A chiral silyl ether as auxiliary for the asymmetric nucleophilic addition to α- and β-silyloxy carbonyl compounds

Article abstract of DOI:10.1016/S0040-4020(02)00553-7

Chiral silicon groups, attached as protective group in proximity to a prostereogenic functionality by means of an ether linkage, can act, at least in specific cases, efficiently as stereochemical directors. The addition of Grignard reagents to α- and β-silyloxy carbonyl compounds (silyloxy is the stereogenic (Me₃C)(BnOCH₂)MeSiO-group) afforded the respective products with stereofacial selectivities of up to 92%. The source of the selectivities is discussed and their dependence upon structural parameters. The potential of the described principle might be increased by the structural optimization of the auxiliary group, which has not been performed yet.

Full text of DOI:10.1016/S0040-4020(02)00553-7

TETRAHEDRON
Pergamon
Tetrahedron 58 (2002) 5885±5894
A chiral silyl ether as auxiliary for the asymmetric nucleophilic
addition to a- and b-silyloxy carbonyl compounds
Michael Trzoss, Jie Shao and Stefan Bienzp
Institute of Organic Chemistry, University of Zurich, Winterthurerstr. 190, CH-8057Zurich, Switzerland
Received 17 April 2002; revised 16 May 2002; accepted 28May 2002
AbstractÐChiral silicon groups, attached as protective group in proximity to a prostereogenic functionality by means of an ether linkage,
can act, at least in speci®c cases, ef®ciently as stereochemical directors. The addition of Grignard reagents to a- and b-silyloxy carbonyl
compounds (silyloxy is the stereogenic (Me3C)(BnOCH2)MeSiO-group) afforded the respective products with stereofacial selectivities of up
to 92%. The source of the selectivities is discussed and their dependence upon structural parameters. The potential of the described principle
might be increased by the structural optimization of the auxiliary group, which has not been performed yet. q 2002 Elsevier Science Ltd. All
rights reserved.
1. Introduction
For an initial investigation, we regarded racemic silyl ethers
of a- and b-hydroxyketones and -aldehydes (compounds of
type 1 and 2, Fig. 1) as suitable substrates to study this
bifunctional effect of the chiral silicon moiety. The addition
of Grignard reagents to the carbonyl group of the
compoundsÐperformed under chelate-controlled condition
in presence of a Lewis acid such as MgBr2, which proved
advantageous in related transformations3,4,6Ðwas expected
to proceed via tridentate transition structures of type II,
affording the respective reaction products with high
stereochemical control.
Silyl groups are well established protective groups in
organic synthesis, particularly for alcohols but also for
carboxylic acids and amines.1 The silyl derivatives are
easily prepared and cleaved, and their reactivities can
usually be readily controlled with the appropriate choice
of the groups attached to silicon. In the course of our
ongoing investigation of the chiral [(benzyloxy)methyl]-
(tert-butyl)methylsilyl group (I) as an auxiliary to control
stereoselective processes,2±5 we got interested in the
combined use of I as a protective group and stereo-
chemically directing auxiliary.
2. Results
A series of silylated compounds of type 1 and 2, the starting
materials for our investigation, were prepared with the
readily available racemic chlorosilane 3.4 Silyl ethers 1b,d
were directly prepared from the commercial a-hydroxy-
ketones 4b,d by their treatment with the chlorosilane in
presence of Et3N and a catalytic amount of DMAP. Ana-
logous monosilylation of 1,2-diol 5a and 1,3-diols 6a,b,
using an excess of the alcohols, afforded the respective
hydroxyethers 7a and 8a,b, and mild oxidation of the
remaining alcohol functions under Swern conditions
delivered aldehydes 1a and 2a and ketone 2b (Scheme 1).
Figure 1. Silicon-based chiral moiety to be used as protective group and
chiral auxiliary for nucleophilic additions to a- and b-hydroxy carbonyl
compounds.
For the preparation of the substrates 1c,e and 2c±e,
aldehydes 1a and 2a were used as the starting materials.
Addition of the appropriate Grignard reagents to the car-
bonyl group of the two substrates gave rise to the respective
alcohols 7c,e/7c0,e0 and 8c±e/8c0 ±e0, which next were
oxidized under Swern conditions to the desired ketones
(Scheme 1).
Keywords: chiral silicon; diastereoselectivity; chelate control; hydroxy
carbonyl compound.
p
Corresponding author. Tel.: 141-1-635-4245; fax: 141-1-635-6812;
e-mail: sbienz@oci.unizh.ch
0040±4020/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(02)00553-7

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M. Trzoss et al. / Tetrahedron 58 (2002) 5885±5894
Scheme 1. Preparation of the silylated a- and b-silyloxy carbonyl compounds used as substrates.
Our investigation of the stereoselective addition of organo-
metallic reagents to the carbonyl group of compounds 1a±e
and 2a±e (Scheme in Table 1) started with the evaluation of
the optimal reaction conditions. Ketone 1b was thus treated
with several organometallic species like PhLi, PhMgBr, and
in situ prepared derivatives thereof, based on Ce(III),
Cr(III), Zn(II), Cu(I), and other metal ions. The reactions
were performed with or without pre-complexation of the
ketone, using the respective metal salts as Lewis acids.
Additionally, the reaction temperature (230 to 21008C)
as well as the solvent (pentane, CH2Cl2, Et2O, THF) were
varied. As in earlier investigations,6 the use of Grignard
reagents, combined with pre-complexation of the ketone
with MgBr2 in a little-donating solvent, turned out to
Table 1. Stereochemical results obtained with the addition of Grignard reagents to pre-complexed chiral a- and b-silyloxy carbonyl compounds
Entry
n
Starting material
R1
R2MgBr
syn/anti add. products
dr
1
2
3
4
5
6
7
8
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
1a
1a
1a
1a
1a
1b
1c
1e
1d
1d
1d
1d
2a
2a
2a
2a
2b
2c
2e
2d
2d
2d
H
H
H
H
MeMgBr
EtMgBr
PhMgBr
i-PrMgBr
t-BuMgBr
PhMgBr
PhMgBr
PhMgBr
MeMgBr
EtMgBr
i-PrMgBr
t-BuMgBr
MeMgBr
EtMgBr
PhMgBr
i-PrMgBr
PhMgBr
PhMgBr
PhMgBr
MeMgBr
EtMgBr
i-PrMgBr
7b/7b0
7c/7c0
7d/7d0
7e/7e0
7f/7f0
66:34
60:40
59:41
53:47
50:50
81:19
72:28
53:47
71:29
66:34
64:34
52:48
43:57
37:63
34:66
36:64
13:87
16:84
37:63
25:75
18:82
20:80
H
Me
Et
i-Pr
Ph
Ph
Ph
Ph
H
H
H
H
Me
Et
i-Pr
Ph
Ph
Ph
7g/7g0
7h/7h0
7i/7i0
9
7g0/7g
7h0/7h
7i0/7i
10
11
12
13
14
15
16
17
182
19
20
21
22
7j0/7j
8b/8b0
8c/8c0
8d/8d0
8e/8e0
8g/8g0
8h/8h0
8i/8i0
2
2
2
2
8g0/8g
8h0/8h
8i0/8i

M. Trzoss et al. / Tetrahedron 58 (2002) 5885±5894
5887
prepared.7 Their treatment with MeMgBr and PhMgBr,
respectively, afforded the mixtures of the enantiomerically
enriched addition products 7g0 and 8g0, which delivered
upon reduction with LiAlH4 in a stereospeci®c process
hydrosilane (2)-(R)-95 and the corresponding enantio-
merically enriched diols (2)-(R)-108 and (2)-(S)-11.9
3. Discussion
Several trends can be extracted from the results presented in
Table 1. (1) The p-facial selectivities obtained under the
in¯uence of the chiral auxiliary I are rather low and differ
for the two types of substrates: compounds of type 1 prefer
syn- and substrates of type 2 anti-attacks of the nucleophiles
(syn and anti with respect to the t-Bu group in proposed
complexes II-1/II-10 and II-2/II-20, respectively, Fig. 2).
(2) Highest selectivities were obtained with compounds of
type 2. (3) With the exception of the aldehydes 1a and 2a,
increase in the size of the R1 group is accompanied for both
types of substrates with a decrease in stereoselectivity. (4)
Expansion of the bulk of the nucleophile results in lowered
selectivities for compounds of type 1 and slightly enhanced
selectivities for compounds of type 2.
Scheme 2. Proof of relative con®gurations by chemical correlation (major
isomers only shown).
represent the best conditions. The addition of the Grignard
reagents to the several carbonyl compounds was ®nally
performed by carrying out the following standard pro-
cedure: the silyl ethers 1a±e or 2a±e were pre-complexed
at 2408C in CH2Cl2 with 5 equiv. of MgBr2 for 15 min
and 3 equiv. of the Grignard reagents in Et2O were added
subsequently at 2788C. The reactions were quenched after
approximately 2 h with aqueous NH4Cl and delivered, after
extraction and chromatography, the respective addition
products, usually in high yields (80±95%). The stereo-
chemical results of the transformations are summarized in
Table 1.
The observed results can be explained to a great extent by
scrutinizing the chelate structures II-1/II-10 and II-2/II-20,
proposed as competing initial arrangements leading to the
two opposite sites of nucleophilic attack at the carbonyl
C-atom for the two types of compounds (Fig. 2). Simple
molecular models, and semi-empirical calculations
(computed for R1ˆMe and XˆBr on the PM3 level), also
suppose that complexes of type II-1 for compounds 1 and
complexes of type II-20 for compounds 2 are each thermo-
dynamically favored over the related stereoisomeric
complexes II-10 and II-2, respectively. This ®nding agrees
well with the observed stereoselectivities, corresponding to
preferred syn-attacks of the nucleophiles at the ketones of
type 1 and anti-attacks at the carbonyl groups of the
compounds of type 2.
