Allyltin compounds, acyl

Free-radical-mediated four-component coupling reactions are rare. However, when an allyltin-mediated radical carbonylation is conducted in the presence of electron-deficient alkenes, four-component coupling reactions take place efficiently to give good yields of p-functionalized <5,fi-unsaturated ketones [40]. The wide scope of this four-component coupling reaction is noteworthy Primary, secondary, and tertiary alkyl bromides and iodides can be used as well as aromatic and vinylic halides. A variety of electron-deficient alkenes, such as methyl vinyl ketone, ethyl acrylate, acrolein, acrylonitrile, and vinyl sulfone, can be used as the acyl radical trap (Scheme 6.23). Fluorous allyltin compounds can also be used in four-component coupling reactions [41]. 

Allyltin compounds behave as excellent unimolecular chain transfer (UMCT) reagents [49] which serve as radical acceptors and sources of tin mediators [50]. Since acyl radicals are nucleophilic radicals, the addition reaction to allyltin, which is regarded as an electron rich alkene, is not a rapid process. Ryu, Sonoda, and coworkers found that unsaturated ketones can be synthesized by a three-component coupling reaction, comprised of alkyl halides, CO, and allyltin reagents [51]. Because of the slow direct addition of alkyl radicals to allyltin compounds [50b], radical car-bonylations with allyltin can be conducted at relatively low CO pressures, and high substrate concentrations (0.1-0.05 M) were used to ensure the chain length. 

Tin.—Allyltin compounds, especially under rhodium-complex catalysis, react with acyl chlorides to give allyl ketones or with aryl halides to give allylarenes. Bridgehead alkyl bromides are reduced on photolysis with Bu"3SnH, whilst the system (Bu"3Sn)20-Br2 oxidizes sulphides to sulphoxides. )V-(Alkoxycar-bonyl)amino-acids are obtained upon treatment of cyclic anhydrides with Bu3SnN3 and heating in an alcohol. ... 

The radical carbonylation of an alkyl iodide in the presence of Kim s sulfonyl oxime ethers [58, 59, 60] provides a new type of multicomponent coupling reaction where plural radical Cl synthons are consecutively combined [61]. In the transformation, allyltin was used to serve as a trap of benzenesulfonyl radical which converts sulfonyl radical to a tin radical, thus creating a chain. Scheme 14 illustrates such an example, where the product was easily dehydroxylated to give the corresponding tricarbonyl compound on treatment with zinc/AcOH. The radical acylation reaction by Kim s sulfonyl oxime ethers can be conducted under irradiation with the addition of hexamethylditin. This is an alternative path for achieving a similar transformation without the use of photolysis equipment. Scheme 15 illustrates several examples where carbon monoxide and Kim s sulfonyl oxime ethers are successfully combined to create new tandem radical reaction sequences [61],... 

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