ic6b01965_si_001.pdf (1.41 MB)
Synthesis of a Sterically Demanding Dispiropiperidine and Its Application in Monoamidodialkyl Zincate Complexes
journal contribution
posted on 2016-09-28, 18:24 authored by Shogo Morisako, Rong Shang, Yohsuke YamamotoThe 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)2 and 6·(THF)2 only 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).