Reactivity of acyclic (pentadienyl)iron(1+) cations with weak carbon nucleophiles

Article abstract of DOI:10.1016/S0022-328X(01)00869-5

The reaction of acyclic tricarbonyl(pentadienyl)iron(1+) cations with allyl trimethylsilane or with excess furan leads to (E,E-diene)iron complexes. Attack of these weak nucleophiles on the transoid form of the pentadienyl cation is presumably faster than

Full text of DOI:10.1016/S0022-328X(01)00869-5

Journal of Organometallic Chemistry 630 (2001) 5–10
www.elsevier.com/locate/jorganchem
Note
Reactivity of acyclic (pentadienyl)iron(1+) cations with weak
carbon nucleophiles
M. Azad Hossain, Myung-Jong Jin, William A. Donaldson *
Department of Chemistry, Marquette Uni6ersity, PO Box 1881, Milwaukee, WI 53201-1881, USA
Received 22 September 2000; received in revised form 4 January 2001; accepted 16 January 2001
This paper is dedicated to Professor Myron Rosenblum on the occasion of his 75th birthday
Abstract
The reaction of acyclic tricarbonyl(pentadienyl)iron(1+) cations with allyl trimethylsilane or with excess furan leads to
(E,E-diene)iron complexes. Attack of these weak nucleophiles on the transoid form of the pentadienyl cation is presumably faster
than attack on the more stable cisoid form. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Carbonyl iron complexes; Dienyl; Nucleophilic attack
1. Introduction
form (i.e. 4 and 4%, Scheme 1) [2]. Nucleophilic attack
directly on the cisoid cation 3 generates Z-diene com-
The reactivity of (cyclohexadienyl)-, (cycloheptadi-
enyl)-, and acyclic (pentadienyl)iron cations (1–3) with
carbon and heteroatom nucleophiles has been exten-
sively examined for the past two decades [1]. The
regioselectivity for nucleophilic attack on these cations
is dependent on the nature of the nucleophile, on the
substituents present on the dienyl ligand, and on the
peripheral ligands about the iron metal.
In solution, the acyclic (pentadienyl)iron cations 3
are known to exist in an equilibrium between the cisoid
form (i.e. 3) and the corresponding less stable transoid
* Corresponding author. Tel.: +1-414-2887374; fax: +1-414-
2887066.
E-mail address: donaldsonw@marquette.edu (W.A. Donaldson).
Scheme 1.
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)00869-5

6
M.A. Hossain et al. / Journal of Organometallic Chemistry 630 (2001) 5–10
signals at ca. l 87 and 81 ppm are characteristic for the
C3 and C2 carbons of (1,3E-diene)iron complexes while
for 6f and 6g, 13C-NMR signals at ca. l 99 and 86 ppm
are characteristic for the C2 and C3 carbons of (2-
methyl-1,3E-diene)iron complexes [12].
plexes, while nucleophilic attack on the transoid cation
4 or 4% gives E-diene products. Thus, reactions of
cations 3 with nucleophiles are subject to inquiry con-
cerning both regioselectivity and diene stereoselectivity.
In general, the reaction of cations 3 with water and
other heteroatom nucleophiles occurs via attack on the
transoid form 4 to afford substituted E-diene products
[3]. In contrast, reaction of cations 3 with carbanion
nucleophiles or organometallic reagents proceeds via
attack on the cisoid form to give Z-diene products [4].
There are only a few reports of the reaction of cations
3 with electron rich aromatics [5] or with allylsilanes [6].
The reaction of (cyclohexadienyl)Fe(CO)+3 cations with
allyl trimethylsilane [7] or with furan [8] has previously
been reported. Herein we report on the reactivity of
acyclic (pentadienyl)Fe(CO)+3 cations 3a–h with these
two nucleophiles.
