Addition of γ-silyloxyallyltins on ethyl glyoxylate: evaluation of the influence of the experimental conditions on the stereochemical course of the reaction

Article abstract of DOI:10.1016/j.tet.2009.12.037

Ethyl glyoxylate was reacted with α-substituted γ-(t-butyldimethylsilyloxy)-allyltributyltin in order to obtain selectively each diastereomer of ethyl 3-(t-butyldimethylsilyloxy)-2-hydroxyhex-4-enoate and subsequently the corresponding diols. Diastereomer

Full text of DOI:10.1016/j.tet.2009.12.037

Tetrahedron 66 (2010) 1570–1580
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Addition of
g
-silyloxyallyltins on ethyl glyoxylate: evaluation of the influence
of the experimental conditions on the stereochemical course of the reaction
,
Alexandre Lumbroso a, Piotr Kwiatkowski b c, Anna Blonska b, Erwan Le Grognec a, Isabelle Beaudet a,
,
c
,
b
,
a,
*
Janusz Jurczak b , Slawomir Jarosz , Jean-Paul Quintard
*
*
a
´
´
`
´
´
Universite de Nantes, CNRS, Chimie et Interdisciplinarite: Synthese, Analyse, Modelisation (CEISAM), UMR CNRS 6230, Faculte des Sciences et des Techniques,
2 rue de la Houssinie`re, BP 92208, 44322 Nantes Cedex 3, France
b Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
c Department of Chemistry, Warsaw University, Pasteura 1, 02-093 Warsaw, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
Ethyl glyoxylate was reacted with a-substituted g-(t-butyldimethylsilyloxy)-allyltributyltin in order to
Received 28 September 2009
Received in revised form 11 December 2009
Accepted 14 December 2009
Available online 21 December 2009
obtain selectively each diastereomer of ethyl 3-(t-butyldimethylsilyloxy)-2-hydroxyhex-4-enoate and
subsequently the corresponding diols. Diastereomers syn-E, anti-E and anti-Z were obtained in good
yields with good to high selectivities and the obtained results were rationalized by consideration of cyclic
or open transition states in agreement with the experimental conditions and with the structure of the
starting reagents.
Keywords:
Ó 2009 Elsevier Ltd. All rights reserved.
g-Silyloxyallyltributyltins
Ethyl glyoxylate
Allylstannation
Diastereoselective synthesis
Reaction mechanisms
1. Introduction
the stereochemical course of the reaction might be predictable, but
in practice the things appear to be much more complicated, even for
Stereocontrolled synthesis of functionalized unsaturated diols
constitutes a topic of high interest due to the possible use of such
precursors as key units in the synthesis of bioactive poly-
the very simple crotyltributyltin, due to a subtle balance involving
transmetallation by metal salts or 1,3-metallotropy on the allyl unit
in addition to the primary expected mechanisms, a situation which
complicates hardly the discrimination between the possible
mechanisms.33
hydroxylated molecules.1–3 For this purpose the addition of
g-oxy-
genated allylmetals to aldehydes appears to be a key reaction,4–7
which might be interesting when allylmetals can be obtained se-
Concerning the oxygenated allyltins, the
proven to isomerize easily and stereospecifically in the presence of
boron trifluoride34 and the reactivity of the
-oxygenated isomers
proved to depend strongly on the structural factors including the
a-isomers have been
lectively either as E or Z isomers, as for instance with g-oxygenated
allyltin reagents.8–11
g
Following the pioneering work developed for these species8,12,13
several groups have used
a
-,
g- or
d-oxygenated allyltins in order to
size of the a
-substituent located on the allyltin35,36 and also the
obtain selectively polyhydroxylated molecules as for instance sugars
or modified sugars with well-defined stereochemistry.14–22 Stereo-
control of this reaction is governed by two types of mechanisms: the
concerted chair- like six-membered transition state which occurs
more readily with trans-isomers23–25 and the open transition state
(operating under Lewis acid assistance through an antiperiplanar
transition state26–28 ora synclinal transition state29–32). Accordingly,
nature of the aldehydes.37
In practice, the complexity of the situation implies a detailed
evaluation of the stereochemical trends by considering both sub-
strate and substitution of the allyltin. Keeping in mind the possible
synthesis of highly functionalized units from glyoxylates and
g
-substituted allyltins, we focused our interest on this specific
reaction.
Taking into account the propensity of
g
-silyloxyallyltins to give
syn-addition with aldehydes and iminium salts under boron tri-
fluoride assistance37–40 and the ability of glyoxylates to afford
enantioselective reactions both using the ester of an enantiopure
alcohol41,42 or using chiral (salen)chromium(III) complex promoted
* Corresponding authors. Tel.: þ33 251125408; fax: þ33 251125402.
E-mail addresses: jurczak@icho.edu.pl (J. Jurczak), sljar@icho.edu.pl (S. Jarosz),
jean-paul.quintard@univ-nantes.fr (J.-P. Quintard).
0040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.12.037

A. Lumbroso et al. / Tetrahedron 66 (2010) 1570–1580
1571
reactions,43 we focused our studies on the stereochemical behav-
iour of the allylstannation of glyoxylate by g-silyloxyallyltins.
In this case we have been unable to separate the diastereomers
obtained from 3-syn-E by liquid chromatography, but we have
found from the 1H NMR spectra recorded at 293 K and 253 K, that
the experimental results were in agreement with a preferred ‘sp’
conformation with concomitant modification of the chemical shifts
in function of the shielding effect of the mandelic aromatic ring. The
same reaction performed on 3-anti-Z, afforded two diastereomeric
bis-O-acetyl mandelic esters, which were isolated as pure products,
but similar NMR studies at 293 K and 253 K did not exhibit the
expected trends, suggesting equilibrium between the ‘sp’ and ‘ap’
conformations.46 We then considered derivatization of 3-anti-E
and 3-anti-Z into 3,5-dinitrobenzoates after removal of the silyl
group, but no suitable crystals were obtained to allow an X-ray
analysis.
2. Results
The reaction of ethyl glyoxylate with g-silyloxyallyltins 1E, 1Z
and 2E was examined under experimental conditions usually
favouring the six-membered transition state (thermal or high
pressure reactions) or open transition states (antiperiplanar or
synclinal transition states) (Scheme 1). The nature of the Lewis
acids and their ability to form monodentate complexes (electro-
philic assistance on the carbonyl group of the aldehyde) or biden-
tate complexes (interactions both with the aldehyde oxygen and
with the ester function) was carefully examined.
H
OTBDMS
Δ, HP
Bu3Sn
EtO
OTBDMS
+
EtO2C
O
R
O
R
or LA
OH
3
(R = Me)
(R = t-Bu)
1
(R = Me)
(R = t-Bu)
4
2
mixture of syn-E / syn-Z / anti-E / anti-Z
Scheme 1.
2.1. Identification of the diastereomers
Finally, we found the unambiguous method to assign the
structure of each isomer, which involved their conversion into the
corresponding acetonide according to Scheme 3.
The syn or anti configurations of these acetonides were estab-
lished on the basis of their 1H NMR spectra through NOESY ex-
periments.47 The key argument was the presence of a dipolar
Before discussing the stereochemical aspects as function of the
experimental conditions, the obtained diastereomers have to be
firmly identified. For this purpose several methods were applied for
mixtures allowing an easier purification of a single isomer, focusing
on the syn/anti identification since the E/Z identification can be
coupling between H2 (a-carboxylic proton) and H4 (vinylic proton)
3
safely assigned from the vicinal JHH coupling constants between
in the syn isomer and the absence of interaction between these two
protons in the anti isomer. On the basis of this key argument the
identity of 3-syn-E and 3-anti-E was firmly established (and cor-
roborated by further data in the NMR spectra, see Fig. 1 and ex-
perimental part).
the ethylenic protons.44 In each case, the syn/anti identification was
based on the previous desilylation of 3 or 4 as diols; then sub-
sequent modifications were attempted in order to obtain an un-
ambiguous assignment.
First, we considered the procedure based on the conversion
of diols into bis-(S)-mandelic esters as reported by Riguera
(Scheme 2).45
Once the E or Z configuration was assigned from the NMR
spectra, the whole set of identification of the obtained adducts was
easily achieved through a correlation with the corresponding
OTBDMS
1) TBAF, THF, 2h(100%)
O(Man*OAc)
O(Man*OAc)
EtO2C
EtO2C
+
EtO2C
2) (S)-O-acetylmandelic acid
DCC, DMAP, CH2Cl2, 24h (94%)
OH
O(Man*OAc)
O(Man*OAc)
3-sy n-E
(racemate)
"S"-[S,R]-"S"
"S"-[R,S]-"S"
Scheme 2.
