Synthesis of enantioenriched indene-derived bicyclic alcohols and tricyclic cyclopropanes via ( - )-sparteine-mediated lithiation of a racemic precursor and kinetic resolution during the cyclocarbolithiation

Article abstract of DOI:10.1016/S0022-328X(00)00832-9

By treatment of the racemic 3-(indenyl)alkyl carbamate rac-8 with sec-BuLi-( - )-sparteine, cyclocarbolithiation occurs, which is accompanied by kinetic resolution during the cyclisation step. After addition of electrophiles, the stereohomogeneous optically active benzobicyclo[3.3.0]octenols of type 13 are obtained. Increasing the temperature from -78 to -40°C or the application of TMEDA instead of ( - )-sparteine yields the formation of the tricyclic cyclopropane 14.

Full text of DOI:10.1016/S0022-328X(00)00832-9

Journal of Organometallic Chemistry 624 (2001) 96–104
www.elsevier.nl/locate/jorganchem
Synthesis of enantioenriched indene-derived bicyclic alcohols and
tricyclic cyclopropanes via (−)-sparteine-mediated lithiation of a
racemic precursor and kinetic resolution during the
cyclocarbolithiation
H. Laqua, R. Fro¨hlich 1, B. Wibbeling1, D. Hoppe *
Organisch-Chemisches Institut der Uni6ersita¨t Mu¨nster, Corrensstraße 40, D-48149 Mu¨nster, Germany
Received 12 September 2000; accepted 24 October 2000
Dedicated to Professor J.F. Normant on the occasion of his 65th birthday
Abstract
By treatment of the racemic 3-(indenyl)alkyl carbamate rac-8 with sec-BuLi–(−)-sparteine, cyclocarbolithiation occurs, which
is accompanied by kinetic resolution during the cyclisation step. After addition of electrophiles, the stereohomogeneous optically
active benzobicyclo[3.3.0]octenols of type 13 are obtained. Increasing the temperature from −78 to −40°C or the application of
TMEDA instead of (−)-sparteine yields the formation of the tricyclic cyclopropane 14. © 2001 Elsevier Science B.V. All rights
reserved.
Keywords: Chiral carbanions; Cyclocarbolithiation; (−)-Sparteine; Kinetic resolution; Lithiated alkyl carbamates
Inspired by the seminal work of Normant and Marek
[5], who found that the (−)-sparteine complexes of
achiral alkyllithiums add with high enantiofacial selec-
tivity onto the double bond of 3-heterosubstituted 1-
phenyl-1-propenes, we applied our method of
(−)-sparteine-mediated enantioselective deprotonation
of alkyl carbamates [6b] successfully to achieve the goal
of asymmetric cyclocarbolithiation starting from 5-
alkenyl carbamates (Scheme 2) [7–9].
Based on the work of Drozd et al. [1] and, more
important, of Bailey et al. [2], the intramolecular cyclo-
carbolithiation of 5-alkenyllithium and related com-
pounds became a powerful synthetic tool in the
construction of five-membered carbo- and hetereocycles
(Scheme 1) [3]. The cyclisation of A proceeds readily in
a 5-exo-trig ring-closure [4] and the intermediate B can
be trapped either by protons or other electrophiles.
Starting from the achiral alkene 1, the base sec-butyl-
lithium–(−)-sparteine (5) removes almost exclusively
the a-pro-S proton and leads to the intermediate 2
which cyclises to form the cyclic benzyllithium com-
pound 3 with both high enantio- and diastereoselectiv-
ity in respect to the stereogenic centers at the
five-membered ring [7a,b]. Despite the fact that the
benzylic position in 3 is configuratively labile, it is
trapped by most electrophiles with formation of the
nearly stereohomogeneous cyclopentanol derivatives 4,
bearing three consecutive stereocenters.
Scheme 1.
* Corresponding author. Fax: +49-251-8339772.
E-mail address: dhoppe@uni-muenster.de (D. Hoppe).
1 X-ray crystal structure analysis.
When starting from racemic alkenyl carbamates, the
generation of two enantioenriched epimers, both with
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(00)00832-9

H. Laqua et al. / Journal of Organometallic Chemistry 624 (2001) 96–104
97
Scheme 2.
Scheme 3.
(S)-configuration at the metal-bearing stereocenter will
occur, although in different amounts through a kinetic
resolution, due to a matched and mismatched situation
[10] in the deprotonation step [9,11] (for the principle,
see Scheme 4).
We report here on another type of efficient kinetic
resolution, namely, that which is involved in the cyclisa-
tion step. A suitable cyclisation precursor rac-8 was
prepared from 3-methyl-1H-indene (6) and the 3-tos-
yloxypropyl carbamate (7a) (Scheme 3) by deprotona-
tion of 6 by means of n-butyllithium–(−)-sparteine
[12,13]. As expected [12], both regioisomers rac-8 and
rac-9 (ratio 1:1) were obtained as racemates. For facili-
tating the separation, the mixture was deprotonated
again and trapped by methyl chloroformate. Only rac-
9, still bearing an acidic proton, was converted into the
ester rac-10, and rac-8 remained unchanged.
of water (Scheme 4). Chromatographic separation af-
forded the benzobicyclo[3.3.0]-octenyl carbamate (−)-
13a (24%; only one diastereomer could be detected by
1H-NMR and TLC), the optically active starting mate-
rial (+)-8 (48%), and traces of the impure tricyclic
cyclopropane 14 (Scheme 4). From carbamate (−)-13a,
the alcohol (−)-15 was liberated [14] and converted to
the (R) Mosher ester [15]. The samples appeared homo-
geneous; no evidence for diastereomeric impurities
1
could be detected in GC, H- and 19F-NMR. From this
it must be concluded that (−)-15 and (−)-13a have
high enantiomeric purities. This is in accordance with
what is expected, since it is determined by the pro-S-se-
lectivity in the deprotonation step, which was always
found to be higher than 97%.
Crystalline (−)-13a could be subjected to single-
crystal structure analysis [16] (Fig. 1) which revealed
the relative configuration. Since we had demonstrated
with numerous examples that the (−)-sparteine depro-
tonation of alkyl carbamates leads without any excep-
rac-8 was kept with sec-butyllithium/(−)-sparteine
(1.5 equivalents) in diethyl ether for 20 h at −78°C
before the reaction mixture was quenched by addition

98
H. Laqua et al. / Journal of Organometallic Chemistry 624 (2001) 96–104
Scheme 4.
