Borane-dimethylamine-boron trifluoride

Acetal cleavage Interestingly, the regioselectivity in the reductive ring opening of 4.6-O-benzylidene glucose and glucosamine derivatives by borane-dimethylamine-boron trifluoride etherate, is dependent on the solvent used. 

Tris(dimethylamino)borane has been prepared by dimethyl-aminolysis of boron trichloride, with or without solvent,1-5 and by the reaction of boron trifluoride with dimethylamine in the presence of a suitable Grignard reagent.6 The procedure described here is a modification of the reaction of dimethylamine with boron trichloride in pentane as the solvent. 

The Step 2 product (0.484 mmol) was treated with borane-dimethylamine complex (1.952 mmol) in 40 ml CH2C12 at 0°C followed by the dropwise addition of 254 ml boron trifluoride diethyl etherate over 30 minutes. Stirring was continued for an additional hour at ambient temperature and the mixture was then quenched with using 15 ml saturated NaHC03 solution. The solution was diluted with 60 ml CH2C12, then washed three times with 100 ml brine, dried, and concentrated. The residue was purified by flash chromatography using hexane/EtOAc, 6 1, and the product isolated in 60% yield. 

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