Another post for the series “This blog is obsessed with dihalogenation reactions”. In previous posts I presented some of the reactions I consider of great relevance on the subject of enantioselective dihalogenation reactions (you can take a look here and here as well :D). All these reactions having in common the synthesis of vicinal halides resulting from anti-addition as an inevitable consequence of the ionic nature of the addition reaction of elemental halogens and related reagents to alkenes.
In other words, the challenge I’d like to highlight in this post is the difficulty of the development of straightforward methodologies for the syn-halogenation of alkenes. A great contribution to this topic is the first catalytic, syn-stereospecific dichlorination of alkenes developed by Denmark and co-workers.
The strategy used is based on a first step of anti-addition of an in-situ generated PhSeCl3 to an alkene followed by a nucleophilic displacement with a chloride ion source leading to a syn-dichlorination product overall. The process is made catalytic by adding an oxidant to the Ph-Se-Se-Ph precatalyst.
This new methodology could be very useful for the synthesis of oligo- and polychlorinated compounds such as chlorosulfolipids, a family of synthetically challenging compounds originally discovered from the membranes of freshwater algae and associated to diarrhetic shellfish poisoning.
Do you want to know more? Take a look to the original paper:
– Catalytic, stereospecific syn-dichlorination of alkenes. Alexander J. Cresswell, Stanley T.-C. Eey & Scott E. Denmark. Nature Chemistry 7, 146–152 (2015).