Preparation of meso-1,3-diphenylallyllithium·(-)-sparteine - Its crystal structure and reactions

Article abstract of DOI:10.1016/S0957-4166(02)00660-2

The X-ray crystal structure of 1,3-diphenylallyllithium, complexed with enantiomerically pure (-)-sparteine, was determined. The crystallized complex is stereohomogeneous. Its subsequent electrophilic substitution reactions proceed with low enantioselecti

Full text of DOI:10.1016/S0957-4166(02)00660-2

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 13 (2002) 2587–2592
Preparation of meso-1,3-diphenylallyllithium (−)-sparteine—its
·
crystal structure and reactions
Felix Marr, Roland Fro¨hlich† and Dieter Hoppe*
Organisch-Chemisches Institut der Universita¨t, Westfa¨lische Wilhelms-Universita¨t, Mu¨nster, Corrensstraße 40,
D-48149 Mu¨nster, Germany
Received 9 October 2002; accepted 15 October 2002
Abstract—The X-ray crystal structure of 1,3-diphenylallyllithium, complexed with enantiomerically pure (−)-sparteine, was
determined. The crystallized complex is stereohomogeneous. Its subsequent electrophilic substitution reactions proceed with low
enantioselectivity. © 2002 Elsevier Science Ltd. All rights reserved.
1. Introduction
testing Pd-catalyzed asymmetric CꢀC bond forma-
tions;8 the intermediate Pd–allyl complexes 5 contain a
symmetrical allyl cation (Scheme 1). Structure determi-
nation for complexes 5 revealed unsymmetrical h3-
bonding of palladium as one origin of stereospecific
addition of nucleophiles to yield enantioenriched prod-
ucts 6. The analogous allyllithium complex 7 is an
umpoled version (Scheme 1). To the best of our knowl-
edge, up to now, no crystal structure of a chirally
modified allyllithium compound with an acyclic sym-
metrical carbon skeleton has been reported.9
Research into enantioselective synthesis is a prospering
field of activity and has become the subject increasing
attention in recent times. Within this research area,
external chiral induction by cations bearing chiral lig-
ands is a widely used methodology.1 Different chiral
ligands are used for chiral modification of organometal-
lic reagents, and the commercially available diamine,
(−)-sparteine 12 has demonstrated its value particularly
in enantioselective synthesis with organolithium
compounds.3
Encouraged by the results obtained with species (1S)-35
we investigated the chiral modification of complex 7
with diamine 1.
Structural information about (−)-sparteine-modified
allyllithium species is still very scarce. Two solid-state
characterizations of (−)-sparteine-modified allyllithium
compounds 24 and 35 from our laboratory and the
structure of the cinnamyllithium derivative 46 reported
by Beak et al. (Fig. 1) provide an unambiguous link
between stereostructure and the stereochemical course
of electrophilic substitutions.3b
We thought of modifying a symmetrical allyllithium
compound with a non-racemic chiral ligand in order to
achieve a differentiation between originally enan-
tiotopic positions in the anion. This concept was very
successfully applied to the chiral modification of meso-
allylpalladium complexes.7 1,3-Diphenylprop-2-enyl
acetate is one of the most frequently used substrates for
* Corresponding author. Tel.: +49-251-8333211; fax: +49-251-
8336531; e-mail: dhoppe@uni-muenster.de
† X-Ray structure analysis.
Figure 1. (−)-Sparteine allyllithium complexes.
0957-4166/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(02)00660-2

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F. Marr et al. / Tetrahedron: Asymmetry 13 (2002) 2587–2592
the allylic carbon atoms in a h3-fashion as was seen for
indenyllithium (1S)-3. The angles of the carbon atoms
chain C76ꢀC80 in (R)-7a of 127.5 0.5° are very similar,
indicating a uniform hybridization. The allylic carbon
atoms C77ꢀC79 are in a planar vicinity (angular sums
of 360.1, 360.0, and 360.0 and 359.9–360.1° for the
other three molecules in the unit cell) pointing out ideal
sp2-hybridization as a consequence of charge delocal-
ization in the allylic unit. The LiꢀN bond lengths of
,
2.008 and 2.018 A are very similar. The different bond
lengths of the lithium cation to the allylic unit are
,
important: The C79ꢀLi bond (2.458 A) is substantially
,
longer than the C78ꢀLi bond (2.225 A) and the C77ꢀLi
,
bond (2.213 A). [For indenyllithium (1S)-3 bond
Scheme 1. Reactions of complexes of meso-ions of 1,3-
diphenylpropene. PMDTA=N,N,N%,N%%,N%%-pentamethyldi-
ethylenetriamine.
