Stereo-controlling Strategies for Underdeveloped Organic Dihalogenations

Abstract: 

Conventional electrophilic dihalogenation of alkenes generally proceeds via an anti-addition pathway through the intermediacy of a cationic three-membered cyclic halonium species.¹ This well-established transformation is one of the most widely utilized organic reactions because of its highly predictable stereospecificity.² However, it is extremely challenging to alter the diastereochemical course, and consequently, the complementary syn-dihalogenation process has been considerably under-developed,³ requiring new mechanistic approaches. Only recently, a few notable achievements were made by inverting one of the stereocenters after anti-addition using a carefully designed reagent system.⁴ Our group investigated report a conceptually distinctive strategy for the simultaneous double electrophilic activation of the two alkene carbons from the same side. Then, the resulting vicinal leaving groups can be displaced iteratively by nucleophilic halides to complete the syn-dihalogenation. For this purpose, thianthrenium dication was employed,⁵ and all possible combinations of chlorine and bromine were added onto internal alkenes successfully with excellent syn-stereospecificity.⁶ Of particular note is the regiodivergent syn-bromochlorination, in which both constitutional isomers can be accessed simply by reversing the addition sequence. Furthermore, the unprecedented syn-dibromination is also noteworthy.

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20241113_대학원 세미나_정원진 교수.pdf