Deprotonation derivatives

Fig. 14 Top [(C5H4COOH)2Con] and deprotonation derivatives. Bottom [(C5H4COOH)2Com]+ and deprotonation derivatives...

Known carbonyl hydrides of mthenium include the unstable HRu(CO)4, as well as the trinuclear H2Ru3(CO)n, tetranuclear H2Ru4(CO)i3 and H4Ru4(CO)i2, and complexes of even higher nuclearity, as well as substitution and deprotonation derivatives. A special feature of mthenium carbonyl chemistry is the existence of series of carbonyl... 

Ketyl radicals are treated as deprotonated derivatives of OH-substituted species immediately after the corresponding OH-substituted radicals. The gegenion of a ketyl is not included in the structural formula but has to be deduced from the description of generation of the radical. 

The remaining references in this section deal with processes closely related to substitution at nickel. The reaction of bis-(00-diethylphosphorodithioato-55 -) nickel(ii) (14) with bidentate nitrogen ligands involves addition rather than substitution. Rates are controlled by steric factors, with addition of 2,9-Me2phen much slower than that of phen, bipy, or pada. Activation entropies are within the range - 20 to - 93 J mol (in benzene), consistent with the expected associative activation step. Kinetic stabilization by cyanide ligands is demonstrated by the relative slowness of proton transfer to doubly deprotonated derivatives of the... 

The hydrogen-bond acceptor properties of a strain phosphine molecule (3), and its deprotonated derivatives (4), (5), and (6) have been examined at the MP2/6-311- -- -G(d,p) level of theory. In addition, complexation of these with metallic atoms, i.e, the anion (4) with Li" ", dianion (5) with Be " ", and the trianion (6) with B + (in order to obtain neutral complexes) has been considered, and the effects of such complexation in their hydrogen-bonding characteristics were analyzed. The results obtained for the complexes were compared with the analogous ones of trimethyl-phosphine oxide. It was shown that the strain decreases the... 

Sulfur ylides contain a carbanion, which is stabilizea oy an adjacent positively-charged sulfur. Ylides derived from alkylsulfonium salts are usually generated and utilized at low temperatures. Oxosulfonium ylides are, however, stable near room temperature. The most common method of ylide formation is deprotonation of a sulfonium salt. What has been said... 

As is broadly true for aromatic compounds, the a- or benzylic position of alkyl substituents exhibits special reactivity. This includes susceptibility to radical reactions, because of the. stabilization provided the radical intermediates. In indole derivatives, the reactivity of a-substituents towards nucleophilic substitution is greatly enhanced by participation of the indole nitrogen. This effect is strongest at C3, but is also present at C2 and to some extent in the carbocyclic ring. The effect is enhanced by N-deprotonation. 

The 5-amino-THISs are very strong bases (35). The hydrochlorides, therefore, have not yet been deprotonized successfully. However, the decreased basicity of the N-acylated derivatives makes these readily accessible from their hydrochlorides (Scheme 28). 

Most of the reactions of ester enolates described so far have centered on stabilized eno lates derived from 1 3 dicarbonyl compounds such as diethyl malonate and ethyl ace toacetate Although the synthetic value of these and related stabilized enolates is clear chemists have long been interested m extending the usefulness of nonstabilized enolates derived from simple esters Consider the deprotonation of an ester as represented by the acid—base reaction... 

Fig. 10. Pharmacophores for angiotension-converting enzyme. Distances in nm. (a) The stmcture of a semirigid inhibitor and distances between essential atoms from which one pharmacophore was derived (79). (b) In another pharmacophore, atom 1 is a potential zinc ligand (sulfhydryl or carboxylate oxygen), atom 2 is a neutral hydrogen bond acceptor, atom 3 is an anion (deprotonated sulfur or charged oxygen), atom 4 indicates the direction of a hydrogen bond to atom two, and atom 5 is the central atom of a carboxylate, sulfate, or phosphate of which atom 3 is an oxygen, or atom 5 is an unsaturated carbon when atom 3 is a deprotonated sulfur. The angle 1- -2- -3- -4 is —135 to —180° or 135 to 180°, and 1- -2- -3- -5 is —90 to 90°.

The first proton to be removed from iV-methylpyrrole by w-butyllithium is from an a-position a second deprotonation occurs to give a mixture of 2,4- and 2,5-dilithiated derivatives. The formation of a 2,4-dilithio derivative is noteworthy since in the case of both furan and thiophene initial abstraction of a proton at C-2 is followed by proton abstraction from C-5 (77JCS(P1)887). iV-Methylindole, benzo[6]furan and benzo[6]thiophene are also deprotonated at C-2. Selenophene and benzo[6]selenophene and tellurophene and benzo[6]tellurophene similarly yield 2-lithio derivatives (77AHC(21)119). 

The dianions derived from furan- and thiophene-carboxylic acids by deprotonation with LDA have been reacted with various electrophiles (Scheme 64). The oxygen dianions reacted efficiently with aldehydes and ketones but not so efficiently with alkyl halides or epoxides. The sulfur dianions reacted with allyl bromide, a reaction which failed in the case of the dianions derived from furancarboxylic acids, and are therefore judged to be the softer nucleophiles (81JCS(Pl)1125,80TL505l). 

There is a marked and unexplained difference in the stability of the dianions derived by deprotonation of coumarilic acid (207) and 4,6-dimethylcoumarilic acid (209) to thermal... 

Azole iV-oxides, iV-imides and iV-ylides are formally betaines derived from iV-hydroxy-, iV-amino- and iV-alkyl-azolium compounds. Whereas iV-oxides (Section 4.02.3.12.6) are usually stable as such, in most cases theiV-imides (Section 4.02.3.12.5) andiV-ylides (Section 4.02.3.12.3) are found as salts which deprotonate readily only if the exocyclic nitrogen or carbon atom carries strongly electron-withdrawing groups. 

If there is no phenyl substituent in the 3-position the amination ability decreases. The acyloxaziridine (104) yields only 11% of a semicarbazide derivative with piperidine. In the presence of strong bases an intramolecular amination competes. Compound (104) reacts with methoxide within a couple of seconds to give phenylhydrazine carboxylic ester (106), and with cyclohexylamine to give the substituted semicarbazide (107). A diaziridinone (105) is assumed to be the common intermediate, formed by an intramolecular reaction from deprotonated (104) (67CB2600). 

Most diaziridines are not sensitive towards alkali. As an exception, diaziridines derived from 2-hydroxyketones are quickly decomposed by heating with aqueous alkali. Acetaldehyde, acetic acid and ammonia are formed from (162). This reaction is not a simple N—N cleavage effected intramolecularly by a deprotonated hydroxy group, since highly purified hydroxydiaziridine (162) is quite stable towards alkali. Addition of small amounts of hydroxybutanone results in fast decomposition. An assumed reaction path — Grob fragmentation of a hydroxyketone-diaziridine adduct (163) — is in accord with these observations (B-67MI50800). 

Diaziridinimines were made analogously. Tri-t-butylguanidine (281) with r-butyl hypochlorite gave (176) in 80% yield. (281) itself is a sufficiently strong base to deprotonate its Af-chloro derivative (69AG(E)448). This procedure also works with methyl- or phenyl-substituted guanidines. 

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