Deprotonation-substitution reactions

In addition to providing fully alkyl/aryl-substituted polyphosphasenes, the versatility of the process in Figure 2 has allowed the preparation of various functionalized polymers and copolymers. Thus the monomer (10) can be derivatized via deprotonation—substitution, when a P-methyl (or P—CH2—) group is present, to provide new phosphoranimines some of which, in turn, serve as precursors to new polymers (64). In the same vein, polymers containing a P—CH group, for example, poly(methylphenylphosphazene), can also be derivatized by deprotonation—substitution reactions without chain scission. This has produced a number of functionalized polymers (64,71—73), including water-soluble carboxylate salts (11), as well as graft copolymers with styrene (74) and with dimethylsiloxane (12) (75). 

In addition to providing many new precursors to functionalized poly(alkyl/arylphosphazenes), the deprotonation/substitution reactions of these N-silylphosphoranimines serve as useful models for similar chemistry that can be carried out on the preformed polymers. New reactions and experimentation with reaction conditions can first be tried with monomers before being applied to the more difficult to prepare polymeric substrates. A considerable amount of preliminary work [e.g., with the silylated monomers (z z) and polymers (2 o) has demonstrated the feasibility of this model system approach. 

Synthesis and polymerization of multifunctional cyclotriphosphazenes have been described <04PS%1>. A series of new nongeminal cyclophosphazenes 52 has been prepared via deprotonation-substitution reactions at the methyl groups of both cis and trans isomers of cyclotriphosphazene 51 with different electrophilic reagents <04PS817>. 

The deprotonation-substitution reactions of methylphenyl substituted cyelotriphosphazenes can be considered to be an important synthetic tool for the expansion of the area of organo-substituted cyclophosphazenes possessing a direet P-C bond. The reaction of tru i-(NPMePh)3 (212) with 3 moles of Bu Li followed by treatment with 3 moles of MeLi affords trans-(NPEtPh)3 (213) in high yield. The same reaction with cw-(NPMePh)3 (212) gives a mixture of bis(ethyl) [cw-(214)] and tris(ethyl) [cw-(213)] derivatives. 

Poly(methylphenylphosphazene) can be derivatized through either deprotonation/substitution reactions at the methyl group or electrophilic aromatic substitution of the phenyl group. These reactions have been used to prepare a variety of new polyphosphazenes with all functional groups attached to the polymer backbone by direct P-C bonds. The synthesis and characterization of several of these new... 

Variations in the Deprotonation-Substitution Reactions. As discussed in the previous paper in this volume, the preparation of copolymers with combinations of alkyl and aryl groups attached to the backbone by P-C bonds is readily achieved by the condensation polymerization of appropriate mixtures of N-silyl hosphoranimines. The highly methylated copolymers 15 are of particuhiar interest in terms of deprotonation-substitution reactions for several reasons. First, with even a low proportion of phen d groups, these copolymers remain soluble in THF, a solvent suitable for deprotonation-substitution reactions. Second, the of the copolymers are significantly lower than... 

In most of the deprotonation-substitution reactions discussed thus far, the degree of substitution has usually not exceeded 50 %. Although this could be due to either electronic ctors associated with the formation of charged sites along the chain or to siiiq)le steric effects, a recent P NMR spectroscopic study of the anion indicates that steric size of the electrophile is the limiting frctor in substitution. When one-half equivalent of fi-BuLi was added to [Me(Ph)PN]]x and the mixture was stirred at room... 

Acetylene-substituted Si-N-P compounds, synthesis, 236-237 Activated aluminas, description, 165 Aerogels, definition, 127 Aggregation of fractals, 104,106 Alcohol-substituted polymers from aldehydes and ketones, deprotonation-substitution reactions, 249-250 Alkenylborazine copolymers, quantitative reactivity studies of copolymerization reactions, 394... 

Alkenylfluorophosphazene copolymers, quantitative reactivity studies of copolymerization reactions, 390-394 Alkoxyalkoxy side groups, synthesis of n-silylphosphoranimines, 311-322 Alkyl-group polymers, deprotonation-substitution reactions, 248-249 Allylboration polymerization, polycyclo-diborazane synthesis, 407-408,409, 410 Alucone polymers characterization ceramics, 177 polymers, 173-178 examples, 166,167/ solid-state NMR spectroscopy limitations, 177,179/ quadrupolar broadening, 177-180 status, 180-181 syntheses ceramics, 170-174 polymers, 166,168-170 synthetic route, 166... 

The proton of terminal acetylenes is acidic (pKa= 25), thus they can be deprotonated to give acetylide anions which can undergo substitution reactions with alkyl halides, carbonyls, epoxides, etc. to give other acetylenes. 

An a ,/3-epoxycarboxylic ester (also called glycidic ester) 3 is formed upon reaction of a a-halo ester 2 with an aldehyde or ketone 1 in the presence of a base such as sodium ethoxide or sodium amide. Mechanistically it is a Knoevenagel-type reaction of the aldehyde or ketone 1 with the deprotonated a-halo ester to the a-halo alkoxide 4, followed by an intramolecular nucleophilic substitution reaction to give the epoxide 3 ... 

