Diastereoselective conjugate additions to alkoxycarbene cations of the iron chiral auxiliary [(η5-C5H5)Fe(CO)(PPh3)C(OMe)CHCHR]+

Article abstract of DOI:10.1016/j.jorganchem.2015.01.026

Abstract The conjugate additions of alkyllithium reagents to alkoxycarbene cations of the iron chiral auxiliary [(η⁵-C₅H₅)Fe(CO)(PPh₃)C(OMe)CHCHR]⁺ proceeded with moderate to excellent diastereoselect

Full text of DOI:10.1016/j.jorganchem.2015.01.026

Accepted Manuscript
Diastereoselective conjugate additions to alkoxycarbene cations of the iron chiral
5
+
auxiliary [(η -C H )Fe(CO)(PPh )=C(OMe)CH=CHR]
5 5
3
Stephen G. Davies, Robert J.C. Easton, Jeffrey M. McKenna, Mario E.C. Polywkam,
James E. Thomson
PII:
S0022-328X(15)00049-2
10.1016/j.jorganchem.2015.01.026
JOM 18891
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 22 December 2014
Revised Date: 24 January 2015
Accepted Date: 28 January 2015
Please cite this article as: S.G. Davies, R.J.C. Easton, J.M. McKenna, M.E.C. Polywkam, J.E. Thomson,
5
Diastereoselective conjugate additions to alkoxycarbene cations of the iron chiral auxiliary [(η -
+
C H )Fe(CO)(PPh )=C(OMe)CH=CHR] , Journal of Organometallic Chemistry (2015), doi: 10.1016/
j.jorganchem.2015.01.026.
5 5
3
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ACCEPTED MANUSCRIPT
Diastereoselective conjugate additions to alkoxycarbene cations of the iron chiral auxiliary
[(η5-C5H5)Fe(CO)(PPh3)=C(OMe)CH=CHR]+
Stephen G. Davies,* Robert J. C. Easton, Jeffrey M. McKenna, Mario E. C. Polywka and James E. Thomson
Conjugate
additions
to
alkoxycarbene
cations
of
the
iron
chiral
auxiliary [(η5-
C5H5)Fe(CO)(PPh3)=C(OMe)CH=CHR]+ proceed with high diastereoselectivity. Subsequent protonation
and demethylation gives iron acyl complexes of opposite relative configuration to those which result from
conjugate addition of the same nucleophile to the corresponding α,β-unsaturated iron acyl complex.
1

ACCEPTED MANUSCRIPT
Diastereoselective conjugate additions to alkoxycarbene cations of the iron chiral auxiliary
[(η5-C5H5)Fe(CO)(PPh3)=C(OMe)CH=CHR]+
Stephen G. Davies,* Robert J. C. Easton, Jeffrey M. McKenna, Mario E. C. Polywka and James E. Thomson
Department of Chemistry, Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford,
OX1 3TA, U.K.
E-mail: steve.davies@chem.ox.ac.uk
Telephone: +44 (0)1865 275695
Fax: +44 (0)1865 275633
Dedicated to Professor Michael P. Mingos on the occasion of his 70th Birthday
Abstract
The diastereoselective conjugate additions of alkyllithium reagents to alkoxycarbene cations of the iron
chiral auxiliary [(η5-C5H5)Fe(CO)(PPh3)=C(OMe)CH=CHR]+ proceed with moderate to excellent
diastereoselectivity. The resultant methoxyvinyl complexes were transformed into the corresponding iron
acyl complexes following a sequence of protonation and demethylation. The overall transformation yields
iron acyl complexes of opposite relative configuration to those which result from the conjugate addition of
the same nucleophile to the corresponding α,β-unsaturated iron acyl complex.
Key words: iron chiral auxiliary, alkoxycarbene cation, conjugate addition, asymmetric synthesis
1. Introduction
The iron chiral auxiliary [(η5-C5H5)Fe(CO)(PPh3)] has been shown to control a wide range of chemical
transformations in a highly diastereoselective fashion.1,2 The generation of the corresponding chiral enolate
equivalent can be effected by deprotonation of an iron acyl complex 1 or following the conjugate addition of
alkyllithium or lithium amide reagents to an α,β-unsaturated iron acyl complex 4. Reactions of (E)-enolates
(i.e., Fe trans to the R group) such as 2 with a range of electrophiles proceed with high diastereoselectivity,
and the configuration of the newly created α-stereogenic centre is completely predictable.3,4 The postulate
for the high levels of diastereoselectivity observed upon alkylation of 2 involves reaction of the enolate in an
anti-conformation (i.e., where the CO ligand is antiperiplanar to the C–OLi bond) with the electrophile
2

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approaching from the less hindered face of the enolate, away from the triphenylphosphine rotor.5 The
generation of (E)-enolates such as 5 upon conjugate addition of alkyllithium or lithium amide reagents to the
corresponding α,β-unsaturated iron acyl complexes 4 also occurs through the preferred anti-conformation
[i.e., where the CO ligand is approximately antiperiplanar to the C(1)=O bond], and the enoyl fragment
adopts a conformation in which the C=O and C=C bonds are s-cis, with attack of the nucleophile from the
less hindered face.6,7 Again, high diastereoselectivity is observed upon alkylation of (E)-enolates such as 5
where the electrophile approaches from the less hindered of the enolate in the reactive anti-conformation.8
An alternative approach to the diastereoselective generation of these α-substituted iron acyl complexes arises
from the deprotonation of an alkoxycarbene cation 7, which generates the corresponding (Z)-methoxyvinyl
complex 8. Subsequent reaction of 8 with a range of electrophiles proceeds with complementary
diastereoselectivity,9 giving products of opposite relative configuration to those generated from alkylation of
the corresponding lithium (E)-enolates 2 (Fig. 1).
Figure 1. Diastereoselective transformations using the iron chiral auxiliary [(η5-C5H5)Fe(CO)(PPh3)].
In extension of this work, it was envisaged that β-substituted iron acyl complexes 13 could be prepared from
α,β-unsaturated alkoxycarbene cations 10 upon diastereoselective conjugate addition to these substrates; in
turn, the α,β-unsaturated alkoxycarbene cations 10 could be obtained from the corresponding α,β-unsaturated
iron acyl complexes 4 upon treatment with Me3OBF4.10 Within the X-ray crystal structure of
methoxycarbene cation 1411 the triphenylphosphine, carbon monoxide and carbene ligands occupy three
adjacent octahedral sites, with each lying approximately orthogonal to the plane of the metal and the other
two ligands. The carbene ligand adopts a conformation that is close orthogonal to the Fe–P bond (to
maximise the stereoelectronic effects between the HOMO on the iron and the empty p orbital on the carbene
carbon),12 but rotated slightly to relieve the eclipsing steric interactions with the CO ligand; the C–OMe
3

