Protonated proton sponges

Table 12 Structural details of the hydrogen bond in protonated proton sponges.

A.J. Bienko et al., Low barrier hydrogen bond in protonated proton sponge. X-ray diffraction, infrared, and theoretical ab initio density functional theory studies. J. Chem. Phys. 119, 4313 4319 (2003)... 

An interesting situation occurs in the dication of the doubly protonated proton sponge 35 2H+ and in the zwitterion of 4,5-dihydroxy-l,8-bis(dimethylamino)naphthalene (111). The asymmetry of both hydrogen bridges in these systems is clearly controlled by electrostatic factors in order to obtain maximal separation of the two positively charged centres in 35 2H+ and, in reverse, to gain an attraction between the cationic and anionic centres in 111. 

Staab, H. A., Krieger, C., Hieber, G., and Oberdorf, K. "1,8-Bis(dimethylamino)-4,5-dihydroxynaphthalene, a Neutral, Intramolecularly Protonated Proton Sponge with Zwilterionic Structure." Angezv. Chem. Int. Ed. Eng., 36,1884-1886 (1997). 

PhCH20CH2Cl, Nal, proton sponge [l,8-bis(dimethylamino)naphthalene], 84% yield. BOMBr can also be used. ... 

The Lewis acid of choice for most of the cyclization reactions is ethylaluminum dichloride, because of its exceptional properties it is a mild Lewis acid, and, as an organometallic compound, can serve as a proton sponge , and thereby inhibit competitive protodesilyla-tion37. The desired precursors reacted smoothly with 1.1 equivalents of ethylaluminum dichloride in toluene or dichloromethane at low temperature to generate diastereoselectively the desired spiro[4.5]decanones38. 

Larhed et al. investigated enantioselective Heck reactions with 2,3-dihydrofuran as alkene [86]. In the coupling with phenyl triflate, conditions previously reported by Pfaltz [87] were attempted under microwave irradiation. Interestingly, the catalytic system Pd2(dba)3/(4S)-4-t-butyl-2-[2-(diphenylphosphanyl)phenyl]-4,5-dihydro-l,3-oxazole, identified by the Swiss team, was found suitable for high-temperature microwave-assisted enantioselective Heck reactions (Scheme 76). Using a proton sponge as a base and benzene as a solvent gave the best conversions (Scheme 76). At tempera-... 

Compounds such as 2, 4, and 5 are known as proton sponges. Another type of proton sponge is quino[7,8-A]quinoline (6). Protonation of this compound also gives a stable monoprotonated ion similar to 3, but the steric hindrance found in 2, 4, and 5 is absent. Therefore 6 is a much stronger base than quinoline (7) (p/fg values of the conjugate acids are 12.8 for 6 and 4.9 for 7), but proton transfers are not abnormally slow. 

Evidence for an intermediate metaphosphorimidate is also provided by a three-phase experiment110b,139) treatment of a suspension of the two functionalized polymers 203 and 205 in dioxane with proton sponge leads to formal transfer of a phosphorodiamidate moiety from 203 to 205 with formation of 206. It appears... 

Reaction of Chlorodimethyl(2,3,4,5-tetramethyl-2,4-cyclopentadien-l-yl)silane with Silica Materials. Chlorodimethyl-(2,3,4,5-tetramethyl-2,4-cyclopentadien-l-yl)silane (excess) was added to a mixture of amine-functionalized silica with hexanes in a drybox. 2,6-Di-tert-butylpyridine (excess) was added as a proton sponge. The mixture was allowed to react while stirring for 24 h. The solid was filtered and washed with hexanes and THF in the drybox. The solid was then contacted with another aliquot of chlorodimethyl-(2,3,4,5-tetramethyl-2,4-cyclopentadien-l-yl)silane and the procedure was repeated. 

Behr JP (1997) The proton sponge A trick to enter cells the viruses did not exploit. Chimia 51 34-36... 

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