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DOI: 10.1055/s-2006-947346
Ruthenium-Catalyzed Ring Expansion Reaction of 1-Acetylenylcyclobutanols with Methyl Vinyl Ketone
Publication History
Publication Date:
24 July 2006 (online)
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Abstract
A novel type of ruthenium-catalyzed cascade ring expansion reaction is reported. A 1,2-rearrangement of acetylenylcyclobutanol followed by carbon-carbon bond formation with methyl vinyl ketone proceeds in one-pot process. This reaction enables to synthesize 2-alkylidenecyclopentanones in a stereoselective manner using appropriate ruthenium catalysts.
Key words
alkynes - ruthenium - ring expansion - domino reaction - stereoselective synthesis
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References and Notes
It is assumed that Lewis acid plays the role as an activating reagent of MVK. The addition of Brønsted acid (CSA), Brønsted base (K2CO3, pyridine) or Lewis base (PPh3) caused a decrease in the product yield and/or an elongation of the reaction time.
12
General Procedure for the Ruthenium-Catalyzed Ring Expansion Reaction (entry 12 in Table 1).
To a stirred solution of ethynylcyclobutanol (1a, 47.7 mg, 202 µmol) in toluene (1.0 mL) were added MVK (70.0 mg, 1.01 mmol), anhyd CeCl3 (10.0 mg, 40.4 µmol) and CpRu(PPh3)2Cl (14.7 mg, 20.2 µmol) at r.t., and stirring was continued for 2 h at 80 °C. After filtration of the reaction mixture using EtOAc with small amount mixture of silica gel and a Celite® pad followed by evaporation of the eluate, the residue was chromatographed on silica gel with hexane-EtOAc (92:8 v/v) as eluent to give the (Z)-cyclopentanone (Z)-2a (33.4 mg, 54%) and (E)-cyclopentanone (E)-2a (8.8 mg, 14%) as colorless oil, respectively.
Compound (Z)-2a: IR (neat): 1713, 1639 cm-1. 1H NMR (400 MHz, CDCl3): δ = 0.87 (6 H, t, J = 7.2 Hz), 1.13-1.46 (16 H, m), 1.75 (2 H, t, J = 7.6 Hz), 2.14 (3 H, s), 2.49 (2 H, td, J = 7.6, 2.0 Hz), 2.54 (2 H, t, J = 7.2 Hz), 2.90 (2 H, dt, J = 7.6, 7.2 Hz), 5.97 (1 H, tt, J = 7.6, 2.0 Hz). 13C NMR (150 MHz, CDCl3): δ = 14.0, 22.4, 22.5, 23.7, 27.3, 29.6, 30.7, 32.5, 35.2, 43.1, 53.6, 136.7, 138.7, 208.2, 212.1. MS: m/z = 306 [M+]. HRMS: m/z calcd for C20H34O2 [M+]: 306.2559; found: 306.2554.
Compound (E)-2a: IR (neat): 1715, 1651 cm-1. 1H NMR (400 MHz, CDCl3): δ = 0.86 (6 H, t, J = 6.8 Hz), 1.14-1.47 (16 H, m), 1.79 (2 H, t, J = 7.2 Hz), 2.16 (3 H, s), 2.40 (2 H, dt, J = 7.5, 2.0 Hz), 2.61 (2 H, t, J = 7.0 Hz), 6.45 (1 H, tt, J = 7.5, 2.0 Hz). 13C NMR (125 MHz, CDCl3): δ = 14.0, 22.5, 23.2, 23.6, 23.7, 29.9, 30.7, 32.5, 35.2, 41.9, 52.5, 134.3, 138.7, 207.1, 210.4. MS: m/z 306 [M+]. HRMS:
m/z calcd for C20H34O2 [M+]: 306.2559; found: 306.2572.
MOPAC 2000/AM1 calculation indicated that (E)-2a is thermodynamically more stable than (Z)-2a by 0.79 kcal/mol.