Synthesis of α-allyloxy-substituted α,β-unsaturated esters via aldol condensation. Convenient access to highly substituted allyl vinyl ethers

Article abstract of DOI:10.1055/s-2000-6424

α-Allyloxy-substituted α,β-unsaturated esters 1a-r have been prepared in 5 steps from commercially available starting materials. The key sequence of the synthesis is an aldol addition between an α-allyloxy-substituted ester 2a-i and an aldehyde R¹CHO followed by mesylation and DBU mediated elimination to afford the 2-alkoxycarbonyl-substituted allyl vinyl ethers 1a-r. The E/Z ratio of the newly generated vinyl ether double bond is apparently determined by the steric bulk of the vinyl ether double bond substituent R¹. Z:E ratios from 3:2-9:1 were obtained.

Full text of DOI:10.1055/s-2000-6424

PAPER
1279
Synthesis of a-Allyloxy-Substituted a,b-Unsaturated Esters via Aldol
Condensation. Convenient Access to Highly Substituted Allyl Vinyl Ethers
Martin Hiersemann
Institut für Organische Chemie der Technischen Universität Dresden, 01062 Dresden, Germany
Fax +493514637030; E-mail: martin.hiersemann@chemie.tu-dresden.de
Received 20 March 2000; revised 15 April 2000
rearrangement/type II carbonyl ene reaction affording
substituted carbocycles (Scheme 2).5
Abstract: a-Allyloxy-substituted a,b-unsaturated esters 1a-r have
been prepared in 5 steps from commercially available starting ma-
terials. The key sequence of the synthesis is an aldol addition be-
tween an a-allyloxy-substituted ester 2a-i and an aldehyde R1CHO
followed by mesylation and DBU mediated elimination to afford
the 2-alkoxycarbonyl-substituted allyl vinyl ethers 1a-r. The E/Z
ratio of the newly generated vinyl ether double bond is apparently
determined by the steric bulk of the vinyl ether double bond substit-
uent R1. Z:E ratios from 3:2-9:1 were obtained.
Oi-Pr
LDA, THF
Ph
CO2i-Pr
-78 °C to 25 °C
Ph
O
Li
89 %
O
O
Key words: allyl vinyl ethers, aldol reactions, eliminations, esters
[2,3]
Without doubt, sigmatropic rearrangements create one of
the most important classes of synthetic transformations.
Several striking examples have proven the utility of sig-
matropic rearrangements for the stereoselective synthesis
of organic compounds.1 In an ongoing effort to further in-
crease the synthetic efficiency, much work is devoted to
extend the scope of classical sigmatropic rearrange-
ments.2 In this regard, we are engaged in a research pro-
gram which focuses on the development of metal
catalyzed Claisen rearrangements and pericyclic domino
reactions which are triggered by a dienolate [2,3]-Wittig
rearrangement. The starting materials for both processes
are a-allyloxy-substituted a,b-unsaturated esters 1.
toluene
200 °C, 19 h
sealed tube
OH
O
Ph
CO2i-Pr
Ph
CO2i-Pr
85 %
[3,3]
ene
OH
CO2i-Pr
Ph
Particularly, we were able to show that the 2-alkoxycarbo-
nyl-substituted allyl vinyl ether 1f can be transformed to
an a-keto ester diastereoselectively employing a combina-
tion of Pd(II)-catalysis and thermal reaction conditions
(Scheme 1).3
Scheme 2
Finally, we have recently established first examples for a
domino ester dienolate [2,3]-Wittig/anionic 3-oxy Cope
rearrangement to afford the corresponding a-keto esters
(Scheme 3).6
Et
5 % PdCl2(PhCN)2
toluene
CO2R
Et
CO2R
n-Pr
O
60 °C, 3 h
150 °C 3 h
n-Pr
O
90 %
anti:syn 95:5
1f, R= CH2CH2OCH3
Z:E= 67:33
O
LDA, THF
-78 °C to 25 °C
CO2i-Pr
Oi-Pr
Scheme 1
O
84 %
O
Furthermore, when treated with an appropriate base a-al-
lyloxy-substituted a,b-unsaturated esters 1 can be trans-
formed to the corresponding dienolates which undergo a
dienolate [2,3]-Wittig rearrangement to 3-alkoxycarbon-
yl-3-hydroxy-substituted 1,5-hexadienes.4 These com-
pounds are substrates for a domino 3-oxy-Cope
1h
Scheme 3
Obviously, it was indispensable to develop a reliable,
flexible and efficient synthetic access to a-allyloxy-sub-
Synthesis 2000, No. 9, 1279–1290 ISSN 0039-7881 © Thieme Stuttgart · New York

1280
M. Hiersemann
PAPER
Table 1 Synthesis of Allyloxy-acetic acid Esters 2a-i
stituted a,b-unsaturated esters 1 to be in the position to
study the scope and limitations of the newly developed
synthetic processes. At the outset, an aldol condensation
strategy seemed to be an ideal approach with respect to
synthetic convergence and substrate availability (Scheme
4).
Cpd.
Rester
R2
R3
RE
RZ
Yield
(%)
2a
2b
2c
2d
2e
2f
2g
2h
2i
Me
Me
Me
i-Pr
i-Pr
i-Pr
i-Pr
i-Pr
MeOEta
H
Me
H
Me
H
H
H
H
H
H
H
H
H
H
H
H
Me
H
n-Pr
H
H
H
n-Pr
H
Me
H
n-Pr
H
H
n-Pr
H
H
n-Pr
Me
H
63
69
62
56
69
78
64
65
64
R1
OH
CO2Rester
CO2Rester
R1
R2
R3
RE
O
O
H
RZ
RZ
R2
a MeOEt: methoxyethyl.
R3
1a-r
3a-r
RE
The aldol addition was realized by treating the esters
2a-i with LDA at -78 °C followed by the addition of
an aldehyde at -78 °C to provide the desired b-hydroxy-
esters 3a-r in good yield but low diastereoselectivity
(Scheme 6, Table 2). The diastereoselectivity was deter-
mined for the corresponding mesylates 4a-p (Table 3).
The relative configuration was not assigned. A deprotona-
tion time of 5 to 10 minutes proved to be sufficient. By uti-
lizing these reaction conditions, we were able to suppress
the enolate [2,3]-Wittig rearrangement of the lithium ester
enolates generated from the 2-allyloxy-acetic acid esters
2a-i.9
R1
HORester
CO2H
R1
O
O
CO2Rester
R3
R3
Br
RE
O
RE
OH
RZ
R2
RZ
R2
2a-i
Scheme 4
The general access to 2-allyloxy-substituted esters 2 was
well established (etherification followed by esterifica-
tion)7 and an example for a chemoselective aldol addition
of an ester enolate from 2 with an aldehyde was also found
in the literature.8 The transformation of the b-hydroxy es-
ter 3 to the desired unsaturated ester 1 via an E2-like elim-
ination would be straightforward with the inherent
possibility of a stereoselective double bond generation via
E2 elimination of a diastereomerically pure b-hydroxy es-
ter 3. We report here, for the first time, detailed synthetic
procedures, and spectroscopic data for the synthesis and
characterization of the a-allyloxy-substituted a,b-unsatur-
ated esters 1a-r.
LDA, THF
-78 °C, 10 min
then
R1CHO
OR
O
-78 °C, 30 min
R1
ORester
R2
2a-i
then
O
aq. NH4Cl
RZ
R3
RE
R= H: 3a-r
MsCl, TEA
CH2Cl2, 0 °C
The 2-allyloxy-substituted esters 2a-i were prepared uti-
lizing a modified literature procedure for the etherifica-
tion of bromoacetic acid with allylic alcohols (see
experimental). The esterification was conveniently real-
ized employing the DCC/DMAP method (Scheme 5, Ta-
ble 1).7 The acids and the esters 2a-i can be purified by
kugelrohr distillation.
R= Ms, 4a-r
Scheme 6
The transformation of the b-hydroxy esters 3a-r to
the desired a,b-unsaturated esters 1a-r was realized by
a two-step procedure. The b-hydroxy ester 3a-r was
mesylated and, following an aqueous work-up the crude
mesylate 4a-r was treated with DBU in THF to provide
the a,b-unsaturated esters 1a-r in high yield as an insep-
arable mixture of double bond isomers (Schemes 6 and 7,
Table 3). The assignment of the double bond configura-
tion is based on NOESY experiments.
