A new development in radical cyclization reaction by using captodative effect by heteroatoms

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In this research program, we have found the following things :1)The 7-edno selective radical cyclization, which we have found and utilized for the synthesis of benzazepine derivatives, was governed not by the steric effects but the neophyl rearrangement of 6-exo radical that was initially formed in the cyclization process. Our kinetic study revealed that the rate constant of the neophyl rearrangement was estimated about 100 times smaller than the rate constant of hydrogen abstraction from tributyltin hydride by alkyl radical. This reflects that virtually no rearrangement took place and a mixture of 6-exo and 7-endo adducts was obtained if the concentration of tin hydride was 10^<-1> M level. The syringe-pump technique kept the concentration of tin under 10^<-5> M level which suppressed direct hydrogen abstraction of 6-exo radical and led the neophyl rearrangement proceeded to give 7-endo radical. We have also revealed the rearrangement is irreversible and one way from 6-exo to 7-endo. This may be due to highly stabilization on 7-endo radical as well as kinetic reason in which the radical center of the 7-endo radical is too far to attack the aromatic ring. There should be several effects for stabilization of 7-endo radical, among which the captodative effects is the one. So we concluded that the neophyl rearrangement and captodative effect, both of which were seldom used in organic synthesis, would be a useful controlling factors to develop a new selective synthetic methodologies.2)To develop a new synthetic method to prepare alpha-thio acrylate derivatives, we have examined several reactions that includes the Mannich reaction and the Baylis-Hillman reaction.