Synthesis of spiroacetal enol ethers by oxidative activation of furan derivatives.

Activation of furan by electron transfer combines with the radical stabilizing effect of the alkynyl substituent (R = Ph, MeC[triple bond]C-) to achieve site-selective cation formation. A tethered hydroxy group acts as a probe of this site-selectivity to produce the ring system present in spirocyclic natural products found in Artemisia and Chrysanthemum species. cis-Dihydroxylation proceeds with high anti-stereoselectivity with respect to the tetrahydropyranyl ring oxygen.