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bond is then close to antiperiplanar to the CO ligand. A similar anti-conformation can therefore be assumed
for the corresponding α,β-unsaturated methoxycarbene cation 10, where the Fe=C and C=C bonds are
orientated s-cis to avoid unfavourable steric interactions between the olefinic group and methoxy substituent.
Based on this conformational analysis, it was predicted that conjugate addition to 10 would occur on the less
hindered face, opposite to the triphenylphosphine rotor, to give methoxyvinyl complex 11. Subsequent
transformation of 11 to the corresponding iron acyl complex 13 could then be achieved by protonation
followed by nucleophilic demethylation of the corresponding methoxycarbene cation 12 (Fig. 2). It was
therefore expected that this reaction sequence would generate the opposite diastereoisomer to that obtained
from the conjugate addition of the same nucleophile to the corresponding α,β-unsaturated iron acyl complex
4 (vide supra).
Figure 2. Proposed synthesis of β-substituted iron acyl complexes 13.
2. Results and discussion
The generation of α,β-unsaturated methoxycarbene cations 22–28 from the corresponding α,β-unsaturated
iron acyl complexes 15–21 was accomplished upon treatment with Me3OBF4,10 with isolation of the cationic
carbene complex by precipitation from cold Et2O giving 22–28 in 91–97% yield (Scheme 1). In each case,
3
the configuration of the C=C bond within 22–28 was confirmed by 1H NMR J coupling constant analyses
(3J2,3 = 15.1–15.6 Hz).
Scheme 1. Reagents and conditions: (i) Me3OBF4, CH2Cl2, rt, 14 h.
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Subsequent reaction of methoxycarbene cations 22–28 with alkyllithium reagents (i.e., MeLi, BuLi and
PhLi) proceeded with excellent diastereoselectivities being observed in almost all cases. Transformation of
the resultant methoxyvinyl complexes 29–46 to the corresponding acyl complexes 65–82 was achieved by
protonation with either TsOH or HBF4, followed by demethylation of methoxy carbene cations 47–64 upon
treatment with NaI (Scheme 2). As expected, the spectroscopic data for the major diastereoisomers 65–82
were found to be different to those for the products arising from conjugate addition of the same nucleophiles
to the corresponding α,β-unsaturated iron acyl complexes 15–21,7 which were in fact in accordance with the
minor diastereoisomeric iron acyl complexes obtained in this case. The relative configurations within 65–82
were therefore confidently assigned on this basis.
R
R'
R
R'
R
R'
R
OC
OC
OC
OC
BF4
X
(i)
(ii)
(ii)
PPh3
PPh3
PPh3
PPh3
Fe
Fe
Fe
Fe
OMe
OMe
OMe
O
A
R
B
C
D
R'
A
B
C
D
yield D (%)
dr D
Et
Pr
Me
Me
Me
Me
Me
Me
23
24
25
26
27
28
29
30
31
32
33
34
47
48
49
50
51
52
65
66
67
68
69
70
78
76
79
72
73
90
97:3
97:3
97:3
97:3
97:3
97:3
iPr
Bu
tBu
Ph
Me
Et
Bu
Bu
Bu
Bu
Bu
Bu
22
23
24
25
27
28
35
36
37
38
39
40
53
54
55
56
57
58
71
72
73
74
75
76
74
66
79
79
73
60
95:5
97:3
97:3
93:7
64:36
97:3
Pr
iPr
tBu
Ph
Me
Et
Ph
Ph
Ph
Ph
Ph
Ph
22
23
24
25
26
27
41
42
43
44
45
46
59
60
61
62
63
64
77
78
79
80
81
82
75
74
79
76
69
65
95:5
97:3
97:3
92:8
97:3
60:40
Pr
iPr
Bu
tBu
Scheme 2. Reagents and conditions: (i) R'Li, CH2Cl2, –78 °C, 2 h; (ii) TsOH or HBF4, rt, 1 h; (iii) NaI, rt, 4 h.
The reduced diastereoselectivity observed in the conjugate addition reactions of BuLi and PhLi to
t
methoxycarbene cation 27 (R = Bu) can be rationalised through a transition state argument. The rates of
addition of these larger alkyllithium reagents to the β-position of this bulky substrate are likely to be much
slower than those for the corresponding conjugate addition of MeLi to 27, and as a result the transition state
is more product-like. Hammond’s postulate13 predicts that the conformation attacked preferentially is the one
which leads to the more stable product; here, the energy of either product arising from conjugate addition to
either the syn- or anti-conformations (i.e., the position of the CO ligand relative to C–OMe bond) are of
similar energy and thus relatively poor diastereoselectivity is observed (Fig. 3). Since both the syn- and anti-
conformers are in rapid equilibrium in this case, it is pertinent to consider the Curtin-Hammett principle,14
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which states that the product distribution formed from two critical conformations is completely independent
of the relative populations of the conformers and depends only upon the difference in free energy of the
transition states, provided that the rates of reaction are considerably slower than the rate of conformational
interconversion. These two results (64:36 dr and 60:40 dr) are in contrast to the high diastereoselectivity
observed for all the other conjugate additions examined (≥92:8 dr in each case). For these highly
diastereoselective reactions the diastereofacial preference of the conjugate addition is consistent with attack
of the nucleophile from the less hindered face of the carbene complex in the anti (i.e., CO ligand to C–OMe
bond), s-cis (i.e., Fe=C to C=C) conformation 83, as opposed to the syn,s-trans conformation 84 (Fig. 3).
The attack of the alkyllithium reagent upon the anti,s-cis-conformer 83 is subject to little steric congestion,
and thus the transition state energy of this pathway is lower than that for the syn,s-trans-conformer 84. It is
apparent that prior co-ordination to the methoxy group of the carbene is not necessary for the addition to
proceed, whereas this criterion (i.e., co-ordination to the acyl carbonyl) is necessary for conjugate addition to
the corresponding iron acyl complexes 15–21.
Figure 3. Reactive conformations anti,s-cis-83 and syn,s-trans-84.
In extending the scope of reagents possible in this reaction, conjugate addition of Grignard reagents, alkyl
coppers and cuprates to methoxycarbene cation 22 (R = Me) gave the corresponding β-substituted iron acyl
complexes with excellent diastereoselectivity (≥97:3 dr in each case), directly comparable to that of the
alkyllithium reagent. However, conjugate addition of the lithium anion of dimethyl malonate to 23 (R = Et)
gave 85 in 70% yield and 91:9 dr, after protonation and demethylation; this lower diastereoselectivity may
well be due to a product-like transition state, and consequently Hammond’s postulate may once again be
applied. While many reactions herein were carried out using preformed reagents, attempts were made to
introduce greater functionality to these complexes by the use of enolates and functionalised alkyllithium-type
reagents. Continuing from our experience with the lithium anion of dimethyl malonate, the lithium enolate
of N,N-dimethylacetamide was chosen as a suitable nucleophile. Following addition of the enolate15 to
methoxycarbene cation 22 and subsequent protonation and demethylation, an 84:16 diastereoisomeric
mixture of 86 and 87, respectively, was isolated in 65% combined yield. The relative configurations within
6

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86 and 87 were assigned by analogy to the other conjugate addition reactions to methoxycarbene cation 22,
and this assignment was confirmed by the preparation of an authentic sample of 87 upon conjugate addition
of the same lithium enolate to α,β-unsaturated acyl complex 15, which gave an 86:14 mixture of 87 and 86,
respectively, in 75% combined yield (Scheme 3).
Scheme 3. Reagentsand conditions: (i) BuLi, dimethyl malonate, CH2Cl2/THF (8:1), –78 °C, 1 h; (ii) HBF4, THF, rt, 1 h then
NaI, rt, 1 min; (iii) LDA, N,N-dimethylacetamide, CH2Cl2, –78 °C, 1 h then MeOH, –78 °C to rt; (iv) TsOH, THF, rt, 1 h then NaI,
rt, 1 min; (v) LDA, N,N-dimethylacetamide, THF, –78 °C to –40 °C, 3 h then MeOH, –78 °C to rt.
Another functionalised nucleophile to be utilised was an anionic acetaldehyde equivalent. Although
numerous examples exist,16 a substituted vinyllithium reagent was chosen as it could be easily produced by
t
halogen-metal exchange of 91 upon treatment with BuLi.17 The subsequent reaction of the vinyllithium
reagent and methoxycarbene cation 22, followed by protonation and demethylation, gave 88 in 96:4 dr
(Scheme 4). In this case, the relative configuration of the major diastereoisomer was assigned by analogy to
the other conjugate addition reactions to methoxycarbene cation 22 where attack of the nucleophile occurs
on the less hindered face of the carbene in the anti,s-trans-conformation.
Scheme 4. Reagents and conditions: (i) tBuLi, 91, Et2O, –78 °C, 1 h then MeOH, –78 °C to rt; (ii) TsOH, THF, rt, 1 h then NaI,
rt, 1 min; (iii) TBDMSCl, imidazole, DMF, rt, 18 h; (iv) BuLi, Et2O, –78 °C, 6 h then –78 °C to rt 24 h.
7

