Contrasteric stereochemical dictation of the cyclobutene ring-opening reaction by a vacant boron p orbital.
Cyclobutene, having a pinacolatoboryl group at the 3-position, was prepared by the reaction of trimethyl borate with a cyclobutenyl anion, which was generated by reductive lithiation of 3-(phenylselenyl)cyclobutene. Its thermal ring-opening reaction provided (Z)-1-borylbuta-1,3-diene selectively despite the arising steric congestion. The contrasteric behavior was accounted for by assuming an electron-accepting interaction of the vacant boron p orbital with the distorted breaking sigma orbital in the inward transition state.
Murakami
Masahiro
M
Department of Synthetic Chemistry and Biological Chemistry, Kyoto University, Katsura, Kyoto 615-8510, Japan. murakami@sbchem.kyoto-u.ac.jp
Usui
Ippei
I
Hasegawa
Munehiro
M
Matsuda
Takanori
T