1. 2 eq NaH
THF;
then
O
HO
R3
R2
RE
BrCH2CO2H
R3
ORester
RZ
RE
O
2. DCC, DMAP
CH2Cl2, 0 °C
ResterOH
RZ
R2
2a-i
The diastereoselectivity for the aldol addition, determined
1
by integration of the H NMR signal of the OSO2CH3
group of the mesylates 4a-q, was in the range of 7:3 for
all b-hydroxy esters 3a-r (Table 3). Based on an E2-like
Scheme 5
Synthesis 2000, No. 9, 1279–1290 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Synthesis of a-Allyloxy-Substituted a,b-Unsaturated Esters via Aldol Condensation
1281
Table 2 Synthesis of b-Hydroxy Esters 3a−r
R1
O
DBU
THF, 25 °C
Prod- R1
uct
Rester
R2
R3
RE
RZ
Yield
(%)
R3
ORester
4a-r
RE
O
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
3o
3p
3q
3r
Me
Me
Et
Et
Me
Et
Me
Me
Me
Me
H
Me
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Me
H
H
H
H
H
H
H
H
H
H
H
H
Me
H
H
H
H
H
Me
n-Pr
H
H
n-Pr
n-Pr
n-Pr
Me
Me
n-Pr
H
H
H
n-Pr
H
H
84
55
64
75
77
62
92
84
88
88
95
79
77
89
78
95
64
80
RZ
R2
1a-r
Scheme 7
MeOEta
MeOEta
i-Pr
H
Et
Me
Me
H
n-Pr
H
H
H
H
Me
H
elimination process, one would assume that the diastereo-
meric ratio of the mesylates 4a-r would be transferred
into the E/Z ratios of the elimination products 1a-r
(Scheme 8). That is obviously not the case. The Z/E ratios
vary roughly from 3:2 (R1 = Me) to 7:3 (R1 = Et) to >9:1
(R1 = i-Pr, Ph, Bn). Other substituents besides R1 have ap-
parently no significant influence on the observed Z/E ra-
tios in 1a-r. We assume that the Z configured esters 1a-
r are thermodynamically more stable and an increasing
steric bulk of the substituent R1 favors the formation of the
Z configured esters 1a-r. We suggest a nucleophilic 1,4-
addition/elimination process with DBU acting as a nu-
cleophile in order to explain the proposed equilibration
between the E and Z configured a,b-unsaturated esters
1a-r (Scheme 8). It should be noted that the DBU medi-
ated elimination of the mesylates 4o-r (R1 = Bn) led to
the formation of a minor amount of the corresponding b,g-
unsaturated esters 6o-r which were easily separated by
column chromatography (Table 3, Scheme 8).
Me
Me
Me
Et
Me
i-Pr
Ph
Bn
Bn
Bn
Bn
i-Pr
i-Pr
i-Pr
i-Pr
i-Pr
i-Pr
i-Pr
i-Pr
n-Pr
H
n-Pr
n-Pr
Me
n-Pr
H
i-Pr
i-Pr
i-Pr
H
H
H
a MeOEt: methoxyethyl.
Table 3 Synthesis of 2-Allyloxy-Substituted a,b-Unsaturated Esters 1a-r
Substrate
Product
Entry Cpd
dra
Cpd.
R1
Rester
R2
R3
RE
RZ
Yield (%) Z:Eb
from 3
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
4a
4b
4c
4d
4e
4f
4g
4h
4i
4j
4k
4l
4m
4n
4o
4p
4q
4r
71:29
c
1a
1b
1c
1d
1e
1f
1g
1h
1i
1j
1k
1l
1m
1n
1o
1p
1q
1r
Me
Me
Et
Et
Me
Et
Me
Me
Me
Me
H
Me
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Me
H
H
H
H
H
H
H
H
H
H
H
H
Me
H
H
H
H
H
Me
n-Pr
H
H
n-Pr
n-Pr
n-Pr
Me
Me
n-Pr
H
H
H
n-Pr
H
H
91
59:41
51d
c
69:31
72:28
60:40
73:27
67:33
61:39
64:36
61:39
76:24
59:41
91:9
>95:5
96:4
97:3
>95:5
96:4
70:30
72:28
78:22
76:24
73:27
70:30
70:30
72:28
69:31
70:30
71:29
60:40
75:25
76:24
c
81
83
81
95
71
89
93
88
MeOEte
MeOEte
i-Pr
H
Et
Me
Me
H
n-Pr
H
H
H
H
Me
H
Me
Me
Me
Et
Me
i-Pr
Ph
Bn
Bn
Bn
Bn
i-Pr
i-Pr
i-Pr
i-Pr
i-Pr
i-Pr
i-Pr
i-Pr
n-Pr
H
77
82
n-Pr
n-Pr
Me
n-Pr
H
52 (42)f
78 g
61 (10)h
80 (10)h
34 g
77 (12)h
i-Pr
i-Pr
i-Pr
H
H
83:17i
H
a Determined from 1H NMR spectra, configuration not assigned.
b Determined from 1H NMR spectra, configuration assigned based on NOESY experiments.
c Not determined.
d Spectra in CDCl3 show a 1:1 mixture with the corresponding Claisen rearrangement product.
e MeOEt: methoxyethyl.
f In parentheses: % yield of recovered mesylate 4m.
g Spectra in CDCl3 show a contamination with the corresponding Claisen rearrangement product.
h In parentheses: % yield of the corresponding b,g-unsaturated ester.
i Determined from the 1H NMR spectrum of the b-hydroxy ester 3r.
Synthesis 2000, No. 9, 1279–1290 ISSN 0039-7881 © Thieme Stuttgart · New York

1282
M. Hiersemann
PAPER
OMs O
materials for diastereoselective sequential pericyclic reac-
tions and for a metal catalyzed Claisen rearrangement.3,4,5
Further work aimed at exploiting the synthetic potential of
the 2-alkoxycarbonyl-substituted allyl vinyl ethers 1 is
currently under way.
OMs O
R1
ORester
+
R1
ORester
R2
O
R2
RZ
RE
O
RZ
R3
R3
RE
anti-4a-r
syn-4a-r
2-3 eq
DBU
THF
All reactions were performed in septum-sealed flame-dried flasks
under an Ar atm. Solvents, reagents, and substrates were transferred
by the means of syringes. All solvents were dried by standard meth-
ods. Reagents were used as purchased unless otherwise noted. All
aldehydes were freshly distilled prior to use for the aldol addition.
MeOH, i-PrOH and 2-methoxy-ethanol were dried by standard
methods and stored over molecular sieves. Commercial n-BuLi so-
lutions in hexanes were titrated following the procedure of Ko-
fron.11 Crude products were purified by column chromatography
employing silica gel (0.040-0.063 mm) and mixtures from EtOAc
N
N
R1
O
O
R1
ORester
R2
ORester
R2
O
O
RZ
RZ
R3
R3
RE
RE
1
and heptane. H and 13C NMR spectra were recorded on a Bruker
AC 300 or a DRX 500 in CDCl3. IR spectra were recorded on a
Nicolet 205 FT-IR spectrometer. Elemental analyses were obtained
on a Carlo Erba CHN-S analyzer.
E-1a-r
Z-1a-r
DBU O
R1
ORester
R2
2-Allyloxy-Substituted Acetic Acids; General Procedure
NaH (100 mmol, 60% suspension in mineral oil) was suspended
in THF (250 mL). Under vigorous stirring, the allylic alcohol
(50 mmol) was added at r.t. and stirring was continued until the gas
extrusion was finished. To this suspension was added a solution of
bromo-acetic acid (50 mmol) in THF (10 mL) at r.t. The reaction
mixture was stirred over night and the reaction was then quenched
by the addition of aq KOH (3 N, 75 mL). The phases were separated
and the organic phase was extracted with aq KOH (3 N, 2 ¥ 75 mL).
The combined aqueous phases were acidified by the addition of
concd HCl (pH<4), an organic phase was formed. The acidic aque-
ous layer was extracted with CHCl3 (3 ¥ 100 mL), the combined or-
ganic phases were separated and dried (MgSO4). The solvents were
evaporated at reduced pressure to afford the crude product which
was purified by kugelrohr distillation (bp, depending on substitu-
ents 80-110 °C, 5 ¥10-2 mbar).
O
RZ
R3
RE
Ph
O
R3 R1
O
R3
Oi-Pr
R2
RE
O
ORester
RZ RE
O
RZ R2
5a-r
6o-r
Scheme 8
Except for the compounds 1b, 1n and 1q, all allyl vinyl
ethers 1a-r are stable colorless oils which can be stored
at 0 °C for weeks without significant decomposition. Gen-
erally, the allyl vinyl ethers 1a-r are vulnerable to the
thermal Claisen rearrangement affording the correspond-
ing a-keto esters 5a-r. The thermal Claisen rearrange-
ment proceeds slowly at or above room temperature for
2-Allyloxy-Substituted Acetic Acid Esters 2a-i; General Proce-
dure
To a stirred solution of the 2-allyloxy-substituted acid (1 equiv) in
CH2Cl2 (2.5 mL/mmol of the acid) at 0 °C were successively added
DMAP (0.05 equiv), DCC (1.1 equiv), and the alcohol (2 equiv).
The reaction mixture was allowed to warm to r.t. overnight. The
most of the ethers 1a-r. Allyl vinyl ethers 1b, 1q precipitate was then removed by filtration and washed with EtOAc.
(R2 = methyl) and 1n (R1 = phenyl) are significantly more
reactive with respect to the Claisen rearrangement so that
only a mixture of the allyl vinyl ethers 1b, 1r, 1n and the
The solvents were then evaporated at reduced pressure and the
crude product was purified by kugelrohr distillation (bp, depending
on substituents 80-110 °C, 1 mbar).
b-keto esters 5b, 5r and 5n were detected by NMR in
Aldol Addition to 3a-r; General Procedure
CDCl3 at room temperature. A detailed study of the ther-
To a stirred solution of LDA [prepared in situ from diisopropyl-
mal and metal catalyzed Claisen rearrangement of the al-
amine (1.3 equiv) and n-BuLi (1.2 equiv)] in THF (2 mL/mmol
of the ester) was added a cooled (-78 °C) solution of the ester
(1 equiv) in THF (2.5 mL/mmol of the ester) at -78 °C. The solu-
tion was stirred for 10 to 15 min and then the aldehyde (1.3-2.0
equiv) was added either neat or as a solution in THF (benzaldehyde,
phenyl-acetaldehyde). The reaction mixture was stirred 30 min at
-78 °C and then quenched by the addition of sat. NH4Cl at -78 °C.
lyl vinyl ethers 1a-r will be reported elsewhere.10
In conclusion, we present a reliable, variable and efficient
general access to a-allyloxy-substituted a,b-unsaturated
esters 1a-r. Unfortunately, the outlined procedure does
not allow general stereocontrol over the vinyl ether double
bond configuration. Nevertheless, bulky substituents The solution was diluted with H2O and CH2Cl2, the layers were then
(R1 = i-Pr, Bn, Ph) on the vinyl ether double bond give ac-
separated and the organic phase was extracted with CH2Cl2 (2¥).
