2-Iodoxybenzoic acid mediated facile conversion of 1,3-diols to 1,2-diketones by oxidative cleavage of the C-C bond

Article abstract of DOI:10.1055/s-2006-950372

1,3-Diols undergo smooth oxidative cleavage of the C-C bond in the presence of 2-iodoxybenzoic acid (IBX) affording 1,2-diketones in excellent yields under mild conditions. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2006-950372

PAPER
4237
2-Iodoxybenzoic Acid Mediated Facile Conversion of 1,3-Diols to
1,2-Diketones by Oxidative Cleavage of the C–C Bond1
2
-Iodoxyb
.
enzoic
Acid
S
Mediated
C
on
.
version of 1,
Y
3-Diols to 1,2-Dik
a
etones dav,* Swapan Kumar Biswas, R. Srinivas
Division of Organic Chemistry, Indian Institute of Chemical Technology, Hyderabad 500007, India
Fax 91(40)27160512; E-mail: yadavpub@iict.res.in
Received 29 June 2006; revised 3 August 2006
O
OH
Abstract: 1,3-Diols undergo smooth oxidative cleavage of the C–C
bond in the presence of 2-iodoxybenzoic acid (IBX) affording 1,2-
diketones in excellent yields under mild conditions.
R2
R1
OH
R1
3.5 equiv IBX
R2
O
DMSO, THF, r.t.
Keywords: 1,3-diol, 1,2-diketone, 2-iodoxybenzoic acid, oxida-
1
2
tion, bond cleavage
R1 = alkyl, aryl
R2 = methyl, alkyl
Scheme 1
1,2-Diketones have received a great attention because of
their wide application in organic synthesis.2–8 1,2-Dike-
tones have also been found in many bioactive compounds,
such as cytotoxic and antiviral hemigeran B and C.9 Sev-
eral approaches have been reported for the preparation of
1,2-diketones which include rearrangement of a,b-epoxy
ketones,10 oxidation of a-hydroxy ketones,11 1,2-diols,12
vicinal dihaloalkenes,13 alkenes or alkynes,14 and ep-
oxides.15 Many of these methods involve expensive re-
agents, hazardous reaction conditions, and high
temperatures which limits their use in large-scale synthe-
sis. Hence, there is a need to develop a mild and efficient
protocol for the preparation of 1,2-diketones.
acid in dimethyl sulfoxide at ambient temperature
(Scheme 1).
In efforts toward the synthesis of biologically active mol-
ecule (+)-membrenone-C,18 we attempted the selective
oxidation of the primary alcohol in a 1,3-diol system in
1b. We found that with an excess of 2-iodoxybenzoic ac-
id, the 1,3-diol system underwent oxidative cleavage to
afford a 1,2-diketone 2b (Scheme 2).
Encouraged by the result obtained by the oxidation of 1b
to 2b, several other 1,3-diol systems with aliphatic and ar-
omatic substituents were oxidized with 3.5 equivalents of
2-iodoxybenzoic acid to yield the respective 1,2-dike-
tones in good yields with a reasonably short reaction time.
Noticeably, the yield of 1,2-diketone was consistent be-
tween a variety of substrates: simple aliphatic 1,3-diols,
sterically hindered 1,3-diols containing variously protect-
ed hydroxy groups (Table 1, entries 1–4), and 1,3-diols
substituted with aryl groups containing electron-with-
drawing or electron-donating substituents (Table 1, en-
tries 5–10). Interestingly cyclic 1,3-diol 1k (Table 1, entry
11) afforded unsaturated diketone 2k in 70% yield.19
2-Alkyl-substituted 1,3-diols with the alkyl as a group
other than methyl under the same reaction conditions gave
the 1,2-diketone in low yield, for example, 2-pentylbu-
tane-1,3-diol gave octane-2,3-dione (2a) in <30% yield.
Hypervalent iodine reagents have attracted increasing in-
terest as oxidants in organic synthesis due to their mild,
selective, and environmentally benign nature.16 Among
various hypervalent iodine reagents, 2-iodoxybenzoic
acid (IBX) is a versatile oxidizing agent because of its
high efficiency, easy availability, mild reaction condi-
tions, and its stability to moisture and air. In recent years,
2-iodoxybenzoic acid has been used as a versatile reagent
in mediating a wide array of transformations with far-
reaching synthetic application.17 However, there are no
reports on the use of 2-iodoxybenzoic acid for the conver-
sion of 1,3-diol into 1,2-ketones.
Herein we report, for the first time, the direct conversion
of 1,3-diols 1 to 1,2-diketones 2 by oxidative cleavage of
the C–C bond using 3.5 equivalents of 2-iodoxybenzoic
O
TBDPSO
TBDPSO
IBX (3.5 equiv)
DMSO, THF, r.t.
78%
OH
OBn
O
OBn OH
1b
2b
Scheme 2
SYNTHESIS 2006, No. 24, pp 4237–4241
x
x.
x
x
.
2
0
0
6
Advanced online publication: 21.11.2006
DOI: 10.1055/s-2006-950372; Art ID: Z13606SS
© Georg Thieme Verlag Stuttgart · New York

