3,5-Bis(trifluoromethyl)phenyl sulfones in the Julia-Kocienski olefination - Application to the synthesis of tri- and tetrasubstituted olefins

Article abstract of DOI:10.1002/ejoc.200600478

3,5-Bis(trifluoromethyl)phenyl (BTFP) sulfones 8a-d are successfully employed in the modified Julia olefination reaction with carbonyl compounds employing phosphazene base P4-tBu at room temp. in THF, affording tri- and tetrasubstituted olefins in good yi

Full text of DOI:10.1002/ejoc.200600478

FULL PAPER
DOI: 10.1002/ejoc.200600478
3,5-Bis(trifluoromethyl)phenyl Sulfones in the Julia–Kocienski Olefination –
Application to the Synthesis of Tri- and Tetrasubstituted Olefins
Diego A. Alonso,[a] Mónica Fuensanta,[a] and Carmen Nájera*[a]
Keywords: Alkenes / Carbanions / Olefination / Sulfones / Phosphazenes
3,5-Bis(trifluoromethyl)phenyl (BTFP) sulfones 8a–d are suc-
cessfully employed in the modified Julia olefination reaction
with carbonyl compounds employing phosphazene base P4-
tBu at room temp. in THF, affording tri- and tetrasubstituted
olefins in good yields. The Julia–Kocienski olefination be-
tween primary alkyl BTFP sulfones 8a,b and aromatic and
aliphatic ketones affords the corresponding trisubstituted al-
kenes in good yields and low stereoselectivities. On the other
hand, higher yields and stereoselectivities are obtained in
the synthesis of trisubstituted olefins through the other ap-
proach, the coupling of secondary alkyl BTFP sulfones 8c,d
with aliphatic, aromatic and α,β-unsaturated aldehydes. For
the first time, tetrasubstituted olefins are synthesized by me-
ans of the Julia–Kocienski protocol when the isopropyl BTFP
sulfone 8c reacts with aliphatic and aromatic ketones, em-
ploying P4-tBu as base at THF reflux.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
fones with a suitable oxophilic electrophile and the employ-
ment of SmI2/HMPA to promote, under neutral conditions,
the reductive elimination at low temperatures.[10] A variant
of the classical Julia reaction, the Julia–Kocienski ole-
fination, also called modified or one-pot Julia ole-
fination,[11,12] has recently emerged as a powerful tool for
olefin synthesis. Since the initial study by Silvestre Julia and
co-workers of the reaction of metallated benzothiazol-2-yl
sulfones (BT sulfones, 1) with carbonyl compounds,[11a] the
versatility of these derivatives has been fully demonstrated
through their application in the total synthesis of a large
number of biologically active natural products[11c] such as
rapamycin,[13] (+)-herboxidiene A,[14] (–)-[15] and (+)-lason-
olide A,[16] rhizoxin D,[17] phorboxazole A[18] and B,[19] per-
idin,[20] (–)-colombiasin A,[21] and (–)-elisapterosin B.[21] In
addition, BT sulfones have been used in the preparation of
a wide variety of olefin moieties such as dienes,[22] tri-
enes,[22b,22c] fluoroalkenes,[23] vinyl ethers,[24] exomethylene
sugars,[25] and α,β-unsaturated esters.[26] Other heterocyclic
derivatives, such as pyridin-2-yl (PYR, 2),[22a,27] 1-phenyl-
1H-tetrazol-5-yl (PT, 3),[28] and 1-tert-butyl-1H-tetrazol-5-
yl (TBT, 4),[29] and most notably the benzothiazol-2-yl[30]
and 1-phenyl-1H-tetrazol-5-yl[31] derivatives have also pro-
vided useful levels of stereoselectivity in the one-pot Julia
olefination.
Introduction
The stereoselective synthesis of tri- and tetrasubstituted
olefins represents one of the long-standing challenges in or-
ganic chemistry. During several decades, a variety of ap-
proaches to the synthesis of olefins have been developed in
an attempt to address regio- and stereochemical demands.
The most generally applicable methods involve the direct
olefination of carbonyl compounds,[1] as in the Wittig,[2]
Horner,[3] Wadsworth–Emmons,[4] Peterson,[5] Johnson,[6]
and classical (Marc) Julia[7] reactions. These methodologies
have played important roles in the synthesis of natural
products containing the (E)- or (Z)-alkene moiety. The clas-
sical Julia olefination, also known as the Julia–Lythgoe ole-
fination, was developed nearly thirty years ago and is based
on a reductive elimination process of β-alkoxy sulfones.[8]
Since its discovery, it has become a crucial step in the syn-
thesis of many natural products.[9] Trisubstituted alkenes
have been prepared by the reductive elimination of β-hy-
droxy sulfones but, in general, the reverse reaction com-
petes. The reverse reaction is favoured when the β-alkoxy
sulfone adduct is sterically encumbered. The olefination of
ketones to prepare trisubstituted alkenes employing Na/Hg
affords moderate yields, unpredictable stereoselectivities
and large amounts of retro-aldol products from the inter-
mediate β-alkoxy sulfones. High yields and moderate ste-
reoselectivities of trisubstituted alkenes are obtained by a
modification of the Julia–Lythgoe olefination reaction, in-
volving the in situ capture of the intermediate β-alkoxy sul-
We have recently shown that the BTFP group 5 (Fig-
ure 1) is a strong electron-withdrawing group, and the cor-
responding BTFP sulfonyl group is an excellent nucleofuge
in base-promoted β-elimination processes.[32–35] Thus, α-ar-
ylsulfonyl acetates 6 (Figure 2) are very soft nucleophiles
under phase-transfer-catalyzed (PTC) conditions and have
been used in the direct synthesis of E aconitates by an alky-
lation-elimination integrated process.[32] On the other hand,
[a] Departamento de Química Orgánica and Instituto de Síntesis
Orgánica (ISO), Facultad de Ciencias, Universidad de Alicante,
Apartado 99, 03080 Alicante, Spain
E-mail: cnajera@ua.es
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D. A. Alonso, M. Fuensanta, C. Nájera
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β-arylsulfonyl ethanol 7 (Figure 2), is an efficient protecting in the synthesis of tri- and tetrasubstituted alkenes through
group for carboxylic acids, easily removed with aqueous the Julia–Kocienski olefination of aldehydes and ketones.[37]
NaHCO3.[33] We have very recently reported the successful
use of alkyl BTFP sulfones 8 (Figure 2) (R = H, alkyl, aryl)
Results and Discussion
in the stereoselective synthesis of 1,1- and 1,2-disubstituted
olefins through the Julia–Kocienski olefination of aliphatic
and aromatic aldehydes and ketones under very simple reac-
tion conditions with KOH and phosphazenes as bases.[34]
The presence of the BTFP group, which can support ipso
substitution of the sulfonate nucleofuge, was also demon-
strated to be responsible for the different reactivity and re-
action pathway observed in a one-pot Julia olefination in-
volving a Smiles rearrangement[35] and spontaneous elimi-
nation of sulfur dioxide and the corresponding phenol de-
rivative[36] (Scheme 1). Now, we report the evaluation and
optimization of BTFP sulfones 8 as nucleophilic partners
Different representative π-deficient BTFP sulfones 8a–d
were prepared in high yields by the reaction of 3,5-bis(tri-
fluoromethyl)benzenethiol[38] with the corresponding alkyl
bromide and NaH as base in CH3CN at room temp. to
afford sulfides 9 (Scheme 2). Thioethers 9 were oxidized
without further purification to the sulfones 8a–c with 30%
H2O2 in the presence of catalytic amounts of MnSO4·H2O
(1 mol-%) and a buffer solution of NaHCO3[39] (Scheme 2).