1
the H-NMR spectroscopic stereochemical assignment
tion [6b] to the removal of the pro-S proton and, in
addition, the carbolithiation takes place with stereore-
tention [6,7], C-6 has the (R)-configuration and can be
taken as the reference stereocenter for assigning the
absolute configuration (1R,5R,6R) to (−)-13a. The
precursor of (−)-13a is solely the lithium intermediate
(R,S)-11, since no diastereomer of (−)-13a was de-
tected. Thus, recovered (+)-8 must arise from the
epimer (S,S)-11 and have the (S)-configuration. In
order to exclude the unlikely event that stereodiscrimi-
nation had already occurred in the deprotonation step,
the reaction mixture was trapped with DOCH3 and, as
expected, [1D]-(+)-8 was isolated.
3
is no problem: the coupling constants JH5,H4a (2.4 Hz)
and JH5,H4b (10.2 Hz) are of very different sizes. In
3
(−)-13c (4.2 Hz) and (−)-13d (2.9 Hz), only a small
coupling constant remained, indicating that the intro-
duced substituent occupies the b-position. Conse-
quently, the electrophile had approached from the less
shielded exo-face. Since alkylations and stannylations
in benzylic position were found to proceed with
stereoinversion, most likely, lithium compound (4S)-12
is the direct precursor. Deuteration of the benzyllithium
intermediate 12 with DOCH3 is less diastereoselective,
leading to a 69:31 mixture of the b- and a-
D isoto-
pomers 13b; spectroscopic configurational assignment is
based on the same 1H-NMR arguments. Possibly,
CH3OD, being a very rapid electrophile, reacting with
stereoretention [18], traps the equilibrium mixture of
(4S)- and (4R)-12.
From these results, it can be concluded that the
epimer (S,S)-11 does not cyclize under the conditions
where the cyclocarbolithiation of (R,S)-11 proceeds
easily. The difference in both transition states is that in
the syn-addition of CꢀLi to the double bond, for for-
mation of (4S)-12 from (R,S)-11 the complexing car-
bamoyloxy residue can occupy a favourable position in
the developing roof-like cis-bicyclus, whereas for (S,S)-
11 this group has to be placed in a congested endo-po-
sition [17]. The originally formed benzyllithium
derivative (4S)-12 is not expected to be configura-
tionally stable [6b] and presumably exists in equilibrium
with its epimer (4R)-12. By addition of electrophiles,
such as ethyl iodide or tributyltin chloride, the
stereohomogeneous substitution products (−)-13c and
(−)-13d are isolated. Due to the rigid structure of 13a,
Fig. 1. Structure of (−)-13a in the crystal.

H. Laqua et al. / Journal of Organometallic Chemistry 624 (2001) 96–104
99
Scheme 5.
1. Cyclopropane formation
−90°C, no intermediate could be trapped. Presumably,
the benzhydryllithium 19 is more reactive than 12 due
to its larger ion-pair separation [20].
In an attempt to prepare a racemic sample of 13a,
TMEDA was used as a ligand instead of 5 for the
deprotonation of rac-8. To our surprise, after protono-
lysis at −78°C not rac-13a, but the tricyclic cyclo-
propane rac-14 was isolated with 48% yield, in addition
to recovered starting material rac-8. The structure of
rac-14 was elucidated by C,H correlation NMR experi-
ments (see Section 2); rac-14 arises by the intramolecu-
lar 1,3-alkylation in the benzyllithium intermediates
rac-12. Cyclopropane formation by intramolecular nu-
cleophilic substitution of a N,N-dialkylcarbamoyloxy
group is a common reaction, which was reported first
by us in 1993 [7,9,19]. Apart from the stereochemical
situation [19] in the precursor, the ligand at the lithium
cation has a great influence on the ease of cycloelimina-
tion. Whereas the TMEDA complex of 12 undergoes
the reaction even at −78°C, for the (−)-sparteine
complex temperatures of −40°C are required to
achieve complete cyclopropane formation. A case, us-
ing the different rates of cyclopropane formation for
kinetic resolution of diastereomers on the stage of a
cyclisation product, derived from a lithiated alkyl car-
bamate, was reported by Nakai et al. [7e].
Altogether, the combination of alkylating an alkylin-
dene by the 3-(tosyloxy)-alkyl carbamate (7a), (−)-
sparteine-assisted
deprotonation,
followed
by
cyclocarbolithiation, which is accompanied by kinetic
resolution, provides facile access to optically active
benzobicyclo[3.3.0]octenols of type 13 and to tricyclic
cyclopropanes such as 14 or 20.
2. Experimental
All reactions involving water- or air-sensitive chemi-
cals were carried out in distilled and dried solvents
under argon. Diethyl ether was distilled from sodium
immediately prior to use. Solvents [diethyl ether,
petroleum ether (boiling range 35–40°C)] used for
chromatography were distilled prior to use. All other
reagents were used as purchased. Melting points: Gal-
lenkamp melting point apparatus (uncorrected). IR:
1
Perkin–Elmer PE 298. H- and 13C-NMR: Bruker AM
300, ARX 400 and Varian 600. Shifts are reported
relative to tetramethylsilane as an internal reference.
CDCl3 was used as solvent. Numbering according to
IUPAC rules. Elemental analysis: Perkin–Elmer 240.
Flash chromatography: Merck Silica Gel 60 (40–63
mm) (100 g for 1 g of material to be separated). Thin-
layer chromatography (TLC): Macherey, Nagel & Co.
When the 1-methyl-3-phenylindenyl-substituted pro-
pyl carbamate rac-17 accompanied by its 1,3-regioiso-
mery rac-18 was subjected to the usual conditions of
(−)-sparteine-assisted deprotonation, the optically ac-
tive analogue (−)-20 was formed with 36% yield
(Scheme 5). Even, when the reaction was carried out at
Sil G/UV254
.

100
H. Laqua et al. / Journal of Organometallic Chemistry 624 (2001) 96–104
2.1. (3-Tosylpropyl)2,2,4,4-tetramethyl-1,3-
oxazolidine-3-carboxylate (7a)
(2%-CH3); 32.8 t (C-2); 59.7 [60.6] s (C-4%); 64.3 t (C-1);
76.3 [76.1] t (C-5%); 96.6 [94.6] s (C-2%); 152.6 [152.1] s
(NCꢁO). EI-MS (m/z (%)): 326 (100) [(M−CH3)+];
169(24) [(M−OCby)+]; 114 (8) [C7H14O].
