An efficient and convenient transformation of α-haloketones to α-hydroxyketones using cesium formate

Article abstract of DOI:10.1016/j.jorganchem.2009.06.031

A new safe and convenient transformation has been developed. In the presence of cesium formate in dry MeOH solution, α-haloketones underwent direct conversion reaction to afford α-hydroxyketone in excellent yields. Furthermore, this methodology can be extended and applied in 2-chloro-N-(1,3-diphenyl-1H-pyrazol-5-yl)acetamide, 2-chloro-N-(2,6-dimethylphen-yl)acetamide, 1-(bromomethylsulfonyl)benzene, and N-(bromomethyl)phthalimide to give the corresponding products in moderate to excellent yields. Crown Copyright

Full text of DOI:10.1016/j.jorganchem.2009.06.031

Journal of Organometallic Chemistry 694 (2009) 3452–3455
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
An efficient and convenient transformation of
using cesium formate
a
-haloketones to a-hydroxyketones
a
a
b
c
d
Fung Fuh Wong a, , Po-Wei Chang , Hui-Chang Lin , Bang-Jau You , Jiann-Jyh Huang , Shao-Kai Lin
*
a Graduate Institute of Pharmaceutical Chemistry, China Medical University, No. 91 Hsueh-Shih Rd., Taichung 40402, Taiwan, ROC
b School of Chinese Medicine Resources, China Medical University, No. 91 Hsueh-Shih Rd., Taichung 40402, Taiwan, ROC
c Development Center for Biotechnology, No. 101, Lane 169, Kangning St., Xizhi City, Taipei County 221, Taiwan, ROC
d Sustainable Environment Research Center, National Cheng Kung University, No. 500, Sec. 3, An-ming Rd., Tainan City 709, Taiwan, ROC
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 27 May 2009
Received in revised form 19 June 2009
Accepted 23 June 2009
Available online 26 June 2009
A new safe and convenient transformation has been developed. In the presence of cesium formate in dry
MeOH solution, -haloketones underwent direct conversion reaction to afford -hydroxyketone in excel-
lent yields. Furthermore, this methodology can be extended and applied in 2-chloro-N-(1,3-diphenyl-1H-
pyrazol-5-yl)acetamide, 2-chloro-N-(2,6-dimethylphen-yl)acetamide, 1-(bromomethylsulfonyl)benzene,
and N-(bromomethyl)phthalimide to give the corresponding products in moderate to excellent yields.
Crown Copyright Ó 2009 Published by Elsevier B.V. All rights reserved.
a
a
Keywords:
a-Haloketone
a-Hydroxyketone
Cesium formate
Transformation
1. Introduction
presence of cesium formate in dry MeOH afforded
tones in good to excellent yields.
a-hydroxyke-
a-Hydroxyketone moieties are structural features [1–7] and
synthetic precursors [8–11] of various biological-active com-
pounds and natural products. General synthetic methods for their
2. Result and discussion
preparation include the irradiation
wave [12] or under a high-pressure mercury lamp condition [13],
-hydroxylation of an enolate with a molybdenum peroxide [14–
a-haloketones under micro-
We chose the strictly geometric 21-bromo-3
a-hydroxyl-3b-
methoxymethyl-5 -pregnan-20-one (1) [42] as the model for the
a
a
selection of best solvents for the transformation. Compound 1
was allowed to react with different equivalent of NaOH in different
solvents, including THF, THF/water, DMF, EtOH, wet MeOH, and
dry MeOH. We found the use of 3.0 equiv of NaOH in dry MeOH
gave the corresponding products 1b and 1c in ꢀ50% total yield as
the best results (ꢀ50%, see Scheme 1). As a result, dry MeOH was
17] or the other oxidizing agents [18], transformation of the enam-
ine derivatives by molecular oxygen [19], metallic-catalyzed oxi-
dative transformation of olefins [20–23] and hydroxylation of
silyl enol ether with m-chloroperbenzoic acid [24,25] or with cer-
tain oxidizing agents [26,27]. Most of the synthetic methodology
could not provide satisfactory reaction conditions due to the
expensive and special instruments required or the expensive and
dangerous heavy metal oxidizing agents needed. As a result, devel-
opment of the direct and non-toxic methods is considered enthu-
chosen as the solvent for the transformation of
the following studies.
