Carbon-carbon bond formation via epititanation and aromatization of acetylenes

Abstract

The dibutyltitanium(IV) diisopropoxide, Bu2Ti(OPri)2, reacts with acetylenes, RCºCR (1), where R = Ph, Pr, to undergo in high yield epimetalation with Ti(OPri)2 by transfer. Our on-going research has demonstrated the transformation of such three-membered titanacycles (2) into 1,2,4,5-tetrasubstituted benzene derivatives (4) in good yields upon reaction of (2) with monomeric acetylenes, R¢CºCH (3), R¢=Ph, Me3Si at room temperature over 2h. A 1:2 molar mixture of PhCºCPh and PhCºCH provided 90% of pure 1,2,4,5-tetraphenylbenzene. The formation of such aromatic products is made possible via the insertion of the monomeric terminal acetylenes to one of the carbon – titanium bonds of (2) and the subsequent Diels-Alder type addition of the second equivalent of the terminal acetylene to the resulting five-membered titanacycles leading to the elimination of Ti(OPri)2.