These compare with bond lengths of 2.29 s, 2.47 s and 2.66 s for
13
2 2
molecular Br , Br–I and I bonds, respectively.
In conclusion, we have demonstrated that bromoiodinanes
with an I(III)–Br bond act as sources of electrophilic bromine.
They are prepared in a novel one step procedure from
iodobenzenecarbinols with NBS, allowing the characterisation of
I(III)–Br bond lengths by X-ray crystallography. These results also
support the proposition that the actual brominating agent in the
Fig. 1 The molecular structures of 3b (left) and 4 (right).
5
DIB–LiBr system is hypervalent iodine compound 2, containing
an I(III)–Br bond.
of anisole (9) to give bromoanisole 10, for the bromolactonisation
of 4-pentenoic acid (11) into bromolactone 12, and the
intermolecular bromoetherification with (deuterated) methanol of
trans-stilbene (13) into (¡)-1,2-bromoether 14. Bromoiodinane 3b
We thank the EPSRC and GlaxoSmithKline Ltd. for an
Industrial CASE award to G. C.
Notes and references
3
1-Bromo-3,3-bis-trifluoromethyl-1,3-dihydro-1l -benzo[d][1,2]iodoxole
3
gave a 7% conversion of 11 into 12 (CDCl , 24 h, r.t.). In contrast,
{
the more reactive bromoiodinane 4 gave quantitative conversion of
5
, 15 h, r.t.), 11 into 12 (CDCl
(
3b; R = H): To a solution of crude 1,1,1,3,3,3-hexafluoro-2-(2-
iodophenyl)-propan-2-ol (5; R = H, 1.5 g, 4.1 mmol) stirring in CHCl
(16 mL) at room temperature was added portion-wise NBS (721 mg,
.1 mmol). The reaction mixture was stirred for 18 h, diluted with further
CHCl (24 mL), washed with water (2 6 40 mL) and brine (50 mL), dried
over MgSO and concentrated to give a sticky orange solid.
Recrystallisation (EtOAc/hexane) yielded 3b (1.00 g, 56%) as shiny yellow
plates: m.p. 190–191 uC; R 0.77 (CH Cl ); FT-IR (NaCl/CDCl ) nmax 1587,
559, 1457, 1437, 1265, 1193 and 1103 cm ; H NMR (270 MHz, CDCl
5
into 10 (CDCl
9
3
3
, 15 h, r.t.) and 13
3
11
into 14 (CDCl , 18 h, r.t.). In all cases, carbinol 6 was the sole
3
4
side-product. It is of interest to note that, in direct contrast to the
use of iodinane 4, attempted bromolactonisation of 11 with
molecular bromine gives significant competitive 1,2-dibromination
3
4
5
of the olefin. This suggests that molecular bromine is not
f
2
2
3
21 1
1
3
)
generated in this system. Bromolactonisation of 11 is therefore
suggested to proceed via a bromonium ion by direct electrophilic
bromine transfer from the iodinane. A bromonium ion is also
implicated as the intermediate in the transformation of 13 into
bromoether 14. The observed para-substitution of 9 is also
consistent with the expected directing group effect of an
electrophilic substitution reaction.
d 8.03 (dd, J = 8.3, 1.1 Hz, 1 H, Ar-H), 7.80 (dt, J = 7.1, 1.5 Hz, 1 H, Ar-
H), 7.74 (dt, J = 6.9, 0.8 Hz, 1 H, Ar-H) and 7.66 (br-d, J = 7.1 Hz, 1 H,
13
3
Ar-H); C NMR (68 MHz, CDCl ) d 133.8, 132.5, 131.9, 130.0, 129.7
(septet, J = 3 Hz), 122.8 (q, J = 289 Hz), 109.9 and 84.2 (septet, J = 33 Hz);
MS (EI ) 450, 448 (M ), 381, 379 (M 2 CF ) and 269 (M 2 Br ); HRMS
+
+
+
+
3
79
4
81
4
calc. for C
447.8396 and 449.8380, respectively; anal. calc. for C
H 0.90; found: C 23.91, H 0.86. Crystal data: C BrF
orthorhombic, Pbca (no. 61), a = 9.663(3), b = 14.7448(17), c = 16.435(3) s,
V = 2341.6(8) s , Z = 8, D
203 K, yellow tablets; 2056 independent measured reflections, R 0.00%,
int
9
H
BrF
6
IO 447.8394 and C
9
H
BrF
6
IO 449.8374, found
BrF IO: C 24.08,
IO, M = 448.93,
9
H
4
6
9
H
4
6
12
The X-ray analyses (Fig. 1, Table 1) of crystals of 3b and 4
show that both iodine centres adopt a planar T-geometry (i.e. a
trigonal bipyramid shape overall), as expected. The five-membered
3
23
21
c a
= 2.547 g cm , m(Mo-K ) = 6.210 mm , T =
2
F refinement, R
absorption-corrected reflections [|F
1
= 0.045, wR
2
= 0.100, 1493 independent observed
| > 4s(|F |), 2hmax = 50u], 164
o
o
3
C OI rings have an envelope conformation, with the oxygen atom
parameters. CCDC 259288. For crystallographic data in CIF or other
electronic format see DOI: 10.1039/b600455e
3
§ 1-Bromo-3,3-dimethyl-1,3-dihydro-1l -benzo[d][1,2]iodoxole (4): To a
solution of crude 2-(2-iodo-phenyl)propan-2-ol (6; 3.00 g, 11.5 mmol)
stirring in CHCl (30 mL) at room temperature was added portion-wise
3
NBS (2.45 g, 13.7 mmol). The reaction mixture was stirred for 18 h, diluted
lying ca. 0.23 s (for 3b) and ca. 0.44 s (for 4) out of the C I plane.
