Publication Details (including relevant citation information):
Eur. J. Org. Chem. 2009, 525-530
1,3-Dipolar cycloaddition of C-aryl-N-aryl- or N-methylnitrones with esters of Feist's acid (3-methylenecyclopropane-trans-1,2-dicarboxylic acid) occurs with the formation of the corresponding spiro[cyclopropane-1,4-isoxazolidine] cycloadducts as single isomer with yields in the range of 17–59 %. The reaction proceeds with inverse regiochemical outcome compared to cycloadditions with unsubstituted methylenecyclopropane. Feist's esters are significantly less active towards cycloaddition with nitrones than methylenecyclopropane and reactions require prolonged heating at elevated temperature. The electronic structures of Feist's esters were investigated by means of molecular photoelectron spectroscopy and theoretical calculations (HF/6-31G*, B3LYP/6-31G*). Both, measured photoelectron HeI spectrum and ground state calculations (HF/6-31G*) of Feist's esters, indicate considerable lowering of the methylenecyclopropane π-**** energies by substitution with an acceptor group. B3LYP calculations of addends and transition states forthe interaction of methylenecyclopropane with C,N-diphenylnitrone correctly predict regiochemical outcome. However, B3LYP calculations do not account for the observed regiochemical outcome and diminished reactivity in reactions of Feist's esters with C,N-diphenylnitrone.