[1,2]-Wittig rearrangement of acetals. Part 2: The influence of reaction conditions1

Article abstract of DOI:10.1016/S0957-4166(00)00028-8

Acetals of seven alcohols with (+)-camphor derived enantiomerically pure 7,8,8-trimethyl-4,7-methanobenzofuran-2-ol were subjected to different reaction conditions favorable for a [1,2]-Wittig rearrangement. Results with regard to conversion, yield and st

Full text of DOI:10.1016/S0957-4166(00)00028-8

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 11 (2000) 1003–1013
[
1,2]-Wittig rearrangement of acetals. Part 2: The influence of
1
reaction conditions
Peter Gärtner, Martin F. Letschnig, Max Knollmüller and Kurt Mereiter
a,∗
a
a
b
a
Institute of Organic Chemistry, Vienna University of Technology, Getreidemarkt 9, A-1060 Vienna, Austria
b
Institute of Mineralogy, Crystallography and Structural Chemistry, Vienna University of Technology, Getreidemarkt 9,
A-1060 Vienna, Austria
Received 17 December 1999; accepted 18 January 2000
Abstract
Acetals of seven alcohols with (+)-camphor derived enantiomerically pure 7,8,8-trimethyl-4,7-meth-
anobenzofuran-2-ol were subjected to different reaction conditions favorable for a [1,2]-Wittig rearrangement.
Results with regard to conversion, yield and stereochemical course depending on the reaction conditions are
discussed. © 2000 Elsevier Science Ltd. All rights reserved.
1
. Introduction
The [1,2]-Wittig rearrangement of acetals has gained much interest as a new method for the synthesis
2
of C-glycosides which cannot be obtained easily by other methods. In our own efforts towards a better
understanding of this reaction we have recently described results with regard to substrate dependence of
1
conversion, yield and stereochemical course. To exclude the possibility that observed differences with
regard to the investigated parameters were due only to the different structure of the substrates we carried
out all the reactions under a standardized protocol. Since the observed yields and stereoselectivities
were only satisfactory to a limited degree we wanted to investigate whether some improvement could
be achieved by running the reaction under other conditions, i.e. varying solvent, temperature, reaction
time, equivalents of base and base activating additives.
2
. Results and discussion
1
The acetals 1–10 were treated with butyl lithium under conditions which were systematically changed
for each experiment (Scheme 1).
∗
Corresponding author. Fax: +43-1-58801-154 92; e-mail: pgaertne@mail.zserv.tuwien.ac.at
0
957-4166/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(00)00028-8
tetasy 3251

