Indium(I) bromide-mediated regioselective Markovnikov hydroselenation, diselenation and hydration of terminal alkynes with diphenyldiselenide in aqueous media

Article abstract of DOI:10.1055/s-2005-921931

The indium(III) selenolate obtained from indium(I) bromide and diphenyldiselenide promotes, alternatively, the Markovnikov hydroselenation, diselenation or hydration of terminal alkynes, depending on the experimental conditions. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2005-921931

LETTER
3091
Indium(I) Bromide-Mediated Regioselective Markovnikov Hydroselenation,
Diselenation and Hydration of Terminal Alkynes with Diphenyldiselenide in
Aqueous Media
R
egioselective
M
l
arkovn
o
ikov Hydros
v
elenation is Peppe,* Ernesto Schulz Lang, Gabriela Nanci Ledesma, Liérson Borges de Castro, Olga Soares do Rego
Barros, Paola de Azevedo Mello
Departamento de Química, Universidade Federal de Santa Maria-UFSM, Campus UFSM, Santa Maria, RS – 97105-900, Brazil
Fax +55(55)2208031; E-mail: peppe@quimica.ufsm.br
Received 8 September 2005
Continuing our studies on the applications of indium com-
Abstract: The indium(III) selenolate obtained from indium(I) bro-
pounds in organic synthesis, we examine here the hy-
mide and diphenyldiselenide promotes, alternatively, the Mark-
droselenation of unactivated alkynes with indium(III)
ovnikov hydroselenation, diselenation or hydration of terminal
selenolates in aqueous media. We envisaged this reaction
on observing that the compounds XIn(SePh)2 (X = Br, I),
prepared from InX and PhSeSePh in THF, MeCN or
CH2Cl2 and X2InSePh, obtained from InX and PhSeX in
THF or CH2Cl2, readily decompose under moisture.
Therefore, we first examined the nature of this decompo-
sition. To a freshly prepared solution of Br2InSePh in
THF, under N2 atmosphere, was added an equivalent
amount of 2,2¢-dipyridyl followed by a 5-fold excess of
water; the resulting solution was allowed to contact with
air. This treatment resulted in the slow deposition of col-
orless crystals of [Br2InOH(bipy)]2·4THF (Scheme 2).5
Benzeneselenol could not be isolated, since it was com-
pletely oxidized to diphenyldiselenide by air.
alkynes, depending on the experimental conditions.
Key words: indium(I) bromide, diphenyldiselenide, vinyl se-
lenides, vinyl diselenides, hydration of alkynes, aqueous media
For many years, the interest in indium chalcogenates was
related to their use as precursors of semiconductors type
InE (E = chalcogene).1 Only recently, it was demonstrat-
ed that some of these compounds can, conveniently, be
used as useful reagents in organic transformations
(Scheme 1). IIn(EPh)2 (E = Se, Te) promotes the hydro-
chalcogenation of 2-alkyn-1-ol derivatives, in non-aque-
ous media, with rigorous regio-, and stereochemical
control; the products correspond to Markovnikov adducts
resulting of an anti addition of the chalcogenol constitu-
ents across the triple bonds.2 IIn(SePh)2 promotes the
ring-opening reaction of epoxydes to the corresponding b-
hydroxy selenides with rigorous regioselectivity; the nu-
cleophile incorporation at the less hindered carbon atom
was observed for alkyl-substituted epoxides, and at the
benzylic carbon atom for aryl derivatives.3 Further,
IIn(SePh)2 was used to prepare unsymmetrical selenides
from organyl halides.4
Br
THF
2
2 InBr + 2 BrSePh
In
SePh
Br
bipy
bipy
H2O
H
O
Br
Br
Br
O2
R3
In
In
R2
PhSeSePh
2 PhSeH
+
OH
R2
H
Br
OH
CH2Cl2
i
O
H
R1
bipy
R3
R1
EPh
(E = Se, Te; R1, R2, R3 = alkyl and aryl)
Scheme 2 Decomposition of Br2InSePh by moisture
O
OH
R3
R4
R1
CH2Cl2
[Br2InOH(bipy)]2·4THF was characterized by X-ray
means.6 The compound, in the solid state, is a centrosym-
metric dimer. The dimerization occurs through the hy-
droxylic oxygen atom, leading to a planar In2O2 four-
membered ring. Two bromine and one bidentate 2,2-dipy-
ridyl ligands complete the hexacoordination at each metal
center. The geometrical arrangement around the indium
centers is a distorted octahedron guarding a cis-relation-
ship between each pair of similar ligands. The THF mole-
cules are loosely held in the lattice and do not show any
interaction with the indium complex.
ii
IIn(EPh)2
+
EPh
R4
R1
R2
R2
R3
( E = Se; R1, R2, R3, R4 = alkyl and aryl)
CH2Cl2
iii
(E = Se; Y = Cl, Br, I, R = alkyl,
benzyl, allyl, etc.)
