Synthesis of the\nSpirocyclic Imine Fragment of Portimines\nUsing a γ‑Hydroxymethyl‑α<i>,</i>β‑butenolide Dienophile in a Diastereoselective Diels–Alder\nReaction

The synthesis of the spirocyclic imine fragment of the\nportimine\nfamily of marine toxins has been achieved. A densely functionalized\nkey lactone-ester intermediate was assembled via a highly diastereoselective\nDiels–Alder cycloaddition, involving a novel γ-hydroxymethyl-α,β-butenolide\ndienophile. A Stille coupling was employed to install the vinyl group.\nSelective elaboration of the two carbonyl groups successfully afforded\nthe spirocyclic imine fragment.