a-haloketones in
To investigate the effect of alkali-metal ions, we treated a dry
MeOH solution of 21-bromo-3 -hydroxyl-3b-methoxymethyl-5
a
a-
siastically for the synthesis of a-hydroxyketones.
pregnan-20-one (1a) in dry MeOH with 5.0 equivlents of the differ-
ent bases including lithium, sodium [43], and potassium hydrox-
ide, and sodium, potassium, and cesium formates at reflux. After
normal workup and purification with column chromatography on
Cesium bases have demonstrated several merits in organic syn-
thetic reactions [28–34], highlighted by comparative high solubil-
ities [35], appropriate basicities and good stabilities [36–41]. In
this work, we reported a safe and convenient method for the prep-
silica gel, the desired a-hydroxyketones (1b and 1c) were isolated
aration of
a
-hydroxyketones from
a-haloketones by using cesium
as solids (see Scheme 1 and Table 1). Among the bases, we found
that the use of alkali formate gave better results (80–87% yields)
than the use alkali hydroxides (16–57% yields). The longer reaction
time was also required for alkali hydroxides (>48 h). Of the alkali
formates for the reaction, sodium [44–46], potassium [46], and
formate (HCO2Cs). Direct transformation of
a
-haloketones in the
* Corresponding author. Tel.: +886 4 220 53366x5603; fax: +886 4 220 78083.
E-mail addresses: wongfungfuh@yahoo.com.tw, ffwong@mail.cmu.edu.tw (F.F.
Wong).
0022-328X/$ - see front matter Crown Copyright Ó 2009 Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.06.031

F.F. Wong et al. / Journal of Organometallic Chemistry 694 (2009) 3452–3455
3453
O
O
X
OH
Base
MeOH
MeO
HO
MeO
HO
1b. C17-β, 1C. C17-α
1a
Scheme 1.
Table 1
in 84% and 64%, respectively. The relatively lower yield of 8b might
due to the light-sensitivity chromophore fullerene in 8a [52].
The synthetic strategy is also applicable to 2-chloro-N-(2,6-
dimethylphenyl)acetamide (9a), 2-chloro-N-(1,3-diphenyl-1H-
pyrazol-5-yl)acetamide (10a), N-bromomethylphthalimide (11a),
and 1-(bromomethylsulfonyl)benzene (12a) to afford the desired
transformation products 9b–12b in 67–95% yields. Only the one
case of bromoacetaldehyde ethylene acetal (13a), the reaction
did not provide the corresponding product 13b. The results indi-
Hydrolysis reaction of 21-bromo-3
one (1a) with various bases.
a-hydroxyl-3b-methoxymethyl-5a-pregnan-20-
Entry Bases
Reaction time
(h)
Yields (1b + 1c,
Ratio of 1b/1c (C17-b/
%)
C17-a)
1
2
3
4
5
6
LiOH
NaOH
KOH
>48
>48
>48
17
51
57
80
81
87
–
–
–
HCO2Na 15
88/12a
93/7a
98/2a
HCO2K
HCO2Cs
15
12
cated the essential role electron-withdrawing groups in
a-carbon
to the halogens, such as carbonyl, amide, imide, and sulfone
groups, for the hydrolysis reaction.
a
The area normalization was focused on 1b/1c (C-17b/C-17
a) ratio and detected
by the column separation.
3. Conclusion
cesium formats [47] were most efficient bases to provide the
hydrolysis products 1b and 1c in high yield (80–87%, see Table
1). The reactivity of hydroxyl and formate anion is reported to de-
pend on the ability of alkali-metal to dissociate from hydroxyl
(ꢁOH) and formate (HCOꢁ2 ) counterions [48,49]. Our study showed
the reactivity of hydrolysis were KOH > NaOH > LiOH and
HCO2Cs > HCO2K > HCO2Na. These results were consistent with
the literature dissociation order of counterion [48,49].
