Borine trimethylaminate

Preparation. The reagent is prepared by reaction of trimethylamine with diborane or with borine carbonyl (BHjCO). In a new procedure developed by Ethyl Corp, an activated aluminum powder and aluminum chloride are added to a solution of triphenyl borate in trimethylamine and the mixture is agitated at 180° under 2,000 p.s.i. of hydrogen. 

Borane-dimethyl sulphide solution (73 mmol, 2.74 m in THF) was added dropwise, with stirring, to the neat alkynylsilane (200mmol), keeping the reaction temperature below 20°C by use of an ice bath. The mixture was stirred for 2 h at 0-5 °C. At this time, the solution of the trialkenyl borane was diluted with THF (200 ml), and then anhydrous trimethylamine A/-oxide (240 mmol, dried by azeotropic distillation with toluene) was added over 5 min at ambient temperature. The resultant slurry was heated (bath temperature 75 °C) for 4h, and then cooled to ambient temperature. The enol borinate thus formed was hydrolysed by the addition of water (100 ml), followed by stirring for 5 min. The layers were separated, and the aqueous phase was extracted with ether (2x 100ml). The combined organic extracts were washed with brine and dried. Concentration and distillation gave the acylsilane (75-91%). 

Trimethylamine oxide Borinic acid esters from boranes... 

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