OTBDMS
acetone / (MeO)2CMe2 (1/1)
CSA cat. ; 12 h
OH
O
TBAF
EtO2C
EtO2C
EtO2C
THF, 2h
OH
OH
O
3-
6-syn-E
syn-E
5-syn-E
(76%)
(26%)
(100%)
(64%)
6-anti-E
3-anti-E
5-anti-E
Scheme 3.

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A. Lumbroso et al. / Tetrahedron 66 (2010) 1570–1580
OTBDMS
OTBDMS
O
1) O3, CH2Cl2/MeOH (4:1)
EtO2C
EtO2C
R
OH
4-
2) PPh3 (3 equiv.)
OH
7-
sy n
3-
syn (E) or syn (E)
72% from 3-sy n (E) or 42% from 4-syn (E)
(R = Me)
(R = t-Bu)
OTBDMS
OTBDMS
EtO2C
1) O3, CH2Cl2/MeOH (4:1)
2) PPh3 (3 equiv.)
O
EtO2C
R
OH
OH
7-
anti
3-anti (Z or E) or 4-anti (Z or E)
(R = Me) (R = t-Bu)
3-anti
4-anti
88% from
(E or Z) or 70% and 53% from
(E and Z)
Scheme 4. Assignment of syn or anti configurations by correlation with the ozonolysis product 7.
aldehydes 7-syn and 7-anti obtained after ozonolysis of the double
bond according to Scheme 4, since 7-syn and 7-anti were prepared
from well identified 3-syn-E and 3-anti-E, the identity of adducts
4-syn and 4-anti was directly deduced.
increases from 2E but with low selectivity in respect to the major
adduct (28% yield, 48% of 4-syn-E). Because of these disappointing
results, we turned our attention to Lewis acids able to form effectively
bidentate or monodentate complexes at room temperature.
We first examined MgBr2 and ZnBr2 (Table 1, entries 9–13),
which afforded the corresponding products in good yields (81–92%)
and good syn-E diastereoselectivity (72–87%) with allyltins 1E and 1Z;
the higher yields were observed for 1E and the higher syn-E selectivity
for 1Z. While, in the presence of ZnBr2, yields appear almost unaffected
48
49
2.2. Modification of the stereochemical course of the reaction
with the experimental conditions
The results obtained for the addition of
g-silyloxyallyl-
by the size of the a-substituent (2E compared to 1E), the stereo-
chemical course of the reaction was shifted to a lower preference for
tributyltins 1 and 2 to ethyl glyoxylate are reported in Table 1. In
this study, outside of the possible Lewis acid additives, we decided
to examine the influence of both: the geometry across the double
bond of the allyltin unit (by using 1E or 1Z) and the steric hindrance
near the tin centre by using 1E or 2E. Behind this study, devoted to
a general understanding of the factors governing the stereo-
selectivity of this process, we expected to find appropriate condi-
tions to prepare the desired isomer as highly prevalent component
in order to consider possibilities to obtain highly functionalized
building blocks of four or six carbon units with well-defined
stereochemistry.
the anti-E isomer, a trend which was previously observed for reaction
involving a-substituted g
-alkoxyallyltins and benzaldehyde.35,36 Good
yields and high syn preference were also noted regardless of the ge-
ometry of 1, when the reaction was performed in the presence of metal
halides able to give monodentate complexes as for instance InCl3
(when used in experimental conditions where transmetallation is
highly disfavoured, entries 14–15).33,50 However, CeCl3$7H2O.10% NaI,
being often used as a mild Lewis acid for the allylstannation of alde-
hydes,51–53 afforded the expected adducts in low yields and high syn-E
selectivity due to the formation of the
b-stannylated aldehyde resulting
from the desilylation of the -silyloxyallyltin.
g
2.2.1. Reactions performed under thermal or high-pressure conditions
(Table 1, entries 1–5). This first set of experiments indicated that
adduct 3-anti-Z was obtained as the major product (73–77% yield
and 88–94% of isomer 3-anti-Z) from reaction of 1E with ethyl
glyoxylate, regardless of the experimental conditions (thermal or
high-pressure, Table 1, entries 1,3). This trend appears also to be
similar with allyltin 1Z but with lower yields and lower selectivities
in favour of 3-anti-E (78% for the thermal reaction and 55% under
high pressure, entries 2,4). Increase of steric hindrance near the tin
centre induced a dramatic decrease both of the yield (8% with 2E
against 77% with 1E) and of the diastereoselectivity of the reaction
(mixture of 4 diastereomers with 4-anti-Z obtained as the major
isomer but in only 57% of the mixture, entry 5).
2.2.3. Reactions performed in the presence of aluminium or ytter-
bium triflates. Al(OTf)3 or Yb(OTf)3 are known to be efficient cata-
lysts in allylstannation reactions,54,55 since the strong withdrawing
effect of the triflate group increases the Lewis acidity of these metal
salts. We applied them in our reactions and, indeed, obtained high
yields of the products from both 1E or 1Z, but while a high syn-E
preference (94%) was noted for 1E, low selectivities were observed
for 1Z: the 3-syn-E adduct (major product) was highly contami-
nated with the 3-anti-E (entries 18–21).
This low selectivity observed for 1Z can be improved when ethyl
glyoxylate was reacted with 1E or 1Z under high pressure in the
presence of Yb(OTf)3 in CH2Cl2. For the allyltin 1E, the high syn-E
preference is still preserved (92%); the same syn-E preference was
noted also for allyltin 1Z (79%). Finally, it is worth noting that re-
action of ethyl glyoxylate with 1 in the presence of trimethylsilyl
triflate afforded only degradation products in spite of the efficiency
of Me3SiOTf to promote additions of similar allyltins on imines.56
2.2.2. Reactions performed in the presence of boron trifluoride or
metal halide. In this set of experiments, we have first evaluated the
reactivity of 1 and 2 with ethyl glyoxylate at ꢀ78 ꢁC in CH2Cl2 in the
presence of boron trifluoride since allyltributyltin and (E)-crotyl-
tributyltin were known to give good yields under these experi-
mental conditions.41
2.2.4. Reactions performed in the presence of a (salen)chromium(III)
complex. When (salen)metal salts complexes have been used as
chiral Lewis acids to promote the allylstannation of aldehydes or
When applied to our reagents (substituted both at the
-positions),thisreactionaffordedaverylowyield(10%orlesswith1E
and 1Z, the 3-syn-E was obtained as the major adduct), which slightly
a and
g

A. Lumbroso et al. / Tetrahedron 66 (2010) 1570–1580
1573
Table 1
Reaction of a-substituted g-silyloxyallyltributyltins with ethyl glyoxylate
H
OTBDMS
EtO
Bu3Sn
OTBDMS
Δ, HP
+
EtO2C
O
R
or LA
O
R
OH
3 or 4
R = Me, t-Bu
1 or 2
Entry
Experimental conditionsa
Allyltin
Adductsb
Nꢁ
Yield (%)
Syn E
‘Syn Z’c
Anti E
Anti Z
1
2
3
4
5
6
7
8
100 ꢁC, 12 h, neat
1E
1Z
1E
1Z
2E
1E
1Z
2E
1E
1Z
1E
1Z
2E
1E
1Z
1E
1Z
1E
1Z
1E
1Z
1E
1Z
1E
1Z
2E
1E
1Z
3
3
3
3
4
3
3
4
3
3
3
3
4
3
3
3
3
3
3
3
3
3
3
3 (8)
3
73
60
77
59
8
10
<3
28
88
81
92
83
86
87
85
16
<3
90
88
0
10
6
6
0
6
0
22
7
0
26
9
7
3
10
18
5
12
0
10
1
5
0
6
2
9
0
78
0
55
4
94
11
88
9
57
12
0
0
3
1
2
1
0
3
3
8
0
2
0
2
1
2
0
4
0
20
1
1
HP (11 Kbars, 41 h, CH2Cl2)
36
17
74
64
48
78
87
72
85
30
78
78
84
85
94
51
94
59
92
79
93d
27
29
92
31
BF3$Et2O (3 equiv), CH2Cl2, ꢀ78 ꢁ
C
7
36
26
10
5
23
4
42
14
7
8
5
3
44
4
9
MgBr2 (2.2 equiv), CH2Cl2, 25 ꢁ
ZnBr2 (2.2 equiv), CH2Cl2, 25 ꢁ
C
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
C
InCl3 (2.2 equiv), CH2Cl2, 25 ꢁ
CeCl3, 10% NaI.(7H2O) (1.0 equiv), CH2Cl2, 25 ꢁ
Al(OTf)3 (10 mol %), CH2Cl2, 25 ꢁ
Yb(OTf)3 (10 mol %), CH2Cl2, 25 ꢁ
Yb(OTf)3 (10 mol %), CH2Cl2, 20 ꢁC, HP, 41 h
(R,R)-(salen)Cr(III) (5 mol %), CH2Cl2, 25 ꢁ
C
C
C
C
92
96
83
74
34
4
12
1
C
30 (36)
72
14 (10)
73
1
0
26
4
2
73d
25
3
4 (9)
3
3
(R,R)-(salen)Cr(III) (5 mol %), CH2Cl2, 20 ꢁC, HP, 41 h
69
66
a
Experimental conditions: see procedures A, B, C, D in the experimental part for further details.
b
c
The ratio syn-E/‘syn-Z’/anti-E/anti-Z was determined on the crude mixture (GC analysis) after NMR identification of each diastereomer as reported in the text.