(2)
The reaction of (1-methoxycarbonylpentadienyl)-
Fe(CO)+3 (3h) with allyl trimethylsilane gave a mixture
of nonatrienoate complexes E,E-5h and E,Z-5h in a
1:1.6 ratio (Scheme 2). Attempts to separate this mix-
ture were unsuccessful. The structure of E,E-5h was
2. Results [9]
1
assigned by comparison of its H- and 13C-NMR spec-
tral data with the literature values [13]. In comparison,
The substituted (pentadienyl)iron cations 3a–h were
prepared by literature procedures [3a–c,10]. The reac-
tion of cations 3a–e with allyl trimethylsilane gave the
corresponding trienyl complexes 5a–e in fair to good
yields (Eq. (1)). The structure of 5a was assigned by
comparison of its 1H-NMR spectral data with the
literature values [6a]. The structures for 5b–e were
the structural assignment for E,Z-5h was based on its
1
NMR spectral data. In particular, the H-NMR signals
at l 6.03 (dd) and 5.31 (dd), and the 13C-NMR signals
at l 92.4 and 86.0 ppm are characteristic of a (2E,4Z-
dienoate)Fe(CO)3 complex [10b]. In a similar fashion,
the reaction of 3h with excess furan gave an inseparable
mixture of E,E-6h and E,Z-6h (1.7:1 ratio). The struc-
tures of these products were assigned by comparison of
their NMR spectral data with that of E,E-5h and
E,Z-5h.
1
assigned on the basis of their H-NMR spectral data
(Table 1). The signals for the proton at C4 of 5b, d, and
e are similar to those for 5a. For complexes 5b, c, and
d, the signals for the endo-methylene proton at C1
appear at ca. l 0.24–0.30 ppm, which is characteristic
of a (1,3E-diene)iron complex. The relative configura-
tion of 5b–d was assigned by analogy to 5a.
3. Discussion
The reaction of cations 3a–g with the weak nucle-
ophiles allyl trimethylsilane or furan occurs in a highly
diastereoselective fashion to afford E-diene products.
While NMR spectroscopy reveals that the cations 3
exist prevalently as the cisoid structure in solution
[3a,b,10], it would appear that reaction with weak
carbon nucleophiles occurs via the less stable (but more
reactive) transoid form of the cation [14]. For the
unsymmetrically substituted pentadienyl cations, nucle-
ophilic attack was found to occur in a regiospecific
fashion. For mono-substituted cations (R1=R2=H,
i.e. 3b, c) and 2,5-disubstituted cations (R1=H, i.e. 3d,
f) C–C bond formation occurs via nucleophilic attack
at the substituted pentadienyl terminus. In contrast, for
the 1,2-disubstituted cations (R5=H, i.e. 3e, g) nucle-
ophilic attack occurs at the unsubstituted pentadienyl
terminus. For cations 3b–g, two possible transoid pen-
tadienyl cations, 4 or 4%, may be considered (Scheme 1).
For cations b, c, d, and f the transoid form 4 should be
more stable than the isomeric structure 4% due to the
(1)
The reaction of cations 3b, c, f, and g with furan (ca.
10 equivalents) gave the corresponding 5-(2%-furyl)-1,3-
diene complexes 6b, c, f, and g in good yields (Eq. (2)).
The structural assignments for complexes 6 are based
on their H- and 13C-NMR spectral data (Tables 1 and
1
2). In particular, signals at ca. l 7.3, 6.3–6.2, and
6.1–5.9 ppm in their 1H-NMR spectra and at ca. l 159,
141, 110, and 104 ppm in their 13C-NMR spectra are
characteristic of a 2-substituted furan functionality [11].
