Dialkyl Phosphonates Ml

PCI3 reacts rapidly with water to form phosphorous acid. In order to avoid the reaction of PCI3 with the water in the air, we carried out the reaction under N2 atmosphere. Moreover, PCI3 reacts exothermically with alcohol to form the intermediate Ml, so PCI3 must be dropped slowly into the solution of alcohol. 

Be cautious PCI3 is very toxic and corrosive. The structures, physicochemical data, and yields of Ml are listed in Table 9.1. 

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Alkali metal salts of 0-alkyl 1-(substituted phenoxyacetoxy)alkylphosphonic acids IIA-IIE could be easily synthesized by the reaction of (9,(9-dialkyl 1-(substituted phenoxyacetoxy)alkylphosphonates lA or IC with corresponding lithium bromide, sodium iodide, or potassium iodide in refluxing acetone. The synthetic route of IIA-IIE is shown in Scheme 3.5. For the synthesis of IIA-IIE, 1-hydrox-yalkylphosphonates M2, substituted phenoxyacetyl chloride MS, and 0,(9-dialkyl 1-(substituted phenoxyacetoxy)alkylphosphonates lA or IC could be prepared according to the known methods as stated in Chap. 2. 0,0-Dialkyl phosphonate Ml was used directly as obtained commercially or prepared by the reaction of phosphorus trichloride and methanol. Ml reacted with different aldehydes to give 0,0-diaUtyl 1-hydroxyalkylphosphonates M2. The substituted phenoxyacetic acids M4 were prepared in satisfactory yields by the reaction of corresponding substituted phenols with 2-chloroacetic acid or ethyl 2-bromoacetate followed by hydrolysis. The substituted phenoxyacetyl chlorides M5 could be easily obtained by the treatment of M4 with excess thionyl chloride. M2 reacted with MS to provide lA or IC (Scheme 3.5). 

One approach is enantioselective hydrophosphonylation. Chiral 1-hydroxyalkylphosphonates M2 could be prepared by the enantioselective hydrophosphonylation of dialkyl phosphonates Ml and aldehydes (Scheme 6.4) [50-54]. 

Dialkyl phosphonates Ml were prepared according to the literature (Scheme 9.1) [1, 2]. Dimethyl phosphonate was also obtained directly from commercial sources. 

Table 9.1 Structure and physicochemical data of 0,0-dialkyl phosphonates Ml ro h...

A solution of di-tc/7-bufyl peroxide in the dialkyl phosphonate was added to a Pyrex liner, which was then placed in a Ag-lined autoclave (.300 mL). After a pressure test and degassing, the fluoroalkene was introduced under vacuum, and the autoclave was then heated and rocked vigorously about a horizontal axis. After reaction the unreacted alkene was taken into the vacuum system and the autoclave was dismantled to obtain liquid products (see Table 8)... 

A mixture of dialkyl phosphonate 8 (1.14 mol) and l,2-dichloro-l,2-difluoroethene (0.38 mol) was sealed into a 300-mL Pyrex tube. The reaction was irradiated with y-rays from a Co source for a period of 230 h at I t (total dosage 16 x lO r.). Distillation of the irradiation products under reduced pressure, after removal of unreacted alkene and dialkyl phosphonate. gave the dialkyl l,2-dichloro-l,2-difluoroethylphos-... 

Dialkyl phosphonates undergo phosphite-phosphonate tautomerism and have two tautomeric forms phosphonate and phosphite [71]. Here M18-2 and Ml are expressed as phosphonate form in Scheme 6.6. 

Method M2-A To a stirred appropriate dialkyl phosphonate (40 mmol) in tri-chloromethane (15 mL), an appropriate aldehyde (44 mmol) in trichloromethane (15 mL) was added at room temperature. The mixture was cooled to 8-10 °C, triethylamine (20 mmol) was added drop wise and then the mixmre was stirred at 20-70 °C for 2-3 h. The component with lower boiling point was evaporated in vacuo to give the corresponding cmde 1-hydroxyalkyIphosphonate. Purification by column chromatography on silica gel and elution with petroleum ether/ acetone (4/1, v/v) or crystallization in ethyl ether gave the corresponding pure 1 -hydroxyalkylphosphonate. 

Although quantitative yields of chloroform were found, low yields of trialkyl phosphite were produced and these decreased with time as the yields of trialkyl phosphate and dialkyl phosphate increased, e.g. in the reaction of sodium n-butoxide (0.06 mol) with phosphorus (0.009 mol) in 30 ml of methanol and 50 ml of n-butanol 47% of phosphite was produced in 3 h. together with 19% of phosphate and 7% of phosphonate. The product composition changed to 34%, 22% abd 21% respectively after 7 h. 

Commercial potassium fluoride (dehydration not necessary) (50 mmol), or finely powdered commercial cesium fluoride (20 mmol) is stirred with dialkyl H-phosphonate (10 mmol) and the carbonyl compound (10 mmol) at room temperature for a period of 0.5 to 1 h. The reaction mixture is extracted with dichloromethane (50 mL) by shaking for... 

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