Alternatively, this minor isomer noted ‘syn-Z’ might be a rearranged Z-isomer instead of syn-Z (see Experimental part).
No ee observed.
d
glyoxylates by allyltributyltin, the homoallyl alcohols were
obtained in good yields and interesting enantiomeric excesses only
with (salen)chromium(III) salts complexes.43,57–59 Furthermore,
use of such hindered complexes for conducting these reactions
under high pressure induces an increase in the yield and in the
enantioselectivity (yields and ee >90% for several examples).60
performed in the presence of (salen)chromium(III) complexes ap-
pears to favour the syn adduct (under 1 or 104 bar) with a good
enantioselectivity for this isomer, but with a poor enantiose-
lectivity on the minor anti-adduct.58
Accordingly, the reactivity and stereochemical trends of the
reaction involving ethyl glyoxylate with 1E, 1Z and 2E in the
presence of (R,R)-(salen)chromium(III) complex (Fig. 2) were ex-
plored in order to examine if a favourable situation could occur
with these reagents.
However when g-substituted allyltins are involved, the stereo-
chemical course of the reaction, in the presence of chiral ligands,
appears to be much more complicated.58,61 While the anti prefer-
ence was observed for sugar allyltins (regardless of their E or Z
configuration) in a high-pressure reaction conducted without any
additive,19 the reaction of crotyltributyltin with butyl glyoxylate
The results are reported in Table 1 (entries 24–28) and appear to
be highly dependent on the geometry of the allyltin double bond.
Compound 1E afforded (at atmospheric pressure) the
H
Me
H
H
H
H
-
H
H
H
BF4
N
O
N
Me
EtO2C
EtO2C
+
Cr
H
O
O
O
H
O
O
6-anti-E
6-syn-E
Figure 1. Acetonides 6-syn-E and 6-anti-E.
Figure 2. (Salen) Chromium(III) complex.

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A. Lumbroso et al. / Tetrahedron 66 (2010) 1570–1580
OTBDMS
CO2Et
OTBDMS
Me
Bu3Sn
10% HCl
EtO2C
O
OH
(R = Me, 100% conversion)
(R = t-Bu, 100% conversion)
R
8
(R = Me)
9 (R = t-Bu)
3-syn-E (95% isolated)
4-syn-E (75% isolated)
Scheme 5.
corresponding adducts in low yield (30%) and with a high prefer-
ence for 3-syn-E. It must be underlined also, that an unexpected
cyclic organotin derivative 8 was obtained as a side product in 36%
yield (entry 24). This observation is interesting because upon
treatment with 10% HCl, this compound afforded adduct 3-syn-E
exclusively (Scheme 5). This type of cyclisation was also observed
starting from allyltin 2E affording compound 9, finally converted
into 4-syn-E upon acidic treatment.
This result is very important, since the overall yield of this re-
action is increased to acceptable level with a high syn preference
(over 93%) and a possibility to obtain very easily 3-syn-E as a pure
product from 8 due to the lower polarity of this last compound.
Stereochemical behaviour of 1Z is completely different, since ad-
ducts were obtained in good yields (72%) with a high preference for
3-anti-E (no cyclic product analogue of 8 was observed, Table 1,
entry 25).
Finally, increase of thesteric hindrancenear thetin centre (entry 26)
afforded the expected adducts in a very low yield and with low selec-
tivity (4 diastereomers obtained together with 10% of cyclic product 9,
analogue of 8 with R¼t-Bu, which is converted into 4-syn-E upon 10%
HCl treatment). When these reactions were performed under high
pressure, the cyclic organotin reagent 8 was not formed and the cor-
responding adducts were obtained in 69–73% yields with high pref-
erence for 3-syn-E (from 1E) and slight preference for 3-anti-E (from
1Z). However, regardless of the experimental conditions (atmospheric
or high pressure) no enantioselectivity was observed [a complemen-
tary run using the (S,S)-(salen)chromium(III) complex corroborated
this lack of enantioselectivity].
considered to occur through a six membered cyclic transition
state.23–25 In agreement with previous studies, when the allyltin 1E
is used, a chair like transition state is expected with ethoxycarbonyl
group and silyl group in pseudo-equatorial positions and the methyl
a
-substituent in a pseudo-axial position due to the steric hindrance
and to the torsional interactions with butyl groups of the tributyl-
stannyl unit (Scheme 6, TS1). In case of 2E, where the bulky -t-butyl
a
group has difficulties both to adopt a pseudo-axial position (chair
like transition state) or a pseudo-equatorial position (t-Bu/SnBu3
interactions), a low anti-Z selectivity was observed together with
very low yields.
Allylstannation of 1Z should afford the syn-E isomer via a chair
like transition state with two groups in pseudo-equatorial posi-
tions (Scheme 6, TS2). However, because of the unfavourable in-
teraction of the methyl group with Bu3Sn, the reaction might
proceed via a twist or boat-like transition state with the methyl
group located in pseudo-equatorial position (Scheme 6, TS3),
which should provide the anti-E isomer (indeed observed as the
major product).
Such evolution from chair like to twist19 or boat transition
state26 has been previously considered under high pressure, but
herein the similar trends observed both for reactions performed
under thermal or under high-pressure conditions are in agreement
with a competition between these two types of cyclic transition
states (TS2 and TS3).
3.2. Reactions achieved in the presence of Lewis acids
For these reactions, excepted with BF3$OEt2 at ꢀ78 ꢁC and
with CeCl3$7H2O/NaI (where an hydrolysis of the enol ether
function is noted before allylstannation), high yields of homo-
allylic alcohols were obtained regardless of the nature of the
Lewis acid [MgBr2, ZnBr2, InCl3, Al(OTf)3 or Yb(OTf)3] with a high
preference for the syn-E adduct starting from 1E or 1Z. Diaster-
3. Discussion
Among the obtained results, those affording good yields com-
bined with good selectivities will be discussed with an attempt of
rationalization in terms of reaction mechanisms by considering the
different types of experimental conditions applied to this reaction.
eoselectivity of the process was modified only when
g-silylox-
yallyltin bearing bulky substituent at the
entry 13).
These results are in agreement with those noted in reaction
proceeding through an open transition state and can be ex-
plained by usual competition between an antiperiplanar transi-
tion state26–28 and a synclinal transition state29–32 since no
a-position was used (2E,
3.1. Reactions achieved under thermal activation
or under high pressure
Under such experimental conditions as previously reported for
more simple allyltin reagents, the allylstannation reaction is usually
H
Me
H
H
H
OTBDMS
O
OTBDMS
O
TBDMSO
EtO2C
H
Me
H
H
Me
EtO2C
O
EtO2C
SnBu3
SnBu3
H
SnBu3
H
TS3 1Z -> anti E
TS1 1E
anti Z
TS2 1Z -> syn E
->
Scheme 6.

A. Lumbroso et al. / Tetrahedron 66 (2010) 1570–1580
1575
transmetallation is expected under these experimental condi-
tions.33 In practice, among the series of transition states, which
might be involved, only meaningful ones are represented in
Scheme 7 taking into account the assistance by the Lewis acid and
the preferred conformation of allyltins in which the Sn–C allyl
bond is orthogonal to the ethylenic double bond.62,63 On the basis
of these schemes involving ZnBr2 as Lewis acid (which remain
valid with minor modification when another Lewis acid is in-
volved), it is likely to have a high syn-E preference starting from
1E through AP1-E (formation of the compound syn-Z appears to
be highly unfavourable through AP2-E). Alternatively when
allyltin 1Z is used, the transition states AP1-Z and AP2-Z can be
involved, but with a preference for AP1-Z due to the higher sta-
bility of this conformation of the allyltin (less steric interactions
between R and OTBDMS). Therefore a syn-E preference is expec-
ted with a higher rate of syn-Z when compared to reaction of the
allyltin 1E.
and the transition state SYNCL-Z allows the best steric
decompression.
The presence of ‘4-syn-Z’ adduct as minor component (or its
regioisomer) might be explained by a partial isomerisation of 2E
into 2Z in the presence of the Lewis acid. The amount of ‘3-syn-
Z’ might be explained similarly (partial isomerisation of 1E into
1Z), but in both cases, if involved, such a process has a small
extent.