Tosyl chloride (4.60 g, 24.0 mmol) was added to a
stirred solution of (3-hydroxypropyl)-2,2,4,4-te-
tramethyl-1,3-oxazolidin-3-carboxylate [6] (4.62 g, 20.0
mmol) in 30 ml of dichloromethane. After addition of
pyridine (3.9 ml, 48.0 mmol), the mixture was stirred
for 16 h at room temperature (r.t.) and then 10 ml 2 M
HCl were added. After separation of the layers and
threefold extraction of the aqueous layer with 10 ml of
diethyl ether, the organic layers were dried with
Na2SO4. After column chromatography with diethyl
ether–petroleum ether (4:1), the tosyl carbamate 7a
(6.71 g, 87%) was obtained as a white solid. M.p.
60–61°C. Anal. Calc. for C18H27NO6S (385.86): C,
56.08; H, 7.06; N, 3.63. Found: C, 56.09; H, 7.25; N,
3.67%. IR (w˜/cm−1, KBr): 2980 (m); 2934 (m); 2881
(w); 1687 (s); 1366 (s); 1187 (s); 949 (m); 866 (s).
1H-NMR (300 MHz): l=1.28 [1.39] (s, 6H, 4%-CH3);
1.53 [1.43] (s, 6H, 2%-CH3); 2.00–2.04 (m, 2H, 2-H);
2.44 (s, 3H, 5¦-H); 4.10–4.15 (m, 4H, 3-H, 1-H); 7.32–
7.37 (m, 2H, 3¦-H); 7.77–7.81 (m, 2H, 2¦-H). 13C-NMR
(75 MHz): l=21.9 q (C-5¦); 25.6 [24.4] q (4%-CH3);
25.6 [26.8] q (2%-CH3); 29.1 t (C-2); 60.0 [60.6] s (C-4%);
60.6 t (C-3); 67.6 t (C-1); 76.6 [76.4] t (C-5%); 96.2 [95.1]
s (C-2%); 128.2 d (C-2¦); 130.2 d (C-3¦); 133.4 s (C-1¦);
145.2 s (C-4¦); 152.6 [151.9] s (NCꢁO). EI-MS (m/z
(%)): 370 (100) [(M−CH3)+]; 326 (23) [(M−C3H7O)+
]; 213 (78) [(M−OCby)+]; 198 (7) [(M−OCby−
CH3)+]; 155 (87) [C7H7O2S+]; 114 (15) [C7H14O+]; 91
(61) [C7H+7 ].
2.3. General procedure for the lithiation and
substitution of the indenes 6 and rac-16
n-Butyllithium (one equivalent, 1.6 M in n-hexane)
was added drop-wise with stirring at −78°C to a
solution of the indene (one equivalent) and (−)-
sparteine (5) (one equivalent) in diethyl ether (2 ml
mmol−1). The electrophile was added and stirring con-
tinued for 4 h at −78°C. After addition of 2 M HCl (1
ml mmol−1) the mixture was warmed to room temper-
ature and the layers were separated. The aqueous layer
was extracted with diethyl ether (3×10 ml) and the
combined ethereal phases were washed with water (10
ml). After the solution had been dried (Na2SO4), the
solvent was evaporated under reduced pressure, and the
products were separated on silica gel with diethyl
ether–petroleum ether.
2.4. Carbamates rac-8 and rac-10
3-Methyl-1H-indene (2.60 g, 20.0 mmol), 4.70 g (20.0
mmol) (−)-sparteine, 12.5 ml (20.0 mmol) n-BuLi, 7.71
g (20.0 mmol) 7a, column chromatography with diethyl
ether–petroleum ether (1:4); yield: 75% (colourless oil;
rac-8/rac-10=1:1).
The mixture (5.18 g, 15.1 mmol) was lithiated again
with 2.34 g (10.0 mmol) (−)-sparteine and 6.25 ml
(10.0 mmol) n-BuLi; 1.0 ml (12.0 mmol) methyl chloro-
fomate was added. Column chromatography with di-
ethyl ether–petroleum ether (1:4) produced rac-8 (43%)
and rac-10 (32%) as colourless oils.
2.2. (3-Iodopropyl)2,2,4,4-tetramethyl-1,3-
oxazolidine-3-carboxylate (7b)
A 0.8 M solution of iodine in DMF was added to a
stirred solution of (3-hydroxypropyl)-2,2,4,4-te-
tramethyl-1,3-oxazolidin-3-carboxylate (3.00 g, 13.0
mmol) and 3.75 g (14.3 mmol) triphenylphosphine in 20
ml of DMF until the colour of the solution remained
brown. After 1 h, 10 ml of saturated aqueous Na2S2O3
solution were added. After separation of the layers and
threefold extraction of the aqueous layer with 10 ml of
diethyl ether the organic layers were dried with Na2SO4.
After column chromatography with diethyl ether–
petroleum ether (1:6) the carbamate 7b (3.73 g, 85%)
was obtained as a colourless oil. Anal. Calc. for
C11H20INO3 (341.19): C, 38.72; H, 5.91; N, 4.11.
Found: C, 38.57; H, 6.32; N, 4.11%. IR (w˜/cm−1, film):
2981 (s); 2869 (m); 1696 (s); 1406 (m); 1360 (m); 1258
2.5. Carbamate rac-8
Anal. Calc. for C21H29NO3 (343.47): C, 73.44; H,
8.51; N, 4.08. Found: C, 73.32; H, 8.48; N, 3.94%. IR
(w˜/cm−1, film): 3065 (m); 2973 (s); 2868 (s); 1710 (s);
1479 (m); 1414 (s); 1348 (s); 1269 (m); 1111 (s); 755 (s).
1H-NMR (300 MHz): l=1.31 (s, 3H, 13-H); 1.33–1.53
(m, 14H, 2%-CH3–4%-CH3–10-H); 1.86 (tt, 2H, 11-H);
3.71 (s, 2H, 5%-H); 3.94 (t, 2H, 12-H); 6.29 (d, 1H, 2-H);
6.68 (d, 1H, 3-H); 7.14–7.29 (m, 4H, PhꢀH). 3J2,3=5.5;
3
3J10,11=5.6; J11,12=6.2 Hz. 13C-NMR (75 MHz): l=
24.0 q (C-13); 24.9 t (C-11); 25.7 [24.6] q (4%-CH3); 25.7
[27.0] q (2%-CH3); 35.4 t (C-10); 53.4 s (C-1); 59.2 [60.5]
s (C-4%); 65.2 t (C-12); 77.6 t (C-5%); 96.1 [94.6] s (C-2%);
121.6, 121.7 d (C-5/C-8); 125.5 d (C-7); 127.0 d (C-6);
129.7 d (C-2); 143.8 s (C-9); 145.2 s (C-4); 145.3 d
(C-3); 152.1 s (NꢁCO). EI-MS (m/z (%)): 343 (1) [M+];
328 (55) [(M−CH3)+]; 171 (100) [(M−OCby)+]; 156
(59) [(M−OCby−CH3)+]; 143 (38) [C11H1+1]; 129 (88)
[C10H+9 ].
