Heteroaromatic Tripoles. 2,6-Bis(hetarenio)pyrimidin-4-olates:  Hybrids between Hetarenium Salts and Cross-Conjugated Mesomeric Betaines

Abstract

A novel tandem nucleophilic displacement reaction on tetrachloropyrimidine 7 leads to molecules with two delocalized positive and one delocalized negative charge, which comprise a common π-electron system, plus one external anion. Thus, treatment of 7 with an excess of heteroaromatic nucleophiles such as 4-(dimethylamino)pyridine, 4-(pyrrolidin-1-yl)pyridine, and 1-methylimidazole, respectively, followed by the addition of water formed the tripolar bis(hetarenio)pyrimidin-4-olates 8, 9, and 10. Addition of anhydrous alcohols furnished the O-alkylated dicationic species 11-16. We contrast the spectroscopic features of the monocationic 8-10 and the dicationic 11-16 and performed a conformational study (PM3). The HOMO/LUMO profile was calculated to evaluate our classification of 8-10 as CCMB derivatives.

Synthesis and characterization of stable betainic pyrimidinaminides

“…The elemental analyses were performed on a CHNS-932 analyzer (LECO) and in the laboratory for elemental analyses of the Institute of Chemistry and Biochemistry of the University of Greifswald, Germany. In accordance with known hetarenium compounds [17][18][19][20][21][22][23][24][25] and Xray crystallographic results of related systems [18][19][20]23], all substances crystallized with considerable amounts of water. Dried compounds (80 °C in vacuo) rapidely picked up water during weighing.…”

Synthesis and Characterization of Stable Betainic Pyrimidinaminides.

“…They are neutral compounds as they possess an e v e n number of positive and negative charges in conjugation or cross-conjugation. In contrast to that, molecules with an odd number of positive and negative charges form a distinct class of compounds, hybrids between mesomeric betaines and heteroarenium salts [17]. In continuation of our previous work on novel mesomeric betaines [18], heteroaromatic tripoles [19][20][21], and betainic nucleobases [22][23][24], we report here the synthesis and characterization of this class of betaines.…”

“…4-(Dimethylamino)pyridinium, 4-(pyrrolidin-1-yl)pyridinium and 3-methylimidazolium groups are known to stabilize highly reactive anions such as the ally anion [25]. As the target increment I is isoconjugate with the benzyl anion II, joining the cationic substituents to the two un-starred positions of II leads to cross-conjugation between the two charges [17,26]. These atoms are "inactive" nodal positions of the highest occupied molecular orbital (HOMO) I I I w h i c h prevent electron shifts to the lowest unoccupied molecular orbital (LUMO) in the ground state.…”

Hetarenium salts from pentafluoropyridine. Syntheses, spectroscopic properties, and applications

“…Catalysis of acylations [1][2][3][4], BaylisHillman [5] and Dakin-West reactions [6], silylations [7], and many other syntheses by DMAP is widely applied in organic synthesis. Stabilization of reactive species such as allyl anions [8], allyl radicals [9], uracilates [10,11], pyrimidinium-olates [12][13][14] as well as -aminides [15,16], pyridinium-olates [17] and heteroaromatics with up to ten positive charges within a common -electron system by 4-(dimethylamino)-pyridinium and other hetarenium substituents [18] was reported. The activation of perhalogenated heteroaromatics by hetarenium substituents can be applied for the preparation of otherwise unavailable functionalized heteroaromatics.…”