Catalytic asymmetric halocyclization

In 2010, Denmark s group demonstrated racemization of the enantiopure (4R,5S)-5-bromo-4-octyl tosylate via bro-miranium ion-to-olefin transfer in acetolysis [41]. While no decrease in enantiospecificity was observed in the absence of the (El-d-octene, in the presence of the ( )-4-octene, the enantiopure bromiraninm ion generated from the (4R,5S)-5-bromo-4-octyl tosylate transferred to the ( )-4-octene, and enantiospecificity was lost at the same time (Table 9.1). Based on these reports, suppression of haliranium ion transfer from the in ifn-generated enantiopure haliranium ion to an umeacted substrate is crucial for the successful catalytic asymmetric halocyclization. 

Until recently the catalytic asymmetric halocyclization remained a long-standing problem. Applications of these methods are sparse, and the halogens are often substituted at the later stages. A brief description will be presented here. 

---