On the reaction of 1,3-diphenylisobenzofuran and (2-iodoethynyl)(phenyl) iodonium triflate. A unique case of oxygen transfer from the diels-alder adduct to the diene

Article abstract of DOI:10.3390/molecules17088795

Reaction of 1,3-diphenylisobenzofuran (DPIBF) with 2-(iodoethynyl)(phenyl)- iodonium triflate at room temperature gave the expected Diels-Alder adduct, but using an excess of DFIBF (2 equiv.) and performing the reaction at 55 °C or heating at this temperature during the concentration stage, the initial orange solution or product mixture became dark brown and the products 1,2-phenylene-1,2-bis(phenylmethanone) and 2-(3-iodo-1,4-diphenylnaphthyl) (phenyl)iodonium triflate were obtained, which suggests an oxygen transfer between DPIBF and the initial adduct.

Full text of DOI:10.3390/molecules17088795

Molecules 2012, 17, 8795-8803; doi:10.3390/molecules17088795
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Communication
On the Reaction of 1,3-Diphenylisobenzofuran and
(2-Iodoethynyl)(phenyl)iodonium Triflate. A Unique Case of
Oxygen Transfer from the Diels-Alder Adduct to the Diene †
Pelayo Camps 1,*, Tània Gómez 1, David Lozano 1, Teresa Calvet 2 and Mercè Font-Bardia 2,3
1
Pharmaceutical Chemistry Laboratory (CSIC Associated Unity), Faculty of Pharmacy,
Biomedicine Institute of the University of Barcelona (IBUB), University of Barcelona,
Joan XXIII av., Barcelona E-08028, Spain; E-Mails: tgomezna7@alumnes.ub.edu (T.G.);
lozanme7@alumnes.ub.edu (D.L.)
2
Crystallography, Mineralogy and Mineral Deposits, University of Barcelona, Martí Franquès st.,
Barcelona E-08028, Spain; E-Mails: mtcalvet@ub.edu (T.C.); mercefont@ub.edu (M.F.-B.)
3
X-ray Diffraction Unity, Scientific and Technologic Centre of the University of Barcelona (CCiTUB),
University of Barcelona, Solé i Sabarís st. 1–3, Barcelona E-08028, Spain
†
Dedicated to Professor Miguel Angel Miranda on the occasion of his 60th birthday.
* Author to whom correspondence should be addressed; E-Mail: camps@ub.edu;
Tel.: +34-934-024-536; Fax: +34-934-035-941.
Received: 13 June 2012; in revised form: 26 June 2012 / Accepted: 10 July 2012 /
Published: 25 July 2012
Abstract: Reaction of 1,3-diphenylisobenzofuran (DPIBF) with 2-(iodoethynyl)(phenyl)-
iodonium triflate at room temperature gave the expected Diels-Alder adduct, but using
an excess of DFIBF (2 equiv.) and performing the reaction at 55 °C or heating at this
temperature during the concentration stage, the initial orange solution or product
mixture became dark brown and the products 1,2-phenylene-1,2-bis(phenylmethanone) and
2-(3-iodo-1,4-diphenylnaphthyl)(phenyl)iodonium triflate were obtained, which suggests
an oxygen transfer between DPIBF and the initial adduct.
Keywords: NMR spectroscopy; structure elucidation; X-ray diffraction

Molecules 2012, 17
8796
1. Introduction
Some time ago, Stang et al. described the preparation of β-functionalized alkynyl(phenyl)iodonium
triflates and 1,2-bis[[(phenyl)trifluoromethanesulfonyloxy]iodo]acetylene and their Diels-Alder
reactions with different dienes, such as cyclopentadiene, 1,3-cyclohexadiene, 2,3-dimethylbutadiene,
furan and 1,3-diphenylisobenzofuran (DPIBF, 2) [1,2]. They also described the reaction of these
adducts with different nucleophiles to give the corresponding substitution products [3,4]. Recently, we
described the preparation of (2-iodoethynyl)(phenyl)iodonium triflate (1) and its reaction with a
1,1-disubstituted cyclopentadienes to give the expected Diels-Alder adducts [5]. Herein, we describe
an unexpected result observed in the reaction of triflate 1 with diene 2.