Sulfone 8d was synthesized in 81% yield from benzylic sul-
fone 8b by deprotonation with phosphazene base P4-tBu[40]
and subsequent reaction with ethyl iodide (Scheme 2).
Figure 1. Heteroaryl and BTFP groups.
Scheme 2. Synthesis of BTFP sulfones 8a–d.
Two different routes can be employed for the synthesis
of trisubstituted olefins 10−either olefination of aldehydes
with secondary alkyl BTFP sulfones, such as the isopropyl
analogue 8c and the 1-phenyl-n-propyl analogue 8d, or re-
Figure 2. BTFP sulfonyl derivatives.
Scheme 1. Mechanism of the Julia–Kocienski olefination with BTFP sulfones.
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3,5-Bis(trifluoromethyl)phenyl Sulfones in the Julia-Kocienski Olefination
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action between ketones and primary alkyl BTFP sulfones, yields (Table 1, entry 3). When the Schwesinger base BEMP
such as the n-pentyl analogue 8a and the benzyl analogue was used, the reaction failed (Table 1, entry 4). However,
8b (Scheme 3, Table 1 and Table 2).
the phosphazene P4-tBu gave an excellent yield of alkene
With respect to the olefination of aldehydes employing 10ca at room temp. in THF (Table 1, entry 5). As shown in
secondary alkyl sulfones 8c and 8d, a preliminary study was Table 1 (entries 2 and 5), the yield of the olefination reac-
first conducted through the coupling between isopropyl tion with KOH at room temp. was good (71%), though the
BTFP sulfone 8c and 6-methoxy-2-naphthaldehyde best result was obtained with the Schwesinger base P4-tBu
(Scheme 3, Table 1). The olefination was carried out, in all at room temp. (95%). From these studies, it could be con-
cases, under Barbier-type conditions (slow addition of the cluded that KOH was an appropriate base to carry out the
base to a mixture of the aldehyde and sulfone). Better yields Julia–Kocienski olefination between benzyl BTFP sulfone
were always observed for the olefination process under 8c and aldehydes, even though higher yields were obtained
these conditions. We also observed better yields when an with the phosphazene base P4-tBu in THF at room temp.
excess (2 equiv.) of sulfone was used. In this manner, the
The olefination of different aromatic and aliphatic alde-
corresponding olefin was produced in a 71% yield, based hydes with sulfones 8c and 8d was then performed accord-
on the ketone as the limiting reagent, when KOH was used ing to the optimized conditions (Table 1, entries 6–13).
as base in THF at room temp. (Table 1, compare entries 1 BTFP sulfone 8c olefinated aryl and alkyl aldehydes in gen-
and 2). Metallated bases such as KHMDS gave very low erally good yields under the above-mentioned reaction con-
Scheme 3. Synthesis of trisubstituted olefins.
Table 1. Olefination of aldehydes with BTFP sulfones 8c,d.[a]
[a] The reactions were carried out in THF overnight and under Barbier conditions. [b] Isolated yield after flash chromatography. [c] Deter-
mined by 1H NMR of the crude reaction mixture. [d] The reaction was carried out in the presence of 0.1 equiv. of TBAB. [e] The reaction
was carried out in the presence of 2.4 equiv. of HMPA.
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Table 2. Olefination of ketones with BTFP sulfones 8a,b.[a]
[a] The reactions were carried out in THF overnight and under Barbier conditions. [b] Isolated yield after flash chromatography. [c] The
reaction was carried out in the presence of 0.1 equiv. of TBAB. [d] CH3CN was used as solvent. [e] THF/DMF (3:1) was used as solvent.
1
[f] In brackets, isolated yield when Barbier conditions were not used. [g] (Z/E), 45:55, as determined by H NMR of the crude reaction
1
mixture. [h] (Z/E), 60:40, as determined by H NMR of the crude reaction mixture. [i] Reaction conversion.
ditions. The olefination process was successful when coup- fin 10de with similar (Z) selectivity but in a lower 35% yield
ling 8c with (E)-cinnamaldehyde affording (E)-4-methyl-1- (Table 1, compare entries 10 and 12). Finally, a highly selec-
phenylpenta-1,3-diene (10cb) in an 89% yield (Table 1, en- tive reaction took place between sulfone 8d and (E)-cinnam-
try 6). Regarding aliphatic aldehydes, isopropyl BTFP sul- aldehyde, affording (1E,3Z)-1,4-diphenylhexa-1,3-diene
fone 8c condensed with 3-phenylpropanal and decanal in (10db) in a 63% yield (Table 1, entry 13).
the presence of phosphazene base P4-tBu at room temp.
