Preparation and Structure Determination of Trimethylamine−Dibromocarboxyborane Esters

We have developed a new method for the preparation of esters of trimethylamine−dibromocarboxyborane (Me3N·BBr2COOR), from trimethylamine−carboxyborane, in a one-pot reaction. The reaction involves the treatment of trimethylamine−carboxyborane with 2.5 equiv of Br2 in the appropriate alcohol for 4 h at 0 °C, for compounds 1−5 (R = Me, Et, n-Pr, CH2CH2Cl, CH2CF3), and 5 equiv of Br2 for 8 h under the same conditions, for compounds 6−8 (R = n-Bu, i-Bu, i-Pe). Compounds 1−5 were obtained in high purity and in essentially quantitative yields (∼99%). Compounds 6−8 were purified from traces of monobromo product and the alcohol by column chromatography. Molecular structures for the compounds 2, 6, and 7 were determined by X-ray crystallography.