An a-halosulfone 1 reacts with a base by deprotonation at the a -position to give a carbanionic species 3. An intramolecular nucleophilic substitution reaction, with the halogen substituent taking the part of the leaving group, then leads to formation of an intermediate episulfone 4 and the halide anion. This mechanism is supported by the fact that the episulfone 4 could be isolated. Subsequent extrusion of sulfur dioxide from 4 yields the alkene 2 ... 

The phenol is deprotonated by KOH to give an anion that carries out a nucleophilic acyl substitution reaction on the fluoronitrobenzene. 

Protonation and deprotonation reactions of corroles have already been mentioned (see Introduction). Attempts to achieve electrophilic substitution reactions, at the corrole, e.g. Friedel-Crafts acylation, have been unsuccessful.1 Heating corroles with acetic anhydride yields the corresponding 21-acetyl derivatives l.8a,b... 

Further examples of electrophilic substitutions of thiopyrans at position 3 and 5 or at position 4 after deprotonation (83AHC145, Section V,G.) have been described in the last decade. Other substitution reactions are still rare. 

Hydroxy-substituted iron-acyl complexes 1, which are derived from aldol reactions of iron-acyl enolates with carbonyl compounds, are readily converted to the corresponding /i-methoxy or /1-acetoxy complexes 2 on deprotonation and reaction of the resulting alkoxide with iodomethane or acetic anhydride (Tabic 1). Further exposure of these materials to base promotes elimination of methoxide or acetate to provide the a,/ -unsaturated complexes (E)-3 and (Z)-3 (Table 2). 

In some cases, the Q ions have such a low solubility in water that virtually all remain in the organic phase. ° In such cases, the exchange of ions (equilibrium 3) takes place across the interface. Still another mechanism the interfacial mechanism) can operate where OH extracts a proton from an organic substrate. In this mechanism, the OH ions remain in the aqueous phase and the substrate in the organic phase the deprotonation takes place at the interface. Thermal stability of the quaternary ammonium salt is a problem, limiting the use of some catalysts. The trialkylacyl ammonium halide 95 is thermally stable, however, even at high reaction temperatures." The use of molten quaternary ammonium salts as ionic reaction media for substitution reactions has also been reported. " " ... 

Synthesis. The 2-phenyM,3,2-diazaboracyclohexane ring system (1) was selected as the starting material in this study because (1) it is prepared easily and in high yield by a three step synthesis from BCI3 (2) the N-H bonds are potential sites for deprotonation and substitution reactions and (3) the trimethylene bridge enhances the rigidity of the N-B-N backbone which should prevent cyclization upon thermolysis of an appropriate precursor. 

The compounds described herein were prepared by three methods. The first route involves deprotonation/substitution at the N-H sites of 1, the second consists of a cleavage reaction of an Si-N derivative of 1 with PhBCI2, and the third route is a transamination reaction between a bis(dimethylamino)boryl derivative of 1 and an aliphatic diamine. In the first approach, compound 1 is deprotonated by treatment with one equivalent of n-BuLi. Quenching of the resulting anion with various electrophiles produces the monosubstituted products 2-4 (eq 3). 

Just as disulfonium dication 34, diselenonium 113 and ditelluronium dication 114 do not undergo deprotonation. Instead, reaction of dication 113 with fluorenyllithium affords bis-selenide and fluorene dimer 103.96 Softer Lewis base such as ra-tolyl magnesium bromide reacts with diselenonium-dication 113 to give 127, a product of nucleophilic substitution at the onium atom (Scheme 48).129... 

Interestingly, deprotonation of the 3-oxo-pyrrolo[l,2-f]oxazole 277 with r-BuLi at —78°C took place at the C-5 position. Addition of an electrophile provided the substituted products 278 in good yields. Stannyl and silyl chlorides, dimethyl sulfate, ketones, and benzaldehyde were successfully used as electrophiles. A significant feature of this lithiation-substitution reaction is the generally high Ar-diastereoselectivity only single diastereomers of products were isolated (Scheme 41) <2001JA315>. 

The base may deprotonate either C3 or C4. Deprotonation of C3 makes it nucleophilic. We need to form a new bond from C3 to C8 via substitution. The mechanism of this aromatic substitution reaction could be addition-elimination or Sr I. The requirement of light strongly suggests SRN1. See Chap. 2, section C.2, for the details of drawing an SRN1 reaction mechanism. 

The interfacial mechanism provides an acceptable explanation for the effect of the more lipophilic quaternary ammonium salts, such as tetra-n-butylammonium salts, Aliquat 336 and Adogen 464, on the majority of base-initiated nucleophilic substitution reactions which require the initial deprotonation of the substrate. Subsequent to the interfacial deprotonation of the methylene system, for example the soft quaternary ammonium cation preferentially forms a stable ion-pair with the soft carbanion, rather than with the hard hydroxide anion (Scheme 1.8). Strong evidence for the competing interface mechanism comes from the observation that, even in the absence of a catalyst, phenylacetonitrile is alkylated under two-phase conditions using concentrated sodium hydroxide [51],... 

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