Intramolecular N–H···O and N–H···N hydrogen bonding patterns in N-benzyl and N-(pyridin-2-ylmethyl) benzamides

• Published in: Tetrahedron letters Vol. 50; no. 3; pp. 316 - 319
• Main Authors: Du, Ping, Jiang, X-Kui, Li, Zhan-Ting
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 2009
• ISSN: 0040-4039; 1873-3581
• DOI: 10.1016/j.tetlet.2008.11.001

This Letter reports the evidences for intramolecular six-membered N–H···O hydrogen bonding in
N-benzyl benzamides and five-membered N–H···N hydrogen bonding in
N-(pyridin-2-ylmethyl) benzamide. Intramolecular six-membered N–H···X (X
=
O or F) hydrogen bonding in 2-methoxyl- or 2-fluorobenzamides is used to lock the amide proton from forming strong intermolecular N–H···O
C hydrogen bonding. As a result, for the first time the new intramolecular hydrogen bonding patterns are observed in the crystal structures of nine amides, whereas the whole molecules give rise to a new class of three-center hydrogen bonding motif.
1H NMR study in chloroform-
d also supports that this weak intramolecular hydrogen bonding pattern exists in solution.