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Sterically Congested Molecules, 6. Lone Electron Pair Donor Quality of the Imino Function: Increased Front Strain and Electronic Substituent Effects on Sterically Accelerated Nitrogen Inversion in Iminocyclopentanes

1993; Wiley; Volume: 126; Issue: 1 Linguagem: Inglês

10.1002/cber.19931260130

0009-2940

Rudolf Knorr, Thi Phung Hoang, Johann Mehlstäubl, Monika Hintermeyer‐ Hilpert, H.‐D. Lüdemann, Elmar W. Lang, Gerhard Sextl, Wilfried Rattay, Petra Bührer,

Asymmetric Synthesis and Catalysis

Abstract The p ‐substituents of 2,6‐dimethyl‐ N ‐(2,2,5,5‐tetramethylcyclopentylidene)anilines are modified without interfering reactions at the CN double bond. The resultant series ( 5 – 8, 10 – 19 ) shows a strong (ca. —4.7 kcal/mol) steric acceleration of ( E / Z ) diastereotopomerization by front strain along the CN double bond but also the usual electronic substituent dependence, characterized by a Hammett s̀ p – correlation (Q = +2.7). Conversely, the substituent constant for lithium at the p ‐position of 7 may be estimated. The volume of activation is 1.5(8) cm 3 mol –1 for 5 . The π donor quality of the imino group corresponds to ca. 55 (±8)% of P π character as evaluated by spectral ( 13 C NMR of 5 and 13 , IR of 13 ) and reactivity data (of 13 ).