Lithiation of Formaldehyde Dimethylthioacetal with BuLi TMEDA in Hexane

2 Lithiation of Formaldehyde Dimethylthioacetal with BuLi TMEDA in Hexane 

A solution of 0.105 mol of BuLi in 69 ml of hexane is placed in the flask. TMEDA (0.12 mol, 13.9 g, dried by distillation from LiAlH4 in a partial vacuum) is added over a few minutes. An additional amount of 50 ml of hexane or pentane is added, after which the solution is cooled to — 40 °C. The S,S-acetal (0.10 mol, 10.8 g, see Exp. 21) is then introduced over a few s, after which the cooling bath is removed. The temperature rises to 0-10 °C within a few minutes. After an additional 5 min (at 10 °C) the desired co-solvent (Et20 or THF, usually 80 ml) is added to the thick suspension with cooling below 0 °C. The resulting suspension (in the case of Et20) or solution (in the case of THF) should be immediately cooled to below — 40 °C, after which the reaction with the desired compound is carried out. 

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