Phosphonium dealkylation

In the reactions characterized in the general sense above, phenyl and benzyl were the organic residues bound to phosphorus. It is not clear which of these groups is removed in the LAH dealkylation step. It should also be noted that as tetraquaternary phosphonium salts, these species do not qualify as crown analogs in the strictest sense because of the absence of lone pair electrons on phosphorus. Furthermore, the quaternary phosphorus can resist oxidation much better than secondary or tertiary phospho-... 

In this context, the treatment of the AT-phosphinyl iminoethers 15 with methyl iodide furnish the P-methyl phosphonium iodides, which by heating experience an 0-dealkylation, reminiscent of the Arbuzov reaction, for yielding the iV-acylphosphazenes 16 [45] (Scheme 16). 

Another series of reactions (Nos 8-15) show different possibilities for the addition of conjugated double bonds on a P(III) atom. Although this type of reaction has been stated to be a concerted six-electron dissociative process, and therefore stereoselective, its scope is limited by the fact that it cannot be generalized to all P(III) compounds as some of them are fairly unreactive, or yield phosphonium salts or may even be dealkylated. 

The condensation of an aldehyde, benzyl carbamate, and triphenyl phosphite, first described by Oleksyszyn et al., 25,26 affords a direct route to a-aminoalkylphosphonates 4 that are conveniently protected for subsequent reactions (Scheme 4). Since dealkylation of the quaternary phosphonium intermediate 3 is not possible in this case, formation of the pen-tavalent product 4 presumably involves activation of the solvent and formation of phenyl acetate. This method is useful for the synthesis of aliphatic and aromatic amino acid analogues. However, monomers with more elaborate side chains are often incompatible with the reaction conditions. The free amine can be liberated by treatment with HBr/AcOH or by hydrogenolysis after removal of the phenyl esters. The phosphonate moiety can be manipulated by ready exchange of the phenyl esters in alkaline MeOH and activation as described in Section 10.10.2.1.1. Related condensations with other trivalent phosphite derivatives have been reported. 27-30 ... 

Phosphonium salts can be dealkylated by treatment with alkoxides to yield alkanes. Although the hydrolytic cleavage of phosphonium salts in solution has been well investigated, the solid-phase variant of this reaction has not yet found broad application. One example, in which traceless linking was based on the alkoxide-induced dealkylation of a resin-bound phosphonium salt, is given in Table 3.48 (Entry 1). 

When the substituent becomes very anion-stabilising, as in 42, the ylid may not react with ketones and anions of phosphonate esters are usually preferred in the Homer-Wadsworth-Emmons (HWE) variant.11 The reagent triethyl phosphonoacetate 46 is made by combining a phosphite (EtO)3P instead of a phosphine, with ethyl bromoacetate. Displacement of bromide 44 gives a phosphonium ion that is dealkylated by bromide 45. 

Dealkylation of phosphonium salts 83 is promoted by NaOH, and isomeric phosphabicyclononanes 84 are readily separated by a sequence of hydrophosphination/dehydrophosphination steps <1997CC1527> (Equation 8). Decomposition of phosphonium salt 85 with NaOH/ethylene glycol resulted in the elimination of toluene and bicyclic compound 86 <1996RJC567> (Equation 9). 

C, and 457°C, respectively [127], Such high temperatures are only tolerated by most liquids for a short time. For example, after 10 h, even at temperatures as low as 200°C, [RMlm][PF ] and l-decyl-3-methyhmidazolium triflate show an appreciable mass loss [179], The ILs with low thermal stability are [EMIm][X], where X=[Tf N]-, [MjN]-, and Br [68], Phosphonium ILs with [Tf N]- or [NCCN) ]-anions decompose completely to volatile products in a single step. The degradation products indicate that Hofmann elimination process and/or dealkylation reactions occurred. Conversely, ILs based on nitrogen cations do not decompose completely... 

These products, most easily explained as arising through nucleophilic attack by phosphorus on the carbonyl carbon followed by dealkylation of a phosphonium intermediate, are accompanied by varying amounts of a substance characterized as R C02C(R ) [P(0)(0R)2]2 by Kamai and Kukhtin (168). 

Aminophosphines, phosphinites and phosphonites from quasi-phosphonium salts with alkyl halides in normal 5 n reactions. The aminophosphonium salts and the salts derived from aryl phosphinites and diaryl phosphonites are stable, but the majority of the quasi-phosphonium salts which contain alkoxy groups are dealkylated during the reaction with the alkyl halide (the Arbuzov reaction, see below). Thio analogues of phosphinites and... 

A detailed study of the desulphurization of the disulphides (301)(R,R = dialkoxy, or alkyl(alkoxy) ) by phosphorus(III) compounds, including (Mc2N)2P, Ph P, or acyclic or cyclic (based on catechol) phosphotriesters or ester amides) considered the role of phosphonium and phosphorane intermediates. The isomerization of (302) into (303), and the decomposition (desulphurization, deoxygenation, or dealkylation) into end products, are influenced by electronic and steric factors. 

Among the other developed approaches to novel P-ylides, the synthesis of a-sulfanyl-a-phosphonyl phosphonium ylides (58) in quantitative yields via the addition of two equivalents of trialkylphosphites to phosphonodithio-formates should be mentioned. The subsequent reaction of these ylides with alkyl or benzyl halides gives stabilized sulfonium ylides (59) while their heating (18-150 h, 110 °C) leads to a-sulfanyl methylene bis-phosphonates through protonation-dealkylation intramolecular reactions. The synthesis... 

Quaternary phosphonium salts are generally stable crystalline solids which have high solubility in polar solvents. They are relatively stable towards dealkylation but hydrolyze in the presence of hydroxide ion to the phosphine oxides ... 

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