To the phosphonate (7.74 mmol) in 50 mL anhydrous diethyl ether cooled to 0 ^oC was added barium oxide (4.22 mmol) followed by water (8.44 mmol) and the mixture was stirred for 15 min. Aldehyde (7.04 mmol) in 10 mL ether (then 2 x 5 mL wash) was added dropwise. The resulting turbid reaction mixture was stirred at 0 ^oC for 1 h, and then quenched with 100 mL of 0.1 M HCl solution. The mixture was partitioned, and the aq. layer was extracted with ethyl ether (3 × 35 mL). The combined organics were washed with brine, dried (MgSO₄), filtered, concentrated and the residue was purified by silica gel column chromatography (10:1 hexanes/ethyl acetate) to give the desired enone as colorless oil (82 %).

Source: Toste, Radosevich, Chan and Shih, ACIEE, 2008, EarlyView. DOI: 10.1002/anie.200800554.

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Points for discussion:

Why barium oxide and water was used (instead of NaH or BuLi) ?

To a mixture of aldehyde (0.0404 mmol) and vinyl iodide (0.162 mmol) (dried azeotropically using benzene, 2 × 2 mL) in anhydrous DMSO (1.3 mL) was added to 1% (w/w) NiCl₂ in CrCl₂ (49.6 mg) under N₂. The resulting mixture was stirred in dark for 13 h at rt, then diluted with aq. saturated NH₄Cl (5 mL). The aq. phase was extracted with DCM (6 × 5 mL) and the combined organic layers were then washed with aq. sat. NH₄Cl (5 mL), dried (Na2SO4), filtered, concentrated and the residue was purified by column chromatography to give the 2 diastereomers in a total of 70% yield.

Points for discussion:

Why the substrates were dried before the reaction?

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