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P. Gärtner et al. / Tetrahedron: Asymmetry 11 (2000) 1003–1013
Scheme 1. [1,2]-Wittig rearrangement of the acetals 1–10
Details for experimental parameters and results with regard to conversion, yield and stereoselectivity
as well as for by-product formation in each series are given in Tables 1–10.
Most of the substrates yielded only the rearranged alcohols 11–18 besides unreacted starting material
1–10 and product 19 which can be formed under these conditions by β-elimination from the acetals.
The relative amount of 19 was usually higher under more basic conditions (1–7, 1–12, 5–5). All
reactions proceeded with complete retention with regard to the former acetal center. The assignment
of configuration for this center as well as for the newly formed alcohol center which is given in Tables
1
13
1
–10 was based on characteristic shift differences observed in the H and C NMR spectra, as described
1
earlier. Only in the rearrangement of 6 was a further by-product 20 formed each time: it is the product of
water addition to 19 and it seems as if the pyridine ring present in the aglycon-part of 6 has a significant
influence on the formation of 20.
Depending on the scale of the reaction and the rate of addition of the base a rise in temperature was
usually observed. Since the temperature seems to be a crucial factor with regard to yield (compare 1–6
with 1–4, 6–2 with 6–1, 7–7 with 7–5) and selectivity (compare 1–6 with 1–4, 7–7 with 7–5) it was
important to observe and control it very carefully for reasons of comparison. In general we always tried
to compare experiments in which the only parameter under question was changed. In the large scale
experiment 1–3 the rise in temperature was already high at the beginning of the addition of the base so
we had to cool the mixture before more base was added. In contrast to other experiments conducted at
lower temperature in this case the stereoselectivity dropped.
Reactions in Et O for most of the acetals gave better selectivities but lower yields (1–4, 2–2, 7–4, 8–2)
2
even if the configuration of the major product was switched (7–4). However, in two experiments yields are
better in this solvent (5–2, 6–4) but selectivities are worse (6–4) compared with experiments performed
in THF under standard temperature conditions. If the reaction was carried out in the apolar solvents
n-hexane or toluene the yield was usually very low (1–9, 1–10, 2–3, 2–4, 5–3, 5–4) and sometimes the
stereoselectivity was inverted (1–9, 1–10, 7–5, 7–8, 8–3, 8–4) compared to the results in THF. For acetals
6–8 which bear additional moieties capable of complex formation with butyl lithium no such influence
on the yield was observed. For the other acetals yields in apolar solvents could be improved if more
equivalents of base at higher temperature (1–11) or additives such as TMEDA (1–12, 2–5, 5–5) or (−)-
sparteine (7–9) were used. But this again resulted in a switch of the configuration of the major isomer
(
1–11, 1–12, 2–5, 7–9). This change in stereoselectivity was also observed when these additives were
used in more polar solvents (3–2), but this time not necessarily improving the yield. One experiment
3–3) in which HMPA was used as an additive in THF even showed no conversion at all. So did another
one in which a polar coordinating solvent was used (4–3).
(

P. Gärtner et al. / Tetrahedron: Asymmetry 11 (2000) 1003–1013
1005
Table 1
Summary of the [1,2]-Wittig rearrangement of acetal 1
If less than 3 equiv. of base were used yields in most of the experiments were lower (1–2, 7–2) even if
the reaction was allowed to proceed longer (1–2) or at higher temperature (7–2). Addition of further base
at a later stage also did not improve the yield significantly (7–3). For acetal 6 with the pyridine-moiety
the yield was not influenced at all, but unexpectedly the stereoselectivity was higher when less base for
a shorter reaction time was used (6–3). It was also the other diastereomer which was formed in excess
under these conditions.
Bearing in mind the proposed radical mechanism2b,c,3 for the [1,2]-Wittig-rearrangement we carried
out one experiment (1–5) in which we irradiated the reaction mixture with a wide-band lamp. As expected
the yield could be improved, but the selectivity dropped to half of the value obtained without irradiation.
However, as was shown by another experiment at elevated temperature without irradiation (1–6), this was
due only to the rise in temperature caused by the irradiation lamp.
The use of t-BuLi at lower temperatures instead of n-BuLi resulted for acetal 1 in a low yield (1–7) and
a slight drop in stereoselectivity whereas no significant changes were observed with acetal 4. The addition
of base in two portions did not influence either the yield or the selectivity (7–6), but if a large excess of

1
006
P. Gärtner et al. / Tetrahedron: Asymmetry 11 (2000) 1003–1013
Table 2
Summary of the [1,2]-Wittig rearrangement of acetal 2
Table 3
Summary of the [1,2]-Wittig rearrangement of acetal 3
Table 4
Summary of the [1,2]-Wittig rearrangement of acetal 4

