A unique site-selective reaction of ketones with new recyclable hypervalent iodine(III) reagents based on a tetraphenylmethane structure

Article abstract of DOI:10.1039/b501475a

We have synthesized new recyclable reagents having a tetraphenylmethane backbone and used them in the site-selective α-tosyloxylation of ketones. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b501475a

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A unique site-selective reaction of ketones with new recyclable
hypervalent iodine(III) reagents based on a tetraphenylmethane
structure{
Toshifumi Dohi,a Akinobu Maruyama,a Misaki Yoshimura,a Koji Morimoto,a Hirofumi Tohma,a
Motoo Shirob and Yasuyuki Kita*a
Received (in Cambridge, UK) 31st January 2005, Accepted 25th February 2005
First published as an Advance Article on the web 16th March 2005
DOI: 10.1039/b501475a
sodium perborate (NaBO3) in acetic acid, or sodium periodate
(NaIO4) and so on, unexpectedly gave disappointing results.
Further investigations finally led us to succeed in synthesizing 1a in
94% yield using m-chloroperbenzoic acid (mCPBA) in CH2Cl2–
acetic acid (AcOH) (1 : 1). Several iodine(III) derivatives such as 1b
and 1c could be also synthesized from 1a by typical synthetic
procedures as reported for phenyliodine bis(trifluoroacetate)
(PIFA),8 hydroxy(tosyloxy)iodobenzene (HTIB)9a in satisfactory
yields. These compounds 1a–c are quite stable and can be stored at
room temparature for long periods without any decomposition.
The iodine(III) reagent 1a was easily purified by recrystallization
from acetic acid and separated from the partially oxidized
byproducts. A single-crystal X-ray analysis of the reagent 1a is
shown in Fig. 1.§ It reveals that it has four symmetrical equivalent
iodine(III) sites and a pentagonal–planar arrangement of three
strong and two weak secondary bonds around each iodine(III)
center, which are similar to those in previously reported
adamantane reagents.
We have synthesized new recyclable reagents having
a
tetraphenylmethane backbone and used them in the site-
selective a-tosyloxylation of ketones.
Over the past two decades, hypervalent iodine(III) reagents have
received much attention due to their low toxicity, ready
availability, easy handling, and reactivities similar to those of
heavy metal reagents1 and in particular, recyclable reagents such as
polymer-supported2–4 and perfluoroalkyl-substituted5 reagents
have been recognized as a useful tool to meet the recent demand
for environmentally benign, ecologically conscious chemical
processes. From these circumstances, we have currently developed
novel, highly recyclable hypervalent iodine(III) reagents having an
adamantane core, in which their high reactivities are obviously
derived from their well-defined tetrahedral structures so as not to
interfere with each iodine(III) site.6 This hypothesis prompted us to
seek other new hypervalent iodine(III) alternatives. In this
communication, we report the concise synthesis of new recyclable
iodine(III) reagents 1a–c having a more small tetraphenylmethane
backbone and utilize them to a unique site-selective a-tosyloxyla-
tion of ketones.
The reactivities of these new reagents 1a–c have been examined
in several oxidative transformations. As expected, the oxidation of
alcohol [eqn. (1)]4a,d,e and phenol [eqn. (2)],4c an oxidative
biarylcoupling reaction4b [eqn. (3)], and the a-tosyloxylation of a
ketone [eqn. (4)]9 smoothly proceeded with excellent yields.
We have synthesized new reagents 1a–c according to Scheme 1.{
Thus, tetrakis-(4-iodophenyl)methane 2 is readily accessible from
tetraphenylmethane in a single step.7 Attempts to oxidize 2 to
tetrakis[4-(diacetoxyiodo)phenyl]methane 1a under standard oxi-
dation conditions, peracetic acid (30% H2O2 and acetic anhydride),
(1)
(2)
(3)
(4)
Scheme 1 Preparation of tetrakis[4-(diacetoxyiodo)phenyl]methane (1a)
and transformation of 1a to 1b and 1c.
