Lewis acid-catalyzed oxidative rearrangement of tertiary allylic alcohols mediated by TEMPO

Article abstract of DOI:10.1016/j.tet.2009.11.104

Two methods for the oxidative rearrangement of tertiary allylic alcohols have been developed. Most of tertiary allylic alcohols studied were oxidized to their corresponding transposed carbonyl derivatives in excellent to fair yields by reaction with TEMPO in combination with PhIO and Bi(OTf)₃ or copper (II) chloride in the presence or not of oxygen. Other primary oxidants of TEMPO such as PhI(OAc)₂, mCPBA, and Oxone were unsatisfactory giving the enone in modest to low yields.

Full text of DOI:10.1016/j.tet.2009.11.104

Tetrahedron 66 (2010) 904–912
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Lewis acid-catalyzed oxidative rearrangement of tertiary allylic alcohols
mediated by TEMPO
*
`
Jean-Michel Vatele
ˆ
Institut de Chimie et Biochimie Mole´culaires et Supramole´culaires (ICBMS), UMR 5246 CNRS, Universite´ Lyon 1, Laboratoire de Chimie Organique 1, bat.CPE,
69622 Villeurbanne Cedex, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Two methods for the oxidative rearrangement of tertiary allylic alcohols have been developed. Most of
tertiary allylic alcohols studied were oxidized to their corresponding transposed carbonyl derivatives in
excellent to fair yields by reaction with TEMPO in combination with PhIO and Bi(OTf)3 or copper (II)
chloride in the presence or not of oxygen. Other primary oxidants of TEMPO such as PhI(OAc)2, mCPBA,
and OxoneÒ were unsatisfactory giving the enone in modest to low yields.
Received 29 September 2009
Received in revised form 24 November 2009
Accepted 24 November 2009
Available online 27 November 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Copper(II) salts
Iodosylbenzene
Oxidation
Rearrangement
TEMPO
1. Introduction
iodoxybenzenesulfonic acid-promoted oxidative rearrangement of
tertiary allylic alcohols with OxoneÒ at 60 ꢀC.9
b,
b
0-Difunctionalized enones are essential and versatile in-
In relation with an ongoing project aimed to explore the use of
TEMPO/co-oxidants in organic synthesis,10 we have recently
reported in preliminary accounts two protocols for the oxidative
rearrangement of tertiary allylic alcohols using TEMPO in the pres-
ence of PhIO or copper(II) salts as primary oxidants (Scheme 1).11 We
now reported in full details, studies of these methods of oxidative
rearrangement of tertiary allylic alcohols as well as with other
TEMPO/co-oxidant systems.
termediates in organic synthesis.1 Moreover, this motif is frequently
encountered in a variety of biologicallyactive natural products.2 One
of the most used strategy for the preparation of this class of com-
pounds is a two-step alkylative 1,3-carbonyl transposition of a,b-
unsaturated ketones, which entails a 1,2-addition of organometallic
reagents followed by an oxidative rearrangement of the resulting
tertiary allylic alcohols. Until recently, the oxidative transposition
step was exclusively effected by using oxochromium (VI)-based
reagents such as CrO3 and mostly its less acidic derivatives, PCC and
PDC.3,4 However, if this oxidation method has been used in a large
number of syntheses,5 for some substrates the yield of rearrange-
ment was low either because of a very slow oxidation reaction5h or
of the formation of by-products such as epoxides5m or fragmenta-
tion products.3b,6 Safety hazards associated with these oxidants and
their toxic by-products have urged organic chemists to develop eco-
friendly strategies for this oxidative rearrangement. In 2004, Iwa-
buchi and co-workers have reported the use of excess of IBX in
DMSO to produce substituted cycloalkenones from cyclic tertiary
allylic alcohols.7 The same author described two more general
method than IBX employing as oxidants either stoichiometric
amount of oxoammonium salts or TEMPO and NaIO4 as a co-oxi-
dant.8 Very recently, Ishihara and co-workers developed a 2-
R2
O
R4
H
OH
R4
TEMPO cat.
Method A or B
R1
R3
R1
R3
R2
Method A: PhIO, Bi(OTf)3 cat. or Re2O7 cat., CH2Cl2
Method B: CuCl2 cat., O2, 4Å MS, CH3CN
Scheme 1.
2. Results and discussion
2.1. Oxidative rearrangement with the TEMPO/PhIO/Lewis
acid system
We started studying the oxidative rearrangement of 1-n-butyl-
2-cyclohexen-1-ol 1a, a representative tertiary allylic alcohol sub-
strate, with TEMPO/PhIO/Yb(OTf)3, a system we recently reported
* Tel.: þ33 472431151; fax: þ33 472431214.
E-mail address: vatele@univ-lyon1.fr
0040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.11.104

J.-M. Vate`le / Tetrahedron 66 (2010) 904–912
905
its ability to oxidize readily and chemoselectively alcohols to car-
bonyl compounds. In the presence of a catalytic amount of TEMPO
and Yb(OTf)3 and PhIO (1.3 equiv), compound 1a afforded the un-
saturated ketone 1b in only 40% (Table 1, entry 1). We therefore
screened the catalytic activity of a range of protic or Lewis acids on
the oxidation of 1a. Among metal triflates tested, Bi(OTf)3 appeared
to be the most efficient to promote the oxidative rearrangement of
1a affording the enone 1b in 77% (entry 4).12 The presence of 4 Å
molecular sieves in the reaction medium reduced the amount of
side products improving the yield (entry 5).13 Disappointingly,
strong acids such as p-toluenesulfonic acid had a weak catalytic
activity on the oxidative rearrangement providing 1b in 64% yield
(entry 6). We finally tested Re2O7 as a catalyst because, in addition
to its Lewis acid character,14 it is known to induce a 1,3-isomeri-
zation of allylic alcohols,15,16 the very likely first step of the oxida-
tive rearrangement mediated by TEMPO/PhIO/Lewis acid.11a
Unfortunately, relatively high loading of Re2O7 was necessary for
the transposition to occur and the desired enone 1a was obtained in
a modest yield (entry 7).