For 6b and 6c (and similarly for 5b and 5c), 13C-NMR

M.A. Hossain et al. / Journal of Organometallic Chemistry 630 (2001) 5–10
7
Table 1
1H-NMR spectral data for (diene)Fe(CO)3 complexes a
Compound H1
H2
H3
H4
H5
Other
b
b
b
5a
1.39 (d, 3H)
0.81 (dd)
5.77 (m), 5.10–4.90 (m, 4H), 2.09 (t,
J=6.9, 2H), 1.39 (m), 1.06 (m & d,
J=6.8, 4H))
J=6.0
1.70 (dd)
J=7.3, 9.8
0.86 (dd)
b
b
5b
0.24 (dd)
5.79 (m), 5.20 (m, 2H), 5.00 (m, 2H),
2.12 (t, J=6.8, 2H), 1.44–1.39 (m), 1.08
(d, J=6.1, 3H)
J=2.4, 8.4
J=2.5, 6.6
J=8.1, 9.8
5c
0.30 (ddd)
1.68 (ddd)
5.22 (m)
5.34 (ddd)
1.21 (ddd)
7.74–7.18 (m, 5H), 5.76–5.62 (m),
5.04–4.98 (m, 2H), 2.52 (dd, J=5.1,
10.2), 2.57–2.44 (m, 2H)
J=1.2, 2.5, 9.1 J=1.0, 2.5, 6.8
J=1.0, 4.9, 8.6 J=0.7, 8.8, 8.8
5d
0.30 (d)
1.76 (d)
2.16 (s, 3H)
5.12 (d)
0.63 (dd)
5.80 (tdd, J=7.2, 10.3, 16.7), 5.00 (m,
2H), 2.10 (m, 2H), 1.42 (m), 1.07 (d,
J=6.7, 3H)
J=2.1
J=2.1
J=8.5
J=8.5, 9.7
5e
0.86 (q)
1.42 (d, 3H)
2.12 (s, 3H)
4.89 (d)
0.98 (m)
5.80 (tdd, J=6.6, 10.1, 16.8), 5.05–5.00
(m, 2H), 2.10 (m), 1.73 (m), 1.63 (m,
2H)
J=7.3
0.97 (dd)
J=7.3
3.64 (s, 3H)
J=9.0
5.24 (dd)
b
E,E-5h
1.36 (dq)
5.86–5.73 (m, 2H), 5.07 (qd, J=1.6,
17.4), 5.02 (m), 2.27–2.12 (m, 2H), 1.82
(dtd, J=6.5, 7.2, 14.7), 1.70 (dtd,
J=6.8, 7.3, 14.7)
J=1.0, 8.0
J=5.3, 8.6
J=1.0, 6.9
E,Z-5h
6b
2.17 (d)
3.67 (s, 3H)
1.77 (dd)
6.03 (dd)
5.31 (dd)
2.70 (br dt)
5.69 (tdd, J=6.6, 10.3, 17.1), 5.05 (m,
2H), 2.40 (br q, J=7.6), 2.27–1.98 (m,
2H), 1.82–1.65 (m)
J=8.3
0.34 (dd)
J=5.4, 8.2
5.26 (m)
J=5.4, 7.6
5.43 (m)
J=4.6, 8.3
1.04 (dd)
7.32 (dd, J=0.7, 1.9), 6.31 (dd, J=1.9,
3.2), 6.01 (dd, J=0.7, 3.2), 2.70 (m),
1.45 (d, J=6.8, 3H)
J=2.2, 9.3
J=2.2, 7.1
J=8.5, 8.5
6c
0.44 (dd)
1.68 (dd)
5.30 (m)
5.59 (dd)
1.46 (br t)
7.3–7.2 (m, 6H), 6.22 (dd, J=1.9, 3.2),
5.94 (dd, J=1.0, 3.2), 3.88 (d, 10.3),
1.68 (dt, J=1.2, 6.9)
J=1.2, 9.3
J=1.2, 6.9
J=4.8, 8.3
J=9.3
6f
0.41 (d)
1.76 (d)
2.13 (s, 3H)
2.37 (s, 3H)
5.43 (d)
1.13 (dd)
7.3–7.2 (m, 6H), 6.24 (dd, J=1.9, 3.2),
5.95 (d, J=3.2), 3.75 (d, J=10.3)
J=2.1
1.88 (s)
J=2.1
7.3–7.1 (m)
J=10.3
5.19 (d)
J=8.1, 10.3
1.30 (m)
6g
7.34 (dd, J=0.7, 1.9), 6.31 (dd, J=1.9,
3.2), 6.07 (dd, J=0.7, 3.2), 2.96 (d,
J=7.3), 2.95 (d, J=6.8)
J=8.3
E,E-6h
E,Z-6h
1.02 (d)
3.64 (s, 3H)
3.69 (s, 3H)
5.81 (dd)
5.36 (dd)
1.51 (ddd)
7.35 (dd, J=0.7, 1.9), 6.30 (dd, J=1.9,
3.2), 6.00 (dd, J=0.7, 3.2), 3.05 (dd,
J=6.7, 15.7), 2.85 (m)
J=8.3
2.24 (d)
J=5.1, 8.1
6.09 (m)
J=5.1, 8.8
5.36 (dd)
J=6.6, 7.6, 8.3
2.96 (m)
7.30 (dd, J=0.7, 1.9), 6.27 (dd, J=1.9,
3.2), 6.00 (dd, J =0.7, 3.2), 2.85 (m),
2.41 (dd, J=9.3, 15.7)
J=8.8
J=5.1, 8.1
a In ppm downfield from SiMe4 (multiplicities: d=doublet, t=triplet, q=quartet, br=broad); coupling in Hz; integration equals 1H unless
otherwise indicated; CDCl3 solution; 300 MHz.
b Peak is obscured by other multiplets (listed in ‘other’).
stabilizing effect of a methyl or phenyl group present
on the carbon bearing the greatest partial positive
charge. For the cations e and g, the transoid cation 4
should be more stable than the isomeric form 4%, due to
the unfavorable steric interactions present where R2 is
the more bulky methyl group (compared to hydrogen).