3.3. Reactions achieved in the presence of
(salen)chromium(III) complex
Once more the (salen)chromium(III) complex must be con-
sidered as a very bulky Lewis acid and while the primary trend
seems a reaction through AP1-E starting from 1E (very high syn-E
preference), the competition with a synclinal transition state
allowing the best decompression (like SYNCL-Z, Scheme 7) get
reinforced with 1Z affording the anti-E adduct as the major
compound.
In both cases, a minor influence on the stereochemical course
of the reaction was noted either under atmospheric pressure or
under high pressure. However, application of high pressure
prevented formation of tetrahydrofuran derivative 8 from the
allyltin 1E.
The unique case involving bulky R substituent (allyltin 2E, entry
13) afforded a mixture of compounds where adduct 4-anti-E be-
comes the major component. Due to the steric hindrance of t-butyl
group combined with dipolar repulsion between the carbonyl and
the t-butyldimethylsilyloxy group, synclinal transition state SYNCL-
E is likely to occur as a competitive pathway as already pointed out
for a-substituted g
-alkoxyallyltributyltins.35–37 Therefore a mixture
of compounds syn-E and anti-E is reasonably expected.
The same arguments can also justify obtaining of appreciable
amounts of the anti-E adducts, when 1Z is allowed to react with
ethyl glyoxylate in the presence of aluminium or ytterbium triflates
because the size of the Lewis acid has also to be taken into account
Formation of an aza-heterocycle of the same type has been al-
ready described in allylstannation of imines by
g-silyloxyallyl-
tributyltins; no further comments were, however, provided to
explain these results.56 Compound 8 appears to be a cyclization
Br2Zn
O
Br2Zn
O
H
OTBDMS
H
H
OTBDMS
H
syn-E
O
O
EtO
EtO
H
H
H
R
R
H
AP1-E
AP1
-Z
Bu3Sn
Bu3Sn
Br2Zn
Br2Zn
O
O
H
OTBDMS
H
H
OTBDMS
H
syn-Z
O
O
EtO
EtO
H
H
R
H
Bu3Sn
H
R
AP2-E
AP2-Z
Bu3Sn
O
SnBu3
Br2Zn
Br2Zn
H
R
R
H
O
H
H
SnBu3
H
anti-E
O
H
O
H
H
EtO
OTBDMS
OTBDMS
EtO
SYNCL
SYNCL-Z
-E
Scheme 7. Possible open transition states for ZnBr2 assisted allylstannation of ethyl glyoxylate.

1576
A. Lumbroso et al. / Tetrahedron 66 (2010) 1570–1580
OTBDMS
H
OTBDMS
H
TBDMSO
EtO2C
SnBu3
Me
H
H
EtO2C
H
EtO2C
SnBu3
SnBu3
O
H
O
O
Me
Me
L.A.
H
L.A.
H
8
OTBDMS
H
H
TBDMSO
EtO2C
SnBu3
OTBDMS
Me
EtO2C
H
10% HCl
SnBu3
EtO2C
O
- Bu3Sn
O
Me
Me
OH
H
H
8
3
E
syn-
Scheme 8. Formation of compound 8 and protonolysis into 3 syn-E.
product derived from the primary formed syn-E junction followed
by a 1,2 shift of tributylstannyl group (Scheme 8).
In terms of mechanisms, even quite difficult to rationalize on
minor isomers, we have been able to propose a reasonable
rationalization of the whole set of results through cyclic transition
states and open transition states (antiperiplanar and synclinal).
Even too complex to be generalized for prediction of stereo-
chemical results, the main trends observed in this work should be
of interest for the choice of appropriate experimental conditions for
Acidic treatment of 8 affords exclusively the 3-syn-E isomer,
providing highly stereoselective access to this compound (97%) with
an acceptable yield (30þ36%) considering the overall trans-
formation. It is of interest to note that functionalized tetrahydrofu-
rans have been previously obtained by treatment of homoallylic
alcohols with very strong Lewis acids like triflates or triflimides.64,65
The cyclic ether analogue 9, obtained under similar conditions
from 2E, afforded the syn-E compound, but of low synthetic in-
terest, since a mixture of the four possible diastereomers was
obtained in this case (Table 1, entry 26). Finally no enantiose-
lectivity with the (R,R)-(salen)chromium(III) complex was ob-
served; this can be hardly discussed because of the lack of
comparison for very similar systems.
reaction of glyoxylates with g-silyloxyallyltributyltins.
5. Experimental section
5.1. General
For 1H, 13C and 119Sn spectra, chemical shifts are given in ppm as
values related to tetramethylsilane (1H, 13C) or tetramethyl-
d
stannane (119Sn) and coupling constants are given in hertz. When
given, assignments were done after HMQC or/and COSY correla-
tions. Mass spectra were recorded either in ESI or in EI mode
(70 eV) in direct introduction mode or GC-MS mode. Organostannyl
fragments are given for 120Sn, which means that the given abun-
dance is broadly one third of the overall abundance of the orga-
nostannyl fragment when compared to organic ones. HRMS spectra
for compounds 3-7 were recorded on a Thermo-Finnigan MAT 95
XL in Lyon I University, while HRMS spectra for stannylated com-
pounds 8 and 9 were obtained on a MALDI-TOF apparatus in INRA
of Nantes. In this last case, the determinations were obtained on the
116Sn isotope in order to have a cleaner measurement (absence of
an Mþ1 contribution in the isotopic pattern). CH2Cl2 was dried
with CaH2 prior to use. TLC analyses were conducted on silica-
4. Conclusion
Allylation of ethyl glyoxylate with
allyltributyltins can afford highly different mixtures of di-
astereomers as function of the experimental conditions, but an
a-substituted g-silyloxy-
increase in the bulk of the
effect both in terms of yields and diastereoselectivity. For less
hindered -methyl -silyloxyallyltributyltin, among the four pos-
a
-substituent (R¼t-Bu) has negative
a
g
sible isomers, three of them can be obtained with good yields and
good selectivities:
ꢂ For the preparation of 3-anti-Z, the thermal reaction of neat
compounds appears to be the more efficient one starting from
1E (73% yield, 94% selectivity).
coated aluminium plates (Silica gel 60F254). g-silyloxyallyltins 1E
and 1Z were prepared according to reported procedures.9 Ozo-
nolysis was carried out with a BMT 802 N apparatus from A.C.W.
(Marcoussis, France).
ꢂ For the preparation of 3-syn-E, the use of 1E combined with an
activation by Al(OTf)3 or Yb(OTf)3 appears to be the more
suitable choice (over 90% yield and 94% syn-E selectivity).
ꢂ For the preparation of 3-anti-E, two types of experimental con-
ditions are possible (with different mechanisms): use of1Z under
thermal conditions (60% yield, 78% anti-E) or in the presence of
(salen) chromium(III) complex (72% yield, 73% anti E).
ꢂ No valuable route can be proposed for the selective synthesis of
3-syn-Z.
5.2. Preparation of g
-silyloxyallyltin 2E40
In a Schlenk tube, a suspension of CuCN (312 mg, 3.48 mmol) in
THF (30 mL), without use of HMPA as co-solvent as previously
reported,40 was cooled to ꢀ78 ꢁC before addition of t-BuLi (4.64 mL,
6.96 mmol). The mixture was stirred for 5 min at ꢀ78 ꢁC and
warmed to ꢀ50 ꢁC. The yellow solution was then cooled to ꢀ78 ꢁC
From these results, it appears that high pressure technique
(10 Kbar), which is believed to improve some results, does not bring
noticeable improvements, except to prevent formation of cyclization
products from 1E in the presence of (salen) chromium(III) complex,
but the stereochemical preference observed in this case (syn-E iso-
mer) can be more easily achieved using Al or Yb triflates catalysis.
and b-tributylstannylacrolein (1 g, 2.90 mmol) dissolved in 5 mL of
THF was added dropwise. The mixture become red and was stirred
at ꢀ78 ꢁC for 15 min. TBDMSCl (1.31 mg, 8.69 mmol) was added in
one portion and the mixture was stirred at ꢀ78 ꢁC for 1 h. Saturated
aqueous NH4Cl was added (25 mL). The organic layer was

A. Lumbroso et al. / Tetrahedron 66 (2010) 1570–1580
1577
separated, the aqueous one extracted with Et2O (3ꢃ50 mL) and the
combined organic extracts were dried (MgSO4). After concentration
under vacuum, the crude product was purified by flash chroma-
tography on silica gel (Hexanes/Et2O 95:5) to give pure 2E as col-
ourless oil (1.5 g, 79%). Physical data were found in good agreement
with those already reported.40
vacuum, the residue was analysed by GC and diastereomers were
separated by flash chromatography on silica gel (Hexanes/Et2O: 9/1).
