Titanium-mediated intramolecular cyclization of tethered propargyl alcohol derivatives. Access to exocyclic bis-allenes and cyclobutene derivatives

Treatment of tethered bis-propargyl alcohol derivatives with (η2-propene)Ti(O-i-Pr)2 afforded four- and five-membered rings bearing conjugated exocyclic bis-allenes. In the case of six- and seven-membered rings, bicyclic cyclobutenes were obtained in the same pot most likely via the intermediate bis-allenes.