,
,
lengths of 2.432 A (C1ꢀLi) and 2.334 A (C3ꢀLi) were
5
,
found.] In addition, the C77ꢀC78 bond (1.392 A) is
marginally longer than the C78ꢀC79 bond (1.380 A),
,
indicating that the negative charge of the allylic anion
might be slightly displaced towards C77. The enan-
tiomeric ratio of the substitution products is determined
by the facial and regioselectivity of the attack by the
electrophile at the diastereotopic carbon moieties C77
and C79. The mode of selection is demonstrated for the
deuteration in Scheme 2 (the allyllithium is drawn
orthogonally to the paper plane): Attack in (R)-7a at
C77 (the right side), suprafacially to the lithium cation,
leads to (S)-8 (path a); an antarafacial attack can lead
to the same product (S)-8 if it occurs at the other end
of the allyllithium (at C79; path a%). After epimerization
of the complex (e.g. by rotation of the meso-allyl anion
by 180 degrees around its horizontal axis) towards
(S)-7a, electrophilic attack along these trajectories (now
named b at C77 and b% at C79, respectively) leads to the
enantiomeric product (R)-8.
2. Results and discussion
1,3-Diphenylpropene is deprotonated smoothly with n-
butyllithium in the presence of an amine ligand in
various solvents at −78°C, the allyllithium 7a is formed
in the presence of (−)-sparteine. Crystals of 7a suitable
for X-ray structure analysis were obtained by deproto-
nation in concentrated solution in THF, addition of
some diethyl ether at −20°C and slowly warming the
reaction mixture to room temperature. Allyllithium 7a
crystallizes in space group P1. The unit cell contains
four almost identical molecules, one of which is
depicted in Fig. 2.10
The lithium cation in homochiral crystals of allyl-
lithium 7a possess (R) configuration,11 it is bound to
Scheme 2. Stereochemical aspects of substitution at (−)-
sparteine-complexed meso-allyllithium.
Figure 2. X-Ray crystal structure of complex (R)-7a.

F. Marr et al. / Tetrahedron: Asymmetry 13 (2002) 2587–2592
2589
Since electrophilic substitution on the asymmetric h3-
coordinated allylic unit in crystalline indenyllithium
(1S)-35 leads to very high ee’s of the products (the same
is true for some complexes 58), we expected a regiose-
lective electrophilic attack on readily crystallizing com-
plex (R)-7a, providing enantioenriched products 8.
Such crystallization is observed for allylic species (S)-2
and (1S)-3, too. In the latter two cases a dynamic
kinetic resolution process occurred in the course of the
crystallization12 leading to virtually homochiral allyl-
lithium reagents; we expected the same behavior for
(R)-7a.
lute configuration (Table 1, entry 3). It cannot be
excluded, that (S)-7a is the predominant—or more
reactive—species in solution formed from re-dissolved
(R)-7a. Semi-empirical calculations of (R)-7a and (S)-
7a show only a very small difference in their relative
energies (approx. 1 kJ/mol),16 and thus, epimerization
seems likely. Replacing the solvent after crystallization
with pentane, which should dissolve the solid complex
(R)-7a less readily, or reacting the dried crystals with
acetone in only a small amount of solvent failed to
enhance the enantioselectivity (Table 1, entries 6-7).
The transmetallation of lithium for titanium is often the
method of choice for stereo- and regioselective addition
to carbonyl compounds.17 For (R)-7a, addition of
Ti(Oi-Pr)4 or Cl(Oi-Pr)3 had no impact on stereoselec-
tivity (Table 1, entries 4-5).
