Direct metalation

Direct Metal Analyses. Calcium ion can be detected to a lower limit of 10 M hy Aequorea bioluminescence. Strontium interferes to a minor extent (270,271). 

Substituent-directed metallations are being used for the synthesis of disubstituted pyridines. A 2-substituent directs to the 3-position, and a 3-substituent usually directs to the 4-position however, in the presence of A/ A/ A[7V -tetratnethylethylenediatnine (TMEDA), 2-metallation may be achieved (12). 

MetaUic soaps are manufactured by one of three processes a fusion process, a double decomposition or precipitate process, or a direct metal reaction (DMR). The choices of process and solvent depend on the metal, the desired form of the product, the desired purity, raw material avadabihty, and cost. 

Direct Metal Reaction. The DMR process is carried out over a catalyst with fatty acids ia a melted state or dissolved ia hydrocarbons. The acid reacts directiy with the metal, suppHed ia a finely divided state, produciag the metal soap and ia some cases hydrogen. Catalysts iaclude water, aUphatic alcohols, and low molecular-weight organic acids. 

The bulk of the TIPS group, introduced with TIPSCl (DMF, Im, 92% yield), directs metallation away from the silyl group as illustrated. ... 

Al-H distances suggests that 3-centre 2-electron bonding occurs as in the boranes (p. 157). The closest Al - Al distance is 324 pm, which is appreciably shorter than in metallic A1 (340 pm), but there is no direct metal-metal bonding and the density of AIH3 (1.477 gcm ) is markedly less than that for A1 (2.699 gcm ) this is because in A1 metal all 12 nearest neighbours are at 340 pm whereas in AIH3 there are 6 A1 at 324 and 6 at 445 pm. 

Direct metallation of oxirane cycle leading to carbenoid species 98SL337. 

Random incorporation of two different acetoacetates can also be avoided by converting one of the acetoacetates to a derivative which carries the future pyridine nitrogen. For example, treatment of ethyl acetoacetate with ammonia gives the corresponding P-aminocrotonate 32. The aldehyde (34) required for preparation of such an unsymmetrical compound is prepared by reaction of the product from direct metallation of 33 with dimethylformamide. Condensation of that aldehyde with methyl acetoacetate and the p-aminocrotonate from isopropyl acetoacetate leads to isradipine (35) [9]. The same aldehyde with ethyl acetoacetate and the P-aminocrotonate from ethyl acetoacetate gives darodipine (36) [10]. In much the same vein, condensation of the ben-zaldehyde 37 with methyl acetoacetate and its P-aminocrotonate derivative affords riodipine (38) [11]. 

The methylisocyanide complex has a dimeric structure with a direct metal-metal bond (2.531 A) and only terminal isocyanides, in a staggered configuration (Figure 3.22). 

We recently demonstrated that organolithium reagents formed by directed metallation of pivaloylanilines would react rapidly with carbon monoxide at 0°C or room temperature to form high yields of dioxindoles (Fig. 16) (ref. 30). This... 

Some group-IB and -IIB boranes or carboranes, especially of Cu, possess M — H—B structure units and are not discussed here because no direct metal-boron bond exists. 

Dihydro-l,2,5-thiadiboroles (Et2C2B2R2S) have remarkable acceptor properties toward metal-ligand moieties. Dihydrothiadiborole-derived complexes can be achieved thermally or photochemically, e.g., Co and Fe sandwich, triple-decked and even tetradecked complexes are known, all having direct metal-boron bonds. 

Directed metallation continues to be developed as a convenient method for regiospecific substitution of pyridines. A mild and general procedure for the preparation of structurally diverse 4-alkyl-2-aminopyridines 37 involves the lithiation/alkylation of aminopyridine derivative 36 <96JOC(61)4810>. 

We have explored rare earth oxide-modified amorphous silica-aluminas as "permanent" intermediate strength acids used as supports for bifunctional catalysts. The addition of well dispersed weakly basic rare earth oxides "titrates" the stronger acid sites of amorphous silica-alumina and lowers the acid strength to the level shown by halided aluminas. Physical and chemical probes, as well as model olefin and paraffin isomerization reactions show that acid strength can be adjusted close to that of chlorided and fluorided aluminas. Metal activity is inhibited relative to halided alumina catalysts, which limits the direct metal-catalyzed dehydrocyclization reactions during paraffin reforming but does not interfere with hydroisomerization reactions. 

In 2003, Livinghouse et al. also reported that chelating bis(thiophosphonic amidates) complexes of lanthanide metals, such as yttrium or neodymium, were able to catalyse intramolecular alkene hydroaminations. These complexes were prepared by attachment of the appropriate ligands to the metals by direct metalation with Ln[N(TMS)2]3- When applied to the cyclisation of 2-amino-5-hexene, these catalysts led to the formation of the corresponding pyrrolidine as a mixture of two diastereomers in almost quantitative yields and diastereos-electivities of up to 88% de (Scheme 10.81). 

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