triflic acid in
benzene to give a solid, which was filtered and washed
with ether as described in the literature.7 In contrast to
that reported in this otherwise valuable publication,
NMR examination of this product clearly indicated it to
be a mixture of the triflate 4a and piperidinium triflate.
Repeated re-crystallisation of this compound from an
acetone/ether mixture provided pure (NMR) 4a as white
needles (10%) with a mp of 81 ꢁC, close to the value
obtained by preparing 4a via a more conventional pro-
cedure (ca. 82 ꢁC),10b but differing significantly from that
reported in Ref. 7 (65 ꢁC), undoubtedly the result of
contamination of 4a by the accompanying piperidinium
triflate. Consistently, similar treatment of the parent bis-
Table 1. Conversion of triazenes into arenediazonium triflates11a
Triazene
Solvent
Product (%),a mp ꢁC (lit.)
3a
3b
3c
3d
AcOEt
AcOEt
AcOEt
CH2Cl2
4a (47), 81 (82)10b
4b (49), 85 (85)10a
4c (60), 55
4d (85), 99
a After re-crystallisation from an acetone/ether mixture.
R2
N
OTf
N
N
N
R2
b
a
N
F3CS(O)2O
R
R1
R
3a R1=Me; R2,R2=(CH2)5
3b R1=H; R2,R2=(CH2)5
8a-d (R as in 4)
4a R=Me
4b R=H
4c R=OMe
4d R=NO2
3c R1=OMe; R2,R2=(CH2)5
3d R1=NO2; R2,R2=(CH2)5
3e R1=Me; R2=Et
3f R1=H; R2=Et
3g R1=OMe; R2=Et
3h R1=NO2; R2=Et
Scheme 2. Reagents and conditions:11 (a) TfOH (2 equiv), AcOEt (or CH2Cl2; 8 mL/mmol); )15 ꢁC, 5 min, then ether, )10 ꢁC, 2–5 h; (b) TfOH
(13 equiv); )10 ꢁC, 2.5 h, then rt, overnight.

C. Picherit et al. / Tetrahedron Letters 45 (2004) 2579–2583
2581
N
N
HO
a
N
O2N
N
O2N
N
b
N
5 mp 172 C
˚
Lit.12 178-180 C
˚
F3CS(O)2O
7 mp 247-250 C
O2N
˚
c
Lit.14 248-252 C
˚
4d
N
SO2Ph
N
O2N
6 mp 126 C
˚
Lit.13 130 C
˚
Scheme 3. Reagents and conditions: (a) 2,3-dimethyl-1,3-butadiene (2 equiv), CH3CN (1.5 mL/mmol); rt, 10 min (32%, after re-crystallisation);
(b) O-TMS-b-naphthol (1 equiv), CH2Cl2; rt, 10 min (quantitative); (c) sodium benzenesulfinate (1 equiv), CH2Cl2; rt, 1 d (92%).
As observed with the parent fluoroborate (or hexaflu-
orophosphate),12 reacting 4d with 2,3-dimethyl-1,3-
butadiene afforded the diazine 5 (Scheme 3). Further-
more, adding sodium benzenesulfinate to a solution of
4d in CH2Cl2 resulted in the immediate precipitation of
the known diazosulfone 6,13 thus confirming the strong
similarity of arenediazonium triflates with more com-
monly encountered ꢁstableꢀ arenediazonium salts. Inter-
estingly, mixing 4d with the O-TMS derivative of
b-naphthol in CH2Cl2 instantaneously resulted in the
quantitative formation of a red solid identified as 7 (mp,
NMR).14;15
lamp) or ultrasonication proved necessary to bring these
solvolysis processes to completion. Indeed, heating 4a at
90 ꢁC in triflic acid for a few hours gave, after hydrolysis,
8a in acceptable yield (43%).
Surprisingly however, 4a reacted only very slowly when
stirred in pure TfOH at room temperature and only
trace amounts of 8a were detected after three hours
under these conditions; a similar result being observed
with added piperidinium triflate. Thus it was not clear
why 8a was so easily produced during the 3a–4a con-
version since all these experiments were conducted in the
cold and, moreover, at low acid concentration.
Aware of reports of the formation of aryl triflate
by-products by treatment of various aryl-N,N-dimethyl
triazenes with CsF in the presence of TfOH,16 glc
analysis of the mother liquors left after crystallisation of
4a revealed the presence of 8a (6–18%). These
by-products were particularly prevalent in the pre-
liminary experiments conducted with excess triflic acid.