The ratios of the diastereomeric products 7b±j/7b0 ±j0 and
1
8b±i/8b0 ±i0 were determined by H NMR spectroscopy on
the crude mixtures (before chromatography), and the
relative con®gurations of the products were determined
pars pro toto with compounds 7g/7g0 and 8g/8g0 by
chemical correlation (Scheme 2). For this purpose, enantio-
merically enriched ketones (S)-1d and (S)-2b were
In addition, the dependence of the stereoselectivities upon
the size of the group R1Ðwith the exception of the par-
ticular behavior of the aldehydes 1a and 2aÐand the
bulkiness of the incoming nucleophile R2 can be explained
with the chelate structures shown in Fig. 2. Increasing
the size of R1 would generally be expected to introduce
additional steric strain into the complexes II-1/II-10 and
II-2/II-20, leading to their overall destabilization. Thus,
with increasing bulk of R1, alternative non-selective reac-
tion paths via `open-chained' transition structures could
progressively become more important and could thus
gradually compete with the `chelate-controlled' processes
(compare entries 6±8and 17±19, respectively, for the two
types of compounds). This would lead to a general loss of
selectivity.
The explanation of the effects observed upon variation of
the R2 group is less straightforward. It might be assumed
that transmetallation of R2 to the chelated Mg21 or forma-
tion of bimetallic intermediates is important for the
observed selectivities. Only this way, the several transition
structures related to the complexes II-1/II-10 and II-2/II-20
Figure 2. Proposed chelate structures for the two diastereotopic attacks (syn
and anti to the t-Bu group) of the nucleophile to the carbonyl group of
compounds of type 1 and 2.

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M. Trzoss et al. / Tetrahedron 58 (2002) 5885±5894
Scheme 3. Stereoselective preparation of tertiary alcohols as potential precursors for frontalin and isocannabinol analogs (major isomers shown only; the
drawings re¯ect but the relative con®gurations).
could `sense' the steric bulk of the incoming nucleophile
(formally variation in the size of the group X). The stereo-
selectivities should then be expected to increase for both
types of substrates on increasing the size of R2, because
the complexes II-1 and II-10 or II-2 and II-20, respectively,
should be discriminated more ef®ciently. This effect is in
fact found for substrates of type 2 (compare entries 13±16
and 20±23) but not for compounds of type 1. For the latter
substrates, the p-facial selectivity drops for larger R2 groups
(compare entries 1±5 and 20±23). This effect might again
be explained with alternative, non-selective `open-chain-
controlled' processes becoming important speci®cally
for compounds 1. Such processes might dominate for
compounds 1 rather than for compounds 2 due to the
more condensed structures of complexes II-1/II-10 (as
compared to II-2/II-20), where the interactions of bulky
R2 (X) groups with the substituents at silicon could lead to
considerable destabilization.
at least in particular casesÐef®ciently as stereochemical
directors. The potential of this principle might be increased
by the structural optimization of the silicon auxiliary. This is
a topic of our ongoing research.
5. Experimental
5.1. General
Unless otherwise stated, manipulations were carried out
under Ar in oven-dried glass equipment. For reactions,
Et2O was freshly distilled from Na with benzophenone
ketyl as indicator; CH2Cl2 was freshly distilled from
CaH2; benzene (anal. grade) was stored over Na. All org.
solvents were distilled prior to use. Anh. MgBr2 was
prepared from 1,2-dibromoethane and Mg in Et2O. Extracts
were washed with sat. aq. NH4Cl solution and brine and
were dried over MgSO4. Solutions for workup procedures
were prepared in deionized H2O. Chromatography: Merck
silica gel 60 (40±63 mm). Mp: Mettler FP5/FP52. IR spec-
tra: neat liquid ®lms between NaCl plates; Perkin±Elmer
With the above results in hand, it is readily understood that
the addition of Grignard reagent 13 to a-silyloxyketone 1b
leads to the alcohols 7k/7k0, with low stereoselectivity only.
Compounds 7k/7k0 are regarded as precursors of frontalin,
the attracting pheromone of the pine beetle (Scheme 3),10
which should be formed upon treatment of the protected
dihydroxyketone with acid.11 On the other hand, it is not
surprising that the addition of Grignard reagent 14, a
sterically demanding ortho-substituted benzene derivative,
to b-silyloxyketone 2b led to the respective addition
products 8l/8l0 with high stereoselectivity (dr 92:8). Access
to products 8l/8l0 should allow the stereoselective synthesis
of tricyclic framework 15 having structural similarity to
isocannabinol by some simple functional group intercon-
versions. Derivatives of 15 have shown interesting physio-
logical properties (Scheme 3).12
1
297 or 781; in cm21, strong bands only. H NMR spectra
in CDCl3; Bruker AC-300 (300 MHz), ARX-300
(300 MHz); d in ppm rel. to CHCl3 (d 7.26), J in Hz. 13C
NMR spectra in CDCl3; Bruker ARX-300 (75.5 MHz); d in
ppm rel. to CDCl3 (d 77.0); multiplicities from DEPT-135
and DEPT-90 experiments. Mass spectrometry (MS):
Finnigan MAT 90 or Finnigan SSQ 700; chemical-ioni-
zation MS (CI-MS) with NH3 as the reactant gas; quasi-
molecular ions and characteristic fragments; in m/z (rel.
%). Diastereomeric ratios (dr) were determined by 1H
NMR on the crude mixtures (before chromatography). The
respective signals are marked with underlining.
5.2. General procedures
4. Conclusion
5.2.1. Swern oxidations. Oxalyl chloride (2.2 mmol) was
added at 2788C in one portion to a stirred solution of
dimethyl sulfoxide (4.4 mmol) in CH2Cl2 (20 mL). The
resultant mixture was stirred for 30 min and a solution
of an alcohol (2.0 mmol) in CH2Cl2 (2 mL) was added
In conclusion, it is shown with the above investigation that
chiral silicon groups, brought into proximity to a prostereo-
genic functionality by means of an ether linkage, can actÐ

M. Trzoss et al. / Tetrahedron 58 (2002) 5885±5894
5889
dropwise via cannula. It was stirred for 30 min at 2788C,
then Et3N (10.0 mmol) was added dropwise, and after
10 min was allowed to warm to 238C over a period of
15 min. Extraction with Et2O and chromatography
(hexane/Et2O 10:3) provided the respective aldehyde or
ketone.
0.76 mmol) provided 1c (206 mg, 0.67 mmol, 88%) as a
colorless oil. IR: 2960, 2930, 2890, 2860, 1720, 1110br.
1H NMR: 7.37±7.24 (m, 5 arom. H); 4.45 (s, SiOCH2);
4.27 (s, PhCH2); 3.32, 3.24 (AB, Jˆ13.4 Hz, SiCH2); 2.49
(q, Jˆ7.3 Hz, CH2Me); 1.03 (t, Jˆ7.3 Hz, CH2Me); 0.96 (s,
t-Bu); 0.15 (s, SiMe). 13C NMR: 211.6 (s, CO); 138.6 (s,
arom. C); 128.2, 127.6 (2d, 2£2 arom. C); 127.5 (d, arom.
C); 77.2 (t, PhCH2); 70.0 (t, SiOCH2); 60.6 (t, SiCH2); 31.5
(t, CH2Me); 26.0 (q, CMe3); 18.1 (s, CMe3); 7.1 (q, CH2Me);
28.0 (q, SiMe). CI-MS: 326 (100, [M1NH4]1); 309 (32,
[M1H]1). Anal. calcd for C17H28O3Si (308.49): C 66.19, H
9.15. Found: C 65.89, H 9.07.
5.2.2. Silylations of alcohols. To a stirred solution
of [(benzyloxy)methyl](tert-butyl)chloro(methyl)silane (3,4
30.0 mmol) in CH2Cl2 (50 mL), Et3N (35.0 mmol), DMAP
(3.0 mmol), and an alcohol (90.0±150.0 mmol) were added
at 08C. The mixture was warmed to 238C and stirred for 2 h.
Extraction with Et2O and chromatography (hexane/Et2O
2:1) provided the respective silylether.
5.3.4.
2-{[[(Benzyloxy)methyl](tert-butyl)methylsilyl]-
oxy}-1-phenylethan-1-one (1d). According to general
procedure given in Section 5.2.2, silylation of 2-hydroxy-
1-phenylethan-1-one (4d, 1.59 g, 11.67 mmol, 3 equiv.)
with 3 (1.00 g, 3.89 mmol) afforded 1d (1.08g, 3.03
mmol, 78%) as a colorless oil. IR: 2950, 2930, 2890,
5.2.3. Grignard additions to the carbonyl compounds. A
2 M solution of MgBr2 in Et2O (5.0 mmol) was added to a
stirred solution of a carbonyl compound (1.0 mmol) in
CH2Cl2 (6 mL) at 2408C. After 15 min, it was cooled to
2788C and a 3 M solution of MeMgBr in Et2O (3.0 mmol)
was added dropwise via cannula. It was quenched after 2 h
by the addition of sat. aq. NH4Cl solution (2 mL). Extraction
with Et2O and chromatography (hexane/Et2O 10:3) afforded
the respective secondary or tertiary alcohols.
