[Br-].C1([P+](C2C=CC=CC=2)(C2C=CC=CC=2)C2C=CC=CC=2)CC1.[Li+].[CH3:25][CH2:26][CH2:27][CH2-:28].[CH2:29]1[O:39][C:32]2([CH2:37][CH2:36]C(=O)[CH2:34][CH2:33]2)[O:31][CH2:30]1>C1COCC1>[C:26]1(=[C:25]2[CH2:36][CH2:37][C:32]3([O:39][CH2:29][CH2:30][O:31]3)[CH2:33][CH2:34]2)[CH2:28][CH2:27]1Cyclopropyltriphenylphosphonium bromide (10.8 g, 28 mmol) was suspended in dry THF (30 mL) and cooled to −60° C. N-Butyllithium (1.6M in THF, 17 mL, 27 mmol) was added dropwise at −40 to −60° C. The temperature was raised to 20° C. and after 3 hours at this temperature, the reaction mixture was cooled to −60° C. 1,4-Cyclohexane dione mono ethylene ketal (4.0 g, 26 mmol) dissolved in THF (30 mL) was added at −60° C. whereafter the temperature was raised to 20° C. After 16 hours the reaction mixture was diluted with THF (75 mL) filtered through hyflo and concentrated in vacuo. The residue was purified by flash chromatography (4×15 cm column of silica) using heptane and ethyl acetate (4:1) as eluent to give 2.5 g of 8-cyclopropylidene-1,4-dioxa-spiro[4.5]decane (cf Synthetic Communications 21(20), 2015-2023, 1991).
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