In all cases, tetraiodide 2, formed after the reactions were
completed, hardly soluble in MeOH, could be recovered as a pure
form after a simple work-up. Since tetraphenylmethane-based
molecule 2 is about four times less soluble than an analgous
{ Electronic supplementary information (ESI) available: details of
experimental procedures and analytical data for new compounds. See
http://www.rsc.org/suppdata/cc/b5/b501475a/
*kita@phs.osaka-u.ac.jp
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˚
Fig. 1 ORTEP drawing of 1a. Selected bond lengths [A] and angles [u]: I1–C5 2.092(5), I1–O1 2.130(4), I1–O2 2.817(4), I1–O3 2.171(4), I1–O4 2.886(4),
O1–I1–C5 81.3(2), O3–I1–C5 80.1(2), O1–I1–O3 161.3(1).
adamantane-based molecule in MeOH,10 2 was usually obtained
with nearly quantitative yield. These results showed that the new
reagents 1a–c are versatile reagents with respect to reactivity as well
as recyclability, compared to other iodine(III) reagents.
a-sulfonyloxylation of 2-butanone 11a using PIDA and (+)-10-
camphorsulfonic acid,9b three times more 12a9 than 13a9
was obtained, (entry 5). Similar to the case for 2-butanone, these
site-selective a-tosyloxylations were observed in other various
ketones (entries 6–8)."11
In addition, it is interesting that the reagent 1a showed a
characteristic behavior in selectivity for the a-tosyloxylation of
2-butanone 11a (Table 1). Such a regioselectivity is not a general
phenomenon.9 Thus, 2-butanone 11a gave the 3-tosyloxylated
product 12a as a major product with a 5.1 : 1 selectivity (entry 1).
1c gave a similar result (entry 2). Phenyliodine diacetate (PIDA)
and the polymer-supported reagent poly(diacetoxyiodo)styrene
(PDAIS)2–4 gave 12a less selectively than did 1a (entries 3 and 4).
Although it has been reported that the reaction occurred
preferentially at the less hindered position in the case of
The following experimental result clearly suggests the structural
importance of 1a to ensure these unique site-selective reactions
(Scheme 2). Thus, a compound 14, which has only one active
iodine(III) site, did not show any change in site-selectivity in
the reaction of 2-butanone 12a compared to PIDA and polymer-
supported reagent. From this, some kind of beneficial
synergistic effects due to the existence of the four active
iodine(III) sites in 1a must be involved in these unique selective
reactions.12
Table 1 Comparision of 1a with other iodine(III) reagents in a-tosyloxylation of ketones
Entry
I(III)
R1
Product
Yielda (selectivity of 12/13)b
1
2
3
4
5d
6
7
8
a
1a
1cc
PIDA
PDAIS
1a
Me (11a)
12a + 13a (R2 5 4-tolyl)
85% (5.1)
68% (5.4)
77% (1.5)
36% (1.7)
66% (3.0)
58% (5.2)
56% (9.0)
61% (.20)
12a9 + 13a9 (R2 5 (+)-10-camphoryl)
Pr (11b)
iBu (11c)
Ph (11d)
12b + 13b (R2 5 4-tolyl)
12c + 13c
12d + 13d
c
b
d
Isolated yields. Determined by 1H-NMR after purification. p-TsOH?H2O was not added. (+)-10-Camphorsulfonic acid and H2O were
added instead of p-TsOH?H2O.
2206 | Chem. Commun., 2005, 2205–2207
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3
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c 5 21.064(6), a 5 84.26(1), b 5 79.63(1), c 5 72.58(1), V 5 3116(1) A ,
Z 5 2, T 5 296(1) K, m 5 21.51 cm21, 25936 reflections measured, 11753
unique reflections, R 5 0.036, Rw 5 0.117. CCDC 257522. See http://
www.rsc.org/suppdata/cc/b5/b501475a/ for crystallographic data in CIF or
other electronic format.
