Notable structural property of 2,4,6-Tri- tert -butylanilide enolates: Interconversion between the rotamers and their reactivity

Organic Letters

Volumn 13, Issue 11, 2011, Pages 2840-2843

  Ohnishi, Yusuke ^a   Sakai, Masahi ^a   Nakao, Shouta ^a   Kitagawa, Osamu ^a  

^a SHIBAURA INSTITUTE OF TECHNOLOGY   (Japan)

Author keywords

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Indexed keywords

EID: 79957822390     PISSN: 15237060     EISSN: 15237052     Source Type: Journal    
DOI: 10.1021/ol200814m     Document Type: Article

References (33)

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23. In N-substituted anilide derivatives, it is well-known that E -rotamers are generally more stable than Z -rotamers. We also previously reported that the isomerization of N-allyl 2,4,6-tri- tert -butyl-acetanilide and -propionanilide under thermal conditions gives the equilibrium mixture of E -major in E / Z ratios of 10.1 and 6.0, respectively (see ref 5a). The thermal instabilities of Z -rotamers have been rationalized on the basis of n-φ repulsion between the lone pairs on the carbonyl oxygen and aromatic ring and steric repulsion with the substituent on nitrogen atom. In anilide enolates 1A and 3A, E -rotamers may be also thermodynamically favored more than Z -rotamers. Typical papers on the E -rotamer preference of N-alkylated anilide derivatives: Pederson, B. F.; Pederson, B. Tetrahedron Lett. 1956, 2995-3001
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32. 2 was observed, while, in the E -isomer, no NOE between these hydrogen atoms was detected.
33. In the allylation with the enolate from acetanilide E-1a, the Z / E ratio of the allylated product 2a was hardly changed by the addition rate of the allyl bromide.