The cycloaddition of the 1,3-butadiene radical cation with acrolein and methyl vinyl ketone

The 1,3-butadiene radical cation reacts with acrolein and methyl vinyl ketone to produce ‘stable’ adducts. The nature of the reaction and the structures of the adducts were investigated by collisional activation decomposition (CAD) combined with tandem mass spectrometry (MS/MS), and also by Fourier transform mass spectrometry. The CAD spectra of gas-phase adducts were compared with those of suitable model compounds. On that basis, it was determined that the 1,3-butadiene radical cation undergoes a cycloaddition with these α,β-unsaturated carbonyl compounds. The butadiene radical cation serves as the ‘ene’, and the acrolein and methyl vinyl ketone react as dienes, forming cycloadducts having 2-ethenyl-2,3-dihydropyran radical cation structures.