1,3-dipolar cycloadditions of five and six membered cyclic nitrones to α,β-unsaturated acid derivatives

The cycloadditions of 3,4-dihydro-2H-pyrrole 1-oxide, 3,4,5,6-tetrahydropyridine 1-oxide, and (S)-3,4-dihydro-2-hydroxymethyl-2H-pyrrole 1-oxide to alpha,beta-unsaturated acid derivatives have been reviewed. As Z-olefins, several five, six, and seven membered lactones with different functionalization at the gamma-position were employed. As E-olefins, gamma-hydroxy-, gamma-alkoxy-, and gamma-oxo-alpha,beta-unsaturated esters have been incorporated to this study. Steric factors play a very important role in the regio- and stereochemical outcome of these 1,3-dipolar cycloadditions. cis-Olefins yield products derived mainly from an exo transition state, while the cycloadducts of trans-olefins result mainly from endo approaches.