Proton sponges disubstituted

A.V. Degtyarev et al., 2,7-Disubstituted proton sponges as borderline systems for investigating barrier-free intramolecular hydrogen bonds. Protonated 2,7-bis(trimethylsilyl)-and 2,7-di (hydroxymethyl)-l,8-bis(dimethylamino)naphthalenes. Tetrahedron 64, 6209-6224 (2008)... 

There are very specific changes of the hydrogen bridge geometry in the cations of 2,7-disubstituted proton sponges. The measurements of such systems were performed for five salts with cations 44 H+, 101-II1,102 H+, 105 H+ and 112 H+. The ortfio-substituents in these cations display a distinct steric pressure on the adjacent A-methyl groups, pushing... 

Rather useful information is given by the spin-spin coupling constants, J (Table 6). For the H—H interactions, as a rule 73j4 is larger than J23, and in some 2,7-disubstituted proton sponges, e.g. 44, the. /3 4 value reaches 9 Hz. The J23 values, in turn, increase on substituting positions 4 and 5 by mesomeric acceptors, such as CHO, apparently due... 

Until recently, there had been no reports on the application of 2,7-disubstituted proton sponges like 44 and 65 in organic synthesis. Their advantage in comparison with compound 1 is their increased basicity coupled with their extremely low C-nucleophilicity. Lately, the 2,7-dimethoxy compound 44 was used for deprotonation of salts of other proton sponges, in particular of 88 and 89 (Section n.C.2)67. In another example, when the proton sponge 1 participated in the azo-coupling reaction, the addition of base 44 increased the degree of interaction (equation 30)56. The yield of the azo compound 269 was nearly quantitative, and the base 44 could be easily recovered. 

From the preparative point of view, most valuable are the chlorination and bromination of proton sponge 1 at positions 2 and 7 with, respectively, V-chlorobenzolriazole (CBT)189 and Af-bromosuccinimide98 (Scheme 30). The method is useful for the preparation of ortho-dihalides 101, 102 and monochloride 175. The monobromide 115, even using one equivalent of NBS, is rarely formed free of significant amounts of the disubstituted 102, which are hard to separate. Consequently, an alternative way to 115 is monolithiation of the corresponding dibromide with butyllithium followed by quenching the reaction mixture with water. 

Reactivity features of double and 2,7-disubstituted naphthalene proton sponges... 

In the course of functionalization reactions, performed recently with the double proton sponges 35 and 118, and orf/zo-disubstituted derivatives 44 and 65, some properties worthy of consideration have been revealed. 

Further increase of nitrogen atom basicity was achieved by the combination of Schwesinger s phosphazene base concept and the Alder s idea of the disubstituted 1,8-naphthalene spacer, as reported by Raab [94]. l,8-Bis(hexamethylttiaminophosphazenyl) naphthalene (HMPN) (126), represents the up to date most basic representative of this class of proton sponges , as evidenced by the theoretically estimated proton affinity of 274kcal mol and the measured pABH (MeCN) = 29.9 (Figure 2.12). HMPN is by nearly 12 orders... 

Recently, Weatherwax et al. reported a highly selective frani-disubstituted (3-lactam synthesis using an imidazoline catalyst in the presence of Proton Sponge (1) as a stoichiometric base [25] (Table 8.5). 

In the case of intermolecular Heck alkenylation of vinyl triflate and 2,2-disubstituted-2,3-dihydrofiiran, Proton Sponge (1) gave higher chemical yield and enantioselectivity compared to the trialkylamines [35] (Table 8.10). 

The last authors also record the NMR spectra of purine and 26 substituted purines (three 2-substituted, twelve 6-substituted and eleven 2,6-disubstituted) and in most cases proton-coupled in addition to decoupled spectra were obtained. Data for some of these compounds are presented in Table 10 and for some purine species in Table 11. C spin lattice relaxation data have also been used to assign a major structural form to the marine sponge nucleoside 1-methylisoguanosine (80CC339) (see Section 4.09.8.2.1). See also (74T3941) for a study of chemical shifts of 6-substituted purines. 

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