Details

Autor(en) / Beteiligte

• Hagemann, Hans
• Dulak, Marcin
• Wesolowski, Tomasz A.
• Chapuis, Christian
• Jurczak, Janusz

Titel

Comparative Infrared, Raman, and Natural-Bond-Orbital Analyses of King's Sultam

Ist Teil von

• Helvetica chimica acta, 2004-07, Vol.87 (7), p.1748-1766

Ort / Verlag

Zürich: WILEY-VCH Verlag

Erscheinungsjahr

2004

Quelle

Wiley-Blackwell Journals

Beschreibungen/Notizen

• By means of 1H‐NOESY‐ and Raman‐spectroscopic analyses, we experimentally demonstrated the presence of the equatorial NMe conformer of King's sultam 4b in solution, resulting from a rapid equilibrium. As a consequence, the value of the N lone‐pair anomeric stabilization should be revised to 1.5–1.6 kcal/mol. Independently from the N tilting, natural bond orbital (NBO)‐comparative analyses suggest that the S d* orbitals do not appear as primordial and stereospecific acceptors for the N lone pair. Second, the five‐membered‐ring sultams do not seem to be particularly well‐stabilized by the SC σ* orbital in the N‐substituted pseudo‐axial conformation, as opposed to an idealized anti‐periplanar situation for the six‐membered‐ring analogues. In this latter case, the other anti‐periplanar CC σ* and C(1′)H/C(2′) σ*orbitals are as important, if not more, when compared to the SC σ* participation. In the pseudo‐equatorial conformation, γ‐sultams particularly benefit from the N lone‐pair hyperconjugation with the anti‐periplanar SO1 σ* and C(2)H/C or C(1′)H/C σ* orbitals. This is also the case for δ‐sultams when the steric requirement of the N‐substituent exceeds 1.6 kcal/mol. When both axial and equatorial conformations are sterically too exacting, the N‐atom is prone to sp2 hybridization or/and conformational changes (i.e., 12c). In that case also, the mode of stereoelectronic stabilization differs from γ‐ to δ‐sultams.