A new transformation method was developed for the prepara-
tion of
a-hydroxyketones from a-haloketones by using cesium
formate. The synthetic strategy was also applicable to 2-chloro-
N-(2,6-dimethylphenyl)acetamide, 2-chloro-N-(1,3-diphenyl-1H-
pyrazol-5-yl)-acetamide, N-bromomethylphthalimide, and 1-(bro-
momethylsulfonyl)benzene to give the corresponding transforma-
tion products in moderate to excellent yields.
For the regioseletivity of the alkali formats toward transforma-
tion, we detected the ratio of 1b/1c (C-17b/C-17
sion reaction by the column separation. We found the lower C-17b/
C17 ratio and yield were obtained by using HCO2Na (see entry 4
in Table 1). When we used HCO2K or HCO2Cs as the transformation
agents in methanol, the reaction provided better C-17b/C17 ratio
a
) for the conver-
4. Experimental
a
4.1. General procedure
a
21-Bromo-3a-hydroxyl-3b-methoxymethyl-5a-pregnan-20-one
(see entry 5 and 6 in Table 1). The best regioseletivity result was
accomplished by using HCO2Cs in MeOH at reflux for 12 h, possibly
due to the novel ‘‘cesium effect” [32,50,51]. Its isomeric ratio of C-
(1) was prepared by following our published procedure [42].
Cesium formate, potassium formate, and sodium formate were
purchased from Aldrich Chemical Co.
17b/C17
a
(1b/1c) was 98/2 and the isolated yield was 87%. For the
(1b/1c)
transformation by alkali formates, the isomers C-17b/C17
a
4.2. Standard procedure for the transformation of a-haloketones to a-
were also determined by the column chromatography. The ratios
were shown in the entry 4–6 of Table 1. The results were consis-
tent with the data by GC. Furthermore, we investigated the reac-
tion of different equivalent of cesium formate (HCO2Cs) including
hydroxyketones (1b–12b)
A
solution of
a-bromoketones (1a–10a), N-(bromo-
methyl)phthalimide (11a), 2-(bromomethyl)tetrahydro-2H-pyran
(12a), or bromoacetaldehyde ethylene acetal (13a, 1.0 equiv) and
cesium formate (HCO2Cs, 3.0 equiv) in dry MeOH (10 mL) was
heated at reflux for >2.0 h. When the reaction was completed,
the solution was filtered to remove the excess amount of HCO2Cs
and the filtrate was concentrated under reduced pressure. The
residue was purified by column chromatography on silica gel or
1.0, 2.0, 3.0 and 5.0 equiv with
a-bromoketone 1a in dry MeOH.
The reaction time would be prolonged to >24 h under the less
amount of HCO2Cs. A reliable procedure for giving the transforma-
tion products involved treatment of
was the use of 3.0 equiv of HCO2Cs in dry MeOH at reflux.
Different -haloketones 2a–13a were then allowed to react
with HCO2Cs in dry MeOH at reflux to give the corresponding
a-hydroxyketone substrates
a
a
-
re-crystallization to give the corresponding
a-hydroxyketones
hydroxyketones 2b–13b for the investigation of the reactivity of
1b–10b and 1c and 11b and 12b in 89–95% yields.
