Tributyltin hydride-mediated free radical cyclization of allene-tethered oxime ethers,oxime esters and hydrazones.Influence of the substitutents borne by the C=N double bond on the course of the reaction

摘要

A set of allenic derivatives 1 bearing a C=N bond in #beta# position and diversely substituted in R~3 and Z was prepared.The behaviour of componds 1 towards the Bu_3Sn radical was tehn studied.Depending on the nature of R~3 and Z,products 2,3,and 4 were obtained in diverse ratios.When thesteric hindrance on the C-atom of the C=N bond was low(R~3=H),the product'normally'cbtained was 2.When the steric hindrance of R~3 was higher ,the formation of 3 and 4 became competitive.In this case,the ratio between 2,3,and 4 can be explainedon the basis of the polarit of R~3 and Z.The higher the electroattactive effect of R~3 and Z,the higher the quantity of2 and 4 in comparison with 3.