5.7. Gas chromatography analysis
GC analysis of the four diastereomers of 3 was performed on an
HP 6890 apparatus (FID, carrier gas N2, split 98/2) using a phenyl-
5.3. General procedure for allylation reactions under thermal
conditions (Procedure A)
silicone capillary column (Macherey Nagel Optima
d3,
30 mꢃ0.25 mmꢃ0.3
mm). The flow rate of carrier gas was
1.3 mL minꢀ1 and the effective analysis was achieved at 110 ꢁC in
isothermal mode (45 min) before heating at 12 ꢁC minꢀ1 until
300 ꢁC for elimination of high boiling organotin residues.
3-anti-E: 32.4; 3-anti-Z: 35.2; 3-syn-E: 36.7; 3-syn-Z: 38.8 min.
GC analyses of the four diastereomers of 4 and those of 3 were
performed using the same column in isothermal mode (80 ꢁC for
100 min) before heating at 12 ꢁC minꢀ1 until 300 ꢁC.
4-syn-Z: 85.05; 4-anti-E: 85.80; 4-syn-E: 86.47; 4-anti-Z:
86.55 min.
Ethyl glyoxylate (309 mg, 3 mmol) and g-oxygenated allyltin 1E,
1Z (475.4 mg, 1 mmol) or 2E (517.5 mg, 1 mmol) were placed in
a Schlenk tube without any solvent, and the mixture was kept at
100 ꢁC for 12 h. The crude product was analysed by GC and di-
astereomers were separated by flash chromatography on silica gel
(Hexanes/Et2O: 9/1).
5.4. General procedure for allylation reactions under
high-pressure conditions (Procedure B)
5.8. Physicochemical data
The
g-oxygenated allyltin 1E/1Z (475.4 mg, 1 mmol) or 2E
(517.5 mg, 1 mmol) and ethyl glyoxylate (306 mg, 3 mmol) were
placed in a 2 mL Teflon cell. The cell was filled with CH2Cl2, closed
and placed in a high-pressure vessel, and the pressure was slowly
increased to 11 kbar at 20 ꢁC. After stabilization of the pressure, the
reaction mixture was kept under these conditions for 41 h before
decompression. Then, the reaction mixture was diluted with Et2O
and dried over MgSO4. After concentration under vacuum, the
residue was analysed by GC and diastereomers were separated by
flash chromatography on silica gel (Hexanes/Et2O 9:1).
According to the procedure B, Yb(OTf)3 (62 mg, 0.1 mmol) or
(salen)chromium(III) complex (34 mg, 0.05 mmol) used as addi-
tives were also added in the 2 mL Teflon cell, which was placed in
the high-pressure vessel under 10 kbar for 41 h.
5.8.1. Ethyl (3E)-3-tert-butyldimethylsilyloxy-2-hydroxy-hex-4-eno-
ate (3-syn-E). IR (neat) 3485, 3012, 2950, 2929, 2856, 1736, 1665,
1256, 1098, 966, 838, 778. HRMS (ESI): m/z calcd for C14H29O4Si
[MþH]þ¼289.1835, found: 288.1837. MS (CI, NH3) m/z:306 ([MþNH4]þ,
100), 289 (23), 185 (4), 174 (38), 157 (42); (EI) m/z: 231 (26), 199 (4), 185
(100), 159 (27), 157 (21), 149 (30), 141 (14), 129 (10), 83 (10), 75 (51), 73
(56). 1H NMR (CDCl3, 300MHz): 5.72 (ddq, 1H, 3J¼15.5, 4J¼0.9, 3J¼6.1),
5.61 (ddq, 1H, 3J¼7.1, 3J¼15.5, 4J¼1.2), 4.42 (bdd, 1H, 3J¼1.9, 3J¼7.1), 4.26
(dq,1H, 2J¼11.1, 3J¼7.1), 4.19 (dq, 1H, 2J¼11.1, 3J¼7.1), 4.02 (dd, 1H, 3J¼1.9,
3J¼9.9), 2.91 (d, 1Hhydroxyl, 3J¼9.9), 1.7 (dd, 3H, 3J¼6.1, 4J¼1.2), 1.30 (t, 3H,
3J¼7.1), 0.85 (s, 9H), 0.0 (s, 6H).13CNMR(CDCl3, 75MHz): 172.7 (C1),130.6
(C5),128.4 (C4), 75.4 (C2), 75.2 (C3), 61.5 (1C), 25.8 (3C),18.1 (1C),17.8 (C6),
14.3 (1C), ꢀ3.9 and ꢀ5.0 (2C).
5.5. General procedure for allylation reactions in the presence
Lewis acid (ZnBr2, MgBr2, InCl3, CeCl3): Procedure C
5.8.2. Ethyl (3Z)-3-tert-butyldimethylsilyloxy-2-hydroxy-hex-4-eno-
ate (3-syn-Z). MS (CI, NH3) m/z: 306 (8), 289 (12),185 (30),174 (53),
157 (100), 92 (19); (EI) m/z (%): 231(4), 199 (6), 185 (96), 159 (28),
157 (28), 149 (40), 141(16), 83 (12), 75 (98), 73 (100), 55 (20). 1H and
13C NMR: No meaningful signals (product always obtained as minor
component in mixture with other isomers).
In a round-bottomed flask under an argon atmosphere, ethyl
glyoxylate (309 mg, 3 mmol) and
g-oxygenated allyltin 1E, 1Z
(475.4 mg, 1 mmol) or 2E (517.5 mg, 1 mmol) were dissolved in dry
CH2Cl2 (15 ml). Lewis acid was added (2.2 equiv) and the mixture
was stirred at room temperature (when using CeCl3.7H2O, 10% NaI,
1.0 equiv was added). The reaction was monitored by TLC (hexanes/
Et2O: 95/5). Water was added, organic layer was separated, the
aqueous one extracted with CH2Cl2 (2ꢃ20 mL), and the combined
extracts were dried (MgSO4). After concentration under vacuum,
the residue was analysed by GC and diastereomers were separated
by flash chromatography on silica gel (Hexanes/Et2O: 9/1).
According to general procedure C, lanthanide triflate (2.2 equiv)
was added at 0 ꢁC and the mixture was allowed to warm-up to
room temperature. Similarly, according to procedure B, (salen)
chromium (III) complex (34 mg, 0.05 mmol) was added in one
portion at room temperature before starting the reaction.
5.8.3. Ethyl (3E)-3-tert-butyldimethylsilyloxy-2-hydroxy-hex-4-enoate
(3-anti-E). IR: 3509, 3036, 2957, 2929, 2857, 1734, 1671, 1256, 1223,
1096, 967, 938, 837, 777. HRMS (ESI): m/z calcd for C14H28O4SiNa
[MþNa]þ¼311.1649, found: 311.1642. MS (CI, NH3) m/z: 306 (8), 289
(12), 271 (11), 185 (38), 174 (76), 157 (100), 92 (30), 74 (20); (EI) m/z:
231 (10), 186 (14), 185 (95), 157 (28), 155 (20), 149 (34), 141 (16), 75
(92), 73 (100), 55 (22). 1H NMR (CDCl3, 300MHz): 5.66 (ddq, 1H,
3J¼15.4, 4J¼0.8, 3J¼6.3,), 5.50 (ddq, 1H, 3J¼15.4, 3J¼7.2, 4J¼1.5), 4.33
(bdd, 1H, 3J¼7.2, 3J¼3.4), 4.24 (dq, 1H, 2J¼10.8, 3J¼7.2), 4.19 (dq, 1H,
2J¼10.8, 3J¼7.2), 4.13 (dd, 1H, 3J¼6.7, 3J¼3.4), 2.90 (d, 1Hhydroxyl
,
3J¼6.7), 1.70 (bd, 3H, 3J¼6.3), 1.28 (t, 3H, 3J¼7.2), 0.86 (s, 9H), 0.03
and 0.05 (2s, 6H). 13C NMR (CDCl3, 75MHz): 172.0 (C1), 129.6 (C4),
128.5 (C5), 76.5 (C3), 75.1 (C2), 61.4, 25.8 (3C), 18.2, 17.8 (C6), 14.3
(1C), ꢀ4.2 and ꢀ4.8 (2C).
5.6. General procedure for allylation reactions in the presence
of BF3$OEt2 (Procedure D)
5.8.4. Ethyl (3Z)-3-tert-butyldimethylsilyloxy-2-hydroxy-hex-4-enoate
(3-anti-Z). IR: 3396, 2930, 1733, 1634, 1235, 1096, 1056, 770. HRMS
(ESI): m/z calcd for C14H28O4SiNa [MþNa]þ¼311.1655, found:
311.1653.
