Oxidative nucleophilic substitution of hydrogen in nitroarenes by silyl enol ethers

Article abstract of DOI:10.1016/S0040-4020(03)01021-4

Enolates generated by treatment of silyl ketene acetals and enol ethers with fluoride ion sources add to nitroarenes to produce σ^H adducts that oxidize either with KMnO₄ to give substituted nitroarenes or with dimethyldioxirane to give substituted phenols. In the latter case the oxidation results in replacement of the nitro group with a hydroxy group. It was shown that high effectiveness of these reactions is not due to stabilization of the σ^H adducts via O-silylation but due to the nature of the accompanying cation.

Full text of DOI:10.1016/S0040-4020(03)01021-4

Tetrahedron 59 (2003) 6261–6266
Oxidative nucleophilic substitution of hydrogen in nitroarenes by
silyl enol ethers
*
Mieczysław Ma˛kosza and Marek Surowiec
Institute of Organic Chemistry, Polish Academy of Sciences, ul. Kasprzaka 44/52, PL-01-224 Warsaw, Poland
Received 11 February 2003; revised 3 June 2003; accepted 26 June 2003
Abstract—Enolates generated by treatment of silyl ketene acetals and enol ethers with fluoride ion sources add to nitroarenes to produce sH
adducts that oxidize either with KMnO4 to give substituted nitroarenes or with dimethyldioxirane to give substituted phenols. In the latter
case the oxidation results in replacement of the nitro group with a hydroxy group. It was shown that high effectiveness of these reactions is
not due to stabilization of the sH adducts via O-silylation but due to the nature of the accompanying cation.
q 2003 Elsevier Ltd. All rights reserved.
1. Introduction
ONSH. High yields were rationalized in term of stabiliz-
ation of the sH adducts via silylation. The aim of this study
was to verify that supposition and to explore other oxidative
transformations of the respective sH adducts.
In our previous papers1,2 we have reported that in the
addition of the 2-phenylpropionitrile carbanion to nitro-
benzene and its derivatives the equilibrium is shifted to the
sH adducts and that these adducts are efficiently oxidized by
external oxidants such as KMnO4 in liquid ammonia
(pathway a in Scheme 1) and dimethyldioxirane (DMD) in
acetone (pathway b in Scheme 1). These two oxidants gave
different products leading to an assumption that they react
with the sH adducts at different places. Permanganate anion
presumably attacks the sH adduct at the addition site of the
nucleophile, producing substituted nitroarenes—products of
oxidative nucleophilic substitution of hydrogen (ONSH),1
whereas oxidation with DMD proceeds at the carbon
bearing the nitro group giving substituted phenols.2
2. Results and discussion
The reaction of silyl ketene acetal 5a with nitrobenzenes
4a–d were carried out in the presence of an equivalent of
TASF in THF and then the resulting sH adducts were
oxidized with KMnO4 in liquid ammonia.6 The expected
products of ONSH were formed in good yield. When DMD
in acetone was used for oxidation of the sH adducts,
substituted phenols were the main products accompanied
with some amounts of substituted nitro compounds,
products of ONSH (Scheme 2).
It was also observed that treatment of this sH adduct with
Me3SiCl gave a substituted nitroso compound, apparently
via silylation of the nitro group followed by elimination of
silanol (pathway c in Scheme 1).3 This reaction is similar to
that observed when sH adducts of the Grignard reagents are
treated with strong acids4 and can be considered as an
intramolecular redox process.
Treatment of 5a and nitroanisole with TASF under the same
conditions resulted in recovery of the nitroarene suggesting
that nucleophilic addition to this less electrophilic arene is
unfavorable.
It is know that the bulky enolate of 5a added to nitrobenzene
in the para position whereas addition of ethyl trimethyl-
silylacetate 5b occur ortho to the nitro group predomi-
nately.5b To avoid formation of products mixtures we
studied the reaction of 5b with p-chloronitrobenzene 4e.
The sH adduct produced when 5b and 4e were treated with
TASF was efficiently oxidized with DMD giving ethyl
(5-chloro-2-hydroxyphenyl)acetate 8b in 62% yield.
Oxidation with KMnO4 in liquid NH3 was less satisfactory
giving the expected ONSH product 8a in low yield
(Scheme 3). Apparently the product 8a, being a strong CH
acid, is deprotonated and further oxidized. It was observed
The sH adducts can also be generated by reaction of
nitroarenes with silyl acetals of ketenes or silyl enol ethers
in the presence of fluoride ion, usually provided by
tris(dimethylamino)sulfonium difluorotrimethylsiliconate
(TASF).5 These sH adducts may be oxidized with DDQ or
Br2 to give nitroarylated esters or ketones the products of
Keywords: carbanions; dimethyldioxirane; nitroarenes; oxidation; phenols.