R-EPh
R-Y
Scheme 1 Organic reactions promoted by indium chalcogenates
SYNLETT 2005, No. 20, pp 3091–3094
Advanced online publication: 28.11.2005
1
9
.1
2
.2
0
0
5
DOI: 10.1055/s-2005-921931; Art ID: S08405ST
© Georg Thieme Verlag Stuttgart · New York

3092
C. Peppe et al.
LETTER
When Br2InSePh or BrIn(SePh)2 prepared in THF or
CH2Cl2 is allowed to react with a terminal alkyne 1 (hex-
1-yne, hept-1-yne or dec-1-yne), no sign of reaction is ob-
tained even after prolonged contact between the reagents.
But, when BrIn(SePh)2 is generated in aqueous ethanol
(95%) and in the complete absence of oxygen, the
Markovnikov hydroselenation product 2 (Scheme 3) is
formed after three hours at room temperature
(Scheme 3).7 It is perfectly feasible to isolate compounds
2 by column chromatography in silica gel with hexane,
but extending the time of reaction, we have observed
isomerization of 2 into the internal vinyl selenides 2¢.8 The
isomerization 2 → 2¢ also occurs slowly in CHCl3
solutions; in this case, the reaction is complete after one
week at room temperature.9
2 InBr + 2 PhSeSePh
n
n
EtOH 95%, 24 h, ∆
O
O
4
5
a
b
c
n
5
6
10
90
5 (%)
70
92
Scheme 4 Hydration of diynes promoted by InBr and PhSeSePh
InBr + PhSeSePh
SePh
Cl
2
2
EtOH 95%, 24 h, ∆
75%
O
6
Equation 1
The reaction of terminal arylalkynes with BrIn(SePh)2 be-
haves differently. From phenylacetylene, we have isolat-
ed a low yield (20%) of a 9:1 mixture of (E)- and (Z)-1,2-
bis(phenylseleno)-1-phenylethylene, under identical ex-
perimental conditions. These regioisomers have been
prepared from diphenyldiselenide, under conditions for
generating the phenylseleno radical (UV radiation).13 It is
well known that the phenylseleno radical is produced by
the exposure of phenylselenol to O2.14 With this last fact
in mind, together with our finding that indium(III) seleno-
lates are readily hydrolyzed to produce the corresponding
selenol (see above), we carried out the reaction of phenyl-
acetylene with diphenyldiselenide in the presence of cata-
lytic amount of InBr (10 mol%) open to the laboratory
atmosphere. After four hours of reflux, the mixture of the
regiosomers (E)- and (Z)-1,2-bis(phenylseleno)-1-phe-
nylethylene (9:1, E:Z) was obtained in 80% yield.15 We
envisage the diselenation of the triple bond occuring
through the pathway depicted in Scheme 5.
RH2C
InBr + PhSe-SePh
RH2C
EtOH 95%, 25 °C
2
3 h, 70–80%
PhSe
1
InBr + PhSeSePh
EtOH 95%, 78 °C
24 h, 82–90%
48 h
O
R
InBr3
EtOH 95%
78 °C, 24 h
R
3
2'
SePh
a
b
c
R
n-C3H7, n-C4H9, n-C7H15
2 (%)
70
80
–
82
80
–
90
2' (%) 68
3 (%)
–
Scheme 3 BrIn(SePh)2-promoted hydroselenation and hydration of
terminal alkynes
A freshly prepared sample of the vinylic selenide 2c (1
mmol) was heated in aqueous ethanol (2 mL) containing
an equimolar amount of indium tribromide. This proce-
dure affords decan-2-one (3c). Alternatively, the ketones
3 were obtained directly from the alkynes 1 by submitting
them to a refluxing EtOH solution (95%) with the indium
selenolate derived from InBr and diphenyldisselenide.10
This sequenced reactions are especific for terminal
alkynes, and no products were detected from the internal
alkyne, octyne-4, even after prolonged heating.