1
(m); 1104 (m). H-NMR (300 MHz): l=1.37 [1.42] (s,
6H, 4%-CH3); 1.55 [1.52] (s, 6H, 2%-CH3); 2.18 (tt, 2H,
2-H); 3.24 (t, 2H, 3-H); 3.73 (s, 2H, 5%-H); 4.17 (t, 2H,
3
3
1-H). J1,2=6.5; J2,3=6.7 Hz. 13C-NMR (75 MHz):
l=1.6 t (C-3); 25.3 [24.1] q (4%-CH3); 25.4 [26.6] q

H. Laqua et al. / Journal of Organometallic Chemistry 624 (2001) 96–104
101
2.8. General procedure for the cyclocarbolithiation of
2.6. Carbamate rac-10
the indenes rac-8 and rac-17 and substitution by
electrophiles
Anal. Calc. for C23H31NO5 (401.50): C, 68.80; H,
7.78; N, 3.49. Found: C, 68.81; H, 7.87; N, 3.25%. IR
(w˜/cm−1, film): 2987 (s); 2934 (m); 2875 (m); 1736 (s);
1703 (s); 1460 (m); 1420 (m); 1368 (m); 1104 (s); 1071
sec-Butyllithium [1.5 equivalents 1.08 M in cyclohex-
ane–n-hexane (92:8)] was added drop-wise with stirring
at −78°C to a solution of the indene (one equivalent)
and (−)-sparteine (5) (1.5 equivalents) in diethyl ether.
After 20 h at −78°C the electrophile was added and
stirring continued for 5 h while the temperature was
slowly raised to r.t. After addition of 2 M HCl (2 ml)
the layers were separated, the aqueous layer was ex-
tracted with diethyl ether (3×10 ml) and the combined
ethereal phases were washed with water (10 ml). After
the solution had been dried (Na2SO4), the solvent was
evaporated under reduced pressure, and the products
were separated on silica gel with diethyl ether–
petroleum ether.
1
(m); 788 (m). H-NMR (300 MHz): l=1.41–1.57 (m,
12H, 4%-CH3–2%-CH3); 1.58 (d, 3H, 10-H3); 2.06 (tt, 2H,
12-H2); 2.62 (t, 2H, 11-H2); 3.61 (s, 3H, OCH3); 3.74 (s,
2H, 5%-H2); 4.20 (t, 2H, 13-H2); 6.18 (q, 1H, 2-H);
7.20–7.33 (m, 4H, PhꢀH). 4J2,10=1.2; 3J11,12=7.7;
3J12,13=6.4 Hz. 13C-NMR (75 MHz): l=22.5 q (C-10);
24.6 t (C-12); 25.8 [24.7] q (4%-CH3); 25.8 [27.1] q
(2%-CH3); 27.6 t (C-11); 52.7 q (OCH3); 58.5 s (C-1);
59.3 [60.1] s (C-4%); 64.5 t (C-13); 77.4 t (C-5%); 95.8
[94.8] s (C-2%); 119.7 d (C-5); 123.4 d (C-8); 126.3 d
(C-7); 127.9 d (C-6); 134.9 d (C-2); 143.3 s (C-9); 143.9
s (C-4); 148.0 s (C-3); 152.9 s (NCꢁO); 174.6 s
(COOCH3). EI-MS (m/z (%)): 386 (14) [(M−CH3)+];
342 (2) [(M−COOCH3)+]; 327 (1) [(M−CH3−
COOCH3)+]; 229 (20) [(M−OCby)+]; 228 (100) [(M−
H−OCby)+]; 169 (91); 115 (6) [C9H+7 ].
2.9. (1R,5R,6R)-1-Methyl-2,3-benzobicyclo[3.3.0]oct-
2-ene-6-yl2,2,4,4-tetramethyl-1,3-oxazolidine-3-carboxy-
late (13a)
rac-8 (117 mg, 0.34 mmol), 120 mg (0.51 mmol)
(−)-sparteine, 0.48 ml (0.51 mmol) sec-BuLi, 5 ml
diethyl ether, column chromatography with diethyl
ether–petroleum ether (1:4) produced (−)-13a (24%)
as a white solid. M.p. 82–83°C. [h]2D0= −62.6 (c=
0.77, CH2Cl2). Anal. Calc. for C21H29NO3 (343.47): C,
73.44; H, 8.51; N, 4.08. Found: C, 73.70; H, 8.80; N,
3.86%. IR (w˜/cm−1, KBr): 2980 (s); 2960 (s); 2875 (s);
1683 (s); 1413 (s); 1348 (s); 1262 (s); 1210 (m); 1104 (s);
2.7. Carbamate rac-17 (65:35 mixture with the
k-regioisomer rac-18)
1-Methyl-3-phenyl-1H-indene (0.69 g, 2.0 mmol),
0.47 g (2.0 mmol) (−)-sparteine, 1.25 ml (2.0 mmol)
n-BuLi, 0.68 g (2 mmol) carbamate 7b; column chro-
matography with diethyl ether–petroleum ether (1:4)
produced a mixture of rac-17 and rac-18 (66%, a/g=
65:35) as a colourless oil. This mixture was used with-
out further separation. Anal. Calc. for C27H33NO3
(419.57): C, 77.29; H, 7.93; N, 3.34. Found: C, 77.19;
H, 8.03; N, 3.23%. IR (w˜/cm−1, film): 2987 (s); 2868
(m); 1697 (s); 1453 (m); 1407 (s); 1348 (s); 1269 (m);
1098 (s); 762 (s). 1H-NMR (300 MHz, g-isomere in
curly brackets): l=1.25–1.59 (m, 15H, 2%-CH3, 4%-CH3,
11-H2, 10-Ha); 1.40 {2.16} (s {d}, 3H, 13-H3); 1.93
{2.38} (m, 1H, 10-Hb); 3.70 (s, 2H, 5%-H2); 3.96 {4.00}
(t, 2H, 12-H2); 6.35 {6.19} (s {q}, 1H, 2-H); 7.13–7.59
1
1065 (s); 912 (w); 861 (w); 775 (s); 538 (w). H-NMR
(600 MHz): l=1.44–1.69 (m, 16H, 7-Hb, 1-CH3, 2%-
CH3, 4%-CH3); 1.82 (m, 1H, 7-Ha); 1.97–2.00 (m, 2H,
8-H2); 2.50 (ddd, 1H, 5-H); 2.80 (dd, 1H, 4-Hb); 3.37
(dd, 1H, 4-Ha); 3.74 (s, 2H, 5%-H2); 4.90 (ddd, 1H, 6-H);
7.12–7.18 (m, 4H, PhꢀH). 3J6,7a=4.2; 3J6,7b=2.4;
3J5,6=1.8; 2J4a,4b=17.4; 3J4a,5=10.2; 3J4b,5=2.4 Hz.
