The iron-mediated intramolecular addition of carboxylates to conjugated dienes

Article abstract of DOI:10.1039/a901628g

Treatment of carboxylic acid functionalized (η⁴-diene)Fe(CO)₃ complexes with 3.0 equiv. of NOBF₄ in the presence of Et₃N generates γ- and δ-lactones containing an α,β-unsaturated aldehyde or oxime functionality

Full text of DOI:10.1039/a901628g

The iron-mediated intramolecular addition of carboxylates to conjugated
dienes
Ming-Chang P. Yeh,* Li-Wen Chuang, Ya-Sheng Hsieh and Ming-Shan Tsai
Department of Chemistry, National Taiwan Normal University, 88 Sec. 4, Ding-Jou Road, Taipei, Taiwan, Republic
of China. E-mail: cheyeh@scc.ntnu.edu.tw
Received (in Cambridge, UK) 1st March 1999, Accepted 25th March 1999
Fe(CO)3
Fe(CO)3
4
Treatment of carboxylic acid functionalized (h -diene)-
Fe(CO)3 complexes with 3.0 equiv. of NOBF4 in the presence
of Et3N generates g- and d-lactones containing an a,b-
unsaturated aldehyde or oxime functionality after NO+
insertion.
R
(
)
n
CO2H
(
)
n CO2H
1a R = H, n = 2
b R = Me, n = 2
2a R = H, n = 3
b R = Me, n = 3
3a n = 1
b n = 2
Nucleophilic additions to conjugated dienes coordinated to a
transition metal have attracted considerable interest in organic
synthesis.1 Transition metals, such as molybdenum, palladium
or iron, have been used to activate dienes towards nucleophilic
O
4
additions. The (h -cyclohexa-1,3-diene)MoCp(CO)2 cations
underwent reaction with a variety of carbon nucleophiles at the
terminal position of the diene ligand to produce neutral (p-
allyl)molybdenum complexes. Hydride abstractions from these
complexes regenerated cationic diene complexes which again
underwent intermolecular nucleophilic attack from the face
opposite the metal, resulting in overall 1,3-stereocontrol in the
six-membered ring.2 With a pendant carboxylic acid group,
neutral (p-allyl)molybdenum complexes underwent intramo-
lecular addition with carboxylates by conversion of the neutral
species to the cationic nitrosyl intermediates (exchange of
neutral CO for NO+) to afford g- and d-lactone derivatives.3 In
the palladium-catalyzed oxidation of conjugated dienes, two
nucleophiles were added in a regio- and stereoselective manner
across the diene. Nucleophiles that could be used in the overall
1,4-addition included carboxylates, amides, alcohols, and
halides.4 Conjugated dienes could also be activated towards
nucleophilic additions by the Fe(CO)3 moiety. The inter-
molecular addition of reactive ester or cyano stabilized
carbanions to diene–iron complexes under CO afforded cyclo-
pentanoids after acid quenching.5 Recently, we have extended
this chemistry into an intramolecular variant. Thus, sequential
additions of carboester functionalized zinc–copper organo-
O
(
)
n
H
O
O
X
(
)
n
HON
R
4 R = H, X = O, n = 1
5 R = Me, X = NOH, n = 1
6 R = H, X = O, n = 2
7 R = Me, X = NOH, n = 2
H
8 n = 1
9 n = 2
