LETTER
Benzylic and Allylic Oxidations
1321
PhI(OOt-Bu)2
1
–
PhI
OOt-Bu
OOt-Bu
O
•
•
•
t-BuOO
t-BuOO
•
2
t-BuOO + PhCH Me
PhCHMe
2
•
•
Ph
Me
Ph
Me
Ph
Me
– t-BuO
6d
8
9
10
7
d
Scheme 2 Proposed mechanism for the generation of tert-butyloxidanyl and oxidation of ethylbenzene (6d) to acetophenone (7d)
A plausible mechanism for the generation of tert-butylox-
idanyl and oxidation of ethylbenzene (6d) to acetophe-
none (7d) is depicted in Scheme 2. Initially, nucleophilic
attack of TBHP on PIFA leads to the formation of the re-
active intermediate peroxyiodane 1 by exchanging two
trifluoromethyl acetate groups for two tert-butylperoxy
(3) (a) Plesnicar, B.; Russell, G. A. Angew. Chem., Int. Ed. Engl.
970, 9, 797. (b) Plesnicar, B. J. Org. Chem. 1975, 40, 3267.
1
(
4) (a) Ochiai, M.; Ito, T.; Masaki, Y.; Shiro, M. J. Am. Chem.
Soc. 1992, 114, 6269. (b) Ochiai, M.; Ito, T.; Takahashi, H.;
Nakanishi, A.; Toyonari, M.; Sueda, T.; Goto, S.; Shiro, M.
J. Am. Chem. Soc. 1996, 118, 7716.
(
5) (a) Traylor, T. G.; Xu, F. J. Am. Chem. Soc. 1987, 109,
6201. (b) Traylor, T. G.; Fann, W.-P.; Bandyopadhyay, D.
J. Am. Chem. Soc. 1989, 110, 8009. (c) Ochiai, M.;
Nakanishi, A.; Ito, T. J. Org. Chem. 1997, 62, 4253.
1
6
groups. Homolytic cleavage of the hypervalent io-
dine(III)–peroxy bond in 1 gives tert-butyloxidanyl and
iodobenzene. Then hydrogen abstraction from the benzyl-
ic position of ethylbenzene by the tert-butyloxidanyl
forms the carbon-centered benzylic radical 8 and tert-
butyl alcohol. Coupling of this radical with tert-
(
4
d) Ochiai, M.; Kajishima, D.; Sueda, T. Heterocycles 1997,
6, 71. (e) Ochiai, M.; Kajishima, D.; Sueda, T. Tetrahedron
Lett. 1999, 40, 5541. (f)Ochiai, M.; Nakanishi, A.; Yamada,
A. Tetrahedron Lett. 1997, 38, 3927. (g) Hypervalent
Iodine Chemistry: Reactivites, Properties, Structures,
Topics in Current Chemistry Series 224; Ochiai, M., Ed.;
Springer: Berlin / Heidelberg, 2003. (h) Sueda, T.;
Takeuchi, Y.; Suefuji, T.; Ochiai, M. Molecules 2005, 10,
1
7
butyloxidanyl may generate 9, which undergoes decom-
position via a radical pathway, resulting in the formation
of acetophenone (7d).
In summary, the present study provides the first example
of direct oxyfunctionalization of benzylic and allylic sub-
strates to the corresponding a,b-unsaturated carbonyl
compounds using a PIFA/TBHP system. The combination
of PIFA and TBHP is a source for the production of the
tert-butyloxidanyl, which is an electrophilic oxidant for
the conversion of allylic and benzylic substrates into the
corresponding enones.
1
95. (i) Catino, A. J.; Nichols, J. M.; Forslund, R. E.; Doyle,
M. P. Org. Lett. 2005, 7, 263. (j) Catino, A. J.; Nichols, J.
M.; Forslund, R. E.; Doyle, M. P. Org. Lett. 2005, 7, 2787.
(k) Nicolaou, K. C.; Baran, P. S.; Zhong, Y.-L. J. Am. Chem.
Soc. 2001, 123, 3183. (l) Dohi, T.; Takenaga, N.; Goto, A.;
Fujioka, H.; Kita, Y. J. Org. Chem. 2008, 73, 7365.
