omega-Halogeno polyenals: Preparation and application to a one-pot synthesis of polyenals from carbonyl compounds

Syntheses of 5-halogeno-2,4-dienals 1a-c are described starting either from the glutaconaldehyde potassium salt or from furan, The 5-bromopenta-2,4-dienal 1b can be transformed efficiently into homologous omega-bromo polyenals 2-4, precursors of omega-bromo polyenol ethers 5b,d, 6 and 7. After bromine-lithium exchange, followed by condensation with carbonyl compounds, 1-bromo-6-methoxyhexa-1,3,5-triene 5b, 1-bromo-8-methoxyocta-1,3,5,7-tetraene 6 and 1-bromo-10-methoxydeca-1,3,5,7,9-pentene 7 lead to various conjugated tri-, tetra- and penta-enals in good yields, in a one-pot procedure.