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

Abstract

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...