Remarkable substituent effects on the oxidizing ability of triarylbismuth dichlorides in alcohol oxidation

Article abstract of DOI:10.1021/jo0485740

Substituent effects on the oxidizing ability of triarylbismuth dichlorides were examined by intermolecular and intramolecular competition experiments on geraniol oxidation in the presence of DBU. It was found that the oxidizing ability of the dichlorides increases with increasing electron-withdrawing ability of the para substituents, and by introduction of a methyl group at the ortho position of the aryl ligands attached to the bismuth. The intermolecular and intramolecular H/D kinetic isotope effects observed for the competitive oxidation of p-bromobenzyl alcohols indicate that the rate-determining step involves C-H bond cleavage. Several primary and secondary alcohols were oxidized efficiently under mild conditions by the combined use of newly developed organobismuth(V) oxidants and DBU.

Full text of DOI:10.1021/jo0485740

Remarkable Substituent Effects on the Oxidizing Ability of
Triarylbismuth Dichlorides in Alcohol Oxidation
,
†
†
†
†
Yoshihiro Matano,* Teppei Hisanaga, Hisatsugu Yamada, Shingo Kusakabe,
‡
†
Hazumi Nomura, and Hiroshi Imahori
Department of Molecular Engineering, Graduate School of Engineering, Kyoto University,
Nishikyo-ku, Kyoto 615-8510, Japan, and Department of Chemistry, Graduate School of Science,
Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
matano@scl.kyoto-u.ac.jp.
Received August 16, 2004
Substituent effects on the oxidizing ability of triarylbismuth dichlorides were examined by
intermolecular and intramolecular competition experiments on geraniol oxidation in the presence
of DBU. It was found that the oxidizing ability of the dichlorides increases with increasing electron-
withdrawing ability of the para substituents, and by introduction of a methyl group at the ortho
position of the aryl ligands attached to the bismuth. The intermolecular and intramolecular H/D
kinetic isotope effects observed for the competitive oxidation of p-bromobenzyl alcohols indicate
that the rate-determining step involves C-H bond cleavage. Several primary and secondary alcohols
were oxidized efficiently under mild conditions by the combined use of newly developed organo-
bismuth(V) oxidants and DBU.
Pentavalent organobismuth compounds are potential
oxidants due to their inherent oxidizing ability derived
from the facile Bi /Bi redox process. This property of
bismuth has been utilized in alcohol oxidation, where
primary and secondary alcohols are oxidized to their
corresponding carbonyl compounds by several types of
organobismuth(V) reagents.2 In most cases, however,
tri(o-tolyl)bismuth dichloride oxidized a variety of alco-
hols in the presence of 1,8-diazabicyclo[5,4,0]undec-7-ene
(DBU) much more rapidly than triphenylbismuth dichlo-
V
III
1
4
ride and tri(p-tolyl)bismuth dichloride. These results
suggested to us that more efficient arylbismuth(V) oxi-
dants could be developed by tuning both the electronic
and the steric factors of the aryl ligands. Thus, we
decided to systematically investigate substituent effects
on the oxidizing ability of triarylbismuth dichlorides, and
to examine the nature of the transition state of the rate-
determining step. The results of the intermolecular and
intramolecular competition experiments on the oxidation
of alcohols by triarylbismuth dichlorides/DBU are re-
ported here.5 Oxidation of some alcohols with newly
developed oxidants, tris(p-trifluoromethylphenyl)bismuth
dichloride, tri(p-nitrophenyl)bismuth dichloride, and tri-
(o-methyl-p-nitrophenyl)bismuth dichloride is also re-
ported.
phenylbismuth(V) compounds of the type Ph
OH, Cl, Br, OAc, ONO , OBiPh Cl; X ) CO
3
BiX
2
(X )
have
2
a-f
2
3
2
3
)
been used, and little is known about the relationship
between the oxidizing ability and the structure of organyl
ligands attached to the bismuth. In 1981, Barton and co-
workers reported results of competition experiments on
the oxidation of allylic alcohols by Ar
3
BiX
2
(X ) Cl, Br,
BiX was
ONO ), in which the relative reactivity of Ar
2
3
2
estimated to be in the order: Ar ) p-tolyl < phenyl <
3
p-chlorophenyl < m-nitrophenyl. Recently, we found that
†
Graduate School of Engineering, Kyoto University.
