Four-component radical cascade

An interesting four-component radical cascade that leads to formation of 3-arylthio-substituted acrylamides 172 and involves thiyl radicals, aromatic acetylenes, and... 

Miura et al. built on Ryu s previous work to achieve four-component radical cascades leading to diketones (Scheme 63) [174]. This outstanding result relies on initial carbonylation of alkyl radicals to form acyl radicals, such as 196. The nucleophilicity of acyl radicals allowed them to react with electron-deficient olefins to form ct-cyano radicals (197), whose phihcity is now reversed. Thus, they were able to add onto stannyl enolates and led to ketyl radicals such as 198. Those latter radicals underwent / -elimination of trib-utylstannyl radicals. This key elimination regenerated the mediator for the initial dehalogenation. This very fine tuning of the radical reactivities is the key element that makes the whole process work. 

The second example in Table 5 shows the cyclization-carbonylation-allylation sequence, in which 5-hexenyl radical cyclization precedes CO trapping. Because of the nucleophilic nature of acyl radicals, in a mixed alkene system comprised of an electron deficient alkene and allyltin, they favor the electron deficient alkene first and the resulting product radical, which have an electrophilic character, and then smoothly add to allyltributyltin. This four-component coupling reaction provides a powerful radical cascade approach leading to y -functionalized, -unsaturated ketones, which are not readily accessible by other methods [52]. 

---