Atom transfer reactions stereoselective radicals

Examples of stereoselective cyclizations involving heteroatom radicals are rare. Tandem oxy radical cyclization and diastereoselective hydrogen atom transfer reactions, however, have also been studied (Eq. (13.58)) [74]. These reactions take advantage of chirality at the y carbon to induce anti-/ cycloaddition. Hydrogen... 

Chiral Lewis acid-catalyzed atom-transfer cyclization is performed by the reaction of a-bromo-a-methyl-(3-keto esters (46) in the presence of Mg(C104)2 and a chiral ligand such as Z fsoxazoline, initiated by Et3B, as shown in eq. 10.22. The Lewis acid promotes not only the atom-transfer radical cyclization, but also high stereoselectivity through the chelation onto Mg2+. Intermediate [X] is a plausible chelated radical intermediate. 

The Kochi reaction has also been used to demonstrate polar effects of remote substituents upon free-radical stereoselectivities in chlorine atom transfer. ... 

Although copper reagents, hahdes and triflates, are widely used in atom-transfer polymerization reactions (ATRP) [63], these processes do not fall under the category of Lewis acid-mediated reactions. Sherrington and co-workers have shown that a vinyl monomer coordinated to a chiral copper Lewis acid (122) undergoes stereoselective polymerization (Sch. 29) [64]. A chiral block-copolymer 124 was prepared under radical conditions. 

Guindon Y, Guerin B, Chabot C, Ogilvie W. Stereoselective radical carbon-carbon bond forming reactions of 3-alkoxy esters atom and group transfer aUylations under bidentate chelation controlled conditions. J/Im Chem Soc. 1996 118 12528-12535. 

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