A reasonable explanation came to light when we noticed
that adding 3a slowly to cold, excess (molar ratio 1/13),
TfOH resulted in the rapid formation of p-tolyl triflate
Table 2. Conversion of triazenes into aryl triflates11b
Triazene
Product (%), bp ꢁC (s)/mp ꢁC
8a (51), 110 (19)
8b (66), 90 (17)
3e
3f
Aryl triflates are also formed by treatment of arene-
diazonium fluoroborates (or o-benzenesulfonimides)
with TfOH,17a;b a related result being observed by
reacting phenyl diazonium fluoroborate with TMS tri-
flate.17c In each case either heating, irradiation (mercury
a
3g
3h
8d (82), 50
a Decomposition.
R2
N
H
N
R2
N
TfO
N
TfOH
R2
N
N
R2
N
N
R2
H
N
R1
R1
TfOH
2TfO
N
R2
3
H
R1
R2
N
TfO
N
R2
fast
H
R1
N
N
OTf
TfOH
TfOH
TfO
(R2)2NH.TfOH
(R2)2NH
(+ (R2)2NH.TfOH, + N2)
R
R
4
8
Scheme 4.

2582
C. Picherit et al. / Tetrahedron Letters 45 (2004) 2579–2583
25.9, 33.0, 45.5, 62.75, 62.79, 80.7, 83.7, 113.7, 122.4,
139.3, 143.8, 148.0; m=z (NH3): 531 (M+1), 405, 169.
6. Thanks are due to Aventis Pharma Developement (Vitry-
8a, a result subsequently developed into a preparative
procedure by using the parent N,N-diethyl triazenes 3e–
h (Table 2).11b
ꢁ
sur-Seine) and Rhodia (Saint-Fons) for support. Drs. M.
Mulhauser (from Aventis), L. Saint-Jalmes and J.-M Paris
(from Rhodia) are acknowledged for a generous gift of the
amine 2 and triflic acid, respectively, and their interest.
These results are taken in part from the thesis and DEA
dissertation of C.P. (Strasbourg, 2003) and F.W. (Stras-
bourg 2001), respectively.
We tentatively suggest that a double protonation of
triazenes 3, competitive with the decomposition of
mono-protonated 3 into a diazonium salt (i.e. 4) owing
to the inherently strong acidity of the medium, occurs
under these conditions. In the event, fast decomposition
of the formed bis-cationic species would deliver 8
alongside an ammonium triflate as observed (Scheme 4).
7. Patrick, T. B.; Willaredt, R. P.; DeGonia, D. J. J. Org.
Chem. 1985, 50, 2232–2235.
8. Conversion of the triazene into a 6-halo compound would
also have been possible: (a) Ku, H.; Barrio, J. R. J. Org.
Chem. 1981, 46, 5239–5241; (b) Moore, J. S.; Weinstein, E.
J.; Wu, Z. Tetrahedron Lett. 1991, 32, 2465–2468; (c)
Barrio, J. R.; Satyamurthy, N.; Ku, H.; Phelps, M. E. J.
Chem. Soc., Chem. Commun. 1983, 443–444; (d) Satia-
murthy, N.; Barrio, J. R. J. Org. Chem. 1983, 48, 4394–
4396; (e) Protiva, J.; Krecek, V.; Leseticki, L. J. Radioanal.
Nucl. Chem. 1986, 107, 331–336.
Whatever the validity of this hypothetical pathway, a
straightforward access to aryl triflates from triazenes has
been disclosed, the only unsatisfactory result being
registered with the p-methoxy derivative 3g, when sub-
stantial amounts of unidentified polyaromatic com-
pounds were formed.
In summary, the use of aprotic Sandmeyer conditions
has proved satisfactory for converting aristeromycin 1b
into the iodide 1e, thence to the potentially useful car-
bocyclic adenosine derivative 1a. Unexpectedly,
attempted preparation of a triazene from 1b proved
difficult. Examination of a little-studied triazene-diazo-
nium triflate conversion was more satisfactory however.
A dichotomy in reactivity of aryl–dialkyl triazenes with
triflic acid has been unveiled resulting in a divergent
access to both aryl and arenediazonium triflates, a class
of diazonium salts which, promisingly, compete with
more commonly encountered stabilised diazonium
derivatives both in terms of thermal stability and reac-
tivity.
9. (a) Buxton, P. C.; Heaney, H. J. Chem. Soc., Chem.
Commun. 1973, 545–546; (b) Rigaudy, J.; Barcelo, J.;
Ahond, M. Bull. Soc. Chim. Fr. 1981, 231–237; (c)
Satyamurthy, N.; Barrio, J. R.; Schmidt, D. G.; Kam-
merer, C.; Bida, G. T.; Phelps, M. E. J. Org. Chem. 1990,
55, 4560–4564; (d) Bhattacharya, S.; Majee, S.; Mukher-
jee, R.; Sengupta, S. Synth. Commun. 1995, 25, 651–657;
(e) Sengupta, S.; Sadhukhan, S. K.; Bhattacharyya, S.
