| Abstract
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A study of the regio- and stereo-chemical behavior of the 1, 3-dipolar cycloaddition of 3, 4, 5, 6, 7-pentahydro-2H-undecane 1-oxide with a series of mono- and di-substituted alkenes has been achieved. The high degree of both regiochemical and stereochemical control observed in these reactions has been explained in terms of steric factors and secondary orbital interaction in the transition states. Significant secondary orbital interactions are observed in the addition reaction of alkenes having conjugated methoxycarbonyl substituents or having oxygen at allylic position. Rate constants for the cycloaddition of 3, 4, 5, 6, 7-pentahydro-2H-undecane 1-oxide to methyl acrylate and methyl methacrylate have been determined at different temperatures by H NMR spectroscopy. The activation parameters indicate the concerted nature of the reaction. Differences in the rates of cycloadditions have been explained in terms of combination of various factors such as torsional strain, bond angle bending strain and steric factors (non-bonded repulsion) in the transition state. The reaction of ethylene with 5, 6, 7, and 8-membered nitrones led us to prepare for the first time the very important parent 5-5, 6-5, 7-5, and 8-5 fused ring systems and determine their nitrogen inversion barriers. The nitrogen inversion barrier in the 8-membered nitrone cycloaddition products has been determined by detailed band shape analysis of proton and carbon NMR spectra and were in the range of 53.5 to 57.4 kJ/mol. The major isomer is shown to be the trans isomer which is in equilibrium with the minor isomer (cis conformer) by a relatively slow nitrogen inversion.
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