A 2-benzothiazolylphenyl (2-Bzt) group has a remarkable effect in accelerating intramolecular [2+2] cycloaddition reactions of allene-ynes. Shigeru Arai and co-workers from Chiba University, Japan, have demonstrated that this directing group is essential for smooth and regioselective formation of functionalized cyclobutenes.

This method enables easy access to cyclobutenes by nickel(II) catalysis, as well as under simple thermal conditions. The role of 2-Bzt is a directing group in the nickel(II) system and a stabilizer for radical species under thermal conditions. The researchers also disclosed that aryl substituents on the allene group increase the rate of cycloaddition and they are now investigating this unique reaction and its applications further.

• A 2-Benzothiazolylphenyl Group Accelerates the Intramolecular [2+2] Cycloaddition of Allene-Ynes,
  Hiroto Hori, Shigeru Arai, Atsushi Nishida,
  Asian J. Org. Chem. 2013.
  DOI: 10.1002/ajoc.201300218