Conformer-specific polar cycloaddition of dibromobutadiene with trapped propene ions

Ardita Kilaj, Jia Wang, Patrik Stranak, Max Schwilk, Uxia Rivero, Lei Xu, O. Anatole Von Lilienfeld, Jochen Kupper, Stefan Willitsch
Diels-Alder cycloadditions are efficient routes for the synthesis of cyclic organic compounds. There has been a long-standing discussion whether these reactions proceed via stepwise or concerted mechanisms. Here, we adopt an experimental approach to explore the mechanism of the model polar cycloaddition of 2,3-dibromo-1,3-butadiene with propene ions by probing its conformational specificities in the entrance channel under single-collision conditions in the gas phase. Combining a
more » ... controlled molecular beam with trapped ions, we find that both conformers of the diene, gauche and s-trans, are reactive with capture-limited reaction rates. Aided by quantum-chemical and quantum-capture calculations, this finding is rationalised by a simultaneous competition of concerted and stepwise reaction pathways, revealing an interesting mechanistic borderline case.
doi:10.5451/unibas-ep85889 fatcat:fwnrrhtygbdt3axuh6ybviif7e