om6b00445_si_002.pdf (1.3 MB)
Loss of Chirality through Facile Lewis Base Mediated Aza-enolate Formation in Na and K (S)‑N‑(α-Methylbenzyl)methallylamides
journal contribution
posted on 2016-08-09, 15:54 authored by Matthew
T. Flynn, Rachel Stott, Victoria L. Blair, Philip C. AndrewsMetalation of (S)-N-(α-methylbenzyl)methallylamine
with nBuM (M = Li, Na, or K) in hexane leads to the
allylic metal amides [(S)-PhCH(CH3)N(CH2C{CH3}CHLi)Li]6, 1, [(S)-PhCH(CH3)N(CH2C{CH3}CH2)Na]n, and [(S)-PhCH(CH3)N(CH2C{CH3}CH2)K]n, respectively. The addition of any Lewis base (here THF, TMEDA,
or PMDETA) to the Na and K amides promotes rapid anion rearrangement
to the aza-enolate complexes [PhC(CH2)N(CH2CH{CH3}2)Na]∞, 2, [PhC(CH2)N(CH2CH{CH3}2)Na·TMEDA]n, 3, [PhC(CH2)N(CH2CH{CH3}2)Na·PMDETA]n, 4, and [PhC(CH2)N(CH2CH{CH3}2)K]n, 5, resulting in loss of chirality.
In contrast, the addition of benzene leads exclusively to the 1-aza-allyl
complexes [(S)-PhCH(CH3)N(CHC{CH3}2)Na]n, 6, and [(S)-PhCH(CH3)N(CHC{CH3}2)K]n, 7, both of which are not observed in the presence of Lewis donors.
Doping a benzene solution of 7 with THF gives the first
observation of reorganization to the intermediate 2-aza-allyl anion.
All seven complexes have been characterized by NMR spectroscopy, with
complexes 1 and 2 also being characterized
by single-crystal X-ray diffraction. Rearrangement to the aza-enolates 2 and 3 is unprecedented under the conditions
employed.
