Creation of quaternary stereocenters by the addition of allyltributyltin to chiral cyclic N-acyliminium ions

Article abstract of DOI:10.1016/S0957-4166(99)00537-6

5,5-Disubstituted pyrrolidinones and 5-substituted pyrrolidinones were obtained with moderate to good diastereoisomeric excess through the cis addition of allyltributyltin and triethylsilane, respectively, to the 4-OTBS group in the N-acyliminium ion prepared from the corresponding 5-hydroxy lactams. Cyclization of an N-allyl-5-propargyl pyrrolidinone and N-allyl-5-allyl-5-substituted pyrrolidinones using Grubbs' catalyst led to the preparation of a dehydropyrrolizinone and dehydroindolizinones containing a quaternary stereocenter. Copyright (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0957-4166(99)00537-6

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 11 (2000) 753–764
Creation of quaternary stereocenters by the addition of
allyltributyltin to chiral cyclic N-acyliminium ions
Cristina Maria Schuch and Ronaldo Aloise Pilli ∗
Instituto de Química, UNICAMP, PO Box 6154, Campinas, SP 13081-970, Brazil
Received 18 October 1999; accepted 17 November 1999
Abstract
5,5-Disubstituted pyrrolidinones and 5-substituted pyrrolidinones were obtained with moderate to good dia-
stereoisomeric excess through the cis addition of allyltributyltin and triethylsilane, respectively, to the 4-OTBS
group in the N-acyliminium ion prepared from the corresponding 5-hydroxy lactams. Cyclization of an N-
allyl-5-propargyl pyrrolidinone and N-allyl-5-allyl-5-substituted pyrrolidinones using Grubbs’ catalyst led to the
preparation of a dehydropyrrolizinone and dehydroindolizinones containing a quaternary stereocenter. © 2000
Elsevier Science Ltd. All rights reserved.
1. Introduction
Despite the great interest in the asymmetric construction of molecules with quaternary stereocenters,1,2
there are few methods available to prepare compounds containing four different non-hydrogen sub-
stituents at the α-nitrogen position of 5- and 6-membered nitrogen heterocycles. The methodology
developed by Meyers and Burgess3 afforded GABA analogues and 2,2-disubstituted pyrrolidines with
good diastereoselectivities. The alkylation of tricyclic N,O-acetals with some organometallic reagents
was utilized for the synthesis of the core ring of the alkaloid FR901483.4 The construction of α-nitrogen
spiro rings through the reduction of hydroxy amides derived from 5- and 6-membered imides was
successfully achieved by Speckamp and Schoemaker5 for the synthesis of perhydrohistrionicotoxin.
The addition of Grignard reagents to chiral imide derivatives from tartaric acid, followed by the
reduction with Et3SiH mediated by BF3·OEt2, has been extensively studied by Yoda et al.6–10 and
applied in the synthesis of some indolizidine alkaloids. In spite of high levels of diastereoselection
observed in the reduction of N-acyliminium ion derived from tartaric and malic acids,11 to the best of our
knowledge, efforts regarding the creation of a quaternary stereocenter through the addition of a second
carbon nucleophile have not been reported.
∗
Corresponding author. Fax: 55 19 7883023; e-mail: pilli@iqm.unicamp.br
0957-4166/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(99)00537-6
tetasy 3172

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We report here the results for the addition of organolithium species to chiral imide derivatives from tar-
taric acid and the transformation of the resulting α-hydroxy quaternary lactams in highly functionalized
5,5-disubstituted pyrrolidinones.12 For this purpose we employed BF3·OEt2 to promote the formation of
N-acyliminium ions13,14 and allyltributyltin as the nucleophile. We also carried out a systematic study on
the reduction of α-hydroxy quaternary pyrrolidinones to afford 5-acetylenic and 5-alkylated lactams. Our
results include the synthesis of a dehydropyrrolizinone ring and some dehydroindolizinones containing
an α-nitrogen quaternary stereocenter by ring-closing metathesis (RCM) of olefins15,16 and an enyne17,18
promoted by Grubbs’ catalyst.
2. Results and discussion
Imides 1 and 2 were readily obtained from tartaric acid in 63 and 83% yields, respectively, after five
steps. Addition of organolithium to chiral imides 1 and 2 in THF at −78°C afforded α-hydroxy lactams
3a–i as diastereoisomeric mixtures, which were used in the next step without purification. The addition
of allyltributyltin, mediated by BF3·OEt2, afforded 5,5-disubstituted pyrrolidinones 5a–d and 5g–j in
36–66% yields from imides 1 and 2 (Scheme 1). Using the same procedure, the addition of triethylsilane
mediated by BF3·OEt2 afforded 5-substituted pyrrolidinones 5e–f and 5k–n in 50–66% yields after two
steps (Scheme 1).
Scheme 1. (a) R1–Li, THF, −78°C; (b) BF3·OEt2, CH2Cl2, −78°C; (c) allyltributyltin (R2=allyl) or Et3SiH (R2=H), −78°C to
0°C
The addition of methyllithium, butyllithium, and lithium acetylides to imides 1 and 2, followed by
allyltributyltin to the corresponding N-acyliminium ion 4, resulted in 5,5-disubstituted pyrrolidinones

C. M. Schuch, R. A. Pilli / Tetrahedron: Asymmetry 11 (2000) 753–764
755
5a–d and 5g–j (Table 1, entries 1–4 and 7–10) in good yields and moderate diastereoselectivities,
except for n-butyllithium which afforded a single diastereoisomer (entries 2 and 8). The addition of
n-butyllithium to imides 1 and 2, followed by reduction, afforded 5-butyl pyrrolidinones 5e and 5k in 89
and 80% d.e., respectively (entries 5 and 11, Table 1), while the addition of lithium acetylides afforded 5-
acetylenic pyrrolidinones (entries 6 and 12–14) with excellent diastereoselectivity and moderate to good
yields.
Table 1
Addition of allyltributyltin and Et3SiH to chiral cyclic N-acyliminium ions 4a–i
The stereochemical assignment of 5,5-disubstituted pyrrolidinones 5a–d and 5g–j was carried out
using NOE studies, as illustrated for compound 5b in Scheme 2: irradiation of one of the allylic hydrogens
led to a 1.0% increment in the H4 signal and a 1.2% increment in the H3 signal. Accordingly, irradiation
of the methyl group at C5 of 5g led to a 2.3% increment in the H4 signal and no increment in the H3
signal.
Scheme 2.

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The cis relative stereochemistry between the OTBS group at C4 and the allyl group at C5 in 5b was
unambiguously established after its conversion to 6b, as depicted in Scheme 3.
