Research news, Dec. 16th, 2013.
Synthesis of Semibullvalene Derivatives via Co2(CO)8-Mediated Cyclodimerization of 1,4-Dilithio-1,3-butadienes
Shaoguang Zhang, Ming Zhan, Qifeng Wang, Chao Wang, Wen-Xiong Zhang, and Zhenfeng Xi*
Org. Chem. Front. DOI:10.1039/C3QO00019B
Co2(CO)8-Mediated cyclodimerization of 1,2,3,4-tetrasubstituted 1,4-dilithio-1,3-butadienes readily afforded octa-substituted semibullvalenes. X-ray crystal structure of 1,2,5,6-tetraethyl-3,4,7,8-tetraphenyl semibullvalene was determined to show an unsymmetrical, localized structure, which is in sharp contrast with the C2 symmetrical structure of its tetramethyl analogue. In addition, this Co2(CO)8-mediated cyclodimerization was found to be dependent on the substitution pattern of 1,4-dilithio-1,3-butadienes. 1,4-Diphenyl dilithio compound gave its corresponding cyclooctatetraene derivative, while the dilithio reagent without substituents at its 1,4-positions afforded a cyclopentadienone [4+2] dimer.