Whitby group

To a solution of tert-butyl[2-(2-{(E)-4-[4,4-di(methoxymethyl)-2-methylcyclo pentyl]-2-butenyl}-1,3-dithian-2-yl)ethoxy]dimethylsilane (117 mg, 0.23 mmol) in THF (3 mL) was added dropwise tetrabutyl ammonium fluoride (0.35 mL of a 1 M solution in THF, 0.35 mmol). The mixture was stirred for 1 h, before being quenched with water (5 mL). The solution was diluted with ether, and the aqueous phase extracted with ether. The combined organic extracts were washed with brine, dried over MgSO₄, filtered and concentrated. To the crude product was added ethanol (5 mL) and Raney nickel (10 g of a 1:1 slurry in water). The mixture was heated at reflux for 2 h, then filtered through a sinter, with ether and water washing. The phases of the filtrate were separated and the aqueous extracted with ether. The combined extracts were washed with brine, dried over MgSO₄ and concentrated. Purification of the crude product by column chromatography (SiO₂, 20% ether in petrol) yielded the title compound (31 mg, 0.11 mmol, 47%).

n-Butyllithium (0.21 mL of a 2.5 M solution in hexanes, 0.525 mmol) was added dropwise to a solution of 2-{(E)-4-[4,4-di(methoxymethyl)-2-methylcyclopentyl]-2-butenyl}-1,3-dithiane (427) in THF (3 mL) under Ar at –40 °C. The reaction was stirred for 2 h and allowed to warm to –20 °C. After cooling to –78 °C, HMPA (0.2 mL) was added, resulting in a bright yellow suspension, which was decolourised on addition of a solution of (2-iodoethoxy)-tert-butyl dimethyl silane (143 mg, 0.5 mmol) in THF (1 mL).  After 30 min, the solution was allowed to warm to room temperature and stirred over night. The reaction mixture was poured into water and ether, and the aqueous layer extracted with ether. The combined organic phases were washed with brine, dried over MgSO­₄, filtered and concentrated. Column chromatography (SiO₂, 10% ether in petrol) furnished the desired compound as a viscous, colourless oil (141 mg, 0.28 mmol, 56%) contaminated with a small amount of an inseparable impurity.