13C-NMR (150 MHz): l=25.3 [24.1] q (4%-CH3); 25.6
[25.3] q (2%-CH3); 26.8 q (1-CH3); 31.9 t (C-7); 36.4 t
(C-8); 39.7 t (C-4); 55.9 s (C-1); 56.3 d (C-5); 59.4 [60.3]
s (C-4%); 76.3 t (C-5%); 84.5 d (C-6); 95.8 [94.8] s (C-2%);
122.8 d, 124.2 d, 126.3 d, 126.8 d, 141.6/150.5 s (PhꢀC);
152.2 s (NCꢁO). EI-MS (m/z (%)): 343 (1) [M+]; 328
(14) [(M−CH3)+]; 171 (78) [(M−OCby)+]; 170 (100)
[(M−H−OCby)+]; 155 (64) [(M−H−OCby−
CH3)+]; 129 (73) [C10H9+]; 114 (39) [C9H+6 ].
3
(m, 9H, PhꢀH). J11,12=6.2 Hz; {4J2,13=1.4 Hz}. 13C-
NMR (75 MHz, g-isomere in curly brackets): l=13.2
{15.7} q (C-13); 24.6 [24.1] q (4%-CH3); 25.0 t (C-11);
25.8 [27.0] q (2%-CH3); 35.9 {34.3} t (C-10); 52.1 s (C-1);
59.6 [60.3] s (C-4%); {61.2 s (C-3)}; 65.3 {66.2} t (C-12);
76.8 t (C-5%); 95.8 [94.8] s (C-2%); 119.8/121.1/123.2/
125.9/126.7/126.8/127.0/127.2/128.0/128.8/ 136.2/139.2/
142.0/142.9 s/d (PhꢀC, C-3, {C-3}, C-2, {C-2}); 153.1
[152.5] s (NꢁCO). EI-MS (m/z (%)): 419 (6) [M+]; 404
(4) [(M−CH3)+]; 246 (65) [(M−OCby−H)+]; 231
(58) [(M−H−CH3−OCby)+]; 205 (51) [(M−
C3H6OCby)+]; 156 (100) [Cby+].
Besides the cyclisation product, 48% of the enan-
tioenriched educt (−)-8 could be reisolated [21].
The deuterated product (−)-13b was synthesized as
described above: 343 mg (1.0 mmol) rac-8, 351 mg (1.5
mmol) (−)-sparteine, 1.39 ml (1.5 mmol) sec-BuLi, 10
ml diethyl ether, 0.5 ml (12.3 mmol) methanol-[D1];
column chromatography with diethyl ether–petroleum
ether (1:4) produced (−)-13b (23%) as a white solid

102
H. Laqua et al. / Journal of Organometallic Chemistry 624 (2001) 96–104
(d.r., 69:31). The physical data are identical with those
of (−)-13a. J4a,5=10.8; J4b,5=2.3 Hz.
2.12. (1R,4R,5R,6R)-1-Methyl-4-(trimethylstannyl)-
2,3-benzobicyclo[3.3.0]oct-2-ene-6-yl2,2,4,4-
tetramethyl-1,3-oxazolidine-3-carboxylate (13d)
3
3
2.10. (1R,4S,5R,8R)-1-Methyl-2,3-
benzotricyclo[3.2.1.04,8]oct-2-ene (14)
398 mg (1.16 mmol) rac-8, 408 mg (1.74 mmol)
(−)-sparteine, 1.61 ml (1.74 mmol) sec-BuLi, 15 ml
diethyl ether, column chromatography with diethyl
ether–petroleum ether (1:40) yielded (−)-13d (32%) as
a colourless oil. [h]2D0= −47.7 (c=0.92, CH2Cl2).
Anal. calc. for C33H55NO3Sn (632.51): C, 62.68; H,
8.77; N, 2.21. Found: C, 62.09; H, 8.97; N, 2.29%. IR
(w˜/cm−1, film): 2955 (s); 2929 (s); 2871 (m); 1682 (s);
1470 (m); 1402 (s); 1375 (s); 1264 (m); 1063 (m); 757
(m). 1H-NMR (600 MHz): l=0.82–0.88 (m, 15H,
SnBu3ꢀH); 1.20–1.58 (m, 28H, 7-Hb, 2%-CH3, 4%-CH3;
1-CH3, SnBu3ꢀH); 1.75–1.80 (m, 1H, 7-Ha); 1.94–1.98
(m, 2H, 8-H); 2.48 (bs, 1H, 5-H); 2.83 (d, 1H, 4-H);
3.74 (s, 2H, 5%-H); 4.84 (m, 1H, 6-H); 6.87–7.08 (m, 4H,
Analogous conditions to the above were used, but
after addition of the base the reaction mixture was
warmed to −40°C. After column chromatography
with diethyl ether/petroleum ether (1:4), 14 (26 mg,
45%) was produced as a colourless liquid. [h]2D0= −
31.7 (c=2.20, CH3Cl). Anal. Calc. for C13H14 (170.26):
C, 91.71; H, 8.29. Found: C, 91.65; H, 8.80%. IR
(w˜/cm−1, film): 3019 (m); 2960 (s); 2868 (m); 1479 (m);
1453 (w); 1019 (w); 745 (s). 1H-NMR (600 MHz):
l=1.07 (dddd, 1H, 6-Hb); 1.49 (s, 3H, 1-CH3); 1.58
(dd, 1H, 7-Hb); 1.78 (ddd, 1H, 6-Ha); 1.88 (dddd, 1H,
5-H); 2.04 (ddd, 1H, 7-Ha); 2.35 (dd, 1H, 4-H); 2.46
2
(dd, 1H, 8-H); 6.95–7.21 (m, 4H, PhꢀH). J7a,7 b=13.2
3
PhꢀH). J4,5=2.9 Hz. 13C-NMR (150 MHz): l=9.9 t,
2
3
3
3
Hz; J8a,8b=11.4; J7a,8a=9.0; J7b,8b=6.0; J7a,5=7.2;
3J7b,8a=9.0; J7b,5=1.8; J4,5=7.2; J4,8=6.6; J5,8
=
3
3
3
3
14.0 q (SnBu3ꢀC); 25.8 [24.6] q (4%-CH3); 26.1 [25.8] q
(2%-CH3); 27.0 t (SnBu3ꢀC); 28.7 q (1-CH3); 29.6 t
(SnBu3ꢀC); 32.2 t (C-7); 35.4 d (C-4); 41.1 t (C-8); 56.4
s (C-1); 59.8 [61.2] s (C-4%); 61.4 d (C-5); 76.6 t (C-5%);
86.6 d (C-6); 96.3 [95.0] s (C-2%); 122.2, 123.2, 124.9,
127.2 d, 148.1/148.6 s (PhꢀC)); 152.0 [151.8] s (NCꢁO).