The combined organic phases were dried (MgSO4) and concentrat-
ed to afford the crude product oil which was purified by column
chromatography (EtOAc/heptane) to afford the b-hydroxy esters
cess to Z configured allyl vinyl ethers stereoselectively
(1m-r, Z:E >9:1). Even as a mixture of double bond iso-
mers, the esters 1 have already been utilized as starting
3a-r as colorless oils (Table 4-6).
Synthesis 2000, No. 9, 1279–1290 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Synthesis of a-Allyloxy-Substituted a,b-Unsaturated Esters via Aldol Condensation
1283
Table 4 Synthesis of b-Hydroxy Esters 3a-ra
Substrate
Aldehyde
Product Yield
IR
Elemental Analysis
Calculated
Ester
g
in substance
n (cm-1)
Found
g (mmol)
R1CHO
%
Formula MW
C
H
C
H
2a
2.0 (11.4)
2b
3.0 (20.8)
2c
2.5 (14.3)
2a
4.9 (28.8)
2i
3.8 (17.5)
2i
1.6 (7.3)
2g
2.4 (12.9)
2g
2.2 (11.8)
2e
3.0 (15.0)
2f
2.8 (14)
2e
2.4 (11.8)
2h
2.5 (14.5)
2e
2.0 (10)
2e
2.0 (10)
2g
2.9 (15)
2e
MeCHO
3a
3b
3c
3d
3e
3f
2.1
84
2.1
55
2.1
64
5.0
75
3.5
76
1.2
62
2.9
92
2.3
84
3.1
88
3.0
88
2.7
95
2.5
79
2.1
77
2.8
89
3.7
78
4.6
95
3475, 2960– C11H20O4 216.3
2875, 1750
3490, 2980– C9H16O4 188.2
2900, 1745
3485, 2960– C12H22O4 230.3
2875, 1750
3470, 2935– C12H22O4 230.3
2875, 1745
3470, 2940– C13H24O5 260.3
2880, 1745
3470, 2960– C14H26O5 274.4
2880, 1750
3470, 2980– C13H24O4 244.3
2880, 1740
3470, 2980– C12H22O4 230.3
2880, 1740
3475, 2980– C13H24O4 244.3
2875, 1740
3470, 2980– C13H24O4 244.3
2875, 1745
3480, 2965– C14H26O4 258.4
2875, 1740
3470, 2980– C11H20O4 216.3
2880, 1740
3475, 2985– C15H28O4 272.4
2885, 1745
3475, 2980– C18H26O4 306.4
2875, 1740
3475, 2980– C18H26O4 306.4
2880, 1740
3480, 2980– C19H28O4 320.4
2875, 1745
60.75
57.56
63.06
62.28
59.63
61.31
63.98
62.04
63.74
63.84
64.73
60.70
66.01
70.53
71.15
70.64
71.54
69.86
9.51
61.09
9.32
8.57
9.63
9.63
9.29
9.55
9.90
9.63
9.90
9.90
10.14
9.32
10.36
8.55
8.55
8.81
8.27
8.27
MeCHO
EtCHO
EtCHO
MeCHO
EtCHO
EtCHO
MeCHO
MeCHO
MeCHO
EtCHO
MeCHO
iPrCHO
PhCHO
BnCHO
BnCHO
BnCHO
BnCHO
8.77
9.76
9.88
9.39
9.57
10.28
9.90
10.11
10.12
10.34
9.49
10.52
8.67
8.67
9.05
8.56
8.41
57.43
62.58
62.58
59.98
61.29
63.91
62.58
63.91
63.91
65.09
61.09
66.14
70.56
70.56
71.22
69.84
69.84
3g
3h
3i
3j
3k
3l
3m
3n
3o
3p
3q
3r
3.1 (15.5)
2d
2.1 (12)
2h
2.6
64
3.1
80
3480, 2980– C17H24O4 292.4
2880, 1740
3480, 2980– C17H24O4 292.4
2880, 1735
2.3 (13.4)
a Colorless oils, isolated as a mixture of diastereomers, ratio see table 3.
Mesylation/Elimination to the Allyl Vinyl Ethers 1a-r; General
Procedure
were separated, and the aqueous layer was extracted with CH2Cl2
(2¥). The combined organic phases were dried (MgSO4), and the
solvent was removed under reduced pressure to afford the crude
product which was purified by column chromatography (EtOAc/
heptane) (Tables 7-9).
To a solution of the b-hydroxy esters 3a-r (1 equiv) in CH2Cl2 (3
mL/mmol of the b-hydroxy ester) at 0 °C was added successively
Et3N (1.3 equiv) and methanesulfonic acid chloride (1.2 equiv). The
reaction was allowed to warm to ambient temperature over night.
The reaction was then quenched by the addition of sat. NaHCO3.
The phases were separated and the aqueous layer was extracted with
CH2Cl2 (2¥). The organic phase was dried (MgSO4) and concentrat-
ed in vacuum to afford the crude mesylate which was dissolved in
THF (2 mL/mmol of the mesylate). 1,8-Diazabicyclo[5.4.0]undec-
7-ene (DBU, 3 equiv) was added at r.t., and the reaction mixture was
stirred at ambient temperature until TLC indicated complete con-
sumption of the starting material. The reaction was then quenched
by the addition of H2O (2 mL/mmol of the mesylate), the phases
Acknowledgement
Financial support from the state of Saxonia (habilitation fellowship)
and the Fonds der Chemischen Industrie is gratefully acknowled-
ged. I thank Prof. H. -U. Reißig and Prof. P. Metz for their support
and Dr. M. Gruner for NMR measurements.
Synthesis 2000, No. 9, 1279–1290 ISSN 0039-7881 © Thieme Stuttgart · New York

1284
M. Hiersemann
PAPER
Table 5 1H NMR Data of b-Hydroxy Esters 3a-r,a 300 MHz, CDCl3
Compound d, J (Hz)
3a
0.90 (t, J = 7.3, 3 H), 1.21 (d, J = 6.5, 3Hmajor), 1.22 (d, J = 6.5, 3Hminor), 1.41 (qt, J1 = J2 = 7.4, 2 H), 2.03 (td, J1 = J2 = 7.4,
2 H), 2.43 (br d, J = 6.5, 1Hmajor), 2.55 (br d, J = 4.9, 1Hminor), 3.74 (d, J = 5.5, 1Hminor), 3.77 (s, 3Hminor), 3.78 (s, 3Hmajor),
3.88-4.21 (m, 4Hmajor, 3Hminor), 5.48-5.61 (m, 1 H), 5.65-5.77 (m, 1H)
1.17-1.24 (m, 3 H), 1.28-1.35 (m, 3 H), 2.36-2.49 and 2.56-2.61 (br m, 1 H), 3.725 and 3.734 and 3.77 (s, 3 H), 3.82-4.10
(m, 3 H), 5.08-5.24 (m, 3 H), 5.58-5.87 (m, 1 H)
3bb
3c
0.90 (t, J = 7.5, 3 H), 0.99 (t, J = 7.5, 3 H), 1.39 (qt, J1 = J2 = 7.4, 2 H), 1.47-1.62 (m, 2 H), 2.03 (dt, J1 = J2 = 7.3, 2 H), 2.31
(br s, 1 H), 3.70-3.84 (m, partially covered, 1 H), 3.78 (s, 3 H), 3.84 (d, J = 4.6, 1Hminor), 3.95 (d, J = 4.9, 1Hmajor), 4.01-
4.11 (m, 1 H), 4.19-4.29 (m, 1 H), 5.48-5.70 (m, 1 H)
3d
3e
3f
0.90 (t, J = 7.5, 3 H), 0.98 (t, J = 7.5, 3Hminor), 0.99 (t, J = 7.5, 3Hmajor), 1.41 (qt, J1 = J2 = 7.4, 1 H), 1.47-1.60 (m, 2 H), 2.03
