铜促进的锗亲电试剂与烷基溴合成四烷基锗

Copper Promoted Synthesis of Tetraalkylgermanes from Germanium Electrophiles and Alkyl Bromides

有机锗化合物由于其区别于硅与锡的独特性质而逐渐受到关注.其中,以烷基三甲基锗为代表的具有光催化自由基反应活性的烷基锗化合物仍缺乏高效、简便的合成方法.本工作使用商业可得的三甲基溴化锗和烷基溴化物为原料,廉价的硫酸铜为催化剂,在镁粉的存在下以较好的产率获得了一系列烷基三甲基锗化合物.机理研究表明反应很可能经历原位格氏试剂历程,添加的铜盐可以加速锗卤化合物与格氏试剂的反应,从而抑制锗卤化合物被镁粉还原产生二锗物种的副反应.相比于传统预先制备的格氏试剂,本工作发展的新方法对酯基或酰胺等官能团有较好的兼容性.该反应还可以拓展到二甲基二氯化锗和其他烷基溴化物一步合成多种四烷基锗以及锗杂环烷烃类化合物.

Organogermanium compounds have been gaining more attention for their unique properties compared to silicon or tin.Among which,tetraalkylgermanes,especially alkyltrimethylgermanes that have been confirmed to be active in photoredox radical reactions,are still lack of efficient and simple synthesis methods.Herein,we report a new protocol using commercially available trimethylgermanium bromide and alkyl bromides as substrates and cheap copper(II) sulfate as catalyst.When using magnesium powder as the reductant,a series of alkyltrimethylgermanes could be generated in moderate to good yield.Mechanism studies suggested a probable in-situ Grignard reaction pathway.The copper salt added could significantly accelerate the reaction between organohalogermanes and Grignard reagents so that the formation of Ge-Ge byproduct from the reduction of organohalogermanes by magnesium could be inhibited.Compared to the traditional method using Grignard reagent and organohalogermanes,this new protocol has better compatibility towards functional groups like esters and amides.The protocol could also be expanded to the synthesis of various tetraalkylgermanes or germacycloalkanes using dichlorodimethylgermane and alkyl bromides.General procedure for the synthesis of alkyltrimethylgermane is:To an oven-dried 25 mL screw-capped tube equipped with a stir bar was charge with 48 mg(2 mmol) magnesium powder and 8.0 mg(0.05 mmol)CuSO_(4).The tube was vacuumed and backfilled with argon for three cycles.6 mL freshly distilled THF was added followed by the addition of 128 μL(1 mmol) trimethylgermanium bromide and 1.5 mmol alkyl bromide.The mixture was sealed with a Teflon stopper,warmed to 60 ℃ and stirred for 10 h.After cooled to room temperature,the resulted mixture was quenched with saturated NH_(4)Cl solution,extracted with diethyl ether and washed with brine.Combined organic layer was dried over Na_(2)SO_(4) and concentrated under reduced pressure.The residue was purified by flash column chromatography on silica gel or distillation to give the desired alkyltrimethylgermane.