Diazo Tetramic Acids Provide Access to Natural-Like Spirocyclic Δ<sup>α,β</sup>-Butenolides through Rh(II)-Catalyzed O–H Insertion/Base-Promoted Cyclization
3-Diazotetramic acids were found to be valid substrates for the recently discovered approach toward natural-like Δα,β-spirobutenolides via Rh(II)-catalyzed O–H insertion into propiolicacids followed by base-promoted intramolecular Michael addition. The target Δα,β-spirobutenolides were obtained in generally high yields and, in the case of chiral 5-monosubstituted 3-diazotetramic acids, high diastereoselectivity