Unprecedented Cyclization of Nicholas Cations onto Unactivated Terminal Alkenes: Tandem Trapping of Cationic Intermediates

Clarisse Olier; Stéphane Gastaldi; Steven D. R. Christie; Michèle P. Bertrand

doi:10.1055/s-2007-968025

LETTER

Unprecedented Cyclization of Nicholas Cations onto Unactivated Terminal Alkenes: Tandem Trapping of Cationic Intermediates

Clarisse Olier^a,b, Stéphane Gastaldi^a, Steven D. R. Christie^b, Michèle P. Bertrand*^a
^a LCMO, UMR 6517, Boite 562, Université Paul Cézanne, Faculté des Sciences et Techniques, St Jérôme, 13397 Marseille Cedex 20, France
e-Mail: michele.bertrand@univ-cezanne.fr;
^b Department of Chemistry, University of Loughborough, Loughborough LE11 3TU, UK

Abstract

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Abstract

Unprecedented 6-endo and 7-endo cyclizations of Nicholas cations generated from ω-ethylenic propargyl alcohols were used to prepare functionalized cyclohexanes and cycloheptanes. The reactions performed in the presence of TiCl₄, BF₃·OEt₂, or HBF₄ led to halides together with the corresponding elimination product. Their ratio depends on the nature of the Lewis acid used to generate the cation, on the solvent and on the temperature. The reactions performed in acetonitrile in the presence of triflic acid led to the corresponding amides in high yields through Ritter reaction.

Key words

alkyne complexes - cyclizations - carbocations - halogenation - amidation

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References

References and Notes

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8

The axial protons in the α-position relative to either the complexed triple bond or the halide are characterized by triplet of triplet patterns (J = 11.6-12.1 and 3.0-3.6 Hz; dtt were observed for protons α to fluorine).

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10

Typical Experimental Procedure for the Preparation of Cyclic Halides In a typical experiment dicobalt hexacarbonyl complex 1c (0.41 mmol, 200 mg, 1.0 equiv) was dissolved in CH₂Cl₂ (3.5 mL, i.e., 8 mL/1 mmol) and 2.0 equiv of HBF₄ (112 µL, 0.82 mmol) was added under nitrogen. After stirring for 10 min at r.t., the reaction mixture was concentrated under reduced pressure. The crude product was purified by liquid chromatography on silica gel eluting with pentane to afford 4c (133 mg, 0.27 mmol, 67%) as a mixture of two diastereomers in a 66:34 ratio.
Hexacarbonyl[-η ⁴ -{[(3-fluorocyclohexyl)ethynyl]benz-ene}]dicobalt ( 4c) Compound cis-4c: ¹H NMR (300 MHz, CDCl₃): δ = 1.23-1.39 (m, 2 H), 1.58-1.58 (m, 3 H), 1.98-2.24 (m, 2 H), 2.53 (br s, 1 H), 3.04 (br t, 1 H, J = 11.9 Hz), 4.68 (dtt, 1 H, ^² J _HF = 48.3 Hz, J = 10.2, 5.1 Hz), 7.28-7.40 (m, 3 H), 7.49-7.52 (m, 2 H). ¹³C NMR (75 MHz, CDCl₃): δ = 23.5 (d, ^³ J _CF = 12.0 Hz, CH₂), 32.8 (d, ^² J _CF = 18.0 Hz, CH₂), 34.5 (CH₂), 40.3 (d, ^³ J _CF = 12.0 Hz, CH), 41.6 (d, ^² J _CF = 18.0 Hz, CH₂), 91.7 (d, ^¹ J _CF = 174.0 Hz, CH), 97.0 (C), 104.0 (C), 128.1 (CH), 129.3 (CH), 129.5 (CH), 138.5 (C), 200.1 (CO). ¹⁹F NMR (286 MHz, CDCl₃): δ = -168.5.
Compound trans-4c: ¹H NMR (300 MHz, CDCl₃): δ = 1.32-1.62 (m, 3 H), 1.74 (m, 1 H), 1.90 (qt, 1 H, J = 13.6, 3.6 Hz), 2.07-2.17 (m, 2 H), 2.43 (m, 1 H), 3.42 (tt, 1 H, J = 12.1, 3.2 Hz), 5.04 (br d, 1 H, ^² J _HF = 47.6 Hz), 7.28-7.50 (m, 3 H), 7.52-7.54 (m, 2 H). ¹³C NMR (75 MHz, CDCl₃): δ = 20.7 (CH₂), 30.5 (d, ^² J _CF = 21.0 Hz, CH₂), 34.9 (CH₂), 36.3 (CH), 39.7 (d, ^² J _CF = 21.0 Hz, CH₂), 89.5 (d, ^¹ J _CF = 168.0 Hz, CH), 91.8 (C), 105.4 (C), 128.1 (CH), 129.3 (CH), 129.6 (CH), 138.6 (C), 200.1 (CO). ¹⁹F NMR (286 MHz, CDCl₃): δ = -183.3.
Anal. Calcd for C₁₉H₁₅Co₂FO₅: C, 49.59; H, 3.29. Found: C, 49.96; H, 3.30. [13]
Typical Experimental Procedure for the Preparation of Cyclic Amides In a typical experiment, dicobalt hexacarbonyl complex 1c (200 mg, 0.41 mmol, 1.0 equiv) was dissolved in MeCN (4 mL, 9 mL/1 mmol) and 1.1 equiv of TfOH (40 µL, 0.45 mmol) was added under nitrogen. After stirring for 10 min at r.t., the reaction mixture was quenched with H₂O and extracted with CH₂Cl₂ (2×). The combined organic layers were washed with brine, dried over MgSO₄ and concentrated under reduced pressure. The residue was purified by chromatography on silica gel eluting with 50:50 pentane-EtOAc to afford 5c (198 mg, 0.38 mmol, 92%) as a single cis-isomer.
cis -Hexacarbonyl[µ-η ⁴ -{ N -[(3-phenylethynyl)cyclo-hexyl]acetamide}]dicobalt ( 5c) ¹H NMR (300 MHz, CDCl₃): δ = 1.11-1.32 (m, 4 H), 1.63 (qt, 1 H, J = 13.2, 3.0 Hz), 1.98 (s, 3 H), 2.06-2.13 (m, 2 H), 2.30-2.38 (m, 1 H), 3.11 (tt, 1 H, J = 11.5, 3.4 Hz), 4.04 (tdt, 1 H, J = 11.9, 8.3, 3.6 Hz), 5.44 (br d, 1 H, J = 8.3 Hz, NH), 7.29-7.45 (m, 3 H), 7.48-7.52 (m, 2 H). ¹³C NMR (75 MHz, CDCl₃): δ = 22.5 (CH₃), 23.7 (CH₂), 32.0 (CH₂), 33.6 (CH₂), 39.7 (CH), 40.4 (CH₂), 47.0 (CH), 90.4 (C), 103.1 (C), 127.6 (CH), 127.9 (CH), 128.1 (CH), 137.1 (C), 168.1 (CO), 198.6 (CO).
HRMS (TOF MS ES⁺): m/z calcd [M + 1] for C₂₂H₁₉NO₇Co₂ [MH⁺]: 527.9898; found: 527.9898.

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13

Elemental analysis is in agreement with the loss of carbon monoxide during the inlet of the sample in the combustion chamber. Unfortunately, HRMS could not be obtained. This compound of low polarity could not be ionized by the electrospray technique at our disposal.