Titanium-Induced Ring Opening of a Strained Bicyclic Acetal

Significance

Substituted tetrahydrofurans are a common structural motif found in numerous natural and medicinal compounds. The diastereoselective synthesis of trans-2,5-disubstituted tetra­hydrofurans has been studied by the groups of Reißig (Eur. J. Org. Chem. 2000, 3893) and Woerpel (J. Am. Chem. Soc. 2005, 127, 10879). In both cases, the addition of allyl silanes to five-membered cyclic oxacarbenium ions gave poor diastereoselectivities. In the present paper, the use of bicyclic 1 and TiCl₄ promotes the ring opening by various C-nucleophiles to provide functionalized trans-substituted products in high selectivities.