Sulfur-Functionalized Olefins for Titanacycle Formation: Tandem Asymmetric Cyclization and the Pummerer Reaction Based on Sulfoxides Promoted by Titanium(II)-to-Titanium(IV) Relay

Reusing the metal: Combination of the sulfoxide-based asymmetric enyne cyclization (TiII mediated) and the Pummerer reaction (TiIV mediated) in tandem was effected by a reagent system consisting of a relay of titanium(II) to titanium(IV), which permits a one-pot synthesis of cyclic aldehydes in an optically active form (see scheme; Tol=p-tolyl).