Phosphazenes arylation reactions

The products from the reactions with phosphorus pentachioride vary even with the nature of the aryl group. Thus, the p-chlorophenyl compound gave a product analogous to (6), but it was accompanied by the dimeric phosphazene, [p-ClCeHiNPClsJa. 

Derivatization reactions. In addition to changing the substituents in the primary precursor phosphines, (MegSi)2NPRR , two other approaches have been used to prepare polymers with more complex substituents attached to the backbone by direct P-C linkages. These are (a) alteration of R and R in the immediate N-silylphosphoranimine precursors, MegSiN=P(OOUCFo)RR , and (b) alteration of R and R in the preformed poly(alkyl/aryl-phosphazenes), (RR P=N]n. Some examples of the former method are described below and in other papers (21-23), while the use of the latter approach to prepare several silylated poly(alkyl/arylphosphazenes) has been recently reported. (20)... 

Another phenoxide activating approach published by Buchwald et al. [18] is based on the reaction of cesium phenoxides with aryl bromides or iodides in the presence of catalytic amounts of copper(I) triflate and ethyl acetate in refluxing toluene (Scheme 3b). In certain cases equimolar amounts of 1-naphthoic acid have been added in order to increase the reactivity of the phenoxide. The authors assume the formation of a cuprate-like intermediate of the structure [(ArO)2Cu] Cs+ as the reactive species. In addition, diaryl ether formation between phenols and aryl halides has been achieved using a phosphazene base forming naked phenoxide in the presence of copper bromide in refluxing toluene or 1,4-dioxane [19]. 

Amino, alkoxy, and aryloxy polyphosphazenes are typically prepared by nucleophilic displacement reactions of poly(dihalophosphazenes). Analogous reactions with organometallic reagents, however, result in chain degradation and cross linking rather than in linear, alkyl, or aryl substituted poly(phosphazenes). The thermolysis of appropriate silicon-nitrogen-phosphorus compounds can be used to prepare fully P—C bonded poly(organophosphazenes). The synthesis of two of these materials and their Si—N—P precursors is described here. 

The reactions of phosphazenes (prepared in situ from aminophosphonium salts and triethylamine) with sulphur tetrafluoride have been further explored. An example is shown in reaction (3), where X is a bridging alkyl or aryl group. However, when X... 

From Amides and Phosphorus(v) I des.— The Kirsanov reaction has been used to advantage in the synthesis of certain P-aryl-phosphazenes ... 

Vinyl phosphazenes have been found to undergo tandem Aza-Witting/l,6-elect-rocyclization as illustrated by the reaction of 564 with tricarbonyl compound 565 to give 566 (Scheme 94) (95T3683). The reaction of 564 with aliphatic, heteroaryl, or aryl aldehydes first produced an intermediate imine 567 that ultimately cyclized to produce imidazol[l,5-a]pyridines 568 in good (65-82%) yields. 

In the presence of the phosphazene Et-P2 base as well as DBU the coupling of aryl iodides with arenethiols only requires catalytic amounts of copper(I) bromide (CuBr). Under these conditions, the reaction can be performed in refluxing toluene to give biaryl thioethers in excellent yields [40] (Scheme 5.22). 

The reaction of 1 -trimethylsilylnaphthalene with pivaldehyde in the presence of 20 mol% Bu-P4 base proceeded smoothly at room temperature to give the alcohol in 91% yield. Other phosphazene bases with weaker basicities, such as Bu-P2 base and BEMP, showed no catalytic activity. As one of the conventional strong organic bases, DBU was found to be inactive. Caesium fluoride (CsF) was then examined as a fluoride anion donor, but no carbon-silicon bond cleavage was observed. Reactions with other aldehydes have been examined that with benzaldehyde was found to proceed somewhat slowly at room temperature. Other aryl aldehydes with electron-donating groups were also employed as electrophiles and the reactions proceeded smoothly at room temperature [57] (Table 5.5). 

Ueno, M., Wheatley, A.E.H. and Kondo, Y. (2006) Phosphazene base-promoted halogen-zinc exchange reaction of aryl iodides using diethylzinc. Chemical Communications, 3549-3550. 

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