EI-MS (m/z (%)): 575(60) [(MꢀC4H9)+]; 404 (100)
[C21H33Sn+]; 290 (37) [C12H27Sn+]; 233 (20) [C8H18Sn+];
177 (29) [C4H10Sn+]; 170 (34) [(M−OCby−
Sn(C12H27))+].
6.6 Hz. 13C-NMR (150 MHz): l=21.6 q (1-CH3); 23.4
t (C-6); 30.2 d (C-5); 32.3 d (C-4); 43.6 d (C-8); 51.7 t
(C-7); 54.7 q (C-1); 121.0 d, 123.5 d, 125.4 d, 126.3 d,
142.6/151.7 q (PhꢀC). EI-MS (m/z (%)): 170 (47) [M+];
155 (58) [(M−CH3)+]; 142 (100) [(M−C2H4)+]; 128
(70) [(M−C3H6)+]; 115 (63) [(M−C4H7)+]; 102 (12)
[C8H+6 ].
2.11. (1R,4R,5R,6R)-4-Ethyl-1-methyl-2,3-
benzobicyclo[3.3.0]oct-2-ene-6-yl2,2,4,4-
tetramethyl-1,3-oxazolidine-3-carboxylate (13c)
2.13. (1R,4R,5R,8R)-1-Methyl-4-phenyl-2,3-
benzotricyclo[3.2.1.04,8]oct-2-ene ((−)-20)
rac-8 (120 mg, 0.35 mmol), 123 mg (0.53 mmol)
(−)-sparteine, 0.49 ml (0.53 mmol) sec-BuLi, 5 ml
diethyl ether, column chromatography with diethyl
ether–petroleum ether (1:4) produced (−)-13c (26%) as
a colourless oil. [h]2D0= −56.3 (c=0.24, CH2Cl2). HR-
MS calc. for C23H33NO3+Na+: 394.2358. Found:
394.2312. IR (w˜/cm−1, film): 2967 (m); 2934 (m); 2868
(m); 1695 (s); 1399 (m); 1339 (m); 1095 (s); 1065 (s); 775
rac-17 (198 mg, 0.47 mmol), accompanied by its
1,3-regioisomere rac-18, 165 mg (0.71 mmol) (−)-
sparteine, 0.65 ml (0.71 mmol) sec-BuLi, column chro-
matography with diethyl ether–petroleum ether (1:4)
produced (−)-20 (36%) as a colourless liquid. HR-MS
calc. for C19H18: 246.1409. Found: 246.1406. [h]2D0= −
11.7 (c=0.61, CH2Cl2). IR (w˜/cm−1, film): 3033 (m);
2954 (s); 2875 (m); 1604 (w); 1460 (m); 1025 (w); 762
1
(w). H-NMR (600 MHz): l=1.03 (t, 3H, EtꢀCH3);
1.41–1.61 (m, 17H, 7-Hb, 1-CH3, EtꢀCH2b, 2%-CH3,
4%-CH3); 1.79–1.83 (m, 2H, 7-Ha, EtꢀCH2a); 1.93–1.96
(m, 2H, 8-H2); 2.15–2.19 (m, 1H, 5-H); 2.88 (dt, 1H,
4-H); 3.75 (s, 2H, 5%-H); 4.97 (m, 1H, 6-H); 7.12–7.23
1
(s). H-NMR (300 MHz): l=1.14–1.27 (m, 1H, 6-Hb);
1.58 (s, 3H, 1-CH3); 1.64 (dd, 1H, 7-Hb); 1.90 (ddd, 1H,
6-Ha); 2.10 (ddd, 1H, 7-Ha); 2.39 (ddd, 1H, 5-H); 2.60
3
(m, 4H, PhꢀH). J4,5=4.2 Hz. 13C-NMR (150 MHz):
2
(d, 1H, 8-H); 6.84–7.38 (m, 9H, PhꢀH). J6a,6b=13.4;
l=12.3 q (EtꢀC); 25.8 [24.6] q (4%-CH3); 25.9 [25.8] q
(2%-CH3); 30.1 q (1-CH3); 31.1 t (EtꢀC); 32.3 t (C-7);
40.6 t (C-8); 51.9 d (C-4); 55.5 s (C-1); 59.5 s (C-4%);
63.0 d (C-5); 77.4 t (C-5%); 84.8 d (C-6); 95.9 s (C-2%);
123.4, 124.4 d, 127.1, 127.6 d, 145.5/150.4 s (PhꢀC);
149.1 s (NCꢁO). EI-MS (m/z (%)): 356 (3) [(M−
CH3)+]; 198 (100) [(M−H−OCby)+]; 169 (34) [(M−
H−C2H5−OCby)+]; 143 (32) [C11H1+1]; 129 (14)
[C10H9].
2J7a,7b=11.2; 3J6b,7b=6.1; 3J6a,7a=3J6b,7a=9.1; 3J6a,5
=
3
3J5,8=6.9; J6b,5=1.9 Hz. 13C-NMR (75 MHz): l=
21.9 q (1-CH3); 24.4 t (C-6); 36.1 d (C-5); 47.8 s (C-1);
51.6 d (C-8); 51.9 t (C-7); 55.1 s (C-4); 121.3/124.4/
126.2/126.9/127.5/128.4/130.3/142.2/145.5/151.7 s,
d
(PhꢀC). EI-MS (m/z (%)): 246 (39) [M+]; 170 (96)
[(M−C6H5+H)+]; 155 (78) [(M−C6H5+H−CH3)+];
142 (100) [C11H+10]; 129 (82) [C10H+9 ].