different substrates (Scheme 2 and Table 2). For alkyl-substituted
a-bromoketones 2a, the reaction provided the desired
a-hydrox-
4.3. 3
pregnan-20-one (1b)
a a,17b-
-Hydroxy-21-(10-hydroxy)-3b-methoxymethyl-5
yketone 2b in high yield (94%, see Table 2). Application of same
reaction conditions to 2-bromo-1-phenylethanone 3a and 2-bro-
mo-1-arylethanones with para-substitutents, including Me, OMe
and CN groups (4a, 5a, and 6a) also gave the corresponding prod-
ucts 3b–6b in good yields (84–92%). The new method was suitable
for 2-bromo-1-(naphthalen-6-yl)ethanone 7a and 1-(bromoace-
tyl)pyrene 8a. The corresponding products 7b and 8b was obtained
TLC Rf 0.31 (50% EtOAc in hexane); mp 126–128 °C; 1H NMR
(CDCl3, 200 MHz) d 0.58 (s, 3H, CH3), 0.71 (s, 3H, CH3), 1.16–2.42
(m, 24 H), 3.14 (s, 2H, CH2), 3.34 (s, 3H, CH3), 4.14 (d, 2H,
J = 4.0 Hz, CH2); 13C NMR (CDCl3, 50 MHz) d 11.19, 13.57, 20.86,
22.91, 24.48, 28.34, 30.19, 31.89, 33.29, 35.50, 36.01, 37.05,

3454
F.F. Wong et al. / Journal of Organometallic Chemistry 694 (2009) 3452–3455
O
O
HCO2Cs (Cesium formate)
X
OH
G
G
dry MeOH
O
X
O
O
R
X
X
MeO
HO
3a. R = H, X= Br
3b. R = H, X= OH
5a. R = OMe, X= Br
5b. R = OMe, X= OH
1a. X = Br
2a. X = Br
2b. X= OH
4a. R = Me, X = Br 6a. R = CN, X = Br
1b. C17-β, X = OH
1c. C17-α, X = OH
4b. R = Me, X = OH 6b. R = CN, X = OH
O
X
O
X
Me
Me
O
X
N
H
7a. X = Br
8a. X = Br
9a. X= Cl
9b. X= OH
7b. X = OH
8b. X = OH
O
O
X
HN
O
S
O
X
X
X
O
O
N
Ph
N
N
O
Ph
10a. X= Cl
11a. X = Br
12a. X = Br
12b. X = OH
13a. X = Br
10b. X= OH
11b. X = OH
13b. X = OH
Scheme 2.
J = 4.0 Hz, CH2); 13C NMR (CDCl3, 50 MHz) d 11.19, 13.57, 20.86,
22.91, 24.48, 28.34, 30.19, 31.89, 33.29, 35.50, 36.01, 37.05,
38.78, 40.15, 45.00, 53.91, 56.81, 59.32, 59.40, 69.42, 71.00,
81.89, 210.44; IR (KBr) 3431 (br, OH), 2976 (m), 2923 (m), 2839
(m), 1711 (s, C@O), 1095 (m, C–O), 1479 (m), 1368 (m), 1290
(m), 1235 (m) cmꢁ1; EIMS m/z (relative intensity) 347 (M – 31,
17), 334 (43), 333 (100), 301 (20), 269 (34), 109(14), 95 (23), 81
(25), 55 (19); HRMS calcd for C23H38O4 378.2770, found 378.2765.
Table 2
Transformation reaction of a-bromoketones with cesium formate (HCO2Cs).
Substrate
X
Reaction time (h)
Products
Yield (%)a
1a
2a
3a
4a
5a
6a
7a
8a
Br
Br
Br
Br
Br
Br
Br
Br
Cl
Cl
Br
Br
Br
12
2
2
2
2
2
2
2
24
ꢀ50
18
ꢀ50
>72
1b
2b
3b
4b
5b
6b
7b
8b
87
94
92
88
85
84
84
64
91
67
95
89
4.5. N-(2,6-Dimethylphenyl)-2-hydroxyacetamid (9b)
9a
9b
10a
11a
12a
13a
10b
11b
12b
13b
TLC Rf 0.13 (50% EtOAc in hexane); mp 61.8–63.7 °C; 1H NMR
(CDCl3, 200 MHz) d 2.18 (s, 6H, CH3), 4.19 (s, 2H, CH2), 7.06–7.08
(m, 3H, ArH); 13C NMR (CDCl3, 50 MHz) d 18.29 (2 ꢂ CH3), 62.12,
127.58 (2 ꢂ CH), 128.23 (2 ꢂ CH), 132.80, 135.36, 170.98; IR
(KBr) 3367 (br, OH), 2958 (m), 2920 (m), 1645 (s, C@O), 1593
(m), 1471 (m), 1072 (m), 769 (m), 707 (m) cmꢁ1; EIMS m/z (relative
intensity) 179 (M+, 50), 148 (M – 31, 100), 121 (48), 120 (34), 106
(23), 105 (28), 91 (12), 77 (16); HRMS calcd for C10H13NO2
179.0946, found 179.0951.
b
–
a
The yield was provided by the column separation.