1
2850, 1705, 1150. H NMR: 7.89±7.85 (m, 2 arom. H);
7.56±7.20 (m, 8arom. H); 5.04 (s, SiOCH 2); 4.41 (s,
PhCH2); 3.37, 3.30 (AB, Jˆ13.4 Hz, SiCH2); 1.00 (s,
t-Bu); 0.20 (s, SiMe). 13C NMR: 197.2 (s, CO); 138.6,
134.9 (2s, 2 arom. C); 133.0 (d, arom. C); 128.5 (d, 2
arom. C); 128.1, 127.7, 127.5 (3d, 3£2 arom. C); 127.3
(d, arom. C); 77.2 (t, PhCH2); 67.7 (t, SiOCH2); 61.1 (t,
SiCH2); 26.0 (q, CMe3); 18.2 (s, CMe3); 27.7 (q, SiMe).
CI-MS: 374 (53, [M1NH4]1); 357 (79, [M1H]1). Anal.
calcd for C21H28O3Si (356.54): C 70.74, H 7.92. Found: C
70.05, H 7.94.
5.3. Aldehydes and ketones 1a±e and 2a±e
5.3.1. 2-{[[(Benzyloxy)methyl](tert-butyl)methylsilyl]oxy}-
acetaldehyde (1a). According to general procedure given
in Section 5.2.1, oxidation of 7a (500 mg, 1.77 mmol)
provided 1a (432 mg, 1.54 mmol, 87%) as a colorless oil.
IR: 2950, 2930, 2890, 2850, 1740, 1480, 1470, 1455, 1255,
5.3.5.
1-{[[(Benzyloxy)methyl](tert-butyl)methylsilyl]-
1
oxy}-3-methylbutan-2-one (1e). According to general
procedure given in Section 5.2.1, oxidation of 7e/7e0
(170 mg, 0.52 mmol) provided 1e (150 mg, 0.46 mmol,
89%) as a colorless oil. IR: 2960, 2920, 2880, 2850, 1730,
1090br. 1H NMR: 7.37±7.24 (m, 5 arom. H); 4.46 (s,
SiOCH2); 4.38(s, PhC H2); 3.33, 3.26 (AB, Jˆ13.4 Hz,
SiCH2); 2.86 (sept., Jˆ6.9 Hz, CHMe2); 1.07 (d, Jˆ
6.9 Hz); 0.98(s, t-Bu); 0.16 (s, SiMe). 13C NMR: 213.6
(s, CO); 138.6 (s, arom. C); 128.2, 127.5 (2d, 2£2 arom.
C); 127.4 (d, arom. C); 77.1 (t, PhCH2); 68.4 (t, SiOCH2);
60.7 (t, SiCH2); 36.0 (d, CHMe2); 26.0 (q, CMe3); 18.1 (s,
CMe3); 17.9 (q, CHMe2); 28.0 (q, SiMe). CI-MS: 340 (100,
[M1NH4]1); 323 (47, [M1H]1). Anal. calcd for
C18H30O3Si (322.52): C 67.03, H 9.38. Found: C 66.48, H
9.50.
1135br., 1100br., 830, 770, 735, 700. H NMR: 9.67 (t,
Jˆ0.8Hz, CHO); 7.37±7.25 (m, 5 arom. H); 4.45 (s,
PhCH2); 4.30 (d, Jˆ0.8Hz, SiOCH 2); 3.32, 3.23 (AB,
Jˆ13.3 Hz, SiCH2); 0.96 (s, t-Bu); 0.16 (s, SiMe). 13C
NMR: 202.3 (d, CHO); 138.2 (s, arom. C); 128.3, 127.7
(2d, 2£2 arom. C); 127.6 (d, arom. C); 77.2 (t, PhCH2);
70.0 (t, SiOCH2); 60.5 (t, SiCH2); 26.0 (q, CMe3); 18.1 (s,
CMe3); 27.9 (q, SiMe). CI-MS: 298(100, [M 1NH4]1); 281
(11, [M1H]1). Anal. calcd for C15H24O3Si (280.44): C
64.24, H 8.63. Found: C 63.32, H 8.59.
5.3.2.
1-{[[(Benzyloxy)methyl](tert-butyl)methylsilyl]-
oxy}acetone (1b). According to general procedure given
in Section 5.2.2, silylation of alcohol 4b (7.37 g, 95.55
mmol, 3 equiv.) with 3 (8.81 g, 31.85 mmol, 1 equiv.)
afforded 1b (7.31 g, 24.83 mmol, 78%) as a colorless oil.
IR: 2960, 2930, 2890, 2850, 1780, 1120br., 1080. 1H NMR:
7.37±7.24 (m, 5 arom. H); 4.45 (s, SiOCH2); 4.25
(s, PhCH2); 3.32, 3.24 (AB, Jˆ13.3 Hz, SiCH2); 2.12
(s, COMe); 0.96 (s, t-Bu); 0.15 (s, SiMe). 13C NMR:
209.0 (s, CO); 138.6 (s, arom. C); 128.3, 127.6 (2d, 2£2
arom. C); 127.5 (d, arom. C); 77.2 (t, PhCH2); 70.0 (t,
SiOCH2); 60.6 (t, SiCH2); 26.0 (q, CMe3); 25.9 (q,
COMe); 18.1 (s, CMe3); 28.0 (q, SiMe). CI-MS: 312
(100, [M1NH4]1); 295 (26, [M1H]1). Anal. calcd for
C16H26O3Si (294.46): C 65.26, H 8.90. Found: C 64.96, H
9.01.
5.3.6. 3-{[[(Benzyloxy)methyl](tert-butyl)methylsilyl]oxy}-
propanal (2a). According to general procedure given in
Section 5.2.1, oxidation of 8a (928mg, 3.13 mmol)
provided 2a (860 mg, 2.91 mmol, 93%) as a colorless oil.
IR: 2950, 2930, 2880, 2850, 1725, 1090, 1070, 835, 775,
735, 700. 1H NMR: 9.78(t, Jˆ2.3 Hz, CHO); 7.37±7.25 (m,
5 arom. H); 4.48(s, PhC H2); 4.10±4.06 (m, SiOCH2); 3.29,
3.23 (AB, Jˆ13.3 Hz, SiCH2); 2.61±2.56 (m, CH2CHO);
0.91 (s, t-Bu); 0.14 (s, SiMe). 13C NMR: 202.1 (d, CHO);
138.7 (s, arom. C); 128.2, 127.6 (2d, 2£2 arom. C); 127.4 (d,
arom. C); 77.1 (t, PhCH2); 60.2 (t, SiOCH2); 58.0 (t, SiCH2);
46.5 (t, CH2CHO); 26.0 (q, CMe3); 18.1 (s, CMe3); 28.0 (q,
SiMe). CI-MS: 312 (100, [M1NH4]1); 295 (10, [M1H]1).
Anal. calcd for C16H26O3Si (294.46): C 65.26, H 8.90.
Found: C 64.93, H 9.08.
5.3.3.
1-{[[(Benzyloxy)methyl](tert-butyl)methylsilyl]-
oxy}butan-2-one (1c). According to general procedure
given in Section 5.2.1, oxidation of 7c/7c0 (235 mg,

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M. Trzoss et al. / Tetrahedron 58 (2002) 5885±5894
5.3.7.
4-{[[(Benzyloxy)methyl](tert-butyl)methylsilyl]-
(t, PhCH2); 60.7 (t, SiOCH2); 59.4 (t, SiCH2); 43.2 (t,
OCH2CH2); 41.4 (d, CHMe2); 26.0 (q, CMe3); 18.1 (s,
CMe3); 17.8(q, CH Me2); 28.1 (q, SiMe). CI-MS: 354
(100, [M1NH4]1); 337 (34, [M1H]1). Anal. calcd for
C19H32O3Si (336.54): C 67.81, H 9.58. Found: C 67.62, H
9.54.
oxy}butan-2-one (2b). According to general procedure
given in Section 5.2.1, oxidation of 8b/8b0 (710 mg,
2.28mmol) provided 2b (635 mg, 2.05 mmol, 90%) as a
colorless oil. IR: 2960, 2930, 2880, 2860, 1715, 1100,
1075. 1H NMR: 7.37±7.24 (m, 5 arom. H); 4.47 (s,
PhCH2); 3.97 (t, Jˆ6.3 Hz, SiOCH2); 3.28, 3.23 (AB,
Jˆ13.3 Hz, SiCH2); 2.62 (t, Jˆ6.3 Hz, OCH2CH2); 2.14
(s, COMe); 0.91 (s, t-Bu); 0.12 (s, SiMe). 13C NMR:
208.0 (s, CO); 138.8 (s, arom. C); 128.2, 127.5 (2d, 2£2
arom. C); 127.4 (d, arom. C); 77.1 (t, PhCH2); 60.7 (t,
SiOCH2); 59.4 (t, SiCH2); 46.5 (t, OCH2CH2); 30.7 (q,
COMe); 26.0 (q, CMe3); 18.1 (s, CMe3); 28.1 (q, SiMe).
CI-MS: 326 (100, [M1NH4]1); 309 (61, [M1H]1). Anal.
calcd for C17H28O3Si (308.49): C 66.19, H 9.15. Found: C
66.17, H 9.18.
5.4. Alcohols 7a±l and 8a±l
5.4.1. 2-{[[(Benzyloxy)methyl](tert-butyl)methylsilyl]oxy}-
ethanol (7a). According to general procedure given in
Section 5.2.2, silylation of ethylene glycol (5a, 0.79 mL,
12.60 mmol, 5 equiv.) with 3 (648mg, 2.52 mmol) afforded
7a (513 mg, 1.81 mmol, 72%) as a colorless oil. IR: 3420br.,
2930, 2850, 1470, 1460, 1450, 1255, 1100br., 935, 830, 775,
1
735, 700. H NMR: 7.38±7.26 (m, 5 arom. H); 4.50 (s,
5.3.8.