(td, J1 = J2 = 7.0, 2 H), 2.36 (d, J =7.0, 1 H), 3.77 (s, 3 H), 3.71-3.97 (m, 3 H), 4.11-4.22 (m, 1 H), 5.47-5.60 (m, 1 H),
5.64-5.77 (m, 1 H)
0.898 (t, J = 7.3, 3Hminor), 0.903 (t, J = 7.3, 3Hmajor), 1.22 (d, J = 6.5, 3Hminor), 1.23 (d, J = 6.4, 3Hmajor), 1.42-1.47 (m, 2 H),
2.30 (td, J1 = J2 = 7.4, 2 H), 2.62-2.64 (br m, 1 H), 3.376 (s, 3Hminor), 3.381 (s, 3Hmajor), 3.60-3.63 (m, 2 H), 3.79-3.81 and
3.90-4.78 (m, 6 H), 5.55-5.59 (m, 1 H), 5.66-5.76 (m, 1 H)
0.87 (t, J = 7.4, 3 H), 0.92-0.98 (m, 3 H), 1.37 (qt, J1 = J2 = 7.4, 2 H), 1.46-1.62 (m, 2 H), 2.01 (dt, J1 = J2 = 6.9, 2 H), 2.37
(d, J = 7.3, 1Hminor), 2.45 (d, J = 6.2, 1Hmajor), 3.34 (s, 3Hmajor), 3.35 (s, 3Hminor), 3.59 (ddd, J1 = J2 = J3 = 4.8, 2 H), 3.72-3.80
(m, 1 H), 3.87-3.92 (m, 2 H), 4.09-4.18 (m 1 H), 4.23-4.40 (m, 2 H), 5.46-5.56 (m, 1 H), 5.63-5.72 (m, 1 H)
0.98 (t, J = 7.5, 3Hminor), 1.02 (t, J = 7.3, 3Hmajor), 1.29 (d, J = 6.2, 6 H), 1.45-1.63 (m, 2 H), 1.67 (s, 3 H), 1.76 (s, 3 H), 2.31
(d, J = 6.2, 1Hmajor), 2.37 (d, J = 6.2, 1Hminor), 3.68-3.88 (m, 2H), 3.92-4.03 (m, 1 H), 4.13-4.23 (m, 1 H), 5.13 (sept, J =
6.3, 1 H), 5.30-5.39 (m, 1 H)
3g
3h
3i
1.208 (d, J = 6.5, 3Hmajor), 1.214 (d , J = 6.2, 3Hminor), 1.29 (d, J = 6.5, 6 H), 1.68 (s, 3 H), 1.76 (s, 3H), 2.48 (d, J = 6.8,
1Hmajor), 2.62 (d, J = 4.9, 1Hminor), 3.65 (d, J = 6.2, 1Hminor), 3.84 (d, J = 4.6, 1Hmajor), 3.91-4.24 (m, 3 H), 5.13 (sept, J = 6.3,
1 H), 5.35 (m, 1 H)
0.90 (t, J = 7.3, 3 H), 1.21 (d, J = 6.5, 3Hmajor), 1.22 (d, J = 6.2, 3Hminor), 1.28 (d, J = 6.2, 6 H), 1.41 (qt, J1 = J2 = 7.4, 2 H),
2.03 (dt, J1 = J2 = 7.3, 2 H), 2.38 (d, J = 7.1, 1Hmajor), 2.54 (d, J = 5.2, 1Hminor), 3.67 (d, J = 5.5 1Hminor), 3.86 (d, J = 4.6,
1Hmajor), 3.88-4.22 (m, 3 H), 5.12 (sept, J = 6.3, 1 H), 5.49-5.61 (m, 1 H), 5.64-5.76 (m, 1 H)
0.90 (t, J = 7.3, 3 H), 1.21 (d, J = 6.5, 3Hmajor), 1.22 (d, J = 6.5, 3Hminor), 1.29 (d, J = 6.5, 6 H), 1.39 (qt, J1 = J2 = 7.4, 2 H),
2.04 (td, J1 = J2 = 7.3, 2 H), 2.49-2.55 (br m, 1Hmajor), 2.60-2.65 (br m, 1Hminor), 3.67 (d, J = 5.8, 1Hminor), 3.86 (d, J = 4.6,
1Hmajor), 3.92-4.11 and 4.19-4.30 (m, 3H), 5.13 (sept, J = 6.3, 1H), 5.49-5.70 (m, 1 H)
3j
3k
3l
0.90 (t, J = 7.5, 3 H), 0.98 (t, J = 7.5, 3Hminor), 0.99 (t, J = 7.5, 3Hmajor), 1.28 (d, J = 6.2, 6Hminor), 1.28 (d, J = 6.5, 6Hmajor),
1.41 (qt, J1 = J2 = 7.4, 2 H), 1.47-1.62 (m, 2 H), 2.03 (td, J1 = J2 = 7.0, 2 H), 2.27-2.37 (m, 1 H), 3.69-3.84 and 3.87-3.96
(m, 3 H), 4.11-4.20 (m, 1 H), 5.12 (sept, J = 6.3, 1 H), 5.48-5.60 and 5.64-5.76 (m, 2 H)
1.23 (d, J = 6.5, 3Hmajor), 1.24 (d, J = 6.2, 3Hminor), 1.28 (d, J = 6.2, 3 H), 1.29 (d, J = 6.2, 3 H), 1.77 (s, 3H), 2.40 (br d, J =
6.2, 1Hmajor), 2.54 (br d, J = 5.5, 1Hminor), 3.69 (d, J = 5.5, 1Hminor), 3.82-3.90 (m, 2Hmajor, 1Hminor), 4.03-4.18 (m, 2 H), 4.93
(br s, 1 H), 4.98 (br s, 1 H), 5.13 (sept, J =6.3, 1 H)
3m
3n
3o
3p
0.75-1.01 (m, 9 H), 1.28 (d, J = 7.1, 6 H), 1.35-1.47 (m, 2 H), 1.79-1.93 (m, 1 H), 1.99-2.06 (m, 2 H), 2.20 (d, J = 7.6,
1Hminor), 2.34 (d, J = 4.6, 1Hmajor), 3.49 (m, 1Hminor), 3.61 (m, 1Hmajor), 3.86-3.93 (m, 2 H), 4.09-4.29 (m, 1 H), 5.07-5.19
(m, 1 H), 5.48-5.58 (m, 1 H), 5.65-5.75 (m, 1 H)
0.89 (t, J = 7.3, 3 H), 0.97 (d, J = 6.5, 3Hminor), 1.08 (d, J = 6.2, 3Hmajor), 1.16 (d, J = 6.2, 3Hmajor), 1.17 (d, J = 6.5, 3Hminor),
1.38 (qt, J1 = J2 = 7.4, 2 H), 1.99 (td, J1 = J2 = 7.3, 2 H), 3.09 (br s, 1 H), 3.82-3.97 and 4.02-4.13 (m, 2 H), 3.97 (d, J = 6.5,
1Hminor), 4.07 (d, J = 5.8, 1Hmajor), 4.84-5.03 (m, 2 H), 5.35-5.50 and 5.57-5.69 (m, 2 H), 7.23-7.41 (m, 5 H)
1.23 (d, J = 6.2, 3Hminor), 1.27 (d, J = 6.2, 3Hminor), 1.30 (d, J = 6.2, 6Hmajor), 1.67 (s, 3 H), 1.76 (s, 3 H), 2.30 and 2.40 (br s,
1 H), 2.73-2.83 and 2.86-2.98 (m, 2 H), 3.72 (d, J = 3.9, 1Hminor), 3.86 (d, J = 5.2, 1Hmajor), 3.92-4.03 and 4.06-4.25 (m, 2
H), 5.10 (sept, J = 6.3, 1Hminor), 5.14 (sept, J = 6.3, 1Hmajor), 5.32-5.41 (m, 1 H), 7.19-7.33 (m, 5 H)
0.90 (t, J = 7.3, 3 H), 1.30 (d, J = 6.2, 6 H), 1.33-1.47 (m, 2 H), 1.96-2.07 (m, 2 H), 2.28 (d, J = 5.8, 1Hmajor), 2.37 (d, J =
7.5, 1Hminor), 2.73-2.97 (m, 2 H), 3.72-3.76 and 3.84-3.96 (m, 2 H), 4.06-4.23 (m, 2 H), 5.06-5.19 (m, 1 H), 5.49-5.76
(m, 2 H), 7.18-7.35 (m, 5 H)
3qb
3r
1.22-1.38 (m, 9 H), 2.14-2.44 (br m, 1 H), 2.30-2.36 and 2.39-2.45 and 2.68-3.00 (br m, 1 H), 3.73-3.76 and 3.85-4.15
(m, 3 H), 5.04-5.22 (m, 3 H), 5.59-5.73 and 5.75-5.90 (m, 1 H), 7.16-7.39 (m, 5 H)
1.27 (d, J = 7.1, 3Hminor), 1.30 (d, J = 6.2, 3Hmajor), 1.76 (s, 3Hmajor), 1.81 (s, 3Hminor), 2.26 (br s, 1Hmajor), 2.37 (br s, 1Hminor),
2.75-2.85 and 2.87-3.00 (m, 2 H), 3.77 (d, J = 3.6, 1Hminor), 3.84 (br s, 1Hminor), 3.88 (d, J = 4.9, 1Hmajor), 3.88 (br s, 1Hmajor),
4.07-4.19 (br m, 2 H), 4.92 (br s, 1Hmajor), 4.95 (br s, 1Hminor), 4.97 (br s, 1Hmajor), 5.01 (br s, 1Hminor), 5.14 (sept, J = 6.3,
1H), 7.16-7.34 (m, 5 H)
a Determined from a mixture of 2 diastereomers. Diastereomeric ratio: see Table 3. The terms Hmajor and Hminor are used to indicate separated
proton resonance for the major or the minor diastereomer.
b Mixture of 4 diastereomers.