P. Gärtner et al. / Tetrahedron: Asymmetry 11 (2000) 1003–1013
1007
Table 5
Summary of the [1,2]-Wittig rearrangement of acetal 5
Table 6
Summary of the [1,2]-Wittig rearrangement of acetal 6
base was used the yield and selectivity could be raised to acceptable values even at low temperature
1–8).
The highly hindered acetals 8 and 9 which could not be rearranged under our standard reaction
(
conditions were also resistant in several experiments in which stronger bases, irradiation and a higher
temperature were applied.
In one experiment with acetal 5 as the substrate in ether, which was carried out for 72 h to see whether
the yield could be further improved, only 37% of 15 was isolated instead of 68%. However, besides 15,
3
3% of 21 was obtained. This phenol must have been formed by ortho-lithiation of 15 followed by air-
4
oxidation (Scheme 2), which is not unprecedented. Obviously, due to the long reaction time some air
must have passed into the reaction flask yielding 21. Anyway, the combined yield of 15 and 21 was not
higher than in the short term experiment.
It is noteworthy that 21 was formed as a single diastereomer, the configuration of which was established
5
by X-ray analysis of the m-nosylate 22 (Fig. 1). This was obtained by treatment of 21 with 3-

1
008
P. Gärtner et al. / Tetrahedron: Asymmetry 11 (2000) 1003–1013
Table 7
Summary of the [1,2]-Wittig rearrangement of acetal 7
Table 8
Summary of the [1,2]-Wittig rearrangement of acetal 8
nitrobenzenesulfonic acid in the presence of triethylamine. The compound crystallizes in the chiral
orthorhombic space group P2 2 2 with four equivalent molecules in the unit cell linked in chains
1
1 1
parallel to b via hydrogen bonds O(2)–H(2o)···O(5) with O(2)···O(5)=2.91 Å. The absolute structure
could be determined via the anomalous dispersion effect of sulfur and was consistent with the known
configuration of the (+)-camphor moiety. The configuration at the carbinol carbon atom C13 was found
6
to be S, as shown in Fig. 1.
A further interesting observation was made when acetal 8 was rearranged in n-hexane. Unexpectedly

P. Gärtner et al. / Tetrahedron: Asymmetry 11 (2000) 1003–1013
1009
Table 9
Summary of the [1,2]-Wittig rearrangement of acetal 9
Table 10
Summary of the [1,2]-Wittig rearrangement of acetal 10
Scheme 2. Stereoselective hydroxylation of 15
one of the phenolic methyl ethers was cleaved selectively during this reaction, giving rise to compound
3 (Fig. 2). Since a separation of the diastereomeric alcohols 18 was not possible and we had already
2
1
been successful via formation of acetals, product 24 (Fig. 2) was synthesized from 18 by a standard
procedure. Unfortunately, in this case even the acetals 24 could not be separated.
7

1
010
P. Gärtner et al. / Tetrahedron: Asymmetry 11 (2000) 1003–1013
Fig. 1. Molecular structure of 22 in crystalline state (20% ellipsoids) with crystallographic atom numbering. Selected geometric
data [Å, °]: O1–C1=1.429(3), O1–C8=1.438(3), C1–C13=1.559(3), C13–O2=1.437(3), C21–O3=1.415(3), O(3)–S=1.582(3),
O1–C1–C13–O2=−177.8(2), C1–C13–O2–H2o=70.7
Fig. 2. By-product 23 derived from 8 by selective ether-cleavage and acetal 24
3. Conclusion
From the obtained data it must be concluded that the yield as well as the selectivity, and this not only
with regard to the absolute value but also the configuration of the newly formed alcohol carbon for the
major isomer, in the [1,2]-Wittig rearrangement of acetals can be heavily influenced by solvent, additives,
temperature and amount of base. Although some general dependencies could be elaborated it is difficult to
predict, for a single experiment under different reaction conditions, what will be the result. However, one
point on which we could shed light is the fact that the earlier proposed mechanism2
b–c,3b–d
in which the
two radical fragments are tightly held together through coordination with the lithium counter-ion cannot
be operative, or at least not in this simple manner; otherwise the selectivity should be higher in solvents
which are not able to coordinate, and more convincingly the configuration of the major isomer should
not be changed. Since the opposite is observed we have to assume that in the presence of coordinating
agents these are involved in the transition state and have a high impact on the stereoselectivity. Only in