‡
Graduate School of Science, Kyoto University.
(1) (a) Kitchin, J. P. In Organic Synthesis by Oxidation with Metal
Results and Discussion
Compounds; Mijs, W. J., De Jonge, C. R. H. I., Eds.; Plenum: New
York, 1986; Chapter 15, pp 817-837. (b) Postel, M.; Du n˜ ach, E. Coord.
Chem. Rev. 1996, 155, 127. (c) Suzuki, H.; Ikegami, T.; Matano, Y.
Synthesis 1997, 249. (d) Komatsu, N. In Organobismuth Chemistry;
Suzuki, H., Matano, Y., Eds.; Elsevier: New York, 2001; Chapter 5,
pp 371-440. (e) Leonard, N. M.; Wieland, L. C.; Mohan, R. S.
Tetrahedron 2002, 58, 8373.
Alcohol oxidation by arylbismuth(V) reagents is con-
sidered to proceed through two main steps: formation
of an alkoxybismuth(V) intermediate (A) and production
of a carbonyl compound via R-hydrogen abstraction. In
(2) (a) Challenger, F.; Richards, O. V. J. Chem. Soc. 1934, 405. (b)
Barton, D. H. R.; Kitchin, J. P.; Motherwell, W. B. J. Chem. Soc., Chem.
Commun. 1978, 1099. (c) Barton, D. H. R.; Lester, D. J.; Motherwell,
W. B.; Papoula, M. T. B. J. Chem. Soc., Chem. Commun. 1979, 705.
(3) See ref 2d. Potassium carbonate was used as a base. The relative
reactivity of Ar
3 2
BiX was determined from the relative ratios of
triarylbismuthanes (Ar
3
Bi) recovered from the reaction mixture, but
3
significant variation was observed for the yield of Ar Bi. Thus, the
(
d) Barton, D. H. R.; Kitchin, J. P.; Lester, D. J.; Motherwell, W. B.;
Papoula, M. T. B. Tetrahedron 1981, 37, Supplement 9, 73. (e) Dodonov,
V. A.; Zinov’eva, T. I.; Osadchaya, N. N. Zh. Obshch. Khim. 1988, 58,
reported relative rate values are not used here for quantitative
discussion.
7
12. (f) Zinov’eva, T. I.; Dolganova, N. V.; Dodonov, V. A.; Prezhbog, I.
(4) Matano Y.; Nomura, H. Angew. Chem., Int. Ed. 2002, 41, 3028.
(5) The substituent effects on the arylation of enolizable substrates
with triarylbismuth dichlorides were examined. See: (a) Barton, D.
H. R.; Bhatnagar, N. Y.; Finet, J.-P.; Motherwell, W. B. Tetrahedron
1986, 42, 3111. (b) Fedorov, A.; Combes, S.; Finet, J.-P. Tetrahedron
1999, 55, 1341.
G. Izv. Akad. Nauk. Ser. Khim. 1998, 681. (g) Suzuki, H.; Ikegami, T.;
Matano, Y. Tetrahedron Lett. 1994, 35, 8197. (h) Matano, Y.; Nomura,
H. J. Am. Chem. Soc. 2001, 123, 6443. (i) Matano, Y.; Nomura, H.;
Suzuki, H.; Shiro, M.; Nakano, H. J. Am. Chem. Soc. 2001, 123, 10954.
(
j) Mitsumoto Y.; Nitta, M. Bull. Chem. Soc. Jpn. 2003, 76, 1029.
