Org Prep Daily

September 6, 2006


Filed under: procedures — milkshake @ 4:34 am


Tin(II) bis-hexamethyldisilazide

This experiment was done with oven-dried glassware under flow of dry Ar.

SnCl2 was dried on highvac at 180C/1h/0.3Torr. Dried SnCl2 36.40g (192 mmol) was dissolved in anh THF 200mL (2h stirring under Ar). The solution was transferred into an oven-dried addition funnel under Ar using a canula.

In another flask, hexamethyldisilazane 78.0mL (370mmol) in anh THF 100mL was cooled on ice bath. BuLi 1.45M solution in hexanes 240mL (384 mmol) was added dropwise over 30 minutes with intense stirring. After complete addition, the cooling bath was removed and the reaction continued at RT for 40min. The obtained LiHMDS solution was cooled to 0C and the SnCl2 solution was added dropwise over 150 min with intense stirring. After the complete addition, the cooling bath was allowed to expire (4C to RT over 3 hours) and the mixture was stirred at RT overnight (14 hours). The solvents were distilled out under Teflon-pump vacuum (15 to 6 Torr), the flask was re-filled with Ar. The residual slurry in the flask was transferred under Ar using a polyethylene tube as a canula into a oven-dried filtration funnel and filtered under positive pressure of Ar, the salts were washed with anhydrous hexane (2x50mL). The filtrates were concentrated under reduced pressure and the residue distilled under Ar through a Vigreaux column (3-inch long), b.p. 100-106C/0.6 Torr.

Y= 66.25g of a bright carrot-orange colored liquid (78.5% th)

The neat product is very sensitive towards oxygen and moisture, the instantly-produced crust has an unpleasant tendency to gum up a tip of the needle. It is therefore much more convenient to handle this reagent as a 1M stock solution in anhydrous hexane. This solution can be stored in SureSeal flask under Ar at room temp.

The procedure is from Schaeffer et al, J. Chem. Educ. 67(4), 347-9 (1990)

Tin(II) bis-hexamethyldisilazide is a mild base useful for cyclisation of aminoesters to lactams, including beta lactams. Workup can be unpleasant due to the tin gunk from decomposed reagent- fluoride workup is recommended, to obtain filtrable Sn salt precipitate. Other workup alternative is stirring the mix overnight with aq. NaOH.

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