Pyrimidine annelated heterocycles - synthesis and cycloaddition of the first pyrimido[1,4]diazepine n-oxides
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Heaney, Frances; Burke, Cathriona; Cunningham, Desmond; McArdle, Patrick (2001). Pyrimidine annelated heterocycles - synthesis and cycloaddition of the first pyrimido[1,4]diazepine n-oxides. Journal of the Chemical Society, Perkin Transactions 1 (6), 622-632
5-Formyl- and 5-acetyl-4-(alkenylamino)pyrimidines 5 have been prepared as precursors to novel pyrimido[1,4]diazepine N-oxides 3. In addition to cyclisation to the targeted dipoles the substrates 5 have also been observed to form imidazopyrimidines 12 and 39 via an intramolecular Michael addition; additionally 5b has been observed to form the pyrimidoazepinone 42. Aldonitrone 3a cycloadded readily to olefinic dipolarophiles; ketodipole 3b did not share this reactivity. Both dipoles reacted with acetylenic dipolarophiles but the ensuing cycloadducts 37 were unstable; facile ring contraction of their isoxazolopyrimidodiazepine skeletons to the pteridine nucleus is noted. The structure of 37c has been determined by X-ray crystallography.