1-{[[(Benzyloxy)methyl](tert-butyl)methylsilyl]-
PhCH2); 3.82 (t, Jˆ4.4 Hz, SiOCH2); 3.72±3.57 (m,
CH2OH); 3.33, 3.21 (AB, Jˆ13.2 Hz, SiCH2); 2.78(br.s,
OH); 0.92 (s, t-Bu); 0.16 (s, SiMe). 13C NMR: 138.1 (s,
arom. C); 128.3, 127.8 (2d, 2£2 arom. C); 127.6 (d, arom.
C); 77.2 (t, PhCH2); 65.5 (t, SiOCH2); 64.0 (t, CH2OH); 60.5
(t, SiCH2); 26.0 (q, CMe3); 18.1 (s, CMe3); 28.0 (q, SiMe).
CI-MS: 300 (100, [M1NH4]1); 283 (5, [M1H]1). Anal.
calcd for C15H26O3 Si (282.46): C 63.79, H 9.28. Found:
C 63.58, H 9.27.
oxy}pentan-3-one (2c). According to general procedure
given in Section 5.2.1, oxidation of 8c/8c0 (210 mg,
0.65 mmol) provided 2c (184 mg, 0.57 mmol, 88%) as a
colorless oil. IR: 2960, 2930, 2880, 2860, 1715, 1100,
1070. 1H NMR: 7.37±7.24 (m, 5 arom. H); 4.47 (s,
PhCH2); 3.97 (t, Jˆ6.3 Hz, SiOCH2); 3.28, 3.23 (AB,
Jˆ13.1 Hz, SiCH2); 2.60 (t, Jˆ6.3 Hz, OCH2CH2); 2.43
(q, Jˆ7.2 Hz, CH2Me); 1.02 (t, Jˆ7.2 Hz, CH2Me); 0.91
(s, t-Bu); 0.12 (s, SiMe). 13C NMR: 210.5 (s, CO); 138.8
(s, arom. C); 128.2, 127.5 (2d, 2£2 arom. C); 127.4 (d,
arom. C); 77.1 (t, PhCH2); 60.7 (t, SiOCH2); 59.5 (t,
SiCH2); 45.3 (t, OCH2CH2); 36.9 (t, CH2Me); 26.0 (q,
CMe3); 18.1 (s, CMe3); 7.5 (q, CH2Me); 28.1 (q, SiMe).
CI-MS: 340 (100, [M1NH4]1); 323 (96, [M1H]1). Anal.
calcd for C18H30O3Si (322.52): C 67.03, H 9.37. Found: C
66.87, H 9.19.
5.4.2. (2Rp,SiRp)- and (2Sp,SiRp)-1-{[[(Benzyloxy)-
methyl](tert-butyl)methylsilyl]oxy}propan-2-ol (7b and
7b0). According to general procedure given in Section
5.2.3, 1a (250 mg, 0.89 mmol) gave upon treatment with
MeMgBr 7b/7b0 (235 mg, 0.79 mmol, 89%, ratio 66:34,
Entry 1 of Table 1) as a colorless oil. Data from mixture.
IR: 3430br., 2960, 2930, 2860, 1090br. 1H NMR (signals of
7b0 are given in italics): 7.31±7.18(m, 5 arom. H); 4.43 (s,
PhCH2); 4.81±3.61 (m, SiOCH2);); 3.44±3.11 (m, SiCH2
and CHOH); 2.85 (br.s, OH); 1.05, 1.02 (2d, Jˆ6.5 Hz,
CHOHMe); 0.87, 0.86 (2s, t-Bu); 0.07, 0.08(2s, SiMe).
13C NMR: 138.3, 138.2 (2s, arom. C); 128.2 (d, 2 arom.
C); 127.7 (d, 2 arom. C); 127.5 (d, arom. C); 77.1 (t,
PhCH2); 69.8, 69.3 (2t, SiOCH2); 68.1, 68.0 (2d, CHOH);
60.4 (t, SiCH2); 26.1, 25.8 (2q, CMe3); 18.3, 18.0 (2q,
CHOHMe); 18.2 (s, CMe3); 28.0, 28.1 (2q, SiMe). CI-
MS: 314 (100, [M1NH4]1); 297 (21, [M1H]1). Anal.
calcd for C16H28O3Si (296.48): C 64.82, H 9.52. Found: C
64.52, H 9.47.
5.3.9.
3-{[[(Benzyloxy)methyl](tert-butyl)methylsilyl]-
oxy}-1-phenylpropan-1-one (2d). According to general
procedure given in Section 5.2.1, oxidation of 8d/8d0
(295 mg, 0.79 mmol) provided 2d (261 mg, 0.70 mmol,
89%) as a colorless oil. IR: 2950, 2930, 2880, 2860, 1680,
1100, 1075. 1H NMR: 7.96±7.93 (m, 2 arom. H); 7.58±7.23
(m, 8arom. H); 4.46 (s, PhC H2); 4.15 (t, Jˆ6.5 Hz,
SiOCH2); 3.30±3.18(m, SiCH and OCH2CH2); 0.89 (s,
2
t-Bu); 0.12 (s, SiMe). 13C NMR: 236.9 (s, CO); 138.8,
137.3 (2s, 2 arom. C); 133.0 (d, arom. C); 128.5 (d, 2
arom. C); 128.2 (d, 4 arom. C); 127.5 (d, 2 arom. C);
127.3 (d, arom. C); 77.1 (t, PhCH2); 60.7 (t, SiOCH2);
59.8(t, SiCH ); 41.7 (t, OCH2CH2); 26.1 (q, CMe3); 18.2
5.4.3. (2Rp,SiRp)- and (2Sp,SiRp)-1-{[[(Benzyloxy)-
methyl](tert-butyl)methylsilyl]oxy}butan-2-ol (7c and
7c0). According to general procedure given in Section
5.2.3, 1a (248mg, 0.88mmol) gave upon treatment with
EtMgBr 7c/7c0 (247 mg, 0.79 mmol, 90%, ratio 60:40,
Entry 2 of Table 1) as a colorless oil. Data from mixture.
IR: 3450br., 2955, 2930, 2855, 1090br. 1H NMR (signals of
7c0 are given in italics): 7.31±7.18(m, 5 arom. H); 4.44,
4.43 (2s, PhCH2); 3.74±3.40 (m, SiOCH2 and CHOH);
3.27±3.12 (m, SiCH2); 2.95 (br.s, OH); 1.45±1.32 (m,
CH2Me); 0.92±0.84 (m, CH2Me and t-Bu); 0.09, 0.08(2s,
SiMe). 13C NMR: 138.3 (s, arom. C); 128.2, 127.7 (2d, 2£2
arom. C); 127.5 (d, arom. C); 77.1 (t, PhCH2); 73.3 (d,
CHOH); 68.2, 67.7 (t, SiOCH2); 60.4 (t, SiCH2); 26.1 (q,
CMe3); 26.0 (t, CH2Me); 18.1 (s, CMe3); 10.0 (q, CH2Me);
28.0 (q, SiMe). CI-MS: 328 (100, [M1NH4]1); 311 (11,
2
(s, CMe3); 28.0 (q, SiMe). CI-MS: 388 (53, [M1NH4]1);
371 (100, [M1H]1). Anal. calcd for C22H30O3Si (370.56): C
71.31, H 8.16. Found: C 70.99, H 7.97.
5.3.10. 1-{[[(Benzyloxy)methyl](tert-butyl)methylsilyl]-
oxy}-4-methylpentan-3-one (2e). According to general
procedure given in Section 5.2.1, oxidation of 8e/8e0
(170 mg, 0.50 mmol) provided 2e (135 mg, 0.40 mmol,
80%) as a colorless oil. IR: 2960, 2930, 2880, 2850, 1720,
1090. 1H NMR: 7.37±7.23 (m, 5 arom. H); 4.48(s, PhC H2);
3.97 (t, Jˆ6.3 Hz, SiOCH2); 3.28, 3.23 (AB, Jˆ16.6 Hz,
SiCH2); 2.66 (t, Jˆ6.3 Hz, OCH2CH2); 2.59 (sept., Jˆ
7.0 Hz, COCHMe2); 1.07 (d, Jˆ7.0 Hz); 0.91 (s, t-Bu);
0.12 (s, SiMe). 13C NMR: 213.3 (s, CO); 138.8 (s, arom.
C); 128.2, 127.5 (2d, 2£2 arom. C); 127.3 (d, arom. C); 77.1

M. Trzoss et al. / Tetrahedron 58 (2002) 5885±5894
5891
[M1H]1). Anal. calcd for C17H30O3Si (310.51): C 65.76, H
9.74. Found: C 66.39, H 9.83.
5.4.7. (2Rp,SiRp)- and (2Sp,SiRp)-1-{[[(Benzyloxy)-
methyl](tert-butyl)methylsilyl]oxy}-2-phenylpropan-2-ol
(7g and 7g0). According to general procedure given in
Section 5.2.3, 1b (100 mg, 0.34 mmol) and 1d (134 mg,
0.38mmol) gave upon treatment with PhMgBr and
MeMgBr, respectively, 7g/7g0 (120 mg, 0.32 mmol, 94%,
ratio 76:24, and 125 mg, 0.33 mmol, 88%, ratio 29:71,
Entries 6 and 9 of Table 1) as colorless oils. 7g and 7g0
were separated by chromatography (hexane/Et2O 10:3).