Non-detectable.
b
38.78, 40.15, 45.00, 53.91, 56.81, 59.32, 59.40, 69.42, 71.00, 81.89,
210.44; IR (KBr) 3431 (br, OH), 2976 (m), 2923 (m), 2839 (m), 1711
(s, C@O), 1095 (m, C–O), 1479 (m), 1368 (m), 1290 (m), 1235 (m)
cmꢁ1; EIMS m/z (relative intensity) 347 (M – 31, 17), 334 (43),
333 (100), 301 (20), 269 (34), 109(14), 95 (23), 81 (25), 55 (19);
HRMS calcd for C23H38O4 378.2770, found 378.2765.
4.6. 2-Hydroxy-N-(1,3-diphenyl-1H-pyrazol-5-yl)acetamide (10b)
TLC Rf 0.2 (50% EtOAc in hexane); mp 164.5–166.4 °C; 1H NMR
(CDCl3, 200 MHz) d 4.19 (s, 2H, CH2), 7.12 (s, 1H), 7.23–7.87 (m,
10H, ArH); 13C NMR (CDCl3, 50 MHz) d 14.19, 62.19, 95.04,
124.66 (2 ꢂ CH), 125.78 (2 ꢂ CH), 128.27, 128.65 (2 ꢂ CH),
129.96 (2 ꢂ CH), 132.74, 136.09, 137.57, 152.09, 167.89; IR (KBr)
3358 (s, OH), 2922 (m), 2852 (m), 2378 (m), 2312 (m), 1708 (s,
C@O), 1598 (m), 1564 (s), 1492 (m), 1460 (m), 1367 (m), 1072
(m), 956 (m), 763(m) cmꢁ1; EIMS m/z (relative intensity) 293
4.4. 3
pregnan-20-one (1c)
a a,17a-
-Hydroxy-21-(10-hydroxy)-3b-methoxymethyl-5
TLC Rf 0.31 (50% EtOAc in hexane); mp 126–128 °C; 1H NMR
(CDCl3, 200 MHz) d 0.58 (s, 3H, CH3), 0.71 (s, 3H, CH3), 1.16–2.42
(m, 24H), 3.14 (s, 2H, CH2), 3.34 (s, 3H, CH3), 4.14 (d, 2H,

F.F. Wong et al. / Journal of Organometallic Chemistry 694 (2009) 3452–3455
3455
(M+, 100), 236 (23), 235 (75), 234 (25), 207 (10), 131 (6), 102 (15),
77 (16); HRMS calcd for C17H15N3O2 293.1164, found 293.1170.
[8] R. Uchida, K. Shiomi, T. Sunazuku, J. Inokoshi, A. Nishizawa, T. Hirose, H.
Tanaka, Y. Iwai, S. Omura, J. Antibiot. 49 (1996) 886.
[9] W.R. Roush, K. Briner, B.S. Kesler, M. Murphy, D. Gustin, J. Org. Chem. 61 (1996)
6098.
[10] O.B. Wallace, D.W. Smith, M.S. Deshpande, C. Polson, K.M. Felsenstein, Bioorg.
Med. Chem. Lett. 13 (2003) 1203.
4.7. 2-(Hydroxymethyl)-1H-isoindole-1,3(2H)-dione (11b)
[11] M. Kawase, H. Sakagami, K. Kusama, N. Motohashi, S. Saito, Bioorg. Med. Chem.
Lett. 9 (1999) 3113.
[12] T. Tanaka, M. Kawase, S. Tani, Bioorg. Med. Chem. Lett. 12 (2004) 501–505.
[13] C.A. Horiuchi, A. Takeda, W. Chai, K. Ohwada, S.-J. Ji, T.T. Takahashi,
Tetrahedron Lett. 44 (2003) 9307–9311.
