Mechanistic Investigations Aided by Isotopic Labeling. 10. Investigations of Novel Furan-2,3-dione Rearrangements by Oxygen-17 Labeling

Article abstract of DOI:10.1021/jo00001a044

The oxa 1,3-diene moiety in 4-benzoyl-5-phenylfuran-2,3-dione (1) adds aryl isocyanides or heterocumulenes via formal <4+1> or <4+2> cycloaddition processes.The unstable primary adducts undergo novel furandione rearrangements to intermediates in which the two oxygen atoms of the lactone moiety in 1 are equivalent.This equivalence was confirmed by (17)O-labeling experiments using (17)O NMR spectroscopic and mass spectroscopic measurements.Comparison of the (17)O chemical shifts in 1, labeled either at the benzoyl and ring oxygens (1a-(17)O) or at both exocyclic ring-carbonyl oxygens (1b-(17)O), with those in the products 2-4 confirmed the proposed pathways of these rearrangements.Reactions involving carbodiimides, isocyanates, and ketene imines were investigated.