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

In the presence of TiCl4, Et3N, and I-2, 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 I-2 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.