Aldolisation-type reaction versus Michael-type addition. Hemiacetal vinylogs: Versatile synthons.
P Duhamel, J Guillemont, JM Poirier, P Chabardes
Index: Duhamel; Guillemont; Poirier; Chabardes Tetrahedron Letters, 1993 , vol. 34, # 26 p. 4197 - 4200
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Abstract
Abstract Depending on the steric hindrance of the reaction centers, hemiacetal vinylogs 1 in the presence of BF 3. OEt 2 can, with enol ethers, lead to a Michael-type addition (4) or an aldolisation-type reaction (3). Hemiacetal vinylog 1b always yields the second reaction leading to β-methoxy-γ, δ-ethylenic carbonyl compounds 4 precursors of polyenic carbonyl compounds 5. Crotonaldehyde and methanol can be used instead of compound 1b.
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