3
This distortion in the position of the oxygen atoms manifests itself
as a twisting about the I–C(1) bond so that the bromine is moved
to the other side of the plane (see Fig. S2 and Fig. S5 in the ESI{);
the torsion angle about the I–C(1) bond is ca. 7u for 3b and ca. 9u
for 4. In both cases, the closest intermolecular approach to the
iodine centre is from the oxygen of a centrosymmetrically related
counterpart at ca. 3.03 s (3b) and ca. 2.94 s (4), forming discrete
dimer pairs (see Fig. S3 and Fig. S6 in the ESI{). Most notably,
whilst the I–C(1) bond length is essentially constant (2.120(8) s in
with further CHCl (30 mL), washed with water (2 6 50 mL) and brine
3
(50 mL), dried over MgSO
Recrystallisation (EtOAc/hexane) yielded 4 (2.34 g, 60%) as shiny yellow
4
and concentrated to give a yellow solid.
8
crystals: m.p. 126–128 uC [lit., 98–100 uC]; FT-IR (NaCl/CDCl
3
) nmax
3076, 3053, 3005, 2980, 2924, 2860, 1589, 1560, 1460, 1435, 1377, 1362,
1215, 1153, 1109, 995, 939 and 860 cm ; H NMR (270 MHz, CDCl
21 1
3
) d
7
.97 (m, 1 H, Ar-H), 7.55–7.49 (m, 2 H, Ar-H), 7.13 (m, 1 H, Ar-H) and
13
1.54 (s, 6 H, CH
3 3
); C NMR (68 MHz, CDCl ) d 149.9, 131.2, 130.5,
3b and 2.112(7) s in 4), the I–O and I–Br bond lengths vary
+
+
129.4, 126.0, 112.1, 84.3 and 29.3; MS (EI ) 342, 340 (M ), 327, 325 (M 2
CH ) and 262 (M 2 Br ); HRMS calc. for C H BrIO 339.8960 and
+
+
79
considerably in 3b and 4, presumably due to the effect of the
electron withdrawing gem-trifluoromethyl groups on the three
centre-four electron O–I(III)–Br bond. The I–O bond length is ca.
3
9
1
0
81
C
9
H
10 BrIO 341.8939, found 339.8959 and 341.8938, respectively; anal.
calc. for C 10BrIO: C 31.70, H 2.96; found: C 31.86, H 2.99. Crystal data:
10BrIO, M = 340.98, triclinic, P1 (no. 2), a = 8.115(2), b = 8.2108(17), c
9.1784(19) s, a = 106.812(12), b = 91.202(18), c = 114.00(2)u, V =
9
H
¯
9
C H
=
2.12 s in 3b and ca. 2.05 s in 4. The I(III)–Br bond lengths are ca.
3
23
21
2.59 s and ca. 2.69 s, respectively. To the best of our knowledge,
528.1(2) s , Z = 2, D
c a
= 2.144 g cm , m(Mo-K ) = 6.769 mm , T =
203 K, yellow blocks; 1581 independent measured reflections, Rint 2.04%,
these bond lengths are the first to be obtained for I(III)–Br bonds.
2
F
absorption-corrected reflections [|F
refinement, R
1
= 0.044, wR
2
= 0.112, 1496 independent observed
| > 4s(|F |), 2hmax = 50u], 109
o
o
parameters. CCDC 259289. For crystallographic data in CIF or other
electronic format see DOI: 10.1039/b600455e
Table 1 Comparative selected bond lengths (s) and angles (u) for 3b
and 4
3
b
4
3b
4
1
A. Varvoglis, Hypervalent Iodine in Organic Synthesis, Academic Press,
London, 1997; Hypervalent Iodine Chemistry: Modern Developments in
Organic Synthesis, ed. T. Wirth, Springer-Verlag, Berlin, 2002.
T. Wirth, Angew. Chem., Int. Ed., 2005, 44, 3656–3665.
D. B. Dess and J. C. Martin, J. Org. Chem., 1983, 48, 4155–4156.
T. Wirth, Angew. Chem., Int. Ed., 2001, 40, 2812–2814.
I–Br
I–C(1)
2.5945(11) 2.6927(8) I–O
2.120(8) 2.112(7)
2.118(6) 2.050(5)
2
3
4
Br–I–O 172.80(17) 172.46(16)
O–I–C(1) 79.0(3) 80.3(2)
Br–I–C(1) 94.1(2) 93.25(18)
I–O–C(7) 116.1(5) 114.5(4)
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Chem. Commun., 2006, 1442–1444 | 1443