The synthetic strategy of novel heterocyclic compounds from a series of urazoles (key compounds), which were prepared by addition-elimination reactions of benzylidene ketones with 4-phenyl-3
H-1, 2, 4-triazole-3, 5 (4
H) -dione (PTAD), was described. Alcoholysis and aminolysis of the urazoles afforded intriguing tricyclic oxazolidinone derivatives (hetero analogues of triquinane sesquiterpenes). The reaction proceeded
via Michael addition of nucleophiles to enone substructure, opening of the urazole ring by backbone participation and final skeletal rearrangements. This methodology was extended to one-pot syntheses of [4.3.3] propellane hetero analogues and 3-cyanoindole derivatives.
While, oxime ethers of the key compounds were photochemically active to rearrange to triazinoindoles,
via cleavage of N-N bond and subsequent skeletal rearrangement from a polar excited state. More active urazoles afforded surprisingly dimers and solvent-incorporated adducts (triazinoindolines) in a stereospecific fashion. On the contrary, sensitized reactions gave cyclobutane derivatives.
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