10.1021/jo0485740 CCC: $27.50 © 2004 American Chemical Society
8676
J. Org. Chem. 2004, 69, 8676-8680
Published on Web 11/16/2004

Oxidizing Ability of Triarylbismuth Dichlorides
SCHEME 1
TABLE 1. Competitive Intermolecular Oxidation of 3
with 1a-m
entry
1
2 (rel ratioa)
entry
1
2 (rel ratioa)
1
2
3
4
5
6
1a + 1c 2a + 2c (80/20)
1a + 1d 2a + 2d (4/96)
1d + 1e 2d + 2e (3/97)
1e + 1f 2e + 2f (4/96)
1g + 1h 2g + 2h (65/35)
1g + 1i 2g + 2i (61/39)
7
8
1g + 1j 2 g + 2j (21/79)
1d + 1g 2d + 2g (60/40)
1f + 1k 2f + 2k (84/16)
1g + 1l 2g + 2l (60/40)
1g + 1m 2g + 2m (12/88)
9
10
11
a
1
Determined by H NMR.
SCHEME 2
2
NO
2
(5.8 × 10 ), although the difference in reactivity is
smaller than that observed for the ortho-unsubstituted
series 1a-f. In most cases, introduction of the o-methyl
groups increases the overall rate of the oxidation, and
this steric effect becomes more significant as the electron-
withdrawing ability of the para-substituents decreases.
Thus, 1i oxidizes 3 about 40 times faster than 1c,
whereas 1j only oxidizes 3 2.4 times faster than 1d. In
the case of the p-nitro derivatives 1f and 1k, introduction
of the o-methyl group retards the reactivity slightly. We
also examined the reactions with other ortho-substitu-
ented derivatives 1l,m. The o-ethyl derivative 1l oxidized
3
more slowly than the o-methyl derivative 1g, indicating
that a suitable size of substituent is necessary for
producing the high efficiency. The effect of the trifluoro-
methyl group is noteworthy. The p-CF
3
derivative 1e
oxidized 3 about 3.1 × 10 times faster than the p-Me
derivative 1c, whereas the o-CF derivative 1m oxidized
only 7 times faster than the o-Me derivative 1g. Thus,
3
3
our system using triarylbismuth dichloride (1) as an
oxidant and DBU as a base, the R-hydrogen is abstracted
by the aryl group attached to the bismuth, affording
equimolar amounts of carbonyl compound, arene, and ate
complex 2 (Scheme 1).6
3
the electronic effect of the o-trifluoromethyl group on the
rate of oxidation is quite different from that of the
p-trifluoromethyl group.
To evaluate the effects of substituents on the second
step, we next carried out competitive intramolecular
First, we determined the relative oxidizing abilities of
triarylbismuth dichlorides by means of competitive in-
termolecular oxidations, using a series of ortho/para-
substituted derivatives 1a-m (Scheme 2). DBU (1.0
equiv) was added to a toluene solution containing ge-
oxidations using triarylbismuth dichlorides bearing two
kinds of aryl groups (Ar1
Ar BiCl
2
: 1n-u). This avoids
2
2
the influence of the first step and enables us to estimate
the relative rates at which the aryl groups abstract the
R-hydrogen. Compounds 1n-u were prepared by oxida-
tive chlorination of the corresponding triarylbismuthanes
-
3
raniol 3 (5 × 10 M) and two kinds of dichlorides 1a-m
(
each 3 equiv) at 24 ( 1 °C. After 3 was oxidized to
geranial (4), the reaction mixture was concentrated in
vacuo and analyzed by H NMR spectroscopy. The
with sulfuryl chloride in CH
2
Cl
2
. Mixed triarylbismuth-
1
anes (Ar1
Ar Bi) were prepared from Ar BiOTf-HMPA
2
1
2
2
relative ratios of the two kinds of ate complexes produced
2
complexes and Ar MgBr according to the reported pro-
(
2a-m, depending on the reactants) were determined