2. Results and Discussion
Triflate 1 was reacted with diene 2 (2 equiv.) in acetonitrile solution at room temperature for
20 h, and the orange reaction mixture was concentrated in a rotary evaporator at 55 °C, taking at a
certain moment a dark brown color. Upon crystallization from CH2Cl2/Et2O, a mixture containing
1,2-phenylene-1,2-bis(phenylmethanone) (4) was obtained, diene 2 being not observed. Crystallization
of the above mixture from CH2Cl2/toluene (twice) gave (3-iodonaphthalen-2-yl)(phenyl)iodonium
triflate (5) in 54% yield, instead of the expected Diels-Alder adduct (3) (Scheme 1).
Scheme 1. Reaction of 2-(iodoethynyl)(phenyl)iodonium triflate (1) with DPIBF (2).
* Reagents and conditions: (a) acetonitrile, rt, 30 min; (b) 2, acetonitrile, 55 °C, until the solution
or the mixture changes color from orange to dark brown.
1
The H- and 13C-NMR data and the elemental analysis did not allow us to differentiate among
triflates 3 and 5. However, the accurate mass measurement of the obtained product showed the
molecular ion to have an m/z value (608.9567 amu) 16 units less than expected for the cation of triflate 3.
This molecular ion might correspond to the cation of triflate 5. The structure of 5 was subsequently
clearly established by X-ray diffraction analysis (Figure 1). Reaction of triflate 5 with NaI and CuI in
acetonitrile [3] gave the recently described [6] 2,3-diiodo-1,4-diphenylnaphthalene (7), which was
fully characterized (Scheme 2).

Molecules 2012, 17
8797
Figure 1. ORTEP of triflate 5.
Scheme 2. Conversion of triflates 3 and 5 into diiodides 6 and 7.
*Reagents and conditions: (a) NaI/CuI, acetonitrile, −35 to 20 °C.
When the reaction of diene 2 (2 equiv.) and triflate 1 was carried out at room temperature for 24 h
and the solvent was evaporated under reduced pressure without heating, a residue containing much
starting diene 2 was obtained. Crystallization of this residue from CH2Cl2/Et2O, always at room
temperature, gave triflate 3 in 67% yield. This triflate was not too stable, and at room temperature the
light yellow solid initially obtained became dark within 24 h. It also decomposed on drying in vacuo at
room temperature. However, it could be characterized by spectroscopic means (1H-, 13C- and 19F-NMR
spectra and accurate mass measurement). The 1H- and 13C-NMR spectra could be completely assigned
on the basis of 1H/1H homocorrelation (COSY 1H/1H) and 1H/13C heterocorrelation spectra (HSQC and
HMBC sequences). Moreover, triflate 3, on reaction with NaI/CuI in acetonitrile (Scheme 2), was
transformed in high yield into the new diiodide 6, whose structure was fully established on the basis of
its analytical and spectroscopic data, including an X-ray diffraction analysis (Figure 2).

Molecules 2012, 17
8798
Figure 2. ORTEP of diiodide 6.
To establish the conditions under which triflates 3 or 5 are formed, we performed the reaction of diene 2
and triflate 1 under different conditions, always in acetonitrile. Thus, reaction of diene 2 (1.2 equiv.)
and triflate 1 at room temperature for 30 min gave an orange solution. After concentration and
crystallization of the orange residue from CH2Cl2/Et2O, without heating at any moment, triflate 3 was
obtained in 92% yield. A similar reaction performed for 20 h gave triflate 3 in quantitative yield.
Reaction of diene 2 (2 equiv.) and triflate 1 at 55 °C for 24 h gave a dark brown solution. After
concentration and crystallization from CH2Cl2/Et2O and CH2Cl2/toluene (twice), always at room
temperature, triflate 5 was obtained in 42% yield. When diene 2 (2 equiv.) and triflate 1 were reacted
at room temperature for 30 min an orange solution was obtained, which on concentration in a rotary
evaporator heating at 55 °C gave a dark brown residue. After crystallization as before, triflate 5 was
obtained in 42% yield.
An attempt to reduce triflate 3 to 5 by reaction with an excess of dimethylsulfide in CH2Cl2 at room
temperature left the starting triflate 3 unchanged. When the above reaction was carried out in a closed
vessel at 55 °C, complete degradation of triflate 3, but not formation of triflate 5 was observed. A
similar result was obtained on heating a solution of triflate 3 in acetonitrile at 55 °C for 3 h.
