Syn–anti selectivity in cycloadditions. Part 4. 1,3-Dipolar cycloadditions of nitrones with polychloronorbornadienes

Abstract

Cyclic and acyclic nitrones reacted smoothly with 1,2,3,4-tetrachloro-, 1,2,3,4,7-pentachloro-, and 1,2,3,4,7,7-hexachloro-norbornadienes to give syn and anti methylene adducts in varying ratios. The structures of the adducts were assigned on the basis of spectroscopic (¹H n.m.r.) and chemical evidence. The syn : anti ratios found are interpreted on the basis of steric and stereo-electronic effects in the cycloaddition transition states. Comparison between the results of the reactions of the E and Z isomers of C-pentamethylphenyl-N-methylnitrone with those of (Z)-C-phenyl-N-methylnitrone, respectively, suggests that the latter 1,3-dipole might be in equilibrium with the E isomer even at room temperature.