Triethylamine-Magnesium bromide

Triethylamine, 322, 328 Triethylamine-Lithium bromide, 322 Triethylamine-Magnesium bromide, 322... 

A solution of ketene trimethylsilyl acetal 76 (6.30 g, 24.9 mmol) in toluene (30 mL) and a solution of aldehyde 77 (8.10 g, 16.6 mmol) in toluene (30 mL) vere successively added to a suspension of magnesium bromide-diethyl ether complex (12.9 g, 49.9 mmol) in toluene (100 mL) at —19 °C. The reaction mixture vas stirred for 1 h at —19 °C then triethylamine (23 mL) and saturated aqueous NaHCOs vere added. The mixture vas extracted vith diethyl ether and the combined organic extracts vere vashed vith brine, dried over Na2S04, filtered, and concentrated. The crude product vas purified by column chromatography (silica gel, hexane-ethyl acetate, 9 1) to afford the aldol adduct 78 (9.60 g, 87%) as a colorless oil. 

One approach (.40) has been to conduct the reaction in the presence of a more electropositive metal, often as an alloy. In the presence of magnesium, tin reacts with ethyl bromide to give tetraethyl tin, and various additives promote the reaction, the sequence of effectiveness being carbitols I > tetrahydrofuran, tetrahydrothiophene > ether triethylamine Br the ions ClOj, PFg, BFj, and BPhj are without effect. It is suggested that this reflects the coordination of the additive (L) to the Grignard reagent that is first formed, making it more reactive towards metallic tin. 

In a 100 mL round-bottomed flask, prepare a solution of aza[18]crown-6, 17, (3.6 g, 15.2 mmol) and triethylamine (4.2 mL, 3.0 g, 30 mmol) in dry diethyl ether (25 mL) at room temperature. Dissolve cinnamyl bromide (3.0 g, 15.2 mmol) in dry diethyl ether (30 mL), add it slowly to the stirred azacrown solution and fit a calcium chloride guard tube (or alternatively run the reaction under an inert atmosphere). Triethylamine hydrobromide precipitation occurs almost immediately however, it is worth stirring the mixture for several hours more to ensure complete reaction. Remove 50 per cent of the solvent by rotary evaporation, wash with aqueous potassium carbonate (25 mL, 2 m solution) and dry over magnesium... 

To a cooled (-78 °C) solution of hexylmangnesium bromide (prepared from 35 mmol of hexyl bromide and 38 mmol of magnesium in 87-90% yield) in THF (60 mL), HMPA (10.8 g, 60 mmol), and CuBr Me2S (0.26 g, 1.25 mol) is added dropwise a mixture of acrolein (1.40 g, 25 mmol) and chlorotrimethylsilane (5.4 g, 50 mmol) in THF (20 mL) over 30 min. The reaction mixture is stirred for 3 h before addition of triethylamine (7 mL) and hexane (100 mL). The organic layer is washed with water to remove HMPA and finally dried by MgS04. The title compound is obtained in 83% yield (94% E by GC analysis) by distillation (74 °C at 1 mmHg). ... 

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