Synthesis 2000, No. 9, 1279–1290 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Synthesis of a-Allyloxy-Substituted a,b-Unsaturated Esters via Aldol Condensation
1285
Table 6 13C NMR Data of b-Hydroxy Esters 3a-r,a 75.5 MHz, CDCl3, d
Compoundb
C-1
C-2
C-3
C-1¢
Other Signals
3a
3b
3c
3d
3e
3f
major
minor
4 dia-
stereomers
major
minor
major
minor
major
minor
major
minor
major
minor
major
minor
major
minor
major
minor
major
minor
major
minor
171.4
171.6
81.2
81.8
68.3
68.4
71.8
71.8
13.6, 18.3, 22.1, 34.3, 51.9, 125.3, 136.1
13.6, 18.7, 22.1, 34.3, 51.9, 125.2, 136.4
18.4, 19.0, 20.5, 21.4, 51.7, 51.77, 51.78, 51.9, 68.31, 68.34, 68.41, 77.0, 77.1, 78.8, 79.2, 79.3, 79.6, 80.7, 81.9, 116.6,
116.5, 117.7, 117.8, 138.7, 138.9, 139.3, 139.4, 171.6, 171.8, 171.9, 172.0
171.4
171.8
171.5
171.9
170.9
171.0
171.0
171.4
170.6
171.0
170.5
170.7
170.3
170.6
170.3
170.5
170.5
170.9
170.1
170.4
170.9
171.1
170.2
170.0
170.6
170.9
170.4
170.8
80.8
80.0
80.5
79.7
81.4
81.6
80.6
79.7
81.5
80.2
81.2
82.3
81.2
82.0
81.3
82.2
80.5
80.0
81.5
82.3
79.0
78.3
81.8
82.4
80.3
78.9
80.1
79.0
73.6
73.8
73.6
73.8
68.3
68.4
73.6
73.8
73.7
73.7
68.3
68.3
68.1
68.2
68.2
68.3
73.7
73.7
68.4
68.5
76.9
77.6
74.0
74.9
73.2
73.5
73.3
73.6
66.3
66.2
71.8
71.8
63.4
63.5
63.3
63.6
67.0
66.9
67.1
67.0
71.6
71.6
66.1
66.0
71.6
71.6
74.7
74.8
71.3
71.4
71.7
71.7
67.0
66.9
71.6
71.6
10.0, 13.6, 22.6, 25.4, 29.5, 51.8, 124.9, 134.8
9.9, 13.6, 22.6, 25.4, 26.2, 51.9, 124.8, 135.0
10.0, 13.6, 22.0, 25.4, 34.2, 51.8, 125.3, 136.1
9.9, 13.6, 22.4, 26.1, 34.2, 51.9, 125.3, 136.3
13.6, 18.4, 22.0, 34.2, 58.7, 70.1, 71.6, 125.4, 136.0
13.6, 18.7, 22.0, 34.2, 58.7, 70.1, 71.6, 125.2, 136.2
10.0, 13.6, 22.1, 25.5, 34.3, 58.8, 70.2, 71.6, 125.3, 136.0
10.0, 13.6, 22.1, 26.1, 34.3, 58.8, 70.2, 71.6, 125.3, 136.2
10.0, 18.0, 21.8, 25.3, 25.5, 68.6, 120.1, 138.4
9.8, 18.0, 21.8, 25.5, 26.1, 68.6, 120.0, 138.6
18.0, 18.2, 21.8, 25.7, 68.6, 120.1, 138.4
18.2, 18.6, 21.8, 25.7, 68.6, 119.9, 138.6
13.6, 18.2, 21.7, 22.0, 34.2, 68.5, 125.5, 135.8
13.6, 18.6, 21.7, 22.0, 34.2, 68.5, 125.3, 136.1
13.6, 18.2, 21.7, 22.5, 29.5, 68.5, 125.1, 134.7
13.6, 18.6, 21.7, 22.5, 29.5, 68.6, 124.9, 134.8
3g
3h
3i
3j
3k
3l
10.1, 13.6, 21.8, 22.1, 25.4, 34.3, 68.6, 125.5, 135.9
9.9, 13.6, 21.8, 22.1, 26.1, 34.3, 68.6, 125.4, 136.1
18.3, 19.5, 21.8, 68.7, 113.4, 141.3
18.3, 18.8, 21.8, 68.7, 113.8, 141.1
3m major
13.6, 17.1, 19.3, 21.8, 22.1, 29.7, 34.3, 68.6, 125.4, 135.9
13.6, 17.9, 19.3, 21.7, 22.1, 30.6, 34.3, 68.5, 125.4, 136.1
13.6, 21.5, 21.7, 22.0, 34.2, 68.6, 125.3, 126.7, 127.7, 128.1, 136.2, 139.6
13.6, 21.3, 21.7, 22.0, 34.2, 68.6, 125.1, 126.9, 127.9, 128.1, 136.2, 138.9
18.0, 21.8, 25.8, 38.9, 68.7, 120.1, 126.4, 128.4, 129.5, 137.9, 138.4
18.0, 21.8, 25.8, 39.7, 68.7, 120.1, 126.4, 128.4, 129.3, 137.8, 138.4
13.7, 21.9, 22.1, 34.3, 38.9, 68.8, 125.4, 126.5, 128.4, 129.5, 136.1, 137.9
13.7, 21.8, 22.1, 34.3, 39.7, 68.8, 125.4, 126.5, 128.4, 129.4, 136.1, 137.8
minor
3n
3o
3p
3q
3r
major
minor
major
minor
major
minor
4 dia-
stereomers
major
minor
20.5, 20.6, 21.5, 21.7, 21.8, 39.1, 39.5, 39.9, 68.6, 68.7, 73.4, 73.5, 77.1, 77.2, 78.5, 78.7, 79.0, 79.2, 79.9, 116.4, 117.6,
117.9, 126.4, 126.5, 128.4, 128.5, 129.3, 129.4, 137.8, 138.0, 138.1, 138.8, 139.6
170.2
170.5
80.6
79.7
73.4
73.6
74.7
74.7
19.5, 21.8, 39.0, 68.8, 113.4, 126.5, 128.4, 129.5, 137.9, 141.2
19.7, 21.8, 39.8, 68.8, 113.5, 126.5, 128.4, 129.3, 137.8, 141.2
a Determined from a mixture of diastereomers. Diasteromeric ratio: see Table 3.
b Though determined from the mixture of diastereomers, the chemical shifts for the major and minor the diastereomer are listed separately.
Relative configuration not assigned.
Synthesis 2000, No. 9, 1279–1290 ISSN 0039-7881 © Thieme Stuttgart · New York

1286
M. Hiersemann
PAPER
Table 7 Synthesis of Allyl Vinyl Ethers 1a-r
Substrate
Alcohol
Producta
Yield
g
IR
Formula
MW
Elemental Analysis
Calculated
in substance
n [cm–1]
Found
g (mmol)
(%)
C
H
C
H
3a
3.9 (17.9)
3b
2.1 (11.2)
3c
2.0 (8.7)
3d
4.9 (20.0)
3e
3.5 (13.3)
3f
0.94 (3.4)
3g
2.7 (11.1)
3h
2.3 (10.0)
3i
3.1 (12.8)
3j
3.0 (12.3)
3k
0.9 (3.3)
3l
2.4 (11.1)
3m
2.0 (7.6)
3n
2.75 (9.0)
3o
3.6 (11.8)
3p
1a
1bb
1c
3.23
91
0.98
51
1.46
79
3.53
83
2.60
81
0.88
95
1.78
71
1.88
89
2960–2875, 1750,
C11H18O3
C9H14O3
C12H20O3
C12H20O3
C13H22O4
C14H24O4
C13H22O3
C12H20O3
C13H22O3
C13H22O3
C14H24O3
C11H18O3
C15H26O3
C18H24O3
C18H24O3
C19H26O3
C17H22O3
C17H22O3
198.3
170.2
212.3
212.3
242.3
256.3
226.3
212.3
226.3
226.3
240.3
198.3
254.4
288.4
288.4
302.4
274.4
274.4
67.18
b
9.27
66.64
9.15
8.29
9.50
9.50
9.15
9.44
9.80
9.50
9.80
9.80
10.06
9.15
10.30
8.39
8.39
8.67
8.08
8.08
1730
b
b
65.51
67.89
67.89
64.44
65.60
68.99
67.89
68.99
68.99
69.96
66.64
70.83
74.97
74.97
75.46
74.42
74.42
2965–2875, 1730
2960–2875, 1730
2960–2875, 1725
2960–2880, 1750
2980–2880, 1720
2940–2880, 1720
2980–2875, 1720
2980–2875, 1720
2965–2875, 1720
2980–2880, 1720
2960–2875, 1720
2980–2875, 1725
2980–2880, 1720
66.67
9.41
(67.85)c
67.37
(9.55)c
9.64
1d
1e
64.84
65.32
66.88
67.24
68.35
9.27
1f
9.54
1g
1h
1i
9.71
10.00
10.04
2.69
93
2.46
88
0.61
77
1j
67.88
9.86
(69.14)d
68.23
(10.03)d
9.93
1k
1l
(70.30)d
66.11
(10.58)d
9.34
1.81
82
1m
1nf
1og
1ph
1qf
1ri,f
1.0e
52e
2.01
78
70.46
73.82
74.80
10.28
8.46
8.52
2.08
61
1.91
81
0.84
34
2.18
77
2980–2875, 1720
75.93
8.82
2.5 (7.8)
3q
2.6 (8.9)
3r
f
f
f
(74.36)d
74.63
(8.41)d
74.08
2980–2875, 1720
3.0 (10.3)
a Colorless oils, isolated as a mixture of double bond isomers as indicated in Table 3.
b Spectra in CDCl3 show a 1:1 mixture with the corresponding Claisen rearrangement product 5b.
c In parentheses: found for the corresponding Claisen rearrangement product 5c.
d In parentheses: found for the corresponding dienolate [2,3]-Wittig rearrangement product.
e 820 mg (42 %) of the mesylate 4m isolated.
f Spectra in CDCl3 show a contamination with the corresponding Claisen rearrangement product 5q.
g 350 mg (10 %) of the corresponding E configured b,g-unsaturated ester isolated 6o.
h 220 mg (19 %) of the corresponding E configured b,g-unsaturated ester isolated 6p.
i 340 mg (12 %) of the corresponding E configured b,g-unsaturated ester isolated 6r.