Racemic allyllithium 7b (Ln=N,N,N%,N%%,N%%-penta-
methyldiethylenetriamine; PMDTA) and the allyl-
lithium complex (R)-7a were reacted with different
electrophiles, yielding substitution products 8 in good
yields (Table 1). Unfortunately the determined ee’s of
the isolated acetone adduct (−)-8a, and allylsilane 8h
are quite low (Table 1, entries 2, and 12-13). The
specific rotation of other enantioenriched products is
also negligible (only two from many examples are
given: Table 1, entries 9 and 11).
The inversion of the configuration of silane 8h by
changing the silylation reagent from chlorotrimethylsi-
lane to trimethylsilyl triflate emphasizes the sensibility
of the stereochemical course of the electrophilic substi-
tution regarding changes of the reaction conditions
(Table 1, entries 12-13). Changes in enantiofacial differ-
entiation in electrophilic substitutions have also been
The crystallization of 7a is almost quantitative, as was
checked by crystallization at rt (removal of the mother
liquor with two additional washings with pentane) and
drying the crystals in vacuo; 95% of the sparteine
complex by weight was isolated (Table 1, entry 7).15
Presumably the employed electrophiles do not differen-
tiate the diastereotopic positions of complex (R)-7a in
an effective manner or show a lack of facial selectivity.
In addition, a base-mediated racemization is possible
for the highly acidic products 8b and 8c. Interestingly,
addition of 7a from homogenous solution in toluene
onto acetone yields adduct (+)-8a with opposite abso-
observed
for
an
cinnamyllithium18
and
a
benzyllithium.19
The following reasons may account for the lack of
stereoselectivity in the electrophilic attack: Rapid inter-
conversion between the epimers (R)- and (S)-7a in
solution, minor diastereofacial selectivity, and/or inade-
quate enantiotopos differentiation between the position
C77 and C79. Obviously, the loose electrostatic connec-
tion between the chiral cation and the well-stabilized
carbanion is insufficient to support stereoselective
reactions.
Table 1. Electrophilic substitution in diethyl ether
Entry
Complex
Electrophile
El
Product
Yield (%)
[h]2D0 (CHCl3)
e.r.
1
2
7b
7a
7a
7a
7a
7a
7a
7b
7a
7b
7a
7a
7a
Acetone
Acetone
Acetone
Acetone
Acetone
Acetone
Acetone
ClCOt-Bu
ClCOt-Bu
p-TsSPh
p-TsSPh
ClSiMe3
TfOSiMe3
COHMe2
COHMe2
COHMe2
COHMe2
COHMe2
COHMe2
COHMe2
COt-Bu
COt-Bu
SPh
rac-8a
(−)-8a
(+)-8a
(−)-8a
(−)-8a
(−)-8a
(−)-8a
rac-8b
(+)-8b
rac-8c
(+)-8c
(R)-8dh
(S)-8d
75
73
42
74
40
64f
45f
86
45
86
62
63
84
–
–
−11.5
n.d.b
−9.9
−10.4
−8.9
−6.0
–
+0.3
–
+0.5
−1.9
+7.3
54.5:45.5 (9% ee)
60.5:39.5 (21% ee)
54:46 (8% ee)
54:46 (8% ee)
53.5:46.5 (7% ee)
52.5:47.5 (5% ee)
–
3a
4c
5d
6e
7g
8
9
n.d.b
10
11
12
13
–
SPh
SiMe3
SiMe3
n.d.b
52.5:47.5 (5% ee)14
61:39 (22% ee)14
a Performed in homogenous solution in toluene.
b n.d.=not determined.
c Addition of 4.3 equiv. Ti(i-PrO)4 1 h prior to acetone.
d Addition of 1.8 equiv. ClTi(i-PrO)3 1 h prior to acetone.
e The ether was displaced after the crystallization by pentane at rt, acetone was added at −78°C.
f The mother liquor of the crystallization—free from crystalline 7a—led to 10% of (−)-8a with e.r. of 52.5:47.5 (5% ee).
g The ether was removed after the crystallization, the residue (washed with pentane) was dried in vacuo (0°C) and acetone/pentane (1: 1) was
added at −78°C.
h Isolated as a mixture with 15% of the starting material.

