Intramolecular deprotonation

The TT-allylpalladium complexes 241 formed from the ally carbonates 240 bearing an anion-stabilizing EWG are converted into the Pd complexes of TMM (trimethylenemethane) as reactive, dipolar intermediates 242 by intramolecular deprotonation with the alkoxide anion, and undergo [3 + 2] cycloaddition to give five-membered ring compounds 244 by Michael addition to an electron-deficient double bond and subsequent intramolecular allylation of the generated carbanion 243. This cycloaddition proceeds under neutral conditions, yielding the functionalized methylenecyclopentanes 244[148], The syn-... 

It has been suggested that the kinetic preference for formation of (3,y-unsaturated ketones results from an intramolecular deprotonation, as shown in the mechanism above.51 The carbonyl-ene and alkene acylation reactions have several similarities. Both reactions occur most effectively in intramolecular circumstances and provide a useful method for ring closure. Although both reactions appear to occur through highly polarized TSs, there is a strong tendency toward specificity in the proton abstraction step. This specificity and other similarities in the reaction are consistent with a cyclic formulation of the mechanism. 

In the dihapto mode the pyridine ring can be protonated intermolecularly at nitrogen, or even intramolecularly deprotonated at carbon. The first evidence for metal C—N insertion is the reaction of the metallaaziridine complex (111) with homogeneity LiHBEt3 in THF at low temperature that yields (112) (Scheme 49).251-254 Experiments with carbon nucleophiles (RMgCl, MeLi) in place of LiHBEt3 have provided valuable information to allow discrimination between... 

Fig. 4. Relevant structures for the discussion of methane activation by (bipyrimi-dine)PtCl2 Methane complex of Pt(II) (A) methyl(hydrido)platinum(IV) complex, the product of the oxidative addition (B) transition state for intramolecular deprotonation of the methane complex ( cr-bond metathesis , sometimes also called electrophilic , C) intermolecular deprotonation of the methane complex ( electrophilic pathway , D).

The reaction of PhS02 with 2-(2 -phenylsulfonyl)-2, 3 -butadienylmalonate 233 affords the five-membered cyclic alkenyl sulfone 235 via a 1,4-addition, intramolecular deprotonation and a SN2 -substitution process [124, 125]. 

The mechanism of this remarkable a-elimination reaction has been scrutinized by several research groups [17,49,51,396-404]. From the experimental data obtained this process is best described as an intramolecular deprotonation of one neopentyl ligand by another, the latter being released as neopentane (Figure 3.4). 

However, it is most surprising that alkyl-substituted 3-azapyrylium salts can undergo formylation and acylation at the side chain. These reactions are examples of the interaction of heterocyclic cations with cationoid electrophiles. Some of these processes are presented in Scheme 12 (90KGS134 91KGS265 94TH1). It is assumed that such transformations are possible due to the intramolecular deprotonation of the methyl group in 79 to form charged anhydro base 80 (see structure 39). The 4-acylmethyl-3-... 

Hine has demonstrated that simple amino acids, such as glycine and p-alanine, are not capable of intramolecular deprotonation in the reaction with isobutyraldehyde-2-d (Scheme 8) [62], Apparently, the carboxylate moiety in the iminium ion intermediate 29 is a relatively weak base and, as such, external bases, present in the buffer used (e.g. acetate ions), are largely responsible for the formation of the enamine intermediate 30. 

The proposed mechanism is given in Scheme 15. Initially the dissociation of water, maybe trapped by the molecular sieve, initiates the catalytic cycle. The substrate binds to the palladium followed by intramolecular deprotonation of the alcohol. The alkoxide then reacts by /i-hydride elimination and sets the carbonyl product free. Reductive elimination of HOAc from the hydride species followed by reoxidation of the intermediate with dioxygen reforms the catalytically active species. The structure of 13 could be confirmed by a solid-state structure [90]. A similar system was used in the cyclization reaction of suitable phenols to dihydrobenzofuranes [92]. The mechanism of the aerobic alcohol oxidation with palladium catalyst systems was also studied theoretically [93-96]. 

