YB TMSBR PROMOTED HOMOCOUPLING REACTIONS OF ALIPHATIC-KETONES, ALPHA,BETA-UNSATURATED KETONES AND ALIPHATIC IMINES/

A powerful reducing reagent, ytterbium dibromide (YbBr2), was synthesi zed by a new method using ytterbium metal and trimethylsilyl bromide ( TMSBr) in tetrahydrofuran-hexamethyl-phosphoramide (THF-HMPA). YbBr2, thus formed in situ, causes coupling reactions of aliphatic ketones, a lpha,beta-unsaturated ketones and aliphatic aldimines to give bis-sily lated 1,2-diols, 1,6-diketones and 1,2-diamines, respectively, in good yields. In the case of aliphatic ketimines, the corresponding reduced and silylated amines are obtained. In this solvent system, the trialk ylsilyl moiety of trialkylsilyl bromide is converted to trialkylsilane s quantitatively. These results show that the Yb/TMSBr reagent generat es YbBr2 in situ and the YbBr2 thus formed acts as a single-electron r eductant for these coupling reactions.