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F. Marr et al. / Tetrahedron: Asymmetry 13 (2002) 2587–2592
3. Conclusion
6.42 (d, 1H, 1CH); 7.10–7.33 (m, 10H, ArCH). J1,2=
3
15.7 Hz, J2,3=6.2 Hz. 13C NMR (75 MHz, CDCl3):
l=39.29 (3CH2); 126.13, 127.04, 128.46, 128.63,
129.16, 131.09 (CH); 137.49, 140.12 (ArC). IR (film):
w˜=3090 w, 3060 m, 3030 s, 2900 w, 1600 m, 1500 s,
1430 m, 970 s, 750 s, 700 s cm−1. GC–MS (EI [70 eV]):
m/z (%)=194 (65) [M+]; 193 (39); 179 (32) [{M−CH3}+
]; 178 (24); 116 (54); 115 (100); 103 (27) [{M−PhCH2}+];
In summary, we have determined the first X-ray struc-
ture of a meso-allyllithium compound in a complex
with
a non-racemic chiral diamine. Lithium/(−)-
sparteine is bonded unsymmetrically in h3-fashion in
crystalline (R)-7a. However, at this time the products 8,
isolated from electrophilic substitutions on (R)-7a show
only low enantiomeric purities.
+
+
91 (55) [tropyllium: C7H7 ]; 65 (34) [C5H5 ]; 51 (23)
[C4H4 ]; 39 (15) [from Ph+].
+
4. Experimental
4.1. General
4.2.2. Preparation of the (−)-sparteine complex, 7a. A
solution of (−)-sparteine (420 mg, 1.8 mmol, 1.2 equiv.)
in Et2O (11 mL) in a flask sealed with a rubber septum
was cooled to −78°C. n-BuLi (1.10 mL, 1.6 molar
solution in hexane, 1.76 mmol, 1.17 equiv.) was added
dropwise with stirring. After 15 min a solution of
1,3-diphenylpropene (290 mg, 1.50 mmol) in ether (3
mL) was added dropwise and stirring was continued for
30 min at −78°C. The flask was removed from the
cooling bath and the reaction mixture was slowly
stirred for 30 min at rt. Then the flask was placed back
into the dry ice/acetone bath and after additional 30
min a solution of the electrophile (1–5 equiv.) was
added and stirring was continued for 2–20 h. A solution
of HOAc (2.0 mL, 1.0N in ether, 2.0 mmol, 1.3 equiv.)
was added at −78°C, then the reaction mixture was
warmed to rt. The diamine was extracted with aqueous
HCl (20 mL, 2.0N) and the aqueous layer was extracted
with ether (3×20 mL). The combined organic layers
were washed with water (20 mL), dried over MgSO4,
filtered and the ether was removed in vacuo. The
resulting residue was subjected to flash column chro-
matography (Merck silica gel 60, 0.040–0.063 mm; gra-
dient Et2O/light petroleum ether bp 36–46°C) yielding
the product 8, characterized by NMR, IR, and elemen-
tal analysis.
All solvents were dried and purified prior to use: Tolu-
ene and Et2O were distilled from sodium benzophenone
ketyl, THF was distilled from potassium benzophenone
ketyl.
N,N,N%,N%%,N%%-Pentamethyldiethylenetriamine
(PMDTA) was distilled from powdered CaH2 and
stored under Ar in the dark. Acid chlorides were dis-
tilled prior to use, chlorotrimethylsilane was distilled
from powdered calcium hydride, and acetone was dried
by heating over phosphorus pentoxide and subsequent
distillation. n-Butyllithium (ca. 1.6 molar in hexanes)
was purchased from Acros; the content of n-BuLi was
determined by titration.20 All other commercially avail-
able reagents were used as received. All reactions were
performed under an atmosphere of Ar in flame-dried
glassware. Flash column chromatography (FCC) was
performed on Merck silica gel 60, 0.040–0.063 mm, and
monitored by thin-layer chromatography (TLC) on
Merck silica gel 60 F254; PE=light petroleum ether, bp
36–46°C. NMR: Bruker ARX 300, AM 360 (NOE
experiments), and AMX 400 (routine 2D spectra); spec-
tra from solutions in CDCl3 (lC=77.0 ppm) are cali-
brated to SiMe4 (lH=0.00 ppm). IR: Nicolet 5 DXC.