addition was carried out for 30 min at 0 °C followed by workup
with saturated aqueous NH4Cl and CH2Cl2 extraction. After
purification by flash column chromatography on silica gel and
distillation under reduced pressure, g-lactone 4† bearing an a,b-
unsaturated aldehyde at the g-position of the ring was obtained
as the major product in 60% yield (entry 1, Table 1). Under the
same reaction conditions, intramolecular cyclization of 1b with
an additional methyl group at the terminal position of the diene
ligand afforded g-lactone 5 with an a,b-unsaturated oxime at
the g-position of the ring in 64% yield (entry 2, Table 1). The
formation of 4 and 5 may result from NO+ insertion. However,
it is important to mention that the intramolecular addition of
5
metallics to (h -pentadienyl)Fe(CO)3 cations furnished bicy-
3
clo[3.3.0]octanones or trisubstituted cyclopentanecarboxylic
acid derivatives depending on the quenching process.6 How-
ever, nucleophiles that could be used to add at the diene ligand
of Fe(CO)3 complexes have been restricted to stabilized
carbanions. It would be of great synthetic interest to extend
these regio- and stereoselective additions to other nucleophiles,
such as oxygen and nitrogen nucleophiles. Here we report, for
the first time, on the intramolecular addition of carboxylates to
carboxylates to (h -allyl)MoCp(CO)(NO) cations to give g and
d-lactones did not involve NO+ insertion.3 A mechanism for
generation of 4 and 5 is suggested in Scheme 1. Addition of
NOBF4 to complexes 1a,b may produce the cationic species 10.
Deprotonation of 10 with Et3N gave carboxylate 11, with attack
exclusively at the terminal position of the diene ligand to
4
Table 1 Intramolecular additions of carboxylates to (h -Diene)Fe(CO)3
4
conjugated dienes by conversion of neutral (h -diene)Fe(CO)3
complexes
complexes to the cationic nitrosyl intermediates (exchange of
neutral CO and NO+). The addition proceeded regiospecifically
to form g- and d-lactones with an a,b-unsaturated aldehyde or
oxime functionality after NO+ insertion.
Starting
complex
Entry
Product
Yield (%)a
1
2
3
4
5
6
1a
1b
2a
2b
3a
3b
4
5
6
7
8
9
60
64
55
53
50
53
The starting acid complexes 1–3 were prepared in two steps
according to literature procedures.6,7 Addition of carboester
5
functionalized zinc–copper reagents to the corresponding (h -
dienyl)Fe(CO)3 cationic salts followed by hydrolysis of the
residue with KOH in MeOH–THF–H2O at 30 °C produced
complexes 1–3 as the major products in good yields (70–90%).
Finally, our intramolecular addition involved the addition of an
MeCN solution of NOBF4 (3.0 equiv.) to 1a in MeCN at 0 °C
under nitrogen and then addition of Et3N (2.0 equiv.). The
a All products were purified by flash column chromatography on silica gel
and distillation under reduced pressure and have been fully characterized by
1H and 13C NMR, IR, mass and high resolution mass spectra.
Chem. Commun., 1999, 805–806
805