Scheme 3. (a) (i) O3/O2, MeOH, −78°C; (ii) DMS, 12 h, rt; (b) HF/MeCN, 5 h, rt (80%, two steps); (c) Et3SiH, BF3·OEt2,
CH2Cl2, −78°C; (d) TBSCl, im., DMF, rt, 5 h (62%, two steps)
The trans stereochemistry of 5-butyl pyrrolidinones 5e and 5k was assigned according to the observ-
ed vicinal coupling constants (J4,5=2.0 and 2.4 Hz, respectively), as described by Yoda et al.8 The
stereochemistry for compounds 5f and 5l–n was assigned from NOE studies which provided higher
increments in the H3 signal rather than in the H4 signal upon irradiation of H5, as depicted for 5m
(Scheme 2). The unexpected increase in the J3,4 and J4,5 values observed for compounds 5f and 5l–n
was assigned to a conformational change in the pyrrolidinone ring due to the relief, in these cases, of the
steric interactions between the nitrogen protecting group and the n-butyl side chain present in 5e and 5k.
Such conformational change is supported by the deshielding effect observed for H3, H4 and H5 signals
in 5-trans-acetylenic pyrrolidinones (5f and 5l–n) relative to 5-trans-butyl pyrrolidinones (5e and 5k).
Additionally, H4 is less shielded than H3 in 5f and 5l–n, in contrast to the behavior observed for 5e and
5k. Accordingly, the hydrogenation of 5l (J3,4=J4,5=6.3 Hz) afforded the corresponding perhydrolactam
with coupling constants for the carbinolic protons (J3,4=J4,5=2.4 Hz) in the same range as observed for
5e and 5k.
Several studies in the literature report on the preferential cis addition of nucleophiles to N-acyliminium
ions 4, revealing that the stereochemical outcome is not ruled by steric effects. Although the reasons for
this unexpected approach remain unknown,8 a stereoelectronic effect analogous to the one proposed by
Cieplak19 and others20,21 may not be ruled out at this moment.22
We have observed the same stereochemical preference in the addition of triethylsilane and allyltribu-
tyltin to N-acyliminium ions 4a–i. A comparison among the products with a quaternary stereocenter
at C5 showed that best selectivities were attained with 5-n-butyl-substituted N-acyliminium ions, in
contrast to 5-methyl and 5-acetylenic substituted ones. Additionally, N-benzyl protected N-acyliminium
ions were more selective than the N-allyl protected ones. These results led us to invoke the allylic A1,3
strain involving the substituent at C5 and the nitrogen protecting group as a control element favoring
the cis approach of the nucleophile in 4b and 4f due to an additional steric hindrance of the si face, as
depicted in Scheme 4. In cases where this effect is less important, the cis approach of the nucleophile
occurred with lower diastereoselection.
Good to excellent diastereoselection was observed in the reduction of 5-acetylenic N-acyliminium
ions with the sterically more demanding triethylsilane, in accordance with previous reports in the
literature.6–11
N-Allyl-5-allyl pyrrolidinones 5g–i were submitted to ring-closing metathesis with Grubbs’ catalyst
(4 mol%) at room temperature to afford dehydroindolizinones 7a–e in moderate to good yields (Scheme
5). The stereochemistry of the major diastereoisomer 7a obtained from a 2:1 mixture of 5g and its C5
epimer was confirmed by NOE experiments: the irradiation of the angular methyl group at C8a led to a
2.0% increment in the H1 signal and no increment in the H2 signal.

C. M. Schuch, R. A. Pilli / Tetrahedron: Asymmetry 11 (2000) 753–764
757
Scheme 4.
Scheme 5.
The enyne metathesis protocol was applied to 5n to afford the highly functionalized dehydropyrrolizi-
none 7f in 78% yield as a single stereoisomer (Scheme 6).
Scheme 6.
However, when pyrrolidinone 5l was submitted to the same conditions the starting material was
recovered in almost quantitative yield, probably due to severe steric strain which develops in the
formation of the intermediate metalacycle required in the reaction mechanism.
3. Conclusion
The BF3·OEt2 promoted addition of allyltributyltin to α-hydroxy lactams 3a–i, prepared from the
reaction of alkyl or alkynyl lithium reagents and imides 1 and 2, occurred cis to the 4-OTBS group to
afford 5,5-disubstituted pyrrolidinones 5a, 5c–d and 5g, 5i–j with moderate diastereoisomeric excess
(33–67%), except for 5b and 5h where a single diastereoisomer was formed (d.e. >95%). The same
stereochemical trend was observed in the triethylsilane reduction of 3b, 3c, and 3f–i mediated by
BF3·OEt2, in accordance with previous reports in the literature.6–11 The relative stereochemistry of

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C. M. Schuch, R. A. Pilli / Tetrahedron: Asymmetry 11 (2000) 753–764
1
the major pyrrolidinones was assigned by H NMR spectroscopy (NOE studies) and for 5b upon its
conversion to the corresponding oxa-azabicyclo[3.3.0]octan-3-one 6b. N-Allyl-5,5-disubstituted pyrroli-
dinones 5g–i and enyne 5n were submitted to ring-closing metathesis with Grubbs’ catalyst to afford the
corresponding bicyclic compounds 7a–f in good yields.
Studies are underway to synthesize 5,5-disubstituted pyrrolidinones derived from malic acid in order
to investigate their utilization in the total synthesis of natural compounds.
4. Experimental
4.1. General
All solvents and reagents were purchased from commercial suppliers and used as received, unless
otherwise indicated. Imide 1 was synthesized from L-(+)-tartaric acid as indicated in the literature.7
Imide 2 was synthesized from D-(−)-tartaric acid as a colorless oil, in 83% overall yield. Commercial
solutions of nBuLi (2.5 M in hexane) and MeLi (1.0 M in ether) were employed. Tetrahydrofuran (THF)
and toluene were distilled from Na–benzophenone ketyl. Dichloromethane was distilled from calcium
hydride. All reactions were performed under a positive argon pressure. The normal processing of organic
extracts consisted of drying over MgSO4, filtration and concentration with a rotary evaporator. 1H NMR
and 13C NMR data were recorded on a Varian Gemini 300, Bruker AC 300P (7.05 T) or Varian Inova
1
(11.7 T) spectrometer. Chemical shifts are reported in δ ppm relative to (CH3)4Si for H and CDCl3
for 13C NMR. Coupling constants J are reported in hertz. IR spectra were obtained on Nicolet Impact
410 FT (film and KBr). High resolution mass spectra (HRMS) were measured on a VG Autospec-
Micromass spectrometer. Chromatographic separations were performed using 70–230 or 230–400 mesh
(E. Merck) silica gel. Thin-layer chromatography was carried out on Macherey–Nagel precoated silica
plates (0.25 mm layer thickness). GC analyses were performed with a HP-5890 chromatograph with a
HP-5 (30 m×0.53 mm×1.3 µm) column. Optical rotations were measured at 25°C with a Polamat A
instrument at the mercury line and converted to the values for the sodium D line (rotation at the Hg
line=1.17 543×rotation at the Na line).