Having optimized the reaction conditions, we tested the scope
of this process on a range of substrates and the results are outlined
in Table 3. Transposed cyclohexenones 1a–4a were obtained in
good to fair yields (entries 1–4). Crowded 4,4-disubstituted cyclo-
hexenol 5a was slowly oxidized and required high loading of cat-
alyst, highlighting the extreme sensitivity of the TEMPO-based
oxidation method to the environment of the carbinol moiety (entry
5).18 In contrast to the oxidative rearrangement with oxy-
chromium(VI)-reagents, diastereomeric mixture of carveol reacted
sluggishly in the presence of TEMPO/PhIO system to afford
3-methylcarvone in only 19% yield accompanied by several by-
products (entry 6).19 Five-membered substrates readily responded
to the TEMPO-based oxidative rearrangement to provide enones
7a–9a in good yields (entries 7–9). 12-Macrocyclic compound 10a
exhibit low reactivity furnishing, after 24 h, the desired enone in
only 35% yield (based on recovered starting material). Iwabuchi and
co-workers have already pointed out that medium and macrocyclic
tertiary allylic alcohols reacted much more slowly using TEMPO/
NaIO4 system than their corresponding five-and six-membered
derivatives.7b We next aimed to extend the scope of our method to
the more challenging acyclic substrates. Indeed, these compounds
are known to be reluctant to undergo 1,3-oxidative rearrangement
and also to give fragmentation products.3a,b,6a,5e Treatment of
compound 11a with PhIO/TEMPO/Bi(OTf)3 or Re2O7 gave a mixture
of products in which the desired enone was not detected (entry 11).
Another interesting extension of this oxidation is that of tertiary
Table 1
Study of the oxidative rearrangement of 1-butyl-2-cyclohexen-1-ol 1a with PhIO/
TEMPO system in the presence of various Lewis or protic acids
OH
PhIO, TEMPO (0.1 equiv)
Catalyst
vinyl carbinols, which furnishes
a,b
-unsaturated aldehydes.3b
1b
1a
O
Conversely to Bi(OTf)3, Re2O7 efficiently catalyzed the oxidative
rearrangement of vinyl alcohol 12a to give 12b in fair yield (entry
12). Under the same reaction conditions, cyclohexanol derivative
13a gave cyclohexylideneacetaldehyde 13b in only modest yield
(entry 13).
Entry
Catalyst (mol %)
Solvent
Temp (ꢀC)
Time (%)
Yielda (%)
1
2
3
4
5
6
7
Yb(OTf)3 (10)
Sc(OTf)3 (20)
Zn(OTf)3 (30)
Bi(OTf)3 (8)
Bi(OTf)3 (8)b
p-TsOH(40)
Re2O7 (15)
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
20
0
20
0
0
20
0
1
0.5
1
1
0.5
1
40
41
30
77
84
64
44
2.2. Aerobic-oxidative rearrangement with Cu(II) salts/TEMPO
1
Even if the oxidative rearrangement with TEMPO/PhIO/Bi(OTf)3
or Re2O7 system gave satisfactory results on most substrates, being
competitive with the other existing methods, this process was not
applicable to acyclic tertiary allylic alcohols. For this reason and in
order to find a more simple procedure, we surveyed the literature
to find a cheap and commercially available reoxidant of TEMPO,
which can also act as a Lewis acid, necessary for the first step of the
oxidative rearrangement: the allylic rearrangement of tertiary al-
lylic alcohols via an allylic cation.11a Because copper(II) salts were
used in many instances as primary oxidants of TEMPO and also are
mild Lewis acids,20 we thought that the couple TEMPO/Cu(II) could
promote the oxidative rearrangement of tertiary allylic alcohols.
The first experiment was quite disappointing since, in the presence
of TEMPO and CuCl2.2H2O (3 equiv), 1-butylcyclohex-2-en-1-ol 1a
led to the transposed enone 1b in 31% yield (Table 4, entry 1).
The enone yield was greatly improved by addition of 4 Å mo-
lecular sieves, which traps HCl formed during the oxidation re-
ducing strongly the formation of dehydration products (entry 2).
Cu(NO3)2 and Cu(ClO4)2 gave similar results than CuCl2 whereas
CuBr2 afforded almost exclusively decomposition products (entries
3–5). With other salts such as CoCl2 and Mn(NO3)2, the conversion
was very slow, giving mainly the corresponding 1,3-transposed
allylic alcohol of 1a and dehydration compounds.21
a
Isolated yield.
4 Å MS was added (0.08 g/mmol).
b
We next examined solvent effects on the TEMPO/PhIO/Bi(OTf)3-
catalyzed oxidative transpositiononcompound1a. AsseeninTable2,
all solvents tested were less efficient than dichloromethane in terms
of yields and catalytic activity. Addition of water to dichloromethane
significantly lowered the reaction rate and the yield by increasing the
amountofby-products(entry6). MuchhighersolubilityofBi(OTf)3 in
water than in dichloromethane might explain the decrease of the
oxidative rearrangement rate by lowering the concentration of the
catalyst in the organic phase.17
Table 2
Solvent dependence of Bi(OTf)3- promoted the oxidative rearrangement of 1a with
PhIO/TEMPO system
OH
PhIO, TEMPO (0.1 equiv)
Bi(OTf)3, Solvent
1b
1a
O
Entry
Solvent
Bi(OTf)3 (mol %)
Time (min)
Yield (%)
Semmelhack and co-workers have shown that, in the presence
of oxygen, copper salts could be used catalytically for the TEMPO-
mediated oxidation of alcohols.20a In the optimized conditions,
copper-catalyzed aerobic oxidative rearrangement of tertiary allylic
alcohol 1a provided the enone 1b in 90% yield (entry 7).
We then tested the scope of this process on a variety of tertiary
allylic alcohols. As seen in Table 5, diversely substituted six-mem-
bered substrates were smoothly converted in good to excellent
1
2
3
4
5
6
THF
50
25
25
8
60a
30a
41
58
63
56
62
35
Toluene
CH3CO2Et
CH3NO2
CH3CN
30b
15b
15
20
30a
CH2Cl2–H2O
120b
a
0 ꢀC.
b
Room temperature.

