Synthesis of the C1–C26 Northern Portion of Azaspiracid‐1: Kinetic versus Thermodynamic Control of the Formation of the Bis‐spiroketal

North–South divide: An efficient synthesis of the entire C1–C26 (northern) portion of azaspiracid-1 is disclosed (see picture). Key transformations include the formation of a bis-spiroketal, the oxidation of a sulfone at C10 to form a β,γ-unsaturated ketone, a tandem Wadsworth–Emmons/hetero-Michael addition to construct ring D, and the highly selective hydroxylation at C20.