A different approach to trisubstituted olefins consisted
(Table 1, entries 7 and 8) to give alkenes 10cc and 10cd in of the olefination of ketones with primary alkyl BTFP sul-
a 52% and 67% yield, respectively. Phosphazene base was fones 8a or 8b (Scheme 3, Table 2). A preliminary base and
also the most effective for the olefination of aldehydes with solvent study was performed with sulfone 8a and 4,4Ј-
BTFP sulfone 8d (Table 1, entries 9–14). Aromatic alde- dichlorobenzophenone. A small screening showed the inef-
hydes such as 6-methoxy-2-naphthaldehyde and benzalde- ficiency of different inorganic bases such as KOH, Cs2CO3
hyde yielded trisubstituted olefins 10da and 10de, respec- and CsOH (Table 2, entries 1–5). The use of KOH in THF,
tively, in good yields and moderate stereoselectivities which was efficient for the olefination of aldehydes with sul-
(Table 1, entries 9 and 10). In both cases, the reaction was fone 8c (see above) only gave a 16% yield of trisubstituted
(Z)-selective, and the selectivity, as shown for the case of olefin 10af (Table 2, entry 1). In the case of Cs2CO3, which
benzaldehyde, could be improved by performing the reac- has been used with little success in the olefination of alde-
tion at low temperature (Table 1, entries 10 and 11). We hydes with activated BT-sulfonyl acetates,[26] the olefination
have previously demonstrated the positive effect of certain reaction failed. When CsOH was employed as a base in
additives such as HMPA on the stereoselectivity and yield different solvents such as THF, CH3CN, and mixtures of
of the olefination reaction of aromatic aldehydes with THF/DMF[29b] the olefination failed, even when performed
BTFP sulfones employing phosphazene base P4-tBu.[34] under heating conditions (Table 2, entries 3–5). In contrast,
However, this was not the case for the reaction between the use of phosphazene P4-tBu in THF gave the desired
benzaldehyde and sulfone 8d, which gave trisubstituted ole- olefin 10af in a 97% yield (Table 2, entry 6). As in the case
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of the olefination of aldehydes with sulfones 8c and d, it yields (Table 2, compare entry 13 to entry 14 and entry 16
became rapidly clear that a Barbier-type procedure and an to entry 17). Finally, dicyclopropyl ketone gave alkenes
excess of the sulfone carbanion were most convenient, since 10ak and 10bk in moderate yields (Table 2, entries 19 and
much better yields were obtained under these conditions 20).
(Table 2, entries 6 and 7). Disappointingly, under the tested
With regard to the synthesis of tetrasubstituted olefins,
reaction conditions, benzyl BTFP sulfone 8b failed to react BTFP sulfone 8c was first assayed under different reaction
with aromatic ketones to any significant extent (Table 2, en- conditions as the olefination reagent for 4,4Ј-dichlorobe-
try 8).[41] This negative result was not surprising, given that nzophenone (Scheme 4 and Table 3). It turned out that, un-
the stabilized sulfone carbanion derived from 8b was ex- der Barbier-type conditions, the phosphazene base P4-tBu
pected to be a poor nucleophile. Under the standard reac- in THF was again the base of choice for the synthesis of
tion conditions, pentyl BTFP sulfone 8a reacted with tetrasubstituted olefins. Under these conditions, sulfone 8c
benzophenone and 4-chlorobenzophenone in good yields to reacted with 4,4Ј-dichlorobenzophenone to provide alkene
give the corresponding trisubstituted olefins 10ag and 10ah, 10cf in a 30% yield (Table 3, entry 4). No improvement in
respectively (Table 2, entries 9–12). As expected, in the lat- yield was detected when the amount of nucleophile was in-
ter case, the observed stereoselectivity was very low creased to a three-fold excess (Table 3, entry 5). The nucleo-
(Table 2, entries 11 and 12). On the other hand, good results philic ability of the enolate derived from 8c was increased
were obtained for the olefination of aliphatic ketones with by heating the reaction mixture at reflux. In this manner,
sulfone 8a under the previously employed conditions (P4- olefin 10cf was produced in a 71% yield (Table 3, entry 6).
tBu, THF, 0° to room temp.) (Table 2, entries 14, 17, and
19). Thus 4-tert-butylcyclohexanone and pentyl sulfone 8a
gave alkene 10ai in 60% yield (Table 2, entry 14). However,
the coupling with the benzyl sulfone 8b afforded alkene 10bi
in only 25% yield (Table 2, entry 15). Concerning the coup-
ling with cyclohexa-1,4-dione monoethylene acetal, both
sulfones reacted to give alkenes 10aj and 10bj in 90% yield
(Table 2, entries 17 and 18). Again, the employment of a
two-fold excess of nucleophile was necessary to obtain good Scheme 4. Olefination of ketones with BTFP sulfones 7c,d.
Table 3. Olefination of ketones with BTFP sulfones 8c,d.[a]
[a] The reactions were carried out in THF overnight and under Barbier conditions. [b] Isolated yield after flash chromatography.
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D. A. Alonso, M. Fuensanta, C. Nájera
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MAT 95S spectrometer. Analytical TLC was visualized with UV
light at 254 nm or with KMnO4. Thin-layer chromatography was
carried out on TLC aluminium sheets with silica gel 60 F254
(Merck). For flash chromatography, silica gel 60 (0.040–0.063 mm)
was employed. Reactions under inert atmosphere (argon) were per-
formed in oven-dried glassware, sealed with a rubber septum, in
anhydrous CH3CN or THF.
Under these conditions, olefination of 4,4Ј-dichlorobenzo-
phenone with sulfone 8d failed to give a product in signifi-
cant yield (Table 3, entry 7). This was probably due to the
lower reactivity of the sterically hindered secondary α-sulfo-
nyl carbanion.[41] Concerning the olefination of aromatic
ketones with BTFP sulfone 8c, the electronic nature of the
substrate proved to be determinant, given that electron-rich
benzophenones such as 4,4Ј-dimethoxybenzophenone gave
a very poor yield. Thus, benzophenone gave 40% of alkene
10cg and 4-chlorobenzophenone gave 70% of 10ch (Table 3,
entries 8 and 9). However, 4,4Ј-dimethoxybenzophenone
provided alkene 10cl in only 10% yield (Table 3, entry 10).
Finally, the olefination reaction with BTFP sulfone 8c was
carried out with monoprotected 1,4-cyclohexane-1,4-dione,
giving alkene 10cj in a moderate 35% yield (Table 3, entry
11). This was probably due to volatilization problems with
the reaction product since the conversion of the reaction
was very high.
