Utilizing the Azaazulene Scaffolds in the Design of New Organic Superbases

Abstract

New neutral organic superbases with 1-azaazulene(s) as a molecular backbone are computationally designed, employing two basic substituents: dimethylaminocyclopropen-imines (CPI) and dimethylaminocyclopropeniminophosphazenes (CPI-P). Their proton affinities, gas basicities, and pKa values in acetonitrile are obtained using density functional theory. Azaazulenes substituted with CPI have a computed PA in the gas phase ranging between 272.9 and 306.8 kcal mol–1, with pKa values in acetonitrile between 28.8 and 36 units. The substitution with the CPI-P group resulted in even stronger superbases, with a PA from 296.5 to 335.2 kcal mol–1 and corresponding pKa values from 33.9 to 50 units. This exceptionally strong thermodynamic basicity is accompanied by very high kinetic basicity as well; contrary to typical proton sponges, the release of a proton from the conjugate superbase does not demand high activation energy. Because synthetic routes for both substituents and azaazulenes are already known, newly designed superbases represent suitable targets for synthesis and application.

Proton affinity and gas phase basicity of diamandoid molecules: diamantane to C131H116

“…Furthermore, the reaction is associated with an exceedingly high kinetic barrier of 41.2 kcal mol −1 (including 3.6 kcal mol −1 to bring both systems into a reactive complex), which does not favor this reaction under normal conditions. Interestingly, the obtained value is exactly the same as that calculated for DMAN, 29 and similar to other typical proton sponges, 30 while significantly higher than that between, for example, PMG and PMG-H + , for which our calculations gave Δ G ‡ = 1.7 kcal mol −1 . Taken together, although our work identified some of the most basic hydrocarbon molecules, that may be beneficial for their potential application in several areas, their suitability as catalysts in reactions where a fast proton exchange is needed will be somewhat limited.…”

Chiral Cyclopropenimine‐catalyzed Asymmetric Michael Addition of Bulky Glycine Imine to α,β‐Unsaturated Isoxazoles

“…[26] One of the most attractive methods for direct deprotonation of substrates with high pK a values is the use of organosuperbases. [27] In fact, triethylamine (Et 3 N), 1,4-Diazabicyclo[2.2.2]octane (DABOC), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) were used as achiral organosuperbases in many reactions. In recent decade, several types of chiral organosuperbases [28,29] including amidine, [30][31][32] guanidine, [33][34][35][36][37][38][39][40][41] cyclopropenimine, [42][43][44][45][46][47] iminophosphorane, [48][49][50][51][52][53][54][55][56] and azaphosphatrane [57][58][59][60] have been developed and used as catalysts for direct deprotonation of substrates with high pK a values in asymmetric Michael reaction, Mannich reaction, amination, oxidation, aldol reaction and [3 + 2] cycloaddition.…”

“…The combination of Cu (I) or silver salts with chiral ligands is usually used for asymmetric Michael additions of glycine imines and nitroalkenes [26] . One of the most attractive methods for direct deprotonation of substrates with high p K a values is the use of organosuperbases [27] . In fact, triethylamine (Et 3 N), 1,4‐Diazabicyclo[2.2.2]octane (DABOC), 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) and 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (TBD) were used as achiral organosuperbases in many reactions.…”

Substituted ketenes offer exceptional carbon bases in gas phase: Computational study by density functional theory method

“…[ 2–5 ] The other organosuperbases that are not naphthalene based were also examined experimentally and computationally. [ 6–17 ] Some of the introduced superbases meet much higher basicity than DMAN, which is mainly due to the unique stability of their conjugate acids. In general, stability and positive charge delocalization in the conjugate acid of the base are provided by the solvation, resonance, IHBs, and use of electron‐donating groups.…”