PtCl<sub>2</sub>‑Catalyzed Intramolecular Cyclization\nof α‑Benzyl Allenoates to Afford Indenes and Furanones

Indene and furanone are important ring structures widely\npresent\nin active pharmaceutical molecules. Here, we have developed a straightforward\nmethod for the synthesis of indene and furanone via PtCl<sub>2</sub>-catalyzed intramolecular cyclization of α-benzyl allenoates.\nBy altering the ester substitution pattern in the α-benzyl allenoates,\nwe can regulate the reaction site, enabling two distinct intramolecular\ncyclization reactions that yield both indene and furanone products,\nrespectively. For α-benzyl-substituted ethyl allenoate, the\nreaction proceeds via a 5-exo cyclization to form indene derivatives.\nIn contrast, for α-benzyl-substituted <i>tert</i>-butyl\nallenoate, the reaction involves ester hydrolysis and intramolecular\ncyclization, yielding furanone products. This method operates efficiently\nunder a 5 mol % PtCl<sub>2</sub> catalyst and exhibits good tolerance\ntoward various functional groups. Furthermore, furanone products can\nbe obtained on a gram scale and further smoothly converted into 1,2-disubstituted\nfuran.