Preparation of 2-alkyl- and 2-acylpropenals from 5-(trifluoromethanesulfonyloxy)-4H-1,3-dioxin: A versatile acrolein α-cation synthon

5-(Trifluoromethanesulfonyloxy)-4H-1,3-dioxin (3) participates in a variety of nucleophilic substitution reactions with cuprate reagents or in palladium catalyzed cross-coupling reactions to provide 5-substituted-4H-1,3-dioxins 5. Upon thermolysis, these compounds undergo facile retrocycloaddition reactions to generate the corresponding 2-substituted acroleins which, if necessary, can be trapped in situ with dienes or heterodienophiles. In particular, the heretofore unknown 2-acylacroleins can be generated using this methodology and trapped with enol ethers to afford 5-acyl-3,4-dihydro-2H-pyrans (6g,h), a substructural unit common to many natural products. (C) 2000 Elsevier Science Ltd.