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3. Conclusions
Herein we have described the utility of cationic methoxycarbene complexes of the iron chiral auxiliary [(η5-
C5H5)Fe(CO)(PPh3)] in the generation of β-substituted iron acyl complexes via a three step process of
diastereoselective conjugate addition, protonation, and demethylation. The resultant iron acyl complexes are
epimeric with respect to the complimentary stereochemical outcome that arises from conjugate addition of
the same nucleophile to the corresponding α,β-unsaturated iron acyl complex. The diastereofacial preference
of the conjugate addition was rationalised by attack of the nucleophile on the carbene complex in the anti
(i.e., CO ligand to C–OMe bond), s-cis (i.e., Fe=C to C=C) conformation on the face opposite to the
triphenylphosphine rotor.
4. Experimental
4.1. General Experimental
All reactions and purifications involving organometallic complexes were carried out under an atmosphere of
dry nitrogen in deoxygenated solvents using a vacuum line and standard Schlenk techniques. All reaction
glassware was flame-dried and allowed to cool under vacuum. Elemental analyses were obtained using a
Carla Elba 1106 analyser. Infra-red spectra were obtained using a Perkin-Elmer 1750 spectrophotometer.
NMR spectra were recorded using the Bruker AM500 (1H; 500.13 MHz and 13C; 125.8 MHz), Bruker
13
13
WH300 (1H; 300.13 MHz) and the Bruker AC200 (1H; 200.13 MHz and C; 50.3 MHz) instruments, C
NMR being obtained with DEPT editing or assigned by analogy with spectra so obtained.18 All chemical
shifts are given in parts per million (ppm) relative to tetramethylsilane (δH = 0.00 ppm) and coupling
constants (J) are given in Hertz (Hz). In all cases, assessment of reaction diastereoselectivity was carried out
by peak integration in the 1H NMR spectra of the crude reaction mixtures. Mass spectra were obtained using
chemical ionisation (CI) on VG MASSLAB VG 20-250.
4.2. General Procedure 1 for the preparation of α,β-unsaturated methoxycarbene complexes 22–28
A solution of the requisite iron acyl complex 15–21 (5.0 mmol) in CH2Cl2 (30 mL) was added via cannula to
Me3OBF4 (6.7 mmol), and the resultant solution was then stirred at rt for 14 h. The reaction mixture was
then transferred to another flask via a filter-cannula and concentrated in vacuo to a volume of ca. 6 mL. The
concentrate was then transferred via cannula to another flask containing Et2O (60 mL) which was being
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stirred at 0 °C. The resultant brick red precipitate was then collected by filtration, washed with Et2O (2 × 20
mL), and dried under high vacuum.
4.2.2. (RS,E)-Carbonyl(cyclopentadienyl)-1-methoxybut-2-en-1-ylidene(triphenylphosphino)iron
tetrafluoroborate 22
C29H28BF4FeO2P requires C, 59.8; H, 4.85%; found: C, 59.9; H, 4.7%; νmax (CH2Cl2) 1960vs (CO), 1050br
–
(BF4 ); δH (300 MHz, acetone-d6) 7.70–7.40 (15H, m, Ph), 7.16 (1H, dq, J 15.1, 6.8, C(3)H), 6.63 (1H, dd, J
15.1, 1.3, C(2)H), 5.12 (5H, d, J 1.4, C5H5), 4.20 (3H, s, OMe), 2.03 (3H, dd, J 6.8, 1.3, C(4)H3); δC (50
MHz, CDCl3) 217.2 (d, J 28.8, CO), 155.6 (C(3)), 142.4 (C(2)), 134.0 (d, J 37.1, i-Ph), 133.7 (d, J 10.4, Ph),
131.9 (p-Ph), 129.7 (d, J 10.2, Ph), 87.7 (C5H5), 66.6 (OMe), 19.7 (C(4)); δP (120 MHz, acetone-d6) 63.8
(PPh3); m/z (FAB+) 495 ([M]+, 100%).
4.2.3. (RS,E)-Carbonyl(cyclopentadienyl)-1-methoxypent-2-en-1-ylidene(triphenylphosphino)iron
tetrafluoroborate 23
C30H30BF4FeO2P requires C, 60.4; H, 5.1%; found: C, 60.3; H, 5.2%; νmax (CH2Cl2) 1955vs (CO), 1050br
–
(BF4 ); δH (300 MHz, acetone-d6) 7.40–7.07 (15H, m, Ph), 7.16 (1H, dt, J 15.2, 6.5, C(3)H), 6.48 (1H, dt, J
15.2, 1.1, C(2)H), 5.14 (5H, d, J 1.5, C5H5), 4.20 (3H, s, OMe), 2.36 (2H, ddq, J 7.4, 6.5, 1.1, C(4)H2), 1.09
(3H, t, J 7.4, C(5)H3); δC (50 MHz, CDCl3) 160.7 (C(3)), 142.3 (C(2)), 133.9 (d, J 9.5, Ph), 132.1 (p-Ph),
129.9 (d, J 10.4, Ph), 88.0 (C5H5), 66.7 (OMe), 28.0 (C(4)), 25.8 (C(5)); δP (120 MHz, acetone-d6) 63.4
(PPh3); m/z (FAB+) 509 ([M]+, 100%).
4.2.4. (RS,E)-Carbonyl(cyclopentadienyl)-1-methoxyhex-2-en-1-ylidene(triphenylphosphino)iron
tetrafluoroborate 24
C31H32BF4FeO2P requires C, 61.0; H, 5.3%; found: C, 59.7; H, 5.1%; νmax (CH2Cl2) 1960vs (CO), 1070br
–
(BF4 ); δH (300 MHz, acetone-d6) 7.70–7.40 (15H, m, Ph), 7.16 (1H, dt, J 15.2, 7.1, C(3)H), 6.54 (1H, dt, J
15.2, 1.1, C(2)H), 5.14 (5H, d, J 1.4, C5H5), 4.20 (3H, s, OMe), 2.34 (2H, ddt, J 7.1, 6.7, 1.1, C(4)H2), 1.56
(2H, qt, J 7.4, 6.7, C(5)H2), 0.96 (3H, t, J 7.4, C(6)H3); δC (50 MHz, CDCl3) 159.7 (C(3)), 141.3 (C(2)),
133.8 (d, J 9.8, Ph), 132.0 (p-Ph), 129.8 (d, J 10.6, Ph), 87.9 (C5H5), 66.7 (OMe), 36.3 (C(4)), 28.9 (C(5)),
13.9 (C(6)); δP (120 MHz, acetone-d6) 63.6 (PPh3); m/z (FAB+) 523 ([M]+, 100%).
9

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4.2.5. (RS,E)-Carbonyl(cyclopentadienyl)-1-methoxy-4-methylpent-2-en-1-
ylidene(triphenylphosphino)iron tetrafluoroborate 25
C31H32BF4FeO2P requires C, 61.0; H, 5.3%; found: C, 59.7; H, 5.2%; νmax (CH2Cl2) 1960vs (CO), 1055br
–
(BF4 ); δH (300 MHz, acetone-d6) 7.80–7.40 (15H, m, Ph), 7.03 (1H, dd, J 15.3, 6.9, C(3)H), 6.34 (1H, d, J
15.3, C(2)H), 5.15 (5H, d, J 1.4, C5H5), 4.22 (3H, s, OMe), 2.59 (2H, d septet, J 6.9, 6.8, C(4)H), 1.20 (6H,
d, J 6.8, C(4)Me2); δC (50 MHz, acetone-d6) 217.2 (d, J 28.0, CO), 164.0 (C(3)), 138.4 (C(2)), 133.5 (d, J
10.1, Ph), 131.8 (p-Ph), 129.6 (d, J 10.0, Ph), 89.7 (C5H5), 66.5 (OMe), 33.0 (C(4)), 21.4 (C(4)Me2); δP (120
MHz, acetone-d6) 63.0 (PPh3); m/z (FAB+) 523 ([M]+, 100%).
4.2.6. (RS,E)-Carbonyl(cyclopentadienyl)-1-methoxyhept-2-en-1-ylidene(triphenylphosphino)iron
tetrafluoroborate 26
C32H34BF4FeO2P requires C, 61.6; H, 5.5%; found: C, 61.25; H, 5.45%; νmax (CH2Cl2) 1960vs (CO), 1050br
–
(BF4 ); δH (300 MHz, acetone-d6) 7.70–7.30 (15H, m, Ph), 7.15 (1H, dd, J 15.3, 7.1, C(3)H), 6.54 (1H, br d,
J 15.1, C(2)H), 5.12 (5H, d, J 1.4, C5H5), 4.19 (3H, s, OMe), 2.50–1.3 (6H, m, C(4)H2, C(5)H2, C(6)H2),
0.91 (3H, t, J 7.3, C(7)H3); δC (50 MHz, acetone-d6) 327.9 (C(1)), 218.0 (d, J 28.2, CO), 159.9 (C(3)), 140.9
(C(2)), 134.6 (br s, i-Ph), 133.6 (d, J 9.9, Ph), 131.8 (p-Ph), 129.6 (d, J 10.7, Ph), 89.6 (C5H5), 66.4 (OMe),
33.2, 22.5 (C(4), C(5), C(6)), 13.6 (C(7)); δP (120 MHz, acetone-d6) 63.6 (PPh3); m/z (FAB+) 537 ([M]+,
100%).
4.2.7. (RS,E)-Carbonyl(cyclopentadienyl)-1-methoxy-4,4-dimethylpent-2-en-1-
ylidene(triphenylphosphino)iron tetrafluoroborate 27
C32H34BF4FeO2P requires C, 61.6; H, 5.5%; found: C, 61.4; H, 5.8%; νmax (CH2Cl2) 1965vs (CO), 1050br
–
(BF4 ); δH (300 MHz, acetone-d6) 7.70–7.40 (15H, m, Ph), 7.02 (1H, d, J 15.6, C(3)H), 6.15 (1H, d, J 15.6,
C(2)H), 5.17 (5H, d, J 1.4, C5H5), 4.23 (3H, s, OMe), 1.11 (9H, s, CMe3); δC (50 MHz, acetone-d6) 166.7
(C(3)), 133.8 (d, J 9.8, Ph), 132.1 (p-Ph), 129.9 (d, J 10.6, Ph), 88.1 (C5H5), 66.7 (OMe), 36.0 (CMe3), 28.5
(CMe3); δP (120 MHz, acetone-d6) 62.4 (PPh3); m/z (FAB+) 537 ([M]+, 100%).
10

