Behavior of modified Hexa-2,4-diyne-1,6-dioles in acidic media – A balance between cyclobutenes and diarylvinylfuran-3(2H)-ones

Cyclobutenes are versatile intermediates in bioactive molecule synthesis and carbon allotrope precursors, yet their preparation via dihalo-allene electrocyclisation is hampered by narrow substrate scope. We report the acid-mediated conversion of electronically and sterically diverse hexa-2,4-diyne-1,6-diols into dibromo cyclobutenes, expanding beyond the known phenyl and p-tolyl systems. Competing formation of diarylvinylfuran-3(2H)-ones is observed for electron-poor substrates. Single-crystal X-ray diffraction and DFT calculations reveal that dehydroxylation is rate-determining, while cyclisation barriers are only modestly affected by electronics. These insights enable selective access to novel fluorescent 3(2H)-furanones from propargylic precursors.