Phosphorus-carbon bonds, preparation

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]. 

Reactions with Simple Alkenes and Aromatic Compounds.—A wide range of conditions continues to be used to form phosphorus-carbon bonds between halogeno-phosphines and alkenes or benzene derivatives. A selection of such reactions (Scheme 2) is outlined for the preparation of the compounds (17)—(23).22-26... 

The phospholyl anions were discovered by Braye and are readily prepared through alkali metal cleavage of the exocyclic phosphorus-carbon bond of phospholes ... 

Reduction of the phosphorus-carbon bond is generally achieved with the aim of preparing new phosphorus compounds, and not with the object of preparing reduced carbon compounds. It is a striking difference from mercury-carbon bond cleavage, which is usually carried out in order to prepare carbon compounds. 

Other chiral monophosphonito-systems, e.g. (63) have also been prepared, and their role in catalysis explored. The vinylphosphonite (64) has been shown to suffer cleavage of the phosphorus-carbon bond in protic solvent systems containing potassium carbonate. 

Miscellaneous Methods of Preparing Phosphines. Palladium-catalysed formation of phosphorus-carbon bonds continues to be developed as a useful route to organophosphines. The reactions of primary or secondary phosphines with aryl- or vinyl-halides in the presence of a palladium catalyst, usually palladium acetate or a zerovalent palladium-phosphine complex, have been used in the synthesis of steroidal phosphines, e.g., (128), the cationic diphosphine system... 

Further examples of the preparation of phosphonates from acetals and phosphorus pentachloride include those leading to (91) and (92). The reaction of phosphorus pentachloride with t-butanol yields the phosphonate (93), which eliminates hydrogen chloride on treatment with base. The phosphorus-carbon bond-forming steps of the reactions leading to (91)—(93) appear to involve the addition of phosphorus pentachloride to electron-rich olefins. 

In addition to the very many procedures available for the preparation of aminoalkyl-phosphonic and -phosphinic acids through phosphorus-carbon bond formation, many of which have just been summarized, the same acids have been obtained through a multitude of procedures which consist in the modification of compounds in which the essential carbon skeleton, and in particular the phosphorus-carbon bond, is already in existence. In the following account, the various types of otherwise functionalized phosphonic and phosphinic acids are considered in the order in which they have so far been listed in this and in the previous chapter. 

Thus far, the survey of phosphazene elastomers has been based on the formation and modification of poly(dlchlorophosphazene). Although a large variety of polymers can be prepared by this approach, there are limitations In the preparation of polyphosphazenes with phosphorus-carbon bonds. The reaction of poly(dlchlorophosphazene) with organometalllc agents, such as RMgX or KLl, results mainly In decomposition and not the desired polymers [NPR.]. There are three possible approaches to the preparation ox polyphosphazenes with phosphorus-carbon bonds polymerization of substituted trlmers, poly(dlfluorophosphazene), and thermolysis of small linear molecules. These three approaches will be discussed In turn. 

The development of a palladium-catalyzed cross-coupling process for the preparation of vinylphosphonates by Hirao was one of the turning points for the preparation of vinylphos-phonates [368]. His chemistry was operationally simple and utilized a readily available palladium(O) compound as the catalyst and triethylamine as the base. The temperatures required for his reaction were mild compared to Arbuzov chemistry, and the phosphorus-carbon bond-forming reaction was compatible with a wide range of functional groups. 

The Corey-Winter reaction provides a useful method for the preparation of olefins that are not accessible by other routes. For instance it may be used for the synthesis of sterically crowded targets, since the initial attack of phosphorus at the sulfur takes place quite distantly from sterically demanding groups that might be present in the substrate molecule. Moreover the required vicinal diols are easily accessible, e.g. by the carbon-carbon bond forming acyloin ester condensation followed by a reductive step. By such a route the twistene 10 has been synthesized ... 

Carbon-phosphorus double bonds are also formed in addition reactions of tris(trimethylsilyl)phosphine 1692 (which can be readily prepared from white phosphorus, sodium, and TCS 14 [13a,b,c]) to give oxazohum fluorides 1691 which then give the azaphospholes 1694, via 1693 [3, 14]. On addition of 1692 to 1695, the diazaphosphole 1696 [3, 15] is prepared, whereas l,3-azaphospholo[l,2a]pyridines 1698 [16] are formed from 1692 and 1697, and 1,3-thiaphospholes 1700 are formed from the dithiohum fluorides 1699 [17]. l,3-Benzodiphospholyl anions 1703 are generated by reaction of acid chlorides with the dihthium salts 1701, via 1702 [18] (Scheme 11.3). 

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