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DOI: 10.1055/s-2008-1042766
[c]-Annelated Pyridines via Intramolecular Diels-Alder Reaction
Contributor(s):Victor Snieckus, Jignesh J. PatelUniversity of Nottingham and GlaxoSmithKline, Harlow, UK
Intramolecular Diels-Alder Reactions of α,β-Unsaturated Oxime Ethers as 1-Azadienes: Synthesis of [c]-Fused Pyridines
Tetrahedron 2008, 64: 874-882
Publication History
Publication Date:
21 February 2008 (online)
Key words
[c]-fused pyridines - hetero-Diels-Alder reaction - oxime ethers
Significance
Reported here is a route to [c]-anellated pyridines via an intramolecular hetero-Diels-Alder reaction of vinyl oxime ethers embodying a tethered acetylene unit. Electron-deficient acetylenes gave the best results for the cyclization. In one case, R3 = R4 = H, a small amount of chromene product A was observed, presumably generated via [3,3]-sigmatropic rearrangement and [1,5]-hydrogen shift; to avoid this, R4 was blocked with a methyl group. The vinyl oxime ethers were prepared in three steps from commercially available salicylaldehydes.
Comment
Intramolecular Diels-Alder reactions of α,β-unsaturated N,N-dimethylhydrazones with alkynes to fused pyridines are known (B. Serckx-Poncin, A. M. Hesbain-Frisque, L. Ghosez Tetrahedron Lett. 1982, 23, 3261; N. Bushby, C. J. Moody, D. A. Raddick, I. R. Waldron J. Chem. Soc., Perkin Trans. 1 2001, 2183). The current report describes the analogous reaction of α,β-unsaturated oxime ethers as 1-azadienes. The substrate scope was inadequately studied. The reported procedure provides a way to complex pyridine derivatives which might have interesting biological properties.