Intramolecular Cyclizations of Allenic Acylureas and -amides

Article abstract of DOI:10.1002/hlca.19870700130

Allenic acids are found to add to dicyclohexylcarbodiimide affording, in the presence of Et2NH, the 4H-1,3-oxazin-4-ones 5 via 4.Under neutral conditions, they add to diaryl- or pyridyl(cyclohexyl)carbodiimides and triphenylketene imine to give the corresponding tricyclo(5.2.2.0 1,5)undeca-4,4,10-trien-3-ones 7,8,9, and 12.The allenic phenyl ester 13a dimerises, on heating in a (2+2) head-to-head fashion, to 14 but fails to undergo intramolecular Diels-Alder cyclization to 15.