Addition Reactions of Radicals with Substituted Alkenes

Addition Reactions of Radicals with Substituted Alkenes 

The most general method for formation of new carbon-carbon bonds via radical intermediates involves addition of the radical to an alkene. The reaction generates a new radical that can propagate a chain sequence. The preferred alkenes for trapping alkyl 

Reactions Involving Carbocations, Carbenes, and Radicals as Reactive Intermediates 

Radicals for addition reactions can be generated by halogen atom abstraction by stannyl radicals. The chain mechanism for alkylation of alkyl halides by reaction with a substituted alkene is outlined below. There are three reactions in the propagation cycle of this chain mechanism addition, hydrogen atom abstraction, and halogen atom transfer. 

The rates of each of these steps must exceed competing chain termination reactions in order for good yields to be obtained. The most important competitions are between (a) the addition step k1 and reaction of the intermediate R- with Bu3SnH, and (b) between the H abstraction step k2 and addition to another molecule of the alkene. If 

No perturbing interaction with substituent—No strong stabilization 

Electron donor on radical, electron acceptor on alkene— Strong stabilization of SOMO by alkene LUMO 

---

Sources of Radical Intermediates Introduction of Functionality by Radical Reactions Addition Reactions of Radicals with Substituted Alkenes Cyclization of Free-Radical Intermediates Fragmentation and Rearrangement Reactions... 

---