Tetrahedron 1997, 53, 2213–2218; (f) Sengupta, S.; Sad-
hukhan, S. K. Tetrahedron Lett. 1998, 39, 715–718; (g)
Gollas, B.; Speiser, B. Angew. Chem. 1992, 104, 336–338;
(h) Lazny, R.; Poplawski, J.; Kobberling, J.; Enders, D.;
Brase, S. Synlett 1999, 1304–1306; (i) Brase, S.; Schroen,
M. Angew. Chem., Int. Ed. 1999, 38, 1071–1073; (j) De
Meijere, A.; Nuske, H.; Es-Sayed, M.; Labahn, T.;
Schroen, M.; Brase, S. Angew. Chem., Int. Ed. 1999, 38,
3669–3672; (k) Wan, W. B.; Brand, S. C.; Pak, J. J.; Haley,
M. M. Chem. Eur. J. 2000, 6, 2044–2052; (l) Lormann, M.;
References and notes
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Dahmen, S.; Brase, S. Tetrahedron Lett. 2000, 41, 3813–
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2000, 39, 3681–3683; (n) Barbero, M.; Degani, I.; Diul-
gheroff, N.; Dughera, S.; Fochi, R. Synthesis 2001, 2180–
2190; (o) Lazny, R.; Sienkiewicz, M.; Brase, S. Tetrahe-
dron 2001, 57, 5825–5832; (p) Chan, D. C. M.; Laughton,
C. A.; Queener, S. F.; Stevens, M. F. G. Bioorg. Med.
Chem. 2002, 10, 3001–3010; (q) Sengupta, S.; Sadhukhan,
S.; Kumar, S.; Rajkumar, S.; Pal, N. Tetrahedron Lett.
2002, 43, 1117–1121; (r) Schunk, S.; Enders, D. J. Org.
Chem. 2002, 67, 8034–8042.
1. Myers, M. R.; Maguire, M. P.; Spada, A. P.; Ewing, W.
R.; Pauls, H. W.; Choi-Sledeski, Y. M. World Appl.
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9801426 (Rhone-Poulenc Rorer Pharmaceuticals) Chem.
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R.; Shay, J. J.; Sledeski, A. W.; Teager, D. S.; Vanasse, B.
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2. Kusaka, T.; Yamamoto, H.; Shibata, M.; Muroi, M.;
Kishi, T.; Mizuno, K. J. Antibiot. 1968, 21, 255–263; See
also: (a) Abel, B. L.; Lindon, J. C.; Noble, D.; Rudd, B. A.
M.; Sidebottom, P. J.; Nicholson, J. K. Anal. Biochem.
1999, 270, 220–230; (b) Jenkins, G. N.; Turner, N. J.
Chem. Soc. Rev. 1995, 24, 169–176.
3. (a) McKenzie, T. C.; Epstein, J. W. J. Org. Chem. 1982,
47, 4881–4884, and references cited therein; (b) Press, J. B.;
Eudy, N. H.; Morton, G. O. J. Org. Chem. 1983, 48, 4605–
4611.
4. (a) Doyle, P. D.; Siegfried, B.; Dellaria, J. F. J. Org. Chem.
1977, 42, 2426–2431; (b) Cadogan, J. I. G.; Roy, D. A.;
Smith, D. M. J. Chem. Soc. (C) 1966, 1249–1250; (c) Ha,
S. B.; Nair, V. Tetrahedron Lett. 1996, 37, 1567–1570, and
cited references; (d) Friedman, L.; Chlebowski, J. J. Org.
Chem. 1968, 33, 1636–1638.
5. 1d: dC (100 MHz, CDCl3): )5.1, )5.0, 18.6, 25.5, 26.2,
28.0, 33.0, 45.8, 63.09, 63.12, 81.1, 84.1, 114.0, 132.7,
144.8, 151.6, 152.1, 152.2; m=z (NH3): 439 (M+1), 405,
381, 325, 169; 1e: dC (100 MHz, CDCl3): )5.4, 18.3, 25.2,
10. (a) Weiss, R.; Wagner, K. G.; Hertel, R. Chem. Ber. 1984,
117, 1965–1972; (b) Knoechel, A.; Zwernemann, O. J.
Labelled Compd. Radiopharm. 1996, 38, 325–336; For an
access to o-trifloxy-arenediazonium triflates from aromatic
diazoketones (and their coupling reaction with phenols),
see: Maas, G.; Tretter, A. Liebigs Ann. Chem. 1985, 1866–
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11. (a) The triazenes 3a–h were prepared as described (see
references in Ref. 8). Though apparently stable (v. infra),
diazonium triflates should be considered as potentially
explosive and all experiments, including subsequent work-
up operations were conducted behind a safety screen.
