Synthesis of Linear 6-Allylated-7-hydroxycoumarins: para-Claisen Rearrangement of 2'-Allylated/Prenylated Derivatives of 4'-Prenyloxy Cinnamic Acid

Linear 6-allylated-7-hydroxycoumarins were synthesized by the para-Claisen rearrangement of 4'-prenyloxy cinnamic acid derivatives under refluxing condition in N,N-diethylaniline. This method eliminates the requirement for an additional Lewis acid, such as boron trifluoride etherate or trichloride, to convert 7-alkoxycoumarins into 7-hydroxycoumarins, unlike alternative techniques.