4.2. General procedure for the addition of organolithium to imides 1 and 2
4.2.1. Synthesis of hydroxylactams 3a–i
To a solution of organolithium reagent (0.7 mmol) in THF (1 mL) at −78°C was added a solution of
imide 1 or 2 (0.35 mmol) in THF (1 mL) dropwise. After complete consumption of the imide, the reaction
was quenched with H2O (1 mL) and the mixture was allowed to stir for 10 min at room temperature, when
it was diluted with CH2Cl2 (10 mL) and washed with brine (5 mL). The organic phase was dried over
MgSO4, filtered, and the solvent was removed under reduced pressure. The resultant oil was employed
in the next step without further purification.
4.2.2. General procedure for the synthesis of 5,5-disubstituted pyrrolidinones 5a–d and 5g–j
To a solution of hydroxylactam 3a–i (0.35 mmol) in CH2Cl2 (3.5 mL), under an argon atmosphere
at −78°C, was added allyltributyltin (0.42 mL, 1.4 mmol) followed by BF3·OEt2 (0.08 mL, 0.7 mmol)
dropwise. Stirring was continued for 15 min at −78°C, followed by 2 h at 0°C. The reaction was quenched
with 10% aq. KF solution (2 mL) and allowed to stir 1 h at rt. The mixture was diluted with CH2Cl2 (10
mL) and washed with brine (5 mL), dried over MgSO4, and the solvent was removed under reduced

C. M. Schuch, R. A. Pilli / Tetrahedron: Asymmetry 11 (2000) 753–764
759
pressure. Purification by column chromatography on silica gel (4% EtOAc/hexane, v/v) afforded 5,5-
disubstituted pyrrolidinones 5a–d and 5g–j as colorless oils (Table 1).
4.2.2.1. (3R,4S,5R)-3,4-Bis[(tert-butyldimethylsilyl)oxy]-1-benzyl-5-allyl-5-methyl-2-pyrrolidinone.
Colorless oil; 45% yield as a 3:1 mixture. Data for the major isomer 5a: 1H NMR (300 MHz): 0.09 (s,
3H), 0.15 (s, 3H), 0.18 (s, 3H), 0.24 (s, 3H), 0.93 (s, 9H), 0.95 (s, 9H), 1.12 (s, 3H), 2.21 (dd, J=7.3 and
14.2, 1H), 2.36 (dd, J=7.3 and 14.2, 1H), 3.90 (d, J=7.1, 1H), 4.16 (d, J=15.4, 1H), 4.36 (d, J=7.1, 1H),
4.72 (d, J=15.4, 1H), 4.95 (dd, J=2.0 and 17.3, 1H), 5.04 (dd, J=2.0 and 10.3, 1H), 5.72 (m, 1H), 7.27
(m, 5H). 13C NMR (75.5 MHz): −4.7, −4.3, −3.8, −3.7, 17.9, 18.4, 25.8, 25.9, 26.0, 39.3, 43.2, 64.3,
76.4, 83.0, 119.3, 127.1, 127.8, 128.4, 133.6, 138.6, 171.6. IR (film, cm−1): 3076, 3030, 2954, 2929,
2856, 1709. HRMS C27H47NO3Si2 (M+−C4H9, calcd): 432.23903; (M+−C4H9, found): 432.23903.
4.2.2.2. (3R,4S,5R)-3,4-Bis[(tert-butyldimethylsilyl)oxy]-1-benzyl-5-allyl-5-n-butyl-2-pyrrolidinone 5b.
1
Colorless oil; 65% yield. H NMR (300 MHz): 0.09 (s, 3H), 0.15 (s, 3H), 0.19 (s, 3H), 0.24 (s, 3H),
0.69 (t, J=7.0, 3H), 0.92 (s, 9H), 0.95 (s, 9H), 0.87–0.96 (m, 4H), 1.40–1.55 (m, 2H), 2.15 (dd, J=7.7
and 14.3, 1H), 2.43 (dd, J=6.6 and 14.3, 1H), 4.05 (d, J=6.6, 1H), 4.19 (d, J=15.4, 1H), 4.36 (d, J=6.6,
1H), 4.55 (d, J=15.4, 1H), 4.84 (dd, J=1.5 and 19.0, 1H), 4.98 (dd, J=1.5 and 10.3, 1H), 5.64 (m, 1H),
7.27 (m, 5H). 13C NMR (75.5 MHz): −4.7, −4.4, −4.0, −3.7, 13.7, 17.9, 18.4, 22.6, 25.5, 25.8, 26.0,
36.5, 39.1, 43.6, 67.3, 76.9, 78.5, 119.2, 127.3, 128.4, 128.7, 133.9, 138.6, 172.5. IR (film, cm−1): 3078,
2954, 2929, 2853, 1709. HRMS C30H53NO3Si2 (M+−C4H9, calcd): 474.28598; (M+−C4H9, found):
474.28603. [α]D=+64.9 (c 1.18, CHCl3).
4.2.2.3. (3R,4S,5S)-3,4-Bis[(tert-butyldimethylsilyl)oxy]-1-benzyl-5-allyl-5-(2-phenyl-1-ethynyl)-2-pyr-
rolidinone. Colorless oil; 56% yield as a 4:1 mixture. Major isomer 5c was isolated by column
chromatography on silica gel (4% EtOAc/hexane, v/v). 1H NMR (300 MHz): 0.16 (s, 3H), 0.18 (s, 3H),
0.23 (s, 3H), 0.24 (s, 3H), 0.95 (s, 18H), 2.56 (dd, J=6.6 and 14.3, 1H), 2.60 (dd, J=7.3 and 14.3, 1H), 4.35
(d, J=7.8, 1H), 4.47 (d, J=7.8, 1H), 4.65 (d, J=2.0, 2H), 4.84 (dd, J=1.8 and 17.2, 1H), 5.04 (dd, J=1.8
and 10.2, 1H), 5.70 (m, 1H), 7.30 (m, 10H). 13C NMR (75.5 MHz): −4.7, −4.5, −4.1, −3.9, 17.8, 18.2,
25.7, 25.8, 40.1, 44.8, 62.8, 75.4, 82.9, 86.9, 89.1, 120.3, 122.0, 127.3, 128.3, 128.4, 128.7, 131.6, 132.5,
138.0, 170.8. IR (film, cm−1): 3408, 3080, 3030, 2954, 2929, 2856, 2229, 1714. HRMS C34H49NO3Si2
(M+−C4H9, calcd): 518.25468; (M+−C4H9, found): 518.25461. [α]D=+24.1 (c 1.06, CHCl3).