P. Gärtner et al. / Tetrahedron: Asymmetry 11 (2000) 1003–1013
1011
cases where coordination within the radical fragment itself is possible is no such dependence observed.
A further consideration which might be of general interest, but which must be secured by some further
experiments, is a possible reaction time or conversion dependence of the stereoselectivity. Experiments
with regard to this aspect will be published in the near future.
4. Experimental
4.1. General
1
13
Melting points are uncorrected. NMR: Bruker AC 200 (200 and 50 MHz for H and C, respectively).
1
13
For H NMR CHCl at δ =7.24 as internal standard; for C NMR CDCl at δ =77.0 as internal
3
H
3
C
standard. Optical rotations were measured with a Perkin–Elmer 241 polarimeter in a 10 cm cell. TLC was
performed with Merck silica gel 60 F254; visualization of the spots with molybdato phosphoric acid (5%
in ethanol) and heating. Column chromatography and vacuum flash chromatography (VFC) were carried
out with Merck silica gel 60 (230–400 mesh). Abbreviation used: PE=petroleum ether. The concentration
of n-butyl lithium in n-hexane was determined by titration with t-butanol using 1,10-phenanthroline as
indicator. For a general procedure for the rearrangements of acetals 1–10 see Ref. 1.
4
.2. [2R-(2α(S*),3aα,4β,7β,7aα)]-Octahydro-α-(2-hydroxyphenyl)-7,8,8-trimethyl-α-phenyl-4,7-
methanobenzofuran-2-methanol 21
n-Butyl lithium (0.49 ml, 1.26 mmol) in n-hexane was added dropwise to a solution of 5 (0.150 g, 0.41
mmol) in anhydrous diethyl ether (2.5 ml) at room temperature. The reaction mixture was stirred for 72
h, quenched with water, and the aqueous phase was extracted twice with diethyl ether. The combined
organic layers were dried with sodium sulfate, filtered and the solvent was evaporated. The crude product
1
was purified by VFC (10 g silica gel, gradient of PE:Et O=30:1 to 10:1). Yield: 0.055 g (37%) of 15 and
2
0
.049 g (33%) of 21. Colorless crystals, mp=154–155°C (n-hexane:CH Cl ), R (PE:Et O=8:1)=0.13,
2 2 f 2
2
0
[
α] =+22.0 (c 0.60, CHCl ); C H O (378.51): calculated: C 79.33, H 7.99; found: C 79.37, H 8.23;
D
3
25 30
3
1
H NMR (200 MHz; CDCl ): δ =0.75–2.45 (m, 17H, aliphatic-H, therein: 0.81, 0.97 and 1.06 (3s, 9H,
CH )), 3.20 (s, 1H, OH), 3.94 (d, 1H, 7a-H), 5.07 (dd, 1H, 2-H), 6.65–7.60 (m, 9H, aromatic-H), 9.22
3
H
3
1
3
(
(
(
s, 1H, Ph-OH); C NMR (50 MHz; CDCl ): δ =11.46/19.93/22.72 (3q, 3 CH ), 28.58 (t, C-5), 32.21
3
C
3
t, C-6), 33.47 (t, C-3), 46.01/48.97 (2s, C-7, C-8), 48.76/49.47 (2d, C-4, C-3a), 85.45 (d, C-2), 86.01
s, C*), 95.38 (d, C-7a), 117.83/119.25 (2d, 2*meta-C), 127.13 (s, ipso-C), 127.66/128.09 (2d, 2*ortho-
0
0
0
0
C , 2*meta-C ), 127.52/128.59/128.73 (3d, para-C, ortho-C, para-C ), 145.03 (s, ipso-C ), 155.88 (s,
ortho-C-OH).
4
.3. [2R-(2α(S*),3aα,4β,7β,7aα)]-2-[(Octahydro-7,8,8-trimethyl-4,7-methanobenzofuran-2-yl)-
hydroxyphenylmethyl]phenyl 3-nitrobenzenesulfonate 22
m-Nitrobenzenesulfonic acid (0.891 g, 0.402 mmol) and anhydrous NEt (0.11 ml, 0.654 mmol)
3
were added dropwise to a solution of 21 (0.10 g, 0.264 mmol) in anhydrous dichloromethane (5 ml)
at 0°C. The cooling bath was removed, the reaction mixture was stirred for 17 h at room temperature
and then quenched with water. The aqueous phase was extracted twice with dichloromethane and
the combined organic layers were dried with sodium sulfate and filtered. The solvent was evaporated
and the crude product was purified by VFC (10 g silica gel, PE:Et O=4:1). Yield: 0.131 g (88%)
2

