Stabilizing effect of tributylstannyl group on adjacent carbon centered radicals

Abstract

Stabilizing effect of the tributylstannyl group on the adjacent carbon centered radicals has been studied. First, the intramolecular cyclization of vinyl radicals was carried out with N-aziridinyl imines as the radical acceptors. Allylic radicals, generated from the cyclization of vinyl radicals, gave two regioisomeric products, endo-cycloalkene as a major product along with exo-methylene cycloalkane as a minor product. But tributyltin substituted allylic radicals, generated from the cyclization of β-tributylstannyl vinyl radicals, gave only endo-cycloalkene. Second, when tributyltin substituted allyl iodides were treated with n-tributyltin hydride and AIBN, two regioisomeric products, allyl-and vinyl-stannanes were obtained in roughly equal ratio. Comparative study using trimethylsilyl substituted allyl iodide showed the similar result. Finally, radical induced ring opening of 3-substituted-1-tributylstannyl-2-vinylcyclopropanes was investigated. Treatment of vinylcyclopropanes with PhSH or $Bu_3SnH$ generated two intermediary carbon radicals, α to tin and β to tin. In case of R=H and Me, α-tributylstannyl carbon radicals were generated predominantly. On the other hand, β-tributylstannyl carbon radicals, followed by β-elimination of tributylstannyl radical, gave a conjugated dienyl product exclusively, when R is phenyl group. In a comparative study, i.e., when R is trimethylsilyl group, two carbon radicals, α to tin and α to silicon, were formed in roughly 1:2 rat10.