New low-valent titanium reagents for dicarbonyl coupling and their use in a general method of annulation

Abstract

Ketones carrying a chain that incorporates a suitably placed oxo function (aldehyde or ketone) undergo intramolecular dicarbonyl coupling when treated with a reagent prepared either from titanium trichloride and C8K (relative molar ratio 1 : 2) or from titanium tetrachloride and sodium–naphthalene (relative molar ratio ca. 1 : 2.75); the reagent is used in excess (16 to 17 mol titanium halide per mol of dicarbonyl compound) and the process is the key step in a general method of anpulation.