I. Gridnev, M. E. Gursky, Y. Bubnov
1996
Citations
0
Influential Citations
16
Citations
Journal
Organometallics
Abstract
The reaction of potassium methylenecyclobutanide with dibutylboron chloride and 9-bromo-9-borabicyclo[3.3.1]nonane yields the corresponding allylic type triorganoboranes 1 and 2. Compounds 1 and 2 exhibit a facile [1,3]-B sigmatropic shift, which results in the reversible coexistence of isomeric 2-(dialkylboryl)-1-methylenecyclobutanes 1a and 2a with 1-((dialkylboryl)methyl)-1-cyclobutenes 1b and 2b. For both compounds 1 and 2, the 2-(dialkylboryl)-1-methylenecyclobutane form (1a, 2a) is predominant at low temperatures, while raising the temperature leads to a shift of the equilibrium in favor of the 1-((dialkylboryl)methyl)-1-cyclobutene form (1b, 2b). Activation parameters for the equilibrium in 1 were found from the 2D 13C−13C spectra (for the transformation 1a → 1b Eact = 35.5 ± 2.5 kJ mol-1, ΔG⧧298 = 53.8 ± 0.5 kJ mol-1; for the transformation 1b → 1a Eact = 33.8 ± 2.5 kJ mol-1, ΔG⧧298 = 52.8 ± 0.5 kJ mol-1). For the equilibrium in 2, the rate constants of the direct and reverse reaction were determi...