from the integral ratios of their aromatic protons (Tables
and 2). The relative rates of 1d/1g and 1f/1k were found
7
cedure. Treatment of 1n-u with 3 in the presence of
DBU in toluene at 24 ( 1 °C gave two kinds of ate
complexes (Scheme 3). The ratios of unsymmetrical ate
complexes 2n-u vs symmetrical ate complexes 2b-d,g
1
to be 60/40 and 84/16, respectively. On the basis of these
results, the relative reactivities of all the dichlorides
1
were determined by H NMR spectroscopy. As shown in
1a-m were estimated. As shown in Table 2, the reaction
Tables 2 and 3, the electronic effect of the para-substit-
uents is negligible in comparison to that observed for the
intermolecular competition experiments. In contrast, the
steric effect on the second step is significant. For example,
the o-tolyl group of 1u abstracted the R-hydrogen 16
times faster than the p-chlorophenyl group. This is
probably because the Bi-C bonds of the alkoxybis-
muth(V) intermediate bearing the o-tolyl groups are
weakened due to steric congestion around the bismuth
center. The small electronic effect observed, as well as
the results from a radical trapping experiment, discards
rate increases with increasing electron-withdrawing abil-
ity of the para-substituents, and the relative rates for
the ortho-unsubstituted series 1a-f are in the following
2
order: Me (0.25) < H (1.0) < Cl (24) , CF
3
(7.7 × 10 ) ,
4
NO (1.9 × 10 ). A similar electronic effect of the para-
substituents was observed for the o-Me-substituted series
g-k: OMe (0.54) < Me (0.63) < H (1.0) < Cl (3.6) ,
2
1
(
6) During the oxidation of 2-propanol with tri(p-chlorophenyl)-
bismuth dichloride/DBU in CDCl , a type A intermediate was observed
), 3.94
), 7.62 (d, 6H, J ) 8.5 Hz, ArH), and
.28 (d, 6H, J ) 8.5 Hz, ArH). In the presence or absence of the alcohol,
3
1
by H NMR spectroscopy: δ 0.98 (d, 6H, J ) 6.0 Hz, CHMe
2
(
8
hept, 1H, J ) 6.0 Hz, CHMe
2
8,9
the possibility of any cationic and radical mechanisms.
a 1‚DBU type complex was also formed as an equilibrium mixture with
and DBU. Thus, the intermediate A may be formed via the complex
‚DBU.
1
1
(7) Matano, Y.; Miyamatsu, T.; Suzuki, H. Organometallics 1996,
15, 1951.
J. Org. Chem, Vol. 69, No. 25, 2004 8677

Matano et al.
intrad
TABLE 2. Substituent Effects Obtained from the Competition Experiments
substituent
intera
intrab
substituent
interc
0.54 (8.6)
0.63 (10)
1.0 (16)
3.6 (58)
p-OMe
p-Me
p-H
0.46
0.92
1.0
o-Me-p-OMe
o-Me-p-Me
o-Me-p-H
0.78 (14)
0.63 (11)
1.0 (18)
0.25
1.0
p-Cl
24
1.1
o-Me-p-Cl
0.67 (12)
2
4
p-CF3
p-NO2
7.8 × 10
1.9
2
3
1.9 × 10
o-Me-p-NO2
o-Et
o-CF3
5.8 × 10 (3.6 × 10 )
0.67 (11)
2
7.3 (1.2 × 10 )
a
Relative reactivity of the dichloride vs 1a. b Relative reactivity of the aryl group vs the phenyl group. Relative reactivity of the
dichloride vs 1g. Values in parentheses are the relative reactivity vs 1a. Relative reactivity of the aryl group vs the o-tolyl group. Values
c
d
in parentheses are the relative reactivity vs the phenyl group.
SCHEME 3
TABLE 3. Competitive Intramolecular Oxidation of 3
with 1n-u
entry
1
2 (rel ratioa)
entry
1
2 (rel ratioa)
1
2
3
4
1n 2c + 2n (20/80)
5
6
7
8
1r
1s
1t
2g + 2r (28/72)
2g + 2s (24/76)
2g + 2t (25/75)
1o
1p
1q
2b + 2o (52/48)
2d + 2p (17/83)
2d + 2q (46/54)
1u 2g + 2u (3/97)
a
1
Determined by H NMR.