Compounds 8a,[34c] 8b,[34c] 9a,[34c] 9b,[34c] 10af,[42] 10ag,[43] 10ai,[10]
10ak,[44] 10bi,[45] 10bj,[46] 10bk,[47] 10ca,[48] 10cd,[49] 10cf,[50] 10cg,[50]
10cj,[51] 10cl,[50] and 10de[52] have been described previously. Com-
pounds 10cb and 10cc, which are commercially available, gave satis-
1
factory spectroscopic and physical data. H NMR assignment and
(E/Z) ratio determination for compounds 10da and 10db were per-
formed with the aid of NOESY experiments on the isomeric mix-
ture obtained after column chromatography.
General Procedure for the Synthesis of 3,5-Bis(trifluoromethyl)-
phenyl Sulfanes 9a–c: To a room temperature solution of 3,5-bis(tri-
fluoromethyl)benzenethiol (835 µL, 5 mmol) and NaH (95%,
150 mg, 6 mmol) in CH3CN (15 mL) under argon was added the
corresponding alkyl bromide (5.5 mmol), and the reaction was
stirred at this temperature for 1 d. After quenching with H2O
(20 mL), the mixture was extracted with EtOAc (2×20 mL). The
combined organic layers were dried (Na2SO4) and concentrated to
afford the corresponding BTFP sulfanes 9a–c, which were used in
the next step without further purification.
Conclusions
In conclusion, the BTFP sulfonyl group has been shown
to be a very stable and excellent activator for the synthesis
of tri- and, for the first time, tetrasubstituted olefins
through the Julia–Kocienski olefination reaction under very
simple reaction conditions. From the assayed bases, the
phosphazene base P4-tBu is the most appropriate base for
3,5-Bis(trifluoromethyl)phenyl Isopropyl Sulfane (9c): (1.23 g, 85%
crude yield); Yellow oil. IR: ν = 3090, 2967, 2928, 2844, 1626, 1370,
˜
1128, 1123 cm–1. 1H NMR (300 MHz, CDCl3): δ = 7.75 (s, 2 H,
3
ArH), 7.67 (s, 1 H, ArH), 3.54 (sept, JH,H = 6.7 Hz, 1 H, CH),
3
this type of coupling. Very good yields of trisubstituted ole- 1.36 (d, JH,H = 6.7 Hz, 6 H, 2 CH3) ppm. 13C NMR (75 MHz,
CDCl3): δ = 140.0 (ArC), 132.1 (q, JC–F = 34.1 Hz, 2 CCF3), 129.8
(ArCH), 123.1 (q, JC–F = 273.3 Hz, 2 CF3), 119.7 (ArCH), 37.9
(CH), 22.7 (2 CH3) ppm. MS: m/z (%) = 288 (55) [M]+, 269 (24),
247 (10), 246 (100), 145 (14), 226 (17), 225 (18).
fins have been obtained through the coupling of secondary
alkyl sulfones 8c and 8d with aromatic, aliphatic and α,β-
unsaturated aldehydes. With respect to the benzylic BTFP
sulfone 8d, the diastereoselectivity of the process was mod-
erate for aromatic aldehydes but excellent in the case of α,β-
unsaturated aldehydes, being in all cases Z-selective. Alter-
natively, primary alkyl sulfones can be coupled with phe-
nones and aliphatic ketones for the preparation of trisubsti-
tuted alkenes under the same reaction conditions. Isopropyl
sulfone 8c was also a very efficient olefinating reagent for
diaryl and dialkyl ketones at THF reflux, affording the cor-
responding tetrasubstituted olefins in moderate to good
yields. Additional applications of BTPF sulfones in ole-
fination and other reactions are currently under investiga-
tion.
General Procedure for the Synthesis of 3,5-Bis(trifluoromethyl)-
phenyl Sulfones 8a–c: To a room temp. stirred solution of the corre-
sponding sulfide 9a–c (1 mmol) and MnSO4 monohydrate (2 mg,
1 mol-%) in CH3CN (23 mL), was slowly added a previously pre-
pared, 0 °C, aqueous mixture comprised of 30% H2O2 (5 mmol,
515 µL) and a buffer solution of NaHCO3 (0.2 , 17 mL). After
stirring for 1 d, the reaction was quenched with a saturated aque-
ous solution of NaCl (30 mL), extracted with EtOAc (2×20 mL)
and dried with anhydrous Na2SO4. Filtration and evaporation of
the solvents afforded the corresponding crude sulfones 8a–c, which
were recrystallized from hexane.
Isopropyl 3,5-Bis(trifluoromethyl)phenyl Sulfone (8c): (304 mg,
95%); White solid; Rf (hexane/EtOAc, 2:1) = 0.77; m.p. 80–83 °C.
1
IR: ν = 3091, 2989, 2937, 1621, 1363, 1286, 1136 cm–1. H NMR
˜
Experimental Section
(300 MHz, CDCl3): δ = 8.35 (s, 2 H, ArH), 8.17 (s, 1 H, ArH),
3
3.28 (sept, 3JH,H = 6.8 Hz, 1 H, CH), 1.35 (d, JH,H = 6.9 Hz, 6 H,
General: Melting points were obtained with a Reichert Thermovar
apparatus and were not corrected. IR data were collected on a
FTIR apparatus (Nicolet Impact 400D), and peaks are reported in
cm–1. Only the most structurally important IR peaks have been
2 CH3). 13C NMR (75 MHz, CDCl3): δ = 140.1 (ArC), 133.0 (q,
JC–F = 34.8 Hz, 2 CCF3), 129.3, 127.3 (ArCH), 122.3 (q, JC–F
=
273.3 Hz, 2 CF3), 55.8 (CH), 15.4 (2 CH3) ppm. MS: m/z (%) =
320 (0.06) [M]+, 301 (14), 279 (10), 213 (15), 149 (21), 43 (100),
41 (24). HRMS: calcd. for C11H10F6O2S [M+] 320.0306, [M+ – F]
301.0322; found 301.0325.
