I2—PPh3 Mediated Spiroannulation of Unsaturated β‐Dicarbonyl Compounds. The First Synthesis of (.+‐.)‐Negundoin A.

Unsaturated β-dicarbonyl compounds, e.g. (I), (III)/(VI), (VIII), and (X) undergo intramolecular cyclization by reaction with a catalytic amount of I2—PPh3 affording spiro enol ether derivatives with complete regio- and stereoselectivity.