Proton sponges other

The proton-transfer behaviour of [47] differs in one important respect from that of the other proton sponges. It is found that the rates of equilibration of the protonated amine with the free amine in mixtures of the two in [ Hg]Me2SO at 30°C is fast on the nmr timescale and averaged proton signals are observed (Zirnstein and Staab, 1987). For mixtures of [33] and the free amine, separate proton signals are observed. Quantitative information about the extent to which the rates of proton transfer for [47] differ from those of the other proton sponges must await detailed kinetic studies. 

Majetich reports a general intramolecular Lewis acid allylation protocol for the synthesis of bicy-clo[5.4.0]undecen-3-ones (168) and bicyclo[4.4.0]decen-3-ones (170), which are 1,6-addition products (Scheme 27). The same precursors, (167) and (169), when submitted to the fluoride ion cyclization protocol, also afford 1,2- and 1,4-addition products.73 Typically, ethylaluminum dichloride, a proton sponge Lewis acid, is used in order to minimize adventitious protonic desilylation. Other 0,y-unsatu-rated silanes also undergo similar intramolecular Lewis acid catalyzed additions for example, the si-lylpropargylic enones (171) undergo intramolecular cyclization to the allenylspiro system (172).74... 

Once internalized, the essential step for the polyplex is to escape rapidly the endosomal vesicle in order to release the nucleic acid in the cytosol and prevent its lysosomal degradation. As the endosomal and lysosomal pH presents values between 4.5 and 6.5 and therefore differs from the neutral pH of 7.4 in other biological compartments [58], some polycations containing protonable residues like PEI facilitate this step by the proton sponge effect [59, 60]. As not all cationic polymers display this attribute, another effective method for enhanced endosomal polyplex release is incorporation of specific endosomal membrane disrupting or pore-forming domains, such as lytic lipid moieties or endosomolytic peptides. 

This section covers primary, secondary, tertiary, and quaternary aminopyrazines (both nuclear and extranuclear) but not (functionally substituted amino)pyrazines such as hydrazino-, hydroxyamino-, or azidopyrazines. General discussions have appeared on the spectra of 2-pyrazinamine,255 257 991 the proton-sponge properties of 2,3,5,6-tetra(pyridin-2-yl)pyrazine in relation to its fine structure,925 the fluorescene properties of 3,6-diamino-2,5-pyrazinedicarboxylic acid derivatives in relation to their fine structures,1646,1659 the basic properties of aminopyrazines and other such azines in relation to their electronic structures,412,928 and the fine structures of 3-amino-2-pyrazinecarboxylic acid1340 and l,4-diacetyl-2,3-diphenylpiperazine.559... 

In this system, the cyclometallation may be favored by the presence of the methyl substituents on the NHC backbone, increasing the a-donor character of the NHC ligand and enhancing the C H activation process. These reactions have been successfully apphed to introduce other ligands onto the metal center, such as alkoxy or amino groups that can be used as proton sponge. 

For other similar cases of incorrect assignment, see References 19-26. Actually, all these bases should be more correctly named proton sponge-like compounds 27. 

A considerable number of proton sponges can be prepared by functionalizing the parent sponge 1 or its suitable derivatives. Thus, the l,F-binaphthyl sponge 36, which possesses interesting properties, is formed by treatment of 1 with some oxidants. This and many other reactions are discussed in Section IV. 

C. Analogues of the Naphthalene Proton Sponge with W-Substituents Other than Alkyl Groups... 

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