Carbocyclization reaction of active methine compounds with unactivated alkenyl or alkynyl groups mediated by TiCl₄-Et₃N

In the presence of TiCl₄, Et₃N, and I₂, iodocarbocyclization reaction of various active methine compounds having alkenyl groups gave iodocycloalkane derivatives in good yields. On the other hand, TiCl₄ and Et₃N promote the carbocyclization of active methine compounds with 4- alkynyl groups in the absence of I₂ to give methylenecyclopentane derivatives in good yields. This reaction proceeds with high streoselectivity through a cis-addition of trichlorotitanium enolates of active methine compounds to alkynes, and the resulting vinyltitanium intermediates can be further functionalized by the reaction with various electrophiles.