Intermolecular reductive cyclodimerization of cyclic α,β-unsaturated ketones promoted by a low-valent titanium reagent:: A facile synthesis of some new spiro compounds

The intermolecular reductive cyclodimerization reactions of cyclic alpha,beta-unsaturated ketones such as 2-benzylideneindanI -ones, 2-beiizylidene-1-tetralones, 3-benzylidenechroman-4-ones, and 3-benzylidenethiochroman-4-ones induced by a low-valent titanium reagent were studied. Some new spiro compounds were prepared in good yields under neutral and mild conditions. High stereoselectivity was achieved and the stereochernistry of the products was confirmed by X-ray diffraction analysis.