Loss of Chirality through Facile Lewis Base Mediated Aza-enolate Formation in Na and K (S)‑N‑(α-Methylbenzyl)methallylamides

Metalation 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(CHC­{CH3}2)­Na]n, 6, and [(S)-PhCH­(CH3)­N­(CHC­{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.