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

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• 作者：Matthew T. Flynn ; Rachel Stott ; Victoria L. Blair ; Philip C. Andrews
• 刊名：Organometallics
• 出版年：2016
• 出版时间：August 22, 2016
• 年：2016
• 卷：35
• 期：16
• 页码：2707-2714
• 全文大小：430K
• 年卷期：0
• ISSN：1520-6041

文摘

Metalation of (S)-N-(α-methylbenzyl)methallylamine with nBuM (M = Li, Na, or K) in hexane leads to the allylic metal amides [(S)-PhCH(CH<sub>3sub>)N(CH<sub>2sub>C{CH<sub>3sub>}═CHLi)Li]<sub>6sub>, 1, [(S)-PhCH(CH<sub>3sub>)N(CH<sub>2sub>C{CH<sub>3sub>}═CH<sub>2sub>)Na]<sub>nsub>, and [(S)-PhCH(CH<sub>3sub>)N(CH<sub>2sub>C{CH<sub>3sub>}═CH<sub>2sub>)K]<sub>nsub>, 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(═CH<sub>2sub>)N(CH<sub>2sub>CH{CH<sub>3sub>}<sub>2sub>)Na]<sub>∞sub>, 2, [PhC(═CH<sub>2sub>)N(CH<sub>2sub>CH{CH<sub>3sub>}<sub>2sub>)Na·TMEDA]<sub>nsub>, 3, [PhC(═CH<sub>2sub>)N(CH<sub>2sub>CH{CH<sub>3sub>}<sub>2sub>)Na·PMDETA]<sub>nsub>, 4, and [PhC(═CH<sub>2sub>)N(CH<sub>2sub>CH{CH<sub>3sub>}<sub>2sub>)K]<sub>nsub>, 5, resulting in loss of chirality. In contrast, the addition of benzene leads exclusively to the 1-aza-allyl complexes [(S)-PhCH(CH<sub>3sub>)N(CH═C{CH<sub>3sub>}<sub>2sub>)Na]<sub>nsub>, 6, and [(S)-PhCH(CH<sub>3sub>)N(CH═C{CH<sub>3sub>}<sub>2sub>)K]<sub>nsub>, 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.