Mukaiyama-Michael reaction of cyclic ketene silyl acetals and enones. Importance of ring flexibility in electron transfer process

Michael reaction of macrocyclic ketene silyl acetals or α-enones occurs smoothly under electron transfer conditions while the reaction of 6-membered analogs is more sluggish, indicating the importance of the ring flexibility to allow the α,β-carbon-carbon bonds of both reaction components to rotate when the radical species are generated.