Data of 7g: IR: 3460, 2950, 2930, 2880, 2860, 1100br.,
5.4.4. (1Rp,SiRp)- and (1Sp,SiRp)-2-{[[(Benzyloxy)-
methyl](tert-butyl)methylsilyl]oxy}-1-phenylethanol (7d
and 7d0). According to general procedure given in Section
5.2.3, 1a (245 mg, 0.87 mmol) gave upon treatment with
PhMgBr 7d/7d0 (249 mg, 0.70 mmol, 80%, ratio 59:41,
Entry 3 of Table 1) as a colorless oil. Data from mixture.
1
IR: 3440br., 2930, 2860, 1100br., 1070, 700. H NMR
1
(signals of 7d0 are given in italics): 7.31±7.15 (m, 10
arom. H); 4.75±4.68(m, C HOH); 4.48±4.42 (m, PhCH2);
3.87±3.78, 3.65±3.53 (m, SiOCH2 and OH); 3.29±3.13 (m,
SiCH2); 0.87 (s, t-Bu); 0.10, 0.09 (2s, SiMe). 13C NMR:
140.6, 140.4 (2s, arom. C); 138.2, 138.0 (2s, arom. C);
128.3, 128.1 (2d, 2£2 arom. C); 127.9, 127.8 (2d, arom.
C); 127.8(d, 2 arom. C); 127.6 (d, arom. C); 126.2 (d, 2
arom. C); 77.2 (t, PhCH2); 74.4 (d, CHOH); 70.1, 69.7 (2t,
SiOCH2); 60.2 (t, SiCH2); 26.1, 25.9 (2q, CMe3); 18.2, 18.1
(2s, CMe3); 27.8, 28.1 (2q, SiMe). CI-MS: 376 (100,
[M1NH4]1); 358(57, [M 1NH4±H2O]1). Anal. calcd for
C21H30O3Si (358.55): C 70.35, H 8.43. Found: C 70.16, H
8.55.
1080, 1070, 700. H NMR: 7.45±7.20 (m, 10 arom. H);
4.48(s, PhC H2); 3.83, 3.77 (AB, Jˆ9.9 Hz, SiOCH2);
3.53 (s, OH); 3.24, 3.17 (AB, Jˆ13.5 Hz, SiCH2); 1.47 (s,
COHMe); 0.86 (s, t-Bu); 0.06 (s, SiMe). 13C NMR: 145.6 (s,
arom. C); 138.4 (s, arom. C); 128.3 (d, 2 arom. C); 127.9 (d,
2 arom. C); 127.7, 127.5 (2d, 2 arom. C); 126.6 (d, 2 arom.
C); 125.2 (d, 2 arom. C); 77.2 (t, PhCH2); 74.4 (s, COH);
72.2 (t, SiOCH2); 60.4 (t, SiCH2); 26.0 (q, CMe3); 25.7 (q,
COHMe); 18.1 (s, CMe3); 28.1 (q, SiMe). CI-MS: 372 (65,
[M1NH4±H2O]1); 355 (100, [M1H±H2O]1). Data of 7g0:
IR: 3460, 2950, 2930, 2880, 2860, 1100br., 1080, 1070, 700.
1H NMR: 7.44±7.19 (m, 10 arom. H); 4.49 (s, PhCH2); 3.73,
(s, SiOCH2); 3.64 (s, OH); 3.21, 3.14 (AB, Jˆ13.5 Hz,
SiCH2); 1.57 (s, COHMe); 0.90 (s, t-Bu); 0.10 (s, SiMe).
13C NMR: 145.4 (s, arom. C); 138.3 (s, arom. C); 128.3 (d, 2
arom. C); 128.0 (d, 2 arom. C); 127.8, 127.6 (2d, 2 arom. C);
126.7 (d, 2 arom. C); 125.2 (d, 2 arom. C); 77.2 (t, PhCH2);
74.3 (s, COH); 72.4 (t, SiOCH2); 60.3 (t, SiCH2); 25.9 (q,
CMe3); 25.7 (q, COHMe); 18.1 (s, CMe3); 28.1 (q, SiMe).
CI-MS: 372 (65, [M1NH4±H2O]1); 355 (100, [M1H±
H2O]1). Anal. calcd for C22H32O3Si (372.59): C 70.92, H
8.66. Found: C 69.25, H 8.51.
5.4.5. (2Rp,SiRp)- and (2Sp,SiRp)-1-{[[(Benzyloxy)-
methyl](tert-butyl)methylsilyl]oxy}-3-methylbutan-2-ol
(7e and 7e0). According to general procedure given in
Section 5.2.3, 1a (258mg, 0.92 mmol) gave upon treatment
with i-PrMgBr 7e/7e0 (256 mg, 0.79 mmol, 86%, ratio
53:47, Entry 4 of Table 1) as a colorless oil. Data from
1
mixture. IR: 3450br., 2960, 2930, 2860, 1100br., 1070. H
NMR (signals of 7e0 are given in italics): 7.31±7.18(m, 5
arom. H); 4.44, 4.43 (2s, PhCH2); 3.75±3.72, 3.59±3.48(m,
SiOCH2); 3.26±3.13 (m, CHOH and SiCH2); 2.95 (s, OH);
1.70±1.56 (m, CHMe2; 0.92±0.82 (m, CHMe2 and t-Bu);
0.09, 0.08 (2s, SiMe). 13C NMR: 138.3, 138.2 (2s, arom. C);
128.2, 127.7 (2d, 2£2 arom. C); 127.5 (d, arom. C); 77.1 (t,
PhCH2); 76.7 (d, CHOH); 66.6, 66.2 (2t, SiOCH2); 60.3 (t,
SiCH2); 30.6 (d, CHMe2); 26.0 (q, CMe3); 18.7, 18.3 (2q,
CHMe2) 18.5, 18.1 (2s, CMe3); 28.0 (q, SiMe). CI-MS: 342
(100, [M1NH4]1); 325 (7, [M1H]1). Anal. calcd for
C18H32O3 Si (324.54): C 66.62, H 9.94. Found: C 66.42, H
9.93.
5.4.8. (2Rp,SiRp)- and (2Sp,SiRp)-1-{[[(Benzyloxy)-
methyl](tert-butyl)methylsilyl]oxy}-2-phenylbutan-2-ol
(7h and 7h0). According to general procedure given in
Section 5.2.3, 1c (232 mg, 0.75 mmol) and 1d (207 mg,
0.58mmol) gave upon treatment with PhMgBr and
EtMgBr, respectively, 7h/7h0 (249 mg, 0.50 mmol, 86%,
ratio 72:28, and 197 mg, 0.51 mmol, 88%, ratio 34:66,
Entries 7 and 10 of Table 1) as colorless oils. Data from
mixture. IR: 3440, 2950, 2930, 2880, 2860, 1460, 1100,
1
1080br., 700. H NMR (signals of 7h are given in italics):
7.29±7.05 (m, 10 arom. H); 4.35 (s, PhCH2); 3.75±3.61 (m,
SiOCH2); 3.21 (br.s, OH); 3.13±2.98(m, SiCH 2); 1.90±1.56
(m, CH2Me); 0.78, 0.74 (2s, t-Bu); 0.66±0.60 (m, CH2Me);
20.02, 20.07 (2s, SiMe). 13C NMR: 143.9, 143.7, 138.2
(3s, 2 arom. C); 128.2, 127.8, 127.7 (3d, 3£2 arom. C);
127.5, 126.4 (2d, 2 arom. C); 125.6 (d, 2 arom. C); 77.1
(t, PhCH2); 76.8(s, COH); 71.8, 71.6 (2t, SiOCH2); 60.3 (t,
SiCH2); 31.1, 30.8(2t, CH2Me); 26.0 (q, CMe3); 18.1 (s,
CMe3); 7.6 (q, CH2Me); 28.1 (q, SiMe). CI-MS: 404 (16,
[M1NH4]1); 386 (100, [M1NH4 ±H2O]1); 369 (54,
[M1H±H2O]1). Anal. calcd for C23H34O3Si (386.61): C
71.46, H 8.86. Found: C 71.42, H 8.94.
5.4.6. (2Rp,SiRp)- and (2Sp,SiRp)-1-{[[(Benzyloxy)-
methyl](tert-butyl)methylsilyl]oxy}-3,3-dimethylbutan-
2-ol (7f and 7f0). According to general procedure given in
Section 5.2.3, 1a (248mg, 0.88mmol) gave upon treatment
with t-BuMgBr 7f/7f0 (242 mg, 0.70 mmol, 80%, ratio
50:50, Entry 5 of Table 1) as a colorless oil. Data from
1
mixture. IR: 3450br., 2950, 2930, 2860, 1110, 1070. H
NMR (signals of one of the isomers are given in italics):
7.38±7.25 (m, 5 arom. H); 4.50, 4.49 (2s, PhCH2); 3.88±
3.83, 3.62±3.53 (m, SiOCH2); 3.33± 3.16 (m, CHOH and
SiCH2); 2.86 (br.s, OH); 0.94, 0.93, 0.91, 0.90 (4s, 2£t-Bu);
0.15 (s, SiMe). 13C NMR: 138.4 (s, arom. C); 128.2, 127.7
(2d, 2£2 arom. C); 127.5 (d, arom. C); 78.9, 78.8
(2d, CHOH); 77.2 (t, PhCH2); 65.0, 64.7 (2t, SiOCH2);
60.4 (t, SiCH2); 33.4, 33.3 (2s, CH(OH)CMe3); 26.1 (2q,
2£CMe3); 18.2, 18.1 (2s, CMe3); 27.88 (q, SiMe). CI-MS:
356 (100, [M1NH4]1); 339 (8, [M1H]1). Anal. calcd for
C19H34O3Si (338.56): C 67.41, H 10.12. Found: C 66.88, H
9.96.
