A facile substrate-encapsulated RCM-based synthesis of 7-membered lactones is reported. Coordination of the α, ω-dienyl ester precursor to the bulky Lewis acid (LA) aluminum tris (2, 6-diphenylphenoxide)(ATPH) provides a protective extended steric pocket to the olefin moieties, thereby favoring intramolecular RCM over intermolecular ADMET oligomerization. The LA-encapsulated esters undergo ring-closure in the presence of Ru-based olefin ...