The dimethyltitanocene methylenation of N-acylamides derived from ortho-vinylanilines, ortho-allylaniline, and ortho-vinylbenzylamine provides the corresponding enamides, which upon exposure to the second generation Grubbs ruthenium catalyst give access to indoles, 1,4-dihydroquinolines, and 1,2-dihydroisoquinolines, respectively. This sequential protocol also allows the synthesis of dihydrobenzoazepines, although the ring-closing metathesis (RCM) step is complicated by the alkene isomerization processes. From certain substrates, the direct annulation is observed in the titanium-mediated step, which is likely to occur through an olefin metathesis-intramolecular olefination sequence.

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The harman-1,4-dihydropyridines 1 and 2, which constitute the originally proposed structures for the indole alkaloids lyaline and lyadine, have been synthesized, and their NMR data have been compared with those available for the natural products. Due to the discrepancies in the spectral data, the structures of lyadine and lyaline should be revised.

Sequential N-Acylamide Methylenation-Enamide Ring-Closing Metathesis: Construction of Benzo-Fused Nitrogen Heterocycles. -The two-step sequence offers a novel and efficient approach to indole, dihydroquinoline, dihydroisoquinoline, benzacepine, and benzoxazepine derivatives. -(BENNASAR*, M. L.; ROCA, T.; MONERRIS, M.; GARCIA-DIAZ, D.; J. Org. Chem. 71 (2006) 18, 7028-7034; Lab. Quim. Org., Fac. Farm., Univ. Barcelona, E-08028 Barcelona, Spain; Eng.) -Jannicke 52-055