Organometallic reagents are among the most powerful tools for C-C bond formation in the arena of organic synthesis. In light of the development of new or improved synthetic methodologies for C-C bond formation, reactions that involve the development of new organometallic reagents are of great interest. In our laboratories, novel organobarium reagents (RBaX) have been prepared.
Barium metal in its reactive form (Ba^*) has been prepared by a similar protocol for reactive calcium reagents. Thus, up to now, ó bonds between the heavier alkaline earth metals and carbon atoms have only been structurally characterized for calcium. Commercially available barium metal cannot be use for this method. Following Rieke’s method for calcium, the corresponding anhydrous metal halide is reduced by lithium naphthalenide or biphenylide at room temperature. Therefore, reduction of anhydrous barium iodide [from finely ground commercially available barium iodide (BaI₂●2H₂O) dried at 150 ^oC under reduced pressure for 12-24 h was achieved. [The color of BaI₂●2H₂O changed from pale yellow to white during the first 1-2 h, with no subsequent change in color]. Under a nitrogen atmosphere, with stirring, lithium biphenylide in dry tetrahydrofuran was added to the BaI₂ solution at room temperature to afford Ba* as a dark brown suspension. The subsequent suspension was utilized for the generation of RBaX via the addition of an alkyl halide.
With such reagents in hand, we have explored efficient C-C bond forming reactions. Moreover, since the structure of Ba* (or RBaX) is unknown, mechanistic investigations of the intermediates and preliminary NMR results will be shared. Also, we have applied these methods toward the preparation of various structurally diverse complex molecules as well as the preparation of a biochemically important aldehyde, 3,4-Dihydroxyphenylacetaldehyde (DOPAL). DOPAL is a toxic metabolite, which is found in catecholamine neurotransmitter systems, that has an important role in medicinal research in the study of alcoholism, Alzheimer's and Parkinson's disease. Thus, our initial results toward the preparation of DOPAL will be presented.