isotope effects are similar to the intramolecular kinetic
isotope effects, indicating that the rate-determining step
involves R-hydrogen abstraction.10 The 3- to 4-fold prefer-
ence for loss of H relative to D observed in the intramo-
lecular competition experiments may support the con-
certed pathway.11
The substituent effects of the aryl ligands on each step
are summarized as follows: (1) The first step is sensitive
to the electronic character of the aryl ligands. As the
electron-withdrawing ability of the aryl ligands increases,
the electrophilicity of the bismuth center is enhanced,
which increases the forward rate of the first step. On the
other hand, introduction of a methyl group at the ortho
position seems to increase the steric congestion around
the bismuth center to destabilize the alkoxybismuth
It is likely that the R-hydrogen is abstracted in a
concerted reaction through a weakly polarized, cyclic
transition state. Thus, the R-hydrogen-abstracting apti-
tude of the aryl ligands strongly depends on the bond
dissociation energy of the Bi-C bonds of the alkoxybis-
muth(V) intermediate A.
To get some insight into the rate-determining step, we
then measured intermolecular and intramolecular H/D
kinetic isotope effects for the R-hydrogen abstraction. The
intermolecular competition reaction of 1e,g with a mix-
12
intermediates A as compared to the starting substrates.
As a result, the equilibrium is shifted to the left side. (2)
The second step is not susceptible to the electronic
character, but rather to the steric character of the aryl
ligands. Introduction of a methyl group at the ortho
position weakens the Bi-C bonds of A due to steric
reasons, which increases the rate of R-hydrogen abstrac-
tion. Therefore, to construct highly efficient Bi(V) oxi-
6 4 2 6 4 2
ture of p-BrC H CH OH and p-BrC H CD OH (each 3
equiv) quantitatively afforded the corresponding alde-
hydes (eq 1). The isotope effects were determined from
6 4 6 4
ratios of p-BrC H CHO/p-BrC H CDO by means of
1
H NMR spectroscopy. Similarly, the intramolecular
isotope effects were estimated by the reaction with
3 2
dants of the type Ar BiX , it is desirable to introduce an
electron-withdrawing substituent at the para position
and/or a moderately bulky substituent like a methyl
group at the ortho position by considering a balance
between these two effects. In this study, p-trifluorom-
ethylphenyl (1e), p-nitrophenyl (1f), and o-methyl-p-
nitrophenyl (1k) derivatives were found to be much
more effective than the previously reported o-tolyl de-
rivative 1g.
6 4
p-BrC H CH(D)OH (eq 2). Regardless of the structure of
(
10) If the first step consists of a slow equilibrium compared to the
second step, it would become a rate-determining step. In such a case,
however, a small secondary isotope effect should be observed for the
intermolecular competition reactions.
(
11) In the Swern oxidation of PhCH(D)OH, the intramolecular H/D
the aryl ligands, the observed intermolecular kinetic
isotope effect of 2.6 ( 0.3 was observed. See: Marx, M.; Tidwell, T. T.
J. Org. Chem. 1984, 49, 788.
(
8) Molecular Rearrangements; de Mayo, P., Ed.; Interscience: New
York, 1964; Vol. 1, p 22, and references therein.
9) Addition of excess 1,1-diphenylethene did not depress the yield
of 4, ruling out the involvement of free radical species.
3
(12) The intermediate A derived from the o-CF derivative 1m may
be destabilized as compared to the intermediate A derived from the
p-CF derivative 1e due to the electronic repulsion between the
o-trifluoromethyl substituents and the alkoxy oxygen atom.
(
3
8678 J. Org. Chem., Vol. 69, No. 25, 2004

Oxidizing Ability of Triarylbismuth Dichlorides
1
6
TABLE 4. Oxidation of Alcohols with 1e
p-bromobenzyl alcohol-R,R-d
2
were prepared by reduction of
p-bromobenzaldehyde and p-bromobenzoic acid ethyl ester,
4
respectively, with LiAlD . DBU was purified by distillation.
Other reagents were used as commercially received.
Triarylbismuth Dichlorides 1. General procedure:
Sulfuryl chloride (0.44 mL, 5.5 mmol) was added to a CH Cl
2 2
solution (30 mL) of triarylbismuthane (5.0 mmol) at -78 °C.