MS (CI, NH3) m/z: 306 (6), 289 (3), 271 (3), 199 (6), 185 (16), 174
(56), 157 (100), 149 (8), 92 (22), 90 (16), 75 (8), 73 (20); (EI) m/z (%):
231(10), 199 (5), 185 (100), 159 (30), 157 (27), 149 (34), 75 (98), 73
(97). 1H NMR (CDCl3, 300MHz): 5.58 (dq, 1H, 3J¼11.2, 3J¼6.6), 5.75
(bdd, 1H, 3J¼11.2, 3J¼8.8), 4.72 (dd, 1H, 3J¼8.8, 3J¼3.2), 4.23 (q, 2H,
In a Schlenk tube, ethyl glyoxylate (103 mg, 1 mmol) and g-oxy-
genated allyltin 1E/1Z (712 mg, 1.5 mmol) or 2E (517.5 mg, 1 mmol)
were dissolved in dry CH2Cl2 (6 mL). The mixture was cooled to
ꢀ78 ꢁC and BF3$OEt2 (380
m
L, 3 mmol) was added dropwise. The
mixture was stirred for 2 h at ꢀ78 ꢁC and quenched with saturated
aqueous NaHCO3 (6 mL). The organic layer was separated, the aque-
ous one was extracted with CH2Cl2 (2ꢃ10 mL) and the combined or-
ganic extracts were dried (MgSO4). After concentration under

1578
A. Lumbroso et al. / Tetrahedron 66 (2010) 1570–1580
3J¼7.1), 4.12 (dd, 1H, 3J¼6.8, 3J¼3.2), 2.99 (d, 1Hhydroxyl, 3J¼6.8), 1.67
(bd, 3H, 3J¼6.6), 1.30 (t, 3H, 3J¼7.1), 0.87 (s, 9H), 0.07 and 0.03 (2s,
6H). 13C NMR (CDCl3, 75MHz): 172.3 (C1), 130.0 (C4), 126.6 (C5), 75.6
(C2), 71.2 (C3), 61.7, 26.0 (3C),18.3,14.5,13.8 (C6), ꢀ4.2 and ꢀ4.7(2C).
(MgSO4). Concentration under vacuum gave the crude product,
which was purified by flash chromatography on silica gel (Hexane/
Et2O: 2/8) to give pure 5-syn-E as a colourless oil (165 mg,
0.95 mmol, 100%).
IR: 3396, 2980, 2929, 2856,1736, 1674, 1636, 1446, 1208, 967.
HRMS (CI): m/z calcd for C8H15O4 [MþH]þ¼175.0970, found:
175.0968; MS (CI, NH3) m/z: 192 (100), 175 (5), 174 (19), 157 (7);
MS (EI) m/z: 159 (9), 104 (66), 83 (21), 76 (77), 71 (93), 43 (71),
41 (100), 39 (73). 1H NMR (CDCl3, 300MHz) 5.78 (ddq, 1H,
3J¼15.3, 3J¼6.3, 4J¼1.2), 5.60 (ddq, 1H, 3J¼15.3, 3J¼6.3, 4J¼1.5),
4.32 (m, 1H), 4.24 (q, 2H, 3J¼7.2), 4.10 (bdd, 1H, 3J¼6.0, 3J¼3.0),
5.8.5. Ethyl (4E)-3-tert-butyldimethylsilyloxy-2-hydroxy-6,6-dime-
thylhept-4-enoate (4-syn-E). IR: 3501, 2957, 2929, 2902, 2857, 1745,
1652, 1472, 1253, 1026, 977, 942, 836, 776. HRMS (ESI): m/z calcd for
C17H34O4SiNa [MþNa]þ¼353.2124, found 353.2123. MS (CI, NH3),
m/z: 348 (4), 331 (2), 313 (4), 273 (5), 227 (17), 216 (33), 199 (100),
181 (17); (EI) m/z: 297 (4), 273(10), 255 (6), 227(100), 199 (11),
181(12), 149 (18), 107(45), 95 (18), 75 (46), 73 (60). 1H (CDCl3,
300MHz): 5.70 (dd, 1H, 3J¼15.7, 4J¼0.6), 5.51 (dd, 1H, 3J¼15.7,
3J¼7.8), 4.41 (ddd, 1H, 3J¼7.8, 3J¼2.4, 4J¼0.6), 4.25 (dq, 1H, 2J¼10.8,
3J¼7.2), 4.17 (dq, 1H, 2J¼10.8, 3J¼7.2), 4.02 (dd, 1H, 3J¼9.7, 3J¼2.4),
3.38 (d, 1Hhydroxyl
,
3J¼6.0), 2.65 (d, 1Hhydroxyl
,
3J¼7.5), 1.70 (bd,
3H, 3J¼6.3), 1.28 (t, 3H, 3J¼7.2). 13C NMR (CDCl3, 75MHz): 172.9
(C1), 129.3 (C4), 128.6 (C5), 74.0 (C3), 73.5 (C2), 61.9 (C), 17.7 (C6),
14.1 (C).
2.92 (d, 1Hhydroxyl
,
3J¼9.7), 1.31 (t, 3H, 3J¼7.2), 1.02 (s, 9H), 0.84 (s,
9H), 0.00 (s, 6H). 13C (CDCl3, 75MHz) 172.7 (C1), 144.7 (C5), 124.2
(C4), 75.9 (C3), 75.5 (C2), 61.5, 33.1, 30.4 (3C), 25.8 (3C), 18.2, 14.3,
ꢀ3.7, ꢀ4.9.
5.8.10. Ethyl (4E)-2,3-dihydroxyhex-4-enoate (5-anti-E). 5-anti-E
was prepared according to the procedure described for 5-syn-E
using 3-anti-E (173 mg, 0.6 mmol), 3 ml of THF and tetrabuty-
lammonium fluoride (1.2 mL, 1 M in THF). 5-anti-E was obtained as
colourless oil (67 mg, 0.38 mmol, 64%).
5.8.6. Ethyl (4Z)-3-tert-butyldimethylsilyloxy-2-hydroxy-6,6-dime-
thylhept-4-enoate or/and rearranged product (noted ‘4-syn-Z’). MS
(EI), m/z (%): 297 (3), 273(5), 227(100), 149 (10), 107(41), 95 (17), 75
(64), 73 (79). 1H NMR (CDCl3, 300MHz) (mixture with 4-syn-E,
meaningful signals non-overlapped with those of 4-syn-E): 5.96
(ddd, 1H, J¼6.1, J¼2.4, J¼1.3), 5.90 (dt, 1H, J¼6.1, J2H¼2), 5.23 (bdt,
1H, Jw6.3, J2Hw2.3), 4.76 (ddd, 1H, J¼6.2, J¼2.1, J¼1.3). 13C NMR
(CDCl3, 75MHz) (meaningful signals: mixture with 4-syn-E): 171.5
(C1), 130.6 (C5), 126.2 (C4), 96.1 (C3), 84.9 (C2), 61.2, 35.5, 28.3 (3C),
26.9 (3C), 17.7, 14.3, ꢀ3.7 and ꢀ4.9.
1H NMR (CDCl3, 300MHz): 5.77 (ddq,1H, 3J¼15.3, 3J¼6.6, 4J¼0.9),
5.50 (ddq, 1H, 3J¼15.3, 3J¼6.9, 4J¼1.5), 4.40–4.20 (m, 4H), 1.71 (bd,
3H, 3J¼6.6), 1.29 (t, 3H, 3J¼7.2). 13C NMR (CDCl3, 75MHz): 172.3 (C1),
130.1 (C5), 127.6 (C4), 74.0 (2C2,3), 62.0 (C), 17.9 (C6), 14.3 (C).
5.9. Identification of syn and anti diastereomers
5.9.1. Attempted identification using mandelic esters. In a round-
bottomed flask 5-syn-E (32 mg, 0.18 mmol) was dissolved in
dichloromethane (1 mL) and (S)-mandelic acid (77 mg, 0.40 mmol),
dicyclohexylcarbodiimide (82 mg, 0.40 mmol) and dimethylami-
nopyridine (5 mg, 0.04 mmol) were successively added. After 24 h
at room temperature under stirring, the mixture was concentrated
under vacuum and the white residue was diluted in ether (2 mL).
The heterogeneous mixture was filtered through a pad of Celite and
the solid was washed with ether (2ꢃ5 mL). The liquid organic
phase was successively washed by water (5 mL), an aqueous satu-
rated NaHCO3 solution (5 mL), water (5 mL), HCl (10%) (5 mL),
water (5 mL), brine (5 mL), dried (MgSO4) and concentrated under
vacuum. The crude product was purified by flash chromatography
on silica gel (hexane/ether: 7/3) to give bis-(S)-mandelic esters ‘S’-
[R,S]-‘S’ and ‘S’-[S,R]-‘S’ as a mixture of diastereomers (89 mg,
0.17 mmol, 94%).