Synthesis 2000, No. 9, 1279–1290 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Synthesis of a-Allyloxy-Substituted a,b-Unsaturated Esters via Aldol Condensation
1287
Table 8 1H NMR Data of Allyl Vinyl Ethers 1a-r,a 300 MHz, CDCl3, d, J (Hz)
Compound 3-H
4-CHn
1.77
1¢-CHn
Other Signals
Z-1a
E-1a
Z-1bb
E-1b c
Z-1c
6.36
(q, J = 7.1, 1H)
4.28
0.90 (t, J = 7.3, 3 H, 6¢-CH3), 1.41 (qt, J1 = J2 = 7.4, 2 H, 5¢-
CH2), 2.03 (td, J1 = J2 = 6.9, 2 H, 4¢-CH2), 3.76 (s, 3 H,
OCH3), 5.68 (m, 2H, 2¢-H, 3¢-H)
(d, J = 7.1, 3 H, CH3) (d, J = 5.8, 2 H)
5.41
(q, J = 7.5, 1H)
1.97
4.20
0.90 (t, J = 7.3, 3 H, 6¢-CH3), 1.41 (qt, J1 = J2 = 7.4, 2 H, 5¢-
CH2), 1.97–2.09 (m, 2 H, 4¢-CH2), 3.80 (s, 3H, OCH3),
5.56–5.71 (m, 2 H, 2¢-H, 3¢-H)
(d, J = 7.5, 3 H, CH3) (d, J = 5.8, 2 H)
6.36
(q, J = 7.1, 1 H)
1.75
4.48
1.36 (d, J = 6.2, 3 H, 1¢-CH3), 3.75 (s, 3 H, OCH3), 5.11 (d,
J = 9.1, 1 H, 3¢-H), 5.15 (d, J = 16.9, 1 H, 3¢-H), 5.74–5.90
(m, 1 H, 2¢-H)
(d, J = 7.1, 3 H, CH3) (qd, J1 = J2 = 6.6,
1 H)
5.57
(q, J = 7.5, 1 H)
1.95
4.35
1.35 (d, J = 6.5, 3 H, 1¢-CH3), 3.79 (s, 3 H, OCH3), 5.11 (d,
J = 9.1, 1 H, 3¢-H), 5.15 (d, J = 16.9, 1 H, 3¢-H), 5.74–5.90
(m, 1 H, 2¢-H)
(d, J = 7.5, 3 H, CH3) (qd, J1 = J2 = 6.5,
1 H)
6.28
2.26
4.38 and 4.43
0.90 (t, J = 7.3, 3 H, 6¢-CH3), 1.03 (t, J = 7.5, 3 H, 5-CH3),
(t, J = 7.6, 1 H)
(qd, J1 = J2 = 7.56,
2 H, CH2)
(AB system, J = 9.7, 1.34 (qt, J1 = J2 = 7.5, 2 H, 5¢-CH2), 1.99–2.12 (m, 2 H, 4¢-
2 H)
CH2), 3.77 (s, 3 H, OCH3), 5.55–5.69 (m, 2 H, 2¢-H, 3 ¢-H)
E-1c
Z-1d
E-1d
Z-1e
5.29
(t, J = 7.6, 1 H)
2.47
4.32
0.92 (t, J = 5.7, 3 H, 6¢-CH3), 1.04 (t, J = 7.3, 3 H, 5-CH3),
1.41 (qt, J1 = J2 = 7.7, 2 H, 5¢-CH2), 1.99–2.12 (m, 2 H, 4¢-
CH2), 3.79 (s, 3 H, OCH3), 5.55–5.69 (m, 2 H, 2¢-H, 3¢-H)
(qd, J1 = J2 = 7.6,
2 H, CH2)
(br d, J = 4.6, 2 H)
6.27
(t, J = 7.6, 1 H)
2.24
4.27
(d, J = 6.2, 2 H)
0.90 (t, J = 7.3, 3 H, 6¢-CH3), 1.02 (t, J = 7.6, 3 H, 5-CH3),
1.41 (qt, J1 = J2 = 7.4, 2 H, 5¢-CH2), 1.99–2.09 (m, 2 H, 4¢-
CH2), 3.77 (s, 3 H, OCH3), 5.68 (m, 2 H, 2¢-H, 3¢-H)
(qd, J1 = J2 = 7.6,
2 H, CH2)
5.29
(t, J = 7.6, 1 H)
2.46
5.84
(d, J = 5.8, 2 H)
0.91 (t, J = 7.5, 3 H, 6¢-CH3), 1.04 (t, J = 7.5, 3 H, 5-CH3),
1.41 (qt, J1 = J2 = 7.4, 2 H, 5¢-CH2), 1.99–2.09 (m, 2 H, 4¢-
CH2), 3.80 (s, 3 H, OCH3), 5.68 (m, 2 H, 2¢-H, 3¢-H)
(qd, J1 = J2 = 7.6,
2 H, CH2)
6.39
(q, J = 7.1, 1 H)
1.76
4.29
0.90 (t, J = 7.3, 3 H, 6¢-CH3), 1.41 (qt, J1 = J2 = 7.4, 2 H, 5¢-
CH2), 2.03 (td, J1 = J2 = 7.0, 2 H, 4¢-CH2), 3.40 (s, 3 H,
OCH3), 3.61–3.71 (m, 2 H, 1¢¢-CH2), 4.28–4.34 (m, 2 H, 2¢¢-
CH2), 5.63 (dt, J1 = 15.3, J2 = 6.0, 1 H, 2¢-H), 5.73 (dt, J1 =
15.4, J2 = 6.0, 1 H, 3¢-H)
(d, J = 7.1, 3 H, CH3) (br d, J = 6.2, 2 H)
E-1e
Z-1f
5.44
1.96
4.20
0.90 (t, J = 7.3, 3 H, 6¢-CH3), 1.41 (qt, J1 = J2 = 7.5, 2 H, 5¢-
CH2), 1.98–2.08 (m, 2 H, 4¢-CH2), 3.40 (s, 3 H, OCH3),
3.61–3.71 (m, 2 H, 1¢¢-CH2), 4.28–4.34 (m, 2 H, 2¢¢-CH2),
5.56–5.80 (m, 2 H, 2¢-H, 3¢-H)
(q, J = 7.5, 1 H)
(d, J = 7.5, 3 H, H3) (br d, J = 6.2, 2 H)
6.31
(t, J = 7.6, 1 H)
2.24
4.28
0.90 (t, J = 7.3, 3 H, 6¢-CH3), 1.02 (t, J = 7.6, 3 H, 5-CH3),
1.40 (qt, J1 = J2 = 7.3, 2 H, 5¢-CH2), 2.03 (td, J1 = J2 = 7.0,
2 H, 4¢-CH2), 3.40 (s, 3 H, OCH3), 3.62–3.70 (m, 2 H, 1¢¢-
CH2), 4.29–4.34 (m, 2 H, 2¢¢–CH2), 5.63 (dt, J1 = 15.3, J2 =
6.2, 1 H, 2¢-H), 5.73 (dt, J1 = 15.3, J2 = 6.0, 1 H, 3¢-H)
(qd, J1 = J2 = 7.6,
2 H, CH2)
(br d, J = 5.8, 2 H)
E-1f
5.31
(t, J = 7.6, 1 H)
2.44
4.20
0.90 (t, J = 7.3, 3 H, 6¢-CH3), 1.03 (t, J = 7.5, 3 H, 5-CH3),
1.41 (qt, J1 = J2 = 7.7, 2 H, 5¢-CH2), 1.98–2.08 (m, 2 H, 4¢-
CH2), 3.39 (s, 3 H, OCH3), 3.62–3.70 (m, 2 H, 1¢¢-CH2),
4.29–4.34 (m, 2 H, 2¢¢-CH2), 5.55–5.75 (m, 2 H, 2¢-H, 3¢-H)
(qd, J1 = J2 = 7.6,
2 H, CH2)
(br d, J = 5.8, 2 H)
Z-1g
E-1g
Z-1h
6.23
(t, J = 7.6, 1 H)
2.24
4.31
1.02 (t, J = 7.6, 3 H, 5-CH3), 1.30 (d, J = 6.2, 6 H, Oi-Pr-
CH3), 1.70 (br s, 3 H, 4¢-CH3), 1.76 (br s, 3 H, 4¢-CH3), 5.09
(sept, J = 6.3, 1 H, Oi-Pr-CH), 5.37–5.47 (m, 1 H, 3¢-H)
(qd, J1 = J2 = 7.6,
2 H, CH2)
(br d, J = 7.5, 2 H)
5.27
2.41
4.23
1.03 (t, J = 7.5, 3 H, 5-CH3), 1.32 (d, J = 5.5, 6 H, Oi-Pr-
CH3), 1.68 (br s, 3 H, 4¢-CH3), 1.76 (br s, 3 H, 4¢-CH3), 5.12
(sept, J = 6.2, 1 H, Oi-Pr-CH), 5.37–5.47 (m, 1 H, 3¢-H)
