Synthesis of a Sterically Demanding Dispiropiperidine and Its Application in Monoamidodialkyl Zincate Complexes.
The new sterically hindered piperidine analog, dispiro[cyclohexane-2,2'-piperidine-6',2″-cyclohexane] (CPC(H), 2), and its N-methylated derivative CPC(Me) (3) were synthesized from commercially available starting materials in short steps. The N-lithiated amide LiCPC (4) was also isolated from 2 as a cyclictrimer in single crystals and showed slightly larger steric hindrance than that of lithium 2,2,6,6-tetramethylpiperidide (LiTMP) in the competitive methylation reaction with methyl trifluoromethanesulfonate. In addition, the heterobimetallic heteroleptic zincate complexes [Li(μ-NR2)(μ-Et)Zn(Et)] (NR2= CPC, 5, and NR2= TMP, 6) were obtained as THF- and TMEDA-coordinated monomer 5·(THF)2, 6·(THF)2, 5·TMEDA, and 6·TMEDA (THF = tetrahydrofuran, TMEDA = N,N,N',N'-tetramethylethylenediamine). These molecular structures bearing different amido ligands in single crystals showed little structural differences from crystallographic studies. Diffusion-ordered spectroscopy (DOSY) revealed that the solution structures of the zincate complexes 5·(THF)2and 6·(THF)2only differ in the number of coordination THF molecules. In the deprotonation reactions with tert-butyl 3-bromobenzoate, the zincate complexes containing the CPC ligand [Li(μ-CPC)(μ-R)Zn(R)] (R = Et (5), tBu) showed moderately improved regioselectivity for the 6 position in comparison to those containing the TMP ligand [Li(μ-TMP)(μ-R)Zn(R)] (R = Et (6), tBu).
Department of Chemistry, Graduate School of Science, Hiroshima University , 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526, Japan.
Shogo
S
Morisako
Department of Chemistry, Graduate School of Science, Hiroshima University , 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526, Japan.
Rong
R
Shang
Department of Chemistry, Graduate School of Science, Hiroshima University , 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526, Japan.
Yohsuke
Y
Yamamoto