?-Face Stereoselection Operative during Cycloaddition of Oxyallyl Cations to Isodicyclopentadiene

Article abstract of DOI:10.1021/jo00220a021

The 1,3-diphenyl-2-oxyallyl dipolar ion, generated by several different reductive methods and therefore complexed to metal ions of various type, has been added to isodicyclopentadiene.Of the six adducts possible, only five were isolated.Although the relative ratios of these ketones varied substantially with conditions, there was always encountered a strong bias for above-plane <3+4> cycloaddition.The structures of the adducts were elucidated by a combustion of X-ray analysis and base-catalyzed equilibration.The stereochemical course of the tetramethyl-2-oxyallyl dipolar species was also examined and shown to prefer above-plane approach.Transition-state profiles are given.The results, particularly for those processes proceeding with extended arrangements of the reaction partners, are shown to be consistent with closed-shell orbital arguments advanced earlier for anti-Alder <4+2> cycloadditions to isodicyclopentadiene.