A. 3-(2-Methoxyethoxy)propene (1). A three-necked, 1000-mL flask equipped with a thermometer, mechanical stirrer, and dropping funnel is charged with 51 g (0.9 mol) of potassium hydroxide (KOH, (Note 1)) and 65 mL (62.3 g, 0.82 mol) of dry 2-methoxyethanol (Note 2). The resulting mixture is cooled in an ice bath, efficient stirring is begun, and 72 mL (100 g, 0.82 mol) of allyl bromide (Note 2) is added dropwise, keeping the internal temperature below 10°C (Note 3). After the solution is stirred overnight, the sticky white solid is collected by suction filtration and the collected solids are washed with 300 mL of hexanes. The combined yellow filtrate and washings are dried thoroughly over sodium sulfate (Na₂SO₄), and the whole mixture is distilled from calcium hydride (CaH₂) through a 6-in. Vigreux column (Note 4). The product (67–69 g, 70–73%) is collected from 115–129°C with the bulk of the material distilling at bp 117–127°C, and is 94% pure (as judged by gas chromatography, (Note 5),(Note 6),(Note 7)).

B. 1-Bromo-3-(2-methoxyethoxy)propane (2). A flame-dried, three-necked, 1000-mL flask that is equipped for magnetic stirring, and has a dry addition funnel and a thermometer, is placed under an inert atmosphere and charged with 209 mL (250 g, 0.209 mol) of a 1.0 M solution of borane-tetrahydrofuran complex (Note 2). The resulting solution is cooled to −10°C using a dry ice/ethylene glycol bath and 3-(2-methoxyethoxy)propene (1, 60 g, 0.52 mol) is added dropwise over ~1 hr keeping the internal temperature of the reaction mixture at or below 0°C. Methanol (1.5 mL) is added to destroy any excess borane, and the reaction mixture is stirred an additional 1 hr below 10°C.

After the reaction mixture is recooled to −15°C (internal temperature), 35 mL (107.8 g, 0.67 mol) of bromine (Br₂) is added dropwise over 1 hr, keeping the reaction temperature between −10° and 0°C. The mixture is stirred a further 1.5 hr at 0°C then recooled to −15°C. While cooling is maintained, 210 mL of a 4 M solution of sodium methoxide (0.84 mol) in methanol (freshly prepared from sodium metal) is added dropwise over 1.5 hr, keeping the reaction temperature between −15° and 0°C. The resulting orange brown solution and white precipitate are slowly warmed to room temperature and stirred overnight (16 hr).

Hexane (100 mL) is added to the reaction mixture causing more white precipitate to form. The mixture is filtered by suction, and the collected solids are washed with two 50-mL portions of hexane. The combined filtrate and washings are partitioned with 200 mL of a mixture (1:3 v/v) of saturated potassium carbonate solution and water (Note 8). The aqueous phase is extracted with three 200-mL portions of hexane. The combined organic phases are partitioned with 100 mL of saturated sodium chloride, dried thoroughly over anhydrous sodium sulfate and concentrated under reduced pressure to afford 65–75 g of crude product. A small amount of additional crude material can be isolated by continuously extracting the combined aqueous layers with hexane for 3 hr.

Distillation of the crude product through a 6-in. Vigreux column at 0.6 mm into a dry ice/acetone-cooled receiver affords 55–70 g of material bp >40°C/0.6 mm that is ~83% pure (as judged by gas chromatography, (Note 6)). To obtain material of greater purity (94%) suitable for further transformation, a second distillation through a 6-in. Vigreux column packed with glass beads is required to afford 53–57 g (52–56%) of the bromide as a colorless liquid, bp 55–65°C/0.6 mm (Note 9).

C. Tetra[3-(2-methoxyethoxy)propyl]stannane (3). A 500-mL, three-necked flask is fitted with a thermometer and a dried addition funnel, charged with 9.1 g (0.375 mol) of magnesium metal turnings (Note 2) and heated with a flame or heat gun while purging with argon. After the flask is cooled, 50 mL of dry tetrahydrofuran (THF) and a crystal of iodine are added, and the addition funnel is charged with 40 mL (52 g, 0.264 mol) of 1-bromo-3-(2-methoxyethoxy)propane (2, (Note 10)). Approximately 2 mL of the bromide is added to the reaction mixture, and the internal temperature of the mixture is monitored. When the temperature rises slightly (~3°C) and the iodine color is discharged indicating that formation of the Grignard reagent has begun, the reaction mixture is immediately cooled to −15°C in a dry ice/ethylene glycol bath, 100 mL of dry THF (Note 10) is added to the addition funnel, and 150 mL of dry THF (Note 10) is directly added to the reaction mixture. The bromide solution is added dropwise over 2 hr while keeping the reaction temperature between −15° and 5°C (Note 11).