BrIn(OH)2
PhSeH
O2
H2O
BrIn(SePh)2
Ph
PhSe
InBr
PhSeSePh
Ph
Ph
SePh
The net result of the sequence of reactions is a new proto-
col for hydration of terminal alkynes promoted by indium
monobromide and diphenyldiselenide. We applied this
methodology to obtain alkanediones 5 in high yields, from
diynes 4 (Scheme 4).11,12
SePh
PhSe
Scheme 5 Suggested catalytic path for the InBr-promoted diselena-
tion of phenylacetylene
The indium(III) selenolate obtained from InBr and diphe-
nyldiselenide reacts with 5-chloropent-1-yne to afford 5-
phenylselenopentan-2-one (6, Equation 1) whose forma-
tion is rationalized in terms of consecutive hydration of
triple bond and nucleophilic displacement of chloride by
the indium selenolate.10
The reactivity of indium(III) selenolates towards alkynes
in aqueous media is understood in terms of the sequence
of reactions described in Scheme 6, where the proposed
equilibrium reaction between the indium(III) hydroxide
species and benzeneselenol is the key process governing
the nature of the products (hydroselenation vs. diselena-
tion).
Synlett 2005, No. 20, 3091–3094 © Thieme Stuttgart · New York

LETTER
Regioselective Markovnikov Hydroselenation
3093
L
of 2,2¢-dipyridyl (bipy) dissolved in 5 mL of THF. As soon
as the solid InBr dissolved giving a pale yellow solution, the
stirring was interrupted and the bipy solution added
dropwise. After addition of the bipy, H2O (5 mmol) was
added, and the flask opened to the lab atmosphere and
monitored for precipitation of colorless crystals. As soon as
these crystals start to deposit in the vessel, any solid
impurities were filtered and the crystals allowed to grow.
This treatment leaded to the deposition of
[Br2InOH(bipy)]2·4THF (42 mg, 0.05 mmol, 10%) after 24
h at r.t. These crystals become an amorphous powder, upon
drying. Analysis of the powder revealed loss of THF. Anal.
Calcd for [Br2InOH(bipy)]2·2THF (%): Br, 30.8; In, 22.1.
Found (%): Br, 30.7; In, 21.9. After removal of
[Br2InOH(bipy)]2·4THF, the THF solution was transferred
to a separation funnel and partitioned in H2O–CH2Cl2. The
CH2Cl2 solution was pumped to dryness and the residue was
purified by column chromatography in silica/hexane to give
PhSeSePh (47 mg, 0.15 mmol, 30%) melting at 60 °C (lit.17
63 °C).
L
L
In
In
SePh + H2O
In
OH
+ PhSeH
L
PhSe
L
L
In
OH
OH
+ PhSeH
H
L
L
active species in
radicalar addition
(diselenation)
active species in
ionic addition
(hydroselenation)
R
R
R
SePh
R
PhSe
PhSe
Scheme 6 Proposed intermediates for InBr-mediated hydroselena-
tion and diselenation of terminal alkynes
(6) Electronic Supplementary Information available:
crystallographic data for the compound
We conclude noting that the reaction leading to the Mark-
ovnikov hydroselenation of terminal alkynes is a useful
finding, since these products can only be selectively ob-
tained, in lower yields, from the highly toxic, air sensitive
and odorous benzeneselenol with Pt(PPh3)4 as catalyst,9 or
as a part of a complex mixture of products containing the
diselenated and the anti-Markovnikov adducts using
palladium catalysts.9,16 This reaction complements our
earlier studies on the hydroselenation of 2-alkyn-1-ol de-
rivatives with the analogous indium(III) selenolate, ob-
tained from indium monoiodide, which also produced
Markovnikov adducts.2a The sum of these results strongly
suggests that the regiochemistry of hydroselenation of tri-
ple bonds mediated by indium(III) selenolates is of gener-
al scope. We finally note that the reaction of hydration of
terminal alkynes to their corresponding methylketones
produces excellent yields; the mild reaction conditions,
suppressing strong acids and expensive transition metal
catalysts, are surely attractive to the organic synthetic
chemist.
[Br2InOH(bipy)]2·4THF: CCDC No 279659.