*
Corresponding author. Tel.: þ48-22-6318788; fax: þ48-22-6326681;
e-mail: icho-s@icho.edu.pl
0040–4020/$ - see front matter q 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/S0040-4020(03)01021-4

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M. Ma˛kosza, M. Surowiec / Tetrahedron 59 (2003) 6261–6266
Scheme 1.
earlier that oxidation of the sH adducts of phenylacetonitrile
to nitrobenzenes with KMnO4 in liquid ammonia gave
ortho- and para-nitrobenzophenones,1e,3 whereas the
analogous reaction with 2-phenylpropionitrile gave ONSH
products in high yields.1
21%, majority of the starting nitroarene 4c 61% was
recovered (Scheme 4).
Due to the high price of TASF and its sensitivity to
moisture, we looked for a more convenient source of
fluoride to promote the reactions of silylated enols with
nitroarenes. We have found that readily available Bu4Nþ
(p-tolyl)3SiF22 97 is almost as efficient as TASF in this
respect. The reaction of 4a with 5a promoted by 9 gave 7a in
72% yield after oxidation with DMD.
Ketone enolates generated by treatment of silyl enol ethers
with TASF are apparently weaker nucleophiles so addition
to nitroarenes is less efficient, e.g. it was reported that the
reactions of 5c with chloronitrobenzenes gave the ONSH
products in yield 30–50%.5b Also in our hands the TASF
promoted addition of 5c to m-chloronitrobenzene 4c
followed by oxidation with DMD gave expected 2-(2-
chloro-4-hydroxyphenyl)cyclohexanone in moderate yield
The efficiency of TASF promoted reactions between
silylated enols and nitroarenes was provisionally rational-
ized in terms of stabilization of the sH adducts by
Scheme 2.

M. Ma˛kosza, M. Surowiec / Tetrahedron 59 (2003) 6261–6266
6263
Scheme 3.
whereas the same reaction without Me3SiCl gave substi-
tuted phenol 2. Analogous results were obtained in the
TASF promoted reaction of 5a with nitrobenzene. Treat-
ment of the sH adduct with Me3SiCl and subsequent
oxidation with DMD gave the ONSH product 6a whereas its
direct oxidation with DMD gave phenol 7a as the main
product. These results indicate unambiguously that O-silyl-
ation of the sH adducts is followed by rapid elimination of
silanol and formation of the nitroso compounds that are
further oxidized with DMD to the nitro compounds. Thus
the sH adducts of enolates produced via treatment of
silylated enols with TASF are not stabilized by O-silylation.
Scheme 4.
O-silylation.5 This is however in contradiction to the
experimental observation that a stoichiometric amount of
fluoride ion is needed for the reaction whereas in the fluoride
promoted reactions of trimethylsilyl enol ethers with
aldehydes where O-silylation takes place, only a catalytic
amount of fluoride ion is needed.8 Moreover silylation of the
sH adducts of the 2-phenylpropionitrile carbanion gave
substituted nitrosoarenes (Scheme 1, path c).
It is well known that nucleophilicity of anions depends very
much on cation–anion interactions. Also oxidation of the
anionic sH adducts is affected by the counter cations.9 One
can therefore suppose that high effectiveness of the TASF
promoted reactions can be due to a nature of cation
associated with the enolate and subsequently the sH
adducts.
In order to clarify whether sH adducts can indeed be
stabilized by O-silylation a mixture of 2-phenylpropionitrile
carbanion and nitrobenzene was treated with Me3SiCl and
subsequently with DMD. The sole product of this reaction
was the substituted nitrobenzene 1, the product of ONSH,
Direct comparison of the reaction of the enolates generated
by treatment of 5a with TASF, deprotonation of methyl iso-
butyrate with LDA and that produced via exchange of Liþ
for tetraalkylammonium cation, Qþ in the latter, revealed
that the results are strongly affected by the nature of the
Scheme 5.

