Low-valent titanium: New synthetic applications

Abstract

During the course of our work on the synthesis of bioactive compounds, new low-valent titanium (LVT)- mediated reactions were discovered. These include: i) a short synthesis of oxygen heterocycles via intramolecular reductive deoxygenation between ketone and ester functions in aromatic systems, ii) an unusual ortho-hydroxyl-assisted reduction/isomerisation of aromatic alkenes, iii) reductive dealkoxylation of aryl alkyl ethers, iv) one-pot synthesis of polycyclic aromatic hydrocarbons from o-alkoxy aromatic aldehydes/ketones involving reductive deoxygenation, reductive dealkoxylation and intramolecular C-C coupling in tandem, v) a novel approach to the deprotection of allyl, propargyl and benzyl ethers of alcohols and phenols and N-benzyl/allyl amines, and vi) modulation of the activity of LVT reagent by nitrogen heterocycles. Mechanism and synthetic implications of these reactions are discussed.