Radical Philicity Inversion in Co- and Fe-Catalyzed Hydrogen-Atom-Transfer-Initiated Cyclizations of Unsaturated Acylsilanes

[1,2]-Radical Brook rearrangement (RBR) has been identified as a viable pathway in M–H (M = Co, Fe) catalyzed hydrogen-atom-transfer reactions involving unsaturated acylsilanes. Guided by the same concept, we have explored two transformations, namely, a Co-catalyzed cycloisomerization reaction and a Fe-catalyzed cyclization/Giese addition reaction. Both reactions involve the generation of a versatile α-siloxy radical intermediate via concomitant philicity inversion and radical translocation, which is mechanistically distinct from coupling reactions involving fragmentation/reduction pathways. Synthesis of cyclic silyl enol ethers and sterically congested cyclopentanol derivatives have been thus achieved with high regio- and diastereo-selectivity.