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J.-M. Vate`le / Tetrahedron 66 (2010) 904–912
Table 3
Bi(OTf)3- or Re2O7-catalyzed oxidative rearrangement of tertiary allylic alcohols with TEMPO in combination with PhIO
Entry
Substrate
Methoda
Time (h)
Temperature (ꢀC)
Product
Yieldb (%)
n-Bu
HO n-Bu
1
A
1
0
84
O
O
1a
1b
Ph
HO Ph
2
3
A
A
1
1
0
0
73
72
2a
2b
3b
HO
O
O
3a
HO
4
5
Ac
16
20
20
67
60
4a
4b
OH
Ac
5
O
5a
5b
O
OH
6
7
Ac
1
1
20
19
80
6a
7a
6b
n-Bu
n-Bu
A
0
OH
7b
O
8
9
A
A
0.5
0.5
0
0
78
78
OH
OH
8b
O
8a
9a
O
9b
O
OH
n-Bu
n-Bu
10
Ac
24
20
22d
10a
10b
n-Bu
OH
n-Bu
e
11
A, B
16
0
-
O
11b
11a

J.-M. Vate`le / Tetrahedron 66 (2010) 904–912
907
Table 3 (continued)
Entry
Substrate
Methoda
B
Time (h)
1
Temperature (ꢀC)
Product
Yieldb (%)
CHO
OH
12
20
20
58
40
12a
12b
OH
CHO
13
B
1
13b
13a
a
General conditions: PhIO (1.2 equiv), TEMPO (0.1 equiv), catalyst. For method A: Bi(OTf)3 (8 mol %) and 4 Å MS (0.08 g/mmol); method B: Re2O7 (20 mol %) and 4 Å MS
(0.13 g/mmol).
b
Isolated yield.
c
25 mol % of Bi(OTf)3 were added.
37% of the starting material were recovered.
A mixture of unidentified products was obtained.
d
e
Table 4
Influence of the copper (II) salt on the oxidative rearrangement of tertiary allylic alcohol 1a mediated by TEMPO
OH
TEMPO (0.1 equiv), Cu2+
MeCN
1b
1a
O
Entry
Cu2þ salt
Equiv
4 Å MS (g/mmol)
Temp (ꢀC)
Time (h)
Yielda (%)
1
2
3
4
5
6
7
CuCl2
CuCl2
Cu(NO3)2
Cu(ClO4)2
CuBr2
3
3
3
3
3
0.2
0.5
d
rt.
rt.
rt.
rt.
0
0.5
1
1
1
1
31b
78
83
81
0.23
0.23
0.23
0.23
0.15
0.15
30
CuCl2
CuCl2
rt.
rt.
72
7
58c,d
90c
a
Isolated yield.
Formation of elimination products.
Under O2 (balloon).
b
c
d
29% of the starting material were recovered.
yields to their corresponding transposed enones (entries 1–7).
However, sterically crowded substrates such as 6a and 14a required
a high loading of CuCl2 to be oxidized at a reasonable rate (entries 6
and 7). It is noticeable than 2-methylcarveol 5a was converted to 3-
methylcarvone in high yield as contrasted with that obtained using
TEMPO/PhIO system (89% versus 19% yield) (entry 5). Aerobic
copper oxidation of five-membered substrates proceeded readily to
termini to generate 1c. In the conditions developed by Rychnovsky
and Vaidyanathan: MCPBA, TEMPO and Bu4NBr catalytic, the epoxide
1d was obtained as a sole product (Table 6, entry 1).23 In contrast, in
the presence of Bi(OTf)3, the allylic rearrangement occurred affording
the desired enone albeit in low yield accompanied by a mixture of
epoxides 1d and 1e (entry 2). Lastly, in the presence of TEMPO,
OxoneÒ and tetrabutylammonium bromide compound 1a gave
a mixture of products, among them the desired enone 1bwas isolated
in less than 10% yield.24
afford b-substituted cyclopentenones in fair yields (entries 8 and 9).
In the presence of 2 equiv of CuCl2, medium and macrocyclic sub-
strates furnished the expected products in high yields (entries 10
and 11). In contrast to the method using PhIO as a bulk oxidant
(Table 3, entry 11), TEMPO/CuCl2 effected the oxidative rearrange-
ment of acyclic compound 11a in a satisfactory yield (entry 12).
TEMPO/CuCl2 system was less effective for the oxidative rear-
rangement of tertiary vinyl carbinols than that of TEMPO/PhIO/
Re2O7 (compare Table 3, entry 12 and Table 5, entry 13).
3. Conclusion
In conclusion, we have successfully developed two mild and
environmentally friendly methods for Lewis acid catalyzed-oxida-
tive rearrangement of tertiary allylic alcohols to
b-disubstituted
enones. The advantages of TEMPO/CuCl2/O2 system over TEMPO/
PhIO/Bi(OTf)3 or Re2O7 system are the availability of its reagents
and their costs and it gives better results for substituted six-
membered cyclic, macrocyclic and acyclic allylic tertiary alcohols.
Unsaturated aldehydes are more readily obtained and with a better
yields from tertiary vinyl carbinols with TEMPO/PhIO oxidizing
process.
2.3. Study of the oxidative rearrangement with other
cooxidants of TEMPO
We first tested TEMPO/PhI(OAc)2 system, which is becoming one
of the most used method for the oxidation of alcohols in organic
synthesis (Table 6).22 This oxidizing system led the allylic alcohol 1a
unchanged after 24 h at room temperature (entry 1). We next
screened several acids and, in all cases, a mixture of the desired enone
1b and of the allylic acetate 1c was obtained in good yields (entries 2
and 4). Evidently, the mechanism of formation of secondary allylic
acetate involve a solvolysis of the tertiary alcohol to an allylic car-
bonium ion which collapses with acetic acid at the lesser substituted
4. Experimental section
4.1. General procedures
1H NMR spectra were recorded in CDCl3
probe temperature on a Bruker AC 200 (200 MHz) spectrometer.