H. Laqua et al. / Journal of Organometallic Chemistry 624 (2001) 96–104
103
2.14. Deprotection of carbamate 13a;
(1R,5R,6R)-1-methyl-2,3-benzobicyclo[3.3.0]-
oct-2-ene-6-ol (15)
Cambridge Crystallographic Data Centre, CCDC no.
149313. Copies of this information may be obtained free
of charge from the Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (Fax: +44-1223-336033;
e-mail: deposit@ccdc.cam.ac.uk or www: http:/
/www.ccdc.cam.ac.uk).
Methanesulfonic acid (21 mg, 0.23 mmol) was added
to a solution of 77 mg (0.22 mmol) of the carbamate 13a
in 3 ml of methanol. After 2 h of refluxing, potassium
carbonate (90 mg, 0.67 mmol) was added and the
reaction mixture was refluxed for additional 2.5 h. The
solvent was evaporated and the residue suspended in 5
ml of diethyl ether. The precipitate was filtered off and
washed with diethyl ether. The solvent was removed
from the filtrate and after column chromatography with
diethyl ether/petroleum ether (1:4) the carbamate (−)-
15 (27 mg, 66%) was obtained as a colourless oil.
HR-MS Calc. for C13H16O: 188.1199. Found: 188.1196.
[h]D20= −63.0 (c=0.61, CH2Cl2). IR (w˜/cm−1, film):
3368 (s); 2921 (s); 2861 (s); 1453 (m); 1019 (w); 769 (m).
1H-NMR (600 MHz): l=1.43 (s, 3H, 1-CH3); 1.57–
1.63 (m, 2H, 7-Hb, OH); 1.66–1.71 (m, 1H, 7-Ha); 1.90
(ddd, 1H, 8-Hb); 2.06 (ddd, 1H, 8-Ha); 2.31 (m, 1H,
5-H); 2.70 (dd, 1H, 4-Hb); 3.26 (dd, 1H, 4-Ha); 4.00 (m,
1H, 6-H); 7.12–7.20 (m, 4H, PhꢀH). 3J6,7a=4.2;
3J6,7b=3.6; 2J8a,8b=12.6; 3J8b,7b=2.4; 3J8a,7a=7.2;
2J4a,4b=17.2; 3J4a,5=9.6; 3J4b,5=2.4 Hz. 13C-NMR
(150 MHz): l=29.1 q (1-CH3); 34.7 t (C-7); 35.5 d
(C-4); 38.8 t (C-8); 55.6 s (C-1); 58.7 d (C-5); 81.5 d
(C-6); 123.0 d, 124.4 d, 126.5 d, 126.9 d, 141.5 s, 151.7
s (PhꢀC). EI-MS (m/z (%)): 188 (38) [M+]; 173 (13)
[(M−CH3)+]; 159 (77) [(M−C2H5)+]; 130 (100) [(M−
C3H5OH)+]; 115 (21) [(M−C3H5OH−CH3)+].
References
[1] (a) V.N. Drozd, Y.A. Ustynyuk, M.A. Tsel’eva, L.B. Dmitriev,
J. Gen. Chem. USSR 1968, 38, 2047; Zh. Obsch. Khim. 38
(1968) 2144. (b) V.N. Drozd, Y.A. Ustynyuk, M.A. Tsel’eva,
L.B. Dmitriev, J. Gen. Chem. USSR 39 (1969) 1951; Zh. Obsch.
Khim. 39 (1969) 1991.
[2] (a) W.F. Bailey, J.J. Patricia, V.C. DelGobbo, R.M. Jarret, P.J.
Okarma, J. Org. Chem. 50 (1985) 1999. (b) W.F. Bailey, T.T.
Nurmi, J.J. Patricia, W. Wang, J. Am. Chem. Soc. 109 (1987)
2442. (c) W.F. Bailey, A.M. Khanolkar, K. Gavaskar, T.V.
Ovaska, K. Rossi, Y. Thiel, K.B. Wiberg, J. Am. Chem. Soc. 113
(1991) 5720. (d) W.F. Bailey, M.J. Mealy, J. Am. Chem. Soc.
122 (2000) 6787. (e) G.S. Gil, U.M. Groth, J. Am. Chem. Soc.
122 (2000) 6789.
[3] Review: I. Marek, J. Chem. Soc. Perkin Trans. 1 (1999) 535.
[4] (a) J.E. Baldwin, J. Chem. Soc. Chem. Commun. (1976) 734. (b)
Review: C.D. Johnson, Acc. Chem. Res. 26 (1993) 476.
[5] (a) S. Klein, I. Marek, J.-F. Normant, J. Org. Chem. 59 (1994)
2925. (b) S. Klein, I. Marek, J.-F. Poisson, J.-F. Normant, J.
Am. Chem. Soc. 117 (1995) 8853. (c) S. Norsikian, I. Marek,
J.-F. Poisson, J.-F. Normant, J. Org. Chem. 62 (1997) 4898. (d)
C. Mu¨ck-Lichtenfeld, H. Ahlbrecht, Tetrahedron 52 (1996)
10025.
[6] (a) D. Hoppe, F. Hintze, P. Tebben, Angew. Chem. 102 (1990)
1457. (b) Review: D. Hoppe, T. Hense, Angew. Chem. 109
(1997) 2376; Angew. Chem. Int. Ed. Engl. 36 (1997) 2282.
[7] (a) M.J. Woltering, R. Fro¨hlich, D. Hoppe, Angew. Chem. 109
(1997) 1804; Angew. Chem. Int. Ed. Engl. 36 (1997) 1764. (b)
M.J. Woltering, R. Fro¨hlich, B. Wibbeling, D. Hoppe, Synlett
1998, 797. (c) M.J. Woltering, M. Oestreich, R. Fro¨hlich, D.
Hoppe, Helv. Chim. Acta 82 (1999) 1860. (d) S.H. Kleinfeld, E.
Wegelius, D. Hoppe, Helv. Chim. Acta 82 (1999) 2413. (e) K.
Tomooka, N. Komine, T. Nakai, Tetrahedron Lett. 38 (1997)
8939. (f) K. Tomooka, N. Komine, T. Sasaki, H. Shimizu, T.
Nakai, Tetrahedron Lett. 39 (1998) 9715.
[8] The principle could also be applied to 5-alkynyl carbamates: D.