Consequently, it appears that triflate 3 is unstable and decomposes at temperatures around 55 °C.
Decomposition of triflate 3 in the presence of DPIBF takes place in part by oxygen transfer between
them. This transformation is clearly observed by a change in the color of the reaction mixture (solution
or concentrate) from orange to dark brown.
A possible mechanism for the reaction of DPIBF with triflate 3 to give dione 4 and triflate 5 is
given in Scheme 3, which starts with the electrophilic attack of the cation of triflate 3 on the
electron-rich diene 2. Although DPIBF can be oxidized by air [7], it seems clear that in our case, most
of dione 4 comes from the oxidation of DPIBF by adduct 3. As previously indicated, much diene 2 is
observed in the reaction of triflate 1 with excess of DPIBF, when adduct 3 is the main product.
Conversely, dione 4 but no diene 2 is the main by-product from the reaction of triflate 1 with an excess
of DPIBF, if adduct 3 has been transformed into triflate 5.

Molecules 2012, 17
8799
Scheme 3. Possible mechanism for the conversion of triflate 3 to 5 on reaction with DPIBF (2).
3. Experimental
3.1. General
Melting points were determined in open capillary tubes. Unless otherwise stated, NMR spectra were
recorded at 25 °C in CDCl3 solution: 1H-NMR (400 MHz), 13C-NMR (100.6 MHz), 19F (376.29 MHz).
All chemical shifts (H, C and F) are reported in parts per million (ppm) related to internal standards
(CHCl3 at H = 7.26 ppm, C = 77.0 ppm and CF3COOH at F −76.55 ppm). Assignments given for the
1H and 13C-NMR spectra are based on DEPT sequences, 1H/1H COSY, 1H/13C HETCOR (gHSQC and
gHMBC sequences for one bond and long range correlations, respectively). In the case of triflate 3,
previous assignment for the adduct of methyl 1-benzylcyclopenta-2,4-dienecarboxylate and triflate 1
were taken into account [5]. Coupling constants J are given in Hertz (Hz). Mass spectra were recorded
on an LC/MSD-TOF instrunent (2006, Agilent Technologies), using electrospray (ESI-MS, positive
mode, capillary: 3.5 kV, fragmentor: 215 V). Unless otherwise stated, IR spectra were recorded using the
attenuated total reflection (ATR) technique and the absorption values are given as wavenumbers (cm–1).
Elemental analyses were done at the Microanalysis Service of the Institut de Química Avançada de
Catalunya (IQAC, CSIC, Barcelona, Spain). Column chromatography was performed on silica gel 60
A C.C. (35–70 mesh). For the thin layer chromatography (TLC), aluminum-backed sheets with silica
gel 60 F254 were used and spots were visualized with UV light and/or 1% aqueous KMnO4.
(3-Iodo-1,4-diphenyl-1,4-dihydro-1,4-epoxynaphthalen-2-yl)(phenyl)iodonium triflate (3). To
a
magnetically stirred suspension of DPIBF (2, 150 mg, 0.55 mmol) in anhydrous acetonitrile (2.5 mL),
a solution of triflate 1 (233 mg, 0.46 mmol) in anhydrous acetonitrile (1 mL) was added dropwise
under an Ar atmosphere and the mixture was vigorously stirred at room temperature for 20 h. The
orange solution was concentrated in vacuo at room temperature and the orange solid residue (418 mg)
was treated with CH2Cl2/Et2O (1:3, 2 mL). The solid triflate 3 (356 mg, quantitative yield) was isolated
as a light yellow solid, m.p. 80–83 °C (dec.) by decantation and washing with Et2O (3 × 0.5 mL) and
CH2Cl2 (3 × 0.5 mL). On drying in vacuo at room temperature this salt became black. The salt was
