Deprotonation lateral

In sulfoxides and sulfones an adjacent CH group is also deprotonated by strong bases. If one considers the sulfinyl (—SO—) or sulfonyl (—SOj—) groups to be functional groups, then these carbanions are d -synthons. It will be shown later (p. 48f. and 65f.), that these anions may either serve as nonfunctional, d -, d - or d -synthons. 

Later it turned out that activation of enamine components could not only be achieved by deprotonation of the nitrogen atom but also by connecting it with certain metals, e.g. Ni(II), Pd(II), or Co(II), and subsequent treatment with base. 

The deprotonation of 4,5-dimethylthiazole and addition of the resulting anion to aldehydes was demonstrated as early as 1948 (48HCA652) and 2-lithiothiazoles were later shown to react with aldehydes, ketones, methyl iodide, and epoxides... 

Methylation of nicotine to the pyridinium iodide with methyl iodide, followed by its conversion to the hydroxide with silver oxide in water, oxidation with potassium permanganate to the A -methyl nicotinic acid hydroxide and subsequent deprotonation with silver oxide yielded Trigollenine as colorless needles (1897CB2117). In a later publication, the formation of nicotinic acid from nicotine was described. Esterification followed by aminolysis and methylation yielded the A -methylnicotinamide... 

A five-membered methanide auracycle [Au(C6F5)2(SPPli2CFl2PPh2)]C104 (25) is described with the monosulfonated dppm, obtained after chlorine elimination of [Au (C6F5)2Cl(SPPh2CH2PPh2)j with a silver salt. After deprotonation of the methylene group (26) and later coordination of additional metal centers affords dinuclear and trinuclear methanide derivatives (27, 28) [210]. 

The titration coordinates evolve along with the dynamics of the conformational degrees of freedom, r, in simulations with GB implicit solvent models [37, 57], An extended Hamiltonian formalism, in analogy to the A dynamics technique developed for free energy calculations [50], is used to propagate the titration coordinates. The deprotonated and protonated states are those, for which the A value is approximately 1 or 0 (end-point states), respectively. Thus, in contrast to the acidostat method, where A represents the extent of deprotonation, is estimated from the relative occupancy of the states with A 1 (see later discussions). The extended Hamiltonian in the CPHMD method is a sum of the following terms [42],... 

Scott was able to leverage the same type of methodology in an impressive display in which /V-methyltryptamine was dimerized directly to afford chimonanthine (7) (Scheme 9.2b) [9c]. Deprotonation of the indole 1H proton with methyl Grignard followed by treatment with FeCl3 accomplished the singleelectron oxidation and dimerization of the indole moiety. The racemic and meso stereoisomeric products were obtained as a mixture in 19 % and 7 % yields, respectively. Takayama later found hypervalent iodine to be a superior oxidant, affording yields of 17 % and 30 %, respectively [9j]. In both cases, however, as in the case of Hendrickson s example, stereocontrol could not be achieved. 

A complementary method was reported 3 years later by Hino, in which a readily enolizable diketopiperazine 48 was directly converted to the epidisulfide by deprotonation with sodium hydride and exposure to sulfur monochloride [38]. As with the Trown method, this method was limited to a specific class of substrates, namely, ones possessing a 1,3-dicarbonyl motif at each of the reactive centers, yet it has also seen subsequent applications in total synthesis [39, 40]. In 1972, Schmidt was able to significantly broaden the scope of the enolate thiolation method by introducing elemental sulfur as the electrophilic agent [41]. In contrast to Hino s method in which formation of a highly reactive, unstable adduct requires readily... 

In order to co clarify the role of complex formation, the new data on stability constants should be accumulated, being collected at strictly similar conditions. It should be also mentioned that any analysis of equilibrium in solutions involving anions of polybasic hydroxy carboxylic acids requires the data on the deprotonation constants of the acid in question. This information would be crucial for conclusions regarding the presence and stability of mixed complexes in the system. Valuable knowledge about the structure of complex compounds present in solutions (and in precursors as well, see later) may be gained by means of vibrational spectroscopy (IR and Raman spectra) and nuclear magnetic resonance. 

A more drastic influence of subphase H concentration can be observed for the sulfolipid analog (8) (Figure 7.). At pH values from 2 up to 5,5 (8) forms two condensed phases, whereas at pH 12, where the nitrogen is deprotonated, there is only one phase present (35). This behavior has a considerable influence on the mono-layer polymerization properties of (8), which is discussed later in this chapter. 

Then later in an aerobic world with mainly iron(III) both, zinc peptidases and iron oxygenases, evolved from these ancestors. Today nature mainly uses zinc centers in metalloenzymes for the hydrolyses of peptide bonds (99,J00). In the commonly accepted mechanism for zinc peptidases, zinc(II) has two tasks It polarizes the carbonyl functionality of the peptide bond that is going to be cleaved and it supports the deprotonation of the coordinated water nucleophile. 

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