The concentration of the Grignard reagent solution is determined by titration. An oven-dried, 10-mL flask with septum is charged with 1 mg of phenanthroline and 3.0 mL of the reaction mixture. 2-Methylpropanol is added until the red-purple color is dissipated and a yellow endpoint is reached. The yield of Grignard reagent is 0.184 mol (70%).

A dry, 1000-mL flask is placed under a nitrogen atmosphere, charged with 4.9 mL (0.042 mol) of tin(IV) chloride (SnCl₄, (Note 1)), and cooled to −78°C in a dry ice/acetone bath with swirling. After the SnCl₄ solidifies on the walls of the flask, the flask is equipped for magnetic stirring. The previously prepared Grignard solution is added to the SnCl₄ as a slow stream via cannula and the reaction mixture is allowed to warm to room temperature with stirring overnight (20 hr). After the solution is stirred at room temperature for ~20 hr, the addition funnel is replaced by a reflux condenser, and the reaction mixture is heated at reflux for 4 hr by means of a heating mantle (Note 12). After the solution is cooled, the solvent is removed under reduced pressure, 300 mL of water is added, and the resulting mixture (a heavy precipitate results) is continuously extracted with 750 mL of hexane for 12–24 hr. The hexane solution is dried over magnesium sulfate (MgSO₄), and the volatile material is removed under reduced pressure, to afford 23.6–24 g (96–97% based on SnCl₄) of the tetraalkylstannane that is not homogeneous as judged by NMR integration. Pure stannane suitable for further transformation is obtained by removal of a low boiling impurity (bp 90–100°C/0.6 mm) under high vacuum to afford 21–23 g of purified stannane. Stannane (bp 210–215°C at 0.005 mm) of even higher purity can be obtained by short-path distillation with some loss due to decomposition (Note 13).

D. Bromotris[3-(2-methoxyethoxy)propyl]stannane (4). A dry, 50-mL, round-bottomed flask is placed under a nitrogen atmosphere and charged with 8.25 g (14.0 mmol) of tetra[3-(2-methoxyethoxy)propyl]stannane (3), and 40 mL of dry carbon tetrachloride (CCl₄) (Note 1). After the mixture is cooled to ~0°C in an ice-water bath, 14 mL of a 1 M solution of bromine (0.014 mol) in CCl₄ is added dropwise (Note 14). The mixture is allowed to warm slowly to room temperature and stand overnight. The solvent is removed under reduced pressure, and the residual brown liquid is purified by Kugelrohr distillation at 0.1 mm. A low boiling fraction (bp <70°C) that contains alkyl bromide is discarded, and the residual material is distilled to afford 6.9–7.4 g (90–96%) of the bromotrialkylstannane (bp 100–110°C) as a pale tan viscous oil that is homogeneous as judged by NMR spectroscopy and of sufficient purity for further transformation (Note 15),(Note 16),(Note 17).

E. Tris[3-(2-methoxyethoxy)propyl]stannane (5). A 100-mL, round-bottomed flask equipped for magnetic stirring is placed under an inert atmosphere and charged with 5.0 g (4.5 mmol) of freshly distilled bromotris[3-(2-methoxyethoxy)propyl]stannane (4) and 40 mL of dry 1,2-dimethoxyethane (Note 10). To the stirred solution is added 2.0 g (54 mmol) of sodium borohydride (NaBH₄) (Note 2) at room temperature in portions at such a rate as is required to control foaming. The resulting white suspension is stirred at room temperature for 2.5 hr (the reaction appears complete nearly instantaneously) and then concentrated under reduced pressure. The residue is taken up in 50 mL of ether, suction filtered through a bed of Celite, and concentrated under reduced pressure to afford 3.47–3.64 g (82–86%) of the trialkyltin hydride as a clear colorless oil that is homogeneous by NMR. The trialkyltin hydride is pure enough for most purposes, but further purification is possible by short-path distillation to afford pure trialkyltin hydride bp 100–120°C (pot temperature) at 0.005–0.01 mm (Note 18).