(dH¼7.25) at ambient

908
J.-M. Vate`le / Tetrahedron 66 (2010) 904–912
Table 5
Copper(II) chloride-catalyzed oxidative rearrangement of tertiary allylic alcohols mediated by TEMPO
Entry
Substrate
Methoda
Time (h)
Productb (yield %)
1
A
7
2
3
A
A
5
6
4
B
8
5
B
48
6
7
B
B
6
10
8
9
A
A
7
7
10
A
48

J.-M. Vate`le / Tetrahedron 66 (2010) 904–912
909
Table 5 (continued)
Entry
Substrate
Methoda
Time (h)
Productb (yield %)
11
12
B
48
B
B
48
30
13
a
Method A: TEMPO (0.1 equiv), CuCl2$2H2O (0.5 equiv), O2 (balloon), 4 Å MS, rt; Method B: TEMPO (0.1 equiv), CuCl2$2H2O (2 equiv), 4 Å MS, rt.
Isolated yield.
b
c Ratio E/Z¼1.8/1.
d Ratio E/Z¼2.5/1.
Table 6
Oxidative rearrangement of 1a with TEMPO/PhI(OAc)2
n-Bu
n-Bu
n-Bu
OH
TEMPO (0.1 equiv)
+
O
PhI(OAc)2, CH2Cl2, RT
OAc
1a
1c
1b
Entry
Catalyst (mol %)
Time (h)
24a
0.75
1
1
1b (%)
1c (%)
1
2
3
4
d
d
d
Bi(OTf)3 (4)
Sc(OTf)3 (5)
p-TSA (20)
41
37
51
32
30
24
a
No reaction occurred.
Table 7
Study of the reaction between 1a and TEMPO/mCPBA/nBu4NBr
n-Bu
n-Bu
n-Bu
O
OH
n-Bu
OH
TEMPO (0.1 equiv)
CH2Cl2
O
+
O
+
mCPBA, nBu4NBr
OH
O °C
1e
1d
1b
1a
Entry
Catalyst (mol %)
Time
1b (%)
1d (%)
1e (%)
1
2
d
2
1
0
9
88
22
0
28
Bi(OTf)3
Data are presented as follows: chemical shift (in ppm on the
d
scale
and stored under a nitrogen atmosphere. Acetonitrile, dichloro-
methane, dimethylformamide were distilled from calcium hydride.
Powdered 4 Å molecular sieves (Aldrich) was dried at 150 ꢀC during
6 h. All other chemicals were used as received. Bi(OTf)3 was
relative to dTMS¼0), multiplicity (s¼singlet, d¼doublet, t¼triplet,
q¼quadruplet, m¼multiplet, br¼broad), integration, coupling
constant and interpretation. 13C NMR spectra were recorded at
ambient probe temperature on a Bruker AC 200 (50.3 MHz) in
CDCl3 used as reference (dC¼77.0). High resolution mass spec-
trometry (HRMS) analyses were conducted using a Thermofinigan-
MAT 95 XL instrument. IR spectra were recorded on a Perkin-Elmer
298 spectrophotometer. Optical rotations were measured on a Per-
kin-Elmer 141 polarimeter at the sodium D line (598 nm). Melting
points were determined on a Bu¨chi 530 apparatus and are un-
corrected. Reagents and solvents were purified by standard means.
Tetrahydrofuran was distilled from sodium wire/benzophenone
obtained from Alfa. Tertiary alcohols 1a7a, 2a7a, 3a25, 4a26, 5a3b
,
6a18, 7a27, 8a6b, 9a28, 11a7a, 12a29, 13a30, 14a31, 15a32 were prepared
following the literature procedures. PhIO was obtained according to
the reported procedure.33
4.2. (E)-1-n-Butyl-2-cyclododecen-1-ol (10a)
To a cooled solution (ꢁ78 ꢀC) of (E)-2-cyclododecen-1-one34
(0.52 g, 2.9 mmol) in THF (10 mL) were added dropwise n-BuLi

910
J.-M. Vate`le / Tetrahedron 66 (2010) 904–912
(2.5 M in hexanes, 1.7 equiv). The reaction was warmed up to
ꢁ30 ꢀC, stirred at this temperature for 1 h and ethanol was added.
After stirring 5 min at this temperature, ether and saturated NH4Cl
solution were added. The aqueous phase was extracted once with
ether and the combined extracts were dried (Na2SO4) and con-
centrated under reduced pressure. The resulting oil was purified by
chromatography on silica gel (ether–petroleum ether, 1/9) to give
4.3.2.4. 3-Ethynyl-2-cyclohexen-1-one (4b). EtOAc–petroleum
ether (1:6), yellow oil. 1H NMR: 2.20 (quintuplet, 2H, J¼6 Hz, H-5),
2.25–2.42 (m, 4H, H-4, H-6), 3.54 (s, 1H), 6.24 (t, 1H, J¼1.5 Hz, H-2).
13C NMR: 22.5, 30.2, 37.3, 82.5, 87.2, 134.0, 142.2, 198.5. Its spec-
troscopic data were in accord with those described in the
literature.36
10a as an oil (0.39 g, 57% yield). IR (film): 3447 cmꢁ1
.
1H NMR
4.3.2.5. 3,6,6-Trimethyl-2-cyclohexen-1-one (5b). EtOAc–petro-
leum ether (1:6), oil. 1H NMR: 1.1 (s, 6H, 2Me), 1.8 (t, 2H, J¼6.1 Hz,
H-5), 1.9 (s, 3H, Me), 2.27 (t, 2H, J¼6 Hz, H-4), 5.74 (sextuplet, 1H,
J¼1.4 Hz, H-2). 13C NMR: 24.1 (Me), 24.5 (2 Me), 28.8, 36.4, 40.5,
125.4, 160.7, 204.9. NMR data were identical with those reported in
the literature.37
(C6D6): 0.9 (t, 3H, J¼6.2 Hz, Me), 1.12–1.6 (m, 23H), 2.12–2.16 (m,
2H), 5.24 (d, 1H, J¼15.6 Hz), 5.46 (ddd, 1H, J¼5.1, 9.8, 15.6 Hz). 13C
NMR: 14.4, 21.8, 23.7, 24.5, 24.8, 25.0, 25.1, 26.0, 26.2, 26.9, 31.2,
40.1, 42.3, 75.5, 128.2, 137.5. HRMS: calcd for C16H30O (Mþ)
238.2297; found: 238.2295.