MS: Finnigan MAT 8200 (EI); Finnigan MAT 8230
(GC–MS); Varian Saturn II (GC–MS). Optical rota-
tions: Perkin–Elmer 341 polarimeter. Melting points:
Gallenkamp MFB 595 (uncorrected values). Elemental
analysis: Elementar Analysensysteme Vario EL III.
GC: Hewlett–Packard 5890, 25 m×0.2 mm HP 1, 107
kPa pre-column pressure N2, 1 min at 50°C/10°C×
min−1/15 min at 290°C; Agilent 6890, 30 m×0.32 mm
HP 5, 1.5 mL×min−1 H2, start at 50°C/10°C×min−1/30
min at 300°C; Hewlett–Packard 6890, 25 m×0.2 mm
HP 1701, 100 kPa pre-column pressure N2, 1 min at
50°C/10°C×min−1/20 min at 270°C. HPLC: A) Knauer
WellChrom Maxi-Star K-1000 pump with mixing unit
A0285 and spectral photometer A0293 at 220 nm; B)
Waters 600E Multisolvent Delivery System and 996
photodiode array detector.
4.2.3. (E)-1-Methyl-3,5-diphenyl-4-penten-2-ol, 8a. Com-
pound 8a was obtained from 1.5 mmol DPP by the
given procedure employing PMDTA as ligand and 5.0
mmol (0.37 mL, 3.4 equiv.) acetone as electrophile (2 h
at −78°C). FCC (66 ccm) with E/PE 1:1 lead to rac-8a
(282 mg, 1.12 mmol, 75%) as colorless resin-like mate-
rial. The enantioenriched samples were synthesized in
the same manner, some of them employing
a
transmetallation to titanium; conditions, yields, and
enantioenrichments are given in Table 1. The ees of
enantioenriched samples were determined on a Bayer
ZWE-805 HPLC column (4×250 mm; 0.5 mL/min
1:40:460 H2O/THF/cyclohexane; tr=10/11 min). [h]2D0=
−11.5; [h]25078=−12.2; [h]25406=−14.5; [h]24306=−31.3;
[h]23065=−70.9 (c 1.0, CHCl3, at e.r.=55.5: 44.5 (9% ee)).
Rf=0.14 (E/PE, 1:5), Rf=0.45 (E/PE, 1:1); tr (HP
1
4.2. Electrophilic substitutions
5)=17.5 min. H NMR (300 MHz, CDCl3): l=1.20 (s,
3H, CH3); 1.25 (s, 3H, CH3%); 1.57 (s, 1H, OH); 3.42 (d,
4.2.1. Synthesis of 1,3-diphenylpropene (DPP). DPP was
synthesized by self-condensation of phenylacetaldehyde
and purified by distillation and subsequent FCC (with
pentane) providing the alkene as a colorless viscous
liquid in 74% yield.21 Rf=0.33 (PE), Rf=0.57 (E/PE,
1:20); tr (HP 5)=14.4 min. 1H NMR (300 MHz,
CDCl3): l=3.49 (d, 2H, 3CH2); 6.31 (dt, 1H, 2CH);
1H, 3CH); 6.48 (d, 1H, 5CH); 6.68 (dd, 1H, 4CH);
3
3
7.14–7.43 (m, 10H, ArCH). J3,4=9.5 Hz, J4,5=15.7
Hz. 13C NMR (75 MHz, CDCl3): l=27.87 (1CH3);
28.14 (2-CH3%); 60.86 (3CH); 72.69 (2C); 126.23, 126.67,
127.28, 128.29, 128.46, 129.13, 129.43, 132.74 (CH);
137.29, 141.26 (ArC). IR (film): w˜=3570 s, 3450 br s,
(OH); 3090 w, 3060 m, 3030 s, 2970 s, 2930 m, 2890 w,

F. Marr et al. / Tetrahedron: Asymmetry 13 (2002) 2587–2592
2591
1600 s, 1500 s, 1450 s, 1370 s, 1160 s, 970 s, 750 s, 700
s cm−1. MS (EI [70 eV]): m/z (%)=194 (100) [McLaf-
ferty: {M−acetone}+]; 179 (18); 115 (33); 91 (18) [tropy-
mixture to warm slowly (approx. 6 h) to rt after 1 h at
−78°C. Purification by FCC (53 ccm) with E/PE (gradi-
ent 1:50“1:10) lead to phenyl thioether 8c (259 mg,
0.86 mmol, 86% rac-8c and 185 mg, 0.62 mmol, 62% in
llium: C7H7 ]; 59 (56) [i-PrOH+]. C18H20O (M=252.36
+
g/mol): calcd C, 85.67; H, 7.99. Found: C, 85.53; H,
7.97.
