Ethyl phosphonate, selective

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. 

When ethyl phosphonates are used, the imine can be selectively deprotected after alkylation by treatment with dilute mineral acid (e.g., 10% HQ), 36"40 and the esters removed subsequently (see Section 10.10.3). When tert-butyl phosphonates are used, imine and ester hydrolysis is accomplished simultaneously under these conditions. These mild hydrolysis conditions are preferable when synthesizing amino acids with functionalized side chains 40 ... 

Demethylation of, POCH3. Phosphate and phosphonate esters are partially dealkylated by tertiary amines. r-Butylamine is superior Tor this cleavage, and it is very selective. Only O—Cl I3 bonds are affected ethyl esters are stable to the amine for several weeks. A benzyl group can be cleaved under forcing conditions.1 [Examples ... 

Figure 8. LC/MS mass chromatograms, positive APCI showing the detection of four isomeric alkyl alkylphosphonic acids (1 Hg/ml) and two dialkylalkyl phosphonates (10 p,g/ml) (upper), negative APCI showing selective detection of the phosphonic acids, a. i-PrMPA and EEPA (unresolved), b. methyl n-PrPA, c. n-PrMPA, d. ethyl methyl methylphosphonate, and e. dimethyl ethylphosphonate (lower)...

A simple procedure for the preparation of trifluoromethylated vinyl- and dienyl-phosphonates with y-alkoxycarbonyl moiety of exclusively or predominantly (Z)-configuration (201) has been described. It involves acylation of ethyl-1,1-bisphosphonate (202) with trifluoroacetic anhydride, addition of selected Reformatsky reagents to the resulting 1-trifluoroacetyl-1,1-ethyl bisphos-phonates (203) and finally spontaneous Horner-Wadsworth-Emmons (HWE) olefination of the adducts (Scheme 55). " ... 

Most of the examples in this chapter have been disubstituted alkenes, a few have been trisubstituted, but none so far has been tetrasubstituted (except cyclic alkenes) as this is the most difficult case of all. One solution49 starts with ethyl lactate 228 and uses a HWE reaction on the enantiomerically pure phosphonate 229 to make the / -enone 230 with very high selectivity. Chelation-controlled addition of a Grignard reagent gives the stereochemically pure allylic alcohol 231. Chelation control is explained in chapter 21. 

Phosphonates. In a Homer-Emmons-based synthesis of di- and trisubstituted (Z)-Q(, -unsaturated esters, the strongly dissociated base system of potassium bis(trimethylsilyl)amide/18-Crown-6 was used to prepare the desired phosphonate anions. This base system, coupled with highly electrophilic bis(trifluoro-ethyl)phosphono esters, gave phosphonate anions which, when allowed to react with aldehydes, gave excellent selectivity for the (Z)-Q , -unsaturated esters (eq 15). ... 

Synthesis of the modified triphosphate subunit was accomplished starting from ethyl bis(bromomethyl)phosphinate 253 (Scheme 51). An Arbusov reaction with triethyl phosphite and trimethyl phosphite, respectively, produced bis (phosphonomethyl)phosphjnate 255 in 40% overall yield. A selective monodemethylation by cyanide and acidificaticHi led to monophosphonic acid 256. Bismethylene triphosphate (BMT) 258 analogues of nucleosides were obtained by coupling of the 5 -free OH nucleosides 257 with phosphonate 256 under Mitsunobu conditions [181,182]. TMSBr mediated deprotection followed by treatment with aqueous anmumia and cation exchange afforded bismethylene analogues 259 of nucleoside triphosphate in yields up to 62%. 

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