Silyls phosphorus halides

In the instances of phosphorous and phosphonous acid systems, the generation of a new C-P bond via the classical Michaelis-Arbuzov reactions as noted above leads to products that are esters themselves. Isolation of the free acid product requires cleavage of the ester linkage in a separate reaction step, generally after isolation and purification of the initial product. The advent of silyl phosphorus reagents for the Michaelis-Arbuzov reaction allowed free acid products to be isolated simply by water workup of the reaction system. Further, since the byproduct was a silyl-halide, the general concern that the by-product halide would participate in an extraneous Michaelis-Arbuzov reaction was obviated. 

Several methods for the preparation of the parent compound in this system, tris(trimethylsilyl)phosphite, have been reported.114 118 The application of this and related reagents in reaction with alkyl halides has been reported and used for the preparation of a variety of phosphonic acid analogues of phospholipids.114119-124 Interestingly, alkyl chlorides appear to be more reactive with the silyl reagents than do alkyl iodides, a reversal of the normally observed trend with alkyl esters of the phosphorus acids. (The particular use of silyl phosphorus reagents for the synthesis of biologically significant compounds has... 

The most convenient synthesis of halogenopyrazines and -quinoxalines is by halogenation of pyrazinones and quinoxalinones with phosphoryl or other acid halides for example, 5-hydroxy-2-pyrazinecarboxylic acid, rather than 5(477)-pyrazinone-2-carboxylic acid, is chlorinated with phosphorus pentachloride/phosphoryl chloride to afford a 63% yield of 5-chloro-2-pyrazinecarbonyl chloride <1994SL814>. Sato and Narita provided an improved synthesis of various halogenopyrazines in which 2(l//)-pyrazinones were activated with chlorotrimethylsilane to give silyl ethers (Section 8.03.7.3). This procedure is most effective for synthesis of bromopyrazines whose overall yields are 62-81% <1999JHC783>. Bromopyrazine is directly prepared by treatment of 2-(l//)-pyrazinone with phosphoryl... 

This was accomplished by coupling either an amine or a phosphide with a silyl halide, followed by metalation. In the case of the obtained aminosilane, the subsequent metalation proceeded smoothly resulting in a stable aminosilylanion. In the case of phosphorus, we observed the formation of the phosphinosilyl anion by NMR, but the compound was not stable under the reaction conditions and rearranged to give the potassium phosphide. 

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