1
012
P. Gärtner et al. / Tetrahedron: Asymmetry 11 (2000) 1003–1013
2
0
of colorless crystals. Mp=203–206°C (n-hexane:CHCl ), R (PE:Et O=1:1)=0.42, [α] =+29.8 (c
3
f
2
D
0
6
0
.62, CH Cl ); C H NO S (563.67): calculated: C 66.06, H 5.90, N 2.48; found: C 66.21, H
.11, N 2.39; H NMR (200 MHz; CDCl ): δ =0.65–2.20 (m, 17H, aliphatic-H, therein: 0.79,
.92 and 1.04 (3s, 9H, CH )), 2.75 (s, 1H, OH), 3.68 (d, 1H, 7a-H), 5.14 (dd, 1H, 2-H), 7.00–7.45
2 2 31 33 7
1
3
H
3
(
1
m, 8H, aromatic-H), 7.55–7.80 (m, 2H, aromatic-H), 8.00–8.08 (m, 1H, aromatic-H), 8.45 (dd,
H, aromatic-H), 8.48 (d, 1H, aromatic-H); 13C NMR (50 MHz; CDCl ): δ =11.48/19.82/22.73
3
C
(
(
-
3q, 3 CH ), 28.54 (t, C-5), 32.12 (t, C-6), 33.28 (t, C-3), 45.97/48.73 (2s, C-7, C-8), 48.59/49.38
2d, C-4, C-3a), 79.87 (s, C*), 83.52 (d, C-2), 94.97 (d, C-7a), 120.05/123.26 (2d, 2*aromatic
C), 127.47/127.54 (2d, 4*aromatic-C), 126.43/126.90/128.33/128.94/129.34/130.42/133.30 (7d,
3
7*aromatic-C), 136.55/137.87/144.03/146.85/148.02 (5s, 5*aromatic-C).
4
.4. [2R-(2α,3aα,4β,7β,7aα)]-4-[[(Octahydro-7,8,8-trimethyl-4,7-methanobenzofuran-2-yl)oxy]-
methyl]-2,6-dimethoxyphenol 23
n-Butyl lithium (2.24 ml, 3.98 mmol) in n-hexane was added dropwise to a solution of 8 (0.5 g, 1.33
mmol) in anhydrous n-hexane (10 ml) under nitrogen at room temperature. The mixture was stirred
for 3 h at room temperature and then quenched with water. The aqueous phase was extracted twice
with diethyl ether and the combined organic layers were dried with sodium sulfate and filtered. The
solvent was evaporated and the crude product was purified by column chromatography (50 g silica gel,
1
gradient of PE:Et O=1:1 to Et O). Yield: 0.099 g (20%) of 18 and 0.039 g (3%) of 23. Colorless oil, R
2
2
f
2
0
(
Et O:PE=2:1)=0.37, [α] =−63.2 (c 0.94, CHCl ); C H O (362.47): calculated: C 69.59, H 8.34;
2
D
3
21 30
5
1
found: C 69.54, H 8.34; H NMR (200 MHz; CDCl ): δ =0.73–2.42 (m, 17H, aliphatic-H, therein: 0.79,
3
H
0
(
.97 and 1.00 (3s, 9H, CH )), 3.86 (s, 6H, 2*O-CH ), 3.94 (d, 1H, 7a-H), 4.35 (d, 1H, Ph-CH ), 4.58