stable for weeks at 4 °C, but decomposed after standing at room temperature for one day. The
analytical sample was not fully dried and contained traces of Et2O and CH2Cl2. IR (ATR) : 3061,
1548, 1494, 1472, 1446, 1287, 1228, 1220, 1180, 1166, 1156, 1021, 993, 916, 905, 851, 835, 757, 737,
703, 675, 653, 633, 591 cm−1. 1H-NMR : 7.10 (dt, J = 2.0 Hz, J′ = 9.0 Hz, 1H, 7-H), 7.15 (dt, J = 2.0 Hz,

Molecules 2012, 17
8800
J′ = 9.0 Hz, 1H, 6-H), 7.19 (tm, J = 9.5 Hz, 2H, Ar-HmetaAr-I+), 7.30 (ddm, J = 8.8 Hz, J′ = 1.5 Hz, 2H,
Ar-HorthoArI+), 7.38 (dd, J = 9.0 Hz, J′ = 1.5 Hz, 1H, 8-H), 7.48 (tm, J = 9.0 Hz, 1H, Ar-HparaArI+),
7.50–7.60 (complex signal, 7H, 5-H, C1-Ar-Hmeta, C4-Ar-Hmeta, C1-Ar-Hpara and C4-Ar-Hpara), 7.75
(dm, J = 8.0 Hz, 2H, C1-Ar-Hortho), 7.85 (dm, J = 7.5 Hz, 2H, C4-Ar-Hortho). 13C-NMR : 96.3 (C, C1),
97.6 (C, C4), 115.1 (C, C2-I+-Ar-Cipso), 120.0 (C, q, J = 320 Hz, CF3SO3), 121.8 (CH, C8), 122.4 (CH,
C5), 126.4 (CH, C6), 126.5 (CH, C1-Ar-Cortho), 126.9 (CH, C7), 127.4 (CH, C4-Ar-Cortho and C,
C1-Ar-Cipso), 128.5 (CH) and 129.3 (CH) (C1-Ar-Cmeta and C4-Ar-Cmeta), 129.6 (CH, C4-Ar-Cpara),
129.8 (CH, C1-Ar-Cpara), 132.0 (CH, C2-I+-Ar-Cmeta), 132.3 (CH, C2-I+-Ar-Cpara), 132.7 (C, C4-Ar-Cipso),
134.3 (CH, C2-I+-Ar-Cortho), 140.6 (C, C3), 142.2 (C, C2), 145.8 (C, C4a), 146.4 (C, C8a). 19F-NMR :
−78.2 (CF3SO3). Accurate mass measurement: Calcd for C28H19I2O [M−CF3SO3]+: 624.9520. Found:
624.9515.
(3-Iodo-1,4-diphenylnaphthalen-2-yl)(phenyl)iodonium triflate (5). To a magnetically stirred
suspension of DPIBF (2, 617 mg, 2.28 mmol) in anhydrous acetonitrile (5 mL), a solution of triflate 1
(575 mg, 1.14 mmol) in anhydrous acetonitrile (3 mL) was added dropwise under an Ar atmosphere
and the mixture was vigorously stirred at room temperature for 20 h. The orange solution was
concentrated in vacuo at 55 °C. In a certain moment the residue became dark brown. Crystallization of
the above residue (1.31 g) from CH2Cl2/Et2O (3:10, 6.5 mL) gave a solid (1.02 g) mixture of triflate 5
and 1,2-phenylenebis(phenylmethanone) (4). After two crystallizations from CH2Cl2/toluene 3:10
(5.2 mL), triflate 5 (477 mg, 54% yield) was obtained as a beige solid, mp 207–208 °C (dec). IR
(ATR) : 3058, 1490, 1470, 1443, 1282, 1266, 1222, 1153, 1023, 990, 835, 766, 722, 698, 666, 633,
1
599 cm–1. H-NMR (500 MHz) : 7.24–7.28 (complex signal, 4H, C1-Ar-Hortho and C4-Ar-Hortho),
7.37–7.42 (complex signal, 2H, Ar-Hmeta Ar-I+), 7.42–7.47 (complex signal, 4H, 5-H, 6-H, 7-H, 8-H),
7.51–7.62 (complex signal, 7H, C1-Ar-Hmeta, C4-Ar-Hmeta, C1-Ar-Hpara, C4-Ar-Hpara, and C2-I+-Ar-Hpara),
13
7.73 (dd, J = 8.5 Hz, J′ =1.0 Hz, 2H, Ar-Hortho ArI+). C-NMR (125.8 MHz) : 105.4 (C, C3), 116.3
(C, C2-I+-Ar-Cipso), 120.3 (C, q, J = 320 Hz, CF3SO3), 128.26 (CH), 128.30 (CH), 128.8 (CH), 129.3
(CH), 130.0 (CH) and 130.1 (CH) (C5, C6, C7, C8, C1-Ar-Cpara and C4-Ar-Cpara), 128.9 (CH), 129.1
(CH), 129.2 (CH) and 129.9 (CH) (C1-Ar-Cortho, C4-Ar-Cortho, C1-Ar-Cmeta and C4-Ar-Cmeta), 129.7 (C,
C2), 131.9 (CH, Ar-Cmeta Ar-I+), 132.4 (CH, C2-I+-Ar-Cpara), 132.5 (C) and 134.6 (C) (C4a and C8a),
134.4 (CH, C2-I+-Ar-Cortho), 141.7 (C, C1-Ar-Cipso), 145.2 (C, C4-Ar-Cipso), 149.3 (C) and 149.8 (C)
(C1 and C4). 19F-NMR : −78.2 (CF3SO3). Accurate mass measurement: Calcd for C28H19I2
[M–CF3SO3]+: 608.9571. Found: 608.9567. Anal. Calcd for C29H19F3I2O3S·0.1CH2Cl2: C 45.58; H
2.52; I 33.10; F 7.43. Found: C 45.35; H 2.50; I 32.60; F 7.16.