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4.2.8. (RS,E)-Carbonyl(cyclopentadienyl)-1-methoxy-3-phenylprop-2-en-1-
ylidene(triphenylphosphino)iron tetrafluoroborate 28
C34H30BF4FeO2P requires C, 63.4; H, 4.7%; found: C, 63.65; H, 4.7%; νmax (CH2Cl2) 1965vs (CO), 1050br
–
(BF4 ); δH (300 MHz, acetone-d6) 7.80–7.40 (22H, m, C(2)H, C(3)H, Ph), 5.26 (5H, d, J 1.4, C5H5), 4.38
(3H, s, OMe); δC (15 MHz, acetone-d6) 151.0 (C(3)), 137.0 (C(2)), 134.8 (d, J 46.1, i-Ph), 133.9 (d, J 9.8,
Ph), 132.8, 132.2, 130.5 (Ph), 130.0 (p-Ph), 130.0 (d, J 9.4, Ph), 88.2 (C5H5), 67.1 (OMe); δP (120 MHz,
acetone-d6) 63.6 (PPh3); m/z (FAB+) 557 ([M]+, 100%).
4.3. General Procedure 2 for the addition of alkyllithium reagents to α,β-unsaturated methoxycarbene
complexes 22–28
The requisite alkyllithium reagent (2.0 mmol) was added to a stirred solution of the requisite
methoxycarbene complexe 22–28 (1.5 mmol) in CH2Cl2 (20 mL) at –78 °C. After 2 h the reaction was
quenched by the addition of MeOH, allowed to warm to rt, passed through a plug of alumina (grade V), and
concentrated in vacuo. The residue was dissolved in THF (20 mL) and either TsOH or HBF4 (2.0 mmol) was
added to the resultant solution. The reaction mixture was stirred at rt for 1 h, then NaI (2.0 mmol) was
added. The resultant mixture was stirred at rt for 4 h then concentrated in vacuo. The residue was dissolved
in CH2Cl2 (2 × 20 mL) and the resultant solution was filtered through a plug of alumina (grade V, eluent
CH2Cl2). The resultant iron acyl complexes were then isolated following purification by flash column
chromatography on alumina (grade V, eluent Et2O).
4.3.1. (RS,SR)-Carbonyl(cyclopentadienyl)-3-methylpentanoyl(triphenylphosphino)iron 65
C30H31FeO2P requires C, 70.6; H, 6.1%; found: C, 70.75; H, 6.3%; νmax (CH2Cl2) 1910vs (CO), 1600vs
(CO); δH (300 MHz, CDCl3) 7.70–7.30 (15H, m, Ph), 4.40 (5H, d, J 1.4, C5H5), 2.93 (1H, dd, J 17.6, 5.1,
C(2)HA), 2.36 (1H, dd, J 17.6, 7.2, C(2)HB), 1.65 (1H, m, C(3)H), 1.24–0.94 (2H, m, C(4)H2), 0.78 (3H, t, J
7.3, C(5)H3), 0.45 (3H, d, J 6.7, C(3)Me); δC (50 MHz, CDCl3) 136.6 (d, J 42.6, i-Ph), 133.4 (d, J 9.9, Ph),
129.6 (p-Ph), 128.0 (d, J 9.4, Ph), 82.6 (C5H5), 73.5 (C(2)), 30.8 (C(3)), 29.5 (C(4)), 19.2 (C(3)Me), 11.4
(C(5)); δP (120 MHz, CDCl3) 72.2 (PPh3); m/z (FAB+) 510 ([M]+, 100%).
11

ACCEPTED MANUSCRIPT
4.3.2. (RS,SR)-Carbonyl(cyclopentadienyl)-3-methylhexanoyl(triphenylphosphino)iron 66
C31H33FeO2P requires C, 71.0; H, 6.3%; found: C, 71.0; H, 6.6%; νmax (CH2Cl2) 1905vs (CO), 1600vs (CO);
δH (300 MHz, CDCl3) 7.50–7.30 (15H, m, Ph), 4.40 (5H, d, J 1.1, C5H5), 2.91 (1H, dd, J 16.6, 4.8, C(2)HA),
2.35 (1H, dd, J 16.6, 7.8, C(2)HB), 1.73–1.56 (1H, m, C(3)H), 1.27–0.87 (4H, m, C(4)H2, C(5)H2), 0.83 (3H,
t, J 7.2, C(6)H3), 0.40 (3H, d, J 6.6, C(3)Me); δC (50 MHz, CDCl3) 136.7 (d, J 42.5, i-Ph), 133.4 (d, J 10.2,
Ph), 129.6 (p-Ph), 128.0 (d, J 9.5, Ph), 85.3 (C5H5), 74.1 (C(2)), 39.4 (C(3)), 29.1 (C(4)), 20.1 (C(5)), 19.7,
14.4 (C(6), C(3)Me); δP (120 MHz, CDCl3) 72.5 (PPh3); m/z (FAB+) 524 ([M]+, 100%).
4.3.3. (RS,RS)-Carbonyl(cyclopentadienyl)-3,4-dimethylpentanoyl(triphenylphosphino)iron 67
C31H33FeO2P requires C, 71.0; H, 6.3%; found: C, 71.0; H, 6.4%; νmax (CH2Cl2) 1900vs (CO), 1600vs (CO);
δH (300 MHz, CDCl3) 7.60–7.30 (15H, m, Ph), 4.40 (5H, d, J 1.0, C5H5), 3.47 (1H, dd, J 13.2, 4.0, C(2)HA),
3.11 (1H, dd, J 13.2, 4.0, C(2)HB), 2.57 (1H, m, C(3)H), 1.66 (1H, m, C(4)H), 0.75 (3H, d, J 7.1, C(3)Me),
0.73 (3H, d, J 7.0, C(4)MeA), 0.34 (3H, d, J 6.8, C(4)MeB); δC (50 MHz, CDCl3) 220.7 (d, J 28.2, CO),
136.6 (d, J 42.5, i-Ph), 133.4 (d, J 10.1, Ph), 129.6 (p-Ph), 128.0 (d, J 9.9, Ph), 85.3 (C5H5), 71.4 (C(2)),
34.4 (C(3)), 32.1 (C(4)), 20.1, 18.2, 15.5 (C(3)Me, C(4)Me2); δP (120 MHz, CDCl3) 72.4 (PPh3); m/z (FAB+)
524 ([M]+, 100%).
4.3.4. (RS,SR)-Carbonyl(cyclopentadienyl)-3-methylheptanoyl(triphenylphosphino)iron 6819
δH (300 MHz, CDCl3) 7.50–7.30 (15H, m, Ph), 4.40 (5H, d, J 0.9, C5H5), 2.95–2.32 (2H, m, C(2)H2), 1.71
(1H, m, C(3)H), 1.29–0.93 (6H, m, C(4)H2, C(5)H2, C(6)H2), 0.86 (3H, t, J 6.9, C(7)H3), 0.41 (3H, d, J 6.6,
C(3)Me).
4.3.5. (RS,RS)-Carbonyl(cyclopentadienyl)-3,4,4-trimethylpentanoyl(triphenylphosphino)iron 69
C32H35FeO2P requires C, 71.4; H, 6.55%; found: C, 71.7; H, 6.8%; νmax (CH2Cl2) 1900vs (CO), 1600vs
(CO); δH (300 MHz, CDCl3) 7.60–7.30 (15H, m, Ph), 4.41 (5H, d, J 1.2, C5H5), 3.04 (1H, m, C(2)HA), 2.26
(1H, m, C(2)HB), 1.75–1.60 (1H, m, C(3)H), 0.75 (9H, s, C(4)Me3), 0.29 (3H, d, J 6.8, C(3)Me); δC (50
MHz, CDCl3) 220.8 (d, J 31.5, CO), 136.6 (d, J 42.6, i-Ph), 133.4 (d, J 10.0, Ph), 129.6 (p-Ph), 128.0 (d, J
9.4, Ph), 85.2 (C5H5), 69.8 (d, J 5.3, C(2)), 38.0 (C(3)), 32.5, 27.3, 15.1 (C(4), C(3)Me, C(4)Me3); δP (120
MHz, CDCl3) 72.4 (PPh3); m/z (FAB+) 538 ([M]+, 100%).
12