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M. Ma˛kosza, M. Surowiec / Tetrahedron 59 (2003) 6261–6266
Table 1. ONSH in nitrobenzene with lithium and tetraalkyl ammonium
salts of methyl isobutyrate carbanion (as in Scheme 5)
4.2. General procedure for the reactions of silyl enol
ethers with nitroarenes
Ammonium salt
Composition of the reaction
mixture (%)
To a stirred solution of silyl enol ether 5a–c (0.5 mmol) and
nitroarene 4a–e (0.5 mmol) in THF (5 mL) at 2708C under
argon, TASF (153 mg, 0.5 mmol) dissolved in MeCN
(1 mL) was added dropwise and the mixture was placed in
cooling bath 2258C for 1 h. After that the mixture was again
cooled to 2708C and oxidant was added.
6a
4a
Bu4NþBF24
79
84
95
18
14
3
Bu4NþBr2
(PhCH2)Et3NþCl2
Procedure A. Powdered KMnO4 (80 mg, 0.5 mmol) and
liquid ammonia (ca. 5 mL, 2708C) was added, the reaction
mixture was stirred for 15 min. and treated with NH4Cl
(106 mg, 2 mmol). The cooling bath was removed and the
ammonia was evaporated. To the residue a saturated
solution of oxalic acid in aq. HCl (20 mL, 10%) was
added and the mixture was extracted with CH2Cl2
(4£10 mL). The combined organic layers were dried over
MgSO4, filtered through silica gel and the solvent was
evaporated (258C, 15 Torr).
cation (Scheme 5). As it is shown in the Table 1 the reaction
of tetraalkyl ammonium salts of enolates with nitrobenzene
proceeds much better than the lithium salt and even better
than the tris(dimethylamino)sulfonium salt (Scheme 5).
3. Conclusion
We have found that sH adducts produced via TASF
promoted addition of enolates to nitrobenzenes are
efficiently oxidized by KMnO4 to form substituted nitro-
arenes, products of ONSH and by DMD to form substituted
phenols. High effectiveness of these reaction is due to the
type of counter ion: tris(dimethylamino)sulfonium cation.
Silylation of the sH adducts does not proceed in these
processes. We have also shown that reaction of lithium
enolates with nitrobenzenes proceeds better upon exchange
of the lithium for a tetraalkylammonium cation. This
protocol offers substantial advantages over the analogous
reaction of silyl enol ethers in the presence of stoichiometric
amounts of TASF.
Procedure B. Water (9 mL, 0.5 mmol) and than an acetone
solution of DMD (ca. 0.6 mmol, 10 mL of ca. 0.06 M) was
added to the mixture. The color changed to bright yellow.
After 5 min of further stirring, saturated aqueous NH4Cl
(0.1 mL) was added and the cooling bath was removed. The
solution was dried over anhydrous MgSO4, the solid phase
was filtered off and washed with acetone (20 mL). The
solvents were evaporated (258C, 15 Torr).
The products were purified by column chromatography on
silica gel or by preparative TLC with hexane/ethyl acetate as
an eluent.
4.2.1. Methyl 2-(4-nitrophenyl)-2-methylpropionate (6a).
Procedure A. Yield 93 mg, 84%, light yellow oil (lit.5b oil).
1H NMR (400 MHz, CDCl3): 8.21–8.16 (m, 2H), 7.53–
7.48 (m, 2H), 3.68 (s, 3H), 1.63 (s, 6H). 13C NMR
(100 MHz, CDCl3): 176.0, 151.9, 146.7, 126.8, 123.6, 52.5,
46.9, 26.4. IR (KBr): 3111, 3006, 2976, 2955, 1730, 1604,
1597, 1519, 1438, 1392, 1347, 1263, 1197, 1156, 1095, 860,
854, 739, 698. Anal. calcd for C11H13NO4: C, 59.19; H,
5.87; N, 6.27. Found: C, 59.27; H, 5.83; N, 6.25.
4. Experimental
4.1. General methods
Melting points are uncorrected. Infrared spectra were
recorded on a Spectrum 2000 spectrometer, solids as
Nujol mulls and liquids as thin films. H and 13C NMR
1
4.2.2. Methyl 2-(4-hydroxyphenyl)-2-methylpropionate
(7a). Procedure B. Yield 80 mg, 82%, pale yellow crystals
mp104–1058C(EtOH),(lit.14 91–948C). 1HNMR(400MHz,
CDCl3):7.22–7.16(m, 2H), 6.81–6.74(m, 2H), 5.83(sbroad,
1H), 3.66 (s, 3H), 1.56 (s, 6H). 13C NMR (100 MHz, CDCl3):
178.0, 154.5, 136.4, 126.9, 115.2, 52.3, 45.8, 26.5. IR (KBr):
3367, 3031, 2990, 2976, 2957, 2942, 2879, 1879, 1698, 1612,
1595, 1516, 1471, 1438, 1368, 1277, 1218, 1205, 1180, 1155,
1097, 974, 827, 779, 657, 546. Anal. calcd for C11H14O3: C,
68.02; H, 7.27. Found: C, 67.92; H, 7.34.
spectra were measured at 400 MHz on a Mercury-400BB
spectrometer. Chemical shifts are reported in ppm relative
to tetramethylsilane as internal standard. Mass spectra were
obtained on AMD 604 Inectra GmbH spectrometer using EI.
