Phosphonates, unsaturated

A nice application of this reaction for the synthesis of cyclic a-sulfanylphos-phonates 63 has been reported [42]. It involves a Rh(II)-catalyzed [2,3]-sigmatropic rearrangement and a ring-closing metathesis of the resulting a-(S-allyl) y,d-unsaturated phosphonates 62 (Scheme 16). However, the last step occurs with a low yield (19%) when R = H. 

Finally, (3-bromoacrylate esters react with trialkyl phosphites to provide the unsaturated phosphonates (Equation 3.24), presumably through an addition-elimination route.392... 

The highest enantioselectivity in the hydrogenation of unfunctionalized tri-substituted alkenes has been achieved with catalyst 14 a. The same catalyst was also used to hydrogenate a,/ -unsaturated phosphonates with enantiomeric excesses (ee) of 70 to 94% [8]. 

The behavior of phosphorus pentachloride toward carbon-carbon multiple bonds has received considerable attention, and the procedure described represents but one example of a wide variety of derivatives of unsaturated phosphonic acids which are accessible. Indene was the first olefinic compound to be reacted... 

Rhodium-catalyzed asymmetric 1,4-addition reactions have been applied to various other a,p-unsaturated compounds as well. Thus, Rh/(5)-binap can catalyze the asymmetric 1,4-addition of arylboroxines to ot,p-unsaturated phosphonates in high yield and ee (Figure 3.37). The key to the success in achieving high yield is the... 

Figure 3.37. Scope of Rh/(5)-binap- or Rh/44-catalyzed as5mmetric 1,4-addition of aryl-boroxines to a,P-unsaturated phosphonates.

In addition, phenylsufonylallene (110), a,(3-unsaturated phosphonates (111), and alkenes with perfluorinated substituents (112) are all useful dipolarophiles. The yields observed with methyl 2-propenoate are significantly lower than those with the corresponding acrylate (entries 7 and 9), because of the additional substituent. On the other hand, the dipolar cycloadditions with either ethyl vinyl ether, 1-hexene, cyclohexene, or a trisubstituted dipolarophile provide the corresponding isoxazolidines in either low yields or not at all (18). 

Hanessian and Compain have also reported a Lewis acid-promoted inverse electron demand hetero-Diels-Alder reaction between dihydrofurans and dihydropyrans with a-keto-/3,7-unsaturated phosphonates to give stmcturally related products <2002T6521>. High-pressure OTr/o-selective hetero-Diels-Alder reactions between a,/3-unsaturated aldehydes and enol ethers in the presence of lanthanide catalysts have also been reported and give 3,4-dihydro-27/-pyrans. Examples include the use of cyclic enol ethers to give 2,3,4,4a,5,8a-hexahydro-277,577-pyrano[2,3-. ]pyrans <1995T8383>. 

The preparation of unsaturated phosphonates and phosphine oxides represents another class of reagents that are extensively used in organic synthesis. For example, allylic phosphonates are commonly employed in the preparation of dienes and polyenes via Horner-Emmons olefmation. Vinyl phosphonates have numerous uses as both synthetic intermediates" and bioactive compounds. 

In 2001, Grubbs and co-workers reported the first intermolecular CM reactions for the preparation of unsaturated phosphonates. " Using the highly active NHC catalyst 5, the CM reactions of both allyl and vinyl phosphonates were... 

In contrast to a,(3-unsaturated phosphonium salts, ot,(3-unsaturated phosphonates (161)1331 alkylate ali-cyclic ketone enolates efficiently, while the homologous diethyl butadiene phosphonate (162)133bintramolecular cyclization. Heathcock reports that... 

Kinetics of formation and decomposition of 58 have been investigated 221). Pyrolysis of 68a yields an cu-unsaturated phosphonous ester derivative 70 204). 

