Catalytic Schmittel-Type [2 + 2] Cycloaddition of γ-Alkynyl Diazoacetates with Terminal Alkynes for Accessing Cyclobuta[a]indenes

Hao Wei,¹ Yan Zhang,¹ Nan-Nan Wang, Rong Fu, Ke Chen,* Wen-Juan Hao,* Bo Jiang*

Instead of the conventional [4 + 2] cycloaddition, a regioselective Schmittel-type [2 + 2] cycloaddition of yne-allene esters, generatedin-situfrom copper-catalyzed dediazotized coupling of γ-alkynyl diazoacetates with terminal alkynes, is reported, enabling a bicyclization process to produce a diverse array of C₁-arylated cyclobuta[a]indenes in moderate to good yields. The protocol features wide functional group compatibility, mild reaction conditions, and experimental simplicity, holding significant potential for building up new tricyclic cyclobutenes.

Org. Lett. 2025, 27, 941-2946; DOI: 10.1021/acs.orglett.5c00525