Appropriate isotope patterns were observed. For analytical
TLC Merck alufolien sheets Kieselgel 60 F254 while for
preparative TLC Lachema silica gel was used. Solvents and
reagents were used commercially except for tetrahydrofuran
that was distilled over potassium benzophenone ketyl before
use.
4.2.3. Methyl 2-(3-chloro-4-nitrophenyl)-2-methyl-
propionate (6b). Procedure A. Yield 123 mg, 95%, yellow
Acetone solution of DMD was prepared according to the
procedure described by Adam.10
1
oil. H NMR (400 MHz, CDCl3): 7.87 (d, 1H, J¼8.6 Hz),
7.53 (d, 1H, J¼2.1 Hz), 7.40 (dd, 1H, J¼8.6, 2.1 Hz), 3.70
(s, 3H), 1.62 (s, 6H). 13C NMR (100 MHz, CDCl3): 175.4,
150.8, 146.1, 129.4 127.1, 125.6, 125.3, 52.6, 49.6, 26.1.
Anal. calcd for C11H12NO4Cl: C, 51.27; H, 4.69; N, 5.44.
Found: C, 51.52; H, 4.62; N, 5.55.
Starting materials were commercial products. Silyl enol
ethers were prepared according to the standard procedures:
1-methoxy-2-methyl-1-trimethylsiloxypropene (5a)11, ethyl
trimethyl-silylacetate (5b)12, 1-(trimethylsiloxy)cyclo-
hexene (5c)13.

M. Ma˛kosza, M. Surowiec / Tetrahedron 59 (2003) 6261–6266
6265
4.2.4. Methyl 2-(3-chloro-4-hydroxyphenyl)-2-methyl-
propionate (7b). Procedure B. Yield 85 mg, 74%, pale
yellow oil. 1H NMR (400 MHz, CDCl3): 7.30 (d, 1H,
J¼2.4 Hz), 7.14 (dd, 1H, J¼8.6, 2.4 Hz), 6.94 (d, 1H,
J¼8.6 Hz), 3.66 (s, 3H), 1.55 (s, 6H). 13C NMR (100 MHz,
CDCl3): 176.9, 150.1, 137.8, 126.4, 125.9, 119.7, 116.0,
52.3, 45.7, 26.4. EIMS(þ) 230 (7.2), 228 (21.9), 171 (32.6),
169 (100.0), 141 (13.6). HR EIMS calcd for C11H13O335Cl
M¼228.0553. Found: 228.0559.
mp 131–1328C (Et2O/hexane). 1H NMR (400 MHz,
CDCl3): 6.96 (d, 1H, J¼8.5 Hz), 6.71 (d, 1H, J¼2.5 Hz),
6.60 (dd, 1H, J¼8.5, 2.5 Hz), 4.06–3.96 (m, 1H), 2.60–2.53
(m, 2H), 2.29–2.14 (m, 2H), 2.08–1.94 (m, 2H), 1.92–1.73
(m, 2H). 13C NMR (100 MHz, CDCl3): 212.2, 155.7, 134.1,
129.5, 127.5, 116.6, 114.5, 53.5, 42.3, 33.8, 27.7, 25.6.
Anal. calcd for C12H13O2Cl: C, 64.15; H, 5.83; Cl, 15.78.
Found: C, 64.01; H, 6.09; Cl, 15.56.
4.3. Oxidation of silylated sH adducts of carbanion of
2-phenylpropionitrile to nitrobenzene with DMD
4.2.5. Methyl 2-(2-chloro-4-nitrophenyl)-2-methylopro-
pionate (6c). Procedure A. Yield 89 mg, 69%, yellow oil.
1H NMR (400 MHz, CDCl3): 8.23 (d, 1H, J¼2.4 Hz), 8.14
(dd, 1H, J¼8.7, 2.4 Hz), 7.63 (d, 1H, J¼8.7 Hz), 3.69 (s,
3H), 1.67 (s, 6H). 13C NMR (100 MHz, CDCl3): 175.9,
149.4, 146.9, 134.6, 127.6, 125.5, 121.8, 52.6, 47.0, 25.7.
