Electrophilic reactions proton sponges

In rare cases the proton sponge can react with Lewis acids as a monodentate ligand. Thus, reaction of 1 with highly electrophilic borane B(C6F5)3 in CD2C12 led to the... 

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... 

There is some evidence that the diols 178 are the hydration products of the intermediate and highly electrophilic l,8-bis(dimethylamino)-4,5-bis(trifluoroacetyl)naphthalene105. The double proton sponge 118 is apparently formed by a cyclodimerisation of monoketone 126 catalysed by trifluoroacetic anhydride (Scheme 32). Obviously, this nice reaction, previously unknown in the naphthalene series, is a consequence of high C-nucleophilicity of the proton sponge. 

An example of proton sponge reaction with sulfur electrophiles is known. The interaction of compound 1 with alkanesulfenyl chlorides led to a series of 4-alkylsulfenyl derivatives 190202. The proton sponge 1 can participate in an azo-coupling reaction, also proceeding at position 456. 

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