Deprotonation of amines

Finally, the LDA deprotonation of amine N-oxides has been reported to generate azomethine ylides that can be trapped in [2 + 3] cycloadditions with simple alkenes.126 For example, N-methylpyrrolidine N-oxide (137) reacts with LDA in the presence of cyclopentene to give adduct (139 Scheme 31). A variety of other N-oxides behave similarly. Interestingly, there are no examples published to date where nonstabilized azomethine ylides generated by the desilylation procedure can be trapped by simple, unactivated alkenes. It is not clear whether these discrepancies are due to some fundamental difference in the reactive intermediate being generated, or whether the differences in environment are responsible for differing behavior. Further work is needed to establish this point. 

Formamidines have been recognized as good activators for the a-deprotonation of amines at the a-position.141 Trapping the anions with trimethylchlorosilane led to the corresponding SMA.142... 

Other selected reactions of (Re)+ derivatives include the deprotonation of S-bound DMSO, S(CH2R)2 (R = sp or sp C) complexes at the Ca atom that are followed by stereospecific rearrangements the deprotonation/reprotonation of [(Re)-()]2-CH2=CHR)]+ to give [(Re)(=CHCH2R)]+ deprotonation of amine and phosphine derivatives [(Re)(EHR2)] " to the amides and phosphides [(Re)(ER2)] epimerization of secondary alcohols catalyzed by [(Re)-(OMe)] unprecedented transformation of N-bound pyrrolyl to C-bound pyrrolyl species. 

Anionic surfactants Acidic - - amine Org Basic Ion pairs Deprotonation of amine carrier [59]... 

Nitrogen ligands are particularly versatile in high-valent, early transition metal chemistry. Deprotonation of amines, amides, and hydrazines generates multiply bonding ligands which help to stabilize the high oxidation states. Aspects of metal-amido and metal-imido chemistry have been reviewed.79,80... 

Finally, a chiral triamine 35, derived from (-)-proline, has been used as the lithium salt for the deprotonation of amines (Section D.2.I.). It is obtained from A-benzyloxycarbonylproline by forming the amide with, .Ar,A -trimethyl-l,2-ethanediamine, cleavage of the protecting group, and lithium aluminum hydride reduction29. 

A. Ray, A. F. Richter, A. G. MacDiarmid, A. J. Epstein, Polyaniline-protonation deprotonation of amine and imine sites, Synthetic Metals 1989, 29, E151. 

Late-transition-metal-amido complexes have been prepared by metathetical substitution reactions, or-bonded ligand exchange, deprotonation of amine complexes, and oxidative addition of N-H bonds. Metathetical substitution is the most common route to late-metal-alkylamido complexes, whereas metathetical substitution and a-bonded ligand exchange have both been used commonly to prepare arylamido compounds. 

Okazaki O, Guengerich FP (1993) Evidence for specilic base catalysis in A-dealkylation reactions catalyzed by cytochrome P450 and chloroperoxi-dase. Diffeiences in rates of deprotonation of amin-ium radicals as an explanation for high kinetic hydrogen isotope effects observed with peroxidases. J Biol Chem 268 1546 1552... 

The deprotonation of amines requires extremely strong bases, such as alkyllithium reagents. For example, lithium diisopropylamide, the sterically hindered base used in some bimolecular elimination reactions (Section 7-8), is made in the laboratory by treatment of N-(l-methylethyl)-2-propanamine (diisopropylamine) with butyllithium. 

Aromatization of indolines is important in completing synthetic sequences in which the directive effects of the indoline ring have been used to achieve selective carbocyclic substitution[l]. Several methods for aromatization have been developed and some of these are illustrated in Table 15.2. A range of reagents is represented. One type of procedure represents use of oxidants which are known to convert amines to imines. Aromatization then provides the indole. Such reagents must not subsequently oxidize the indole. Mereuric acetate (Entry 1) is known to oxidize other types of amines and presumably reacts by an oxidative deprotonation ot- to the complexed nitrogen. 

The bulky triphenylmethyl group has been used to protect a variety of amines such as amino acids, penicillins, and cephalosporins. Esters of N-trityl a-amino acids are shielded from hydrolysis and require forcing conditions for cleavage. The a-proton s also shielded from deprotonation, which means that esters elsewhere in the molecule can be selectively deprotonated. 

Aminolysis of esters often reveals general base catalysis and, in particular, a contribution to the reaction rate fi om terms that are second-order in the amine. The general base is believed to function by deprotonating the zwitterionic tetrahedral intermediate. Deprotonation of the nitrogen facilitates breakdown of the tetrahedral intermediate, since the increased electron density at nitrogen favors expulsion of an anion ... 

The mechanism of the indolization of aniline 5 with methylthio-2-propanone 6 is illustrated below. Aniline 5 reacts with f-BuOCl to provide A-chloroaniline 9. This chloroaniline 9 reacts with sulfide 6 to yield azasulfonium salt 10. Deprotonation of the carbon atom adjacent to the sulfur provides the ylide 11. Intramolecular attack of the nucleophilic portion of the ylide 11 in a Sommelet-Hauser type rearrangement produces 12. Proton transfer and re-aromatization leads to 13 after which intramolecular addition of the amine to the carbonyl function generates the carbinolamine 14. Dehydration of 14 by prototropic rearrangement eventually furnishes the indole 8. 