Thus, in all cases the concentration of transoid cation 4%
should be less than that of transoid cation 4.

8
M.A. Hossain et al. / Journal of Organometallic Chemistry 630 (2001) 5–10
Table 2
13C-NMR spectral data for (diene)Fe(CO)3 complexes a
Compound C1
C2
C3
C4
Other
b
5a
5b
5c
E,E-5h
E,Z-5h
6b
6c
6f
57.3 84.3
39.7 80.9
39.5 81.0
45.9 87.5
45.6 92.4
40.0 81.7
39.8 81.8
43.2 99.7
83.0 b 70.9b 136.3 (CꢀC), 116.5 (CꢀCH2), 44.3, 38.9, 22.4, 19.2
87.4
87.3
83.4
86.0
87.5
87.6
87.7
72.0
69.8
64.8
60.6
67.9
65.8
63.2
212.1 (M–CO), 136.3 (CꢀC), 116.5 (CꢀCH2), 44.2, 38.9, 22.4
211.4 (M–CO), 136.0 (CꢀC), 116.7 (CꢀCH2), 144.7, 128.5, 126.9, 126.5 (4×Ar), 51.5, 44.7
173.3 (CO2R), 137.3 (CꢀC), 116.0 (CꢀCH2), 51.8 (OMe), 36.0, 33.6
173.2 (CO2R), 136.1 (CꢀC), 115.4 (CꢀCH2), 51.5 (OMe), 36.7, 28.9
212 (M–CO), 159.1, 141.2, 110.0, 103.5 (4×furan), 37.8, 20.7
212 (M–CO), 157.6, 141.7 b, 110.0, 105.8 (4×furan), 141.9 b, 128.6, 127.5, 127.0 (4×Ar), 49.8
212 (M–CO), 158.0 c, 141.7, 110.0, 105.6 (4×furan), 142.0 c, 128.5, 127.5, 127.0 (4×Ar), 49.8,
22.7
6g
65.1 98.2
85.5
55.9
212 (M–CO), 154.7 c, 141.2, 110.2, 105.2 (4×furan), 139.4 c, 129.4, 128.2, 126.3 (4×Ar), 32.4,
19.8
E,E-6h
E,Z-6h
45.8 86.8
46.0 93.2
83.5
85.4
60.8
56.7
172.4 (CO2R), 154.7, 141.4, 110.1, 105.5 (4×furan), 51.5 (OMe), 32.2
173.0 (CO2R), 154.6, 141.3, 110.2, 105.4 (4×furan), 51.6 (OMe), 27.3
a In ppm downfield from SiMe4; CDCl3 solution; 75 MHz.
b The assignments for these peaks may be interchanged.
c Quarternary carbon as assigned by APT.
storing over activated molecular sieves. The substituted
(pentadienyl)iron cations 3a–h were prepared by litera-
ture procedures [3a–c,10].
For the methoxycarbonyl substituted pentadienyl
cation 3h, reaction with allyl trimethylsilane or furan
occurs via nucleophilic attack on both the cisoid form
3h and the transoid form 4h (Scheme 3). No reaction
occurs via the transoid form 4h% since this is greatly
destabilized due to the proximity of the ester sub-
stituent to the carbon bearing the greatest partial posi-
tive charge. The electron withdrawing ester substituent
increases the electrophilicity of the cisoid form of the
pentadienyl cation 3h such that it is more nearly equal
in reactivity to the transoid cation 4h. Nucleophilic
attack on 3h occurs at the unsubstituted pentadienyl
terminus since this site is better able to stabilize the
partial positive charge. Notably, the reaction of cation
3h with water results in the formation of (methyl 6-hy-
droxy-2E,4Z-hexadienoate)Fe(CO)3, via attack on the
cisoid form of the cation at the unsubstituted dienyl
terminus [16].
