Organic superbases

This result has been further substantiated by the work of Koppel et al. <2001PCA9575>. They conducted a theoretical study of the basicity of phosphorus imines and ylides. Verkade bases 6-8 were included. They showed basicities comparable to commercially used organic superbases (/-BUP4 phosphazene imine), with compound 8 in particular giving calculated basicities similar to Li3P and Li20. 

Suarez, D., Menendez, J.A., Fuente, E., and Montes-Moran, M.A. (2000). Pyrone-like structures as novel oxygen-based organic superbases. Angew. Chem., Int. Ed. Engl, 39, 1320-23. 

Chamorro, E., Escobar, C.A., Sienra, R. and Perez, P. (2005) Empirical energy-density relationships appUed to the analysis of the basicity of strong organic superbases. Journal of Physical Chemistry A, 109, 10068-10076. 

Allen, C.W. (1994) Linear, cyclic, and pol3mieric phosphazenes. Coordination Chemistry Reviews, 130, 137-173 AUen, C.W. (1996) Phosphazenes. Organophosphorus Chemistry, 27, 308-351 Kondo, Y., Ueno, M. and Tanaka, Y. (2005) Organic synthesis using organic superbase. Journal of Synthetic Organic Chemistry, 63, 453 63. 

Kovacevic, B. and Maksic, Z.B. (2001) Basicity of some organic superbases in acetonitrile. Organic Letters, 3, 1523-1526. 

Kovacevic, B., Maksic, Z.B., Vianello, R. and Primorac, M. (2002) Computer aided design of organic superbases the role of intramolecular hydrogen bonding. New Journal of Chemistry, 26, 1329-1334. 

Costa, M., Chiusoli, G.P., Taffurelli, D. and Dalmonego, G. (1998) Superbase catalysis of oxazolidin-2-one ring formation from carbon dioxide and prop-2-3m-l-amines under homogeneous or heterogeneous conditions. Journal of the Chemical Society — Perkin Transactions 1, 1541-1546 Kovacevic, B. and Maksic, Z.B. (2001) Basicity of some organic superbases in acetonitrile. Organic Letters, 3, 1523-1526. 

A density functional theory (B3LYP/6-311 - -G ), ab initio (HF/3-21G ) and semi-empirical (PM3) study of intrinsic basicities, protonation energies or protonation enthalpies of phosphazene bases has been reported. The study shows that the organic superbases can reach the basicity level of the strongest inorganic superbases, such as alkali metal... 

Figure 6.1 The pK values (in MeCN) of conjugate acids of typical organic superbases...

Organic superbases effectively generate carbonyl-stabilized ylides to promote Wittig reactions. In the synthesis of (-)-mycalolide A (68) by Panek and Liu, construction of... 

Ether synthesis by alkylation of alcohol using an inorganic base is sometimes troublesome. In such cases, soluble organic superbases are often effective. Knapp et al. performed the alkylation of 145 with isopropyl bromoacetate using the strong soluble base BEMP, achieving 95% yield [46]. Intramolecular ester enolate alkylation of 147 with EDA took place to give 148, which was effectively led to the natural product octosyl acid A (149) (Scheme 7.33). 

Maksic, Z.B. and Kovacevic, B. (1998) Toward organic superbases the electronic structure and the absolute proton affinity of quinodiimines and some related compounds. Journal of Physical Chemistry A, 102, 7324-7328. 

Despotovic, I., Maksic, Z.B. and Vianello, R. (2007) Computational design of Brpnsted neutral organic superbases-[3]iminoradialenes and quinoimines are important synthetic targets. New Journal of Chemistry, 31, 52-62. 

Superbases have been classified as those with gas-phaseproton affinities > lOOOkJ/mol, greater than the bases listed in Table 6.6. Examples of organic superbases are shown in Figure 6.1. These are weak bases in water but exhibit superbasic characteristics in organic solvents. 

Scheme 27 y-Selective addition of butenolides catalyzed by organic superbase... 

The basicities in water and in aqueous surfactant solution of another 15 aryl-Pl(pyrrolidino) [(NC4Hs)3P=N-Ar] and aryl-Pl(dimethylamino) [(NMe2)3P=N Ar] phosphazenes (Ar = mono or di substituted phenyl rings) have been measured and correlated with previous data using acetonitrile and THE. A comparison with other bases such as guanidines, amines and pyridines showed that, in all cases, the phosphazenes were the strongest bases. The results confirmed earlier conclusions about the partly ylidic character of the NP double bond. Density functional theory calculations have shown that the phosphazenes (41) and (42) are very powerful neutral organic superbases at the site marked by an asterisc (the calculated pA a values in acetonitrile were 44.8 and 37.8, respectively). ... 

In total, seven PILs based on five organic superbases and two p-diketones, illustrated in Fig. 3.4, were investigated as ionic extractants for La and Ba " solvent extractions in the aprotic IL [C4mim][NTf2] [91]. The La and Ba ... 

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