Isopropyl methylphosphinate

Organophosphorus compounds. Phosphorus-carbon bond fonnation takes place by the reaction of various phosphorus compounds containing a P—H bond with halides or tritlates. Alkylaryl- or alkenylalkylphosphinates are prepared from alkylphosphinate[638]. The optically active isopropyl alkenyl-methylphosphinate 778 is prepared from isopropyl methylphosphinate with retention[639]. The monoaryl and symmetrical and asymmetric diarylphosphi-nates 780, 781, and 782 are prepared by the reaction of the unstable methyl phosphinate 779 with different amounts of aryl iodides. Tnmethyl orthoformate is added to stabilize the methyl phosphinate[640]. 

Isopropyl (/ )-( —)-methylphosphinate (134) has been prepared" in > 90% optical purity by Raney nickel desulphurization of optically pure O-isopropyl (5)-(-f-)-methyIphosphonothioate (135). The phosphonate (134) is rapidly racemized by base, but not by acid, unlike secondary phosphine oxides"" [although whether these have been prepared optically active now seems doubtful (see Chapter 4)]. The phosphinate (134) can be reconverted into 89% optically pure (5)-( + )-(135) by addition of sulphur in dioxan. As shown in the Scheme, a series of interconversions has been used to establish the configurations. 

Cycloamylose forms inclusion complexes stereoselectively with the enantiomers of isopropyl methylphosphinate (124) from which it was possible to isolate one enantiomer with an optical purity of 66%. The absolute configuration of menthyl methylphosphinate has been revised to the opposite of that previously assigned. 

Benschop, H.P. and Van den Berg, G.B., Stereospecific inclusion in cycloamyl-oses partial resolution of isopropyl methylphosphinate and related compounds, Chem. Commun., 1431, 1970. 

We have studied the reaction of methyl trifluoromethanesul-fonate (methyl triflate) with isopropyl methylphosphinate (1), and have used this system to develop a new procedure for the stereospecific synthesis of trivalent (P ) organophosphorus esters. 

Neat isopropyl methylphosphinate (1) reacts exothermically on dropwise addition to methyl triflate to form a phosphonium salt (2), NMR 6 +73.4 (downfield from external H,P0.) J = 656 Hz, which yields isopropyl methyl methylphosphonite (3), when slowly added to a cold benzene solution containing excess tri-ethylamine (TEA). On warming to room temperature, the product was obtained as a benzene/TEA solution, which separated from a heavier liquid layer that consisted mainly of amine salt byproducts in benzene/TEA. When (R)-(+)-l (25% enantiomorphic excess) was used, a solution of (R)-(+)-3 (5 +176.6) was obtained in 60% yield, 90 mole-% pure with respect to its organophosphorus content. 2(Pie specific rotation of this product was calculated to be [a]D + 67.7 (c 2.6, benzene), if optically pure (+)-l starting material... 

The enantiomerically pure forms of isopropyl alkenylmethylphosphinates have been prepared by the reactions between 1-bromoalkenes and (R) or (S) isopropyl methylphosphinate catalyzed by Pd(0)-Et N. 

The cycloamyloses are probably best known for the noncovalent complexes they form by inclusion of organic molecules within the cycloamylose annuli. The formation of such inclusion compounds, including gas adducts, and their interesting properties have been reviewed. Reports in this field include the partial resolution of chiral sulfoxides and isopropyl methylphosphinate by stereospecific inclusion into cyclo-... 

The optically active isopropyl methylvinylphosphinate 65 (97 % ee) was prepared from isopropyl methylphosphinate 64 (97 % ee) with complete retention of stereochemistry [19],... 

When enantiomerically pure phosphines or derivatives and achiral palladium catalysts are employed, the stereochemistry of the P-C bond formation depends on the protective group X but also on the reaction conditions. Xu and co-workers reported that isopropyl methylphosphinate, 45, couples with aryl and vinyl halides with clean retention of configuration at the phosphorus atom (Scheme 6.20). 

Methyl phenyl sulfone 1-Methyl-4-(phenylthlo)benzene (2-Methylphenyl)thlourea A/-Methyl-A/ -phenylthlourea Methyl phosphate Methylphosphine Methylphosphonicacid Methylphosphonic dltluorlde Methylphosphonofluondicacid, isopropyl ester... 

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