Halocyclization process

Transfer of a halonium ion to l,o)-alkenols or l,co-alkenoic acids which are capable of undergoing halocyclization is a key method to generate 4-, 5- and 6-membered heterocyclic rings via the so-called halocyclization processes 1,2,3,4,5,6,7). This synthetic method would be far more valuable if the halogen transfer to an achiral alkene could be conducted in a chiral fashion (exemplified in Figure 1) as it would produce optically active heterocycles that could be further functionalized through manipulation of the halomethyl group. 

A final type of oxidative carbon-carbon bond forming dearomatization process involves electrophile-induced dearomatization. The most common variant of this reaction entails activation of an alkyne or alkene moiety with an electrophilic halide source to initiate intramolecular dearomatization accompanied by formal arene oxidation (Scheme 15.26) [72]. Proper positioning of an electron-donating methoxy group is crucial for success of this transformation. Other examples of halocyclization-dearomatization reactions involving appropriately substituted arenes tethered to alkynes and alkenes have been reported, along with an intramolecular Pummerer-type dearomatization initiated by an electrophilic thionium ion [73, 74]. 

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