5.4.9. (2Rp,SiRp)- and (2Sp,SiRp)-1-{[[(Benzyloxy)-
methyl](tert-butyl)methylsilyl]oxy}-3-methyl-2-phenyl-
butan-2-ol (7i and 7i0). According to general procedure
given in Section 5.2.3, 1e (221 mg, 0.69 mmol) and 1d
(134 mg, 0.38mmol) gave upon treatment with PhMgBr
and i-PrMgBr, respectively, 7i/7i0 (206 mg, 0.52 mmol,
75%, ratio 53:47, and 108mg, 0.29 mmol, 77%, ratio

5892
M. Trzoss et al. / Tetrahedron 58 (2002) 5885±5894
34:64, Entries 8and 11 of Table 1) as colorless oils. Data
from mixture. IR: 3450, 2960, 2930, 2880, 2860, 1470,
1100br., 1090, 700. H NMR (signals of 7i are given in
in Section 5.2.2, silylation of propane-1,3-diol (6a, 1.48g,
19.45 mmol, 5 equiv.) with 3 (1.00 g, 3.89 mmol) afforded
8a (1.01 g, 3.38mmol, 87%) as a colorless oil. IR: 3400br.,
2950, 2930, 2880, 2850, 1090, 1070, 835, 775, 735, 700. 1H
NMR: 7.38±7.25 (m, 5 arom. H); 4.49 (s, PhCH2); 3.93±
3.89 (m, SiOCH2); 3.81±3.74 (m, CH2OH); 3.31, 3.23 (AB,
Jˆ13.2 Hz, SiCH2); 2.69 (t, Jˆ5.7 Hz, OH); 1.80±1.72 (m,
OCH2CH2); 0.93 (s, t-Bu); 0.13 (s, SiMe). 13C NMR: 138.4
(s, arom. C); 128.3 (d, 2 arom. C); 127.8 (d, arom. C); 127.5
(d, 2 arom. C); 77.2 (t, PhCH2); 62.4 (t, SiOCH2); 61.2 (t,
CH2OH); 60.4 (t, SiCH2); 34.3 (t, OCH2CH2); 26.1 (q,
CMe3); 18.1 (s, CMe3); 28.0 (q, SiMe). CI-MS: 314 (100,
[M1NH4]1); 297 (74, [M1H]1). Anal. calcd for C16H28O3
Si (296.48): C 64.82, H 9.52. Found: C 64.29, H 9.65.
1
italics): 7.29±7.08(m, 10 arom. H); 4.37, 4.34 (2s, PhCH2);
3.97±3.81 (m, SiOCH2); 3.16 (br.s, OH); 3.07±2.96 (m,
SiCH2); 2.04±1.90 (m, CHMe2; 0.82±0.67 (m, CHMe2 and
t-Bu); 20.01, 20.09 (2 s, SiMe). 13C NMR: 143.6, 143.2,
138.0 (3s, 2 arom. C); 127.8, 127.3 (2d, 2£2 arom. C);
127.0, 125.9 (2d, 2 arom. C); 125.8, 125.6 (2d, 2£2 arom.
C); 78.0 (s, COH); 76.7 (t, PhCH2); 68.8 (t, SiOCH2); 59.9
(t, SiCH2); 34.8, 34.7 (2d, CHMe2); 25.5 (q, CMe3); 17.6,
17.2 (2s, CMe3); 16.5 (q, CHMe2); 28.5, 28.7 (2q, SiMe).
CI-MS: 418(6, [M 1NH4]1); 400 (16, [M1NH4±H2O]1);
383 (100, [M1H±H2O]1). Anal. calcd for C24H36O3Si
(400.63): C 71.95, H 9.06. Found: C 71.04, H 8.97.
5.4.13. (2Sp,SiRp)- and (2Rp,SiRp)-4-{[[(Benzyloxy)-
methyl](tert-butyl)methylsilyl]oxy}butan-2-ol (8b and
8b0). According to general procedure given in Section
5.2.2, silylation of (^)-butane-1,3-diol (6b, 1.23 g, 13.65
mmol, 5 equiv.) with 3 (700 mg, 2.73 mmol) afforded 8b/
8b0 (760 mg, 2.46 mmol, 90%, ratio 1:1). Analogous to
Section 5.3.2, 2a (100 mg, 0.34 mmol) gave upon treatment
with MeMgBr 8b/8b0 (90 mg, 0.29 mmol, 85%, ratio 43:57,
Entry 13 of Table 1). Colorless oils; data from mixture. IR:
3420br., 2960, 2930, 2850, 1090. 1H NMR (signals of 8b are
given in italics): 7.37±7.25 (m, 5 arom. H); 4.49 (s, PhCH2);
4.06±3.81 (m, SiOCH2 and CHOH); 3.33±3.20 (m, SiCH2
and OH); 1.67±1.60 (m, OCH2CH2); 1.18(d, Jˆ6.1 Hz,
CHOHMe); 0.93 (s, t-Bu); 0.14, 0.13 (2s, SiMe). 13C
NMR: 138.5, 138.4 (2s, arom. C); 128.6 (d, 2 arom. C);
127.7, 127.6 (2d, 2 arom. C); 127.5 (d, arom. C); 77.1 (t,
PhCH2); 67.4, 67.0 (2d, CHOH); 62.9, 62.4 (2t, SiOCH2);
60.4, 60.2 (2t, SiCH2); 40.3 (t, OCH2CH2); 26.1, 26.0 (2q,
CMe3); 23.3, 23.2 (2q, CHOHMe); 18.1, 18.0 (2s, CMe3);
28.0, 28.2 (2q, SiMe). CI-MS: 328 (100, [M1NH4]1); 311
(88, [M1H]1). Anal. calcd for C17H30O3 Si (310.51): C
65.76, H 9.74. Found: C 65.56, H 9.61.
5.4.10. (2Rp,SiRp)- and (2Sp,SiRp)-1-{[[(Benzyloxy)-
methyl](tert-butyl)methylsilyl]oxy}-3,3-dimethyl-2-phenyl-
butan-2-ol (7j and 7j0). According to general procedure
given in Section 5.2.3, 1d (124 mg, 0.35 mmol) gave upon
treatment with t-BuMgBr 7j/7j0 (78mg, 0.19 mmol, 54%,
ratio 48:52, Entry 12 of Table 1) as a colorless oil. Data
from mixture. IR: 3450, 2950, 2930, 2850, 1135, 1090,
1
1070, 840, 830, 700. H NMR (signals of 7j are given
in italics): 7.28±7.00 (m, 10 arom. H); 4.34±4.12 and
3.95±3.91 (m, PhCH2 and SiOCH2); 3.31, 3.04 (2br.s,
OH); 3.01±2.87 (m, SiCH2); 0.76 (s, t-Bu); 0.60, 0.58(2 s,
Sit-Bu); 20.04, 20.13 (2 s, SiMe). 13C NMR: 143.5, 138.6,
138.0 (3s, 2 arom. C); 128.7, 127.8 (2d, 2£2 arom. C); 127.6
(d, arom. C); 126.8, 126.1 (2d, 2£2 arom. C); 126.1 (d, arom.
C); 80.2, 79.9 (2s, COH); 77.2 (t, PhCH2); 66.5 (t, SiOCH2);
60.5 (t, SiCH2); 36.8(s, CMe3); 26.2, 25.8(2q, C Me3 and
SiCMe3); 17.9 (s, SiCMe3); 27.9, 28.2 (2q, SiMe). CI-MS:
432 (26, [M1NH4]1); 414 (19, [M1NH4±H2O]1); 397
(100, [M1H±H2O]1). Anal. calcd for C25H38O3Si
(414.66): C 72.41, H 11.58. Found: C 72.13, H 9.24.
5.4.11. (2Rp,SiRp)- and (2Sp,SiRp)-1-{[[(Benzyloxy)-
methyl](tert-butyl)methylsilyl]oxy}-2-methyl-5-(2-methyl-
1,3-dioxolan-2-yl)pentan-2-ol (7k and 7k0). According to
general procedure given in Section 5.2.3, 1b (295 mg,
1.00 mmol) gave upon treatment with 3-(2-methyl-1,3-
dioxolan-2-yl) prop-1-yl magnesium bromide (13)13 7k/
7k0 (360 mg, 0.85 mmol, 85%, ratio 60:40) as a colorless
oil. Data from mixture. IR: 3460, 2960, 2930, 2860, 1380,
1250, 1100, 1070, 840. 1H NMR (signals of 7k0 are given in
italics): 7.37±7.24 (m, 5 arom. H); 4.48(s, PhC H2); 3.97±
3.87 (m, OCH2CH2O); 3.54, 3.48(AB, Jˆ9.9 Hz, SiOCH2);
3.28, 3.20 (AB, Jˆ13.4 Hz, SiCH2); 2.40 (br.s, OH); 1.66±
1.39 (m, (CH2)3); 1.31 (s, Me); 1.12, 1.09 (2s, COHMe);
0.92 (s, t-Bu); 0.13 (s, SiMe). 13C NMR: 137.2 (s, arom.
C); 128.2, 127.7 (2d, 2£2 arom. C); 127.5 (d, arom. C);
110.1 (s, OCO); 77.1 (t, PhCH2); 72.4, 72.3 (2s, COH);
71.1, 71.0 (2t, SiOCH2) 64.6 (t, OCH2CH2O); 63.7, 60.4
(2t, SiCH2); 39.8, 38.7, 37.9(3t, CH2CH2CH2); 26.0 (q,
CMe3); 23.7, 23.1, 22.8(3t, COH Me and Me); 18.5 (s,
CMe3); 18.3, 18.2 (2t, CH2CH2CH2); 28.2 (q, SiMe).