" Typical procedure for site-selective a-tosyloxylation reaction of ketones: A
mixture of 2-butanone (14.4 mg, 0.2 mmol), 1a (64.8 mg, 0.050 mmol),
p-toluenesulfonic acid monohydrate (38.1 mg, 0.2 mmol), CH3CN (2 mL)
was heated at 70 uC in a sealed tube. After 24 h, the mixture was cooled to
ambient temperature. Then, MeOH (2 mL) was added to the reaction
mixture and the precipitate was filtered. Recovery of 2 was quantitative.
After evaporation, the crude products were purified by column
chromatography (SiO2/hexane-AcOEt 5 10/1) to give pure 12a and 13a
as a mixture of two isomers (12a : 13a 5 5.1 : 1).
Scheme 2 a-Tosyloxylation using 14.
1 Recent reviews see: (a) Y. Kita, T. Takada and H. Tohma, Pure Appl.
Chem., 1996, 68, 627; (b) A. Varvoglis, Hypervalent Iodine in Organic
Synthesis, Academic Press, San Diego, CA, 1997; (c) T. Kitamura and
Y. Fujiwara, Org. Prep. Proc. Int., 1997, 29, 409; (d) M. Ochiai, in
Chemistry in Hypervalent Compounds, ed. K. Akiba, Wiley-VCH, New
York, 1999, ch. 12; (e) T. Wirth and U. H. Hirt, Synthesis, 1999, 1271;
(f) V. V. Zhdankin and P. J. Stang, Chem. Rev., 2002, 102, 2523–2584;
(g) Hypervalent Iodine Chemistry ed. T. Wirth, Springer-Verlag, Berlin,
Heidelberg, 2003.
In conclusion, we have developed new recyclable hypervalent
iodine(III) reagents 1a–c, having a tetraphenylmethane structure.
These recyclable reagents are not only useful oxidation tool, but
also show a unique selectivity during the a-sulfonyloxylation
reaction of ketones. To our knowledge, this is the first example of
the selective a-functionalization at more hindered position of
ketones by hypervalent iodine(III) compounds.13 Further studies
on their reactivities, and applications in these fields are currently
underway in our laboratory.
2 (a) H. Togo, G. Nogami and M. Yokoyama, Synlett, 1998, 534; (b)
H. Togo and K. Sakuratani, Synthesis, 2003, 21; (c) K. Sakuratani and
H. Togo, ARKIVOC, 2003, VI, 11.
3 (a) S. V. Ley, A. W. Thomas and H. Finch, J. Chem. Soc., Perkin Trans.
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J. Chem. Soc., Perkin Trans. 1, 2002, 1850.
4 (a) H. Tohma, S. Takizawa, T. Maegawa and Y. Kita, Angew. Chem.,
Int. Ed., 2000, 39, 1306; (b) H. Tohma, H. Morioka, S. Takizawa,
M. Arisawa and Y. Kita, Tetrahedron, 2001, 57, 345; (c) H. Tohma,
H. Morioka, Y. Harayama, M. Hashizume and Y. Kita, Tetrahedron
Lett., 2001, 42, 6899; (d) H. Tohma, T. Maegawa, S. Takizawa and
Y. Kita, Adv. Synth. Catal., 2002, 344, 328; (e) H. Tohma, T. Maegawa
and Y. Kita, ARKIVOC, 2003, VI, 62; (f) H. Tohma, T. Maegawa and
Y. Kita, Synlett, 2003, 723.
5 C. Rocaboy and J. A. Gladysz, Chem. Eur. J., 2003, 9, 88.
6 H. Tohma, A. Maruyama, A. Maeda, T. Maegawa, T. Dohi, M. Shiro,
T. Morita and Y. Kita, Angew. Chem., Int. Ed., 2004, 43, 3595.
7 (a) M. Simard, D. Su and J. D. Wuest, J. Am. Chem. Soc., 1991, 113,
4696; (b) D. Su and F. M. Menger, Tetrahedron Lett., 1997, 38, 1485.
