Diamines proton sponges

A, A, A",/V-Tetramethylnaphthalene-l,8-diamine ( Proton Sponge ) Hydrogen Fluoride Complex (2) 3H... 

Af,Ar,AOV -Tetramethylnaphthalene-l,8-diamine described as Proton Sponge 38 (see Section 1.2) has the ability to act as a fluoride ion donor when its hydrofluoridc is used. Furthermore, it may be used to promote oligomerization reactions of fluorinated alkenes, e.g. 3, and poly-fluoroalkylation reactions with activated perfluoroaromatic compounds, e.g. 4.38... 

Phenyltrichlorostannane reacts with 1 surplus amine to yield the hexacoordinate tin compound 2c only. An elimination of HCl from 2c seems to be impossible. Even reaction with a proton sponge, Ai, A, A, A -tetramethylnaphthalene-1,8-diamine, failed. 2c crystallizes in a non-centrosymmetric monoclinic space group (Cc). The molecule involves the all-d5 configuration of the salen type ligand. The angle (93.9°) of C19-Sn-Cl indicates a real cis arrangement of the chlorine atom and the phenyl group (Fig. 2) [2]. 

Alder and coworkers have synthesized proton sponges 28-30 with moderate to high yield by treating diamine 4 with a,[Pg.937]

C and 15N NMR spectra of proton sponge 1 (Table 7) and its derivatives have been recorded. 11 MAS and 13C NMR spectra of a solid sample of the diamine 1 have revealed a strong asymmetry of the molecule. All the four CH3 groups, like all the ring carbon atoms, appear as separate signals, i.e. they are non-equivalent (Table 7). This has been interpreted in terms of electrostatic interactions between neighbouring molecules in the crystal lattice. 

The nitration of 1 with one equivalent of HNO3 in H2SO4 gave two products the 4-nitro derivative 108 and the binaphthyl proton sponge 36 in 70 and 10% yield, respectively164,187. The reaction proceeds even at —20 °C and is completed within 5 min. These conditions are essentially milder than those for the naphthalene nitration. This is somewhat astonishing, since in such an acidic medium the diamine 1 seems to exist entirely as cation 1 H+, which should be more inert towards electrophiles than the naphthalene itself. One of the reasonable explanations of this discrepancy is that the reaction proceeds via very small equilibrium amounts of the non-protonated 1 or the non-chelated cation l H+-c. Any of them, under the action of the nitronium cation, is oxidized to the radical cation 1+ , which either dimerises or reacts with N02 to give the reaction products 36 and 108 (Scheme 27). There are several indirect pieces of evidence in favour of this. One of them... 

In conjunction with proton sponge, the activated phosphate 256 turned out to be an effective reagent in the direct synthesis of peptides and branched amides from carboxylic acids (equation 21). In this process, diamine 1 surpassed in its efficiency for such bases as triethylamine, V,iV-dimethylaniline, 2,6-lutidine and Hiinig bases225. 

Dehydrochlorination of acid chlorides of type RCH2COCI by proton sponge 1 in order to produce monoketenes is not directly realized232,233, but proceeds in the presence of benzoylquinine (BQ) as a shuttle base . The in situ generated ketenes were used further for the synthesis of optically active /3-lactams 258 (Scheme 48). Additionally, a method providing fraws-isomers of 258 with the help of diamine 1 has recently been elaborated234. 

Proton sponges (PS) are organic diamines with unusually high basicity. The exceptional basicity of the very first proton sponge, OMAN (1) was reported by Alder in 1968 [2]. This compound has a basicity about 10 million times higher (pKa = 12.1 in water) than other similar organic amines (its experimentally measured proton affinity (PA) in the gas phase is... 

Alder, R.W. (2005) Design of C2-chiral diamines that are computationally predicted to be a milhon-fold more basic than the original proton sponges. Journal of the American Chemical Society, 127, 7924-7931. 

Medium-ring monocyclic diamines (lOa-e) have pA H.i values 12 in aqueous solution, so they cannot be measured by potentiometric methods <88CC1528>. Studies in DMSO with the proton sponge, 2,7-dimethoxy-l,8-bis(dimethylamino)naphthalene, indicate that (lOe) has the highest pATn value in this series. This results from internal hydrogen bonding as indicated by NMR measurements and effective force-field calculations. 

Wozniak and Mallinson studied proton sponges, such as l,8-bis(dimethyl-amino)naphthalene (DMAN), which are aromatic diamines characterized by exceptional basicity. For these compounds protonation causes substantial redistribution of p, which may be traced by observing the changes in the properties of p at BCPs. 

From these data, further basicity increase should be expected for the phenanthrene sponge 12. This expectation, however, is not justified and the pKa value of 12 is only 11.5, despite its being rather short (2.54 A) and linearity of the IHB (167°) in the cation 12411 (Table 5). It is assumed that the principal reason for the reduced basicity of diamine 12 lies in its helicene-like structure, which is retained in the corresponding cation, i.e. the protonation in this case does not result in steric relief1. Even more pronounced helicene strain is manifested in the cation of benzophenanthrene sponge 13411, having a basicity (pKa = 5.8) only a little higher than that of dimethylaniline. 

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