2-Alkenylfurans via Feist-Benary and Wittig Reactions

Significance

3-Acyl-2-alkenylfurans are prepared by the Feist-Benary cyclocondensation of (2,4-dioxo-butylidene)phosphoranes with α-halo­ketones or α-chloroacetaldehyde followed by an E-diastereoselective Wittig reaction. The starting (2,4-dioxobutylidene)phosphorane is readily available from the reaction of Ph₃P with ethyl 4-chloro­acetoacetate. The scope of the reaction was tested for a variety of different R¹ and R² substituents but little variation in R³. The olefin contained alkyl, alkenyl, EWG as well as EDG substituents. The high E-diastereoselectivity of the Wittig reaction is probably due to the presence of Li salt in the reaction mixture. Generally, the diastereoselectivity of the products was found to be much higher when aromatic aldehydes rather than aliphatic aldehydes were employed.