(qd, J1 = J2 = 7.6, H, (br d, J = 6.5, 2 H)
CH2)
(t, J = 7.8, 1 H)
6.32
(q, J = 6.3, 1 H)
1.76
(d, J = 7.1, 3 H,
CH3)
4.33
(d, J = 7.1, 2 H)
1.29 (d, J = 6.5, 6 H, Oi-Pr-CH3), 1.70 (s, 3 H, 4¢-CH3), 1.76
(s, 3 H, 4¢-CH3), 5.10 (sept, J = 6.5, 1 H, Oi-Pr-CH), 5.37–
5.49 (m, partially covered, 1H, 3¢-H)
Synthesis 2000, No. 9, 1279–1290 ISSN 0039-7881 © Thieme Stuttgart · New York

1288
M. Hiersemann
PAPER
Table 8 (continued)
Compound 3-H
4-CHn
1′-CHn
Other Signals
E-1h
E-1i
5.40
(q, J = 7.1, 1 H)
1.94
(d, J = 7.1, 3 H,
CH3)
4.23
(d, J = 6.8, 2 H)
1.32 (d, J = 6.5, 6H, Oi-Pr-CH3), 1.68 (s, 3H, 4′-CH3), 1.76
(s, 3 H, 4′-CH3), 5.13 (sept, J = 6.5, 1 H, Oi-Pr-CH), 5.37–
5.49 (m, partially covered, 1H, 3′-H)
6.32
1.76
4.27
0.90 (t, J = 7.3, 3 H, 6′-CH3), 1.29 (d, J = 6.2, 6 H, Oi-Pr-
(q, J = 7.14, 1 H)
(d, J = 7.14, 3 H,
CH3)
(br d, J = 5.84, 2 H) CH3), 1.40 (qt, J1 = J2 = 7.4, 2 H, 5′-CH2), 2.03 (dt, J1 = J2
= 6.8, 2 H, 4′-CH2), 5.10 (sept, J = 6.3, 1 H, Oi-Pr-H), 5.60
(dt, J1 = 15.3, J2 = 6.01, 1 H, 2′-H), 5.7 (dt, J1 = 15.6, J2 =
6.2, 1 H, 3′-H)
Z-1i
5.40
1.93
4.19
0.90 (t, J = 7.3, 3H, 6′-CH3), 1.32 (d, J = 6.2, 6 H, Oi-Pr-
(q, J = 7.36, 1 H)
(d, J = 7.47, 3 H,
CH3)
(br d, J = 5.84, 2 H) CH3), 1.41 (qt, J1 = J2 = 7.5, 2 H, 5′–CH2), 1.99–2.08 (m, 2
H, 4′-CH2), 5.13 (sept, J = 6.3, 1 H, Oi-Pr-H), 5.56–5.79 (m,
2 H, 2′-H, 3′-H)
Z-1j
E-1j
Z-1m
6.33
(q, J = 7.1, 1 H)
1.77
(d, J = 7.1, 3 H,
CH3)
4.41
0.90 (t, J = 7.3, 3 H, 6′-CH3), 1.29 (d, J = 6.2, 6 H, Oi-Pr-
CH3), 1.34–1.45 (m, 2 H, 5′-CH2), 2.05 (m, 2 H, 4′-CH2),
5.13 (sept, J = 6.5, 1 H, Oi-Pr-CH), 5.56–5.67 (m, 2 H, 2′-
H, 3′-H)
(br d, J = 5.5, 2 H)
5.40
(q, J = 7.5, 1 H)
1.94
(d, J = 7.5, 3 H,
CH3)
4.22
0.91 (t, J = 7.5, 3 H, 6′-CH3), 1.32 (d, J = 6.5, 6 H, Oi-Pr-
CH3), 1.34–1.45 (m, 2 H, 5′-CH2), 2.05 (m, 2 H, 4′-CH2),
5.10 (sept, J = 6.5, 1 H, Oi-Pr-CH), 5.56–5.67 (m, 2 H, 2′-
H, 3′-H)
(br d, J = 4.2, 2 H)
6.0
2.89
(mc, 1 H, CH)
4.26
0.90 (t, J = 7.5, 3 H, 6′-CH3), 1.01 (d, J = 6.25, 6 H, 5-CH3),
1.29 (d, J = 6.3, 6 H, Oi-Pr-CH3), 1.41 (qt, J1 = J2 = 7.4, 2
H, 5′-CH2), 2.03 (dt, J1 = J2 = 7.1, 2 H, 4′-CH2), 5.07 (sept,
J = 6.3, 1 H, Oi-Pr-CH), 5.61 (dt, J1 = 15.3, J2 = 6.0, 1 H,
2′-H), 5.72 (dt, J1 = 15.3, J2 = 6.0, 1 H, 3′-H)
(d, J = 10.1, 1 H)
(br d, J = 5.8, 2 H)
Z-1n
6.97
(s, 1 H)
–
–
4.43
(d, J = 5.8, 2 H)
0.87 (t, J = 7.3, 3 H, 6′-CH3), 1.32–1.42 (m, partially cov-
ered, 2 H, 5′-CH2), 1.35 (d, J = 6.5, 6 H, Oi-Pr-CH3), 2.01
(td, J1 = J2 = 6.9, 2 H, 4′-CH2), 5.16 (sept, J = 6.3, 1 H, Oi-
Pr-CH), 5.60–5.81 (m, 2 H, 2′-H, 3′-H), 7.21–7.40 (m, 3 H,
aryl-H), 7.76–7.81 (m, 2 H, aryl-H)
Z-1o
Z-1p
6.38
(t, J = 7.6, 1 H)
3.57
(d, J = 7.8, 2 H,
CH2)
4.41
(d, J = 7.1, 2 H)
1.28 (d, J = 6.2, 6 H, Oi-Pr-CH3), 1.70 (s, 3 H, 4′-CH3), 1.76
(s, 3 H, 4′-CH3), 5.10 (sept, J = 6.3, 1 H, Oi-Pr-CH), 5.46
(mc, 1 H, 2′-H), 7.17–7.33 (m, 5 H, aryl-H)
6.38
3.56
4.35
0.90 (t, J = 7.3, 3 H, 6′-CH3), 1.28 (d, J = 6.5, 6 H, Oi-Pr-
CH3), 1.40 (qt, J1 = J2 = 7.4, 2 H, 5′-CH2), 2.03 (td, J1 = J2
= 7.1, 2 H, 4′-CH2), 5.08 (sept, J = 6.3, 1 H, Oi-Pr-CH), 5.65
(dt, J1 = 15.3, J2 = 6.0, 1 H, 2′-CH), 5.75 (dt, J1 = 15.3, J2 =
6.0, 1 H, 3′-CH), 7.17–7.33 (m, 5 H, aryl-H)
(t, J = 6.5, 1 H)
(d, J = 7.8, 2 H,
(d, J = 6.3, 2 H)
CH2)
Z-1qc
Z-1r
6.37
(t, J = 7.6, 1 H)
3.55 and 3.56
(d, J = 7.5, 1 H,
CH)
4.58
1.27 (d, J = 6.2, 6 H, Oi-Pr-CH3), 1.40 (d, J = 6.2, 3 H, 1′-
CH3), 5.07 (sept, J = 6.3, 1 H, Oi-Pr-CH), 5.13 (d, J = 10.4,
1 H, 3′-CH2), 5.18 (d, J = 17.5, 1 H, 3′ CH2), 5.86 (ddd, J1
= 17.4, J2 = 10.1, J3 = 7.5, 1 H, 2′-CH), 7.11–7.34 (m, 5 H,
aryl-H)
(qd, J1 = J2 = 6.7,
1 H)
6.36
(t, J = 7.6, 1 H)
3.59
(d, J = 7.8, 2 H,
CH2)
4.29
(s, 2 H)
1.28 (d, J = 6.2, 6 H, Oi-Pr-CH3), 1.86 (s, 3 H, 2′-CH3), 4.96
(br s, 1 H, 3′-CH2), 5.07 (br s, 1 H, 3′-CH2), 5.09 (sept, J =
6.25, 1 H, Oi-Pr-CH), 7.17–7.34 (m, 5 H, aryl-H)
a Determined from a mixture of double bond isomers as indicated in Table 3, assignment of the double configuration is based on NOESY ex-
periments of selected allyl vinyl ethers.
b Determined from 1:1 mixture with the corresponding Claisen rearrangement product 5b.
c Contaminated by the corresponding Claisen rearrangement product 5b, 5q.