(7) The Markovnikov hydroselenation of the alkynes involved
the following steps: aqueous EtOH (95%, 2 mL) was
deoxygenated by refluxing it, under N2 atmosphere, for 2 h
in a Schlenk tube. After cooling to r.t., the tube was charged
with PhSeSePh (314 mg, 1 mmol) and InBr (195 mg, 1
mmol). Continuous stirring led to the dissolution of the red
solid InBr after 15–30 min. At this point, the alkyne (1
mmol) was added via syringe, and the reaction monitored by
TLC. After 3 h, the reaction was quenched with H2O and the
organics extracted with CH2Cl2 (2 × 10 mL). The extract
was dried (Na2SO4) and evaporated to dryness under vacuo.
The oily residue was purified by columnn chromatography
(silica gel/hexane) to produce the vinylic selenides 2; yields
are given in Scheme 3. Spectroscopic Data for Compounds
2a–c are as follow:
2-Phenylselenohex-1-ene (2a) [63831-76-5]:9 yield 70%;
colorless oil. 1H NMR (CDCl3): d = 7.50 (m, 2 H), 7.22 (m,
3 H), 5.43 (s, 1 H), 5.08 (s, 1 H), 2.25 (t, J = 7.4 Hz, 2 H),
1.47 (quint., J = 7.3 Hz, 2 H), 1.27 (sext., J = 7.4 Hz, 2 H),
0.85 (t, J = 7.3 Hz, 3 H). 13C NMR and DEPT-135 (CDCl3):
d = 143.44 (Cquat.), 134.66 (Car-H), 129.11 (Car-H), 129.06
(Cquat.), 127.63 (Car-H), 116.05 (=CH2), 38.01 (CH2), 30.82
(CH2), 21.88 (CH2), 13.79 (CH3).
2-Phenylseleno-hept-1-ene (2b) [211189-33-2]:18 yield
80%; colorless oil. 1H NMR (CDCl3): d = 7.47 (m, 2 H),
7.22 (m, 3 H), 5.41 (s, 1 H), 5.03 (s, 1 H), 2.20 (t, J = 7.3 Hz,
2 H), 1.46 (quint., J = 7.3 Hz, 2 H), 1.20 (m, 4 H), 0.80 (t,
J = 7.1 Hz, 3 H). 13C NMR (CDCl3): d = 143.52, 134.68,
129.13, 129.09, 127.67, 116.13, 38.31, 31.01, 28.37, 22.39,
14.00.
Acknowledgment
We are grateful to CNPq and FAPERGS for the award of scolar-
ships to P.D.M. and L.B.D., respectively.
References
2-Phenylselenodec-1-ene (2c): colorless oil. 1H NMR
(CDCl3): d = 7.48 (m, 2 H), 7.22 (m, 3 H), 5.43 (s, 1 H), 5.04
(s, 1 H), 2.21 (t, J = 7.3 Hz, 2 H), 1.47 (quint., J = 7.3 Hz, 2
H), 1.20 (s, 10 H), 0.82 (t, J = 6.8 Hz, 3 H). 13C NMR and
DEPT-135 (CDCl3): d = 143.50 (Cquat.), 134.67 (Car-H),
129.13 (Car-H), 129.04 (Cquat.), 127.65 (Car-H), 116.07
(=CH2), 38.32 (CH2), 31.83 (CH2), 29.32 (CH2), 29.19
(CH2), 28.81 (CH2), 28.67 (CH2), 22.64 (CH2), 14.09 (CH3).
(8) Compounds 2¢a were prepared as a 2:3 mixture of
stereoisomers (Z:E) following the same experimental
conditions described above,7 except the reaction time, which
in this case was 48 h.
(1) Lazell, M.; O’Brien, P.; Otway, D. J.; Park, J. H. J. Chem.
Soc., Dalton Trans. 2000, 4479.
(2) (a) Barros, O. S. D.; Lang, E. S.; de Oliveira, C. A. F.; Peppe,
C.; Zeni, G. Tetrahedron Lett. 2002, 43, 7921. (b) Barros,
O. S. D.; Lang, E. S.; Peppe, C.; Zeni, G. Synlett 2003, 1725.
(3) Barros, O. S. D.; de Carvalho, A. B.; Lang, E. S.; Peppe, C.
Lett. Org. Chem. 2004, 1, 43.
(4) (a) Ranu, B. C.; Mandal, T. J. Org. Chem. 2004, 69, 5793.
(b) Ranu, B. C.; Mandal, T.; Samanta, S. Org. Lett. 2003, 5,
1439.