ACCEPTED MANUSCRIPT
4.3.6. (RS,RS)-Carbonyl(cyclopentadienyl)-3-phenylbutanoyl(triphenylphosphino)iron 70
C34H31FeO2P requires C, 73.1; H, 5.6%; found: C, 73.2; H, 5.6%; νmax (CH2Cl2) 1900vs (CO), 1600vs (CO);
δH (300 MHz, CDCl3) 7.60–7.00 (20H, m, Ph), 4.22 (5H, d, J 1.4, C5H5), 3.37 (1H, dd, J 16.5, 5.9, C(2)HA),
3.07–2.85 (1H, m, C(3)H), 2.71 (1H, dd, J 16.5, 7.2, C(2)HB), 0.76 (3H, d, J 6.9, C(4)H3); δC (50 MHz,
CDCl3) 146.3 (i-Ph), 135.8 (d, J 41.8, i-Ph), 131.9 (d, J 10.0, Ph), 130.0 (p-Ph), 127.4 (Ph), 127.2 (d, J 9.3,
Ph), 126.9 (p-Ph), 125.6 (Ph), 85.3 (C5H5), 73.3 (C(2)), 35.4 (C(3)), 14.2 (C(4)); δP (120 MHz, CDCl3) 71.3
(PPh3); m/z (FAB+) 558 ([M]+, 100%).
4.3.7. (RS,RS)-Carbonyl(cyclopentadienyl)-3-methylheptanoyl(triphenylphosphino)iron 71
C32H35FeO2P requires C, 71.4; H, 6.55%; found: C, 71.2; H, 6.7%; νmax (CH2Cl2) 1910vs (CO), 1600vs
(CO); δH (300 MHz, CDCl3) 7.63–7.42 (15H, m, Ph), 4.39 (5H, d, J 1.3, C5H5), 2.83 (1H, dd, J 16.9, 7.9,
C(2)HA), 2.50 (1H, dd, J 16.9, 4.8, C(2)HB), 1.56 (1H, m, C(3)H), 1.18–0.72 (6H, m, C(4)H2, C(5)H2,
C(6)H2), 0.84 (3H, t, J 7.0, C(7)H3), 0.72 (3H, d, J 6.5, C(3)Me); δC (50 MHz, CDCl3) 136.6 (d, J 42.7, i-
Ph), 133.4 (d, J 9.5, Ph), 129.6 (p-Ph), 128.0 (d, J 9.5, Ph), 82.3 (C5H5), 74.3 (d, J 5.2, C(2)), 36.2 (C(3)),
29.4, 29.2, 22.8 (C(4), C(5), C(6)), 20.3, 14.2 (C(7), C(3)Me); δP (120 MHz, CDCl3) 72.5 (PPh3); m/z
(FAB+) 538 ([M]+, 100%).
4.3.8. (RS,RS)-Carbonyl(cyclopentadienyl)-3-ethylheptanoyl(triphenylphosphino)iron 72
C33H37FeO2P requires C, 71.7; H, 6.75%; found: C, 72.1; H, 6.7%; νmax (CH2Cl2) 1910vs (CO), 1595vs
(CO); δH (300 MHz, CDCl3) 7.70–7.40 (15H, m, Ph), 4.40 (5H, d, J 0.9, C5H5), 2.95 (1H, dd, J 16.9, 6.9,
C(2)HA), 2.39 (1H, dd, J 16.9, 5.5, C(2)HB), 1.54 (1H, m, C(3)H), 1.20–0.80 (8H, m, C(4)H2, C(5)H2,
C(6)H2, C(1')H2), 0.84 (3H, t, J 7.3, C(2')H3), 0.82 (3H, t, J 7.0, C(7)H3),; δC (50 MHz, CDCl3) 221.3 (d, J
38.7, CO), 136.9 (d, J 42.1, i-Ph), 133.4 (d, J 10.2, Ph), 129.6 (d, J 9.2, Ph), 128.0 (d, J 9.5, Ph), 85.3
(C5H5), 71.3 (d, J 5.4, C(2)), 35.1 (C(3)), 32.5, 29.1, 23.0 (C(4)H2, C(5)H2, C(6)H2, C(1')H2), 14.2, 10.7
(C(7), C(2')); δP (120 MHz, CDCl3) 72.5 (PPh3); m/z (FAB+) 552 ([M]+, 100%).
4.3.9. (RS,RS)-Carbonyl(cyclopentadienyl)-3-propylheptanoyl(triphenylphosphino)iron 73
C34H39FeO2P requires C, 72.1; H, 6.9%; found: C, 72.2; H, 7.0%; νmax (CH2Cl2) 1895vs (CO), 1600vs (CO);
δH (300 MHz, CDCl3) 7.60–7.30 (15H, m, Ph), 4.39 (5H, d, J 1.3, C5H5), 2.94 (1H, dd, J 17.0, 6.4, C(2)HA),
2.38 (1H, dd, J 17.0, 5.8, C(2)HB), 1.60–0.76 (11H, m, C(3)H, C(4)H2, C(5)H2, C(6)H2, C(1')H2, C(2')H2),
13

ACCEPTED MANUSCRIPT
0.83 (3H, t, J 7.0, CH3), 0.82 (3H, t, J 7.1, CH3); δC (50 MHz, CDCl3) 136.7 (d, J 42.7, i-Ph), 133.4 (d, J
9.6, Ph), 129.6 (p-Ph), 128.0 (d, J 9.4, Ph), 85.3 (C5H5), 71.8 (C(2)), 36.4, 33.2, 29.7, 29.0, 23.0 (C(3), C(4),
C(5), C(6), C(1'), C(2')), 14.6, 14.1 (C(7), C(3')); δP (120 MHz, CDCl3) 72.5 (PPh3); m/z (FAB+) 566 ([M]+,
100%), 538 ([M–CO]+, 40%).
4.3.10. (RS,RS)-Carbonyl(cyclopentadienyl)-3-isopropylheptanoyl(triphenylphosphino)iron 74
C34H39FeO2P requires C, 72.1; H, 6.9%; found: C, 71.9; H, 7.0%; νmax (CH2Cl2) 1900vs (CO), 1600vs (CO);
δH (300 MHz, CDCl3) 7.60–7.30 (15H, m, Ph), 4.40 (5H, d, J 1.0, C5H5), 3.04 (1H, dd, J 17.2, 5.4, C(2)HA),
2.27 (1H, dd, J 17.2, 4.9, C(2)HB), 1.60–0.90 (8H, m, C(3)H, CHMe, C(4)H2, C(5)H2, C(6)H2), 0.83 (3H, t,
J 7.3, C(7)H3), 0.78 (3H, d, J 6.7, CHMeAMeB), 0.73 (3H, d, J 6.7, CHMeAMeB); δC (50 MHz, CDCl3) 220.4
(d, J 31.5, CO), 136.6 (d, J 42.5, i-Ph), 133.4 (d, J 9.3, Ph), 129.6 (p-Ph), 128.0 (d, J 9.3, Ph), 85.2 (C5H5),
68.3 (C(2)), 39.0 (C(3)), 29.6, 28.9, 23.0 (C(4), C(5), C(6)), 28.6 (CHMe2), 18.9, 14.1 (C(7), CHMe2); δP
(120 MHz, CDCl3) 72.5 (PPh3); m/z (FAB+) 566 ([M]+, 100%).
4.3.11. (RS,RS)-Carbonyl(cyclopentadienyl)-3-tert-butylheptanoyl(triphenylphosphino)iron 75
Data for mixture: C35H41FeO2P requires C, 72.4; H, 7.1%; found: C, 72.5; H, 7.2%; νmax (CHCl3) 1910vs
(CO), 1600s (CO); m/z (FAB+) 580 ([M]+, 100%). Data for (RS,RS)-epimer: δH (300 MHz, CDCl3) 7.50–
7.30 (15H, m, Ph), 4.42 (5H, d, J 1.0, C5H5), 3.35 (1H, dd, J 18.0, 5.1, C(2)HA), 2.16 (1H, dd, J 18.0, 4.5,
C(2)HB), 1.53 (1H, m, C(3)H), 1.06 (2H, m, C(4)H2), 0.79 (9H, s, CMe3), 0.78 (3H, t, J 7.2, C(7)H3), 0.68
(4H, m, C(5)H2, C(6)H2); m/z (FAB+) 580 ([M]+, 100%). Data for (RS,SR)-epimer: δH (300 MHz, CDCl3)
7.60–7.30 (15H, m, Ph), 4.42 (5H, d, J 1.0, C5H5), 3.12 (1H, dd, J 18.1, 6.5, C(2)HA), 2.52 (1H, dd, J 18.1,
3.0, C(2)HB), 1.50 (1H, m, C(3)H), 1.35–1.18 (6H, m, C(4)H2, C(5)H2,) C(6)H2), 0.90 (3H, t, J 6.8, C(7)H3),
0.54 (9H, s, CMe3).
4.3.12. (RS,RS)-Carbonyl(cyclopentadienyl)-3-phenylheptanoyl(triphenylphosphino)iron 76
C37H37FeO2P requires C, 74.0; H, 6.2%; found: C, 74.2; H, 6.3%; νmax (CH2Cl2) 1910s (CO), 1600m (CO);
δH (300 MHz, CDCl3) 7.60–7.15 (20H, m, Ph), 4.12 (5H, d, J 1.2, C5H5), 3.43 (1H, dd, J 16.4, 7.3, C(2)HA),
2.79 (1H, m, C(3)H), 2.63 (1H, dd, J 16.4, 6.1, C(2)HB), 1.34–0.79 (6H, m, C(4)H2, C(5)H2, C(6)H2), 0.75
(3H, t, J 7.2, C(7)H3); m/z (FAB+) 600 ([M]+, 100%).
14