CI-MS: 363 (67, [M2C2H5O2]1); 267 (100). Anal. calcd
for C23H40O5Si (424.65): C 65.05, H 9.49. Found: C
62.41, H 9.05.
5.4.14. (3Sp,SiRp)- and (3Rp,SiRp)-1-{[[(Benzyloxy)-
methyl](tert-butyl)methylsilyl]oxy}pentan-3-ol (8c and
8c0). According to general procedure given in Section
5.2.3, 2a (100 mg, 0.34 mmol) gave upon treatment with
EtMgBr 8c/8c0 (96 mg, 0.30 mmol, 88%, ratio 37:63,
Entry 14 of Table 1) as a colorless oil. Data from mixture.
IR: 3450br., 2960, 2930, 2860, 1080. 1H NMR (signals of 8c
are given in italics): 7.37±7.24 (m, 5 arom. H); 4.49 (s,
PhCH2); 4.03±3.82 (m, SiOCH2); 3.79±3.68(m, C HOH);
3.34±3.21 (m, SiCH2 and OH); 1.73±1.40 (m, OCH2CH2
and CH2Me); 0.97± 0.90 (m, CH2Me); 0.93 (s, t-Bu);
0.14, 0.13 (2s, SiMe). 13C NMR: 138.5 (s, arom. C);
128.3, 127.7 (2d, 2£2 arom. C); 127.5 (d, arom. C); 77.2
(t, PhCH2); 72.7, 72.3 (d, CHOH); 63.1, 62.6 (t, SiOCH2);
60.5, 60.3 (2t, SiCH2); 38.1 (t, OCH2CH2); 30.2 (t, CH2Me);
26.1 (q, CMe3); 18.1, 18.0 (s, CMe3); 10.0, 9.9 (2q, CH2Me);
28.0, 28.1 (2q, SiMe). CI-MS: 342 (54, [M1NH4]1); 325
(100, [M1H]1). Anal. calcd for C18H32O3Si (324.53): C
66.62, H 9.94. Found: C 66.37, H 10.03.
5.4.15. (1Rp,SiRp)- and (1Sp,SiRp)-3-{[[(Benzyloxy)-
methyl](tert-butyl)methylsilyl]oxy}-1-phenylpropanol
(8d and 8d0). According to general procedure given in
Section 5.2.3, 2a (100 mg, 0.34 mmol) gave upon treatment
with PhMgBr 8d/8d0 (120 mg, 0.32 mmol, 95%, ratio
5.4.12. 3-{[[(Benzyloxy)methyl](tert-butyl)methylsilyl]-
oxy}propanol (8a). According to general procedure given

M. Trzoss et al. / Tetrahedron 58 (2002) 5885±5894
5893
34:66, Entry 15 of Table 1) as a colorless oil. Data from
mixture. IR: 3420br., 2950, 2930, 2880, 2860, 1090, 1070,
700. 1H NMR (signals of 8d are in given italics): 7.39±7.20
(m, 10 arom. H); 4.99±4.93 (m, CHOH); 4.50 (s, PhCH2);
4.03±3.85 (m, SiOCH2); 3.67 (br.s, OH); 3.36±3.18(m,
SiCH2); 2.00±1.90 (m, OCH2CH2); 0.96 (s, t-Bu); 0.16,
0.15 (2s, SiMe). 13C NMR: 144.7 (s, arom. C); 138.4
(s, arom. C); 128.3 (d, 4 arom. C); 127.8 (d, 2 arom. C);
127.5, 127.1 (2d, 2 arom. C); 125.8(d, 2 arom. C); 77.2
(t, PhCH2); 73.3, 72.9 (2d, CHOH); 62.5, 62.1 (2t, SiOCH2);
60.4, 60.3 (2t, SiCH2); 40.9 (t, OCH2CH2); 26.1 (q, CMe3);
18.0 (s, CMe3); 28.0, 28.1 (2q, SiMe). CI-MS: 390 (18,
[M1NH4]1); 237 (90); 117 (100). Anal. calcd for
C22H32O3Si (372.58): C 70.92, H 8.66. Found: C 70.87, H
8.56.
Section 5.2.3, 2c (150 mg, 0.46 mmol) and 2d (50 mg,
0.13 mmol) gave upon treatment with PhMgBr and
EtMgBr, respectively, 8h/8h0 (166 mg, 0.41 mmol, 90%,
ratio 16:84, and 48 mg, 0.12 mmol, 89%, ratio 82:18,
Entries 18and 21 of Table 1) as colorless oils. Data from
mixture. IR: 3490, 2950, 2930, 2880, 2850, 1470, 1085,
1
1050, 700. H NMR (signals of 8h are given in italics):
7.42±7.18(m, 10 arom. H); 4.43 (s, OH); 4.37 (s,
PhCH2); 3.88±3.54 (m, SiOCH2); 3.19±3.04 (m, SiCH2);
2.23±1.70 (m, OCH2CH2 and CH2Me); 0.90 (s, t-Bu);
0.75 (t, CH2Me); 0.05, 0.02 (2s, SiMe). 13C NMR: 146.1,
138.6 (2s, 2 arom. C); 128.2, 127.8, 127.5 (3d, 3£2 arom.
C); 127.4, 126.0 (2d, 2 arom. C); 125.7 (d, 2 arom. C); 77.7
(s, COH); 76.9 (t, PhCH2); 61.7 (t, SiOCH2); 60.1 (t,
SiCH2); 42.2 (t, OCH2CH2); 36.6 (t, CH2Me); 26.0 (q,
CMe3); 17.9 (s, CMe3); 7.53 (q, CH2Me); 28.5 (q, SiMe).
CI-MS: 418(8, [M 1NH4]1); 256 (50); 145 (100). Anal.
calcd for C24H36O3Si (400.63): C 71.95, H 9.06. Found: C
72.33, H 8.81.
5.4.16. (3Rp,SiRp)- and (3Sp,SiRp)-1-{[[(Benzyloxy)-
methyl](tert-butyl)methylsilyl]oxy}-4-methylpentan-3-ol
(8e and 8e0). According to general procedure given in
Section 5.2.3, 2a (100 mg, 0.34 mmol) gave upon treatment
with i-PrMgBr 8e/8e0 (100 mg, 0.30 mmol, 87%, ratio
36:64, Entry 16 of Table 1) as a colorless oil. Data from
5.4.19. (3Sp,SiRp)- and (3Rp,SiRp)-1-{[[(Benzyloxy)-
methyl](tert-butyl)methylsilyl]oxy}-4-methyl-3-phenyl-
pentan-3-ol (8i and 8i0). According to general procedure
given in Section 5.2.3, 2e (100 mg, 0.30 mmol) and 2d
(50 mg, 0.13 mmol) gave upon treatment with PhMgBr
and i-PrMgBr, respectively, 8i/8i0 (110 mg, 0.26 mmol,
88%, ratio 37:63, and 49 mg, 0.11 mmol, 87%, ratio
80:20, Entries 19 and 22 of Table 1) as colorless oils.
Data from mixture. IR: 3490, 2960, 2930, 2880, 2860,
1
mixture. IR: 3480br.m, 2950, 2930, 2860, 1080. H NMR
(signals of 8e are given in italics): 7.37±7.24 (m, 5 arom.
H); 4.49 (s, PhCH2); 4.10±3.82 (m, SiOCH2); 3.60±3.52 (m,
CHOH); 3.35±3.16 (m, SiCH2 and OH); 1.72±1.53 (m,
OCH2CH2 and CHMe2; 0.93 (s, t-Bu); 0.89 (d, Jˆ8Hz,
CHMe2); 0.15, 0.14 (2s, SiMe). 13C NMR: 138.5 (s, arom.
C); 128.2, 127.7 (2d, 2£2 arom. C); 127.5 (d, arom. C); 77.2
(t, PhCH2); 76.2, 75.9 (2d, CHOH); 63.4, 63.0 (2t, SiOCH2);
60.5, 60.4 (2t, SiCH2); 35.4 (t, OCH2CH2); 33.7 (d,
CHMe2); 26.1 (q, CMe3); 18.5, 17.8 (2q, CHMe2) 18.1,
18.0 (2s, CMe3); 28.0, 28.1 (2q, SiMe). CI-MS: 356 (26,
[M1NH4]1); 339 (100, [M1H]1). Anal. calcd for
C19H34O3Si (338.56): C 67.41, H 10.12. Found: C 67.17,
H 10.21.
1
1470, 1090, 1075, 705. H NMR (signals of 8i are given
in italics): 7.39±7.17 (m, 10 arom. H); 4.41, 4.37 (2s,
PhCH2); 4.23 (s, OH); 3.83±3.45 (m, SiOCH2); 3.19±2.97
(m, SiCH2); 2.36±2.24 (m, CHMe2; 1.96±1.86 (m,
OCH2CH2); 0.99 (d, Jˆ6.5 Hz, CHMe); 0.87 (s, t-Bu);
0.69 (d, Jˆ6.5 Hz, CHMe); 0.01, 20.09 (2s, SiMe). 13C
NMR: 145.8, 138.7 (2s, 2 arom. C); 128.2, 127.6 (2d, 2£2
arom. C); 127.5, 127.3 (2d, 2 arom. C); 126.2, 125.9 (2d,
2£2 arom. C); 79.5 (s, COH); 76.8(t, Ph CH2); 61.9 (t,
SiOCH2); 60.3, 60.1 (2t, SiCH2); 39.4 (t, OCH2CH2); 38.9
(d, CHMe2); 26.0 (q, CMe3); 17.9 (s, CMe3); 17.3, 16.7 (2q,
CHMe2); 28.5 (q, SiMe). CI-MS: 432 (8, [M1NH4]1); 159
(100). Anal. calcd for C25H38O3Si (414.66): C 72.41, H 9.24.
