A novel Lewis acid catalyzed intermolecular cascade annulation of alkynols with α-ketoesters has been developed. This simple and efficient cascade annulation proceeds through a 5-exo-dig cyclization of alkynols followed by annulation with α-ketoester to provide a wide variety of unsaturated γ-spiroketal-γ-lactones (1,6-dioxaspiro[4.4]non-3-en-2-ones) related to many natural products.
Herein we disclose an unprecedented intramolecular cascade strategy for the construction of α,β-unsaturated [5,5]- and [6,5]-oxaspirolactones, that capitalize on the π-electrophilic Lewis acid-catalyzed 5-exo-dig or 6-exo-dig mode of cyclization of...
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