Stereochemistry of Radical Reactions

Stereoselectivity of Radical Reactions: Cyclic Systems

“…Six-membered ring radicals have been investigated in detail because of their importance in carbohydrate chemistry [2]. Model systems have been examined to clarify the different effects involved in the stereochemical control [S].…”

1,3-Stereoinduction in Radical Reactions

“…[1] Now we show for the first time how this knowledge can be used to obtain high-affinity peptidic compounds. As a lead structure for the derivatization of the RGD motif the cyclic pentapeptide cyclo(-Arg-GlyAsp-d-Phe-Val-) was chosen, which binds selectively a v b 3 -integrins.…”

“…However, most radical polymerizations are more or less unselective, [1a] with the exception of a few sterically highly demanding methacrylates. [2] On the other hand it has been shown during the last few years that acyclic radicals can react with high stereoselectivity; [1,3] the addition of Lewis acids has proved to be activation barrier than the 40 ± 60 kcal mol À1 computed for the TS of the intramolecular isomerization at various levels (such as 46.1 kcal mol À1 at the B3LYP/6-311 G(3df) level [22a] ). [22,23] However, according to Seel, Budenz, and Werner, [21] a bimolecular complex [FSSF´SSF 2 ] (g) forms at temperatures below À 80 8C; this suggests that the actual isomerisation mechanism may not be unimolecular.…”

“…As trapping reaction we chose hydrogen transfer, and assumed that the stereochemical effects observed in this process should be transferable to the radical addition reaction in the chain propagation step of polymerizations. [1,8] …”

Titanocene-Catalysed Electron Transfer-Mediated Opening of Epoxides

“…Most of these reactions constitute typical free radical reactions where the usual selectivities are substratecontrolled. [2] Reagent-controlled radical transformations have emerged more recently. [3] In this context, epoxides that can be readily prepared by a number of methods [4] are a very interesting class of radical precursors.…”