Synthesis of β, γ-Unsaturated Valerolactones

Abstract In recent years various attempts have been made to use reagent equivalents1) in order to effect reactions which are not otherwise accessible by means of conventional reagents. Particularly it is to be noted that synthetic equivalents for unreactive dienophiles, such as carbon dioxide,2,3,4) ketene,3,5) allene,6) and acetylene,7) have greatly extended the scope of the cycloaddition reactions into systems not normally generated by the thermal process.