中文摘要：

α-卤代共轭烯酮是有机合成中的一个重要砌块.从机理上划分,有两类基本反应可用于制备α-卤代共轭烯酮：一类经过Baylis-Hillman类型的Michael加成/α-卤代/β-消除过程;另一类则通过溴单质的亲电加成及随后的溴化氢消除来实现.前一种方法依赖于是否容易形成Baylis-Hillman类型的暂时烯醇负离子,而烯酮β-位置的取代基会阻碍亲核试剂的共轭加成从而抑制上述暂时的烯醇负离子的形成.后一种方法得益于溴单质的强亲电性,可以用于位阻较大的底物,但副反应如非选择性的过度溴代使得该方法的收率不高,在较大量制备中收率的重现性很差.本工作报道了一种以三溴化氢吡啶复合物为溴化试剂的制备α-溴代-β-取代烯酮的方法.该反应适用于较大量制备,所用试剂具有较低腐蚀性和毒性.

英文摘要：

a-Haloenone is an important building block in organic synthesis, especially in natural product synthesis. There are at least 4 different reaction modes of this class of compounds： 1, crossing coupling reactions at the a-position; 2, conjugate additions at the fl-position; 3, deprotonation at the a＇-position; 4, deprotonation at the ）,-position. Representative examples of the utilities of a-haloenone include the syntheses of diversonol and the core structures of lomaiviticins and guanacastepenes. From a mechanistic perspective, two types of a-halogenation methods have been developed previously： one through a se- quential Baylis-Hillman-type Michael addition/a-halogenation/fl-elimination process; the other one involving an electrophilic bromination followed by a fl-elimination. The success of the former type of reactions highly depends on the formation of the transient enolate; the fl-substituent on the enone substrates drastically slows down the rate of the first Michael addition step which is responsible for the enolate formation. The latter takes advantage of the strong electrophilicity of molecular bromine to overcome the steric effect of the substrates. However, quite a few side reactions including non-selective bromination often occur, resulting in modest to low yield and poor reproducibility of the desired product on a large scale. Here, we report a pro- tocol for a-bromination offl-substituted enones using pyridine hydrobromide perbromide as a brominating reagent. Cyclic enones prove to be suitable substrates for this reaction, and the corresponding products were obtained in 〉80% yield in general. Notably, fl-phenyl cyclohexenone, a rather unreactive substrate due to both steric and electronic reasons, was bromi- nated smoothly. These bromination products may serve as useful synthon in organic synthesis. For acyclic enones and enoates, the reaction has to be performed at elevated temperature, which may be attributable to the rather poor acidity of the a-proton of the dibromo intermediate. The reac