129548-86-3Relevant articles and documents
Lithiation of 2-Me3SiCHRC5H4N (R = H or SiMe3): Influence of Solvent on the Nature of the Product (from X-Ray Structure Determinations) and Asymmetric Induction. A Note on the Lithiation of Some Analogous 3- and 4-Methylpyridines
Papasergio, Rocco I.,Skelton, Brian W.,Twiss, Paul,White, Allan H.,Raston, Colin L.
, p. 1161 - 1172 (1990)
Metallation of 2-Me3SiCHRC5H4N (R = H or SiMe3) using LiBun in hexane, and in the presence of diethyl ether, and the ditertiary amines tmen (N,N,N',N'-tetramethylethylenediamine) or sp yields crystalline lithium complexes.These have been characterized using X-ray diffraction data for > (1), >2> (2), > (3), >2> (4), >2> (5), and > (6).In (1), (3), (4), and (6) the hydrocarbyl group acts as an η3-aza-allyl through the ring nitrogen , ipso-carbon , and adjacent ring carbon ; in (4) the nitrogen centre also bridges to another metal centre .Complex (2) has two co-ordinated lithium centres, each lithium bound by the ipso-carbon and a nitrogen centre from a centrosymmetric ligand and is thus an alkylmetal species; it can be recrystallized from tetrahydrofuran even though the lithiums are co-ordinatively unsaturated.In complex (5), the anionic ligand acts as an amide bridging two metal centres through the ring N .Treating (6) with MeI in hexane at -78 deg C yields 2-pyridine of 20percent estimated optical purity.The isomeric complex > under the same conditions gave no asymmetric induction; other metallations of 4-Me3SiCH2C5H4N, and some of 3-Me3SiCH2C5H4N are also reported.
The First X-ray Structures of N-Lithiated 4-Alkylidene-1,4-dihydropyridines Li(TMEDA)>2: Comparison of the X-ray and MNDO Geometries and Investigation of Lithium Coordination in Solution
Anders, Ernst,Opitz, Andreas,Boese, Roland
, p. 1267 - 1272 (2007/10/02)
The 4-ethyl- and -isopropylpyridines 5a and b were transformed into the lithiated compounds Li(TMEDA)>2 (6a) and Li(TMEDA)>2 (6b) by reaction with LDA and in the presence of TMEDA.These compounds were recrystallized from a toluene/hexane solution to obtain suitable crystals for X-ray investigations.Both structures are dimeric containing nonstoichiometric amounts of toluene in the crystals.The structural parameters of the heterocyclic moieties of 6a or b are typical of N-lithiated 4-alkylidene-1,4-dihydropyridines.MNDO geometries compare quite well with the X-ray structure of 6a.The lithium atom of 6a in solution prefers the same type of coordination as in the crystal: Two-dimensional 6Li,1H-HOESY showed Li contacts only to ortho-hydrogen atoms (Figure 3). 6a and b react differently with chlorotrimethylsilane (8). the variations of the alkylidene moieties of 6a and b, although seemingly small, are decisive.While the α,α-dimethyl compound 6b reacts exclusively as an N nucleophile, the α--methyl compound 6a functions also exclusively as a Cα nucleophile. Key Words: 4-Alkylpyridines, lithiated / Lithium coordination in solution / Calculations, MNDO