listed. NMR spectra were recorded with
a Bruker AC-300
(300 MHz for H1 NMR and 75 MHz for 13C NMR) spectrometer
with CDCl3 as solvent and TMS as internal standard, unless other-
wise noted; chemical shifts are given in δ (ppm) and coupling con-
stants (J) in Hz. Low-resolution electron-impact (EI) mass spectra
were obtained at 70 eV with Shimadzu QP-5000 and Agilent 5973
spectrometers; fragment ions (m/z) are given, with relative inten-
sities (%) in parenthesis. HRMS were recorded with a Finnigan
Experimental Procedure for the Synthesis of 1-Phenyl Propyl 3,5-
Bis(trifluoromethyl)phenyl Sulfone (8d): Under an argon atmo-
sphere, to a 0 °C stirred solution of sulfone 8b (368 mg, 1 mmol)
in anhydrous THF (20 mL), was added dropwise the phosphazene
base P4-tBu (1  solution in n-hexane, 1.1 mL, 1 mmol). The mix-
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3,5-Bis(trifluoromethyl)phenyl Sulfones in the Julia-Kocienski Olefination
FULL PAPER
ture was stirred for 30 min at the same temperature before the ad-
dition of ethyl iodide (80 µL, 1 mmol). The reaction mixture was
stirred overnight at room temperature and quenched with a satu-
rated solution of NH4Cl (5 mL). The mixture was extracted with
EtOAc (2×10 mL), and the organic phase was dried (Na2SO4), fil-
tered and the solvent evaporated to afford crude sulfone 8d which
was purified by flash chromatography (hexane/EtOAc, 9:1) to yield
pure 8d, (320.6 mg, 81%). White solid; Rf (hexane/EtOAc, 2:1) =
m, 9 H, ArH), 1.79 (s, 6 H, 2 CH3) ppm. 13C NMR (75 MHz,
CDCl3): δ = 142.8, 141.6, 135.8, 131.7, 131.2, 129.8, 128.0, 127.9,
126.2 (C=C, ArCH), 22.5, 22.4 (CH3) ppm. MS: m/z (%) = 244
(33) [M+ + 2], 271 (9) [M+ + 1], 242 (100) [M]+, 227 (19), 207 (16),
192 (27), 191 (17), 189 (13), 178 (15), 165 (26), 129 (30), 115 (18), 91
(13). HRMS: calcd. for C16H15Cl [M+] 242.0862; found 242.0871.
(Z/E)-6-Methoxy-2-(2-phenyl-1-butenyl)naphthalene (10da): Colour-
less oil; R (pentane) = 0.44. IR: ν = 3062, 2975, 2925, 2867 cm–1.
˜
f
0.64; m.p. 69–71 °C. IR: ν = 3094, 3064, 2962, 2926, 2872, 1634,
˜
1H NMR (300 MHz, CDCl3): δ = 7.72 (d, JH,H = 8.6 Hz, 2 H,
3
1610, 1357, 1285, 1141 cm–1. 1H NMR (300 MHz, CDCl3): δ =
7.99 (s, 1 H, ArH), 7.83 (s, 2 H, ArH), 7.33–7.23 (m, 3 H, ArH),
7.06 (d, 3JH,H = 7.0 Hz, 2 H, ArH), 3.99 (dd, 3JH,H = 11.4 Hz, 3.9,
1 H, SCH), 2.64–2.51 (2 m, 2 H, 2 CH2), 2.29–2.13 (2 m, 2 H, 2
CH2), 0.94 (t, 3JH,H = 7.4 Hz, 3 H, CH3) ppm. 13C NMR (75 MHz,
CDCl3): δ = 140.0 (ArC), 132.3 (q, JC–F = 35.3 Hz, 2 CCF3), 131.1
ArH), 7.52–7.19 (2 m, 20 H, ArH), 7.19–6.92 (2 m, 20 H, ArH),
6.81 [s, 1 H, (E)-HC=C], 6.55 [s, 1 H, (Z)-HC=C], 3.93 [s, 3 H,
3
(E)-OCH3], 3.86 [s, 3 H, (Z)-OCH3], 2.81 [q, JH,H = 7.5 Hz, 2 H,
3
3
(E)-CH2], 2.55 [q, JH,H = 7.4 Hz, 2 H, (Z)-CH2], 1.12 [t, JH,H
=
7.5 Hz, 3 H, (E)-CH3], 1.09 [t, 3JH,H = 7.4 Hz, 3 H, (Z)-CH3] ppm.
13C NMR (75 MHz, CDCl3): δ = 157.6, 157.4, 144.5, 144.2, 142.7,
141.5, 133.6, 133.0, 132.9 (C=CH, ArC), 129.4, 129.3, 128.8, 128.7,
128.6, 128.4, 128.3, 127.7, 127.6, 127.1, 126.8, 126.6, 126.5, 125.8,
125.1, 118.9, 118.4, 105.6, 105.4 (C=CH, ArCH), 55.3, 55.2
(OCH3), 30.3, 29.7 (CH2), 12.9 (2 CH3) ppm. MS: m/z (%) = 289
(23) [M+ + 1], 288 (100) [M]+, 273 (26), 241 (12), 215 (11), 171
(11), 115 (11). HRMS: calcd. for C21H20O [M+] 288.1514; found
288.1495.
(ArC), 129.7, 129.4, 129.37, 128.8, 126.8 (ArCH), 122.2 (q, JC–F
=
272.2 Hz, 2 CF3), 73.6 (CH), 20.3 (CH2), 11.4 (CH3) ppm. MS:
m/z (%) = 396 (0.06) [M]+, 119 (64), 91 (100). HRMS: calcd. for
C17H14F6O2S [M+] 396.0619, [M+ – F] 377.0635; found 377.0653.
Typical Procedure for the Julia–Kocienski Olefination of 4-Chloro-
benzophenone with BTFP Sulfone 8c: Under a Barbier protocol, to
a room temp. stirred solution of sulfone 8c (96 mg, 0.3 mmol) and
4-chlorobenzophenone (32 mg, 0.15 mmol) in anhydrous THF
(6 mL) under argon, was added dropwise the phosphazene base P4-
tBu (1  solution in n-hexane, 393 µL, 0.36 mmol). After stirring
the reaction overnight at reflux, the solvent was evaporated, H2O
(5 mL) was added, and the mixture was extracted with pentane
(2×10 mL). The organic phase was dried (Na2SO4), filtered, and
the solvent evaporated to afford the corresponding crude olefin,
which was purified by flash chromatography to give pure alkene
10ah as a mixture of isomers (31 mg, 75%).
