Butadiene monoepoxide and cyclopropane carboxaldehyde: pyrolysis and structure

The results of pyrolyzing both butadiene monoepoxide and cyclopropane carboxaldehyde are presented. The pyrolysis temperature range was 341[degrees]C to 395[degrees]C. Rate data obtained from the pyrolysis of cyclopropane carboxaldehyde indicates that the rearrangement of cyclopropane carboxaldehyde to 2,3-dihydrofuran is first order. Arrhenius parameters for this rearrangement, containing large errors, are E[lowered a] = 45 [plus-minus] 4 Kcal/mole, Log A = 12 [plus-minus] 1. Lanthanide-induced chemical shift experiments were performed on butadiene monoepoxide, cyclopropane carboxaldehyde and crotonaldehyde in solution using tris(dipivalomethanato)europium(III). The results of these experiments were interpreted to indicate the preferred ground state conformations of the molecules studied. The conformation assigned to butadiene monoepoxide is that in which the vinyl group is anti to the oxide ring. The conformation assigned for cyclopropane carboxaldehyde is with the carbonyl anti to the cyclopropyl ring. In a similar manner the conformation assigned to crotonaldehyde is anti. The assignments were based on correlations of [delta]Eu to 1/r[raised 3] , where [delta]Eu is the slope of a line for a particular proton.obtained by plotting the chemical shifts of that proton vs. the molar ratio of metal complex [Eu(DPM)[lowered 3]] to substrate, and r is the vector distance from the estimated position of the europium to that proton. Some of the products formed in the pyrolysis of cyclopropane carboxaldehyde are generated via a biradical intermediate. This contention is supported by the thermodynamics of the system under investigation, and by careful comparison with other three membered ring systems, such as vinylcyclopropane.