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Double proton sponges

SCHEME 10. Protonation of some double proton sponges in H NMR (8 in ppm in DMSO-dg)... [Pg.960]

The oxidation of compound 32 occurs in a similar manner but even more easily136. Its radical cation can be stored unchanged in acetonitrile for months. The UV spectrum of 32+ (7.max = 480 nm, lg e = 3.1) is very close to that of neutral 32 itself, from which one can conclude that the naphthalene moiety does not take part in the oxidation. As found by cyclovoltammetry, the double proton sponge 35, unlike its isomer 79, is oxidized with reversible two-electron transition, composed of two superimposed one-electron steps at Eli2 —0.50 V (Table 13)45. Apparently, the driving force for this process is the formation of the resonance-stabilized dication 133 (equation 8), which was isolated in the form of black crystals with I3- anions (kmax = 643 nm, lg e = 4.02) and investigated in... [Pg.968]

TABLE 18. Ionization constants for double proton sponges at 25 °C... [Pg.978]

Occasional formation of such salts in a small amount on nitration of compound 1, e.g. with N2O4 in 1,2-dichloroethane, indicates that the process could be initiated with common oxidants47. However, a question arises here as to why a similar cyclization is not observed for acenaphthene sponges (cf. Scheme 22) The answer may be that the N N distance in these sponges is remarkably longer (Table 4) and thus the cyclization becomes unfavourable. That the double proton sponge 35 with an N N distance yet shorter than 1 (Table 4) is very prone to cyclize to dihydroperimidinium salts44,64,137, confirms this explanation (Section IV.B.8). [Pg.983]

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. [Pg.991]

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. [Pg.996]

The proton sponges are exceptionally strong bases (see Section 4, p. 321 for a discussion) and one of the reasons for this is the strong hydrogen bonds with double-minimum potentials (A[8( H) — 8( H)] 0.5 present in the... [Pg.278]

Quite interestingly, the minor product 2-pheny 1-2,5-dihydrofuran (200) has the opposite configuration, i.e., (5)-200, compared to that of (/ )-199. However, this compound is produced with a significantly lower enantiomeric excess. It is possible that this is caused by a kinetic resolution effect in the alkene complex 205 the jr-bound hydridopalladium moiety in complex 205 could add again to the double bond. Base influence is also noteworthy, and the highest enantiomeric excess was achieved with l,8-bis(bisdimethylamino)naphthalene ( proton sponge ). [Pg.350]

In 1964, Paquette reported that although the 9,10-double bond of simple phenanthrenes can be formed using the Ramberg-Backlund reaction (NaOH in aqueous dioxane), the sterically crowded 4,5-dimethyl-phenanthrene cannot be made by this method. Staab has now shown that the highly strained proton sponge 4,5-bis(dimethylamino)phenanthrene (15) can be prepared using Meyers modification of the re-... [Pg.876]

Reactivity features of double and 2,7-disubstituted naphthalene proton sponges... [Pg.996]

On treatment with proton sponge 1, cationic rhodium complexes of type 262 have been shown to undergo double intramolecular dehydrofluorinative/C—C coupling to produce quantitatively rhodium complexes of hybrid cyclopentadienyl-phosphine ligands 263 (equation 27)240. [Pg.1015]


See other pages where Double proton sponges is mentioned: [Pg.436]    [Pg.935]    [Pg.958]    [Pg.978]    [Pg.996]    [Pg.436]    [Pg.1202]    [Pg.436]    [Pg.935]    [Pg.958]    [Pg.978]    [Pg.996]    [Pg.436]    [Pg.1202]    [Pg.31]    [Pg.296]    [Pg.381]    [Pg.278]    [Pg.137]    [Pg.932]    [Pg.377]    [Pg.409]    [Pg.102]    [Pg.22]    [Pg.265]    [Pg.108]    [Pg.94]    [Pg.71]    [Pg.100]    [Pg.137]    [Pg.20]    [Pg.997]    [Pg.203]   
See also in sourсe #XX -- [ Pg.935 , Pg.936 , Pg.978 , Pg.996 ]




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