Allenic acylureas

Allenic acylureas 152, prepared in situ from the corresponding allenic acid 151 and carbodiimides, afforded lactams in good yields [126]. 

The reaction of /V-cyclohexyl-/V-(2-pyridyl)carbodiimide and the allenic acid 83 in dry tetrahydrofuran at ambient temperature for 3 days afforded a 2 1 mixture of isomeric 2-oxo-2H- and 4-oxo-4/7-pyrido[l,2-a]pyrimid-ines 88 and 87 instead of the expected Diels-Alder adduct (92HCA1262). The formation of an activated ester 84 was suggested in the first step, which underwent a 1,5- or 1,3-acyl migration, giving rise to the isomeric pyrido(l,2-a]pyrimidines 87 and 88 via acylureas 85 and 86, respectively (Scheme 6). 

The reaction of allenic acid 500 with carbodiimides affords tricycloundecatrienones 502. The reaction proceeds through (he initially formed linear N-acylurea derivative 501." ... 

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See also in sourсe #XX -- [ , ]

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