Intermolecular and intramolecular Diels-Alder cycloadditions of 3-ylidenepiperazine-2,5-diones and 5-acyloxy-2(1h)-pyrazinones.
The 3-ylidenepiperazine-2,5-diones 16 and 39 and 5-acyloxy-2(1H)-pyrazinones 17 can serve as starting materials for the Diels-Alder reactions of alkenes and alkynes to the piperazine ring, under acidic conditions or in the presence of acetyl chloride, to afford tricyclic piperazine-2,5-diones 19, 20, 23-25, 27, 44, and 45. Intramolecular cycloadditions occur if 3-ylidenepiperazine-2,5-diones 30 and 32 are used as the starting materials. This procedure is a convenient path to bridged bicyclo[2.2.2]diazaoctane ring systems such as 31 and 33, the former being found in biologically active secondary mold metabolites, such as VM55599 (1) or brevianamide A (5), which have been isolated from various fungi. The synthesis of the indole compound 31 provided evidence for the proposed biochemical pathway with a Diels-Alder reaction as key step. Quantum chemical calculations have revealed that piperazinones with a cationic azadiene moiety are the most reactive species in Diels-Alder cycloadditions.
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Institut für Chemie, Humboldt-Universität Berlin, Hessische Strasse 1-2, 10115 Berlin, Germany.
Wessig
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Liebscher
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D000215:Acylation; D003500:Cyclization; D005658:Fungi / Q000737:chemistry; D007202:Indicators and Reagents; D008968:Molecular Conformation; D010879:Piperazines / Q000737:chemistry*; D011719:Pyrazines / Q000737:chemistry*
D007202:Indicators and Reagents; D010879:Piperazines; D011719:Pyrazines