4238
J. S. Yadav et al.
Substrate
PAPER
Table 1
Entry
1
Producta
Time (h)
3.5
Yieldb (%)
75
OH
O
1a
1b
2a
2b
OH
O
2
3
2.5
2.5
78
75
O
TBDPSO
TBDPSO
OH
OBn OH
OBn
O
1c
2c
O
OH
OH
O
O
OH
O
O
O
4
5
1d
1e
2d
2e
2.5
2.8
76
84
O
OBn OBn OH
OH OH
O
O
OBn OBn
O
6
7
1f
2f
3.0
3.0
81
81
OH
OH
O
O
Cl
Cl
1g
2g
OH OH
O
O
OPh
OPh
8
9
1h
1i
2h
2i
2.8
3.0
3.0
3.0
80
83
78
70c
OH
OH
O
O
O2N
O2N
OH
O
OH
O
F
F
10
11
1j
2j
OH OH
O
O
MeO
MeO
O
1k
2k
OH OH
O
a Reaction conditions: 1,3-diol (1 mmol), IBX (3.5 mmol).
b Isolated yields.
c IBX (4.0 mmol) was used.
We have carried out the reaction using fewer equivalents were surprised to note that there was no hydroxy aldehyde
of 2-iodoxybenzoic acid in the case of 2-methyloctane- in the mixture of the products formed. The products 2a, 3,
1,3-diol (1a). Thus, treatment of compound 1a with one and 4 were separated and further oxidized individually
equivalent of 2-iodoxybenzoic acid gave a mixture of with one equivalent of 2-iodoxybenzoic acid. Thus, treat-
products 2a, 3, and 4 in a ratio of 55:15:30 in 35% yield ment of compound 3 with one equivalent of 2-iodoxyben-
after recovery of 60% starting diol (1a) (Scheme 3).20 We zoic acid gave a-formyl ketone 4 together with diketone
Synthesis 2006, No. 24, 4237–4241 © Thieme Stuttgart · New York

PAPER
2-Iodoxybenzoic Acid Mediated Conversion of 1,3-Diols to 1,2-Diketones
4239
O
O
OH
O
O
OH
OH
OH
IBX (1 equiv)
+
+
C5H11
H
C5H11
C5H11
DMSO, THF, r.t.
C5H11
O
1a
2a
3
4
O
O
O
IBX (1 equiv)
O
+
C5H11
C5H11
H
DMSO, THF, r.t.
C5H11
O
3
2a
4
IBX (2 equiv)
IBX (1 equiv)
DMSO, THF, r.t.
DMSO, THF, r.t.
O
C5H11
O
2a
Scheme 3
2a. Further oxidation of a-formyl ketone 4 with one tack; simultaneous ring cleavage gives the 1,2-diketone,
equivalent of 2-iodoxybenzoic acid resulted in a single and on workup formic acid and 2-iodosobenzoic acid are
product, the diketone 2a. This experiment clearly shows formed.21
that three equivalents of 2-iodoxybenzoic acid exclusive-
ly oxidize the 1,3-diol system to give a 1,2-diketone.
protocol for the conversion of 1,3-diols into 1,2-diketones
In conclusion, we have developed a mild and efficient
A plausible mechanism is shown in Scheme 4. The a- using the inexpensive and environmentally benign oxi-
formyl ketone 4 tautomerizes to form the keto–enol inter- dant 2-iodoxybenzoic acid (IBX). The protocol is useful
mediate 5, which forms a spirocyclic intermediate 6 with in obtaining 1,2-diketones in the presence of acid- and
2-iodoxybenzoic acid most likely through nucleophilic at- base-sensitive protecting groups (Table 1, entries 2–4). In
O
H
OH OH
O
H
O
O
+
OH
OH
..
R
R
R
R
H
OH
_
O
OH
O
I
I
1
4
5
O
O
R = alkyl, aryl
O
O
H
O
H
O
O
O
+
H
O
R
OH
..
OH
O
H
O
I
O
R
+
I
R
O
O
I
O
O
O
O
2
O
O
6
workup
IO
+
HCOOH
COOH
Scheme 4
Synthesis 2006, No. 24, 4237–4241 © Thieme Stuttgart · New York