Protocol for the triazene–diazonium triflate conversion: To
a cooled (dry ice/methanol bath), well-stirred, solution of
3a (1.12 g, 5.5 mmol) in AcOEt (46 mL) was added
dropwise over 5 min freshly distilled triflic acid (1 mL;
11.3 mmol; 2 equiv). A white precipitate formed immedi-
ately. The mixture was maintained at ca. )10 ꢁC and ether

C. Picherit et al. / Tetrahedron Letters 45 (2004) 2579–2583
2583
(10 mL) was added. The solids were filtered, washed with
cool ether, then dried in vacuo. Recrystallisation of the
white solid thus obtained (acetone/ether) afforded the pure
(NMR) diazonium triflate 4a (696 mg, 47%) as colourless
needles (mp 81 ꢁC). In the case of the p-nitro derivative 3d,
evaporation of the solvent (CH2Cl2, owing to the poor
solubility of 3d in AcOEt) was followed by crystallisation
of the resulting syrup from an acetone/ether mixture to
give the triflate 4d as a crystalline solid (82%). As
previously noticed, the thermal stability of these arene-
diazonium triflates is remarkable. Thus brief heating of a
small amount (ca. 100 mg) of the nitro derivative 4d to
100–110 ꢁC (oil bath) failed to induce any change on the
basis of NMR analysis; (b) Elimination of the ammonium
triflate at the work-up stage proved tedious with the
piperidine derivatives and only N,N-diethyltriazenes 3e–h
were used for preparative purpose. Protocol for the
triazene-aryl triflate conversion: 3f (3.01 g; 16.98 mmol)
was gradually added, over 2.5 h, to freshly distilled triflic
acid (20 mL; 226 mmol; 13 equiv), the internal temperature
being maintained at )10 ꢁC with a cooling bath (dry ice/
methanol). The resulting dark mixture was allowed to
reach room temperature then stirred overnight before
being poured into iced water (180 mL). The mixture was
extracted with CH2Cl2 (3 · 45 mL), the pooled organic
extracts being then washed with brine (4 · 60 mL), and
dried (MgSO4). The black oil (2.84 g) left by evaporation
of the solvent was distilled (bp 90 ꢁC at 17 s) using a short
path distillation apparatus to give the triflate 8b as a pale
yellow oil (2.54 g; 66%). Selected data: 4c: mp 55 ꢁC; dH
(D2O): 4.09 (s, 3H), 7.37–7.44 (m, 2H), 8.45–8.53 (m, 2H);
4d: mp 99 ꢁC; dH (acetone-d6): 8.84–8.91 (m, 2H), 9.2–9.28
(m, 2H); 8d: mp 50 ꢁC; dH (CDCl3): 7.48 (d, J ¼ 9:3 Hz,
2H), 8.35 (d, J ¼ 9:3 Hz, 2H). All NMR at 200 MHz. Aryl
triflates were identified by comparison with authentical
samples18 and by NMR, TLC and GLC analyses. For a
review on aryl triflates, see: Ritter, K. Synthesis 1993, 735–
762
12. (a) Carlson, B. A.; Sheppard, W. A.; Webster, O. W. J.
Am. Chem. Soc. 1975, 97, 5291–5293; (b) Hartnagel, M.;
Grimm, K.; Mayr, H. Liebigs Ann. Chem. 1997, 71–80.
13. Ahern, M. F.; Leopold, A.; Beadle, J. R.; Gokel, G. W. J.
Am. Chem. Soc. 1982, 104, 548–554.
14. Kaupp, G.; Herrmann, A.; Schmeyers, J. Chem. Eur. J.
2002, 8, 1395–1406.
ꢁ
15. We acknowledge Mr. G. Medard for his contribution to
this work, especially for exploratory experiments on the
use of these anhydrous diazo-coupling conditions for
colouring lipophilic materials.
16. (a) Pages, T.; Langlois, B. J. Fluorine Chem. 2001, 107,
321–327; (b) Pages, T.; Langlois, B. R.; Le Bars, D.;
Landais, P. J. Fluorine Chem. 2001, 107, 329–335.
17. (a) Nazaretyan, P.; Kamenskaya, O. I. Zh. Org. Khim.
1976, 12, 690; (b) Yoneda, N.; Fukuhara, T.; Mizokami,
T.; Suzuki, A. Chem. Lett. 1991, 459–460; (c) Olah, G. A.;
Wu, A.-H. Synthesis 1991, 204–206. Aryl triflates have
also been obtained by treating arenediazonium fluorobo-
rates with ionic liquid triflates.19
18. Frantz, D. E.; Weaver, D. G.; Carey, J. P.; Kress, M. H.;
Dolling, U. H. Org. Lett. 2002, 4, 4717–4718.
19. Laali, K. K.; Gettwert, W. J. J. Fluorine Chem. 2001, 107,
31–34.