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DOI: 10.1055/s-0028-1087516
Formation of Polysubstituted Tetrahydrofurans on an Iron Tricarbonyl η5-Pentadienyl Template
Publication History
Publication Date:
15 January 2009 (online)
Abstract
Formation of an iron tricarbonyl complexed η5-pentadienyl system through cleavage of a carbon-carbon sigma bond has provided entry to a series of highly substituted tetrahydrofurans via a 1,3-dipolar cycloaddition reaction.
Key words
cycloaddition - iron - diene complexes
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References and Notes
Typical Procedure - Preparation
of Complex 4e
Iron tricarbonyl 2-buta-1,3-dienyl-cyclopropane-1,1-dicarboxylic
acid dimethyl ester (0.100 g, 0.29 mmol) was added to a flame-dried
round-bottom flask under an atmosphere of nitrogen and dissolved
in dry CH2Cl2 (5 mL). p-Anisaldehyde
(0.060 g, 0.60 mmol) and ZnBr2 (0.193 g, 0.86 mmol) were
added and the reaction mixture stirred for 1.0 h at r.t. The resulting
mixture was filtered through a pad of Celite and SiO2,
then concentrated in vacuo, and the residue purified by silica flash
chromatography eluting in PE-Et2O (4:1 v/v)
to yield the two inseparable title complex diastereomers as a yellow-orange
oil (0.101 g, 73%, dr = 4:1); HRMS-FAB: m/z calcd for C22H22O9Fe, [M+]: 486.0613;
found: 486.0623. IR (neat film): νmax = 3006, 2954,
2841 (sp³ CH), 2048, 1979 (MCO), 1742, 1738,
1732 (C=O) cm-¹. Assigned
from combined spectrum: (i) ¹H NMR (400 MHz,
CDCl3): δ (major diastereomer, cis) = 7.19-7.26
(2 H, m, ArH), 6.71-6.75 (2 H, m, ArH), 5.36-5.39
(1 H, m, CH2CHCH), 5.20-5.23
(1 H, m, CH2CHCH), 5.01-5.08 [1
H, m, CH(Ar)], 4.32-4.37 (1 H, m, CHCH2C), 3.71 (3 H, s, CO2CH3),
3.68 (3 H, s, OCH3), 3.09 (3 H, s, CO2CH3),
2.64-2.72 (1 H, m, CHCHHC),
2.37-2.44 (1 H, m, CHCHHC),
1.78-1.81 (1 H, m, CHHCHCH),
1.09 (1 H, t, J = 8.8 Hz, CH2CHCHCH), 0.51 (1 H, dd, J = 2.1,
9.6 Hz, CHHCHCH). ¹³C
NMR (100 MHz, CDCl3): δ (major diastereomer, cis) = 171.2, 171.1 (CO2CH3), 159.4,
131.6 (ArC), 129.9, 113.2 (2 C, s, ArCH), 87.5 (CH2CHCH), 84.7 [CH(Ar)],
83.7 (CH2
CHCH), 78.4 (CHCH2C), 66.0 [C(CO2CH3)2],
59.4 (CH2CHCHCH), 55.2 (OCH3),
53.0, 52.3 (CO2
CH3),
41.1 (CH2CHCH), 40.4 (CHCH2C).(ii) ¹H NMR
(400 MHz, CDCl3) δ (minor diastereomer, trans) = 7.19-7.26
(2 H, m, ArH), 6.71-6.75 (2 H, m, ArH), 5.36-5.39
(1 H, m, CH2CHCH), 5.12-5.23
(1 H, m, CH2CHCH), 5.01-5.08 [2
H, m, CHCH2C, CH(Ar)],
3.65-3.71 (6 H, m, OCH3, CO2CH3),
3.15 (3 H, s, CO2CH3), 2.92 (1 H, dd, J = 7.1, 13.1 Hz, CHCHHC), 2.10 (1 H, dd, J = 7.4,
13.1 Hz, CHCHHC), 1.78-1.81
(1 H, m, CHHCHCH), 0.91 (1 H, t,
J = 9.1 Hz, CH2CHCHCH), 0.38-0.40 (1 H, m, CHHCHCH). ¹³C
NMR (100 MHz, CDCl3): δ (minor diastereomer, trans) = 170.3, 170.3 (CO2CH3), 159.4,
131.5 (ArC), 129.5, 113.2 (2 C, s, ArCH), 87.3 (CH2CHCH), 84.1 [CH(Ar)],
83.6 (CH2
CHCH), 79.0 (CHCH2C), 66.0 [C(CO2CH3)2],
62.0 (CH2CHCHCH), 55.2 (OCH3),
53.8, 52.3 (CO2
CH3),
40.9 (CH2CHCH), 40.7 (CHCH2C). MS:
m/z (%) = 486
(<1) [M+], 430 (28),
402 (66), 135 (100).
Crystal Data for
4a
C18H20FeO10, M = 452.19, a = 7.4917
(12), b = 10.4811 (16), c = 13.916
(2) Å, α = 72.126
(3), β = 78.035 (3), γ = 74.455
(2)˚, V = 992.6
(3) ų; colourless crystal, 0.76 × 0.04 × 0.02
mm³, D
calc = 1.513
g cm-³, µ = 0.813 mm-¹;
7243 data, 3482 unique (R
int = 0.0381).
Data were measured on a Bruker SMART 1000 diffractometer with MoKα radiation at 150 K. Data
were corrected for absorption. The structure was solved by Patterson
synthesis and refined on F
² values;
H atom coordinates on atoms C(6), C(7), C(8), and C(9) were freely
refined, other H atom parameters were constrained; R = 0.0432 [for
2567 observed data with F
² > 2σ(F
²)] and wR = 0.1046
(for all data). Deposition no. 696186. Crystal data have been deposited with
the Cambridge Crystallographic Data Centre. Data can be retrieved
in CIF format by quoting the relevant deposition number in an e-mail
request to deposit@ccdc.cam.ac.uk.