The term Knoevenagel reaction however is used also for analogous reactions of aldehydes and ketones with various types of CH-acidic methylene compounds. The reaction belongs to a class of carbonyl reactions, that are related to the aldol reaction. The mechanism is formulated by analogy to the latter. The initial step is the deprotonation of the CH-acidic methylene compound 2. Organic bases like amines can be used for this purpose a catalytic amount of amine usually suffices. A common procedure, that uses pyridine as base as well as solvent, together with a catalytic amount of piperidine, is called the Doebner modification of the Knoevenagel reaction. 

Thus, deprotonation of the aminium radical from a secondary or primary amine will at last form an amino radical instead of an aminoalkyl radical and a CH2CH2CN radical. This amino radical will then serve as one of the active species for the initiation of polymerization. 

The well-known photopolymerization of acrylic monomers usually involves a charge transfer system with carbonyl compound as an acceptor and aliphatic tertiary amine, triethylamine (TEA), as a donor. Instead of tertiary amine such as TEA or DMT, Li et al. [89] investigated the photopolymerization of AN in the presence of benzophenone (BP) and aniline (A) or N-methylaniline (NMA) and found that the BP-A or BP-NMA system will give a higher rate of polymerization than that of the well-known system BP-TEA. Still, we know that secondary aromatic amine would be deprotonated of the H-atom mostly on the N-atom so we proposed the mechanism as follows ... 

The end group of the polymers, photoinitiated with aromatic amine with or without the presence of carbonyl compound BP, has been detected with absorption spectrophotometry and fluororescence spectrophotometry [90]. The spectra showed the presence of tertiary amino end group in the polymers initiated with secondary amine such as NMA and the presence of secondary amino end group in the polymers initiated with primary amine such as aniline. These results show that the amino radicals, formed through the deprotonation of the aminium radical in the active state of the exciplex from the primary or secondary aromatic amine molecule, are responsible for the initiation of the polymerization. 

A-Acido imines (R R"C = N —X=0) like /V-acyl (X = CR) /V-sulfonyl [X = S(R)=0]2-7 or /V-diphenylphosphinoylimines [X = P(C6H5)2]3 are masked inline derivatives of ammonia. Compared to the imines themselves these activated derivatives are better electrophiles showing less tendency to undergo undesired deprotonation rather than addition of organometal-lics1812 The apparent advantages of these compounds have been exploited for asymmetric syntheses of amines, amides, amino acids and /J-lactams1-8 I6. 

In the reaction of amines such as NH3, NH2NH2, MeNH2, C6HUCH2NH2, and Ph(OMe)NH2, only monosubstitution can be obtained even in the presence of a large excess of the amine. This is taken into account by the deprotonation of the acidic monosubstituted complex by free amine leading to an iminocyclohexadienyl complex. The latter cannot be subjected to nucleophilic substitution of the second... 

The basic principle of all diazotizations of aromatic amines with a hydroxy- or a sulfonamido group in the 4-position relative to the amino group involves a deprotonation of the OH or NH group, respectively, after diazotization of the amino group. There is also a case of a deprotonation of a CH group in the 4-position of an aniline derivative, namely in the diazotization of 4-aminophenylmalononitrile (2.41) which, by the sequence of steps shown in Scheme 2-23, yields 3-diazo-6-dicyanomethylene-1,4-cyclohexadienone (2.42), as found by Hartzler (1964). This product can also be represented by a zwitterionic carbanion-diazonium mesomeric structure. 

In contrast to region B, the rates in region C for the three amines shown in Figure 3-3 were found to be the same. This is as expected, since the substituent effects on the equilibrium in Scheme (3-21) and on the deprotonation of the A-nitro-soanilinium ion should approximatively cancel. 

We mention Williams work briefly here because it may also explain Blangey s observations strongly basic primary amines unequivocally form 7V-nitrosoanilinium ions in strongly acidic media. In contrast to the rate-limiting deprotonations of the less basic aromatic and heteroaromatic nitrosoamine cations discussed in this section, the TV-nitroso cation of a strongly basic amine deprotonates extremely slowly. Therefore, the nitroso rearrangement, the Fischer-Hepp reaction, competes effectively with the 7V-deprotonation. 

Enantioselective deprotonation of prochiral 4-alkylcyclohexanones using certain lithium amide bases derived from chiral amines such as (1) has been shown (73) to generate chiral lithium enolates, which can be trapped and used further as the corresponding trimethylsilyl enol ethers trapping was achieved using Corey s internal quench described above. 

The different reactivity mentioned above also proves the validity of inequality ki, k3> >k4 used in the simplification of our model. On the contrary, in the presence of CHA less than one equivalent the signals of both the la and Ih appear, a large extent of deuteration at C-3 is observed both in the cis and tram isomers and in the product flavone (2). Using an excess of amine both isomer gave 2 deuterated at C-3 to an extent ca. 80-85 %. Considering the kinetic profile of the interconversion we conclude that it takes place via an enolate where the rate determining step is the deprotonation at C-3. 

These phosphinous amide anions are presumably responsible for the formation of the by-products AT-phosphino phosphinous amides 11 and mono-phosphazenes derived from diphosphanes 12 in the sequential treatment of primary amines with n-BuLi and chlorophosphanes for preparing NH phosphinous amides [75,88] (Scheme 14). Compounds 11 and 12 are presumably derived from anions 9 and 10, respectively, generated by deprotonation of the newly formed phosphinous amide with the lithiated amine R NHLi. In solution, 9 can establish a metallotropic equilibrium with 10. 

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