6) (a) Catir, M.; Kilic, H. Synlett 2003, 1180. (b) Catir, M.;
Kilic, H. Synlett 2004, 2151.
(
(
7) (a) Bonvin, Y.; Callens, E.; Larrosa, I.; Henderson, D. A.;
Oldham, J.; Burton, A. J.; Barrett, A. G. M. Org. Lett. 2005,
7
, 4549. (b) Shaabani, A.; Soleimani, K.; Bazgir, A. Synth.
Acknowledgment
Commun. 2004, 34, 3303.
(
8) General Procedure for Oxidation of Benzylic and Allylic
Substrates with PIFA/TBHP System
Financial support from Ataturk University is gratefully acknowl-
edged. In addition, M.C. would like to thank the Scientific and
Technological Research Council of Turkey (TUBITAK) for a scho-
larship.
(
Caution! Although we have never experienced an
explosion, the oxidation of substrates with PIFA/TBHP
system should be carried out behind shields.) To a solution
of substrate (2 mmol) and anhyd TBHP (40 mmol) in CH Cl
2
2
References and Notes
(10 mL) at –30 °C was added NaHCO (20 mmol). Then a
3
freshly prepared solution of PIFA (5.0 mmol) in CH Cl (10
2
2
(
1) (a) Hypervalent Iodine Chemistry: Modern Developments in
Organic Synthesis; Wirth, T., Ed.; Topics in Current
Chemistry Series 224, Springer: Berlin/Tokyo, 2003.
mL) was added over 2 h. The temperature was slowly
increased to r.t. over 4 h. On completion of reaction, the
18
excess TBHP was reduced by adding DMS (40 mmol) and
(
b) Varvoglis, A. The Organic Chemistry of
Polycoordinated Iodine; VCH Publishers: New York, 1992.
c) Varvoglis, A. Hypervalent Iodine in Organic Synthesis;
Ti(Oi-Pr) (0.15 mmol) at r.t. while the reaction proceeding
4
was monitored by peroxide testing (KI, AcOH). The
suspension was filtered, and the solution was washed with
sat. NaHCO solution and H O. The organic layer was dried
(
Academic Press: London, 1997. (d) Moriarty, R. M.;
Prakash, O. Hypervalent Iodine in Organic Chemistry:
Chemical Transformations; Wiley-Interscience: Chichester,
3
2
over MgSO , and the solvent was removed at reduced
4
pressure (20 °C/50 mbar). The products were purified on a
silica gel column (40 g) by eluting with hexane–EtOAc
2008. (e) Stang, P. J.; Zhdankin, V. V. Chem. Rev. 1996, 96,
1123. (f) Zhdankin, V. V.; Stang, P. J. Chem. Rev. 2002,
102, 2523. (g) Wirth, T.; Hirt, U. H. Synthesis 1999, 1271.
(
95:5). The first fractions gave iodobenzene. Further elution
afforded analytically pure ketone. The ketones 7a–l are
known, and analytical data were found to be identical with
those reported.
(
h) Stang, P. J. J. Org. Chem. 2003, 68, 2997. (i) Moriarty,
R. M. J. Org. Chem. 2005, 70, 2893. (j) Wirth, T. Angew.
Chem. Int. Ed. 2005, 44, 3656. (k) Varvoglis, A.
Tetrahedron 1997, 53, 1179. (l) Zhdankin, V. V.; Stang,
P. J. Chem. Rev. 2008, 108, 5299.
9
H-Fluoren-9-one (7b)
1
Yellow solid, mp 81–82 °C (CH Cl –hexane). H NMR (200
2
2
MHz, CDCl ): d = 7.63 (dd, J = 7.3, 1.0 Hz, 2 H), 7.30–7.20
3
(
2) Milas, N. A.; Plesnicar, B. J. Am. Chem. Soc. 1968, 90, 4450.
13
(
m, 2 H), 7.48–7.45 (m, 4 H). C NMR (50 MHz, CDCl ):
3
Synlett 2010, No. 9, 1319–1322 © Thieme Stuttgart · New York