(1E,3Z)-1,4-Diphenyl-1,3-hexadiene (10db): Colourless oil; Rf (pen-
tane) = 0.25. IR: ν = 3076, 3058, 3022, 2962, 2914, 2854, 2892,
˜
1
1598, 1501 cm–1. H NMR (300 MHz, CDCl3): δ = 7.34–7.04 (m,
3
10 H, ArH), 6.72 (dd, JH,H = 15.6 Hz, 10.8, 1 H, HC=CHPh),
6.47 (d, 3JH,H = 15.8 Hz, 1 H, C=CHPh), 6.21 (d, 3JH,H = 10.9 Hz,
3
1 H, HC=CEtPh), 2.43 (q, JH,H = 7.3 Hz, 2 H, CH2), 0.97 (t,
3JH,H = 7.4 Hz, 3 H, CH3) ppm. 13C NMR (75 MHz, CDCl3): δ =
146.1, 140.8, 137.7 (HC=CEtPh, ArC), 131.3, 128.7, 128.4, 128.1,
127.0, 126.9, 126.7, 126.2, 125.8 (3 =CH, ArCH), 32.06 (CH2),
13.05 (CH3) ppm. MS: m/z (%) = 234 (34) [M]+, 206 (18), 205 (100),
204 (13), 202 (14), 128 (11), 115 (15), 91 (18). HRMS: calcd. for
C18H18 [M+] 234.1409; found 234.1419.
(Z/E)-1-(4-Chlorophenyl)-1-phenyl-1-hexene (10ah): Colourless oil;
R (hexane) = 0.56. IR: ν = 3017, 3058, 2959, 2924, 2849, 1599
˜
f
cm–1. H NMR (300 MHz, C6D6): δ = 7.31–7.17 (m, 14 H, ArH),
1
3
3
7.10 (d, JH,H = 8.7 Hz, 2 H, ArH), 6.97 (d, JH,H = 8.3 Hz, 2 H,
ArH), 6.09 (t, 3JH,H = 7.5 Hz, 1 H, C=CH), 6.01 (t, 3JH,H = 7.5 Hz,
1 H, C=CH), 2.20–2.07 (m, 4 H, 2 CH2); 1.41–1.24 (m, 8 H, 4
CH2), 0.91–0.87 (m, 6 H, 2 CH3) ppm. 13C NMR (75 MHz, C6D6):
δ = 142.4, 141.3, 140.3, 140.2, 139.8, 138.7, 132.6, 132.4 (ArC,
C=CH), 131.3, 130.88, 130.81, 129.8, 128.4, 128.3, 128.2, 128.1,
127.1, 127.99, 126.92 (ArCH, C=CH), 32.0, 29.49, 29.48, 22.3
(CH2), 13.9 (CH3) ppm. MS: m/z (%) = 272 (1) [M+ + 2], 271 (11)
[M+ + 1], 270 (54) [M]+, 235 (16), 229 (32), 228 (17), 227 (100),
214 (29), 193 (13), 192 (52), 191 (35), 189 (18), 179 (20), 178 (16),
165 (18), 151 (11), 149 (25), 125 (10), 115 (31), 91 (17). HRMS:
calcd. for C18H19Cl [M+] 270.1175; found 270.1195.
Acknowledgments
This work has been supported by the Dirección General de In-
vestigación of the Ministerio de Educación y Ciencia (CTQ2004-
00808/BQU), by the Generalitat Valenciana (CTIOIB/2002/320,
GRUPOS03/134, GRUPOS05/11 and GV05/157) and the Univer-
sity of Alicante. M. F. thanks the University of Alicante for a pre-
doctoral fellowship.
[1] a) T. Takeda, Modern Carbonyl Olefination, Wiley-VCH,
Weinheim, 2004; b) V. N. Korotchenko, V. G. Nenajdenko, E. S.
Balenkova, A. V. Shastin, Russ. Chem. Rev. 2004, 73, 957–989.
[2] a) G. Wittig, G. Geissler, Justus Liebigs Ann. Chem. 1953, 580,
44–68; b) B. E. Maryanoff, A. B. Reitz, Chem. Rev. 1989, 89,
863–927.
[3] a) L. Horner, H. Hoffmann, H. C. Wipel, G. Klahre, Chem.
Ber. 1959, 92, 2499–2505; b) J. Clayden, S. Warren, Angew.
Chem. Int. Ed. Engl. 1996, 35, 241–270.
[4] a) W. S. Wadsworth Jr, W. D. Emmons, J. Am. Chem. Soc. 1961,
83, 1733–1738; b) J. Boutagy, R. Thomas, Chem. Rev. 1974, 74,
87–89.
[5] a) D. J. Peterson, J. Org. Chem. 1968, 33, 780–784; b) L. F.
van Staden, D. Gravestock, D. J. Ager, Chem. Soc. Rev. 2002,
31, 195–200.
8-Pentylidene-1,4-dioxaspiro[4.5]decane (10aj): Yellow oil; Rf (hex-
ane/EtOAc, 2:1) = 0.69. IR: ν = 2956, 2920, 2884, 1453, 1375, 1375,
˜
1285, 1135, 1086, 1026 cm–1. 1H NMR (300 MHz, CDCl3): δ =
3
5.14 (t, JH,H = 7.0 Hz, 1 H, C=CH), 3.96 (s, 4 H, 2 OCH2), 2.27–
2.19 (4 m, 14 H, 7 CH2), 2.00–1.98 (4 m, 14 H, 7 CH2), 1.68–1.63
3
(4 m, 14 H, 7 CH2), 1.32–1.29 (4 m, 14 H, 7 CH2), 0.88 (t, JH,H
= 6.9 Hz, 3 H, CH3) ppm. 13C NMR (75 MHz, CDCl3): δ = 136.4
(C=CH), 123.1 (C=CH), 109.1 (OCO), 64.2 (2 OCH2), 36.3, 35.5,
33.5, 32.2, 27.0, 24.9, 22.2 (7 CH2), 13.9 (2 CH3) ppm. MS: m/z
(%) = 210 (41) [M]+, 181 (10), 167 (19), 153 (22), 109 (13), 99 (15),
87 (17), 86 (100). HRMS: calcd. for C13H22O2 [M+] 210.1620;
found 210.1587.
[6] C. R. Johnson, J. R. Shanklin, R. A. Kirchhoff, J. Am. Chem.
