NEW LOW-VALENT TITANIUM REAGENTS FOR DICARBONYL COUPLING AND THEIR USE IN A GENERAL-METHOD OF ANNULATION

New low-valent titanium reagents have been prepared by reducing TiCl3 (1 mol) with C8K (2 mol) or by reducing TiCl4 (1 mol) with Na-naphthalene (2.75 mol). Ketones carrying a chain that incorporates a suitably placed oxo function (aldehyde or ketone) undergo intramolecular dicarbonyl coupling to produce a bicyclic compound when treated with an excess (16-17 mol of titanium halide per mol of dicarbonyl compound) of one of these reagents. The procedure works well even for highly oxygenated substrates and constitutes a general method of annulation. Other reducing agents besides C8K or Na-naphthalene are suitable, and a brief examination of Na(Hg) and Na-K alloy was made. The C8K/TiCl3 system was also used to convert a cis-1,2-diol into the corresponding olefin.