Nonactivated methylene carbon

Think, for a moment, about the principal role played by the central carbon of a functional group in forming C-C bonds. Then ask how many C-C bonds that particular carbon is capable of forming until it gets rid of all heteroatoms directly substituted on it as well as unsaturations. This number could be anything from a maximum of four, for stable species of carbon, to a minimum of zero in the case of nonactivated hydrocarbon methylenes and methane. Then give this number a name, say Functionality Number, abbreviated as FN. 

By contrast, the use of allyltins /3-substituted by an electron-withdrawing group represents a particularly attractive option, due to their enhanced reactivity towards nucleophilic carbon radicals. For this purpose several allyltins were prepared with amide, ester, chloride, nitrile, trimethylsilyl and sulfones functionalities [292]. They have been used for the synthesis of 1,4-dienes [293] or 10-15 membered a-methylene lactones [294], in aminoacids [295] or carbohydrate chemistry [296]. The /3-functionalization by nonactivating alkyl groups is tolerated as well and was used in the synthesis of prostaglandins [297] or /3-lactams [298]. This was also applied to radical cascade reactions with up to four elementary steps with an excellent diastereoselectivity control (Scheme 6.34) [299]. 

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