TLC Rf 0.56 (50% EtOAc in hexane); mp 101.5–102.2 °C; 1H NMR
(CDCl3, 200 MHz) d 5.06 (s, 2H, CH2), 7.71–7.75 (m, 2H, ArH), 7.85–
7.90 (m, 2H, ArH); 13C NMR (CDCl3, 50 MHz) d 57.37, 68.69, 123.74
(2 ꢂ CH), 131.82, 132.63, 134.42 (2 ꢂ CH), 167.96; IR (KBr) 2929
(br, OH), 1712 (s, C@O), 1683 (m), 1413 (m), 1350 (m), 1327 (m),
1165 (m), 1083 (m), 987 (m), 960 (m), 912 (m), 727 (m), 711 (m)
cmꢁ1; EIMS m/z (relative intensity) 176 (M+, 70), 160 (M – 17,
100), 133 (8), 117 (1), 104 (16), 76 (20), 50 (10); HRMS calcd for
C9H7NO3 177.0426, found 177.0430.
[14] E. Vedejs, J. Am. Chem. Soc. 96 (1974) 5944.
[15] E. Vedejs, J.E. Telschow, J. Org. Chem. 41 (1976) 740.
[16] E. Vedejs, S. Larsen, Org. Synth. Collect. VII (1990) 277.
[17] R. Gamboni, C. Tamm, Tetrahedron Lett. 27 (1986) 3999.
[18] K. El-Qisairi, H.A. Qaseer, J. Organomet. Chem. 659 (2002) 50–55.
[19] T. Cuvigny, G. Valette, M. Larcheveque, H. Normant, J. Organomet. Chem. 155
(1978) 147.
[20] S. Baskaran, J. Das, S. Chandrasekaran, J. Org. Chem. 54 (1989) 5182.
[21] T. Takai, T. Yamada, T. Mukaiyama, Chem. Lett. (1991) 1499.
[22] S.I. Murahashi, T. Saito, H. Hanaoka, Y. Murakami, T. Naota, H. Kumobayashi, S.
Akutagawa, J. Org. Chem. 58 (1993) 2929.
4.8. Hydroxymethyl phenyl sulfone (12b)
[23] B. Plietker, J. Org. Chem. 69 (2004) 8287.
[24] G.M. Rubottom, M.A. Vazquez, D.R. Pelegrina, Tetrahedron Lett. 15 (1974)
4319.
[25] Y. Horiguchi, E. Nakamura, I. Kuwajima, Tetrahedron Lett. 30 (1989) 3323.
[26] T. Takai, T. Yamada, O. Rhode, T. Mukaiyama, Chem. Lett. (1991) 281.
[27] F.A. Davis, A.C. Sheppard, J. Org. Chem. 52 (1987) 954.
[28] S.T. Ali Shah, K.M. Khan, H. Hussain, M.U. Anwar, M. Fecker, W. Voelter,
Tetrahedron 60 (2005) 6652–6656.
[29] R.N. Salvatore, R.A. Smith, A.K. Nischwitz, T. Gavin, Tetrahedron Lett. 46 (2005)
8931–8935.
[30] A.S. Dnagle, R.N. Salvatore, R.M. Cross, E.A. Kapxhiu, S. Sahab, C.H. Yoon, K.W.
Jung, Tetrahedron Lett. 44 (2003) 5695–5698.
[31] E.E. Dueno, F. Chu, S.-I. Kim, K.W. Jung, Tetrahedron Lett. 40 (1999) 1843–
1846.
[32] R.J. Cohen, D.L. Fox, R.N. Salvatore, J. Org. Chem. 69 (2004) 4265–4268.
[33] T. Watanabe, T. Ishikawa, Tetrahedron Lett. 40 (1999) 7795–7798.
[34] M.T. Honaker, B.J. Sandefur, J.L. Hargett, A.L. McDaniel, R.N. Salvatore,
Tetrahedron Lett. 44 (2003) 8373–8377.
TLC Rf 0.4 (50% EtOAc in hexane); mp 71.0–72.6 °C; 1H NMR
(CDCl3, 200 MHz) d 2.98 (s, 2H, CH2), 7.49–7.58 (m, 3H, ArH),
7.84–7.88 (m, 2H, ArH); 13C NMR (CDCl3, 50 MHz) d 44.42,
127.28 (2 ꢂ CH), 129.37 (2 ꢂ CH), 133.72, 140.50; IR (KBr) 3024
(br, OH), 2926 (m), 1583 (m), 1446 (m), 1330 (m), 1280 (m),
1147 (m), 1085 (m), 960 (m), 929 (m), 750 (m), 690 (m), 528 (m)
cmꢁ1; EIMS m/z (relative intensity) 171 (M+, 1), 156 (32), 141 (M
– 31, 32), 125 (6), 94 (32), 77 (100), 69 (11), 57 (14), 51(27); HRMS
calcd for C7H8O3S 172.0194, found 172.0198.