(5) [Br2InOH(bipy)]2·4THF was prepared by stirring equimolar
quantities of InBr and PhSeBr (1 mmol) in 20 mL of dry
THF (Na/benzophenone), in a three-neck round-bottom
flask, equipped with an addition funnel charged with 1 mmol
(Z,E)-2-Phenylselenohex-2-ene (2¢a):9 colorless oil. 1H
NMR (CDCl3): d = 7.40 (m, 2 H), 7.19 (m, 3 H), 5.91 (t,
Synlett 2005, No. 20, 3091–3094 © Thieme Stuttgart · New York

3094
C. Peppe et al.
LETTER
J = 7.4 Hz, 0.4 H), 5.74 (t, J = 7.0 Hz, 0.6 H), 2.19 (q, J = 7.3
Hz, 1.2 H), 2.04 (q, J = 7.3 Hz, 0.8 H), 1.95 (s, 3 H), 1.38
(sext, J = 7.4 Hz, 2 H), 0.88 (t, J = 7.3 Hz, 1.8 H), 0.87 (t,
J = 7.3 Hz, 1.2 H). 13C NMR and DEPT-135 (CDCl3):
d = 137.46 (C–H), 134.67 (C–H), 133.08 (C–H), 132.55 (C–
H), 130.56 (Cquat), 129.75 (Cquat), 128.99 (C–H), 128.91 (C–
H), 127.43 (Cquat), 126.80 (C–H), 126.77 (C–H), 125.69
(Cquat.), 33.90 (CH2), 31.54 (CH2), 26.47 (CH3), 22.58 (CH2),
22.40 (CH2), 19.98 (CH2), 13.78 (CH3), 13.70 (CH3). MS
(70 eV, EI, for 80Se): m/z (unassigned Z,E-isomers, %): 240
(24, 40) [M], 157 (17, 10), 130 (9, 64), 116 (100, 4), 55 (87,
100).
Tetradecan-2,13-dione (5c) [7029-11-0]:22 yield 90%;
colorless solid; mp 74 °C. 1H NMR (CDCl3): d = 2.34 (t,
J = 7.5 Hz, 4 H), 2.07 (s, 6 H), 1.49 (quint., J = 7.3 Hz, 4 H),
1.19 (br s, 12 H). 13C NMR (CDCl3): d = 209.25, 43.79,
29.80, 29.36, 29.33, 29.14, 23.86. MS (70 eV, EI):
m/z (%) = 211 (2), 169 (8), 58 (100).
(12) (a) For hydration of alkynes catalyzed by mercury salts, see:
Budde, W. L.; Dessy, R. E. J. Am. Chem. Soc. 1963, 85,
3964. (b) For hydration of alkynes catalyzed by transition
metals, see: Lucey, D. W.; Atwood, J. D. Organometallics
2002, 21, 2481; and references therein.
(13) Ogawa, A.; Yokoyama, H.; Yokoyama, K.; Masawaki, T.;
Kambe, N.; Sonoda, N. J. Org. Chem. 1991, 56, 5721.
(14) (a) Masawaki, T.; Uchida, Y.; Ogawa, A.; Kambe, N.;
Miyoshi, N.; Sonoda, N. J. Phys. Org. Chem. 1988, 1, 115.
(b) Masawaki, T.; Ogawa, A.; Kambe, N.; Murai, S.;
Sonoda, N. J. Phys. Org. Chem. 1988, 1, 119.
(9) The isomerization 2a → 2¢a was detected before in CDCl3
solutions. As in our case, Beletskaya and co-workers found
a 2:3 (Z:E) mixture of isomers: Ananikov, V. P.; Malyshev,
D. A.; Beletskaya, I. P.; Aleksandrov, G. G.; Eremenko, I. J.
Organomet. Chem. 2003, 679, 162.
(10) Heptan-2-one (3b) [110-43-0]:19 colorless liquid. 1H NMR
(CDCl3): d = 2.39 (t, J = 7.5 Hz, 2 H), 2.10 (s, 3 H), 1.54
(quint., J = 7.3 Hz, 2 H), 1.26 (m, 4 H), 0.86 (t, J = 6.8 Hz, 3
H). 13C NMR (CDCl3): d = 209.16, 43.66, 31.27, 29.71,
23.47, 22.34, 13.82.