Soc. 1973, 95, 6462–6463.
[7] M. Julia, J.-M. Paris, Tetrahedron Lett. 1973, 14, 4833–4836.
[8] For a review on desulfonylation reactions, see: C. Nájera, M.
Yus, Tetrahedron 1999, 55, 10547–10658.
1-(4-Chlorophenyl)-1-methyl-2-phenyl-1-propene (10ch): Colourless
oil; R (hexane) = 0.53. IR: ν = 3083, 3064, 3026, 2983, 2918, 2848,
˜
f
1649, 1600, 1568, 1482, 1450, 1401, 1369 cm–1. 1H NMR
(300 MHz, CDCl3): δ = 7.30–7.16 (2 m, 9 H, ArH), 7.11–7.03 (2
Eur. J. Org. Chem. 2006, 4747–4754
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
4753

D. A. Alonso, M. Fuensanta, C. Nájera
FULL PAPER
[9]
[10]
Eur. J. 2006, 12, 1185–1204; f) H. Motoyoshi, M. Horigome,
H. Watanabe, T. Kitahara, Tetrahedron 2006, 62, 1378–1389.
[31] For the latest applications of PT-sulfones in total synthesis, see:
a) N. Cramer, S. Laschat, A. Baro, H. Schwalbe, C. Richter,
Angew. Chem. Int. Ed. 2005, 44, 820–822; b) C. Jasper, R. Wit-
tenberg, M. Quitschalle, J. Jakupovic, A. Kirschning, Org. Lett.
2005, 7, 479–482; c) X. Gao, D. G. Hall, J. Am. Chem. Soc.
2005, 127, 1628–1629; d) D. Bondar, J. Liu, T. Müller, L. A.
Paquette, Org. Lett. 2005, 7, 1813–1816; e) M. J. Schnermann,
D. L. Boger, J. Am. Chem. Soc. 2005, 127, 15704–15705; f) S.
Hara, K. Makino, Y. Hamada, Tetrahedron Lett. 2006, 47,
1081–1085.
E. N. Prilezhaeva, Russ. Chem. Rev. 2000, 69, 367–408.
I. E. Markó, F. Murphy, L. Kumps, A. Ates, R. Touillaux, D.
Craig, S. Carballares, S. Dolan, Tetrahedron 2001, 57, 2609–
2619.
a) J. B. Baudin, G. Hareau, S. A. Julia, O. Ruel, Tetrahedron
Lett. 1991, 32, 1175–1178; b) J. B. Baudin, G. Hareau, S. A.
Julia, R. Lorne, O. Ruel, Bull. Soc. Chim. Fr. 1993, 130, 336–
357; c) J. B. Baudin, G. Hareau, S. A. Julia, R. Lorne, O. Ruel,
Bull. Soc. Chim. Fr. 1993, 130, 856–878.
For a recent review, see: P. R. Blakemore, J. Chem. Soc., Perkin
Trans. 1 2002, 2563–2585.
R. Bellingham, K. Jarowicki, P. Kocienski, V. Martin, Synthesis
1996, 285–296.
[11]
[12]
[13]
[32] a) D. A. Alonso, C. Nájera, M. Varea, Tetrahedron Lett. 2001,
42, 8845–8848; b) D. A. Alonso, C. Nájera, M. Varea, Helv.
Chim. Acta 2002, 85, 4287–4305.
[14]
[15]
P. Kocienski, Synthesis 1996, 652–666.
E. Lee, H. Y. Song, J. W. Kang, D.-S. Kim, C.-K. Jung, J. M.
Joo, J. Am. Chem. Soc. 2002, 124, 384–385.
[33] D. A. Alonso, C. Nájera, M. Varea, Synthesis 2003, 277–287.
[34] a) D. A. Alonso, C. Nájera, M. Varea, Tetrahedron Lett. 2004,
45, 573–577; b) D. A. Alonso, M. Fuensanta, C. Nájera, M.
Varea, Phosphorus Sulfur Silicon Relat. Elem. 2005, 180, 1119–
1131; c) D. A. Alonso, M. Fuensanta, C. Nájera, M. Varea, J.
Org. Chem. 2005, 70, 6404–6416.
[16]
a) S. H. Kang, S. Y. Kang, C. M. Kim, H.-W. Choi, H.-S. Jun,
B. M. Lee, C. M. Park, J. W. Jeong, Angew. Chem. Int. Ed.
2003, 42, 4779–4782; b) S. H. Kang, S. Y. Kang, H.-W. Choi,
C. M. Kim, H.-S. Jun, J.-H. Youn, Synthesis 2004, 1102–1114.
a) J. A. Lafontaine, D. P. Provencal, C. Gardelli, J. W. Leahy,
Tetrahedron Lett. 1999, 40, 4145–4148; b) J. A. Lafontaine,
D. P. Provencal, C. Gardelli, J. W. Leahy, J. Org. Chem. 2003,
68, 4215–4234; c) Y. Jiang, J. Hong, S. D. Burke, Org. Lett.
2004, 6, 1445–1448.
a) G. Pattenden, A. T. Plowright, J. A. Tornos, T. Ye, Tetrahe-
dron Lett. 1998, 39, 6099–6102; b) G. Pattenden, M. A.
González, P. B. Little, D. S. Millan, A. T. Plowright, J. A.
Tornos, T. Ye, Org. Biomol. Chem. 2003, 1, 4173–4208; c) G.
Pattenden, M. A. González, Angew. Chem. Int. Ed. 2003, 42,
1255–1258.
[17]
[35] W. E. Truce, E. M. Kreider, W. W. Brand, Org. React. 1970, 18,
99–215.
[36] Very recently, the application of 4-nitrophenyl sulfones in the
modified Julia olefination of aldehydes has been reported: D.
Mirk, J.-M. Grassot, J. Zhu, Synlett 2006, 1255–1259.
[37] To the best of our knowledge, only one example has been re-
cently reported on the synthesis of a trisubstituted olefin
through a modified Julia olefination employing a secondary
[18]
[19]
alkyl PT sulfone. See ref.[30a]
.
[38] D. A. Alonso, C. Nájera, in Electronic Encyclopedia of Rea-
gents for Organic Synthesis (RN00619) (Ed.: L. A. Paquette),
Wiley, 2005.
