Selenium-Stabilized Carbocations. Formation of 2-(Phenylseleno)allyl Cations and Their Reactions with Furan, Pyrrole, and Thiophene

Article abstract of DOI:10.1021/jo00174a017

β-Bromovinyl selenides I (R₁ = H, CH3, C2H5; R₂ = H, CH3; R₃ = H, CH3) have been prepared in excellent yields from allenes and benzeneselenenyl bromide.On treatment with silver perchlorate in nitromethane at -15 deg C and in the presence of a weak base, these β-bromovinyl selenides reacted smoothly with electron-rich aromatic molecules such as furan, N-methylpyrrole, thiophene, or 1,3,5-trimethoxybenzene to give electrophilic substitution products exclusively and in good yields (60-70 percent).From this and from the systematic absence of <4 + 3 -> 7> cycloaddition product s it is tentatively concluded that the actual reactive species might be III rather than allylic cation II.It has also been shown that the substitution products can be efficiently deselenated by the use of tri-n-butyltin hydride at reflux in benzene and in the presence of azobis(isobutyronitrile)(AIBN).