The phenylselenenyl chloride/silver tetrafluoroborate induced purino-selenenylation of the unsaturated phosphonate derivatives 50 gives the adducts 52 in modest yields but with a good control of the stereoselectivity (>80% de). This stereoselectivity is in good agreement with preferential formation of the seleniranium salt 51 which undergoes stereoselective opening by a purine base to give the adducts 5296. 

The reaction of perfluoroalkylated a,/f-unsaturated phosphonates such as 6 with saturated, methanolic ammonia solution affords diethyl 2-amino-2-(perfluoroalkyl)phosphonates (c.g., 8) and methanolic adducts such as 7. Reaction with benzylamine yields diethyl 2-benzylamino-2-(perfluoroalkyl)phosphonates (e. g., 9) which, upon hydrogenation, also give diethyl 2-amino-2-(perfluoroalkyl)phosphonates.5 ... 

The first asymmetric synthesis of an a-mercapto y-unsaturated phosphonate (203) using the readily available chiral dimenthylphosphonyl ester group and a carbanionic [2,3] sigmatropic rearrangement was achieved. Absolute configuration of the newly formed chiral centre of nonracemic thiol (203) was determined. 

The synthesis was initiated from the unsaturated phosphonate 95 prepared in several steps from the D-glucal as shown in O Scheme 41. The 1,4-addition of a soft nucleophile provided the adduct which, upon acetylation, was easily converted into the target 96. 

I.2.I.4.2.I.8.6. Esters of Unsaturated Phosphonic Acids, Phosphinic Acids, Vinyl Phosphanes... 

In an investigation of the reaction between isobutene and PCls, it has been shown that, as the temperature of reaction is raised, the proportion of unsaturated phosphonic dichloride (30) increases at the expense of the saturated compound (31) ... 

Several addition reactions of unsaturated phosphonic and phosphinic esters have been reported during the course of the year. Dithiophosphoric acids add to 2-alkoxy-vinylphosphine esters in the expected manner, and in the addition of phenyl azide to vinylphosphonates, the initial triazole (95) may be thermolysed to a C-phosphory-lated aziridine, but in the presence of triethylamine the final products are 2-anilino-vinylphosphonates. ... 

Pergament, I., and Srebnik, M., Hydroboration of unsaturated phosphonic esters. Synthesis of borono-phosphonates and trisubstituted vinylphosphonates. Org. Lett., 3, 217, 2001. 

Anisimov, K.N., and Nesmeyanov, A.N., Derivatives of unsaturated phosphonic acids. Part 15. Neutral esters of P,P-phenylchlorovinylphosphonic and P-phenylethynylphosphonic acids, Izv. Akad. Nauk SSSR, Ser. Khim., 1006, 1955 Chem. Abstr., 50, I I267li. 1956. 

Mashlyakovskii, L.N., and lonin, B.I., Unsaturated phosphonic acids and their derivatives. Part 1. Synthesis of alkadienyl-, aUtenynyl-, and alkynyl-phosphonic dichlorides, Zh. Obshch. Khim., 35, 1577, 1965 J. Gen. Chem. USSR (Engl. Transl.). 35, 1582, 1965. 

Conant, J.B.. and Coyne, B.B., Addition reactions of the phosphorus halides. Part 5. The foimation of an unsaturated phosphonic acid, J. Am. Chem. Soc., 44, 2530, 1922 Chem. Abstr., 17, 273a. 1923. Gajda. T.. A convenient synthesis of diethyl 1-chloroalkylphosphonates, Synthesis, 111, 1990. Pudovik, A.N.. Zimin, M.G., and Sobanov, A.A., Reactions of dialkyl phosphites withketones activated by electronegative groups, Zh. Obshch. Khim., 42, 2174. 1972 Chem. Abstr., 78, 58543, 1973. Johnson. R.A.. Aryhnethylphosphonates and phosphonic acids useful as anti-inflammatory agents, their preparation, and their activity, Upjohn, U.S. Patent Appl. US 5500417, 1996 Chem. Abstr. 124. 307587. 1996. 

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