ACCEPTED MANUSCRIPT
4.3.13. (RS,SR)-Carbonyl(cyclopentadienyl)-3-phenylbutanoyl(triphenylphosphino)iron 77
C34H31FeO2P requires C, 73.1; H, 5.6%; found: C, 73.5; H, 5.8%; νmax (CH2Cl2) 1910vs (CO), 1600vs (CO);
δH (300 MHz, CDCl3) 7.70–7.10 (20H, m, Ph), 4.42 (5H, d, J 1.0, C5H5), 3.11 (1H, dd, J 16.5, 9.5, C(2)HA),
2.98 (1H, ddq, J 9.5, 6.8, 3.8, C(3)H), 2.88 (1H, dd, J 16.5, 3.8, C(2)HB), 1.14 (3H, d, J 6.8, C(4)H3); δC (50
MHz, CDCl3) 147.8 (i-Ph), 136.4 (d, J 42.6, i-Ph), 133.3 (d, J 10.1, Ph), 129.7 (p-Ph), 128.7 (Ph), 128.0 (d,
J 9.4, Ph), 127.0 (p-Ph), 82.3 (C5H5), 74.2 (C(2)), 35.4 (C(3)), 21.5 (C(4)); δP (120 MHz, CDCl3) 72.4
(PPh3); m/z (FAB+) 558 ([M]+, 100%).
4.3.14. (RS,SR)-Carbonyl(cyclopentadienyl)-3-phenylpentanoyl(triphenylphosphino)iron 78
C35H33FeO2P requires C, 73.4; H, 5.8%; found: C, 73.4; H, 5.8%; νmax (CH2Cl2) 1910vs (CO), 1595vs (CO);
δH (300 MHz, CDCl3) 7.70–6.90 (20H, m, Ph), 4.38 (5H, d, J 1.2, C5H5), 3.22 (1H, dd, J 16.4, 8.3, C(2)HA),
2.70 (1H, dd, J 16.4, 4.7, C(2)HB), 2.85 (1H, m, C(3)H), 1.72–1.40 (2H, m, C(4)H2), 0.68 (3H, t, J 7.3,
C(5)H3); δC (50 MHz, CDCl3) 145.8 (i-Ph), 136.4 (d, J 43.0, p-Ph), 133.3 (d, J 10.2, Ph), 129.6 (p-Ph),
128.0 (d, J 9.2, Ph), 127.9 (Ph), 127.8 (p-Ph), 125.4 (Ph), 85.3 (C5H5), 72.6 (d, J 5.0, C(2)), 42.9 (C(3),
C(4)), 29.0 (C(5)); δP (120 MHz, CDCl3) 72.3 (PPh3); m/z (FAB+) 572 ([M]+, 100%).
4.3.15. (RS,SR)-Carbonyl(cyclopentadienyl)-3-phenylhexanoyl(triphenylphosphino)iron 79
C36H35FeO2P requires C, 73.7; H, 6.0%; found: C, 74.05; H, 6.1%; νmax (CH2Cl2) 1895vs (CO), 1600vs
(CO); δH (300 MHz, CDCl3) 7.41–6.93 (20H, m, Ph), 4.36 (5H, d, J 1.4, C5H5), 3.17 (1H, dd, J 16.5, 8.2,
C(2)HA), 2.87 (1H, m, C(3)H), 2.65 (1H, dd, J 16.5, 4.8, C(2)HB), 1.52–0.87 (4H, m, C(4)H2, C(5)H2), 0.77
(3H, t, J 7.2, C(6)H3); δC (50 MHz, CDCl3) 220.5 (d, J 30.6, CO), 146.1 (i-Ph), 136.4 (d, J 42.8, i-Ph), 133.3
(d, J 10.0, Ph), 129.6 (p-Ph), 128.7 (Ph), 128.0 (d, J 8.9, Ph), 127.1 (Ph), 125.3 (p-Ph), 85.3 (C5H5), 72.8 (d,
J 4.8, C(2)), 41.2 (C(3)), 38.7, 20.7 (C(4), C(5)), 14.2 (C(6)); δP (120 MHz, CDCl3) 72.4 (PPh3); m/z (FAB+)
586 ([M]+, 100%).
4.3.16. (RS,RS)-Carbonyl(cyclopentadienyl)-3-phenyl-4-methylpentanoyl(triphenylphosphino)iron 80
C36H35FeO2P requires C, 73.7; H, 6.0%; found: C, 73.4; H, 6.0%; νmax (CH2Cl2) 1900vs (CO), 1595vs (CO);
δH (300 MHz, CDCl3) 7.60–6.90 (20H, m, Ph), 4.29 (5H, d, J 1.1, C5H5), 3.65 (1H, dd, J 12.8, 4.0, C(2)HA),
3.09 (1H, dd, J 12.8, 5.6, C(2)HB), 3.00 (1H, m, C(3)H), 2.66 (1H, m, C(4)H), 0.76 (3H, d, J 6.7, C(4)MeA),
0.68 (3H, d, J 6.7, C(4)MeB); δC (50 MHz, CDCl3) 220.7 (d, J 31.0, CO), 144.5 (i-Ph), 136.2 (d, J 42.7, i-
15

ACCEPTED MANUSCRIPT
Ph), 133.3 (d, J 9.8, Ph), 129.6 (p-Ph), 128.8 (Ph), 128.0 (d, J 9.8, Ph), 127.6 (Ph), 125.3 (p-Ph), 85.4
(C5H5), 68.3 (C(2)), 47.3 (C(3)), 33.4 (C(4)), 20.6, 20.0 (C(4)Me2); δP (120 MHz, CDCl3) 71.6 (PPh3); m/z
(FAB+) 586 ([M]+, 100%).
4.3.17. (RS,SR)-Carbonyl(cyclopentadienyl)-3-phenylheptanoyl(triphenylphosphino)iron 81
C37H37FeO2P requires C, 74.0; H, 6.2%; found: C, 74.3; H, 6.4%; νmax (CH2Cl2) 1910s (CO), 1600m (CO);
δH (300 MHz, CDCl3) 7.80–7.20 (20H, m, Ph), 4.37 (5H, d, J 1.6, C5H5), 3.17 (1H, dd, J 16.1, 8.1, C(2)HA),
3.06 (1H, m, C(3)H), 2.87 (1H, dd, J 16.1, 4.6, C(2)HB), 1.86–0.83 (6H, m, C(4)H2, C(5)H2, C(6)H2), 0.78
(3H, t, J 7.2, C(7)H3); m/z (FAB+) 600 ([M]+, 100%).
4.3.18. (RS,RS)-Carbonyl(cyclopentadienyl)-3-phenyl-4,4-dimethylpentanoyl(triphenylphosphino)iron
82
C37H37FeO2P requires C, 74.0; H, 6.2%; found: C, 74.2; H, 6.3%; νmax (CH2Cl2) 1900vs (CO), 1600vs (CO);
δH (300 MHz, CDCl3) 7.70–7.07 (20H, m, Ph), 4.24 (5H, d, J 1.1, C5H5), 0.78 (9H, s, C(4)Me3); m/z (FAB+)
600 ([M]+, 100%). Data for (RS,SR)-epimer: δH (300 MHz, CDCl3) [selected peaks] 7.67–7.07 (20H, m, Ph),
3.99 (5H, d, J 1.0, C5H5), 0.70 (9H, s, C(4)Me3).
4.4. (RS,SR)-Carbonyl(cyclopentadienyl)-3-ethyl-4,4-bismethoxycarbonylbutanoyl(triphenyl-
phosphino)iron 85
BuLi (1.70 M in hexanes, 0.20 mL, 0.34 mmol) was added to a stirred solution of dimethyl malonate (0.08
mL, 0.68 mmol) in THF (5 mL) at 0 °C, and and the resultant mixture was stirred at rt for 15 min. The
reaction mixture was then added to a solution of 23 (100 mg, 0.17 mmol) in CH2Cl2 (40 mL) at –78 °C, and
the resultant mixture was stirred at –78 °C for 1 h. MeOH (1 mL) was then added and the reaction mixture
was allowed to warm to rt and concentrated in vacuo. The residue was extracted with Et2O (2 × 20 mL) and
the combined organic extracts were filtered through alumina (grade V). The filtrate was then concentrated in
vacuo, then THF (10 mL) and HBF4 (0.40 mL, 0.18 mmol) were added sequentially. The resultant mixture
was stirred at rt for 1 h, NaI (100 mg, 0.68 mmol) was added, and the reaction mixture was stirred at rt for 1
min then concentrated in vacuo. The residue was extracted with CH2Cl2 (2 × 20 mL) and the combined
organic extracts were filtered through alumina (grade V, eluent CH2Cl2) and concentrated in vacuo.
Purification by flash column chromatography on alumina (grade I, eluent CH2Cl2) gave 85 as a yellow gum
16

