On the unusual 2J coupling dependence on syn/anti CHO conformation in 5-X-furan-2-carboxaldehydes

✍ Scribed by Carlos Pérez; Reynier Suardíaz; Pedro J. Ortiz; Rachel Crespo-Otero; Gloria M. Bonetto; José A. Gavín; José M. García de la Vega; Jesús San Fabián; Rubén H. Contreras

• Publisher: John Wiley and Sons
• Year: 2008
• Tongue: English
• Weight: 123 KB
• Volume: 46
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.2268

✦ Synopsis

Abstract

A remarkable difference for ^2^J coupling constant in syn and anti conformers of 5‐X‐furan‐2‐carboxaldehydes (X = CH~3~, Ph, NO~2~, Br) and a rationalization of this difference are reported. On the basis of the current knowledge of the Fermi‐contact term transmission, a rather unusual dual‐coupling pathway in the syn conformer is presented. The additional coupling pathway resembles somewhat that of the J~HH~ in homoallylic couplings, which are transmitted by hyperconjugative interactions involving the π~CC~ electronic system. The homoallylic coupling pathway can be labeled as σ*~CH~ ← π~CC~ → σ*~CH~. In the present case, this additional coupling pathway, using an analogous notation, can be labeled as σ*← LP~1~(O~1~)··· LP~2~(O~C~) →σ*(σ*) where O~1~ and O~C~ stand for the ring and carbonyl O atoms, respectively. This additional coupling pathway is not activated in the anti conformers since both oxygen lone pairs do not overlap. Copyright © 2008 John Wiley & Sons, Ltd.