4.3. General procedure for the oxidative rearrangement of
tertiary alcohols
4.3.2.6. (S)-2,3-Dimethyl-5-isoprenylcyclohex-2-en-1-one
20
(6b). Ether–petroleum ether (1:7), oil, [
a
]
þ103 (c,1.2, CHCl3)lit.38
D
26
[a
]
þ103.5 (c, 2.1).1H NMR: 1.74 (s, 3H, Me),1.76 (s, 3H, Me),1.94 (s,
D
4.3.1. With TEMPO/PhIO/Bi(OTf)3 or Re2O7. To a solution of tertiary
alcohol (1 mmol) in CH2Cl2 (5 mL) were added PhIO (0.264 g,
1.2 equiv), TEMPO (15.6 mg, 0.1 equiv) and 4 Å molecular sieves
(0.08 and 0.13 g/mmol with Bi(OTf)3 and Re2O7, respectively). The
suspension was cooled to 0 ꢀC and Lewis acid was added. When
high loading of Bi(OTf)3 (25 mol %) was used (Table 3, entries
4,5,6,10), it was added in three portions in 10 min. Generally, dis-
solution of PhIO is indicative of the end of the reaction. The reaction
mixture was poured onto a column of silica gel (w20 g) and eluted
with a mixture of EtOAc–petroleum ether.
3H, Me), 2.25 (dd,1H, J¼2.7, 4.8 Hz), 2.34 (m, 2H), 2.53 (dd,1H, J¼3.8,
5.4 Hz), 2.6 (m,1H), 4.43 (s,1H), 4.78 (s,1H).13C NMR: 11.1, 20.8, 21.9,
38.3, 41.6, 42.8, 110.6,131.1, 147.2, 154.6, 199.4. Its spectroscopic data
were in agreement with those described in the literature.19a
4.3.2.7. 3-n-Butyl-2-cyclopenten-1-one (7b). EtOAc–petroleum
ether (1:5), yellow oil. 1H NMR: 0.88 (t, 1H, J¼7.1 Hz, Me), 1.2–1.41
(m, 2H), 1.45–1.6 (m, 2H), 2.32–2.40 (m, 4H), 2.51–2.55 (m, 2H),
5.88 (quintuplet, 1H, J¼1.3 Hz). 13C NMR: 13.8, 22.4, 29.2, 31.5, 33.2,
35.3, 129.4, 183.3, 210.1. Spectroscopic data were consistent with
the literature data.38
4.3.2. With TEMPO/CuCl2. (Method A, Table 5) In the presence of
oxygen: To a solution of tertiary allylic alcohol (1 mmol) in CH3CN
(5 mL) were successively added TEMPO (15.6 mg, 0.1 equiv), 4 Å
molecular sieves (0.15 g) and CuCl2$2H2O (58 mg, 0.5 equiv). The
brown reaction mixture was stirred at room temperature under
oxygen (balloon) for a period of time indicated in Table 5. The light
brown suspension was diluted with ether, washed twice with wa-
ter, dried (Na2SO4) and evaporated under reduced pressure. The
residue was purified by flash chromatography on silica gel.
(Method B, Table 5) with an excess of CuCl2: To a solution of
tertiary allylic alcohol (1 mmol) in CH3CN (5 mL) were successively
added TEMPO (15.6 mg, 0.1 equiv), 4 Å molecular sieves (0.2 g)
except for 12a (35 mg) and CuCl2$2H2O (0.34 g, 2 equiv). The brown
reaction mixture was stirred at room temperature for a period of
time indicated in Table 5. The reaction mixture was worked up as
indicated above.
4.3.2.8. 3-Vinyl-2-cyclopenten-1-one
(8b). EtOAc–petroleum
ether (1:4), yellow oil. 1H NMR: 2.41 (m, 2H), 2.72 (m, 2H), 5.48
(d, 1H, J¼10.5 Hz), 5.73 (d, 1H, J¼17.5 Hz), 6.0 (s, H), 6.78 (dd, 1H,
J¼10.5, 17.5 Hz). 13C NMR: 26.5, 34.7, 122.4, 131.0, 132.7, 172.1, 209.6.
NMR data were consistent with those reported in the literature.39
4.3.2.9. 2,3-Dimethyl-2-cyclopenten-1-one (9b). EtOAc–petro-
leum ether (1:5), yellow oil. 1H NMR: 1.64 (s, 3H, Me), 2.0 (s, 3H, Me),
2.31 (m, 2H), 2.44 (m, 2H). 13C NMR: 8.2, 17.6, 31.9, 34.5, 136.6, 170.4,
210.3. NMR data were identical with those described in the
literature.38
4.3.2.10. (Z,E)-3-n-Butyl-2-cyclododecen-1-one (10b). Ether–pe-
troleum ether (5:95), oil. IR (neat): 1681, 1611 cmꢁ1. 1H NMR (mix-
ture of Z,E diastereomers): 0.92 (t, 3H, J¼7.2 Hz, Me (E)), 0.94 (t, 3H,
J¼7.1 Hz, Me (Z)),1.1–1.75 (m, 36H), 2.1 (t, 2H, J¼7.6 Hz, CH2 (E)), 2.18
(t, 2H, J¼7.5 Hz, CH2 (Z)), 2.39–2.48 (m, 6H, 2CH2 (Z), CH2 (E)), 2.64 (t,
2H, J¼6.5 Hz, CH2 (E)), 6.14 (s, 1H (E)), 6.26 (s, 1H (Z)). 13C NMR
(mixture of Z,E diastereomers): 14.0, 14.1, 22.4, 22.6, 23.2, 23.4 (2C),
23.7, 24.2, 24.6, 24.7, 24.8, 25.0, 25.1, 25.3, 26.1, 26.4, 26.9, 27.1, 29.9,
31.6, 31.9, 35.8, 38.8, 41.5, 42.1, 126.1, 127.7, 156.7, 161.1, 203.1, 204.6.
