Diaryl phosphine oxide

Tan also found that guanidine 21, acting as a base to activate the o [3], X [3] tautomers of diaryl phosphine oxides, catalyzes the asymmetric phospha-Michael reachon of aryl nitroalkenes (Scheme 5.42) [76]. He later employed 21 to realize highly enantioselective Michael additions of dithiomalonate and 3-keto thioesters with a range of acceptors, including maleimides, cyclic enones, furanone, and acyclic 1,4-dicarbonylbutenes [77]. 

Subsequently, the highly enantioselective Michael addition of malonates and 1,2,4-triazole to cyclic and acyclic enones, as well as the first phospha-Michael reaction of cyclic enones and diaryl phosphine oxides was reported using a similar catalyst.In 2012, Huang, Wang and coworkers demonstrated that primary amine-thiourea 39 can efficiently catalyse the... 

In 2010, Wang and co-workers [142] introduced phosphine oxides as nucleophiles to the asymmetric allylic substitution of BH carbonates. With quinidine as catalyst, the reaction proceeded smoothly to approach optically active allylic diaryl phosphine oxides in modest to good yields and enantioselectivities. A subsequent study showed that an additive was cmcial to the reaction with dialkyl phosphine oxides for example, excellent enantioselectivity was afforded with Na2C03 as the additive while a racemic product formed with NaOH as the additive [143]. 

Pyridines with phosphonate substituents are valuable for medicinal chemistry or iV,P-bisdentate ligands (Scheme 46) (13JA9322).Thus, a C-H phosphorylation process was developed where the heterocycle directs ortho-palladation. This intermediate can be intercepted by H-phosphonates and diaryl phosphine oxides to provide phosphonate-substituted pyridines. 

Phosphorus nucleophiles Asymmetric Michael addition of diaryl phosphine oxides to a,/ -unsaturated A-acylated oxazolidinones (299) has been reported to proceed with excellent enantioselectivities (<99% ee) in the presence of a catalyst generated from Et2Zn and the polydentate ligand (301). °... 

A synthesis of A-substituted a-aminobenzylphosphinic acids starts from ammonium hypophosphite this is allowed to react with primary amines together with aldehydes or ketones in the presence of HC1.60 The nature of the products and general success of the Atherton-Todd reaction for the preparation of dialkyl- and diaryl-phosphinic amides from secondary phosphine oxides depends on the order in which reactants are mixed and on the choice of polyhalogen reactant.61... 

Litvina, M.N., Chmutova, M.K., Myasoedov, B.F., Kabachnik, M.1.1996. Extraction and separation factors of lanthanides and americium in aqueous nitric acid- diaryl(dialkyl)-(dialkylcarbamoyl-methyl)phosphine oxide systems. Radiochemistry 38 (6) 494 -99. 

The palladium-catalysed cross-coupling of aryl halides or vinyl halides with dialkyl phosphonates (31) to yield dialkyl arylphosphonates and dialkyl vinylphosphonates, respectively, was first reported by Hirao and co-workers 69 the halides used most frequently are bromides and the reaction is stereospecific with haloalkenes. Subsequently, analogous reactions of alkyl alkylphosphinates (32), alkyl arylphosphinates (32), alkyl phosphinates (33), and secondary phosphine oxides (34), replacing [P—H] bonds with [P—C] bonds to yield various phosphinates and tertiary phosphine oxides, have been developed (Figure 7.1). Alkyl phosphinates (33) may be mono- or diarylated as desired by the selection of appropriate conditions. Aiyl and vinyl triflates have also found limited... 

However, phosphonic diesters are suitable starting materials on the way to tertiary phosphine oxides,399,428,429,435,436 and yields of 80-90% of dialkyl- and diaryl-phenylphosphine oxides have been achieved on treatment of diphenyl phenylphosphonate with an excess of the Grignard reagent.436... 

Diaryl ketones are directly reduced to hydrocarbons with EtiSiH-BFi OEt2. In the reduction of phosphine oxides" (i-PrO)4Ti is used as the Lewis acid catalyst. 

Arylphosphonic acid esters are produced in the reaction of diaryl iodonium salts with trialkyl phosphites in the presence of copper salts, but despite the simplicity of the procedure yields are low owing to side reactions. The cyclic bisarylphosphinic acid (66) is conveniently prepared by fusion of the phosphine oxide (67) with sodium hydroxide. A successful... 

Mention might be here of reactions between the sodium salts (or the magnesium equivalent) of secondary phosphine oxides (the diaryl compounds appear to have been exclusively examined) and benzenesulphonyl chloride (reaction 16) and that between chlorodiphenylphorphine and sodium arylsulphinates (equation 17) in DMF ", when the... 

Diaryl secondary phosphine oxides have been used to synthesize biphosphine ligands (42) via a substitution-reduction sequence. ... 

Scheme 22 Synthesis of chiral diaryl-methyl and alkyl-methylphenyl phosphine oxides 69...

The use of aryl tosylates as electrophiles is attractive, because they can be prepared from readily available phenols with less-expensive reagents than those required for synthesis of the corresponding triflates. Importantly, tosylates are more stable towards hydrolysis than triflates, yet significantly less reactive as electrophiles. As a result, protocols for traditional cross-coupHng reactions were only recently developed (see Chapter 2). In contrast, catalytic direct arylations with aryl tosylates were not reported until recently. Interestingly, a rathenium complex derived from heteroatom-substituted secondary phosphine oxide (HASPO) preligand 78 [40] allowed for direct arylations with both electron-deficient, as well as electron-rich aryl tosylates [41]. As pronucleophiles, pyridine, oxazoline and pyrazole derivatives could be efficiently functionalized. Selective mono- or diarylation reactions could be accomplished through the judicious choice of the... 

The most satisfactory laboratory preparation of (6.236) involves addition of an alcohol or phenol to a dialkyl or diaryl chlorophosphine in the presence of a base such as pyridine or triethylamine (6.237). This reaction is carried out in anhydrous ether near 0°C, the low temperature being necessary to prevent isomerisation of reactive products to phosphine oxides (6.108). 

Alkylaryl and diaryl sulfides do not react with the /rani -dioxo species presumably because of their decreased nucleophilicity. Of note, an Fe(TPP)Cl/PhIO system effects oxidation of dialkyl, alkylaryl and diaiyl sulfides, via a proposed ClFe(TPP)0 intermediate the axial ligand trans to the 0x0 ligand is likely critical. The chemistry of eq. 27 would imply that Ru(porp)(0)(OSR2) is a more efficient 0-atom donor than Ru(porpXO)2, while data for phosphine oxidation (see Section 3.1) imply that the Ru-monooxo species disproportionates more quickly than reacting with phosphine. The kinetic data for thioether systems could be consistent with the type of mechanism described for the phosphine systems, and a careful re-evaluation of the thioether systems is needed. With Fe systems, of course, disproportionation to a dioxo species is unknown. Relevant to this discussion are the findings that LRu(porp)(0) species are better catalyst precursors than the corresponding Ru(porp)(0)2 for oxidation of saturated hydrocarbons... 

There were a couple of reports of cross-coupling reactions of pyrazoles published. Palladium-catalyzed cross-coupling between 3,4-, and 5-halopyr-azoles 32 and H-phosphonates, H-phosphinates, and secondary phosphine oxides to give pyrazoles 33 was accomplished in moderate-to-good yields (13OL5550). 1,3,5-Triarylaminopyrazoles 35 were prepared by Ullmann coupling firom l,3-diaryl-5-aminopyrazoles 34 and aryl halides in the presence ofcopper(I) iodide (13T570). 

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