3 3 2
13
d, 1H, Ph-CH ), 5.19 (d, 1H, 2-H), 5.52 (s, 1H, Ph-OH), 6.57 (s, 2H, aromatic-H); C NMR (50 MHz;
2
CDCl ): δ =11.64/20.44/22.85 (3q, 3 CH ), 28.85 (t, C-5), 32.43 (t, C-6), 38.57 (t, C-3), 45.93 (d, C-3a),
3
C
3
4
1
6.97 (s, C-8), 47.60 (s, C-7), 48.41 (d, C-4), 56.22 (q, 2*O-CH ), 68.79 (t, Ph-CH -O), 91.26 (d, C-7a),
3 2
04.26 (d, C-2), 104.97 (d, 2*ortho-C), 129.38 (s, ipso-C), 134.11 (s, para-C), 146.90 (s, 2*meta-C).
.5. [2R-[2α(2S*,3aR*,4R*,7S*,7aR*),3aα,4β,7β,7aα]]-Octahydro-2-[[(octahydro-7,8,8-
4
trimethyl-4,7-methanobenzofuran-2-yl)oxy](3,4,5-trimethoxyphenyl)methyl]-7,8,8-trimethyl-4,7-
methanobenzofuran 24
A solution of (MBE) O (0.876 g, 2.34 mmol), 8 (0.44 g, 1.17 mmol) and 4-methylbenzenesulfonic acid
2
monohydrate (0.038 g, 0.2 mmol) in anhydrous dichloromethane (7 ml) was stirred for 30 min at room
temperature. Sodium sulfate was added and stirring was continued for a further 90 min. The reaction
mixture was washed with a saturated sodium hydrogen carbonate solution, the aqueous phase was
extracted twice with dichloromethane, and the combined organic layers were dried with sodium sulfate
and filtered. The solvent was evaporated and the crude product was purified by column chromatography
(
80 g silica gel, PE:Et O=3:1). Yield: 0.287 g (44%) of 24. Colorless rigid foam. R (PE:Et O=2:1)=0.27;
2
f
2
1
C H O (554.77): calculated: C 73.61, H 9.08; found: C 74.02, H 9.27; H NMR (200 MHz; CDCl ):
3
4
50
6
3
δ =0.70–2.50 (m, 68H, aliphatic-H (A,B)), 3.75–3.88 (m, 18H, 6*O-CH ), 3.73/3.87 (2d, 2*1H, 7a-
H
3
0
0
0
H, 7a -H (A)), 3.89/4.10 (2d, 2*1H, 7a-H, 7a -H (B)), 4.10-4.25 (m, 2H, 2*2 -H (A,B)), 4.35 (d, 1H,
C*-H (B)), 4.56 (d, 1H, C*-H (A)), 4.97 (dd, 1H, 2-H (B)), 5.27 (dd, 1H, 2-H (A)), 6.56 (s, 2*2H,
1
3
aromatic-H (A,B)); C NMR (50 MHz; CDCl ): δ =11.41/11.83/11.91/20.25/20.44/20.62/22.78/22.84
3
C
0
8q, 12 CH (A,B)), 28.91/31.30/32.39/32.55/33.31/38.34/38.92 (7t, C-3 (A,B), C-3 (A,B), C-6 (A,B),
3
(
0
0
0
0
C-6 (A,B), C-5 (A,B), C-5 (A,B)), 46.80/47.06/47.40/47.92 (4s, C-7 (B), C-7 (B), C-8 (B), C-8 (B)),

