Department of Chemistry and Biochemistry, Baylor University, Waco, Texas 76706, United States.
J Am Chem Soc. 2022 Jul 27;144(29):13294-13301. doi: 10.1021/jacs.2c04588. Epub 2022 Jul 12.
A new strategy is described for the Lewis base-catalyzed bromochlorination of unsaturated systems that is mechanistically distinct from prior methodologies. The novelty of this method hinges on the utilization of thionyl chloride as a latent chloride source in combination with as little as 1 mol % of triphenylphosphine or triphenylphosphine oxide as Lewis basic activators. This metal-free, catalytic chemo-, regio-, and diastereoselective bromochlorination of alkenes and alkynes exhibits excellent site selectivity in polyunsaturated systems and provides access to a wide variety of vicinal bromochlorides with up to >20:1 regio- and diastereoselectivity. The precision installation of Br, Cl, and I in various combinations is also demonstrated by simply varying the commercial halogenating reagents employed. Notably, when a chiral Lewis base promoter is employed, an enantioselective bromochlorination of chalcones is possible with up to a 92:8 enantiomeric ratio when utilizing only 1-3 mol % of (DHQD)PHAL.
描述了一种新的路易斯碱催化不饱和体系的溴氯化策略，其在机理上有别于先前的方法。该方法的新颖之处在于使用亚硫酰氯作为潜在的氯源，并结合使用 1 mol%的三苯基膦或三苯基氧膦作为路易斯碱性活化剂。这种无金属、催化的化学、区域和立体选择性的烯烃和炔烃的溴氯化反应，在多不饱和体系中表现出优异的位点选择性，并提供了广泛的各种邻位溴氯化物，区域和立体选择性高达 20:1 以上。通过简单改变所使用的商业卤化试剂，还证明了 Br、Cl 和 I 以各种组合进行精确安装的可能性。值得注意的是，当使用手性路易斯碱促进剂时，仅使用 1-3 mol%的(DHQD)PHAL 即可实现查耳酮的对映选择性溴氯化，对映体比值高达 92:8。
