Totally Procedures

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?