X-Ray diffraction data for triflate 5. A prismatic crystal (0.1 × 0.1 × 0.2 mm) was selected and
mounted on a MAR345 diffractometer with an image plate detector. Unit-cell parameters were
determined from 177 reflections (3 <  < 31°) and refined by least-squares method. Intensities were
collected with graphite monochromatized MoKα radiation; 23,699 reflections were measured in the
range 1.91 ≤  ≤ 32.36. 8,297 of which were non-equivalent by symmetry [Rint (on I) = 0.058].
Reflections (5,839) were assumed as observed by applying the condition I >2(I). Lorentz-polarization
but no absorption corrections were made. The structure was solved by direct methods, using SHELXS
computer program and refined by full-matrix least-squares method with SHELX-97 computer program [8],
using 23,699 reflections (very negative intensities were not assumed). The minimized function was

Molecules 2012, 17
8801
w||Fo|2 – |Fc|2|2, where w  [2(I) + (0.0339P)2 + 1.5431P]−1, and P  |Fo|2  2|Fc|23, f, f', and f"
were taken from International Tables of X-ray Crystallography [9]. All H atoms were computed and
refined, using a riding model, with an isotropic temperature factor equal to 1.2 times the equivalent
temperature factor of the atom to which it is linked. The final R (on F) factor was 0.050, wR(on |F|2) 
0.108 and goodness of fit  1.138 for all observed reflections. Number of refined parameters was 343.
Max. shift/esd  0.00, mean shift/esd  0.00. Max. and min. peaks in final difference synthesis were
0.970 and −0.582 eÅ−3, respectively [10].
2,3-Diiodo-1,4-diphenyl-1,4-dihydro-1,4-epoxynaphthalene (6). To a cold (−35 to −40 °C),
magnetically stirred solution of NaI (23 mg, 0.154 mmol) and CuI (29 mg, 0.154 mmol) in anhydrous
acetonitrile (2.3 mL) under an Ar atmosphere, triflate 3 (120 mg, 0.154 mmol) was added. The mixture
was allowed to warm to room temperature and was stirred overnight at this temperature. The solvent
and volatile products were eliminated under reduced pressure and the residue was extracted with
CH2Cl2 (4 × 2 mL). The combined organic extracts were filtered through a PTFE filter and were
concentrated under reduced pressure to give diodide 6 as a light yellow solid (74 mg, 87% yield). The
analytical sample of 6 was obtained as a light yellow solid (58 mg, 69% yield of crystallized product)
by crystallization from CH2Cl2/MeOH 5:2 (0.7 mL), m.p. 158–160 °C (dec.). IR  3053, 1599, 1544,
1492, 1449, 1342, 1327, 1304, 1132, 1025, 998, 943, 917, 905, 854, 761, 755, 738, 705, 698, 674, 652,
1
590 cm−1. H-NMR  7.10–7.12 [m, 4H, 6(7)-H], 7.46–7.50 [complex signal, 4H, 5(8)-H and phenyl-
13
Hpara], 7.52–7.56 (m, 4H, phenyl-Hmeta), 7.89–7.92 (dm, J = 8.0 Hz, 4H, phenyl-Hortho). C-NMR 
96.7 [(C, C1(4)], 121.2 [CH, C5(8)], 125.7 [CH, C6(7)], 126.4 [(C, C2(3)], 128.0 (CH, phenyl-Cortho),
128.2 (CH, phenyl-Cmeta), 128.9 (CH, phenyl-Cpara), 134.1 (C, phenyl-Cipso), 148.3 [C, C4a(8a)].
