Bromination of hydrosilanes, ethers and epoxides using hexabromoacetone

Abstract

An efficient method for the preparation of bromosilanes from hydrosilanes has been disclosed. Tri-isopropylsilane was treated with hexabromoacetone (HBA) with the ratio of 1.0:0.25 at room temperature for 20 min in THF furnishing tri-isopropylbromosilane in excellent yield. The reaction conditions could be modified to make the reaction more efficient by using UV irradiation, sonication or performing at refluxing THF. The quantitative yield of bromosilane was successfully accomplished within 15 min. Under these optimized conditions, various hydrosilanes such as triphenylsilane, dimethylphenylsilane, and chlorodimethylsilane could be applied. The target products could be attained in good to excellent yields. In addition, a mild and efficient ether cleavage, epoxide ring-opening method using HBA/PPh3 was developed. Two types of ether were studied including linear and cyclic ethers. In the case of the cleavage of linear ether, dibenzyl ether (DBE) was transformed to benzyl bromide using HBA/PPh₃ with mole ratio of HBA:PPh₃ 1:2 at refluxing toluene for 4 h. For the opening of cyclic ether, excess THF was cleaved using HBA/PPh₃ with mole ratio of HBA:PPh₃ 1:2 at refluxing THF within 15 min to produce 1,2-dibromobutane in quantitative yield. Furthermore, the same reactions were done under microwave irradiation at 130 °C for only 1 min to produce high yield of the product. For the opening of epoxides, the formation of bromohydrin and dibromo products could be controlled using undried and dried CH₃CN and the mole ratio of HBA:PPh₃ at 0.5:1.0 and 2:3, giving bromohydrin and dibromo products in quantitative yield.