[39] This is a simple, green and general method for the oxidation
of sulfides to sulfones: D. A. Alonso, C. Nájera, M. Varea, Tet-
rahedron Lett. 2002, 43, 3459–3461.
a) D. A. Evans, V. J. Cee, T. E. Smith, D. M. Fitch, P. S. Cho,
Angew. Chem. Int. Ed. 2000, 39, 2533–2536; b) D. R. Li, Y. Q.
Tu, G.-Q. Lin, W.-S. Zhou, Tetrahedron Lett. 2003, 44, 8729–
8732; c) D. R. Li, C. Y. Sun, C. Su, G.-Q. Lin, W.-S. Zhou,
Org. Lett. 2004, 6, 4261–4264.
[40] a) R. Schwesinger, Encyclopedia of Reagents for Organic Syn-
thesis (Ed.: L. A. Paquette), Wiley, Chichester, 1995; vol. 6, p.
4110; b) R. Schwesinger, H. Schlemper, C. Hasenfratz, J. Willa-
redt, T. Dambacher, T. Breuer, C. Ottaway, M. Fletschinger, J.
Boele, H. Fritz, D. Putzas, H. W. Rotter, F. G. Bordwell, A. V.
Satish, G.-Z. Ji, E. M. Peters, K. Peters, H. G. von Schnering,
L. Walz, Liebigs Ann. 1996, 1055–1081; c) D. Seebach, A. K.
Beck, A. Studer, Modern Synthetic Methods, Sauerländer AG,
Aarau, Switzerland, 1995, vol. 7, 1–178.
[41] In this experiment, Ͼ90% of the starting BTFP sulfone 8d was
recovered, indicating that the failure of the reaction was not
due to decomposition of the sulfone carbanion.
[42] I. Kerner, W. Klein, F. Korte, Tetrahedron 1972, 28, 1575–1578.
[43] C. Ha, J. H. Horner, M. Newcomb, T. R. Varick, B. R. Arnold,
J. Lusztyk, J. Org. Chem. 1993, 58, 1194–1198.
[44] G. Koebrich, D. Merkel, Angew. Chem. Int. Ed. Engl. 1970, 9,
243–244.
[20] a) N. Furuichi, H. Hara, T. Osaki, M. Nakano, H. Mori, S.
Katsumura, J. Org. Chem. 2004, 69, 7949–7959; b) B. Vaz, R.
Alvarez, R. Brückner, A. R. de Lera, Org. Lett. 2005, 7, 545–
548.
[21] D. C. Harrowven, D. D. Pascoe, D. Demurtas, H. O. Bourne,
Angew. Chem. Int. Ed. 2005, 44, 1221–1222.
[22] a) A. B. Charette, C. Berthelette, D. St-Martin, Tetrahedron
Lett. 2001, 42, 5149–5153; Corrigendum: A. B. Charette, C.
Berthelette, D. St-Martin, Tetrahedron Lett. 2001, 42, 6619; b)
A. Sorg, R. Brückner, Synlett 2005, 289–293; c) B. Vaz, R.
Alvarez, J. A. Souto, A. R. de Lera, Synlett 2005, 294–298.
[23] D. Chevrie, T. Lequeux, J. P. Demoute, S. Pazenok, Tetrahedron
Lett. 2003, 44, 8127–8130.
[24] S. Surprenant, W. Y. Chan, C. Berthelette, Org. Lett. 2003, 5,
4851–4854.
[25] D. Gueyrard, R. Haddoub, A. Salem, N. S. Bacar, P. G. Goekj-
ian, Synlett 2005, 520–522.
[26] P. R. Blakemore, D. K. H. Ho, W. M. Nap, Org. Biomol. Chem.
2005, 3, 1365–1368.
[27] P. Mauleón, J. C. Carretero, Org. Lett. 2004, 6, 3195–3198.
[28] a) P. R. Blakemore, W. J. Cole, P. J. Kocienski, A. Morley, Syn-
lett 1998, 26–28; b) P. Jankowski, K. Plesniak, J. Wicha, Org.
Lett. 2003, 5, 2789–2792.
[45] R. P. Polniaszek, A. L. Foster, J. Org. Chem. 1991, 56, 3137–
3146.
[46] T. Satoh, K. Takana, H. Ota, H. Someya, K. Matsuda, M.
Koyma, Tetrahedron 1998, 54, 5557–5574.
[47] V. Usieli, S. Sarel, J. Org. Chem. 1973, 38, 1703–1708.
[48] M. Yasuda, R. Kojima, R. Ohira, T. Shiragami, K. Shima,
Bull. Chem. Soc. Jpn. 1998, 71, 1655–1660.
[29] a) P. J. Kocienski, A. Bell, P. R. Blakemore, Synlett 2000, 365–
366; b) C. Aïssa, J. Org. Chem. 2006, 71, 360–363.
[30] For the latest applications of PT-sulfones in total synthesis, see:
a) C. Marti, E. M. Carreira, J. Am. Chem. Soc. 2005, 127,
11505–11515; b) S. Dandapani, M. Jeske, D. P. Curran, J. Org.
Chem. 2005, 70, 9447–9462; c) M. F. Jacobsen, J. E. Moses,
R. M. Adlington, J. E. Baldwin, Tetrahedron 2006, 62, 1675–
1689; d) G. Toschi, M. S. Baird, Tetrahedron 2006, 62, 3221–
3227; e) D.-R. Li, D.-H. Zhang, C.-Y. Sun, J.-W. Zhang, L.
Yang, J. Chen, B. Liu, C. Su, W.-S. Zhou, G.-Q. Lin, Chem.
[49] H. Tanaka, K. Hashimoto, K. Suzuki, Y. Kitaichi, M. Sato, T.
Ikeno, T. Yamada, Bull. Chem. Soc. Jpn. 2004, 77, 1905–1914.
[50] J. H. Incremona, J. C. Martin, J. Am. Chem. Soc. 1970, 92,
627–634.
[51] G. Revial, I. Jabin, M. Pfau, Tetrahedron: Asymmetry 2000, 11,
4975–4983.
[52] G. Guanti, L. Banfi, R. Riva, Tetrahedron 1995, 51, 10343–
10360.
Received: June 2, 2006
Published Online: August 15, 2006
4754
www.eurjoc.org
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2006, 4747–4754