5.8.7. Ethyl (4E)-3-tert-butyldimethylsilyloxy-2-hydroxy-6,6-dime-
thylhept-4-enoate (4-anti-E). IR: 3447, 2958, 2929, 2857, 1734,
1652,1473,1387,1257,1203, 976, 837, 777. HRMS (ESI): m/z calcd for
C17H34O4SiNa [MþNa]þ¼353.2124, found: 353.2124. MS (CI, NH3),
m/z: 348 (66), 331 (10), 313 (2), 273 (7), 227 (31), 216 (57), 199
(100), 181 (12); EI, m/z: 273 (16), 255 (8), 227 (100), 199 (24), 181
(30), 149 (9), 107 (18), 95 (10), 75 (17), 73 (13), 57 (8). 1H NMR
(CDCl3, 300MHz): 5.60 (dd, 1H, 3J¼15.4, 4J¼0.7), 5.41 (dd, 1H,
3J¼15.4, 3J¼7.5), 4.33 (ddd, 1H, 3J¼7.5, 3J¼3.3, 4J¼0.7), 4.23 (dq, 1H,
2J¼11.1, 3J¼7.2), 4.19 (dq, 1H, 2J¼11.1, 3J¼7.2), 4.13 (dd, 1H, 3J¼6.6,
3J¼3.3), 2.92 (d, 1Hhydroxyl
,
3J¼6.6), 1.29 (t, 3H, 3J¼7.2), 1.00 (s, 9H),
0.88 (s, 9H), 0.06 and 0.02 (2s, 6H). 13C NMR (CDCl3, 75MHz): 172.0
(C1), 144.8 (C5), 123.3 (C4), 77.4 (C3), 75.6 (C2), 61.4, 33.1, 29.4 (3C),
25.9 (3C), 18.3, 14.4, ꢀ4.0 and ꢀ4.7.
The same procedure was used for 5-anti-Z (54 mg, 0.31 mmol).
The crude product was purified by flash chromatography on silica
gel (hexane/ether: 7/3) to give pure bis-(S)-mandelic esters ‘S’-
[R,R]-‘S’ and ‘S’-[S,S]-‘S’ (160 mg, 0.30 mmol, 98%).
5.8.8. Ethyl (4Z)-3-tert-butyldimethylsilyloxy-2-hydroxy-6,6-dime-
thylhept-4-enoate (4-anti-Z). IR: 3526, 2957, 2857, 1717, 1653, 1252,
1097, 863, 836, 810, 777. MS (CI, NH3), m/z: 348 (12), 331(4), 216
(100), 199 (85), 181 (6), 175 (11); MS (EI), m/z: 273 (9), 228 (18), 227
(100), 199 (7), 181 (11), 149 (15), 107 (36), 95 (23), 75 (62), 73 (71),
57 (23). 1H NMR (CDCl3, 300MHz): 5.39 (dd, 1H, 3J¼12.4, 4J¼0.9),
5.22 (dd, 1H, 3J¼12.4, 3J¼9.1), 4.94 (ddd, 1H, 3J¼9.1, 3J¼2.7, 4J¼0.9),
4.28 (dq, 1H, 2J¼10.5, 3J¼7.2), 4.20 (dq, 1H, 2J¼10.5, 3J¼7.2), 4.11 (dd,
1H NMR spectra of bis-(S)-mandelic esters in 4:1 CS2/CD2Cl2
were recorded on a 400 MHz apparatus at 298 K and 253 K, but
while DdT1T2 might be in agreement with Riguera’s reports when
considering only the ‘syn’ isomers, consideration of DdT1T2 in the
case of the ‘anti’ isomers exhibited inconsistent variations of these
parameters (see Supplementary data: 1H NMR spectra at 298 and
253 K and DdT1T2 values in ppm).
1H, 3J¼7.8, 3J¼2.7), 3.10 (d, 1Hhydroxyl
,
3J¼7.8), 1.30 (t, 3H, 3J¼7.2),
1.13 (s, 9H), 0.85 (s, 9H), 0.07 and 0.03 (2s, 6H). 13C NMR (CDCl3,
75MHz): 172.1 (C1), 144.5 (C5), 128.8 (C4), 75.4 (C2), 71.9 (C3), 61.4,
32.9, 31.1 (3C), 25.6 (3C), 18.0, 14.2, ꢀ3.8 and ꢀ4.3.
5.9.2. Identification using acetonide derivatives
5.9.2.1. Ethyl 2,2-dimethyl-5-[(1E)-prop-1-en-1-yl]-1,3-dioxolane-4-
5.8.9. Ethyl (4E)-2,3-dihydroxyhex-4-enoate (5-syn-E). In a round-
bottomed flask 3-syn-E (274 mg, 0.95 mmol) was dissolved in THF
(5 mL) and tetrabutylammonium fluoride (1.9 mL, 1 M in THF) was
added. The mixture was stirred 2 h at room temperature and water
(5 mL) was added. After dilution of the mixture with Et2O, the or-
ganic layer was separated and the aqueous layer extracted with
Et2O (3ꢃ5 mL). The organic extracts were combined and dried
carboxylate (6-syn-E). To
a
solution of 5-syn-E (134 mg,
0.77 mmol) in a 1:1 mixture of acetone/2,2-dimethoxypropane
(29 mL) in a round-bottomed flask, CSA (87 mg, 0.38 mmol) was
added in one portion. After 12 h, the reaction was partitioned be-
tween Et2O (30 ml) and water (30 ml) and the organic layer was
separated and dried (MgSO4). Concentration under reduced pres-
sure gave crude acetonide, which was purified by flash

A. Lumbroso et al. / Tetrahedron 66 (2010) 1570–1580
1579
chromatography on silica gel (Hexanes/Et2O 6:4) to afford pure
6-Syn-E as a colourless oil (125 mg, 0.58 mmol, 76%).
1251, 1111, 838, 776. HRMS (MALDI-TOF): m/z calcd for
C26H54O4SiNa116Sn [MþNa]þ¼597.2707, found 597.2692; MS (CI,
NH3) m/z: 596 (3), 579 (MþHþ, 100); MS (EI) m/z (%): organotin
fragments: 578 (3), 521 (16), 389 (7), 291.0 (31), 235.0 (8), 179 (25),
121 (4). organic fragments 185.0 (28), 155 (100), 83 (16), 73 (14).
IR: 3446, 2927, 2855, 1689, 1590, 1757, 1449, 1097, 968. HRMS
(CI): m/z calcd for C11H19O4 [MþH]þ¼215.1283, found 215.1280; MS
(CI, NH3) m/z: 232 (100), 215 (10), 174(95), 157 (83), 144 (21); MS
(EI) m/z: 199 (8), 157 (45), 144 (22), 87 (38), 83 (100), 73 (24), 43
(55). 1H NMR (CDCl3, 300MHz): 5.87 (ddq, 1H, 3J¼15.1, 3J¼6.5,
4J¼0.9), 5.54 (ddq, 1H, 3J¼15.1, 3J¼7.5, 4J¼1.8), 4.49 (bt, 1H, 3J¼8.0),
4.24 (dq, 1H, 2J¼10.6, 3J¼7.1), 4.22 (dq, 1H, 2J¼10.6, 3J¼7.1), 4.16 (d,
1H, 3J¼8.0), 1.75 (dd, 3H, 3J¼6.5, 4J¼1.8), 1.47 and 1.46 (2s, 6H), 1.28
(t, 3H, 3J¼7.1). A NOESY experiment showed strong interaction
between H2 and H4, attesting of the configuration of this di-
astereomer (see Fig. 1). 13C NMR (CDCl3, 75MHz): 170.4 (C1), 132.0
(C5), 127.4 (C4), 111.0 (C), 80.4 (C3), 79.3 (C2), 61.4 (C), 27.1, 25.9, 17.9
(C6), 14.3.
3
3
1H NMR (CDCl3, 300MHz): 4.56 (dd, H3, JH2H3¼4.9, JH3H4¼3.7,
3
3JSn–H¼33), 4.32 (d, H2, JH2H3¼4.9), 4.30–4.20 (m, H5þ1Hester
:
2J¼10.8, 3J¼6.0), 4.09 (dq, 1Hester
,
2J¼10.8, 3J¼7.2), 1.61 (dd, H4,
3JH4H5¼6.3, JH3H4¼3.7), 1.55–1.39 (m, 3H6þ6Hb), 1.37–1.25 (m,
3
3Hþ6Hg), 0.95–0.83 (m, 24H), 0.06 (s, 6H). NOE experiments:
H5
O
EtO2C
H2
Me
4%
TBDMSO
SnBu3
H3
H4
7.8 %
5.9.2.2. Ethyl
2,2-dimethyl-5-[(1E)-prop-1-en-1-yl]-1,3-dioxo-
16.6 %
lane-4-carboxylate (6-anti-E). 6-anti-E was prepared according to
the procedure described for 6-syn-E using 5-anti-E (83 mg,
0.48 mmol), 18 mL of a 1:1 mixture of acetone/2,2-dimethox-
ypropane and CSA (52 mg, 0.24 mmol). 6-anti-E was obtained as
a colourless oil (27 mg, 0.12 mmol, 26%).