4.2.2.4. (3R,4S,5S)-3,4-Bis[(tert-butyldimethylsilyl)oxy]-1-benzyl-5-allyl-5-[(tert-butyldimethylsilyl)-
oxy]propargyl-2-pyrrolidinone. Colorless oil; 36% yield as a 5:1 mixture. Data for the major isomer
5d: 1H NMR (300 MHz): 0.12 (s, 6H), 0.17 (s, 3H), 0.19 (s, 3H), 0.23 (s, 3H), 0.25 (s, 3H), 0.93 (s, 9H),
0.96 (s, 9H), 0.97 (s, 9H), 2.41 (dd, J=7.0 and 14.3, 1H), 2.55 (dd, J=7.0 and 14.3, 1H), 4.26 (s, 2H), 4.31
(d, J=7.7, 1H), 4.36 (d, J=7.7, 1H), 4.50 (d, J=15.0, 1H), 4.73 (d, J=15.0, 1H), 5.00 (dd, J=1.8 and 12.1,
1H), 5.09 (m, 1H), 5.60 (m, 1H), 7.29 (m, 5H). 13C NMR (75.5 MHz): −5.3, −4.6, −4.5, −4.0, −3.9,
17.9, 18.2, 18.3, 25.7, 25.8, 40.0, 44.7, 51.4, 62.6, 75.3, 82.7, 84.3, 85.8, 120.2, 127.3, 128.3, 128.9,
132.3, 137.9, 170.6. IR (film, cm−1): 3502, 3064, 3032, 2960, 2929, 2856, 1716. HRMS C35H61NO4Si3
(M+−C4H9, calcd): 586.32042; (M+−C4H9, found): 586.32034.

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C. M. Schuch, R. A. Pilli / Tetrahedron: Asymmetry 11 (2000) 753–764
4.2.2.5. (3S,4R,5S)-3,4-Bis[(tert-butyldimethylsilyl)oxy]-1,5-diallyl-5-methyl-2-pyrrolidinone.
Colorless oil; 65% yield as a 2:1 mixture. Major isomer 5g was isolated by column chromatography on
1
silica gel (4% EtOAc/hexane, v/v): H NMR (500 MHz): 0.13 (s, 3H), 0.15 (s, 3H), 0.16 (s, 3H), 0.21
(s, 3H), 0.94 (s, 9H), 0.95 (s, 9H), 1.27 (s, 3H), 2.25 (dd, J=7.6 and 14.2, 1H), 2.40 (dd, J=7.3 and 14.2,
1H), 3.68 (dd, J=6.1 and 15.9, 1H), 3.89 (d, J=7.3, 1H), 4.00 (ddt, J=1.5, 5.6 and 15.9, 1H), 4.30 (d,
J=7.3, 1H), 5.13 (m, 4H), 5.80 (m, 2H). 13C NMR (75.5 MHz): −4.3, −4.2, −3.8, −3.7, 18.0, 18.4, 25.7,
25.9, 26.0, 39.6, 42.5, 63.9, 76.2, 83.2, 116.7, 119.3, 133.7, 134.4, 171.0. IR (film, cm−1): 3080, 2954,
2924, 2853, 1709, 1641. HRMS C23H45NO3Si2 (M+−C4H9, calcd): 382.22338; (M+−C4H9, found):
382.22325. [α]D=−60.8 (c 0.56, CHCl3).
4.2.2.6. (3S,4R,5S)-3,4-Bis[(tert-butyldimethylsilyl)oxy]-1,5-diallyl-5-n-butyl-2-pyrrolidinone 5h.
Colorless oil; 66% yield. 1H NMR (300 MHz): 0.12 (s, 3H), 0.16 (s, 6H), 0.20 (s, 3H), 0.88–1.00 (s, br,
21H), 1.2–1.6 (m, 6H), 2.17 (dd, J=14.3 and 8.0, 1H), 2.46 (dd, J=14.3 and 7.0, 1H), 3.77 (t, br, J=6.6,
2H), 4.04 (d, J=7.0, 1H), 4.31 (d, J=7.0, 1H), 5.07 (dd, J=14.3 and 1.8, 2H), 5.13 (dd, J=10.2 and 1.5,
1H), 5.18 (dd, J=17.2 and 1.5, 1H), 5.7–5.9 (m, 2H). 13C NMR (75.5 MHz): −4.7, −4.4, −4.0, −3.7,
13.8, 17.8, 18.3, 22.6, 25.3, 25.8, 26.0, 36.0, 39.5, 43.0, 66.6, 76.7, 78.6, 116.9, 119.2, 134.0, 134.3,
171.7. IR (film, cm−1): 3078, 2954, 2929, 2853, 1709, 1641. HRMS C26H51NO3Si2 (M+−C4H9, calcd):
424.74980; (M+−C4H9, found): 424.74956. [α]D=−57.5 (c 2.81, CHCl3).
4.2.2.7. (3S,4R,5R)-3,4-Bis[(tert-butyldimethylsilyl)oxy]-1,5-diallyl-5-(2-phenyl-1-ethynyl)-2-pyrrol-
idinone. Colorless oil; 63% yield as a 2.6:1 mixture. Data for the major isomer 5i: 1H NMR (500 MHz):
0.15 (s, 3H), 0.18 (s, 3H), 0.22 (s, 3H), 0.25 (s, 3H), 0.94 (s, 9H), 0.96 (s, 9H), 2.67 (dd, J=7.6 and 16.6,
1H), 2.72 (m, 1H), 4.06 (m, 2H), 4.28 (d, J=7.8, 1H), 4.44 (d, J=7.8, 1H), 5.16 (m, 4H), 5.92 (m, 2H),
7.32 (m, 5H). 13C NMR (125.5 MHz): −4.6, −4.4, −3.9, −3.8, 18.0, 18.3, 25.8 25.9, 40.3, 44.4, 62.6,
75.3, 82.8, 86.3, 89.0, 117.4, 120.3, 122.1, 128.4, 128.7, 131.4, 132.6, 133.6, 170.2. IR (film, cm−1):
3080, 2954, 2929, 2865, 1722, 1643. HRMS C30H47NO3Si2 (M+−C4H9, calcd): 468.23903; (M+−C4H9,
found): 468.23929.
