[Synthesis]
General procedure for the synthesis of ethyl 1-oxaspiro[2.5]octane-6-carboxylate from ethyl 4-oxocyclohexanecarboxylate and trimethylsulfonium oxide iodide:
Procedure 9a: To a mixture containing trimethylsulfonium oxide iodide (3.9 g, 11.76 mmol) and potassium tert-butoxide (cf. Synthetic Communications, 33(12), 2135-2143) was added ethyl 4-oxocyclohexanecarboxylate (1 g, 5.87 mmol, Aldrich) in a DMSO ( 20 ml) solution. The reaction mixture was stirred at room temperature overnight. After completion of the reaction, the mixture was poured into water and extracted with ether. The organic phase was dried over anhydrous sodium sulfate, filtered and concentrated under reduced pressure to afford ethyl 1-oxaspiro[2.5]octane-6-carboxylate (704.5 mg, 65% yield), which could be used in subsequent reactions without further purification.
Another batch of compounds prepared by the same method showed the following NMR hydrogen spectral data: 1H NMR (400MHz, CDCl3): δ 4.06 (2H, q), 2.49-2.59 (2H, m), 2.26-2.28 (1H, m), 1.63-2.04 (6H, m), 1.27-1.49 (2H, m), 1.20 ( 3H, t), cis/trans isomer ratio 65:35. |