Found: C 72.44, H 9.06.
5.4.17. (2Rp,SiRp)- and (2Sp,SiRp)-4-{[[(Benzyloxy)-
methyl](tert-butyl)methylsilyl]oxy}-2-phenylbutan-2-ol
(8g and 8g0). According to general procedure given in
Section 5.2.3, 2b (150 mg, 0.48mmol) and 2d (50 mg,
0.13 mmol) gave upon treatment with PhMgBr and
MeMgBr, respectively, 8g/8g0 (168mg, 0.43 mmol, 90%,
ratio 13:87, and 48 mg, 0.12 mmol, 92%, ratio 75:25,
Entries 17 and 20 of Table 1) as colorless oils. Data from
mixture. IR: 3490, 2950, 2930, 2880, 2860, 1470, 1090,
5.4.20. (2Rp,SiRp)- and (2Sp,SiRp)-4-{[[(Benzyloxy)-
methyl](tert-butyl)methylsilyl]oxy}-2-[2-(2-{[tert-butyl-
(dimethyl)silyl]oxy}ethyl)phenyl]butan-2-ol (8l and 8l0).
According to general procedure given in Section 5.2.3, 2b
(200 mg, 0.65 mmol) gave upon treatment with Grignard
reagent 14, prepared from {[(2-bromophenyl)ethyl]oxy}-
(tert-butyl)dimethylsilane,14 recovered 2b (130 mg, 0.42
mmol, 65%) and 8l/8l0 (60 mg, 0.11 mmol, 17% (74%
based on consumed 2b) ratio 8:92) as colorless oils. Data
from mixture. IR: 3480, 2960, 2920, 2880, 2850, 1470,
1
1070, 700. H NMR (signals of 8g are given in italics):
7.45±7.18(m, 10 arom. H); 4.53, 4.52 (2s, OH); 4.44,
4.38(2s, PhC H2); 3.88±3.59 (m, SiOCH2); 3.21±3.08(m,
SiCH2); 2.19±1.98(m, OCH CH2); 1.52 (s, COHMe); 0.91
2
(s, t-Bu); 0.06, 0.01 (2s, SiMe). 13C NMR: 147.9 (s, arom.
C); 138.6 (s, arom. C); 128.2 (d, 2 arom. C); 128.0, 127.6
(2d, 2£2 arom. C); 127.4, 126.2 (2d, 2 arom. C); 125.0 (d, 2
arom. C); 76.9 (t, PhCH2); 75.2 (s, COH); 61.8(t, SiOCH 2);
60.1 (t, SiCH2); 43.5 (t, OCH2CH2); 31.2 (q, COHMe); 26.0
(q, CMe3); 17.9 (s, CMe3); 28.5 (q, SiMe). CI-MS: 404
(100, [M1NH4]1); 386 (52, [M1NH4±H2O]1). Anal.
calcd for C23H34O3Si (386.60): C 71.46, H 8.86. Found: C
71.27, H 8.80.
1
1460, 1255, 1090, 835, 775. H NMR (signals of 8l are
given in italics): 7.45±7.12 (m, 9 arom. H); 4.66 (s, OH);
4.45, 4.41 (2s, PhCH2O); 3.92±3.68(m, C H2CH2Ph and
SiOCH2); 3.30±2.98(m, SiCH and CH2Ph); 2.28±2.06
2
(m, COHCH2); 1.60 (s, COHMe); 0.91, 0.84 (2, 2£t-Bu);
0.09, 0.05 (2s, SiMe); 20.02, 20.03 (2s, SiMe2). 13C NMR:
145.8, 138.7, 136.3 (3s, 3 arom. C); 131.9, 128.2, 127.5,
127.3, 126.6, 125.9 (6d, 9 arom. C); 75.7 (t, PhCH2O);
75.6 (s, COH); 65.4, 61.5, 60.5, 60.4 (3t, SiOCH2, SiCH2
5.4.18. (3Rp,SiRp)- and (3Sp,SiRp)-1-{[[(Benzyloxy)-
methyl](tert-butyl)methylsilyl]oxy}-3-phenylpentan-3-ol
(8h and 8h0). According to general procedure given in

5894
M. Trzoss et al. / Tetrahedron 58 (2002) 5885±5894
and CH2CH2Ph); 44.5, 37.1 (2t, OCH2CH2 and CH2Ph);
30.8(q, COH Me); 26.1, 25.9 (2q, 2£CMe3); 18.4, 18.0
(2s, 2£CMe3); 25.4 (q, SiMe2); 28.5 (q, SiMe). CI-MS:
545 (86, [M1H]1); 544 (100, [M1NH4±H2O]1). Anal.
calcd for C31H52O4Si2 (544.91): C 68.33, H 9.62. Found:
C 68.40, H 9.51.
References
1. Greene, T. W. Protective Groups in Organic Synthesis; Wiley:
New York, 1981. Kocienski, P. J. Protecting Groups; Georg
Thieme: Stuttgart, 1994.
2. Koch, P.; Kunz, R. W.; Bienz, S. Molecules Online 1999, 3, 9.
È
Fassler, J.; Enev, V.; Bienz, S. Helv. Chim. Acta 1999, 82,
Fassler, J.; Linden, A.; Bienz, S. Tetrahedron 1999, 55, 1717.
È
5.5. Proof of relative con®gurations
561. Bratovanov, S.; Bienz, S. Tetrahedron: Asymmetry 1997,
8, 1587. Huber, P.; Bratovanov, S.; Bienz, S.; Syldatk, C.;
Pietzsch, M. Tetrahedron: Asymmetry 1996, 7, 69.
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as Auxiliaries for Enantioselective Synthesis: Access to
Optically Active Silanes by Biotransformation and the
Enantiospeci®c Preparation of (R)-(1)-1-Phenylethanol.
Biochemical Engineering; Schmid, R. D., Ed.: Stuttgart,
1995; Vol 3, p 70.
5.5.1. (2)-(R)-2-Phenylpropan-1,2-diol ((2)-(R)-10).
According to general procedure given in Section 5.2.3,
(S)-1d7 (90 mg, 0.25 mmol) was treated with MeMgBr.
After workup without chromatography, the crude mixture
of 7g/7g0 was dissolved in Et2O (2 mL), LiAlH4 (10 mg,
0.25 mmol, 1 equiv.) was added at 2308C, and it was stirred
for 3 h. After warming to 2108C, dilute aq. H2SO4 was
added to neutral pH. It was extracted with Et2O and
chromatographed (hexane/Et2O 2:1) to afford (2)-(R)-10
(33 mg, 0.22 mmol, 87%, [a]Dˆ25.3 (c 1.40, Et2O), lit.:
[a]Dˆ28.6 (c 1.18, Et2O)8) as a colorless oil.
3. Enev, V.; Stojanova, D.; Bienz, S. Helv. Chim. Acta 1996, 79,
391.
5.5.2.
(2)-(S)-3-Phenylbutan-1,3-diol
((2)-(S)-11).
4. Chapeaurouge, A.; Bienz, S. Helv. Chim. Acta 1993, 76, 1876.
Bienz, S.; Chapeaurouge, A. Helv. Chim. Acta 1991, 74, 1477.
5. Bienz, S. Chimia 1997, 51, 133.
According to general procedure given in Section 5.2.3,
(S)-2b (115 mg, 0.30 mmol) was treated with PhMgBr.
After workup without chromatography, the crude mixture
of 8g/8g0 was dissolved in Et2O, LiAlH4 (11 mg,
0.30 mmol, 1 equiv.) was added at 2308C, and it was stirred
for 3 h. After warming to 2108C, dilute aq. H2SO4 was
added to neutral pH. It was extracted with Et2O and
chromatographed (hexane/Et2O 2:1) to afford (2)-(S)-9
(42 mg, 0.25 mmol, 85%, [a]Dˆ223.2 (c 0.76, benzene),
lit.: of (1)-(R)-11, [a]Dˆ165.2 (c 0.41, benzene)9 as a
colorless oil.
6. Gassmann, S.; Guintchin, B.; Bienz, S. Organometallics 2001,
20, 1849.
7. Trzoss, M.; Shao, J.; Bienz, S. in preparation.
8. Archelas, A.; Furstoss, R. J. Org. Chem. 1999, 64, 6112.
9. Hosokawa, T.; Yagi, T.; Ataka, Y.; Murahashi, S.-I. Bull.
Chem. Soc. Jpn. 1988, 61, 3380.
10. Kienzer, G. W.; Fentiman, A. F.; Page, T. F.; Folz, R. L.; Vite,
J. P.; Pitman, G. B. Nature 1969, 221, 477.
11. Yus, M.; Ramon, D. J. J. Org. Chem. 1992, 57, 750.
12. WuÈnsch, B.; Bauschke, G. Liebigs Ann. Chem. 1992, 345.
13. Redlich, H.; Schneider, B.; Hoffmann, R. W.; Geueke, K.-J.
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Acknowledgements
14. Feldman, K. S.; Bruendl, M. M.; Schildknegt, K.; Bohnstedt,
A. C. J. Org. Chem. 1996, 61, 5440.
We would like to thank the Swiss National Science Foun-
dation for their generous ®nancial support and the Chinese
Scholarship Counsel for the fellowship of S. J.