ACCEPTED MANUSCRIPT
(150 mg, 70%, 91:9 dr); C34H35FeO6P requires C, 65.2; H, 5.6%; found: C, 65.3; H, 5.6%; νmax (CH2Cl2)
1910vs (CO), 1725s (C=O, ester), 1590vs (C=O); δH (300 MHz, CDCl3) 7.60–7.20 (15H, m, Ph), 4.39 (5H,
d, J 0.9, C5H5), 3.67 (3H, s, CO2Me), 3.64 (3H, s, CO2Me), 3.24 (1H, d, J 5.7, C(4)H), 3.10 (1H, dd, J 17.4,
6.1, C(2)HA), 2,78 (1H, dd, J 17.4, 5.9, C(2)HB), 2.25 (1H, m, C(3)H), 1.33–1.12 (2H, m, C(1')H2), 0.75
(3H, t, J 7.4, C(2')H3); δC (50 MHz, CDCl3) 136.6 (d, J 42.6, i-Ph), 133.3 (d, J 9.6, Ph), 129.6 (p-Ph), 128.0
(d, J 9.7, Ph), 85.1 (C5H5), 66.6 (C(2)), 53.7 (C(4)), 51.9, 51.8 (2 × CO2Me), 36.4 (C(3)), 23.9 (C(1')), 11.7
(C(2')); δP (120 MHz, CDCl3) 73.0 (PPh3); m/z (FAB+) 626 ([M]+, 100%).
4.5. (RS,RS)-Carbonyl(cyclopentadienyl)-3-methyl-5-(N,N-dimethylamino)-5-oxopentanoyl(triphenyl-
phosphino)iron 86
N,N-Dimethylacetamide (0.240 mL, 2.60 mmol) was added to a stirred solution of LDA [prepared from
iPr2NH (0.360 mL, 2.60 mmol) and BuLi (1.50 M in hexanes, 1.60 mL, 2.40 mmol)] at –78 °C, and the
resultant mixture was allowed to warm to –10 °C then cooled to –78 °C. A solution of 22 (300 mg, 0.52
mmol) in CH2Cl2 (2 mL) was added and the reaction mixture was stirred at –78 °C for 1 h before MeOH (1
mL) was added. The reaction mixture was then allowed to warm to rt and concentrated in vacuo. The residue
was extracted with Et2O (2 × 20 mL) and the resultant solution was filtered through alumina (grade V, eluent
Et2O). The filtrate was then concentrated in vacuo, THF (10 mL) and TsOH (0.200 g, 1.05 mmol) were
added sequentially to the residue, and the resultant mixture was stirred at rt for 1 h. NaI (200 mg, 1.33
mmol) was then added, the reaction mixture was stirred at rt for 1 min, then concentrated in vacuo. The
residue was extracted with CH2Cl2 (2 × 20 mL) and the combined organic extracts were filtered through
alumina (grade V, eluent CH2Cl2) and concentrated in vacuo. Purification by flash column chromatography
on silica gel (eluent CH2Cl2/MeOH, 99:1) gave an 84:16 mixture of 86 and 87, respectively.
Recrystallisation (CH2Cl2/Et2O) gave an 84:16 mixture of 86 and 87, respectively, as a red crystalline solid
(190 mg, 65%). Data for mixture: C32H34FeNO3P requires C, 67.7; H, 6.0; N, 2.5%; found: C, 67.4; H, 6.2;
N, 2.5%; νmax (CH2Cl2) 1913vs (CO), 1635s (C=O, amide), 1610vs (C=O); m/z (FAB+) 568 ([M+H]+, 15%),
383 (100%). Data for 86: δH (300 MHz, CD2Cl2) 7.51–7.33 (15H, m, Ph), 4.39 (5H, d, J 0.7, C5H5), 2.95
(1H, dd, J 17.2, 5.2, C(2)HA), 2.84 (3H, s, NMeA), 2.82 (3H, s, NMeB), 2.64 (1H, dd, J 17.2, 7.4, C(2)HB),
2.04 (1H, m, C(3)H), 1.79 (1H, dd, J 14.5, 4.3, C(4)HA), 1.50 (1H, dd, J 14.5, 9.7, C(4)HB), 0.71 (3H, d, J
6.6, C(3)Me); δC (50 MHz, CD2Cl2) 220.6 (d, J 29.3, CO), 172.0 (NCO), 136.5 (d, J 43.2, i-Ph), 133.3 (d, J
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9.7, Ph), 129.7 (p-Ph), 128.0 (d, J 9.6, Ph), 85.3 (C5H5), 73.4 (C(2)), 40.1, 37.6 (NMe2), 35.2 (C(4)), 27.1
(C(3)), 19.9 (C(3)Me); δP (120 MHz, CD2Cl2) 76.3 (PPh3).
4.6. (RS,SR)-Carbonyl(cyclopentadienyl)-3-methyl-(N,N-dimethylamino)-5-oxopentanoyl(triphenyl-
phosphino)iron 87
i
N,N-Dimethylacetamide (0.230 mL, 2.50 mmol) was added to a solution of LDA [prepared from Pr2NH
(0.350 mL, 2.50 mmol) and BuLi (1.50 M in hexanes, 1.60 mL, 2.40 mmol)] at –78 °C, and the resultant
mixture was allowed to warm to –10 °C then cooled to –78 °C. The resultant mixture was added via cannula
to a solution of 15 (240 mg, 0.50 mmol) in THF (5 mL) at –78 °C and the resultant mixture warmed to –40
°C over a period of 3 h. MeOH (1 mL) was then added, and the reaction mixture was allowed to warm to rt
and concentrated in vacuo. The residue was extracted with CH2Cl2 (2 × 20 mL), and filtered through a plug
of alumina (grade V, eluent CH2Cl2), and concentrated in vacuo. Purification by flash column
chromatography on silica gel (eluent CH2Cl2/MeOH, 99:1) gave an 86:14 mixture of 87 and 86, respectively.
Recrystallisation (CH2Cl2/Et2O) gave an 86:14 mixture of 87 and 86, respectively, as yellow needles (210
mg, 75%). Data for mixture: C32H34FeNO3P requires C, 67.7; H, 6.0; N, 2.5%; found: C, 67.9; H, 6.3; N,
2.4%; νmax (CH2Cl2) 1913vs (CO), 1635s (C=O, amide), 1610vs (C=O); m/z (FAB+) 568 ([M+H]+, 10%),
383 (100%). Data for 87: δH (300 MHz, CD2Cl2) 7.51–7.33 (15H, m, Ph), 4.40 (5H, d, J 1.0, C5H5), 3.00
(1H, dd, J 17.3, 5.8, C(2)HA), 2.93 (3H, s, NMeA), 2.85 (3H, s, NMeB), 2.54 (1H, dd, J 17.3, 6.3, C(2)HB),
2.14 (1H, dd, J 14.0, 5.4, C(4)HA), 2.01 (1H, m, C(3)H), 1.87 (1H, dd, J 14.0, 8.0, C(4)HB), 0.50 (3H, d, J
6.5, C(3)Me); δC (50 MHz, CD2Cl2) 220.6 (d, J 31.8, CO), 172.6 (NCO), 136.5 (d, J 43.2, i-Ph), 133.3 (d, J
9.6, Ph), 129.6 (p-Ph), 128.0 (d, J 9.4, Ph), 85.3 (C5H5), 72.9 (C(2)), 40.4, 37.5 (NMe2), 35.3 (C(4)), 27.0
(C(3)), 19.9 (C(3)Me); δP (120 MHz, CD2Cl2) 76.3 (PPh3).
4.7. (RS,RS)-Carbonyl(cyclopentadienyl)-3-methyl-5-oxopentanoyl(triphenyl-phosphino)iron 88
tBuLi (1.70 M in hexanes, 2.95 mL, 2.50 mmol) was added to a stirred solution of 91 (600 mg, 2.50 mmol)
in Et2O (15 mL) at –78 °C, and the resultant mixture was stirred at –78 °C for 2 h. A solution of 22 (290 mg,
0.50 mmol) in CH2Cl2 (10 mL) was then added via cannula, and the deep red solution immediately turned
orange. The reaction mixture was stirred at –78 °C for 1 h then MeOH (1 mL) was added. The resultant
mixture was allowed to warm to rt, filtered through alumina (grade V, eluent CH2Cl2), and concentrated in
vacuo. The residue was dissolved in THF (10 mL) and TsOH (150 mg, 0.80 mmol) was added to the
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resultant solution. The reaction mixture was stirred at rt for 1 h, NaI (130 mg, 0.85 mmol) was added, and
the reaction mixture was stirred at rt for 1 min, then concentrated in vacuo. The reaction mixture was
extracted with CH2Cl2 (2 × 20 mL) and the combined organic extracts were filtered through a plug of
alumina (grade V, eluent CH2Cl2), then concentrated in vacuo. Sequential purification by flash column
chromatography on silica gel (eluent 40–60 °C petrol/Et2O, 5:1) and recrystallisation (Et2O, –30 °C) gave 88
as yellow plates (62 mg, 24%, 96:4 dr); C30H29FeO3P requires C, 68.7; H, 5.6%; found: C, 68.6; H, 5.4%;
νmax (CH2Cl2) 1914vs (CO), 1720s (C=O, aldehyde), 1606vs (C=O); δH (500 MHz, CDCl3) 9.43 (1H, dd, J
3.1, 1.6, C(5)H), 7.67–7.37 (15H, m, Ph), 4.41 (5H, s, C5H5), 2.94 (1H, dd, J 17.4, 5.6, C(2)HA), 2.56 (1H,
dd J 17.4, 7.3, C(2)HB), 2.19 (1H, m, C(3)H), 1.81 (1H, app dd, J 16.0, 4.1, C(4)HA), 1.61 (1H, ddd, J 16.0,
8.6, 3.1, C(4)HB), 0.75 (3H, d, J 6.7, C(3)Me); δC (125 MHz, CDCl3) 276.0 (d, J 22.6, C(1)), 220.5 (d, J
31.2, CO), 203.3 (C(5)), 136.5 (d, J 42.7, i-Ph), 133.4 (d, J 9.2, Ph), 129.8 (p-Ph), 128.1 (d, J 9.3, Ph), 85.3
(C5H5), 72.6 (C(2)), 50.2 (C(4)), 24.8 (C(3)), 20.3 (C(3)Me); δP (200 MHz, CDCl3) 76.7 (PPh3); m/z (FAB+)
525 ([M+H]+, 10%), 383 (100%).
4.8. O-(tert-Butyldimethylsilyl)-2,2,2-tribromoethanol 90
2,2,2-Tribromoethanol 89 (5.00 g, 17.7 mmol) and imidazole (3.00 g, 44.2 mmol) were added sequentially
to a stirred solution of TBDMSCl (3.20 g, 21.2 mmol) in DMF (10 mL), and the resultant mixture was
stirred at rt for 18 h. The reaction mixture was then partitioned between EtOAc (50 mL) and 0.1 M aq HCl
(50 mL), the aqueous layer was extracted EtOAc (3 × 40 mL), and the combined organic extracts were
washed sequentially with satd aq NaHCO3 (100 mL), H2O (100 mL) and brine (100 mL) then dried, filtered
and concentrated in vacuo. Purification by distillation (bp 115–117 °C; 10 mmHg) gave 90 as a colourless
oil (6.25 g, 89%);17 δH (200 MHz, CDCl3) 4.29 (2H, s, C(1)H2), 0.98 (9H, s, SiCMe3), 0.20 (6H, s, SiMe2).
4.9. (Z)-1-Bromo-2-(tert-butyldimethylsilyloxy)ethene 91
BuLi (1.60 M in hexanes, 33.2 mL, 53.2 mmol) was added to a stirred solution of 90 (10.6 g, 26.6 mmol) in
Et2O (120 mL) at –78 °C, and the resultant mixture was stirred at –78 °C for 6 h then allowed to warm to rt
and stirred at rt for 24 h. Satd aq NaHCO3 (20 mL) was then added, the aqueous layer was extracted with
Et2O (3 × 30 mL), and the combined organic extracts were dried, filtered and concentrated in vacuo.
Purification by distillation (bp 88–90 °C; 20 mmHg) gave 91 as a colourless oil (3.20 g, 51%);17 δH (200
19

