Directed ortho metalation, also compounds

Other examples of intramolecularly coordinated (by 0 as well as by N groups) organolithium compounds can be found in Setzer and Schleyer (2) and Seebach (4). Two recent reviews are also pertinent. Klumpp (34) deals with 0- and N-assisted lithiation and carbolithiation of nonaromatic compounds, and Snieckus (34a) deals with directed (by amide and carbamate groups) ortho metalation in polysubstituted aromatics. 

Activation of aromatic compounds by transition-metal complexes was initially studied with Cr(CO)3 complexes. Nucleophilic addition of 2-lithio-l,3-dithianes to arene-chromium(O) complexes 185 followed usually by iodine-promoted decomplexation affords the corresponding 2-arylated 1,3-dithianes 186. The reaction of //-(toluene)- and (anisole)tricarbonylchromium (185) with compound 161 gave mixtures (52 46 and 10 90, respectively) of ortho and meta substituted derivatives (186) (Scheme 54)244. The meta directing effect was also observed (mainly better than 95%) with amino and fluoro substituted complexes245. 

A dye molecule that has found widespread attention in the synthetic metals community is phthalocyanine 186, which can be readily made from ortho-dicyanobenzene 187 in a metal-assisted cyclotetramerization that directly provides metal complex derivatives 188 (see scheme 44) [251]. A tuning of the electronic properties is possible via the central atom and, for example, by proceeding to the related tetranaphthalene compound 189 [252]. The importance of phthalocyanines 188 in both fundamental and industrial research comes from the great number of possible applications [253]. Also, 188 can be stacked into columnar arrays by using axial ligands at the metals or by linking silicon centers as central atoms by suitable spacers [254]. The introduction of long chain alkoxy... 

We therefore wished to avoid the formation of the 4-lithio species, and examined the use of a non-exchangeable group at the 4- position in place of the iodide. We chose to study the 4-chloropyridine derivative 45 based on the fact that chlorine is known to direct ortho-lithiations at -78 °C and does not undergo halogen-metal exchange. Chloropyridines are also susceptible to nucleophilic aromatic substitution with alkoxides, and as such this compound contains a handle for the introduction of the methoxy group at the 4-position as required later in the synthesis. 

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