HRMS calcd for C16H28O (M)þ 236.2140; found: 236.2139.
4.3.2.1. 3-n-Butyl-2-cyclohexen-1-one (1b). EtOAc–petroleum
ether (1:5), oil. 1H NMR: 0.88 (t, 1H, J¼7.1 Hz, Me), 1.2–1.53 (m, 4H,
2CH2), 1.95 (quintuplet, 2H, J¼6.2 Hz), 2.18 (t, 2H, J¼7.7 Hz, CH2),
2.25–2.35 (m, 4H, 2CH2), 5.84 (s, 1H). 13C NMR: 13.8, 22.3, 22.8, 29.1,
29.7, 37.4, 37.8, 125.6, 166.8, 199.9. Its spectroscopic data were in
accordance with those reported in the literature.7a
4.3.2.2. 3-Phenyl-2-cyclohexen-1-one
(2b). EtOAc–petroleum
4.3.2.11. (Z,E)-2,5-Dimethyl-4-nonen-3-one (11b). Ether–petro-
ether (1:4), solid; mp 62–63 ꢀC (hexane) (lit.7a mp 64–65 ꢀC). 1H
NMR: 2.13 (quintuplet, 2H, J¼6.5 Hz, H-5), 2.27 (t, 2H, J¼6.2 Hz, H-
6), 2.75 (td, 2H, J¼1.2, 6.2 Hz, H-4), 6.4 (t, J¼1.3 Hz, H-2), 7.3–7.4 (m,
3H), 7.5–7.6 (m, 2H). 13C NMR: 22.8, 28.1, 37.3, 125.4, 126.1 (2C),
128.8 (2C), 130.0, 138.8, 159.8, 199.9. Its spectroscopic data were in
perfect agreement with those described in the literature.7a
leum ether (2:98), yellow oil. IR (film): 1680, 1610 cmꢁ1 1H NMR
.
(mixture of Z,E diastereomers): 0.91 (t, 3H, J¼7 Hz, Me (Z)), 0.92
(t, 3H, J¼7 Hz, Me (E)), 1.08 (d, 6H, J¼7 Hz, 2Me (Z)), 1.09 (d, 6H,
J¼7 Hz, 2Me (E)), 1.26–1.51 (m, 8H, H-7, H-8, (Z, E)), 1.88 (d, 3H,
J¼1.4 Hz, Me (Z)), 2.13 (d, 3H, J¼1.4 Hz, Me (E)), 2.14 (t, 2H, J¼7 Hz,
H-6 (E)), 2.14–2.68 (m, 4H, H-6 (Z), H-2 (E, Z)), 6.08 (br s, 1H, H-4
(Z)), 6.1 (q, 1H, J¼1.2 Hz, H-4 (E)). 13C NMR: 14.3, 14.5, 18.8 (4C), 19.7,
22.8, 23.3, 25.9, 30.1, 30.8, 34.0, 41.5, 41.8, 41.9, 122.3, 122.9, 159.8,
160.4, 204.8, 205.4. NMR data were in accordance with those de-
scribed in the literature.40
4.3.2.3. 3-Vinyl-2-cyclohexen-1-one
(3b). EtOAc–petroleum
ether (1:5), yellow oil. 1H NMR: 1.98 (quintuplet, 2H, J¼6 Hz, H-5),
2.25–2.5 (m, 4H, H-4, H-6), 5.41 (d, 1H, J¼10.7 Hz), 5.63 (d, 1H,
J¼17.5 Hz), 5.88 (s, 1H, H-2), 6.43 (dd, J¼10.7, 17.4 Hz). 13C NMR:
22.2, 24.3, 24.9, 37.7,120.7,128.2,137.9,156.9, 200.3. NMR data were
identical with those described in the literature.35
4.3.2.12. (Z,E)-3-Methyl-2-hepten-1-al (12b). Ether–petroleum
ether (1:5), liquid. IR (film): 1673, 1631 cmꢁ1. 1H NMR: 0.89 (t, 1H,

J.-M. Vate`le / Tetrahedron 66 (2010) 904–912
911
J¼7.2 Hz, Me (E)), 0.91 (t, 1H, J¼7.2 Hz, Me (Z)), 1.21–1.38 (m, 4H, H-
5, H-6 (Z, E)), 1.4–1.52 (m, 4H, H-5, H-6 (Z, E)), 1.95 (s, 3H, Me (Z)),
2.13 (s, 3H, Me (E)), 2.16 (t, 2H, J¼7.6 Hz, H-4 (E)), 2.55 (t, 2H,
J¼7.5 Hz, H-4 (Z)), 5.84 (d, 1H, J¼8.1 Hz, H-2 (E)), 5.86 (d, 1H,
J¼8.1 Hz, H-2 (Z)), 9.93 (d, 1H, J¼8.2 Hz, H-1 (Z)), 9.96 (d, 1H,
J¼8.1 Hz, H-1 (E)). 13C NMR: 14.2 (2C), 17.8, 22.6, 22.9, 25.4, 29.6,
31.3, 32.7, 40.7,127.6,128.7,164.8,165.3,191.1,191.7. HRMS: calcd for
C8H13O (MꢁHꢁ)þ 125.0966; found: 125.09645.
(br s, 1H, H-1). 13C NMR: 14.4, 18.7, 23.1, 27.0, 27.2, 29.5, 37.6, 61.9,
64.8, 67.4. NMR data were in good agreement with those reported
in the literature.43
References and notes
1. For recent examples of the uses of substituted enones in organic synthesis, see:
´
´
(a) Dominguez, M.; Alvarez, R.; Martras, S.; Rarres, J.; Pares, X. R.; de Lera, A. Org.
