Treatment of terminal olefinsbearingelectron-withdrawing groups with (R,R)-pentane-2,4-diol (2) in the presence of PdCl2–CuCl–O2 in 1,2-dimethoxyethane gives cyclic acetals such as (3) and (12b)via attack at the terminal carbon atom; the corresponding acetals are similarly formed from propane-1,3-diol (5) and ethylene glycol (8).