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+Fe(CO)2(NO)
+Fe(CO)2(NO)
O–
4.8 Hz, respectively, of the adjacent fused protons in 8 and 9
NO+
Et3N
demand cis-fused bicyclic skeletons. These values are con-
sistent with the couling constants observed for the cis fused
bicyclo g- and d-lactones reported in the literature.8 Rigorous
proof of the structure of 8 was further accomplished by X-ray
diffraction analysis.‡ Although the iron-mediated intramo-
lecular cyclisation works well for the formation of fused
1a,b
R
R
R
CO2H
O
10
11
4
Fe(CO)2(NO)
bicyclic lactones 8 and 9 from (h -cyclohexa-1,3-diene)-
Fe(CO)3 acid complexes, attempts to obtain fused bicyclo g-
Fe(CO)2(NO)
O
4
and d-lactones from intramolecular cyclisation of (h -cyclo-
hepta-1,3-diene)Fe(CO)3 acid complexes 17 and 18 have thus
far failed.
O
R
O
O
We thank the National Science Council of the Republic of
China for the financial support.
13
12
NO+
+Fe(CO)2(NO)
Notes and references
R
† Selected data for 4: dH(CDCl3) 9.63 (1H, d, J 7.3), 6.80 (1H, dd, J 15.6,
4.4), 6.37 (1H, dd, J 15.6, 7.3), 5.21 (1H, m), 2.61 (3H, m) and 2.05 (1H, m);
dC(CDCl3) 192.2, 175.6, 150.9, 131.8, 77.5 and 27.8; nmax(CH2Cl2)/cm21
3040w, 3012w, 2959w, 2928, 2872, 1779m, 1732m, 1603m, 1460w,
1375w, 1236w, 1198w, 1113w and 1045m; m/z (EI) 140 (M+, 48%), 123
(38), 111 (42), 98 (29), 95 (47), 85 (43), 81 (82), 70 (13), 67 (25), 56 (23)
and 55 (57); HRMS: calc. for C7H8O3 140.0437, found 140.0471.
‡ Crystal data for 8: C8H9NO3, M = 167.16, monoclinic, a = 9.535(2),
b = 7.052(1), c = 12.691(3) Å, U = 791.4(3) Å3, T = 298 K, space group
P21/c, Z = 4, m(Mo-Ka) = 0.71073 mm21, 2395 reflections measured,
2298 unique (Rint = 0.012), which were used in all calculations. The final
wR(F2) was 0.078 (all data). Single crystals of compound 8 were
recrystallised from hexane–EtOAc. The structure was solved using direct
methods and refined by full-matrix least-squares on F2. CCDC 182/1211.
See http://www.rsc.org/suppdata/cc/1999/805/ for crystallographic files in
.cif format.
ON
R = H
O
4
5
O
R = CH3
14
Scheme 1 Proposed reaction pathway for the formation of lactones 4 and 5.
produce the postulated neutral (p-allyl)Fe(CO)2(NO) inter-
mediate 12. Syn/anti isomerization of 12 via p-allyl/s-allyl
interconversion of the allyl ligand produced 13.8 Intermediate
13 may undergo nitrosyl migration with an additional NO+ to
3
give 14. However, neutral complexes, such as (h -allyl)Fe-
(CO)2NO, underwent internal CO (rather than NO+) insertion
upon treatment with 1,2-bis(diphenylphosphino)ethane to give
an iron acyl intermediate. Quenching the iron acyl intermediate
with I2/EtOH produced a b,g-unsaturated carboxylic ester.9
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1989, 28, 1173.
3
Thus, it is reasonable to suggest that complex (h -allyl)Fe-
(CO)2NO 13 may undergo nitrosyl insertion with an excess of
NOBF4 (3.0 equiv. of NO+) to produce 14. The primary nitroso
compound (R = H) hydrolyzed to 4, while the secondary
nitroso derivative (R = CH3) underwent nitroso–oxime tauto-
merization to produce 5 after aqueous workup and flash column
chromatograph of the residue.
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Increasing the tether length by one with complexes 2a and 2b
(entries 3 and 4, Table 1) also allowed intramolecular
cyclisation to provide d-lactones 6 (55%) and 7 (53%),
respectively, as the only product in each case. The results are
consistent with complexes 1a and 1b. Thus, the substrate with
an additional methyl group at the diene ligand, 2b, produced
lactone 7 with an a,b-unsaturated oxime functionality at the d-
position of the ring, while complex 2a generated d-lactone 6
bearing an a,b-unsaturated aldehyde functionality. However,
preliminary attempts to prepare b- and w-lactones were
unsuccessful. No cyclization has been observed for acid
complexes 15 and 16.
Fe(CO)3
Fe(CO)3
(
)
n
CO2H
(
)
n
CO2H
15 n = 1
16 n = 4
17 n = 1
18 n = 2
Using the same methodology, we are able to construct fused
bicyclic lactones 8 and 9 via intramolecular addition of
carboxylates to cyclic diene–iron complexes 3a and 3b,
respectively. Fused bicyclic lactones 8† (50%) and 9 (64%)
bearing an a,b-unsaturated oxime functionality were obtained
as the only diastereoisomer in each case. The cis-stereo-
chemistry at the ring juncture in lactones 8 and 9 was fixed by
anti addition of carboxylates at the terminal position of the
diene ligands and 1H NMR studies provided evidence support-
ing the structure assignments. The coupling constants of 5.3 and
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Chem. Commun., 1999, 805–806