Phosphonate, cleavage

Me3SiBr, CH3CN, 1-2 h, 25°, >97% yield. This reagent is also useful for the cleavage of ethyl phosphates and phosphonates. ... 

NH4OH, MeOH. These conditions result in cleavage of only one ethyl group of a diethyl phosphonate. Selective monodeprotection of a number of alkyl-protected phosphates is fairly general for cases where cleavage occurs by the release of phosphate or phosphonate anions. 

Addition of the alcohol 42 to a solution of BF3 Et20/TMSCN in DCM provided the nitrile 43 in 83% yield. Hydrolysis of nitrile 43 then furnished amide 44 in 85% yield. Demethylation of the methoxyindole 44 with BBra in DCM provided the hydroxyindole 45 in 80% yield. This was followed by alkylation of 45 with the bromide 46 under phase transfer conditions to provide the phosphonate ester 47 and subsequent cleavage of the methyl ester by TMS-I furnished trimethylsilyl phosphonic acid 48, which upon alcoholic workup afforded LY311727. 

The (a-sulfanylalkyl)phosphonates and their difluorinated derivatives are also, by easy radical cleavage of the C-S bond, useful precursors of phospho-nomethyl or phosphonodifluoromethyl radicals, which can be added to double bonds and so, introduced in a variety of structures. Besides, the use of phospho-nodithioformates as radical trapping agents and their use as RAFT reagent for controlled polymerization open a new interesting field of appHcation for these dithioesters. 

The biotransformation of methyl phenyl phosphonate to benzene by K. pneumoniae (Cook et al. 1979) (Figure 2.7a). Further examples of the cleavage of the carbon-phosphorus... 

Bohman and Allenmark resolved a series of sulphoxide derivatives of unsaturated malonic acids of the general structure 228. The classical method of resolution via formation of diastereoisomeric salts with cinchonine and quinine has also been used by Kapovits and coworkers " to resolve sulphoxides 229, 230, 231 and 232 which are precursors of chiral sulphuranes. Miko/ajczyk and his coworkers achieved optical resolution of sulphoxide 233 by utilizing the phosphonic acid moiety for salt formation with quinine. The racemic sulphinylacetic acid 234, which has a second centre of chirality on the a-carbon atom, was resolved into pure diastereoisomers by Holmberg. Racemic 2-hydroxy- and 4-hydroxyphenyl alkyl sulphoxides were separated via the diastereoisomeric 2- or 4-(tetra-0-acetyl-D-glucopyranosyloxy)phenyl alkyl sulphoxides 235. The optically active sulphoxides were recovered from the isolated diastereoisomers 235 by deacetylation with base and cleavage of the acetal. Racemic 1,3-dithian-l-oxide 236... 

Reactions and Properties of Phosphonic and Phosphinic Acids and their Derivatives.-A free radical mechanism has been proposed to account for the cleavage of the phosphorus-carbon bond in the alkylphosphonic acids (155) by E coli to give a mixture of alkane (methane only, from methylphosphonic acid) and terminal alkene. 

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. 

Gross, H. and Keitel, I., a-Substituted phosphonates. 58. A direct phosphorylation of 7,7-bisphosphorylated quinonemethide nucleus with trivalent phosphorus-hydrogen compounds via carbon-carbon cleavage, Phosph., Sulf., Silic. Relat. Elem., 62, 35, 1991. 

The addition of any one of several dialkyl chlorophosphates to an arylalkyne-derived vinyl zirconocene in the presence of catalytic amounts of CuBr in THF leads to the corresponding vinyl phosphonate in high yields (78—92% see, for example, Scheme 4.38) [25]. Here, alkyl-substituted acetylenic starting materials do not react beyond the initial hydrozirconation stage. Vinyl phosphonates may be readily converted to acyloins by oxidation to the diol followed by base-induced cleavage. 

Other types of ester have been studied (Fendler and Fendler, 1975 Bender and Komiyama, 1978 Szejtli, 1982), though in much less detail. Brass and Bender (1973) studied the cleavage of two diaryl carbonates and three diaryl methylphosphonates in basic buffers (Table A5.ll). For the carbonates, reacting with /1-CD, introduction of p-nitro groups increases the acceleration ratio and worsens substrate binding, so that KTs barely alters. More interesting are the results for the phosphonates in that the effects of nitro groups depend on their position and on the CD. 

In this chapter, the words cleavage and de-esterification are often used to make it clear that reactions other than hydrolysis may be involved in the breakdown of some inorganic esters. This is particularly true for nitrates, and various phosphates and phosphonates, as discussed in the relevant sections. 

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