4.2. General procedure for reaction of cations 3 with
allyl trimethylsilane
To a suspension of 3 (0.2–0.5 mmol) in CH2Cl2 (ca.
5–20 ml) was added allyl trimethylsilane (1.5–2.0 mole
equivalents). The reaction mixture was stirred at room
temperature for 8–24 h and then treated with water
and extracted with CH2Cl2. The combined organic ex-
tracts were washed with brine, dried (MgSO4) and
concentrated. The residue was purified by column chro-
matography (SiO2). The following compounds were
prepared by the above procedure.
In general, reaction of weak carbon nucleophiles with
acyclic (pentadienyl)Fe(CO)+3 cations occurs via the
more reactive transoid form of the cation. The regiose-
lectivity for this reaction is dictated by the more stable
of the two possible transoid forms, 4 or 4%.
4. Experimental
4.1. General data
1
All H- and 13C-NMR spectra were recorded at 300
and 75 MHz respectively using a GE Omega GN-300
spectrometer. All IR spectra were recorded on either a
Mattson 4020 FT-IR or a Nicolet 560 Magna-IR spec-
trophotometer. High resolution mass spectra were per-
formed at the Nebraska Center for Mass Spectrometry.
Methylene chloride was distilled from P2O5 followed by
Scheme 2.

M.A. Hossain et al. / Journal of Organometallic Chemistry 630 (2001) 5–10
9
4.2.6. Tricarbonyl(methyl 2,4-8-nonatrienoate)iron (5h)
The reaction of 3h (200 mg, 0.487 mmol) with allyl
trimethylsilane (0.11 ml, 0.68 mmol) gave a golden
yellow oil (130 mg, 88%). Examination of the 1H-
NMR spectrum of this product indicated that it con-
sisted of a mixture of the known E,E-5h [13] and
E,Z-5h. Integration of the signals at l 5.24 and 5.31
ppm indicated that the ratio of stereoisomers E,E-5h
and E,Z-5h was 1:1.6. FAB-HRMS m/z 306.0190
[calc. for C13H14O5Fe m/z 306.0190]. IR (cm−1, hex-
anes): 2059, 1990, 1720.
4.3. General procedure for reaction of cations 3 with
excess furan
To a suspension of 3 (0.25–0.5 mmol) in CH2Cl2
(ca. 8–15 ml) was added excess furan (5.5 mmol).
The reaction mixture was stirred at room temperature
for 3–12 h and then treated with saturated aqueous
NaHCO3 and extracted with CH2Cl2. The combined
organic extracts were washed with brine, dried
(MgSO4) and concentrated. The residue was purified
by column chromatography (SiO2). The following
compounds were prepared by the above procedure
Scheme 3.
4.2.1. Tricarbonyl(6-methyl-2,4,8-nonatriene)iron (5a)
The reaction of 3a (80 mg, 0.21 mmol) with allyl
trimethylsilane (0.05 ml, 0.3 mmol) gave 5a as a yel-
1
low oil (28 mg, 48%). The H-NMR spectral data for
this product were similar to the literature values [6a].
4.3.1. Tricarbonyl[5-(2%-furyl)-1,3-hexadiene)iron (6b)
The reaction of 3b (185 mg, 0.500 mmol) with fu-
ran gave 6b as a dark yellow oil (100 mg, 69%).
EI-HRMS m/z 288.0084 [calc. for C13H12O4Fe m/z
288.0085]. IR (cm−1, neat): 2044, 1973.
4.2.2. Tricarbonyl(5-methyl-1,3,7-octatriene)iron (5b)
The reaction of 3b (185 mg, 0.500 mmol) with allyl
trimethylsilane (0.15 ml, 0.95 mmol) gave 5b as a
yellow oil (100 mg, 70%). EI-HRMS m/z 262.0284
[calc. for C12H14O3Fe m/z 262.0291]. IR (cm−1, hex-
anes): 2047, 1978.
4.3.2. Tricarbonyl[5-(2%-furyl)-5-phenyl-1,3-
pentadiene)iron (6c)
4.2.3. Tricarbonyl(5-phenyl-1,3,7-octatriene)iron (5c)
The reaction of 3c (215 mg, 0.500 mmol) with allyl
trimethylsilane (0.15 ml, 0.95 mmol) gave 5c as a
golden yellow oil (135 mg, 77%). EI-HRMS m/z
324.0457 [calc. for C17H16O3Fe m/z 324.0447]. IR
(cm−1, hexanes): 2047, 1973.