(15) (E)-1-Phenyl-1,2-phenylselenoethene [132330-37-1]:13 1
H
C
NMR (CDCl3): d = 7.09–7.52 (m, 15 H), 7.02 (s, 1 H). 13
NMR and DEPT-135 (CDCl3): d = 139.51 (Cquat.), 133.01
(CH), 132.08 (CH), 131.13 (Cquat.), 130.62 (Cquat.), 130.44
(Cquat.), 129.24 (CH), 129.15 (CH), 128.59 (CH), 128.28
(CH), 128.24 (CH), 127.43 (CH), 127.40 (CH), 126.04
(CH). MS (70 eV, EI for 80Se): m/z (%) = 416 (42) [M], 259
(56), 178 (100), 157 (71). We were not able to obtain a pure
sample of the minoritary Z-isomer for NMR studies;
nevertheless GC-MS analysis, 416 [M], is consistent with
the proposed structure.
Decan-2-one (3c) [693-54-9]:20 colorless liquid. 1H NMR
(CDCl3): d = 2.35 (t, J = 7.4 Hz, 2 H), 2.06 (s, 3 H), 1.50
(quint., J = 7.2 Hz, 2 H), 1.21 (br s, 10 H), 0.81 (t, J = 7.2 Hz,
3 H). 13C NMR and DEPT-135 (CDCl3): d = 208.94 (C=O),
43.62 (CH2), 31.68 (CH2), 29.60 (CH3), 29.22 (CH2), 29.04
(CH2), 28.99 (CH2), 23.73 (CH2), 22.49 (CH2), 13.89 (CH3).
MS (70 eV, EI): m/z (%) = 156 (2) [M], 138 (10), 113 (10),
99 (82), 71 (100).
(16) Kuniyasu, H.; Ogawa, A.; Sato, K.-I.; Ryu, I.; Sonoda, N.
Tetrahedron Lett. 1992, 33, 5525.
5-Phenylselenopentan-2-one (6) [66241-86-9]:2a,21 1H NMR
(CDCl3): d = 7.41 (m, 2 H), 7.18 (m, 3 H), 2.83 (t, J = 7.1
Hz, 2 H), 2.49 (t, J = 7.1 Hz, 2 H), 2.01 (s, 3 H), 1.87 (quint.,
J = 7.0 Hz, 2 H). 13C NMR (CDCl3): d = 207.74, 132.44,
129.84, 128.94, 126.73, 42.82, 29.80, 27.00, 23.84.
(11) Nonan-2,8-dione (5a) [30502-73-9]:22 yield 70%; colorless
liquid. 1H NMR (CDCl3): d = 2.36 (t, J = 7.3 Hz, 4 H), 2.06
(s, 6 H), 1.51 (quint., J = 7.5 Hz, 4 H), 1.21 (quint., J = 6.8
Hz, 2 H). 13C NMR (CDCl3): d = 208.97, 43.34, 29.85,
28.49, 23.37. MS (70 eV, EI): m/z (%) = 138 (10), 99 (61),
71 (100).
(17) Sharpless, K. B.; Lauer, R. F. J. Am. Chem. Soc. 1973, 95,
2697.
(18) Ogawa, A.; Kudo, A.; Hirao, T. Tetrahedron Lett. 1998, 39,
5213; report the preparation of this compound, but do not
describe spectroscopic data..
(19) Casado, R.; Contel, M.; Laguna, M.; Romero, P.; Sanz, S. J.
Am. Chem. Soc. 2003, 125, 11925.
(20) Ragagnin, G.; Betzemeier, B.; Quici, S.; Knochel, P.
Tetrahedron 2002, 58, 3985.
(21) Liotta, D.; Sunay, U.; Santiesteban, H.; Markiewicz, W. J.
Org. Chem. 1981, 46, 2605.
Decan-2,9-dione (5b) [16538-91-3]:23 yield 92%; colorless
solid; mp 52–53 °C. 1H NMR (CDCl3): d = 2.35 (t, J = 7.4
Hz, 4 H), 2.06 (s, 6 H), 1.50 (quint., J = 6.8 Hz, 4 H), 1.20 (t,
J = 7.3 Hz, 4 H). 13C NMR (CDCl3): d = 209.01, 43.57,
29.78, 28.86, 23.56. MS (70 eV, EI): m/z (%) = 170 (1) [M],
152 (19), 128 (13), 113 (47), 58 (100).
(22) (a) Nishinaga, A.; Rindo, K.; Matsuura, T. Synthesis 1986,
1038. (b) Zahalka, H. A.; Januszkiewicz, K.; Alper, H. J.
Mol. Catal. 1986, 35, 249.
(23) Satoh, T.; Taguchi, D.; Suzuki, C.; Fujisawa, S. Tetrahedron
2001, 57, 493.
Synlett 2005, No. 20, 3091–3094 © Thieme Stuttgart · New York