Synthesis 2000, No. 9, 1279–1290 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Synthesis of a-Allyloxy-Substituted a,b-Unsaturated Esters via Aldol Condensation
1289
Table 9 13C NMR Data of Allyl Vinyl Ethers 1a-r,a 75.5, CDCl3, d
Compound C-1
164.5
C-2
C-3
C-1¢
Other Signals
Z-1a
E-1a
Z-1c
E-1c
Z-1d
E-1d
Z-1e
E-1e
Z-1f
E-1f
Z-1g
E-1g
Z-1h
E-1h
Z-1i
145.3
124.6
72.9
11.4 (4-CH3), 13.6 (6¢-CH3), 22.0 (5¢-CH2), 34.3 (4¢-CH2), 51.7 (OCH3), 125.4 (2¢-CH2),
136.1 (3¢-CH2)
12.5 (4-CH3), 13.6 (6¢-CH3), 22.0 (5¢-CH2), 34.3 (4¢-CH2), 51.7 (OCH3), 124.6 (2¢-CH2),
135.7 (3¢-CH2)
13.2 (5-CH3), 13.6 (6¢-CH3), 19.1 (4-CH2), 22.6 (5¢-CH2), 29.4, (4¢-CH2), 51.7 (OCH3),
124.9 (2¢-CH2), 134.5 (3¢-CH2)
13.6 (6¢-CH3), 14.6 (5-CH3), 20.2 (4-CH2), 22.5 (5¢-CH2), 29.7, (4¢-CH2), 51.7 (OCH3),
124.6 (2¢-CH2), 134.0 (3¢-CH2)
13.2 (5-CH3), 13.6 (6¢-CH3), 19.2 (4-CH2), 22.1 (5¢-CH2), 34.3 (4¢-CH2), 51.7 (OCH3),
125.4 (2¢-CH2), 136.0 (3¢-CH2)
13.6 (6¢-CH3), 14.7 (5-CH3), 20.2 (4-CH2), 22.1 (5¢-CH2), 34.3 (4¢-CH2), 51.7 (OCH3),
124.6 (2¢-CH2), 135.6 (3¢-CH2)
11.4 (4-CH3), 13.5 (6¢-CH3), 22.0 (5¢-CH2), 34.2 (4¢-CH2), 58.8 (OCH3), 63.5 (1¢¢-CH2),
70.3 (2¢¢-CH2), 125.4 (2¢-CH2), 135.9 (3¢-CH2)
12.4 (4-CH3), 13.5 (6¢-CH3), 22.0 (5¢-CH2), 34.2 (4¢-CH2), 58.8 (OCH3), 63.5 (1¢¢-CH2),
70.1 (2¢¢-CH2), 124.7 (2¢-CH2), 135.2 (3¢-CH2)
13.1 (5-CH3), 13.6 (6¢-CH3), 19.2 (4-CH2), 22.0 (5¢-CH2), 34.3 (4¢-CH2), 58.9 (OCH3),
63.6 (1¢¢-CH2), 70.4 (2¢¢-CH2), 125.4 (2¢-CH2), 136.0 (3¢-CH2)
13.6 (6¢-CH3), 14.6 (5-CH3), 19.2 (4-CH2), 22.0 (5¢-CH2), 34.3 (4¢-CH2), 58.9 (OCH3),
63.6 (1¢¢-CH2), 70.2 (2¢¢-CH2), 124.7 (2¢-CH2), 135.3 (3¢-CH2)
13.2 (5-CH3), 17.9 (4¢-CH3), 19.1 (4-CH2), 21.8 (Oi-Pr-CH3), 25.7 (4¢-CH3), 68.3 (Oi-Pr-
CH), 120.1 (2¢-CH), 138.5 (3¢-C)
14.7 (5-CH3), 18.1 (4¢-CH3), 20.3 (4-CH2), 21.8 (Oi-Pr-CH3), 25.7 (4¢-CH3), 68.2 (Oi-Pr-
CH), 119.8 (2¢-CH), 137.4 (3¢-C)
11.3 (4-CH3), 17.9 (4¢-CH3), 21.8 (Oi-Pr-CH3), 25.7 (4¢-CH3), 68.1 (Oi-Pr-CH), 120.1 (2¢-
CH), 138.5 (3¢-C)
12.6 (4-CH3), 18.1 (4¢-CH3), 21.8 (Oi-Pr-CH3), 25.7 (4¢-CH3), 68.3 (Oi-Pr-CH), 119.8 (2¢-
CH), 137.4 (3¢-C)
11.3 (4-CH3), 13.6 (6¢-CH3), 21.8 (Oi-Pr-CH3), 22.1 (5¢-CH2), 34.3 (4¢-CH2), 68.2 (Oi-Pr-
CH), 125.6 (2¢-CH2), 136.0 (3¢-CH2)
12.6 (4-CH3), 13.6 (6¢-CH3), 21.8 (Oi-Pr-CH3), 22.1 (5¢-CH2), 34.3 (4¢-CH2), 68.4 (Oi-Pr-
CH), 125.0 (2¢-CH2), 135.2 (3¢-CH2)
11.3 (4-CH3), 13.6 (6¢-CH3), 21.8 (Oi-Pr-CH3), 22.6 (5¢-CH2), 29.4 (4¢-CH2), 68.1 (Oi-Pr-
CH), 125.1 (2¢-CH2), 134.5 (3¢-CH2)
12.5 (4-CH3), 13.6 (6¢-CH3), 21.8 (Oi-Pr-CH3), 22.5 (5¢-CH2), 29.7 (4¢-CH2), 68.3 (Oi-Pr-
CH), 124.9 (2¢-CH2), 133.7 (3¢-CH2)
13.2 (5-CH3), 13.6 (6¢-CH3), 19.1 (4-CH2), 21.8 (Oi-Pr-CH3), 22.1 (5¢-CH2), 34.3 (4¢-
CH2), 68.2 (Oi-Pr-CH), 125.5 (2¢-CH2), 135.9 (3¢-CH2)
13.6 (6¢-CH3), 14.7 (5-CH3), 20.2 (4-CH2), 21.8 (Oi-Pr-CH3), 22.1 (5¢-CH2), 34.3 (4¢-
CH2), 68.4 (Oi-Pr-CH), 124.9 (2¢-CH2), 135.2 (3¢-CH2)
11.2 (4-CH3), 19.6 (2¢-CH3), 21.8 (Oi-Pr-CH3), 68.2 (Oi-Pr-CH), 113.3 (3¢-CH2), 141.6
(2¢-C)
12.5 (4-CH3), 19.3 (2¢-CH3), 21.8 (Oi-Pr-CH3), 68.3 (Oi-Pr-CH), 112.6 (3¢-CH2), 140.8
(2¢-C)
13.6 (6¢-CH3), 21.8 (Oi-Pr-CH3), 22.1 (5¢-CH2), 22.3 (i-Pr-CH3), 23.6 (4-CH), 34.3 (4¢-
CH2), 68.3 (Oi-Pr-CH), 125.6 (2¢-CH2), 135.6 (3¢-CH2)
13.5 (6¢-CH3), 21.9 (Oi-Pr-CH3), 22.0 (5¢-CH2), 34.2 (4¢-CH2), 68.7 (O-i-Pr-CH)
18.0 (4¢-CH3), 21.8 (Oi-Pr-CH3), 25.8 (4¢-CH3), 31.9 (4-CH2), 68.4 (Oi-Pr-CH), 120.1 (2¢-
CH), 126.2, 126.8, 128.4, 128.5, 138.8, 139.4 (aryl-C, 3-C, 3¢-C)
13.6 (6¢-CH3), 21.8 (Oi-Pr-CH3), 22.1 (5¢-CH2), 31.9, 34.3 (4¢-CH2, 4-CH2), 68.4 (Oi-Pr-
CH), 125.5, 126.2, 126.6, 128.4, 128.5, 139.3 (aryl-C, 3¢-CH2, 2¢-CH2)
20.8 (1¢-CH3), 21.8 (Oi-Pr-CH3), 32.1 (4-CH2), 68.4 (Oi-Pr-CH), 116.9 (3¢-CH2)
19.7 (2¢-CH3), 21.8 (Oi-Pr-CH3), 31.8 (4-CH2), 68.5 (Oi-Pr-CH), 113.5 (3¢-CH2), 126.2,
126.3, 128.5, 139.3, 141.4 (aryl-C, 2¢-C, 3-CH).
164.2
164.5
164.1
164.6
164.2
163.8
163.8
164.0
163.8
163.8
163.6
163.6
163.7
163.5
163.6
163.4
163.5
163.7
163.7
163.4
163.5
163.9
144.9
144.0
144.0
143.9
143.9
145.1
145.0
143.8
144.0
144.6
144.8
145.9
145.8
145.8
145.6
145.8
145.6
144.4
144.6
146.2
145.6
143.2
112.7
131.3
119.5
131.2
119.7
124.7
113.4
131.5
120.2
130.6
119.2
123.9
112.4
123.8
113.0
124.9
112.6
130.5
119.4
123.3
112.6
136.0
69.8
67.5
64.8
73.0
69.8
72.7
69.9
72.9
69.9
68.2
66.1
68.2
66.2
72.8
70.2
67.2
65.2
72.9
70.0
75.6
73.0
73.0
E-1i
Z-1j
E-1j
Z-1k
E-1k
Z-1l
E-1l
Z-1m
Z-1nb
Z-1o
164.2
163.5
144.6
145.2
b
c
72.5
68.3
Z-1p
163.4
145.1
136.2
72.9
Z-1qb
Z-1r
163.6
163.3
144.1
145.4
b
c
78.5
76.0
a Determined from a mixture of double bond isomers as indicated in Table 3.
b Only characteristic signals, determined from a 1:1 mixture with the corresponding Claisen rearrangement product 5.
c Not unambiguously assignable.
Synthesis 2000, No. 9, 1279–1290 ISSN 0039-7881 © Thieme Stuttgart · New York

1290
M. Hiersemann
PAPER
(5) Hiersemann, M. manuscript submitted.
(6) Hiersemann, M. Synlett 2000, 415.
(7) For experimental procedures, see: Brückner, R. Chem. Ber.
1989, 122, 703.
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Article Identifier:
1437-210X,E;2000,0,09,1279,1290,ftx,en;Z01400SS.pdf
Synthesis 2000, No. 9, 1279–1290 ISSN 0039-7881 © Thieme Stuttgart · New York