Anal. calcd for C11H12NO4Cl: C, 51.27; H, 4.69; N, 5.44.
Found: C, 51.43; H, 4.80; N, 5.31.
To a stirred solution of t-BuOK (123 mg, 1.1 mmol) in THF
(5 mL) cooled to 2708C, under argon a solution of
2-phenylpropionitrile (144 mg, 1.1 mmol) and nitrobenzene
(123 mg, 1 mmol) in THF (1 mL) was added dropwise
during 1 min. After that the mixture was stirred for 5 min
and Me3SiCl (120 mg, 1.1 mmol) in THF (1 mL) was
added. The mixture was stirred for 5 min water (18 mL,
1 mmol) and after 2 min an acetone solution of DMD (ca.
1.1 mmol, 19 mL of ca. 0.06 M) was added. After 5 min of
further stirring, saturated aqueous NH4Cl (0.1 mL) was
added and the cooling bath was removed. The solution was
dried over anhydrous MgSO4. The solid phase was removed
by filtration and washed with acetone (40 mL). The solvents
were evaporated (258C, 15 Torr). The products were purifed
by column chromatography on silica gel with mixture
hexane/ethyl acetate 20:1 as an eluent to give 1 (197 mg,
78%) and nitrobenzene (16 mg, 13%).
4.2.6. Methyl 2-(2-chloro-4-hydroxyphenyl)-2-methylo-
propionate (7c). Procedure B. Yield 74 mg, 64%, orange
1
oil (lit.15 oil). H NMR (400 MHz, CDCl3): 7.23 (d, 1H,
J¼8.6 Hz), 6.98 (s broad, 1H), 6.84 (d, 1H, J¼2.6 Hz), 6.71
(dd, 1H, J¼8.6, 2.6 Hz), 3.74 (s, 3H), 1.61 (s, 6H). 13C
NMR (100 MHz, CDCl3): 179.0, 155.4, 133.6, 127.4, 125.3,
117.8, 114.0, 52.7, 46.2, 26.2. EIMS(þ) 230 (6.23), 228
(17.2), 193 (50.4), 171 (33.3), 169 (100.0), 143 (16.6), 141
(48.6). HR EIMS calcd for C11H13O335Cl M¼228.0553.
Found: 228.0558.
4.2.7. Methyl 2-(2-cyano-4-hydroxyphenyl)-2-methylo-
propionate (7d). Procedure B. Yield 76 mg, 69%, pale
yellow crystals mp 134–1358C (EtOH). 1H NMR
(400 MHz, CDCl3): 7.28 (d, 1H, J¼8.3 Hz), 7.01 (d, 1H,
J¼2.6 Hz), 6.96 (dd, 1H, J¼8.3, 2.6 Hz), 3.81 (s, 3H), 1.66
(s, 6H). 13C NMR (100 MHz, CDCl3): 178.1, 154.8, 139.5,
127.3, 121.1, 120.3, 117.8, 111.9, 52.9, 46.8, 26.8. EIMS(þ)
219 (9.4), 203 (2.9), 193 (1.7), 187 (6.4), 160 (100.0), 144
(11.0), 132 (29.1). HR EIMS calcd for C12H13NO3
M¼219.08954. Found: 219.08807.
4.3.1.
2-Phenyl-2-(4-nitrophenyl)propionitrile
(1).
Yellow crystals mp 79–818C (EtOH), (lit.1 768C). Spectro-
scopic data consistent with that reported in the literature.1
The same reaction without Me3SiCl gave 2 (181 mg, 81%)
and 1 (18 mg, 7%).2
4.3.2. 2-Phenyl-2-(4-hydroxyphenyl)propionitrile (2).
Colorless crystals mp 84–868C (hexane/CH2Cl2), (lit.2
84–868C). Spectroscopic data consistent with that reported
in the literature.2
4.2.8. Ethyl (5-chloro-2-nitrophenyl)acetate (8a).
Procedure A. Yield 16 mg, 13%, yellow crystals mp 59–
608C (EtOH), (lit.1661–638C). 1H NMR (400 MHz,
CDCl3): 8.09 (d, 1H, J¼8.7 Hz), 7.45 (dd, 1H, J¼8.7,
2.3 Hz), 7.35 (d, 1H, J¼2.3 Hz), 4.22 2 4.11 (m, 2H), 4.00
(s, 2H), 1.26 (dt, 3H, J¼7.1, 1.2 Hz). 13C NMR (100 MHz,
CDCl3): 172.3, 169.3, 139.8, 133.2, 131.8, 128.7, 126.8,
61.5, 39.7, 14.1.
