A chloroborole with a new substitution pattern is presented. Methyl groups in the butadiene backbone are revealed to allow rearrangement to form non-cyclo-conjugate borabutadienes. The thermodynamic driving force is loss of anti-aromatic destabilization. Computationally, methyl groups in the backbone of boroles are found to be more C−H acidic than methyl groups attached to the boron atom.
The attempted syntheses of 3,4-dimethylborole derivatives further bearing bulky SiMe2
t-Bu groups in 2,5-position are reported. Isolation of base-stabilized adducts to the chloroborole were achieved. The respective free borole was found to be unstable and revealed 1,3-hydrogen atom shift isomerization to a 1-bora-1,3-butadiene with an s-trans orientation and lacking cyclic conjugation of the π-system. Computational probing indicates elevated C−H acidity of methyl groups attached to the butadiene backbone in boroles, exceeding the C−H acidity of respective boron-bound methyl groups. Derivatization attempts of the new chloroborole are reported.Zum Volltext