The reaction mixture was allowed to warm to room temper-
ature, and gently refluxed for 2-3 h for the substrates bearing
the ortho-substituents or the para-electron-withdrawing sub-
stituents. The resulting mixture was evaporated under reduced
pressure to leave a colorless or pale yellow solid, which was
2 2
recrystallized from CH Cl /hexane to give triarylbismuth
1
dichloride 1. New compounds were characterized by H NMR,
FABMS, and elemental analyses, and the data are sum-
marized in the Supporting Information.
Intermolecular Competition Reactions. A toluene solu-
tion of DBU (0.10 M × 0.20 mL, 0.020 mmol) was added to a
mixture of two kinds of triarylbismuth dichlorides 1a-j (0.060
mmol each), 3 (0.020 mmol), and toluene (2 mL) at 24 (1 °C.
The mixture was stirred for 0.5-3 h at the same temperature,
and the resulting mixture was concentrated under reduced
a
Isolated yield. b Data from ref 4.
TABLE 5. Oxidation of 2,2,2-Trifluoro-1-phenylethanol
pressure. The residue was taken up with CDCl
3
(ca. 2 mL)
and the resulting CDCl solution was measured immediately
3
1
by H NMR spectroscopy. Each reaction was carried out three
times and the average values are listed in Table 1. Due to the
low-yield formation of 2b as compared to 2a,c, the reliable data
could not be obtained for the reaction with use of 1b and 1a,c.
The signals due to 2a-m were assigned by comparison with
oxidant (equiv)
reaction conditions
yield/%a
1
1
1
1
g (1.1)
e (1.1)
f (1.1)
k (1.1)
C6D6, rt, 32 h
98b
>95
>95
>95
1
CDCl3, rt, 50 min
CDCl3, rt, 5 min
CDCl3, rt, 5 min
CH2Cl2, rt, 3 h
authentic specimen observed independently. The H NMR data
of 2a-m are summarized in the Supporting Information.
Intramolecular Competition Reactions. A toluene solu-
tion of DBU (0.10 M × 0.20 mL, 0.020 mmol) was added to a
mixture of 1k-r (0.020 mmol), 2 (0.020 mmol), and toluene
c
Dess-Martin (3.7)
76
a
NMR yield. b Data from ref 4. c Data from ref 14a. Isolated
(
4 mL) at 24 ( 1 °C. The reaction mixture was worked up and
yield.
1
analyzed by H NMR spectroscopy as described above. Each
reaction was carried out three times and the average values
With new bismuth(V) oxidants 1e,13 1f, and 1k in
hand, we examined the oxidation of some primary and
secondary alcohols. The reaction times and yields are
summarized in Tables 4 and 5, together with those
reported for 1g. As expected, the oxidation with 1e
proceeded more rapidly than that with 1g in all cases. It
is noteworthy that 2,2,2-trifluoro-1-phenylethanol can be
rapidly oxidized by 1e,f,k to the corresponding trifluoro-
methyl ketone at room temperature. The efficiency of
this oxidation is higher than that of the Dess-Martin
oxidation (Table 5).
In summary, we systematically examined the substitu-
ent effects on the oxidizing ability of triarylbismuth di-
chlorides by the competition experiments on geraniol
oxidation in the presence of DBU. Highly efficient Bi(V)
5
1
are listed in Table 3. The H NMR data of 2n-u are
summarized in the Supporting Information.
H/D Kinetic Isotope Experiments. A C
DBU (0.50 M × 0.020 mL, 0.010 mmol) was added to a
mixture of 1e,g (0.010 mmol), p-BrC CH OH (0.030
mmol), p-BrC CD OH (0.030 mmol), and C (1 mL) at
4 ( 1 °C. In the intramolecular competition experi-
ments, p-BrC CH(D)OH (0.010 mmol) was used as the
substrate. After 15-20 min, the reaction mixture was ana-
6 6
D solution of
6
H
4
2
6
H
4
2
6 6
D
2
6 4
H
14
1
lyzed by H NMR spectroscopy, and the ratio of p-BrC
6 4
H CHO/
1
4a
p-BrC H CDO was estimated by comparing the integral value
6
4
6 4
of the formyl proton of p-BrC H CHO with that of the aro-
matic protons of the two aldehydes. In these reactions, no
other products derived from the alcohols were detected. Each
reaction was carried out three times and the average values
are shown in eqs 1 and 2.
