Studies toward (-)-gymnodimine: concise routes to the spirocyclic and tetrahydrofuran moieties

[formula: see text] (-)-Gymnodimine is a member of a unique class of potent marine toxins possessing imines within a spirocylic array. Herein we report the synthesis of the tetrahydrofuran fragment and a strategy toward the spirocyclic imine fragment of this family of toxins. Key reactions include an asymmetric anti-aldol reaction to set the stereochemistry of the tetrahydrofuran and a formal, intermolecular Diels-Alder reaction involving an alpha-methylene-delta-lactam and a dienyne.