Superbases, proton sponges

Strucmrally related, superbasic proton sponges have been designed by Estrada [24]. A minimal framework was provided by the stmctures of 3,6,7,8-tetraazatricyclo[3.1.1.1 ] octane (26) and 4,8,9,10-tetraazatricyclo[5.1.1.1 ]decane (30). These molecules, possessing two pairs of nitrogen atoms fixed in a configuration where two nitrogen atoms are in... 

T4.5 Start from Section 4.14 Superacids and superbases which covers classical examples of superbases, nitrides, and hydrides of s-block elements. However, there are several groups of superbases that you can look at. For example, amides (diisopropylamide related) are commonly used superbases. More modem are phosphazene bases which are neutral rather bulky compounds containing phosphorus and nitrogen. An interesting topic is a proton sponge (or Alder s base) and its derivatives as well as several theoretical and practical approaches used in rational design of superbases. 

Raab, V., Kipke, J., Gschwind, R.M. and Sundermyer, J. (2002) l,8-Bis(tetramethylguanidino) naphthalene (TMGN) a new, superbasic and kinetically active proton sponge . Chemistry - A European Journal, 8, 1682-1693. 

The trend that proton sponges with high thermodynamic basicity typically have a low kinetic basicity (kinetic activity in proton exchange reactions) is a serious limitation of proton sponges the captured proton does not usually take part in rapid proton exchange reactions, which would allow such neutral superbases to serve as catalysts in base-catalysed reactions. Their further limitations are moderate solubility in aprotic nonpolar solvents and stability towards auto-oxidation. 

In summary, guanidinophosphazenes belong to the most basic, experimentally determined class of superbases, followed by phosphazenes, proazaphosphatranes and guanidines. Amidines and classical proton sponges generally show less pronounced basicity. 

Korzhenevskaya, N.G., Schroeder, G., Brzezinski, B. and Rybachenko, V.I. (2001) Concept of superbasicity of l,8-bis(dialkylaminio)naphthalenes ( proton sponges ). Russian Journal of Organic Chemistry, 37, 1603-1610. 

Raab, V., Gauchenova, E., Merkoulov, A. et al. (2005) l,8-Bis(hexamethyltriaminopho-sphazenyl)naphthalene, HMPN A superbasic bisphosphazene proton sponge . Journal of the American Chemical Society, 127, 15738-15743. 

In this chapter, the synthetic utility of Proton Sponge (1) was reviewed. This superbase, although not a main player, is indispensable for various mild and selective transformations in organic synthesis. Despite the unique characteristics of superbases, their exploitation is still limited. Recently, various types of proton sponges, including chiral ones, have been developed, and are likely to have a wide range of applications in organic and asymmetric synthesis. 

Very recently [49], it was shown that l,8-bis(dimethylammo)-naphthalene (OMAN), a superbasic compound (called proton sponge ) with a pfC, of 12.21 [116] is a powerful matrix because it enables the detection of fatly acids (both saturated and moderately unsaturated) in low-picomolar amounts. Therefore, both, 9-AA and DMAN seem more suitable than MTPFPP because all fatty acids can be easily and accurately detected, while the MTPFPP matrix is less suitable for unsaturated fatty acids due to the -tl4amu artifact and the lower achievable sensitivity. Unfortunately, DMAN is not stable under high-vacuum conditions and, thus, there are time-dependent spectral changes. This even holds for the free fatty acids [50]. 

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