PtCl4-Catalyzed Domino Synthesis of Fused Bicyclic Acetals

At sixes and sevens: The synthesis of [4.2.1]‐ and [3.2.1]‐fused bicyclic acetals by an intramolecular double alkoxylation of alkyne diols is reported. The course of the reaction depends on the substitution of the triple bond. Terminal alkynes give the [3.2.1]bicyclic product by a 6‐exo pathway, whereas aryl alkynes undergo almost exclusively a 7‐endo cyclization to give the [4.2.1]bicycles (see scheme, Ts=toluene‐4‐sulfonyl).