Grignard-like reaction

As the number of nitrogen heteroatoms increases, the stability of lithium azoles decreases the 5-lithio derivatives of 1,2,3-triazoles 778 ring-open spontaneously. l-Methyltetrazol-5-yllithium decomposes to nitrogen and lithium methyl-cyanamide above 50 G, although it gives the expected Grignard-like reactions with bromocyanogen, esters, ketones, and sulfur at lower temperatures. 

Grignard (-like) reactions are emerging solid-phase reactions that have not yet been exhaustively studied. One is, therefore, tempted to conclude that the use of Grignard reactions in solid-phase chemistry is under-developed. A reason might be that the high reactivity of Grignard reagents coupled with the need for anhydrous conditions complicates with solid supported synthesis. 

Halogen-free solutions may be obtained by cleavage of a disilane with elemental lithium or methyllithium, or by reaction of disilylmercury compounds with lithium. Other methods of preparation have been reviewed1, and this same source discusses the Grignard-like reactions of silyllithium and other silylmetal reagents. 

About at the same time, the organometallic and coordination chemistry of the classical divalent rare earths Sm°, Fu° and Yb" had started because the diiodide precursors could now be made by solution chemistry. Especially that of Sm° (the most reactive of the "common" divalent rare earths) gained momentum with the milestone discovery by Kagan et al. that Sml2 could be made in THF solution by the simple Grignard-like reaction of Sm with diiodoethane at room temperature (Namy et al., 1977). 

Reaetions. Smia (or Ybla) in THF-CH3OH reduces a, 8-unsaturated acids and esters to saturated acids and esters in high yield. Of more interest, aldehydes are much more easily reduced than ketones so that selective reduction is possible. In the presence of an alkyl halide ketones undergo a Grignard-like reaction ... 

D.F.Evans prepared divalent organo ytterbium for the first time by the reaction of ytterbium metal with organic halides in THF at - 20 C. Magnetic susceptibility measurements showed that 75-92% of the ytterbium is present in the divalent state. Samarium reacts more slowly, giving a mixture of divalent and trivalent species, as expected from the greater instability of the divalent state when Sm is compared to Yb (30). These solutions give Grignard-like reactions for example, PhSmI reacts with benzophenone to afford Ph C(OH) in 72% yield. 

The detailed investigation of reactions of (Me5C5)2Ln(Et20) (Ln = Sm, Eu, Yb) with alkyl- and arylhalides RX, fulfilled by Finke, Watson and coworkers [59 - 61], has shown the complicated character of these processes. The proposed scheme of the reactions of ytterbium and samarium derivatives includes the interspheric electron transfer, oxidation of metal to Ln(III), free radicals R generation and Grignard-like reactions ... 

However, saturated organoborane derivatives appeared to be unreactive toward carbonyl compounds. Early studies involving alkylborane additions to aldehydes resulted in the reduction of the aldehyde via 3-hydrogen elimination. Grignard-like reactions were successful only after modification of the carbonyl group, the trialkylborane, or by adding transition metal catalysts. ... 

---