Acetylenic phosphonates

Organyl tellurolate anions effect 1,4-additions to acetylenes bearing electron-withdrawing groups such as acetylenic ketones, aldehydes, esters, diacetylenic ketones, " as well as acetylenic phosphonates and sulphones giving 2-substituted vinyl tellurides with Z configuration. 

The synthesis of a,ft--unsaturated halides has been realized via new dephosphorylation reactions of ,/l-clhylcnic and acetylenic phosphonic acid monoesters with (biscollidine)iodine(I) or (biscollidine)bromine(I) hexafluorophosphate (Scheme 6)23... 

In aU cases studied, the acetylenic phosphonates are transformed without formation of the isomeric... 

The reverse reaction has been reported. Thus, low-temperature treatment of sodium enolates of ethyl 2-methylacetoacetate or ethyl 2-oxocyclopentanecarboxylate with diethyl 3-iodo-1-propynylphosphonate in THF gives the corresponding alkylation products in better yields. These acetylenic phosphonates are hydrolyzed with acidic HgSO4 to produce diethyl 4-(ethoxycarbonyl)-2,5-dioxoalkylphosphonates in good yields (78-80%, Scheme 8.64). ... 

Aryl-substituted acetylenic phosphonic acids are formed by reaction of the appropriate acetylene with phosphorus pentachloride, followed by treatment of the initial adduct (70) with base. Improved yields of... 

The cyclization reaction of non-conjugated acetylenic phosphonate dimethyl esters (167 n = 2, 3, 4) in the presence of (bis-collidine) bromo- and iodohexafluorophosphates led to the formation of halo enol phostones (Scheme 58). This cyclization allowed the formation of 6 to 8-membered compounds, either by endo or exo pathways vide supra Scheme 56). 

The most advantageous method for synthesis of 4 -phosphonate 50 starts fipom chlorobutyne 14c and sodium diethyl phosphite in DMF (Scheme 9). Compound 50 was obtained in the same (23%) yield as from chlcHX>adenallene 45 (Scheme 8), but the procedure is shorter. Acetylenic phosphonate 55 and isomaization product 56 are likely intermediates which, unda the conditions employed, are of limited stalnlity. By contrast, but-... 

The following conclusions can be drawn from this investigation (i) Allenic and acetylenic phosphonates 53c, 53c, 55c and 55e are not stable under the conditions of Mi-chaelis-Arbuzov and Michaelis-Becker reactions (ii) chloroadenallene 45, chloiobutyne 14c and 14e can serve as synthons for stereo- and regioselective syntheses of phosphonates 47,50,60c and 60e (iii) the scope and limitations of allene formation (compound 61) during Michaelis-Arbuzov reaction certainly deserve attention. 

With acyl halides, the corresponding acyl phosphonates are obtained. Furthermore allylic and acetylenic halides, as well as a-halogenated carboxylic esters and dihalides, can be used as starting materials. If substituents R and R are different, a mixture of products may be obtained, because the reaction product RX 5 can further react with phosphite 1 that is still present ... 

Simpson and Burt have studied the same reactions in the presence of various amounts of ethanol and have plotted graphs of phosphonate (81 R = Ph) and phenyl acetylene produced against moles of alcohol added. Acetylene in the product reached a maximum (around 60%) when two moles of ethanol were added and stayed fairly constant beyond this, which suggests that the attack-on-halogen contribution to the mechanism is approximately 60%. The rest of the reaction presumably follows some other mechanism and the authors suggest the addition-elimination route (79) in view of the isolation of the phosphonate (83) from the reaction of tri(isopropyl) phosphite with the bromoacetylene (84). 

Preparation of diethyl 3,3-diethoxypropynyl-l-phosphonate — Reaction of a sodium salt of a dialkyl phosphite with an acetylenic halide492... 

A photoinitiated reaction has been reported of trialkyl phosphite with an electron-deficient vinylic halide for which an olefinic carbon is covalently bound to a metallic center (Figure 6.24).92 Unfortunately, only low yields of the target phosphonate are obtained. In another report involving a transition metal bound to carbon, an acetylenic carbon covalently bound to an iron center has been found to undergo... 

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. 

An unusual reaction of electron-deficient acetylenes (usually DMAD is used) and triarylphosphines or -phosphites with Cjq leads to methanofullerenes that bear an a-ylidic ester (Scheme 3.11). Selective hydrolysis of the phosphite ylides yields phosphonate esters, phosphine oxides or phosphonic acids [49-51]. 

Louerat, F., Bougrin, K., Loupy, A., Ochoa de Retana, A.M., Pagalday, J. and Palacios, F., Cycloaddition reactions of azidomethyl phosphonate with acetylenes and enamines. Synthesis of triazoles, Heterocycles, 1998, 48, 161-170. 

An attractive alternative to the direct preparation of enamines from mono-substituted phosphonate reagents is the use of dimethyl diazomethylphosphonate (Me0)2P(0)CH= N2. Treatment of this diazo compound with t-BuOK (or with LiOH or K2C03), followed by various ketones in the presence of secondary amines, delivered the corresponding enamines251-253 (equation 17). In the presence of amines, (MeO)2P(0)CH= N2 and RCHO afforded the terminal acetylenes RC=CH. 

Selective phosphonate ester dealkylation. Alkyl phosphonate esters are selectively and nearly quantitatively cleaved by bromotrimethylsilane in the presence of alkyl carboxylate esters, carbamates, acetylenes, ketones, and halides. Alkyl iodides do not exchange under the reaction conditions. The resulting bis(trimethylsilyl) phosphonates are hydrolyzed in acetone by a small excess of water. 

The catalyst (PPh3)3RuCl in the presence of DPPB is an efficient reagent for the hydrophosphorylation of olefins. The reaction is highly sensitive to olefin substitution and monosubstituted olefins can be reliably converted to their aliphatic phosphonates in the presence of other olefins. Additionally, a trimethyl-silyl group is an effective acetylene protecting functionality that reverses the normal preference for alkyne hydrophosphorylation over a terminal olefin (Scheme 54). 

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