Free radical rearrangements of R3Sn and R3Si groups

Abstract

The free radical rearrangements involving two kinds of Group IV elements, R$_3$Sn and R$_3$Si group, and their competitions in migration with well known pathways mainly hydrogen atom transfer were studied. 1,5-Bu$_3$Sn group transfer from allylic carbon to alkoxy oxygen preferred 1,5-H atom transfer from allylic carbon to alkoxy oxygen over twenty times. The only minor product was caused by the migration of H atom of $\alpha$-stannyl group, and any other types of competitive reactions did not observed. 1,5-Bu$_3$Sn group transfer from enoxy oxygen to alkoxy oxygen was found to be greatly favored over 1,5-H atom transfer from allylic carbon to alkoxy oxygen or 6-exo cyclization of the alkoxy radical. 1,5-Bu$_3$Sn group transfer was found from enoxy oxygen to carbon. 1,5-Bu$_3$Sn group transfer from allylic carbon to carbon was inferior to the 1,5-H atom transfer. 1,6-Bu$_3$Sn group transfer from allylic carbon to alkoxy oxygen was found to have a preferrence over 1,5-H or 1,6-H atom transfer from allylic carbon to alkoxy oxygen about ten times. 1,6-Bu$_3$Sn group transfer from enoxy oxygen to alkoxy oxygen has been found. The radical rearrangements involving 1,5-R$_3$Si group transfer from carbon to alkoxy oxygen revealed a strong preferrence for 1,5-H atom transfer over 1,5-TMS group one. TBS group transfer from enoxy oxgen to alkoxy oxygen was investigated. Exocyclic epoxy silyl enol ether was reacted with Bu$_3$SnH under radical condition and 2-Silyloxymethylcycloalkanone, via 1,5-TBS group transfer from enoxy oxygen to alkoxy oxygen, was obtained as a major product. 1,5-TBS group transfer was applied to the radical cyclization and only the 5-exo type bicyclic compounds were obtained. By changing the R$_3$Si group from TBS to TMS group, more higher yield of products was obtained in much shorter reaction time without the side product or starting material. In the reaction of exocyclic epoxyketone with (TMS)$_3$SiH, it was found that the selective reaction o...