the presence of (−)-sparteine, respectively) as colorless
20
436
crystals. [h]2D0=+0.4; [h]25708=+0.5; [h]25406=+0.6; [h]
=
+0.6; [h]23605=+2.0 (c 1.02, CHCl3). Rf=0.56 (E/PE,
1
4.2.4. (E)-2,2-Dimethyl-4,6-diphenyl-5-hexen-3-one, 8b.
Compound 8b was synthesized by the given procedure
employing PMDTA or (−)-sparteine, respectively. The
reaction mixture was neutralized 1 h after the addition
of 2,2-dimethylpropanoyl chloride; FCC (63 ccm) of
the crude products with E/PE 1:20 lead to ketone 8b
(360 mg, 1.29 mmol; 86% for the racemate; 194 mg,
0.70 mmol, 45% for (+)-8b) as colorless crystals.
1:50). H NMR (300 MHz, CDCl3): l=4.92 (d, 1H,
1CH); 6.29 (d, 1H, 3CH); 6.46 (dd, 1H, 2CH); 7.13–
3
3
7.43 (m, 15H, ArCH). J1,2=8.2 Hz, J2,3=15.6 Hz. 13C
NMR (75 MHz, CDCl3): l=56.62 (1CH); 126.42,
127.42, 127.55, 127.95, 128.44, 128.62, 128.69, 129.16,
131.52, 133.08 (2CH/3CH/ArCH); 134.87, 136.70,
140,24 (ArC). MS (EI[70 eV]): m/z (%)=302 (0.2) [M+];
193 (100) [{M−SPh}+]; 115 (67); 91 (24) [tropyllium:
+
C7H7 ]. C21H18S (M=302.43 g/mol): calcd C, 83.39; H,
[h]2D0=+0.3; [h]25078=+0.2; [h]52046=+0.4; [h]24306=+1.0;
[h]23065=+2.9 (c 0.97, CHCl3; e.r. not determined). Mp=
106°C (PE/Et2O). Rf=0.36 (E/PE, 1:20); tr (HP 5)=
6.00. Found: C, 83.17; H, 5.78.
4.2.6. (E)-1,3-Diphenyl-3-trimethylsilyl-1-propene, 8d23.
The racemic silane was formed by the silylation of
allylic anion 7b with chlorotrimethylsilane in the pres-
ence of PMDTA; FCC (63 ccm) with pentane lead to a
mixture of the desired silane rac-8h (0.88 mmol, 45%)
and the starting material (231 mg together) as colorless
liquid. In the presence of (−)-sparteine employing the
given procedure—employing 0.69 mL (5.5 mmol, 3.7
equiv.) SiMe3Cl with a reaction time of 6 h—yielded a
mixture of (R)-(E)-8d (0.95 mmol, 63%) and some
starting material (286 mg together); the use of
1
18.3 min. H NMR (300 MHz, CDCl3): l=1.17 (s, 9H,
t-Bu(CH3)3); 5.01 (d, 1H, 4CH); 6.41 (d, 1H, 6CH);
3
6.54 (dd, 1H, 5CH); 7.14–7.40 (m, 10H, ArCH). J4,5
=
8.3 Hz, J5,6=15.7 Hz. 13C NMR (75 MHz, CDCl3): l
(ppm)=26.42 (t-Bu(CH3)); 45.53 (t-BuC); 56.01 (4CH);
126.37, 127.04, 127.48, 128.19, 128.46, 128.73, 130.01,
131.15 (CH); 136.88, 139.11 (ArC); 213.38 (CꢁO). IR
(KBr): w˜=3090 w, 3070 m, 3030 s, 2970 s, 2930 m, 2870
w, 1700 s, w (CꢁO), 1600 s, 1490 s, 1450 s, 1370 m, 970
s, 750 s, 690 s cm−1. MS (EI [70 eV]): m/z (%)=278 (2)
[M+]; 193 (100) [{M−t-Bu(CO)}+]; 178 (10); 115 (39); 91
3
trimethylsilyl trifluoromethanesulfonate in this protocol
(16) [tropyllium: C7H7 ]; 85 (9) [t-Bu(CO)+]; 57 (60)
+
20
578
lead to (S)-(E)-8d (see Table 1). [h]2D0=−1.9; [h]