4.4. Oxidative substitution of hydrogen in nitrobenzene
with lithium and tetraalkyl ammonium enolates of
methyl isobutyrate
To a stirred solution of LDA (1.5 mmol, 0.8 mL, 1.8 M) in
THF (10 mL) cooled to 2708C, under argon, methyl
isobutyrate (154 mg, 1.5 mmol) was added. The solution
was stirred for 10 min and
4.2.9. Ethyl (5-chloro-2-hydroxyphenyl)acetate (8b).
Procedure B. Yield 67 mg, 62%, colorless crystals mp
62–638C (EtOH), (lit.17 478C). 1H NMR (400 MHz,
CDCl3): 7.68 (s broad, 1H), 7.14 (dd, 1H, J¼8.7, 2.5 Hz),
7.08 (d, 1H, J¼2.5 Hz), 6.86 (d, 1H, J¼8.7 Hz), 4.21 (q, 2H,
J¼7.1 Hz), 3.63 (s, 2H), 1.30 (t, 3H, J¼7.1 Hz). 13C NMR
(100 MHz, CDCl3): 173.6, 153.9, 130.5, 128.9, 125.3,
122.2, 118.9, 62.2, 37.7, 14.0. Anal. calcd for C10H11ClO3:
C, 55.96; H, 5.17; Cl, 16.52. Found: C, 55.76; H, 5.25; Cl,
15.96.
(a) Treated with Bu4NþBr2, Et3(PhCH2)NþCl2,
Bu4NþBF24 (3 mmol), stirred for 15 min and nitro-
benzene (123 mg, 1 mmol) was added.
(b) Stirred additional 15 min and nitrobenzene (123 mg,
1 mmol) was added.
After 10 min powdered KMnO4 (160 mg, 1 mmol) and
liquid ammonia (ca. 10 mL, 2708C) was added to these
mixtures, and after 15 min., NH4Cl (212 mg, 4 mmol) was
added. The cooling bath was removed and ammonia was
evaporated. A saturated solution of oxalic acid in aq. HCl
4.2.10. 2-(2-Chloro-4-hydroxyphenyl)cycloheksanone
(8c). Procedure B. Yield 31 mg, 21%, pale yellow crystals

6266
M. Ma˛kosza, M. Surowiec / Tetrahedron 59 (2003) 6261–6266
1 1977, 884. (c) Bartoli, G.; Leardini, R.; Medici, A.; Rosini,
G. J. Chem. Soc. Perkin Trans. 1 1978, 692. (d) Bartoli, G.;
Bosco, M.; Melandri, A.; Boicelli, A. C. J. Org. Chem. 1979,
44, 2087.
(20 mL, 10%) was added to the residue and the mixture was
extracted with CH2Cl2 (4£10 mL). The combined organic
layers were dried over MgSO4, filtered through silica gel
and the solvent was evaporated (258C, 15 Torr).
5. (a) RajanBabu, T. V.; Fukunaga, T. J. Org. Chem. 1984, 49,
4571. (b) RajanBabu, T. V.; Reddy, G. S.; Fukunaga, T. J. Am.
Chem. Soc. 1985, 107, 5473. (c) RajanBabu, T. V.; Chenard,
B. L.; Petti, M A. J. Org. Chem. 1986, 51, 1704.
6. Ma˛kosza, M.; Surowiec, M. J. Organomet. Chem. 2000, 624,
167.
The product 6a was purified by column chromatography on
silica gel with hexane/ethyl acetate 20:1 as an eluent, yields
of 6a are given in Table 1.
Acknowledgements
7. Ma˛kosza, M.; Bujok, R. In preparation.
8. (a) Noyori, R.; Yokoyama, K.; Sakata, J.; Kuwajima, I.;
Nakamura, E.; Shimizu, M. J. Am. Chem. Soc. 1977, 99, 1265.
(b) Nakamura, E.; Shimizu, M.; Kuwajima, I.; Sakata, J.;
Yokoyama, K.; Noyori, R. J. Org. Chem. 1983, 48, 932.
9. Ma˛kosza, M.; Adam, W.; Zhao, C.-G.; Surowiec, M. J. Org.
Chem. 2001, 66, 5022.
The authors thanks the State Committee for Scientific
Research for financial support of this work (grant no. PBZ
6.01).
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