74331-49-0Relevant academic research and scientific papers
1-azabicyclo[3.3.1]nonan-2-one: Nitrogen versus oxygen protonation
Sliter, Brian,Morgan, Jessica,Greenberg, Arthur
experimental part, p. 2770 - 2781 (2011/06/19)
Protonation of typical unstrained amides and lactams is heavily favored at oxygen. In contrast, protonation of the highly distorted lactam 1-azabicyclo[2.2.2]octan-2-one is heavily favored at nitrogen. What structures occupy "crossover boundaries" where N- and O-protonation are nearly equienergetic Density function theory calculations at the B3LYP/6-31G* level, as well as QCISD(T)/6-31G* calculations, predict that 1-azabicyclo[3.3.1]nonan-2-one favors N-protonation at nitrogen only very slightly (1H and 13C NMR as well as ultraviolet (UV) studies of this lactam, in its combination with sulfuric acid, confirm predominant protonation at nitrogen. Although the calculations very slightly favor the N-protonated chair-chair conformation, experimental spectra clearly support the N-protonated boat-chair. Broadened resonances in the 13C NMR spectrum suggest an exchange phenomenon. Variable-temperature studies of the 13C NMR spectra support dynamic exchange between the major tautomer (N-protonated) and the minor tautomer (O-protonated) in a roughly 4:1 mixture. The findings also support the published prediction that a twisted bridgehead lactam with the nitrogen lone pair (nN) as HOMO will protonate at nitrogen.
Tin-mediated esterification in macrolide synthesis
Steliou,Poupart
, p. 7130 - 7138 (2007/10/02)
A neutral and relatively simple new method for effecting internal macrocyclic esterification of omega -hydroxycarboxylic acids, based on a tin 'template-driven' extrusion process, is discussed and its application to the synthesis (macrocyclization step) of the macrolide antibiotics zearalenone, ingramycin, and nodusmicin detailed. An efficient, formal total synthesis of pyrenophorin using this technique is also presented. Attempts to extend the methodology to include the macrocyclization of omega -bromo carboxylic acids or omega -mercapto carboxylic acids were unsuccessful. However, although beta - and omega -amino carboxylic acids preferentially gave way to polymer formation, 4-,5, and 6-amino carboxylic acids readily condensed to give the corresponding five-, six-, and seven-membered lactams in excellent yields. For example, in this way, the bridged lactam 1-azabicyclo- left bracket 3. 3. 1 right bracket nonan-2-one was prepared in 77% yield as compared to the previously reported yield of less than 2%.
