- Model studies related to synthesis and 1,4-dipolar cycloaddition reactions of mesoionic heterocycles
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The reaction of 2-(substituted amino)pyridine with reactive malonic acid derivatives provided an extremely facile synthesis of the mesoionic compound 4-oxo-4H-pyrido[1,2-a]pyrimidin-1-ium-2-olates. N,N'-Disubstituted amidine reacted with diethyl malonate to afford 4-quinolone in a one-pot cyclization and rearrangement (type A/I) of 4-oxopyridiniumolate 6. The latter compound was isolated via a reaction of acyclic amidine with AME's. A cycloaddition reaction of the mesoionic pyrimidine 6 with maleic anhydride or N- phenylmaleimide yielded [2+4] cycloadducts. Triphenyl pyrrolopyridinetrione 12 was achieved via a ring transformation of the cycloadduct 4-benzyl-3,5- dioxo-1,2,6-triphenyl-2,6-diazabicyclo[2.2.2]octane-7,8-dicarboxylic anhydride 11d. In contrast, the cycloadduct 4-ethyl derivative 11c and substituted 3,5-dioxo-1,2,6-triphenyl-2,6-diazabicyclo[2.2.2]octane-7,8- dicarboxylic N-phenylimides did not give 12 under the same reaction conditions. The mechanistic pathway for the formation of 12 was studied. Dimethyl acetylenedicarboxylate reacted with 6b,c to furnish 2-oxo-1,2- dihydropyridine-4,5-dicarboxylates.
- Issac, Yvette Abd El-Sayed
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p. 503 - 509
(2007/10/03)
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- Mesoionic Six-membered Heterocycles, III. - Reactions of o-Quinonoid Compounds with 6-Oxo-6H-1,3-diazin-1-ium-4-olates
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Mesoionic 6-oxo-6H-1,3-diazin-1-ium-4-olates 9 react with tetrachloro-o-benzoquinone (2, R=Cl) to give 1 : 1 adducts 12 which can formally be derived from ketene tautomers 13 of 9.The structure of 12f has been clarified by X-ray crystallography.
- Friedrichsen, Willy,Schmidt, Regine,Hummel, Gerrit J. van,Ham, Dirk M. W. van den
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p. 521 - 531
(2007/10/02)
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