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This work was financially supported by the Industrial
Technology Research Grant Program from New Energy and
Industrial Technology Development Organization (NEDO) of
Japan and a Grant-in-Aid for Scientific Research (S).
Toshifumi Dohi,a Akinobu Maruyama,a Misaki Yoshimura,a
Koji Morimoto,a Hirofumi Tohma,a Motoo Shirob and Yasuyuki Kita*a
aGraduate School of Pharmaceutical Sciences, Osaka University, 1-6
Yamada-oka, Suita, Osaka, Japan. E-mail: kita@phs.osaka-u.ac.jp;
Fax: +81-6-6879-8229; Tel: +81-6-6879-8225
bRigaku Corporation, 3-9-12 Matsubara, Akishima, Tokyo, 196-8666,
Japan
Notes and references
{ Synthesis of 1a: To a stirred solution of tetrakis-(4-iodophenyl)methane 2
(620 mg, 0.75 mmol) was dissolved in CH2Cl2 (75 mL)–AcOH (75 mL),
then mCPBA (1.55 g, 9.0 mmol) was added to the mixture at room
temperature. The reaction mixture was stirred for 2 days under the same
reaction conditions. The resultant slightly clouded solution was filtered to
give clear solution. CH2Cl2 was removed under reduced pressure and
hexanes was added to the residue and stirred for 1 h to precipitate
tetrakis[4-(diacetoxyiodo)phenyl]methane 1a. After filtration, the crude 1a
was washed with hexanes and Et2O several times, and dried in vacuo to give
1a (910.8 mg, 94%) as a colorless crystal; mp (decomp.) 218–220 uC (from
AcOH–CH2Cl2–hexanes by vapor diffusion method). 1H NMR (CDCl3,
9 (a) G. F. Koser, A. G. Relenyi, A. N. Kalos, L. Rebrovic and
R. H. Wettach, J. Org. Chem., 1982, 47, 2487; (b) E. Hatzignigoriou,
A. Varvoglis and M. Bakola-Christianopoulou, J. Org. Chem., 1990, 55,
315.
10 The solubility of 2 in several solvents at 25 uC is as follows: 12 mg L21
(MeOH); 20 mg L21 (CH3CN); 28 mg L21 (n-hexane).
11 In each cases, an adamantane based reagent gave the products less
selectively than that of 1a: 12/13 4.3 (for 11a); 3.1 (for 11b); 1.9 (for 11c);
5.3 (for 11d).
12 Yamamoto and co-workers have reported highly regioselective alkyla-
tion at the more-hindered a-site of unsymmetrical ketones using a
sterically encumbered Lewis acid: S. Saito, M. Ito and H. Yamamoto,
J. Am. Chem. Soc., 1997, 119, 611.
13 Regiospecific a-sulfonyloxylations by copper(II) oxide have been
reported: (a) J. C. Lee and Y. Choi, Tetrahedron Lett., 1998, 39, 3171;
(b) J. C. Lee, S. H. Oh and I.-G. Song, Tetrahedron Lett., 1999, 40, 8877.
3
25 uC): d 5 8.02 (d, 3J(H,H) 5 9.6 Hz, 8H; ArH), 7.30 (d, J (H,H) 5
9.6 Hz, 8H; ArH), 2.02 (s, 24H, OCOCH3). 13C NMR (CDCl3, 25 uC):
d 5 176.6, 147.6, 134.8, 133.0, 119.8, 65.69, 20.5. IR (KBr): 1686w,
1637.5w, 1647w, 1560m, 1541w, 1521w, 1508w, 1475w, 1458w, 1396w,
1364w, 1288w, 1003w, 912m, 808w, 743m, 669m cm21. Anal. Calcd for
C41H40I4O16?2H2O: C, 36.96; H, 3.33. Found: C, 36.80; H, 3.19%.
§ Crystal data for 1a: C41H40I4O16?5.19CH3CO2H?0.81CH2Cl2,
¯
M 51676.84, triclinic, space group P1, a 5 12.520(4), b 5 12.608(3),
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Chem. Commun., 2005, 2205–2207 | 2207