4.2.2.8. (3S,4R,5R)-3,4-Bis[(tert-butyldimethylsilyl)oxy]-1,5-diallyl-5-[(tert-butyldimethylsilyl)oxy]-
propargyl-2-pyrrolidinone. Colorless oil; 48% yield as a 2.7:1 mixture. Data for the major isomer 5j:
1H NMR (300 MHz): 0.11 (s, 6H), 0.13 (s, 3H), 0.17 (s, 3H), 0.20 (s, 3H), 0.21 (s, 3H), 0.91 (s, 9H),
0.93 (s, 9H), 0.96 (s, 9H), 2.57 (d, J=7.3, 2H), 3.96 (m, 2H), 4.23 (d, J=7.7, 1H), 4.32 (d, J=7.7 Hz, 1H),
4.34 (s, 2H), 5.17 (m, 4H), 5.83 (m, 2H). 13C NMR (75.5 MHz): −5.2, −4.5 −4.4, −4.1, −3.9, −3.8,
17.9, 18.2, 18.3, 25.7, 25.8, 25.9, 40.1, 44.2, 51.5, 62.2, 75.3, 82.7, 84.3, 85.1, 117.4, 120.3, 132.6, 133.6,
170.1. IR (film, cm−1): 3080, 2954, 2929, 2865, 1722, 1643. HRMS C31H59NO4Si3 (M+−C4H9, calcd):
536.30477; (M+−C4H9, found): 536.30461.
4.2.3. Reduction of hydroxy lactams 3a–i with Et3SiH, mediated by BF3·OEt2
To a solution of hydroxylactam 3a–i (0.35 mmol) in CH2Cl2 (3.5 mL), under an argon atmosphere at
−78°C, was added Et3SiH (0.20 mL, 1.4 mmol) followed by BF3·OEt2 (0.08 mL, 0.70 mmol) dropwise.
Stirring was continued for 15 min at −78°C, followed by 30 min at 0°C. The reaction was quenched
with H2O (1 mL) and extracted with CH2Cl2 (2×5 mL). The organic phase was washed with brine (5
mL), dried over MgSO4, and the solvent was removed under reduced pressure. Purification by column
chromatography on silica gel (8% EtOAc/hexane, v/v) afforded pyrrolidinones 5e–f and 5k–n (Table 1).

C. M. Schuch, R. A. Pilli / Tetrahedron: Asymmetry 11 (2000) 753–764
761
4.2.3.1. (3R,4S,5S)-3,4-Bis[(tert-butyldimethylsilyl)oxy]-1-benzyl-5-n-butyl-2-pyrrolidinone.
1
Colorless oil; 61% yield as a 17:1 mixture. Data for the major isomer 5e: H NMR (500 MHz):
0.00 (s, 3H), 0.09 (s, 3H), 0.20 (s, 3H), 0.22 (s, 3H), 0.85 (s, 9H), 0.94 (s, 9H), 0.90 (t, J=7.0, 3H),
1.2–1.3 (m, 4H), 1.6–1.7 (m, 2H), 3.15 (ddd, J=2.0, 2.9 and 4.5, 1H), 3.85 (t, J=2.0, 1H), 3.91 (d, J=15.4,
1H), 4.03 (d, J=2.0, 1H), 5.09 (d, J=15.4, 1H), 7.28 (m, 5H). 13C NMR (75.5 MHz): −5.2, −4.9, −4.7,
−4.5, 13.8, 17.7, 18.0, 22.6, 25.5, 25.7, 27.1, 29.7, 43.8, 64.6, 75.6, 78.4, 127.4, 127.8, 128.6, 136.4,
172.3. IR (film, cm−1): 3064, 3030, 2954, 2924, 2856, 1705. HRMS C27H49NO3Si2 (M+−C4H9, calcd):
434.74500; (M+−C4H9, found): 434.74508.
4.2.3.2. (3R,4S,5R)-3,4-Bis[(tert-butyldimethylsilyl)oxy]-1-benzyl-5-(2-phenyl-1-ethynyl)-2-pyrroli-
dinone 5f. Colorless oil; 62% yield. 1H NMR (300 MHz): 0.15 (s, 3H), 0.17 (s, 3H), 0.18 (s, 3H), 0.26
(s, 3H), 0.89 (s, 9H), 0.96 (s, 9H), 4.00 (d, J=6.1, 1H), 4.16 (d, J=14.6, 1H), 4.19 (d, J=6.4, 1H), 4.32
(dd, J=6.1 and 6.4, 1H), 5.12 (d, J=14.7, 1H), 7.36 (m, 10H). 13C NMR (75.5 MHz): −4.7, −4.5, −4.1,
−4.0, 17.8, 18.3, 25.7, 25.8, 44.3, 53.6, 77.2, 80.4, 84.6, 87.4, 122.0, 127.6, 128.4, 128.5, 128.7, 128.8,
131.6, 136.1, 170.3. IR (film, cm−1): 3061, 3032, 2954, 2930, 2856, 2225, 1716. HRMS C31H45NO3Si2
(M+−C4H9, calcd): 478.22338; (M+−C4H9, found): 478.22337. [α]D = +58.4 (c 2.77, CHCl3).
4.2.3.3. (3S,4R,5S)-3,4-Bis[(tert-butyldimethylsilyl)oxy]-1-allyl-5-n-butyl-2-pyrrolidinone. Colorless
oil; 60% yield as a 9:1 mixture. Data for the major isomer 5k: 1H NMR (500 MHz): 0.08 (s, 3H), 0.10
(s, 3H), 0.16 (s, 3H), 0.17 (s, 3H), 0.88 (s, 9H), 0.90 (s, 9H), 0.92 (t, J=7.1, 3H), 1.31 (m, 4H), 1.61 (m,
2H), 3.28 (m, 1H), 3.42 (dd, J=6.8 and 15.9, 1H), 3.84 (t, J=2.4, 1H), 3.97 (d, J=2.4, 1H), 4.36 (ddd,
J=2.0, 4.4 and 16.0, 1H), 5.15 (dq, J=1.2 and 10.4, 1H), 5.20 (dq, J=2.0 and 17.0, 1H), 5.70 (m, 1H).
13C NMR (125.5 MHz): −5.2, −4.8, −4.5, −4.4, 13.8, 17.7, 18.0, 22.6, 25.5, 25.7, 27.0, 29.8, 42.6,
64.6, 76.1, 78.4, 117.3, 132.4, 171.9. IR (film, cm−1): 3082, 2954, 2929, 2858, 1705, 1645. HRMS
C23H47NO3Si2 (M+−C4H9, calcd): 384.68520; (M+−C4H9, found): 384.68400.
