1,8-Diazabicyclo(5.4.0)undec-7-ene → 1-(2-Tert-butoxycarbonyl-4-methoxy-but-2e-enyl)-cyclopentane carboxylic acid

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Reaction Steps

To a solution of the product from stage b) above (6.11 g, 20.49 mmol) in toluene (50 ml) was added 1,8-diazabicyclo[5.4.0]undec-7-ene (3.7 ml, 24.58 mmol), and the resultant solution was then heated at reflux under nitrogen for 5 h. The solution was then cooled to room temperature and the solvent was removed under reduced pressure. To the resultant residue was then added deionised water (100 ml) and the mixture was then extracted with tert-butyl methyl ether (30 ml). The phases were then separated and the aqueous phase was acidified to pH 2 with hydrochloric acid (15 ml of a 2 M solution) and then extracted with tert-butyl methyl ether (2×30 ml). The combined organic extracts were then washed with water (30 ml) and then brine (30 ml) and dried over magnesium sulfate. The solvent was then removed under reduced pressure to give the crude title compound (6.29 g), which was then crystallised from heptane (15 ml) at 0° C. The resultant solid was collected by filtration was then washed with ice-cold heptane (2×5 ml) to give the title compound as a white solid (1.79 g, 6.0 mmol, 29%, E-isomer assigned on basis of chemical shifts); 1H NMR (400 MHz, CDCl3), δ: 1.47 (s, 9H), 1.45-1.70 (m, 6H), 2.05-2.10 (m, 2H), 2.74 (s, 2H), 3.36 (s, 3H), 4.09 (d, 2H), 6.75 (t, 1H); 13C NMR (100 MHz, CDCl3) δ: 23.9, 28.0, 34.1, 35.0, 55.0, 58.6, 69.2, 80.8, 132.7, 139.1, 167.1, 183.3.

Provenance & Evidence