Self-terminating Oxidative Radical Cyclizations
In one specific type of radical addition called self-terminating oxidative radical cyclization, alkynes are oxidized to ketones with intramolecular radical cyclization and the radical species are inorganic rather than carbon based. This type of reaction is self-terminating because propagating is not possible and the initiator is used in stoichiometric amounts.
As an example a nitrate radical is generated by photolysis of CAN which reacts with an alkyne to generate first a very reactive vinyl radical and then via a 1,5-hydrogen atom transfer (HAT) and 5-exo-trig ring-closure a ketyl radical. The ketyl dislodges a nitrite radical which is not reactive enough for propagation and the ketone is formed.
The radical species in effect is a single oxygen atom synthon. Other inorganic radical that show this type of reactivity are sulfate radical ions (from ammonium persulfate) and hydroxyl radicals.
Read more about this topic: Free-radical Addition
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