13C NMR (CDCl3, 75MHz) 170.1 (C1), 82.9 (C2, 3JSn–C¼17), 80.6 (C5,
2JSn–C<5), 78.6 (C3, 2JSn–C¼7), 60.8 (Cester), 39.3 (C4, 1JSn–C¼266/254),
2
3
1H NMR (CDCl3, 300MHz): 5.87 (dq, 1H, 3J¼15.2, 3J¼6.4), 5.35
(ddq, 1H, 3J¼15.2, 3J¼7.8, 4J¼1.2), 4.76 (bt, 1H, 3Jw7.5), 4.60 (d, 1H,
3J¼7.1), 4.21 (dq, 1H, 2J¼10.8, 3J¼7.2), 4.16 (dq, 1H, 2J¼10.8, 3J¼7.2),
1.71 (dd, 3H, 3J¼6.4, 4J¼1.2), 1.62 and 1.39 (2s, 6H), 1.25 (t, 3H,
3J¼7.2). A NOESY experiment exhibited no interaction between H2
and H4 (Cf Fig. 1). 13C NMR (CDCl3, 75MHz): 169.8 (C1), 132.1 (C5),
125.3 (C4), 110.9 (C), 78.9 (C3), 77.7 (C2), 61.0, 27.1, 25.7, 17.9 (C6),
14.4.
29.2 (3C, JSn–C¼20), 27.6 (3C, JSn–C¼59), 25.2 (3C), 23.5 (C6,
1 1
3JSnC¼23), 17.8 (CIV, JSiC¼68), 14.3 (Cester), 13.7 (3C), 8.7 (3C, JSn–
¼324/309), ꢀ4.3, ꢀ4.7. 119Sn (CDCl3, 112MHz) ꢀ18.2.
C
5.11.2. Ethyl [5-(tert-butyl)-3-(tert-butyldimethylsilyloxy)-4-(tribu-
tylstannyl)-tetrahydrofuran]-2-carboxylate (9). IR: 2955, 2928,
2855, 1732, 1464, 1254, 1122, 1057, 1122, 836, 774. HRMS (MALDI-
TOF): m/z calcd for C29H60O4SiNa116Sn [MþNa]þ¼639.3176, found
616.3160; MS (CI, NH3) m/z: 638 (22), 621(MþHþ, 100), 563 (17),
489 (12). MS (EI) m/z (%) Organotin fragments: 563 (65), 291 (89),
235 (60),179 (63),121 (6). Organic fragments: 227 (32),197 (100), 75
(23), 73 (24), 57 (44). 1H NMR(CDCl3, 300MHz) 4.51 (d, H3,
5.10. Ozonolysis of compounds 3 and 4
5.10.1. General procedure for ozonolysis. Ozone gas was bubbled in
a solution of 3 or 4 (1 mmol) in 10 mL of a 4:1 mixture of CH2Cl2/
MeOH at ꢀ78 ꢁC during 10 min. Argon was then passed through the
solution for 10 min at ꢀ78 ꢁC to remove any excess of ozone. Tri-
phenylphosphine was added (723 mg, 2.76 mmol) and the mixture
was warmed up to room temperature and stirred for 12 h. The
crude solution was concentrated under reduced pressure and then
purified by flash chromatography on silica gel (hexanes/Et2O 7:3) to
give pure aldehydes 7-syn (72% yield from 3-syn-E and 42% from 4-
syn-E) and 7-anti (88% yield from 3-anti-E, 89% from 3-anti-Z, 53%
from 4-anti-Z and 70% from 4-anti-E) as colourless oils.
3
3
3JH2H3¼3.3, JH3H4¼0, JSn–H¼36), 4.26 (dq, 1Hester
,
2J¼10.2, 3J¼7.2),
3
4.25 (d, JH2H3¼3.3), 4.07 (dq, 1Hester
,
2J¼10.2, 3J¼7.2), 3.83 (d, H5,
3JH4H5¼5.6, 3JSn–H¼65), 1.62 (d, H4, 3JH4H5¼5.6, 3JH3H4¼0), 1.56–1.41
(m, 6Hb), 1.39–1.24 (m, 6Hgþ3Hester
:
3J2H¼7.2), 0.94 (s, 9H), 0.93–
0.86 (m, 15H), 0.82 (s, 9H), 0.04 and 0.09 (2s, 6H). 13C NMR (CDCl3,
2
75 MHz): 168.8 (C1), 92.3 (C5), 83.6 (C2), 78.1 (C3, JSn–C¼14), 60.7,
34.8 (CIV, 3JSn–C¼22), 33.5 (C4, 1JSn–C¼270–258), 29.3 (3C, 2JSn–C¼19),
27.6 (3C, JSn–C¼58), 26.4 (3C), 25.8 (3C), 18.0 (CIV), 14.3, 13.7 (3C),
3
9.1 (3C, 1JSn–C¼319–304), ꢀ4.0, -5.2. 119Sn (CDCl3, 112MHz): ꢀ11.8.
5.12. Hydrolysis of 8 or 9 into 3-syn-E and 4-syn-E
5.10.2. Ethyl 3-tert-butyldimethylsilyloxy-2-hydroxy-4-oxobutanoate
(7-syn). IR (neat) 3446, 2856, 2359, 1734, 1254, 1097, 837, 779. MS
(CI, NH3) m/z: 294 (100), 277 (10). 1H NMR (CDCl3, 300MHz): 9.66
(d, 1H, 3J¼0.9), 4.57 (dd, 1H2, 3J¼9.7, 3J¼1.8), 4.37 (dd, 1H3, 3J¼1.8,
3J¼0.9), 4.32 (dq, 1H, 2J¼10.5, 3J¼6.9), 4.17 (dq, 1H, 2J¼10.5, 3J¼6.9),
3.08 (d, 1Hhydroxyl, 3J¼9.7), 1.31 (t, 3H, 3J¼6.9), 0.89 (s, 9H), 0.10 and
0.02 (s, 6H). 13C NMR (CDCl3, 75MHz): 201.8 (C4), 171.5 (C1), 78.9
(C3), 72.2 (C2), 62.3, 25.7 (3C), 18.2, 14.2, ꢀ4.1, ꢀ4.4.
In a round-bottomed flask 8 (105 mg, 0.18 mmol) was dissolved
in THF (10 mL) and HCl (10%) was added dropwise (1 mL). After
stirring 30 min at room temperature, water (5 mL), Et2O (20 mL)
was added. The organic layer was separated, washed with water
(2ꢃ5 mL) and dried over MgSO4. Concentration under vacuum gave
the crude product, which was purified by flash chromatography on
silica gel (hexane/ether: 6/4) to give pure 3-syn-E as a colourless oil
(49 mg, 0.17 mmol, 95%).
5.10.3. Ethyl 3-tert-butyldimethylsilyloxy-2-hydroxy-4-oxobutanoate
(7-anti). 1H NMR (CDCl3, 300MHz): 9.61 (d, 1H, 3J¼0.6), 4.52 (dd,
1H, 3J¼5.7, 3J¼1.9), 4.34 (dq, 1H, 2J¼10.8, 3J¼7.2), 4.27 (dd, 1H,
The same procedure was used for 9 (24 mg, 0.04 mmol). The
crude product was purified by flash chromatography on silica gel
(Hexane/Et2O:7/3) to give pure 4-syn-E as a colourless oil (10 mg,
0.030 mmol, 75%).
3J¼1.9, 3J¼0.6), 4.18 (dq, 1H, 2J¼10.8, 3J¼7.2), 3.13 (d, 1Hhydroxyl
,
3J¼5.7), 1.27 (t, 3H, 3J¼7.2), 0.91 (s, 9H), 0.11 (s, 6H). 13C NMR (CDCl3,
75MHz): 201.9 (C4), 171.4 (C1), 80.2 (C3), 73.1 (C2), 62.5, 25.7 (3C),
18.2, 14.3, ꢀ4.4, ꢀ4.8.
Acknowledgements
We gratefully acknowledge Chemtura (Bergkamen) for gift of
organotin starting materials, ICSN (CNRS, Gif-sur-Yvette) for a Ph.D.
grant (AL), CNRS and MESR for financial support. We wish also to
warmly acknowledge Egide programs (PHC Polonium Nꢁ14160ZM)
and French Embassy in Poland for supporting this work.
5.11. Characterization of tetrahydrofuran derivatives 8 and 9
5.11.1. Ethyl 3-tert-butyldimethylsilyloxy-5-methyl-4-tributylstannyl-
tetrahydrofuran-2-carboxylate (8). IR: 2928, 2855, 1733, 1463, 1375,

1580
A. Lumbroso et al. / Tetrahedron 66 (2010) 1570–1580
33. Fargeas, V.; Zammattio, F.; Chre´tien, J.-M.; Bertrand, M.-J.; Paris, M.; Quintard,
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