3 2
oxidants of the type Ar BiX were developed successfully
Oxidation of Alcohols by 1e/DBU. DBU (46 mg, 0.30
mmol) was added to a mixture of 1e (0.30 mmol), alcohol (0.27
mmol), and toluene (3 mL), and the resulting mixture was
stirred at room temperature. After the alcohol had been
consumed (checked by TLC), the precipitates were filtered off
through a thin Celite bed. The filtrate was concentrated under
reduced pressure to leave an oily residue, which was then
passed through a short silica gel column (ca. 50 mL of hexane/
EtOAc as eluent) to afford the carbonyl compound. The
reaction proceeded similarly on a larger scale (1.0-2.0 mmol
of alcohol). In the reaction of 4-phenyl-1-butanol, 4-phenylbu-
tanal was formed in a good NMR yield (ca. 90%) with a small
amount of byproduct bearing a formyl group.
by introducing an electron-withdrawing substituent at
the para position and/or a methyl group at the ortho
position.
Experimental Section
Compounds. Triarylbismuth dichlorides 1 were prepared
from the corresponding triarylbismuthanes and sulfuryl chlo-
1
5
ride as described below. p-Bromobenzyl alcohol-R-d and
(
13) Chen, X.; Ohdoi, K.; Yamamoto, Y.; Akiba, K. Organometallics
993, 12, 1857.
14) Trifluoromethyl carbinols are known to resist oxidation and,
1
(
at present, only a few methods are available for their conversion to
the corresponding trifluoromethyl ketones. For example, see: (a)
Linderman, R. J.; Graves, D. M. J. Org. Chem. 1989, 54, 661. (b)
Mark o´ , I. E.; Giles, P. R.; Tsukazaki, M.; Chell e´ -Regnaut, I.; Gautier,
A.; Brown, S. M.; Urch, C. J. J. Org. Chem. 1999, 64, 2433. (c) Kesavan,
V.; Bonnet-Delpon, D.; B e´ gu e´ , J.-P.; Srikanth, A.; Chandrasekaran,
S. Tetrahedron Lett. 2000, 41, 3327.
Oxidation of 2,2,2-Trifluoro-1-phenylethanol by 1e,f,k/
DBU. DBU (0.030 mmol) was added into an NMR tube
(15) Corey, E. J.; Link, J. O. Tetrahedron Lett. 1989, 30, 6275.
(16) Pollack, S. K.; Raine, B. C.; Hehre, W. J. J. Am. Chem. Soc.
1981, 103, 6308.
J. Org. Chem, Vol. 69, No. 25, 2004 8679

Matano et al.
containing a mixture of 1e (0.030 mmol), 2,2,2-trifluoro-1-
Japan (MEXT) and Toray Chemical Award in Synthetic
Organic Chemistry, Japan. H.I. also thanks Grant-in-
Aid from MEXT, Japan (21st Century COE on Kyoto
University Alliance for Chemistry) for financial support.
3
phenylethanol (0.027 mmol), and CDCl (1.0 mL), and the
resulting mixture was shaken quickly at room temperature.
1
The mixture was then monitored by H NMR at several
intervals, revealing that R,R,R-trifluoroacetophenone was formed
in a good conversion yield. The reactions with 1f and 1g were
similarly performed, where the starting alcohol was consumed
within 5 min.
Supporting Information Available: Spectral and
1
analytical data for 1h-u and H NMR data for 2. This
material is available free of charge via the Internet at
http://pubs.acs.org.
Acknowledgment. This work was supported by a
Grant-in-Aid (No. 14540494) from the Ministry of
Education, Culture, Sports, Science, and Technology of
JO0485740
8680 J. Org. Chem., Vol. 69, No. 25, 2004