Acknowledgments
We are grateful to the China Medical University (CMU96-126)
and the National Science Council of Republic of China (NSC-96-
2221-E-039-007) for financial support.
[35] A. Apelblat, E. Korin, J. Chem. Thermodyn. 38 (2006) 152–157.
[36] H. Kunz, R. Kullmann, P. Wernig, J. Zimmer, Tetrahedron Lett. 33 (1992) 1969.
[37] W.H. Kruizinga, B. Strijtveen, R.M. Kellogg, J. Org. Chem. 46 (1981) 4321.
[38] T. Sato, J. Otera, H. Nozaki, J. Org. Chem. 57 (1992) 2166.
[39] W.H. Kruizinga, R.M. Kellogg, J. Am. Chem. Soc. 103 (1981) 5183.
[40] D.N. Reinhoudt, F. de Jong, H.P.M. Tomassen, Tetrahedron Lett. 20 (1979)
2067.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jorganchem.2009.06.031.
[41] B.P. Czech, Heterocyclic. Chem. 22 (1985) 1297.
[42] 21-Bromo-3
a-hydroxyl-3b-methoxymethyl-5
a-pregnan-20-one
(1)
was
prepared by following our published procedure, see: F.F. Wong, C.-Y. Chen,
T.-H. Chen, J.-J. Huang, H.-P. Fang, M.-Y. Yeh, Steroids 71 (2006) 77.
[43] M. Numazawa, M. Nagaoka, J. Org. Chem. 50 (1985) 81–84.
[44] W.H. Pirkle, K.A. Simmons, J. Org. Chem. 48 (1983) 2520–2527.
[45] G.F. Hennion, E.J. Watson, J. Org. Chem. 23 (1958) 658–661.
[46] R.B. Ehlinger, L. Mass, US Patent 4,105,848.
References
[1] R.M. Moriarty, B.A. Berglund, R. Penmasta, Tetrahedron 33 (1992) 6065.
[2] F. Babudri, V. Fiandanese, G. Marchese, A. Punzi, Tetrahedron 55 (1999) 2431.
[3] D. Villemin, N. Cheikh, B. Mostefa-Kara, N. Bar, N. Choukchou-Braham, M.A.
Didi, Tetrahedron Lett. 47 (2006) 5519–5521.
[4] E. Lipka, M.P. Vaccher, C. Vaccher, C. Lens, Bioorg. Med. Chem. Lett. 15 (2005)
501–504.
[5] C. Len, A. Selouane, A. Weilling, F. Coicon, D. Postel, Tetrahedron Lett. 44 (2003)
663–666.
[6] A. Edelsbacher, E. Urban, W. Weidenauer, Manatsh. Chem. 123 (1992) 741–
747.
[47] Y. Masuda, W. Morita, X. Wang, Y. Yukawa, Thermochim. Acta 352–353 (2000)
61–67.
[48] R. Cacciapaglia, L. Mandolini, J. Org. Chem. 53 (1988) 2579–2582.
[49] J. March, in: Advanced Organic Chemistry: Reaction Mechanisms and
Structure, 4th ed., John Wiley & Sons, New York, 1992, pp. ; pp. 348–352.
[50] A. Ostrowicki, F. Vogtle, in: E. Weber (Ed.), Topic in Current Chemistry, vol.
161, Springer-Verlag, Heidelberg, 1992, p. 37.
[51] C. Galli, Org. Prep. Proced. Int. 24 (1992) 287.
[52] N.M. Spijker, J. Org. Chem. 55 (1990) 756–758.
[7] D. Villemin, L. Liang, Tetrahedron Lett. 37 (1996) 8733–8734.