Formation of Polysubstituted Tetrahydrofurans on an Iron Tricarbonyl η⁵-Pentadienyl Template

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.

cycloaddition - iron - diene complexes

References and Notes

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2 Tsuji J. Shimizu I. Ohashi Y. Tetrahedron Lett.  1985,  26:  3825 

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6

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): ν_max = 3006, 2954, 2841 (sp^³ 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).

7 Iwata C. Takemoto T. Chem. Commun.  1996,  2497 

8

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) Å^³; colourless crystal, 0.76 × 0.04 × 0.02 mm^³, 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 [e-mail].

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