685134-26-3Relevant academic research and scientific papers
Perturbation of Conjugation in Allylic Lithium Compounds Due to Stereochemical Control of Internal Lithium Coordination: Crystallography, NMR, and Calculational Studies
Fraenkel, Gideon,Chow, Albert,Fleischer, Roland,Liu, Hua
, p. 3983 - 3995 (2004)
Several allylic lithium compounds have been prepared with ligands tethered at C2. These are with (CH3OCH2CH 2)2NCH2-, 6, 1-TMS 5, 1,3-bis(TMS) 8, and 1,1,3-tris(TMS) 9. Allylic lithiums with (CH3-OCH2CH 2)2NCH2C(CH3)2-, are 10, 1-TMS 11, and 1,3-bis(TMS), 12 compounds with -C(CH3) 2CH2N-((S)-(2-methoxymethyl)-pyrrolidino) at C 2 13, 1-TMS 14, and 1,3-bis(TMS) 15. In the solid state, 8-10 and 12 are monomers, 6 and 13 are Li-bridged dimers, and 5 and 7 are polymers. In solution (NMR data), 5, 7-12, 14, and 15 are monmeric, and 6 is a dimer. All samples show lithium to be closest to one of the terminal allyl carbons in the crystal structures and to exhibit one-bond 13C-7Li or 13C1-7Li spin coupling, for the former typically ca. 3 Hz and for the latter 6-8 Hz. In every structure, the C 1-C2 allyl bond is longer than the C2-C 3 bond, and both lie between those for solvated delocalized and unsolvated localized allylic lithium compounds, respectively, as is also the case for the terminal allyl 13C NMR shifts. Lithium lies 40-70° off the axis perpendicular to the allyl plane at C1. These effects are variable, so the trend is that the differences between the C 1-C2 and C2-C3 bond lengths, 13δ3-13δ1 values, and the 13C1-7Li or 13C-6Li coupling constants all increase with decreasing values of the torsional angle that C1-Li makes with respect to the allyl plane.
