Synthesis of Furans through Silver-Catalyzed Propargyl-Claisen Rearrangement Followed by Cyclocondensation

摘要

The generation of highly substituted furans from propargyl vinyl ethers bearing a free hydroxy group was investigated. In the presence of catalytic amounts of AgBF4, a formal [3,3] sigmatropic rearrangement takes place in the first stage of the sequence. The resulting allenyl carbonyl intermediates then undergo cyclocondensation, which upon double-bond isomerization leads directly to the five-membered heterocyclic products. This domino reaction allows the synthesis of various tri- and tetrasubstituted furan products; an example leading to pyrroles in an analogous way is also described.