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.