, 924 cm À1 ; HR-ESI-MS: molecule not ionized in ESI, GC/MS: m/z (%): 332, vol.942, p.105, 0957.

, A solution of 2 (100 mg, 0.45 mmol) in CH 2 Cl 2 (2.5 mL) was treated with PPh 3 (236 mg, 0.90 mmol), cooled to 0 C, treated with CBr 4 (375 mg, 1.13 mmol), stirred at 0 C for 1 h, and evaporated. The crude was absorbed on SiO 2 and column chromatography (SiO 2 pre-treated with hexane/Et 3 N 99:01; hexane) gave 5 (128 mg, quant.) as a colorless oil, vol.6, p.8, 2005.

H. Nmr, CDCl 3 ): d ¼ 5.17 (br s, 1H), 3.61 (dd, MHz, vol.9, issue.400

, Hz, 1H), 2.49 (br s, 1H), 2.02e1.74 (m, 4H), 1.70e1.48 (m, 3H), 1.63 (s, 3H), Hz, 1H), 3.49 (dd, J ¼ 9, vol.9

, 925 cm À1 ; HR-ESI-MS: molecule not ionized in ESI, GC/MS: m/z (%): 286 (4, vol.958, p.105, 0991.

, Microwave-assisted approach. Iodo derivative 4 (11.85 g, 35.7 mmol) was treated with t-BuOK (1 M in THF) (46.4 mL, 46.4 mmol), stirred at 65 C in a microwave oven for 30 min, diluted with Et 2 O (150 mL) and H 2 O (150 mL). The two layers were separated and the aqueous layer was extracted with Et 2 O (4 Â 75 mL). The combined organic layers were washed brine, vol.6, p.8, 2005.

, Thermal approach. A solution of iodo derivative 4 (6.46 g, 19.43 mmol) in melted t-BuOH (13 mL) was treated with t-BuOK

, mmol), stirred at reflux for 3.5 h, diluted with Et 2 O (60 mL) and H 2 O (60 mL). The two layers were separated and the aqueous layer was further extracted with Et 2 O (4 Â 30 mL). The combined organic layers were dried over MgSO 4 , filtered, and evaporated. Column chromatography (SiO 2 ; cyclohexane) gave AD (2.52 g, 63%) as a colorless oil

¼. À13,

, CHCl 3 ))

, 64 (br s, 1H), 2.55 (br s, 1H), 2.06e1.83 (m, 3H), 1.77 (m, 1H), 1.74 (s, 3H), 1.67 (dq, CDCl 3 ): d ¼ 5.06 (br s, 1H), 4.87 (br s, 1H), vol.4

. Gc/ms, , vol.18, p.119

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, In both cases, only traces amounts of AD were detected (<5%)

, The synthesis was easily achieved by treatment of 2 with TsCl (2 equiv) in CH 2 Cl 2 at 23 C in the presence of 4-DMAP (2.4 equiv). The tosyl derivative was isolated in 99% yield without further purification. However, the subsequent elimination step was low yielding

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