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.

本研究开发了一种以三甲胺-羧基硼烷（trimethylamine−carboxyborane）为原料，通过一锅法反应（one-pot reaction）制备三甲胺-二溴羧基硼烷（trimethylamine−dibromocarboxyborane，通式为Me3N·BBr2COOR）酯类化合物的新方法。针对化合物1~5（R分别为甲基、乙基、正丙基、2-氯乙基、2,2,2-三氟乙基），该反应需在0℃下将三甲胺-羧基硼烷与2.5当量的溴单质置于适宜醇类溶剂中反应4小时；针对化合物6~8（R分别为正丁基、异丁基、异戊基），则需在相同条件下使用5当量溴单质反应8小时。化合物1~5可获得高纯度产物，收率近乎定量（约99%）。化合物6~8需通过柱层析法（column chromatography）除去痕量单溴代副产物与残留醇类以完成纯化。通过X射线晶体衍射法（X-ray crystallography）确定了化合物2、6与7的分子结构。