The reaction of 3c (215 mg, 0.500 mmol) with fu-
ran gave 6c as a dark yellow oil (140 mg, 80%).
EI-HRMS m/z 350.0246 [calc. for C18H14O4Fe m/z
350.0240]. IR (cm−1, neat): 2048, 1977.
4.3.3. Tricarbonyl[5-(2%-furyl)-2-methyl-5-phenyl-1,3-
pentadiene)iron (6f)
The reaction of 3f (110 mg, 0.250 mmol) with fu-
ran gave 6f as a dark yellow oil (70 mg, 77%). EI-
HRMS m/z 364.0399 [calc. for C19H16O4Fe m/z
364.0396]. IR (cm−1, neat): 2048, 1977.
4.2.4. Tricarbonyl(2,5-dimethyl-1,3,7-octatriene)iron
(5d)
The reaction of 3d (200 mg, 0.526 mmol) with allyl
trimethylsilane (0.16 ml, 1.0 mmol) gave 5d as a yel-
low oil (40 mg, 28%). IR (cm−1, hexanes): 2045,
1970.
4.3.4. Tricarbonyl[5-(2%-furyl)-2-methyl-1-phenyl-1,3-
pentadiene)iron (6g)
The reaction of 3g (220 mg, 0.500 mmol) with fu-
ran gave 6g as a dark yellow oil (145 mg, 80%).
EI-HRMS m/z 364.0398 [calc. for C19H16O4Fe m/z
364.0396]. IR (cm−1, neat): 2050, 1979.
4.2.5. Tricarbonyl(7-methyl-1,5,7-nonatriene)iron (5e)
The reaction of 3e (200 mg, 0.526 mmol) with allyl
trimethylsilane (0.16 ml, 1.0 mmol) gave 5e as a yel-
low oil (55 mg, 38%). EI-HRMS m/z 192.0596 [calc.
for C10H16Fe (M+−3CO) m/z 192.0603]. IR (cm−1
,
hexanes): 2040, 1970.

10
M.A. Hossain et al. / Journal of Organometallic Chemistry 630 (2001) 5–10
[4] (a) W.A. Donaldson, M. Ramaswamy, Tetrahedron Lett. 30
(1989) 1339;
4.3.5. Tricarbonyl[methyl 6-(2%-furyl)-
2,4-hexadienoate)iron (6h)
(b) W.A. Donaldson, P.T. Bell, M.-J. Jin, J. Organomet. Chem.
441 (1992) 449;
(c) W.A. Donaldson, M.-J. Jin, Tetrahedron 49 (1993) 8787;
(d) M.-C.P. Yeh, B.-A. Sheu, H.-W. Fu, S.-I. Tau, L.-W.
Chuang, J. Am. Chem. Soc. 115 (1993) 5941.
The reaction of 3h (250 mg, 0.500 mmol) with furan
gave 6h a dark yellow oil (140 mg, 86%). Integration of
the signals at l 5.81 and 6.09 ppm indicated that the
ratio of stereoisomers E,E-6h and E,Z-6h was 1.7:1.
EI-HRMS m/z 276.0079 [calc. for C12H12O4Fe (M+−
2CO) m/z 276.0084]. IR (cm−1, neat): 2052, 1984, 1710.
[5] T.G. Bonner, K.A. Holder, P. Powell, J. Organomet. Chem. 77
(1974) C37.
[6] (a) M. Uemura, T. Minami, Y. Yamashita, K. Hiyoshi, Y.
Hayashi, Tetrahedron Lett. 28 (1987) 641;
(b) W.A. Donaldson, J. Organomet. Chem. 395 (1990) 187;
(c) W.A. Donaldson, M.-J. Jin, Bull. Soc. Chim. Belg. 102 (1993)
297.
Acknowledgements
[7] L.F. Kelly, A.S. Narula, A.J. Birch, Tetrahedron Lett. 21 (1980)
871.
This work was supported by the National Institutes
of Health (GM-42641). The authors are grateful to Dr
Young K. Yun for performing the reaction of 3h with
allyl trimethylsilane.
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[9] All compounds shown are racemic mixture of enantiomers. Only
one enantiomer has been diagrammed for clarity.
[10] (a) W.A. Donaldson, M.-J. Jin, P.T. Bell, Organometallics 12
(1993) 1174;
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