Reinvestigation of the reactions of camphorketene: Structural evidence for pseudopericyclic pathways¹

The stereochemistry of the dimers (3 and 4) of camphorketene (2) have been determined. The crystal structures of 3, 20 and of related compounds show ground-state distortions that are interpreted as prefiguring planar, pseudopericyclic transition states for retro-cycloadditions to form α-oxoketenes. The B3LYP/6-31G optimized geometry for the transition structure (10) for the dimerization of s-Z-formylketene (8) is consistent with this mechanism. Trapping of 2 with alcohols shows selectivity comparable to other α-oxoketenes. The lack of reaction of 2 with benzaldehyde and the lack of enol tautomers in camphoric acid derivatives is attributed to angle strain in the bicyclic camphor moiety.