4.2.3.4. (3S,4R,5R)-3,4-Bis[(tert-butyldimethylsilyl)oxy]-1-allyl-5-(2-phenyl-1-ethynyl)-2-pyrrolidin-
1
one 5l. Colorless oil; 66% yield. H NMR (500 MHz): 0.17 (s, 3H), 0.18 (s, 3H), 0.22 (s, 3H), 0.24
(s, 3H), 0.94 (s, 9H), 0.95 (s, 9H), 3.71 (dd, J=7.6 and 15.1, 1H), 4.19 (d, J=6.3, 1H), 4.21 (d, J=6.3,
1H), 4.31 (t, J=6.3, 1H), 4.45 (ddt, J=1.5, 4.6 and 15.1, 1H), 5.26 (m, 2H), 5.78 (m, 1H), 7.3–7.4 (m,
5H). 13C NMR (125.5 MHz): −4.8, −4.4, −4.1, −4.0, 17.9, 18.2, 25.7, 25.8, 43.1, 53.8, 77.1, 80.5, 84.6,
87.0, 118.7, 122.0, 128.4, 128.8, 131.6, 131.7, 170.1. IR (film, cm−1): 3082, 2954, 2929, 2856, 2225,
1720, 1645. HRMS C27H43NO3Si2 (M+−C4H9, calcd): 428.20773; (M+−C4H9, found): 428.20774.
[α]D=+5.6 (c 1.51, CHCl3).
4.2.3.5. (3S,4R,5R)-3,4-Bis[(tert-butyldimethylsilyl)oxy]-1-allyl-5-(2-trimethylsilyl-1-ethynyl)-2-pyr-
rolidinone 5m. Colorless oil; 50% yield. 1H NMR (500 MHz): 0.15 (s, 3H), 0.16 (s, 3H), 0.18 (s, 9H),
0.19 (s, 3H), 0.21 (s, 3H), 0.92 (s, 9H), 0.94 (s, 9H), 3.60 (dd, J=7.8 and 15.1, 1H), 3.93 (d, J=6.3, 1H),
4.14 (d, J=6.6, 1H), 4.20 (dd, J=6.3 and 6.6, 1H), 4.39 (ddt, J=1.5, 4.9 and 15.1, 1H), 5.20 (dd, J=1.5 and
10.0, 1H), 5.23 (dd, J=1.5 and 14.2, 1H), 5.73 (m, 1H). 13C NMR (125.5 MHz): −4.8, −4.4, −4.1, −4.0,
−0.37, 17.9, 18.2, 25.8, 43.0, 53.8, 77.1, 80.5, 92.6, 100.8, 118.8, 131.6, 170.0. IR (film, cm−1): 3311,
3238, 3084, 2956, 2930, 2858, 2177, 1722, 1645. HRMS C24H47NO3Si3 (M+−C4H9, calcd): 424.21595;
(M+−C4H9, found): 424.21596. [α]D=+4.4 (c 1.95, CHCl3).

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C. M. Schuch, R. A. Pilli / Tetrahedron: Asymmetry 11 (2000) 753–764
4.2.3.6. (3S,4R,5R)-3,4-Bis[(tert-butyldimethylsilyl)oxy]-1-allyl-5-[(tert-butyldimethylsilyl)oxy]-
1
propargyl-2-pyrrolidinone 5n. Colorless oil; 52% yield. H NMR (300 MHz): 0.11 (s, 6H), 0.15 (s,
6H), 0.18 (s, 3H), 0.21 (s, 3H), 0.91 (s, 18H), 0.93 (s, 9H), 3.59 (dd, J=7.6 and 15.4, 1H), 3.99 (d,
br, J=5.6, 1H), 4.13 (d, J=6.2, 1H), 4.18 (dd, J=6.2 and 5.6, 1H), 4.35 (d, J=1.5, 2H), 4.41 (dd, J=4.6
and 15.4, 1H), 5.19 (m, 2H), 5.69 (m, 1H). 13C NMR (75.5 MHz): −5.4, −4.9, −4.6, −4.3, 17.7, 18.1,
25.6, 25.8, 42.9, 51.5, 53.5, 77.2, 80.1, 80.2, 85.8, 118.6, 131.6, 170.3. IR (film, cm−1): 3084, 2954,
2936, 2858, 2177, 1728. HRMS C28H55NO4Si3 (M+−C4H9, calcd): 496.27347; (M+−C4H9, found):
496.27340. [α]D=−11.2 (c 1.52, CHCl3).
4.3. Synthesis of (4R,7R,8S)-4-n-Butyl-5-benzyl-7-[(tert-butyldimethylsilyl)oxy]-1-oxa-5-azabicyclo-
[3.3.0]octan-6-one 6b
A solution of 5b (0.097 g, 0.18 mmol) in MeOH (4 mL) was treated with O3/O2 stream at −78°C for
2 h. After argon purging, methyl sulfide (0.3 mL) was added to the colorless solution, stirred overnight,
and evaporated to give an oil. This crude mixture was diluted with 3 mL of CH3CN and a 40% aqueous
solution of HF was added (0.3 mL). The mixture was vigorously stirred for 6 h at room temperature.
After neutralization with solid KHCO3 the organic layer was separated, dried over MgSO4, and the
solvent evaporated at reduced pressure. Lactol 6a was obtained as a white powder (0.042 g, 0.14 mmol)
in 80% yield and used in the next step without further purification. To a solution of 6a (0.14 mmol) in
dry CH2Cl2 under an argon atmosphere at −78°C was added Et3SiH (0.05 mL, 0.35 mmol) followed by
BF3·OEt2 (0.02 mL, 0.18 mmol) dropwise. Stirring was continued for 1 h. The reaction was quenched
with H2O (0.5 mL) and extracted with CHCl3 (3×5 mL). The organic phase was dried over MgSO4
and the solvent was removed under reduced pressure. The crude oil was dissolved in DMF (0.5 mL),
imidazole (0.010 g) was added, followed by a solution of TBSCl (0.030 g, 0.20 mmol) in DMF (0.2 mL).
The stirring was continued for 5 h at room temperature. The reaction was quenched with H2O, extracted
with CHCl3 (3×5 mL), and washed with brine. The organic phase was dried over MgSO4 and the solvent
removed under reduced pressure. Purification of the crude mixture by column chromatography on silica
gel (10% EtOAc/hexane, v/v) afforded bicyclic compound 6b as a colorless oil (0.035 g, 0.086 mmol) in
62% yield. 1H NMR (500 MHz): 0.13 (s, 3H), 0.14 (s, 3H), 0.75 (t, J=7.1, 3H), 0.85 (s, 9H), 0.9–1.0 (m,
1H), 1.0–1.3 (m, 3H), 1.4–1.5 (m, 1H), 1.5–1.6 (m, 1H), 1.6–1.7 (m, 1H), 1.8–1.9 (m, 1H), 3.47 (dt, J=5.8
and 8.8, 1H), 3.65 (ddd, J=3.9, 7.4 and 8.8, 1H), 3.91 (s, 1H), 4.06 (d, J=15.1, 1H), 4.09 (s, 1H), 4.67 (d,
J=15.1, 1H), 7.21 (m, 5H). 13C NMR (125.5 MHz): −5.2, −4.6, 13.8, 18.2, 22.8, 25.6, 26.6, 35.9, 36.7,
44.0, 67.2, 73.6, 75.7, 87.3, 127.5, 128.2, 128.5, 138.1, 173.1. IR (film, cm−1): 2954, 2929, 2858, 1699.