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MHz, CDCl3) 6.77 (1H, d, J 3.8 C(2)H), 5.24 (1H, d, J 3.8 C(1)H), 0.97 (9H, s, SiCMe3), 0.20 (6H, s,
SiMe2).
References and notes
1
For reviews of the iron chiral auxiliary, see: (a) Davies, S. G. Pure Appl. Chem. 1988, 60, 13; (b) Davies,
S. G. Aldrichimica Acta 1990, 23, 31.
2 Davies, S. G.; Seeman, J. I. Tetrahedron Lett. 1984, 25, 1845.
3
(a) Davies, S. G.; Dordor, I. M.; Walker, J. C.; Warner, P. Tetrahedron Lett. 1984, 25, 2709; (b)
Bashiardes, G.; Davies, S. G. Tetrahedron Lett. 1987, 28, 5563; (c) Davies, S. G.; Polywka, R.; Warner, P.
Tetrahedron 1990, 46, 4847; (d) Case-Green, S. C.; Davies, S. G.; Hedgecock, C. J. R. Synlett 1991, 779; (e)
Baker, T. M.; Bodwell, G. J.; Davies, S. G.; Edwards, A. J.; Metzler, M. R. Tetrahedron 1993, 49, 5635; (f)
Bashiardes, G.; Bodwell, G. J.; Collingwood, S. P.; Costello, J. F.; Davies, S. G.; Fletcher, A. M.; Garner,
A.; Preston, S. C.; Thomson, J. E. Tetrahedron 2014, 70, 8938.
4 Baird, G. J.; Bandy, J. A.; Davies, S. G.; Prout, K. J. Chem. Soc., Chem. Commun. 1983, 1202.
5 Davies, S. G.; Seeman, J. I.; Williams, I. H. Tetrahedron Lett. 1986, 27, 619.
6
(a) Broadley, K.; Davies, S. G. Tetrahedron Lett. 1984, 25, 1743; (b) Davies, S. G.; Ichihara, O. Chem.
Commun. 1990, 1554; (c) Davies, S. G.; Dupont, J.; Easton, R. J. C.; Ichihara, O.; McKenna, J. M.; Smith,
A. D.; de Sousa, J. A. A. J. Organomet. Chem. 2004, 689, 4184.
7
For a review of α,β-unsaturated iron acyl chemistry, see: Davies, S. G.; Dordor-Hedgecock, I. M.; Easton,
R. J. C.; Preston, S. C.; Sutton, K. H.; Walker, J. C. Bull. Soc. Chim. Fr. 1987, 608.
8 Davies, S. G.; Walker, J. C. J. Chem. Soc., Chem. Commun. 1985, 209.
9 Baird, G. J.; Davies, S. G.; Jones, R. H.; Prout, K.; Warner, P. J. Chem. Soc., Chem. Commun 1984, 745.
10 (a) Baird, G. J.; Davies, S. G.; Maberley, T. R. Organometallics 1984, 3, 1764; (b) Davies, S. G.; Fletcher,
A. M.; Maberly, T. R.; Thomson, J. E. New J. Chem. 2013, 37, 3406.
11 Blackburn, B. K.; Davies, S. G.; Whittaker, M. Conformational Analysis for Ligands Bound to the Chiral
Auxiliary [(C5H5)Fe(CO)(PPh3)]. In Stereochemistry of Organometallic and Inorganic Compounds:
Chemical Bonds – Better Ways to Make Them and Break Them; Bernal, I. Ed.; Elsevier: Amsterdam 1989;
Vol. 3, pp 141–223.
12
Schilling, B. E. R.; Hoffmann, R.; Faller, J. W. J. Am. Chem. Soc. 1979, 101, 592; and references cited
therein.
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13 Hammond, G. S. J. Am. Chem. Soc. 1955, 77, 334.
14 Seeman, J. I. Chem. Rev. 1983, 83, 83; and references cited therein.
15 Woodbury, R. P.; Rathke, M. W. J. Org. Chem. 1977, 42, 1688.
16
(a) Wollenberg, R. F.; Albizati, K. F.; Peries, R. J. Am. Chem. Soc., 1977, 99, 7365; (b) Ficini, J.; Falou,
S.; Touzin, A.-M.; d'Angelo, J. Tetrahedron Lett. 1977, 18, 3589; (c) Lau, K. S. Y.; Schlosser, M. J. Org.
Chem. 1978, 43, 1595; (d) Duhamel, L.; Tombret, F. J. Org. Chem. 1981, 46, 3741; and references cited
therein.
17 Pirrung, M. C.; Hwu, J. R. Tetrahedron Lett. 1983, 24, 565.
18
13
In many cases, the peaks corresponding to C(1), i-Ph and the CO ligand were not observed in the C
NMR spectra of these iron complexes.
19 (a) Liebeskind, L. S.; Fengl, R. W.; Welker, M. E. Tetrahedron Lett. 1985, 26, 3075; (b) Liebeskind, L. S.;
Welker, M. E. Tetrahedron Lett. 1985, 26, 3079.
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Diastereoselective conjugate additions to alkoxycarbene cations of the iron chiral auxiliary
[(η5-C5H5)Fe(CO)(PPh3)=C(OMe)CH=CHR]+
Stephen G. Davies,* Robert J. C. Easton, Jeffrey M. McKenna, Mario E. C. Polywka and James E. Thomson
Highlights
• Conjugate additions to [(η5-C5H5)Fe(CO)(PPh3)=C(OMe)CH=CHR]+ are highly diastereoselective
• Subsequent protonation and demethylation gave the corresponding iron acyl complexes
• Opposite stereochemical outcome to the 1,4-addition to α,β-unsaturated iron acyl complexes
• Methodology complimentary to previous examples
1