Biomol. Chem. 2004, 2, 3368–3373; (b) Li, C.-C.; Wang, C.- H.; Liang, B.; Zhang,
X.-H.; Deng, L.-J.; Liang, S.; Chen, J.- H.; Wu, Y.-D.; Yang, Z. J. Org. Chem. 2006, 71,
6992–6997; (c) Chavan, S. P.; Thakkar, M.; Kalbote, U. R. Tetrahedron Lett. 2007,
48, 535–537; (d) Yu, M.; Popchapsky, S. S.; Snider, B. B. J. Org. Chem. 2008, 73,
9065–9074; (e) Michalak, K.; Michalak, M.; Wicha, J. Tetrahedron Lett. 2008, 48,
6807–6809.
4.3.2.13. Cyclohexylideneacetaldehyde (13b). Ether–petroleum
ether (1:6), liquid. IR (film): 1674, 1625 cmꢁ1 1H NMR: 1.64–1.76
.
(m, 6H), 2.3 (t, 2H, J¼6.5 Hz), 2.71 (t, 2H, J¼6.5 Hz), 5.82 (d, 1H,
J¼8.3 Hz), 10.02 (d, 1H, J¼8.3 Hz). 13C NMR: 26.5, 28.5, 29.0, 30.0,
38.5, 125.7, 168.6, 191.0. Its spectroscopic data were in agreement
with those described in the literature.41
2. For examples of natural products bearing a b-disubstituted enone function, see:
(a) Fukinone: Naya, K.; Takagi, I.; Kawaguchi, Y.; Asada, Y.; Hirose, Y.; Shinoda,
N. Tetrahedron 1968, 24, 5871–5879; (b) Hernandulcin: Compadre, C. M.; Pez-
zuto, J. M.; Kinghorn, A. D.; Kamath, S. K. Science 1985, 227, 417–419; (c) Tet-
rahydrodicranenone B: Ichikawa, T.; Namikawa, M.; Yamada, K.; Sakai, K.;
Kondo, K. Tetrahedron Lett. 1983, 24, 3337–3340; (d) Azadiradione: Lavie, D.;
Levy, E. C.; Jain, M. K. Tetrahedron 1971, 27, 3927–3939; (e) Dichotenone A and
B: Ali, M. S.; Pervez, M. K.; Saleem, M.; Ahmed, F. Nat. Prod. Res. 2003, 17, 301–
306; (f) Dolabellatrienone: Miyaoka, H.; Isaji, Y.; Mitome, H.; Yamada, Y. Tet-
rahedron 2003, 59, 61–75; (g) Cyanthiwigin U: Pfeiffer, M. W. B.; Philipps, A. J. J.
Am. Chem. Soc. 2005, 127, 5334–5335; (h) Sarcodictyenone: Yamazaki, T.; Ishi-
kawa, M.; Uemura, M.; Kanda, Y.; Takei, H.; Asaoka, M. Tetrahedron 2008, 64,
1895–1900.
4.3.2.14. 2-t-Butyldiphenyloxymethyl-3-methyl-2-cyclohexen-1-
one (14b). Ether–petroleum ether (1:6), solid: mp 61–63 ꢀC. IR
(neat): 3049, 1667, 1634 cmꢁ1. 1.04 (s, 9H, 3 Me), 1.91 (quintuplet,
2H, J¼6.2 Hz, H-5), 1.99 (s, 3H, Me), 2.32–2.40 (m, 4H, H-6, H-4),
4.47 (s, 2H), 7.4 (m, 6H), 7.7 (m, 4H). 13C NMR: 19.5, 21.5, 22.1, 27.0
(3Me), 33.1, 37.6, 56.3, 127.6 (4C), 129.6 (2C), 134.0 (2C), 134.5, 135.8
(4C), 160.5, 197.6. HRMS calcd for C24H31O2Si (MþHþ) 379.2093;
found: 379.2094.
3. (a) Babler, J. H.; Coghlan, M. J. Synth. Commun. 1976, 469–474; (b) Dauben, W.
G.; Michno, D. M. J. Org. Chem. 1977, 42, 682–685; (c) Sundararaman, P.; Herz,
W. J. Org. Chem. 1977, 42, 813–819.
4. For examples of the oxidative rearrangement with chromium (VI)-reagents on
diversely functionalized tertiary allylic alcohols, see: (a) Brown, P. S.; McElroy,
A. B.; Warren, S. Tetrahedron Lett. 1985, 26, 249–251; (b) Ohler, E.; Zbiral, E.
Synthesis 1991, 357–361; (c) Nangia, A.; Rao, B. Tetrahedron Lett. 1993, 34, 2681–
2684; (d) Luzzio, F. A.; Moore, W. J. J. Org. Chem. 1993, 58, 2966–2971; (e) Surya
Prakash, G. K.; Tongco, E. C.; Mathew, T.; Vankar, Y. D.; Olah, G. A. J. Fluorine
Chem. 2000, 101, 199–202.
5. (a) Mehta, G.; Reddy, A. V. Tetrahedron Lett. 1979, 20, 2625–2628; (b) Nakano, T.;
Martin, A.; Rojas, A. Tetrahedron 1982, 38, 1217–1219; (c) Murai, A.; Abiko, A.;
Masamune, T. Tetrahedron Lett. 1984, 25, 4955–4958; (d) Mori, K.; Kato, M.
Tetrahedron Lett. 1986, 27, 981–982; (e) Alvarez, F. C.; Vander Meer, R. K.;
Lofgren, C. S. Tetrahedron 1987, 4, 2897–2900; (f) Drew, J.; Letellier, M.; Morand,
P.; Szabo, A. G. J. Org. Chem. 1987, 52, 4047–4052; (g) Majetich, G.; Lowery, D.;
Khetani, V.; Song, J.- S.; Hull, K.; Ringold, C. J. Org. Chem. 1991, 56, 3988–4001;
(h) Majetich, G.; Song, J.-S.; Leigh, A. J.; Condon, S. M. J. Org. Chem. 1993, 58,
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agoza, R. J. J. Nat. Prod. 1993, 56, 2133–2141; (j) Trost, B. M.; Pinkerton, A. B. Org.
Lett. 2000, 2, 1601–1603; (k) Nagata, H.; Miyazawa, N.; Ogasawara, K. Chem.
Commun. 2001, 1094–1095; (l) Hanada, K.; Miyazawa, N.; Ogasawara, K. Org.