HRMS C23H37NO3Si (M+−C4H9, calcd): 346.18385; (M+−C4H9, found): 346.18156. [α]D=+77.3 (c
0.22 , EtOAc).
4.4. General procedure for olefin metathesis
4.4.1. Synthesis of dehydroindolizinones 7a–e
To a solution of 5g, 5h, or 5i (0.10 mmol) in CH2Cl2 (5 mL), under an argon atmosphere at rt, was
added a solution of bis(tricyclohexylphosphine)benzylidine ruthenium(IV) dichloride (Grubbs’ catalyst,
0.003 g, 0.004 mmol) in CH2Cl2 (0.4 mL) The mixture was stirred at rt for 12 h. The solvent was removed
under reduced pressure and the oily residue was purified by column chromatography on silica gel (8%
EtOAc/hexane, v/v) to afford dehydroindolizinones 7a–e.

C. M. Schuch, R. A. Pilli / Tetrahedron: Asymmetry 11 (2000) 753–764
763
4.4.1.1. (1R,2S,8aS)-1,2-Bis[(tert-butyldimethylsilyl)oxy]-8a-methyl-1,2,3,5,8,8a-hexahydro-3-indoli-
zinone. Colorless oil; 74% yield as a 2:1 mixture. The major isomer 7a was isolated by column
chromatography on silica gel (8% EtOAc/hexane, v/v). 1H NMR (500 MHz): 0.13 (s, 3H), 0.15 (s, 3H),
0.16 (s, 3H), 0.22 (s, 3H), 0.92 (s, 9H), 0.93 (s, 9H), 1.32 (s, 3H), 1.82 (dd, J=5.9 and 17.6, 1H), 2.43 (d,
J=17.6, 1H), 3.44 (dd, J=2.0 and 18.3, 1H), 3.93 (d, J=5.9, 1H), 4.10 (d, J=5.9, 1H), 4.36 (d, J=18.3, 1H),
5.66 (m, 1H), 5.76 (m, 1H). 13C NMR (125.5 MHz): −4.6, −4.3, −4.1, −3.8, 18.0, 18.2, 23.4, 25.8, 25.9,
31.0, 38.0, 57.6, 77.8, 81.8, 122.8, 124.2, 169.9. IR (film, cm−1): 3035, 2954, 2929, 2856, 1716, 1651.
HRMS C21H41NO3Si2 (M+−C4H9, calcd): 354.19208; (M+−C4H9, found): 354.19209. [α]D=−52.4 (c
1
1.30, CHCl3). Data for the minor isomer 7b: H NMR (500 MHz): 0.11 (s, 3H), 0.14 (s, 3H), 0.15 (s,
3H), 0.23 (s, 3H), 0.92 (s, 9H), 0.94 (s, 9H), 1.15 (s, 3H), 2.20 (m, 2H), 3.49 (d, br, J=19.5, 1H), 3.87 (d,
J=7.1, 1H), 4.16 (dd, J=7.1 and 1.1, 1H), 4.24 (d, br, J=19.5, 1H), 5.68 (m, 2H). 13C NMR (125.5 MHz):
−4.8, −4.5, −4.2, −4.0, 17.8, 17.9, 18.5, 25.7, 25.8, 37.6, 37.7, 56.7, 76.3, 83.9, 121.5, 122.8, 170.0.
4.4.1.2. (1R,2S,8aS)-1,2-Bis[(tert-butyldimethylsilyl)oxy]-8a-n-butyl-1,2,3,5,8,8a-hexahydro-3-indoli-
zinone 7c. Colorless oil; 71% yield. 1H NMR (300 MHz): 0.11 (s, 3H), 0.15 (s, 3H), 0.17 (s, 3H), 0.22
(s, 3H), 0.92 (s, br, 12H), 0.93 (s, 9H), 1.0–1.2 (m, 1H), 1.2–1.4 (m, 3H), 1.4–1.6 (m, 1H), 1.6–1.9 (m,
2H), 2.45 (d, br, J=17.6, 1H), 3.34 (dd, J=1.8 and 18.3, 1H), 4.10 (d, J=5.3, 1H), 4.13 (d, J=5.3, 1H), 4.36
(d, J=18.3, 1H), 5.70 (m, 2H). 13C NMR (125.5 MHz): −4.6, −4.5, −4.0, −3.7, 14.0, 18.0, 18.3, 22.9,
25.4, 25.8, 26.0, 30.3, 33.4, 38.5, 60.3, 77.5, 78.2, 122.9, 124.3, 170.5. IR (film, cm−1): 3035, 2956,
2929, 2858, 1720, 1651. HRMS C24H47NO3Si2 (M+−C4H9, calcd): 396.23903; (M+−C4H9, found):
396.23891. [α]D=−39.8 (c 1.71, CHCl3).
4.4.1.3. (1R,2S,8aR)-1,2-Bis[(tert-butyldimethylsilyl)oxy]-8a-(2-phenyl-1-ethynyl)-1,2,3,5,8,8a-hexa-
hydro-3-indolizinone. Colorless oil; 38% yield as a 4:1 mixture. The major isomer 7d was isolated by
column chromatography on silica gel (8% EtOAc/hexane, v/v). 1H NMR (300 MHz): 0.16 (s, 3H), 0.19
(s, 3H), 0.24 (s, 3H), 0.25 (s, 3H), 0.94 (s, 9H), 0.95 (s, 9H), 2.32 (dd, J=2.4 and 17.4, 1H), 2.53 (d,
br, J=17.4, 1H), 3.71 (d, br, J=17.9, 1H), 4.13 (d, J=6.8, 1H), 4.42 (d, br, J=16.5, 1H), 4.51 (d, J=6.8,
1H), 5.77 (m, 2H). 7.35 (m, 5H). 13C NMR (75.5 MHz): −4.7, −4.5, −3.9, −3.9, 18.0, 18.2, 25.8, 32.0,
38.8, 56.3, 76.9, 81.7, 83.4, 89.4, 122.2, 123.4, 124.2, 128.3, 128.5, 131.5, 131.7, 168.9. IR (film, cm−1):
3035, 2956, 2929, 2858, 1720, 1651. HRMS C28H43NO3Si2 (M+−C4H9, calcd): 440.20773; (M+−C4H9,
found): 440.20775. [α]D=+25.0 (c 0.68, CHCl3). Data for the minor isomer 7e: colorless oil. 1H NMR
(500 MHz): 0.07 (s, 3H), 0.16 (s, 3H), 0.17 (s, 3H), 0.24 (s, 3H), 0.95 (s, 9H), 0.97 (s, 9H), 2.37 (d, br,
J=17.3, 1H), 2.75 (d, br, J=17.3, 1H), 3.71 (d, br, J=17.1, 1H), 3.99 (d, J=7.3, 1H), 4.26 (d, br, J=17.1,
1H), 4.32 (dd, J=1.5 and 7.3, 1H), 5.80 (m, 2H), 7.35 (m, 5H). 13C NMR (75.5 MHz): −4.6, −4.1, −4.0,
−3.9, 18.0, 18.3, 25.8, 25.9, 37.5, 38.4, 56.3, 76.4, 83.3, 85.2, 86.2, 122.0, 122.3, 122.6, 128.2, 128.3,
131.7, 170.8.
