„Ferngesteuerte”︁ nucleophile Eigenschaften der Anionen einiger 4‐Alkylpyridine: AM 1‐ und MNDO‐Berechnungen sowie experimentelle Untersuchungen

Abstract

Aus einfach zuganglichen Pyridinderivaten 10 gelingt mittels Natriumbis(trimethylsiyl)amid (11) die Herstellung der Natriumsalze 12a-c. In ihrer Reaktionsweise gegenuber Elektrophilen 13 weichen die Salze 12 von dem bisher beobachteten Verhaiten seitenkettenmetallierter N-Heteroaromaten 1-4 ab, indem sie sich uberwiegend zu N-derivatisierten 4-Alkyliden-1,4-dihydropyridinen 5a-f umsetzen. Auf der Basis von MNDO-und AM 1-Berechnungen an vereinfachten Modellverbindungen 2a -j wird dieser Befund erkllrt.Seit den Untersuchungen von Ziegler und Zeiser" uber die Herstellung lithiierter Picoline 1 besitzen seitenketten-' metallierte N-Heteroaromaten wie 1 -4 zentrale Bedeutung als einfach zugangliche reaktive Zwischenstufen; die aus ihnen herstellbare Produktpalette ist groD4-?Experimentell wurde nach unserer Kenntnis bisher die ausschlieDliche Bevorzugung des C(a)-Zentrums fur den Angriff zahlreicher, elektronisch recht unterschiedlicher Elektrophile 7 nachgewiesen; G1. (1) faBt einige Umsetzungen fur das Beispiel des 4-Picolins unter Bildung von 6 zusammen.Die Natur der Metalle beeinfluDt bei Anwesenheit mehrerer deprotonierbarer Alkylseitenketten (etwa in der 2-oder 4-Position des Pyridinrings) den Ort der Deprotonierung j4).Wir berichten hier einerseits iiber die Ergebnisse semiempirischer quantenmechanischer Berechnungen mittels der M N D 0 " ) -und (sofern moglich")) der AM 1 ")-Methode an den Modellverbindungen 2a-2j, mit deren Hilfe die bisherigen experimentellen Befunde erklart werden konnen. Andererseits folgt aus dieser Studie eine experimentell uberpriifbare Moglichkeit, die relative Nucleophilie der N( 1)-"Remote Controlled" Nucleophilicity of Anions of some QAlkylpyridines: AM 1-and MNDO-Calculations, Experimental TestsThe easily accessible pyridines 10 are transformed into sodium salts 12a -c by reaction with sodium bis(trimethylsilyl)amide (11). With electrophiles 13, the salts 12 usually react to give N-substituted 4-alkylidene-1,4-dihydropyridines 5a -f. This reaction behaviour differs from the normal behaviour of side chain metalated N-heterornatic compounds 1 -4. Explanations are provided by MNDO and AM1 calculations using the model compounds 2a-j.und C(a)-Zentren durch Variation der Substituenten an C(a) zu steuern.

Electron-rich pyridines with para-N-heterocyclic imine substituents: ligand properties and coordination to CO2, SO2, BCl3 and PdII complexes

“…26,27 Apart from neutral pyridines, the incorporation of anionic groups leads to negatively charged pyridines (V-VII), which outperform DMAP in terms of their nucleophilicity and catalytic activity in the urethane-forming reaction. [28][29][30] To date, the development of electron-rich pyridines has mainly been focused on their application in organocatalysis, while their properties as ligands in coordination chemistry have received little attention. The attempt to prepare transition metal complexes with VII was unsuccessful due to single electron transfer processes from the electron-rich pyridine.…”

C-Sulfonylation of 4-Alkylpyridines: Formal Picolyl C–H Activation via Alkylidene Dihydropyridine Intermediates

“…Several 4-methylpyridine derivatives were converted to the corresponding picolyl sulfones using slightly modified reaction conditions. Exposure of 4-picoline ( 1n ) to conditions shown in Table , entry 5 produced significant quantities of the known bis­(sulfonyl) methylpyridine in addition to desired monosulfone 3na , as revealed in 1 H NMR spectra of crude reaction mixtures . To avoid picolyl bis­(sulfonylation), the amount of sulfonyl chloride 2a was reduced to 2.0 equiv, and 3na was obtained accompanied by little to no bis­(sulfone) as indicated by TLC.…”

“…Exposure of 4-picoline (1n) to conditions shown in Table 1, entry 5 produced significant quantities of the known bis(sulfonyl) methylpyridine in addition to desired monosulfone 3na, as revealed in 1 H NMR spectra of crude reaction mixtures. 25 To avoid picolyl bis(sulfonylation), the amount of sulfonyl chloride 2a was reduced to 2.0 equiv, and 3na was obtained accompanied by little to no bis(sulfone) as indicated by TLC. Sulfonylation of 3-bromo-4-picoline and 4-methylquinoline also were performed using these modified conditions to afford 3oa and 3pa, respectively.…”

“…Notably, related picolyl sulfonylations of 4-picoline and 4-benzylpyridines performed under similar reaction conditions have been reported previously, first by Földi and later by Anders and co-workers. 23 − 25 Aside from these limited reports, it does not appear that direct sulfonylation of alkylpyridines has been examined in any detail despite the attractive reactivity profile of picolyl sulfones. Accordingly, we have investigated the utility of this transformation for functionalization of diverse alkylpyridine substrates and found that a wide range of 4-picoline derivatives can be efficiently sulfonylated in good yield under exceedingly mild reaction conditions, as described below.…”

Elucidation of Unconventional Bonding in Lithium Organic Compounds

“…[272] In contrast to the 2-isomer, it was experimentally proven that an alkylation at the nitrogen atom is achievable with 4-picolyllithium. [148,273] Acid chlorides and even trimethylsilyl chloride yielded in an N-C bond formation with lithium and sodium derivatives of the 4-picolyl anion. Nonetheless, the C-alkylation remains the standard reaction pathway of 4-PicLi.…”