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125, 1712–1713; (n) Boyer, F. D.; Hanna, I. Org. Lett. 2007, 9, 2293–2295.
6. (a) Liotta, D.; Brown, D.; Hoekstra, W.; Monahan, R., III. Tetrahedron Lett. 1987,
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1989, 30, 1033–1036.
4.3.2.15. 3-Methyl-2-cyclohepten-2-one (15b). Ether–petroleum
ether (1:3), liquid. IR (film): 1652 cmꢁ1. 1H NMR: 1.75–1.8 (m, 4H),
1.95 (s, 3H, Me), 2.42 (t, 2H, J¼5.7 Hz), 2.57 (t, 2H, J¼6.2 Hz), 5.92
(s, 1H). 13C NMR: 21.8, 25.5, 28.0, 34.9, 42.9, 130.2, 159.0, 204.2. Its
physical data were identical with those described in the
literature.32
¨
4.4. Study of the oxidative rearrangement of 1a with other
reoxidants of TEMPO
4.4.1. PhI(OAc)2 as a primary oxidant in the presence of Lewis acids
(Table 6, entry 2). To a solution of 1a (0.154 g, 1 mmol) in CH2Cl2
(3 mL) were added PhI(OAc)2 (0.386 g, 1.2 equiv), TEMPO
(15.6 mg, 10 mol %), Bi(OTf)3 (26 mg, 4 mol %). The reaction
mixture was stirred for 45 min at room temperature and poured
into a column of silica gel. Elution with EtOAc–petroleum ether
(5:95) gave the allylic acetate 1c (62 mg, 32%) as an oil; IR
(film):1725, 1660 cmꢁ1 1H NMR: 0.88 (t, 3H, J¼7 Hz, Me), 1.18–
1.42 (m, 4H), 1.59–1.82 (m, 4H), 1.88–2 (m, 4H), 2.02 (s, 3H, Me),
5.24 (br s, 1H, CHOAc), 5.43 (br s, 1H, CH]C). 13C NMR: 14.0,
19.2, 21.5, 22.4, 28.3, 28.4, 29.6, 37.3, 68.9, 119.3, 144.9, 170.9. Its
NMR data were consistent with the literature data.42 Further
elution with EtOAc–petroleum ether (1:6) furnished the enone
1b (62 mg, 41%), which NMR data were identical with those
described in 4.3.1.
7. (a) Shibuya, M.; Ito, S.; Takahashi, M.; Iwabuchi, Y. Org. Lett. 2004, 6, 4303–
4306; (b) Tello-Aburto, R.; Ochoa-Teran, A.; Olivo, H. F. Tetrahedron Lett. 2006,
47, 5915–5917.
8. (a) Shibuya, M.; Tomizawa, M.; Iwabuchi, Y. J. Org. Chem. 2008, 73, 4750–4752;
(b) Shibuya, M.; Tomizawa, M.; Iwabuchi, Y. Org. Lett. 2008, 73, 4715–4718.
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`
`
10. (a) Vatele, J.-M. Tetrahedron Lett. 2006, 47, 715–718; (b) Vatele, J.-M. Synlett
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11. (a) Vate`le, J.-M. Synlett 2008, 1785–1788; (b) Vate`le, J.-M. Synlett 2009,
2143–2145.
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1997, 249–267; (b) Leonard, N. M.; Wieland, L. C.; Mohan, R. S. Tetrahedron
2002, 58, 8373–8397; (c) Gaspard-Iloughmane, H.; Le Roux, C. Eur. J. Org. 2004,
2517–2532.
13. For examples of the use of molecular sieves as acid scavenger, see: (a) Vate`le,
J.-M. Tetrahedron 2002, 58, 5689–5698; (b) Urata, H.; Hu, N.-X.; Maekawa,
H.; Fuchikami, T. Tetrahedron Lett. 1991, 32, 4733–4736; (c) Banks, A. R.;
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15. For recent exemples of Re2O7- induced 1,3-isomerization of allylic alcohols, see:
(a) Hansen, E. C.; Lee, D. J. Am. Chem. Soc. 2006, 128, 8142–8143; (b) Park, S.; Lee,
D. Synthesis 2007, 2313–2316.
16. For other oxorhenium(VII) derivatives-catalyzed 1,3-allylic rearrangement of
allylic alcohols, see: Bellemin-Laponnaz, S.; Le Ny, J. P. Compt. Rend. Chem. 2002,
5, 217–224.
4.4.2. mCPBA as a primary oxidant (Table 7, entry 2). To a solution
of 1a (0.154 g, 1 mmol) in CH2Cl2 (3 mL) were added TEMPO
(15.6 mg, 10 mol %) and nBu4NBr (32 mg, 10 mol %). The reaction
mixture was cooled to 0 ꢀC and Bi(OTf)3 (65 mg, 10 mol %) and
mCPBA (294 mg, 1.2 equiv) were successively added. After stirring
the reaction mixture for 1 h at 0 ꢀC, a saturated solution of NaHCO3
was added. The aqueous phase was extracted once with CH2Cl2 and
the combined organic extracts were washed once with water, dried
(Na2SO4) and evaporated under reduced pressure. Purification of
the residue on silica gel using EtOAc–petroleum ether (1:5) gave
a mixture of the unsaturated ketone 1b and of the epoxide 1d
(ratio:1/3), which structure was confirmed by NMR spectra.38
Further elution with EtOAc–petroleum ether (1:3) afforded the
rearranged epoxide 1e (47 mg, 28%). 1H NMR: 0.91 (t, 3H, J¼7 Hz,
Me), 1.15–1.9 (m, 12H), 2.26 (br s, 1H, OH), 3.14 (s, 1H, H-2), 3.99
17. During their studies of TEMPO-mediated oxidative rearrangement of tertiary
allylic alcohols, Iwabuchi and co-workers have shown the modulating effect of
water on the reaction rate of the transformation. Water can either accelerate or
slow down the process depending on the reaction conditions (see Ref. 8).

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J.-M. Vate`le / Tetrahedron 66 (2010) 904–912
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