4.4.2. Synthesis of dehydropyrrolizinone 7f
To a solution of 5n (0.070 g, 0.14 mmol) in dry toluene (7 mL), under an argon atmosphere at rt, was
added a solution of Grubbs’ catalyst (0.009 g, 0.011 mmol) in toluene (1.1 mL). The mixture was heated
at reflux for 2.5 h and cooled to rt. The solvent was removed under reduced pressure and the resultant
oily residue was purified by column chromatography on silica gel (10% EtOAc/hexane, v/v) to afford
7f (0.060 g, 0.11 mmol) in 78% yield, as a colorless oil. 1H NMR (500 MHz, C6D6): 0.02 (s, 3H), 0.07
(s, 3H), 0.08 (s, 3H), 0.20 (s, 3H), 0.30 (s, 3H), 0.44 (s, 3H), 0.98 (s, 9H), 1.00 (s, 9H), 1.15 (s, 9H),
3.31 (d, br, J=16.4, 1H), 3.87 (dd, J=7.1 and 8.1, 1H), 4.06 (d, J=14.0, 1H), 4.20 (d, J=14.0, 1H), 4.26

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C. M. Schuch, R. A. Pilli / Tetrahedron: Asymmetry 11 (2000) 753–764
(m, 1H), 4.36 (d, br, J=16.4, 1H), 4.45 (d, J=8.1, 1H), 5.05 (d, J=1.7, 1H), 5.49 (d, J=17.1, 2H). 13C
NMR (125.5 MHz, C6D6): −5.4, −5.3, −4.1, −3.9, −3.7, −2.7, 17.8, 18.3, 18.6, 25.9, 26.0, 26.2, 50.4,
63.7, 68.6, 79.1, 83.7, 115.2, 122.7, 139.3, 140.6, 173.4. IR (film, cm−1): 3390, 2954, 2930, 2858, 1732.
HRMS C28H55NO4Si3 (M+−C4H9, calcd): 496.27347; (M+−C4H9, found): 496.27340. [α]D=−25.5 (c
3.00, hexane).
Acknowledgements
The authors thank FINEP for financial support and FAPESP and CNPq for fellowships.
References
1. Fuji, K. Chem. Rev. 1993, 93, 2037–2066.
2. Corey, E. J.; Guzman-Perez, A. Angew. Chem., Int. Ed. Engl. 1998, 37, 388–401.
3. Burgess, L. E.; Meyers, A. I. J. Am. Chem. Soc. 1991, 113, 9858–9859.
4. Yamazaki, N; Suzuki, H.; Kibayashi, C. J. Org. Chem. 1997, 62, 8280–8281.
5. Schoemaker, H. E.; Speckamp, W. N. Tetrahedron 1980, 36, 951–958.
6. Yoda, H.; Shirakawa, K.; Takabe, K. Chem. Lett. 1991, 489–490.
7. Yoda, H.; Shirakawa, K.; Takabe, K. Tetrahedron Lett. 1991, 32, 3401–3404.
8. Yoda, H.; Kitayama, H.; Yamada, W.; Katagiri, T.; Takabe, K. Tetrahedron: Asymmetry 1993, 4, 1451–1454.
9. Yoda, H.; Kitayama, H.; Katagiri, T.; Takabe, K. Tetrahedron: Asymmetry 1993, 4, 1455–1456.
10. Yoda, H.; Shimojo, T.; Takabe, K. Tetrahedron Lett. 1999, 40, 1335–1336.
11. Huang, P. Q.; Wang, S. L.; Ye, J. L.; Ruan, Y. P.; Huang, Y. Q.; Zheng, H.; Gao, J. X. Tetrahedron 1998, 54, 12547–12560.
12. Pilli, R. A.; Schuch, C. M. 10th IUPAC Symposium on Organometallic Chemistry Directed Towards Organic Synthesis
(OMCOS 10); Versailles, France, P-432, 1999.
13. Pilli, R. A.; Russowsky, D. Trends in Organic Chemistry 1997, 6, 101–123.
14. Speckamp, W. N.; de Koning, H. In Stereoselective Synthesis (Houben-Weyl) Vol. E21; Helmchen, G.; Hoffmann, R. W.;
Mulzer, J.; Schaumann, E., Eds. Formation of C–C bonds by addition to imino groups via N-acyliminium ions. Georg
Thieme Verlag: Stuttgart, 1996; pp. 1953–2009.
15. Fu, G. C.; Nguyen, S. T.; Grubbs, R. H. J. Am. Chem. Soc. 1993, 115, 9856–9857.
16. Grubbs, R. H.; Miller, S. J.; Fu, G. C. Acc. Chem. Res. 1995, 28, 446–452.
17. Kinoshita, A.; Mori, M. Synlett 1994, 1020–1022.
18. Barrett, A. G. M.; Baugh, S. P. D.; Braddock, D. C.; Flack, K.; Gibson, V. C.; Procopiou, P. A. Chem. Commun. 1997,
1375–1376.
19. Cieplak, A. S. J. Am. Chem. Soc. 1981, 103, 4540–4552.
20. Jeroncic, L. O.; Cabal, M. P.; Danishefsky, S. J.; Shulte, G. M. J. Org. Chem. 1991, 56, 387–395.
21. Danishefsky, S. J.; Cabal, M. P.; Chow, K. J. Am. Chem. Soc. 1989, 111, 3456–3457.
22. Ryu, Y.; Kim, G. J. Org. Chem. 1995, 60, 103–108.