4240
J. S. Yadav et al.
PAPER
(s, 3 H), 1.81–1.68 (m, 1 H), 1.08 (d, J = 7.3 Hz, 3 H), 1.06 (s, 9 H),
0.99 (d, J = 7.3 Hz, 3 H).
13C NMR (100 MHz, CDCl3, proton-decoupled): d = 13.4, 14.2,
19.1, 23.4, 27.1, 38.9, 41.5, 66.5, 73.6, 85.2, 127.2, 128.3, 129.9,
133.1, 136.2, 138.5, 198.5, 202.1.
addition to its simplicity and efficiency, this method pro-
vides high yields of 1,2-diketones with high selectivity.
Melting points were recorded on a Büchi R-535 apparatus and are
uncorrected. IR spectra were recorded on a Perkin Elmer FT-IR
MS (ESI): m/z = 539 [M + 23]+, 472, 407.
1
240-c spectrophotometer using KBr optics. H NMR spectra were
recorded on Gemini 200, Avance-300 and Varian-unity 400 spec-
trometers in CDCl3 using TMS as internal standard. MS were
recorded on a Finnigan MAT 1020 mass spectrometer operating at
70 eV and ESI/MS.
Anal. Calcd for C32H40O4Si: C, 74.38; H, 7.80. Found: C, 74.42; H,
7.86.
(4R,5R,6R)-5,7-(Isopropylidenedioxy)-4,6-dimethylheptane-
2,3-dione (2c)
Liquid.
1,2-Diketones 2; General Procedure
IBX (3.5 mmol) was dissolved in DMSO (1 mL) and to this a soln
of 1,3-diol (1 mmol) in THF (4 mL) was added. The mixture was
stirred at r.t. for the indicated time (Table 1). On completion of the
reaction (TLC), the mixture was diluted with Et2O (10 mL), filtered
through Celite and washed with sat. aq NaHCO3 soln and brine, and
dried (anhyd Na2SO4). The organic layer was concentrated in vacuo
and the resulting product was directly charged on a small column
(silica gel, EtOAc–n-hexane) to afford the pure 1,2-diketone.
Spectroscopic data for 1-phenylpropane-1,2-dione (2e),22 1-(4-chlo-
rophenyl)propane-1,2-dione (2f),22 1-(4-nitrophenyl)propane-1,2-
dione (2h),231-(4-methoxyphenyl)propane-1,2-dione (2j),24 and
naphthalene-1,2-dione (2k)25 are identical to those reported in the
literature.
IR (KBr): 2928, 1715, 1622, 1472, 1442, 1365, 1109, 714 cm–1.
1H NMR (300 MHz, CDCl3): d = 4.06 (ABq, J = 3.8, 10.8 Hz, 1 H),
3.65 (ABq, J = 4.5, 12.1 Hz, 1 H), 3.48 (t, J = 11.3 Hz, 1 H), 3.38–
3.30 (m, 1 H), 2.28 (s, 3 H), 1.90–1.74 (m, 1 H), 1.29 (s, 3 H), 1.26
(s, 3 H), 1.09 (d, J = 6.8 Hz, 3 H), 0.80 (d, J = 6.8 Hz, 3 H).
13C NMR (100 MHz, CDCl3, proton-decoupled): d = 11.9, 18.9,
24.5, 29.5, 30.7, 41.9, 65.8, 74.1, 98.3, 198.9, 201.2.
MS (ESI): m/z = 251 [M + 23]+, 186, 130.
(4R,5R,6R)-5,7-Bis(benzyloxy)-4,6-dimethylheptane-2,3-dione
(2d)
Liquid.
IR (KBr): 2926, 2855, 1713, 1606, 1497, 1454, 1356, 1092, 739,
699 cm–1.
1-Hydroxy-2-methyloctan-3-one (3)
Liquid.
1H NMR (300 MHz, CDCl3): d = 7.34–7.11 (m, 10 H), 4.52–4.34
(m, 4 H), 4.10 (q, J = 6.8, 14.4 Hz, 1 H) 3.85–3.75 (m, 1 H), 3.61–
3.56 (m, 1 H), 3.53–3.40 (m, 2 H), 2.01 (s, 3 H), 1.10 (d, J = 6.8 Hz,
3 H), 1.10 (d, J = 6.8 Hz, 3 H).
13C NMR (75 MHz, CDCl3, proton-decoupled): d = 13.6, 14.4, 24.8,
36.8, 40.8, 71.8, 73.1, 73.7, 84.9, 127.4, 127.5, 127.8, 127.9, 128.2,
128.3, 137.8, 138.5, 198.1, 201.8.