Accurate mass measurement: Calcd for C22H15I2O [M+H]+: 548.9207. Found: 548.9188; Calcd for
[M+H−I]+: 422.0162. Found: 422.0158. Anal. Calcd for C22H14I2O: C 48.20, H 2.57, I 46.30. Found: C
48.25; H 2.64; I 46.22.
X-ray diffraction data for diiodide 6. A prismatic crystal (0.1 × 0.1 × 0.2 mm) was selected and
mounted on a MAR345 diffractometer with an image plate detector. Unit-cell parameters were
determined from 289 reflections (3 <  < 31°) and refined by least-squares method. Intensities were
collected with graphite monochromatized MoKα radiation; 10,713 reflections were measured in the
range 1.92    32.03. 4,303 of which were non-equivalent by symmetry (Rint (on I) = 0.045). 3,705
reflections were assumed as observed by applying the condition I >2(I). Lorentz-polarization but no
absorption corrections were made. The structure was solved by direct methods, using SHELXS computer
program and refined by full-matrix least-squares method with SHELX-97 computer program [8],
using 10,713 reflections (very negative intensities were not assumed). The minimized function was
w||Fo|2–|Fc|2|2, where w  [2(I) + (0.0258P)2 + 1.0315P]–1, and P  |Fo|2 + 2|Fc|23, f, f', and f" were
taken from International Tables of X-ray Crystallography [9]. All H atoms were computed and refined,
using a riding model, with an isotropic temperature factor equal to 1.2 times the equivalent temperature
factor of the atom to which it is linked. The final R (on F) factor was 0.031, wR(on |F|2)  0.072 and
goodness of fit  1.171 for all observed reflections. Number of refined parameters was 226. Max.
shift/esd  0.00, mean shift/esd  0.00. Max. and min. peaks in final difference synthesis were 0.395
and −0.620 eÅ−3, respectively [10].

Molecules 2012, 17
8802
2,3-Diiodo-1,4-diphenylnaphthalene (7). To a cold (−35 to −40 °C), magnetically stirred solution of
NaI (92 mg, 0.61 mmol) and CuI (117 mg, 0.61 mmol) in anhydrous acetonitrile (10 mL) under an Ar
atmosphere, triflate 5 (455 mg, 0.60 mmol) was added. The mixture was allowed to warm to room
temperature and was stirred overnight at this temperature. The solution was separated from the
inorganic salts by decantation. The salts were washed with CH2Cl2 (2 × 2 mL). The combined organic
phases were concentrated under reduced pressure to give a solid residue (758 mg) that was subjected to
column chromatography (silica gel, 30 g, hexane/EtOAc mixtures) to give the volatile iodobenzene
(12 mg, 10%) on elution with hexane and product 7 as a white solid, m.p. 269–271 °C (328 mg,
quantitative yield) on elution with hexane/EtOAc 99:1. IR  3058, 2921, 2844, 1490, 1480, 1439,
1
1364, 1270, 1260, 1107, 1073, 1027, 840, 764, 719, 697, 667, 599 cm−1. H-NMR  7.23–7.27
(dm, J = 6.8 Hz, 4H, Ar-Hortho phenyl), 7.28–7.32 [m, 2H, 6(7)-H], 7.30–7.35 [m, 2H, 5(8)-H], 7.48
13
(tm, J = 8.5 Hz, 2H, Ar-Hpara phenyl), 7.55 (m, 4H, Ar-Hmeta phenyl). C-NMR  112.7 [C, C2(3)],
126.9 [CH, C6(7)], 127.8 [CH, C5(8)], 128.0 (CH, Ar-Cpara phenyl), 128.6 (CH, Ar-Cmeta phenyl),
129.6 (CH, Ar-Cortho phenyl), 132.4 [C, C4a(8a)], 146.4 (C, Ar-Cipso phenyl), 146.7 [C, C1(4)]. Anal.