=
[t-Bu+]. C20H22O (M=278.39 g/mol): calcd C, 86.29; H,
−2.1; [h]25406=−2.3; [h]42306=−4.4 (c 1.07, benzene); repre-
7.97. Found: C, 86.14; H, 7.97.
senting 5% op for pure (R)-(E)-8d.23a Rf=0.33 (PE),
Rf=0.57 (E/PE, 1:20); tr (HP 5)=16.6 min. H NMR
1
S-Phenyl p-toluenethiosulfonate22 was synthesized from
p-toluenesulfinic acid sodium salt and 0.5 equiv.
diphenyl disulfide in CH2Cl2 in the presence of iodine
(0.5 equiv.) at rt according to Scheme 3. Purification by
FCC with E/PE gave the pure thio ester as colorless
crystals in 92% yield.
(300 MHz, CDCl3): l=–0.03 (s, 9H, SiMe3); 3.08 (d,
1H, 3CH); 6.32 (d, 1H, 1CH); 6.55 (dd, 1H, 2CH);
3
3
7.04–7.34 (m, 10H, ArCH). J1,2=15.7 Hz, J2,3=9.9
Hz. 13C NMR (75 MHz, CDCl3): l (ppm)=−2.80
(SiMe3); 43.84 (3CH); 124.72, 125.86, 126.57, 127.08,
128.12, 128.36, 128.46, 130.51 (CH); 138.20, 142.31
(ArC). GC–MS (TOF): m/z (%)=266 (18) [M+]; 115
1H NMR (300 MHz, CDCl3): l=2.41 (s, 3H, p-CH3);
7.20 (d, 2H, ArCH); 7.28–7.40, 7.41–7.51 (each m,
+
(20); 73 (100) [SiMe3 ]. C18H22Si (M=266.45 g/mol).
3
4H+3H, ArCH). JAr,Ar=8.3 Hz. 13C NMR (75 MHz,
CDCl3): l=21.59 (p-CH3); 127.58 (o-ArCH); 128.10
(1PhC); 129.34 (o-/m-PhCH); 131.25 (p-PhCH); 136.54
(m-ArCH); 140.40 (1ArCH); 144.67 (p-ArCH); 126.84
(o-ArCH); 129.71 (m-ArCH); 140.63 (1ArC); 144.73
(p-ArC). C13H12O2S2 (M=264.36 g/mol).
4.3. Supplementary material
Crystallographic data (excluding structure factors) for
the structure in this paper have been deposited with the
Cambridge Crystallographic Data Centre as supple-
mentary publication number CCDC 190371. Copies of
the data can be obtained, free of charge, on application
to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK
[fax: +44 (0) 1223-336033 or e-mail: deposit@
ccdc.cam.ac.uk].
4.2.5. (E)-1,3-Diphenyl-1-prop-2-enyl phenyl sulfide, 8c.
Compound 8c was formed by reaction of the allyl-
lithium (1 mmol) with 2.0 equiv. S-phenyl p-
toluenethiosulfonate in ether, allowing the reaction
References
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2592
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2568.0(4) A , Z=4, zcalcd=1.124 g cm−3, v=0.64 cm−1
,
,
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,
11. The (−)-sparteine is not C2-symmetric, and therefore the
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16. Calculated with MOPAC on MP3 niveau. The allyllic
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17. Hoppe, D.; Zschage, O. Angew. Chem. 1989, 101, 67;
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