IR (KBr): 3447, 2923, 1658, 1321, 827 cm–1.
1H NMR (200 MHz, CDCl3): d = 3.75–3.56 (m, 2 H), 2.80–2.63 (m,
1 H), 2.47 (t, J = 7.4 Hz, 2 H), 1.65–1.48 (m, 2 H), 1.38–1.22 (m, 4
H), 1.11 (d, J = 7.4 Hz, 3 H), 0.91 (t, J = 6.7 Hz, 3 H).
MS (ESI): m/z = 181 [M + 23]+, 159 [M + 1]+, 128, 100.
HRMS: m/z [M+] calcd for C9H18O2: 158.1306; found: 158.1319.
MS (ESI): m/z = 391 [M + 23]+, 343, 277, 261, 145, 91.
HRMS: m/z [M+] calcd for C23H28O4: 368.1987; found: 368.1996.
2-Methyl-3-oxooctanal (4)
Liquid.
IR (KBr): 3326, 2921, 1722, 1656, 1271, 779 cm–1.
1-(3-Phenoxyphenyl)propane-1,2-dione (2g)
Low-melting solid.
1H NMR (200 MHz, CDCl3): d = 9.71 (s, 1 H), 3.44 (q, J = 6.7, 13.4
Hz, 1 H), 2.48– 2.30 (m, 2 H), 1.54–1.35 (m, 6 H), 1.13 (d, J = 7.4
Hz, 3 H), 0.90 (t, J = 6.7 Hz, 3 H).
MS (ESI): m/z = 157 [M + 1]+, 128.
HRMS: m/z [M+] calcd for C9H16O2: 156.1150; found: 156.1158.
IR (KBr): 2931, 1713, 1676, 1580, 1489, 1438, 1231, 1112, 858,
741, 700 cm–1.
1H NMR (400 MHz, CDCl3): d = 7.72 (d, J = 7.4 Hz, 1 H), 7.62 (s,
1 H), 7.42 (t, J = 8.2 Hz, 1 H), 7.34 (t, J = 8.2 Hz, 2 H), 7.13 (t,
J = 7.4 Hz, 2 H), 7.00 (d, J = 7.4 Hz, 2 H), 2.49 (s, 3 H).
Octane-2,3-dione (2a)
Liquid.
IR (KBr): 2915, 1645, 1618, 1325, 1219, 772 cm–1.
1H NMR (200 MHz, CDCl3): d = 2.70 (t, J = 7.4 Hz, 2 H), 2.31 (s,
3 H), 1.45–1.22 (m, 6 H), 0.90 (t, J = 6.7 Hz, 3 H).
13C NMR (100 MHz, CDCl3, proton-decoupled): d = 26.4, 117.5,
119.8, 121.2, 123.5, 125.2, 131.0, 133.1, 156.7, 158.5, 190.3, 201.5.
MS (EI): m/z = 241 [M]+, 209, 198, 170, 142, 116, 78, 53.
Anal. Calcd for C15H12O3: C, 74.99; H, 5.03. Found: C, 74.97; H,
5.06.
13C NMR (50 MHz, CDCl3, proton-decoupled): d = 14.4, 22.7, 24.6,
25.2, 31.4, 35.7, 198.0, 198.6.
1-(4-Fluorophenyl)propane-1,2-dione (2i)
Low-melting solid.
MS (ESI): m/z = 143 [M + 1]+, 130, 101, 98.
IR (KBr): 3067, 2350, 1713, 1676, 1581, 1484, 1353, 1285, 1133,
864, 755, 690 cm–1.
(4R,5R,6R)-5-(Benzyloxy)-7-(tert-butyldiphenylsiloxy)-4,6-di-
methylheptane-2,3-dione (2b)
Liquid.
1H NMR (400 MHz, CDCl3): d = 8.08 (t, J = 7.4 Hz, 2 H), 7.14 (t,
J = 8.2 Hz, 2 H), 2.49 (s, 3 H).
IR (KBr): 2932, 1712, 1637, 1460, 1427, 1389, 1111, 823, 740, 703,
612 cm–1.
1H NMR (400 MHz, CDCl3): d = 7.62 (t, J = 7.3 Hz, 4 H), 7.39–7.30
(m, 5 H), 7.29–7.19 (m, 4 H), 7.10–7.07 (m, 2 H), 4.45–4.30 (ABq,
J = 3.9, 11.7 Hz, 2 H), 3.80–3.74 (m, 2 H), 3.72–3.61 (m, 2 H), 2.01
13C NMR (100 MHz, CDCl3, proton-decoupled): d = 25.9, 116.5,
129.9, 133.2, 166.3, 190.4, 199.3.
MS (ESI): m/z = 166 [M]+, 131, 102.
Synthesis 2006, No. 24, 4237–4241 © Thieme Stuttgart · New York

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2-Iodoxybenzoic Acid Mediated Conversion of 1,3-Diols to 1,2-Diketones
4241
Anal. Calcd for C9H7FO2: C, 65.06; H, 4.25. Found: C, 65.08; H,
4.26%.
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Synthesis 2006, No. 24, 4237–4241 © Thieme Stuttgart · New York