Deprotonation of this intermediate gives a sulphur ylide, which undergoes intramolecular deprotonation via a five-membered ring transition state and fragmentation to yield the product and DMS (odour ) ... 

From these observations, Woerpel and Cleary proposed a mechanism to account for allylic silane formation (Scheme 7.23).85 Silacyclopropane 94 is formed from cyclohexene silacyclopropane 58 through silylene transfer. Coordination of the Lewis basic benzyl ether to the electrophilic silicon atom86-88 generates pentacoordinate siliconate 95 and increases the nucleophilicity of the apical Si-C bond.89 Electrophilic attack by silylsilver triflate 96 forms silyl anion 97. Intramolecular deprotonation and elimination then affords the silylmethyl allylic silane. 

On the basis of these results, a mechanism (Scheme 8.10) involving the intermediacy of a silver-carbene 54 was proposed in which the insertion product arises from the formation of the halonium ylide 55, followed by a 1,2 shift (55 —> 26, or 51 or 52). Alternatively, if the substrate and thus the halonium ylide 56 contain a (3-hydrogen, this could be removed by an intramolecular deprotonation with concomitant loss of halide resulting in formation of the olefin 57 and the a-haloacetate 53. At this stage, no independent evidence has been obtained to support this pathway thus this mechanism is purely speculative (see text below). Indeed, although the pathway has been depicted as involving metal-free intermediates, it is quite likely that this is not the case, but this awaits independent experimental verification. 

YouwHiseea few mechanisms in this chapter wherewe have written an intramolecular deprotonation. This saves writing two steps—protonation of the enoiate and deprotonation of N (here)—but quite possibly this is not the actual mechanism by which the proton transfer takes place. Any proton wiii do, as will any base—do not take the arrows here too literally. 

It was observed136 that the / -oxochlorocarbenium ions 272 formed by acylation of vinyl chlorides 270 can undergo an intramolecular deprotonation to give the more stable hydroxycarbenium ions 274. In this case the carbonyl oxygen performs the function of an internal base (equation 75). The formation of 3-azapyrylium hexachloroantimonates 277 can be then explained by reaction of nitriles not with the more reactive chlorocarbenium ions 272, but with the more stable and less reactive hydroxycarbocations 274 (equation 75, path b). 

Another catalytic cycle can be drawn. The first step, oxidative addition of Pd(0) to Bn-OR, is the same as before. The Bn-Pd(II)-OR complex might then form a cr-bond complex with H2, with the H-H cr bond acting as a two-electron donor. The H atoms are made electrophilic upon coordination. Intramolecular deprotonation of the cr complex by OR would then give ROH and Bn-Pd(II)-H, and the latter would undergo reductive elimination to complete the catalytic cycle. 

The study illustrated the remarkably high activity of [Ru (edta) (OOH)] , the Ru equivalent of Compormd 0, as compared to [Ru (edta)(0)] and [Ru (edta)(OH)] , the Ru equivalents of Compounds 1 and II, respectively, toward the deOTadation of ORII. In the proposed formation of [Ru (edta)(OOH)r as the intermediate with the highest catalytic activity at pH 4, the role of the dangling acetate arm assisting the intramolecular deprotonation of the coordinated hydrogen peroxide that leads to the stabilization of the hydroperoxo complex [Ru (edta)(OOH)] is schematically demonstrated in Scheme 10. Thus, the complexes that are equivalents for Compoimds I and II are practically nonreactive on the time scale observed for the degradation catalyzed by [Ru° (edta)(OOH)] (75). 

The second case is hopeless as the Grignard reagent destroys itself by intramolecular deprotonation. This synthesis could be rescued by putting a... 

You will see a few mechanisms in this chapter where we have written an intramolecular deprotonation. 

Oxidation of a tertiary amine with a peroxide (mCPBA) forms an A-oxide that undergoes an intramolecular deprotonation with syn stereoselectivity upon heating. This reaction is known as a Cope elimination. If given a choice, this deprotonation will occur on a less hindered P-carbon, giving rise to a less substituted alkene product (this regioselectivity, known as the Hofmann rule, is the opposite predicted by Zaitsev s rule). 

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