P. Gärtner et al. / Tetrahedron: Asymmetry 11 (2000) 1003–1013
1013
0 0
8.20/47.06/46.80/46.48 (4s, C-7 (A), C-7 (A), C-8 (A), C-8 (A)), 48.78/48.45/47.76/45.82 (4d, C-4
B), C-4 (B), C-3a (B), C-3a (B)), 49.2/49.01/48.45/46.17 (4d, C-4 (A), C-4 (A), C-3a (A), C-3a (A)),
4
(
0
0
0
0
5
6.01 (s, 2*meta-OCH (B), 2*meta-OCH (A)), 60.71 (s, para-OCH (B), para-OCH (A)), 78.07(d,
3
3
3
3
0
0
0
C* (B)), 81.99 (d, C* (A)), 82.37 (d, C-2 (B)), 84.51 (d, C-2 (A)), 91.38/90.83 (2d, C-7a (B), C-7a (B)),
9
0
3.72/91.55 (2d, C-7a (A), C-7a (A)), 102.28 (d, C-2 (B)), 103.26 (d, C-2 (A)), 105.07 (d, 2*ortho-C
(
(
B)), 106.31 (d, 2*ortho-C (A)), 137.31/136.64/135.67 (3s, para-C (B), para-C (A), ipso-C (B), ipso-C
A)), 152.74 (s, 2*meta-C (A)), 152.92 (s, 2*meta-C (B)).
References
1
2
. Gärtner, P.; Letschnig, M. F.; Knollmüller, M.; Völlenkle, H. Tetrahedron: Asymmetry 1999, 10, 4811.
. (a) Tomooka, K.; Yamamoto, H.; Nakai, T. J. Am. Chem. Soc. 1996, 118, 3317. (b) Tomooka, K.; Nakai, T. J. Synth. Org.
Chem. Jpn. 1996, 54, 1000. (c) Tomooka, K.; Yamamoto, H.; Nakai, T. Liebigs Ann. 1997, 1275. (d) Tomooka, K.; Kikuchi,
M.; Igawa, K.; Keong, P.-H.; Nakai, T. Tetrahedron Lett. 1999, 40, 1917.
3
. (a) Wittig, G.; Löhman, L. Liebigs Ann. Chem. 1942, 550, 260. (b) Schöllkopf, U. Angew. Chem. 1970, 82, 795; Angew.
Chem., Int. Ed. Engl. 1970, 9, 763. (c) Schöllkopf, U. In Methoden der Organischen Chemie (Houben-Weyl); Müller, E.; Ed.;
Thieme: Stuttgart, 1970; Vol. 13/1, p. 228. (d) Marshall, J. A. In Comprehensive Organic Synthesis; Trost, B. M.; Fleming,
I.; Eds.; Pergamon Press: Oxford, 1991; Vol. 3, p. 975.
4
5
. (a) Meyer, N.; Seebach, D. Chem. Ber. 1980, 113, 1304. (b) Tanoue, Y.; Terada, A.; Seto, I.; Umezo, Y.; Tsuge, O. Bull.
Chem. Soc. Jpn. 1988, 61, 1221.
. Crystal data of 22 (m-nosylate of 21): C31
H33NO
7
S, M=563.64, orthorhombic, space group P2
1
2
1
2
1
, a=10.176(3),
3
3
−1
b=12.377(4), c=22.164(8) Å, α=β=γ=90°, U=2791.5(16) Å , Z=4, D
c
=1.341 Mg/m , T=296(2) K, µ=0.166 mm
,
F(000)=1192, colorless plate (0.03×0.25×0.30 mm) from ethanol. Diffraction data were collected with a Siemens/Bruker
SMART CCD area detector 3-circle diffractometer (sealed X-ray tube, graphite monochromator, Mo-Kα radiation,
λ=0.71073 Å, 0.3° ω-scans, 8×606 frames covering the entire reciprocal space with θmax=25°). Structure solution by direct
2
methods, refinement by full-matrix least squares on F (Sheldrick, G. M.; SHELX-97, A System of Computer Programs for
Crystal Structure Determination; University of Göttingen, 1997). Data/restraints/parameters=4925/3/377; final R1=0.0468
(observed data), R1=0.0588 (all data), wR2=0.0947 (all data).
6
7
. Further details on the crystal structure determination have been deposited with the Cambridge Structural Database.
. Noe, C. R.; Knollmüller, M.; Steinbauer, G.; Jangg, E.; Völlenkle, H. Chem. Ber. 1988, 121, 1231.