Hoppe, M. Oestreich, Tetrahedron Lett. 39 (1998) 1745.
[9] Asymmetric cyclocarbolithiation reactions, using classical ap-
proaches to generate the enantioenriched, open-chain lithium
intermediate: (a) I. Coldham, R. Hufton, D.J. Snowden, J. Am.
Chem. Soc. 118 (1996) 5322. (b) I. Coldham, J.-C. Ferna`ndez,
D.J. Snowden, Tetrahedron Lett. 40 (1999) 1819. (c) R.W.
Hoffmann, R. Koberstein, K. Harms, J. Chem. Soc. Perkin
Trans. 2 (1999) 183. (d) A. Krief, B. Kenda, B. Remacle,
Tetrahedron Lett. 36 (1995) 7917.
[10] Review: S. Masamune, W. Choy, J.S. Petersen, L.R. Sita,
Angew. Chem. 97 (1985) 1.
[11] Other examples for efficient kinetic resolutions: (a) J. Haller, T.
Hense, D. Hoppe, Synlett (1993) 726. (b) T. Hense, D. Hoppe,
Synthesis (1997) 1394.
2.15. (R) Mosher ester of (−)-15
Pyridine (0.1 ml) was added to 8 mg (0.04 mmol) of
the alcohol (−)-15 in 0.5 ml of dichloromethane. After
addition of 10 mg (0.04 mmol) of (R)-a-methoxy-a-tri-
fluoromethylphenylacetyl chloride, the mixture was
stirred for 24 h. Direct chromatographic separation
[diethyl ether–petroleum ether (1:4)] afforded 16 mg
(100%) of the Mosher ester of (−)-15 as a colourless oil.
ESI-HR-MS calc. for C23H33NO3+Na+: 427.1560.
Found: 427.1585. 1H-NMR (600 MHz): l=1.51 (s, 3H,
1-CH3); 1.56–1.71 (m, 2H, 7-H2); 1.82–1.96 (m, 2H,
8-H2); 2.43 (m, 1H, 5-H); 2.76 (m, 1H, 4-Hb); 3.35 (dd,
1H, 4-Ha); 3.57 (s, 3H, OCH3); 5.16 (m, 1H, 6-H);
7.10–7.58 (m, 9H, PhꢀH). 19F-NMR (564 MHz): l= −
71.85 (s, 3F, CF3). No second diastereomer could be
detected. ESI-MS (m/z (%)): 427 (100) [M++Na]; 171
(32) [(M−C10H8F3O3)+].
[12] The (−)-sparteine complex of lithiomethylindene delivers car-
bonyl adducts with high enantiomeric excesses, but all attempts
to achieve enantioselective alkylations have failed so far [13].
Despite that, (−)-sparteine was used, since better regioselectivi-
ties were observed in comparison to the lithium TMEDA
complex.
3. Supplementary material
Crystallographic data (excluding structure factors) for
the structural analysis have been deposited with the

104
H. Laqua et al. / Journal of Organometallic Chemistry 624 (2001) 96–104
[13] I. Hoppe, M. Marsch, K. Harms, G. Boche, D. Hoppe, Angew.
Chem. 107 (1995) 2328; Angew. Chem. Int. Ed. Engl. 34 (1995)
2158.
[14] F. Hintze, D. Hoppe, Synthesis (1992) 1216.
[15] J.A. Dale, D.L. Dull, H.S. Mosher, J. Org. Chem. 34 (1969)
2543.
refinement SHELXL-97 (G.M. Sheldrick, Universita¨t Go¨ttingen,
1997), graphics SCHAKAL (E. Keller, Universita¨t Freiburg, 1997).
[17] We have carried out PM3 calculations on the diastereomorphic
transition states and found a difference of DDH‡ of 2.6 kcal
mol−1 in favour of the observed reaction path. However, for the
sake of simplicity, the ligand (−)-sparteine was removed from
the model compounds.
[16] X-ray crystal structure analysis of (−)-13a: formula
C
21H29NO3, M=343.45, colourless crystal 0.25×0.20×0.10
[18] For benzylic substitution reactions see: (a) C. Derwing, D.
Hoppe, Synthesis (1996) 149. (b) A. Carstens, T. Kra¨mer, D.
Hoppe, Angew. Chem. (1990) 102, 1455. (c) P. Beak, A. Basu,
D.J. Gallagher, Y.S. Thayumanavan, Acc. Chem. Res. 29 (1996)
552. (d) F. Hammerschmidt, A. Hanninger, Chem. Ber. 128
(1995) 1069.
[19] (a) D. Hoppe, M. Paetow, F. Hintze, Angew. Chem. 105 (1993)
430; Angew. Chem. Int. Ed. Engl. 32 (1993) 394. (b) M. Paetow,
M. Kotthaus, M. Grehl, R. Fro¨hlich, D. Hoppe, Synlett (1994)
1034. (c) S. Norsikian, I. Marek, S. Klein, J.F. Poisson, J.F.
Normant, Chem. Eur. J. 5 (1999) 2055.
,
mm, a=7.267(2), b=10.064(2), c=13.385(3) A, i=94.51(2)°,
V=975.9(4) A , zcalc=1.169 g cm−3, v=6.13 cm−1, empirical
3
,
absorption correction via „ scan data (0.8625T50.941), Z=2,
monoclinic, space group P21 (no. 4), u=1.54178 A, T=223 K,
,
ꢀ/2q scans, 2274 reflections collected (−h, +k, 9l), [(sin q)/
u]=0.62 A−1, 2109 independent (Rint=0.017) and 1823 ob-
,
served reflections [I]2|(I)], 242 refined parameters, R=0.037,
wR =0.097, max. residual electron density 0.14 (−18) e A
2
−3
,
,
Flack parameter −0.1(3), positional disorder at 011, refined
with split positions (0.74(1): 0.26(1)), hydrogens calculated and
refined as riding atoms. Data set was collected with an Enraf–
Nonius CAD4 diffractometer. Programs used: data collection
EXPRESS (Nonius B.V., 1994), data reduction MOLEN (K. Fair,
Enraf–Nonius B.V., 1990), structure solution SHELXS-97 (G.M.
Sheldrick, Acta Crystallogr., Sect. A 46 (1990) 467), structure
[20] The configuration and the enantiomeric purity of (−)-18 or of
its precursors could not be assessed. In analogy to the cyclo-
propane 14, the proposed absolute configuration and a high
enantiomeric excess are most likely.
[21] The enantiomeric excess could not be determined.
.