I sub(2)-PPh sub(3) mediated spiroannulation of unsaturated beta -dicarbonyl compounds. The first synthesis of ( plus or minus )-negundoin A

An efficient and stereoselective spiroannulation of unsaturated enols is reported. Unsaturated beta -dicarbonyl compounds undergo cyclization by reaction with catalytic I sub(2)-PPh sub(3), affording the corresponding spiro enol ether derivatives, with complete regio- and stereoselectivity, under mild conditions. Utilizing this new methodology, the first total synthesis of the anti-inflammatory diterpene negundoin A and a naturally occurring trypanocidal aldehyde is reported.