Calcd for C22H14I2: C 49.65, H 2.65, I 47.69. Found: C 49.81; H 2.71; I 47.55.
4. Conclusions
Triflate 1 reacts with DPIBF at room temperature to give the corresponding Diels-Alder adduct 3 in
high yield. Adduct 3 is thermally unstable, decomposing in solution at about 55 °C. Reaction of triflate
1 with an excess (2 equiv.) of DPIBF in acetonitrile solution at 55 °C gave a mixture of dione 4 and
triflate 5. A similar oxygen transfer among triflate 3 and dimethylsulfide was not observed. To the best
of our knowledge, no similar oxygen transfer has been ever described. Also, the easy access to diiodide
7 as compared with the described procedure [7] might be of interest in connection with the preparation
of rubrenes [6,11].
Supplementary Material
IR and NMR spectra of triflates 3 and 5 and diiodides 6 and 7. Detailed information can be accessed
at: http://www.mdpi.com/1420-3049/17/8/8795/s1.
Acknowledgments
Financial support from Ministerio de Ciencia e Innovación (MICINN) CTQ2011-22433 and a
fellowship to T. G. (MICINN) are gratefully acknowledged.
References and Notes
1. Stang, P.J.; Zhdankin, V.V. Preparation and Chemistry of PhI+C=CI+Ph·2−OTf, Bis[phenyl[[
(trifluoromethyl)sulfonyl]oxy]iodo]acetylene, a Novel Difunctional Acetylene, Bis(iodonium)
Species and a Stable C2-Transfer Agent. J. Am. Chem. Soc. 1991, 113, 4571–4576.
2. Williamson, B.L.; Stang, P.J.; Arif, A.M. Preparation, Molecular Structure, and Diels-Alder
Cycloaddition Chemistry of -Functionalized Alkynyl(pheny1)iodonium Salts. J. Am. Chem. Soc.
1993, 115, 2590–2597.

Molecules 2012, 17
8803
3. Stang, P.J.; Schwarz, A.; Blume, T.; Zhdankin, V.V. Reactions of bicycloalkenyldiiodonium salts
with nucleophiles. Tetrahedron Lett. 1992, 33, 6759–6762.
4. Ryan, J.A.; Stang, P.J. Synthesis of Bicyclic Enediynes from Bis[phenyl[(trifluoromethanesulfonyl)-
oxy]iodo]acetylene: A Tandem Diels−Alder/Palladium(II)- and Copper(I)-Cocatalyzed Cross-
Coupling Approach. J. Org. Chem. 1996, 61, 6162–6165.
5. Camps, P.; Gómez, T. Synthesis and reactions of a new 1,1-disubstituted cyclopentadiene.
ARKIVOC 2011, iii, 128–139.
6. Yang, F.; Jin, T.; Bao, M.; Yamamoto, Y. Facile synthesis of dihaloheterocycles via electrophilic
iodocyclization. Tetrahedron 2011, 67, 10147–10155.
7. Johansson, E.; Skramstad, J. Air oxidation of an Isoindene: Formation of Isobenzofuran and
Acetone. J. Org. Chem. 1981, 46, 3752–3754.
8. Sheldrick, G.M. A program for automatic solution of crystal structure refinement, University of
Göttingen, Göttingen, Germany. Acta Crystallogr. 2008, A64, 112–122.
9. International Union of Crystallography. International Tables of X-ray Crystallography;
Kynoch Press: Birmingham, UK, 1974; Volume 2, pp. 99–100,149.
10. CCDC 873344 (triflate 5) and CCDC 87335 (diiodide 6) contains the supplementary
crystallographic data for this paper. These data can be obtained free of charge from the CCDC, 12
Union Road, Cambridge CB2 1EZ, UK; fax: +44-1223-336033; E-Mail: deposit@ccdc.cam.ac.uk.
11. Dodge, J.A.; Bain, J.D.; Chamberlin, A.R. Regioselective Synthesis of Substituted Rubrenes.
J. Org. Chem. 1990, 55, 4190–4198.
Sample Availability: Not available.
© 2012 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article
distributed under the terms and conditions of the Creative Commons Attribution license
(http://creativecommons.org/licenses/by/3.0/).