Nucleophilic phosphanes

Another well established reaction in solution-phase chemistry using a nucleophilic phosphane is the Staudinger reaction. A polystyrene-supported alternative proved to be less efficient, however. The hydrolysis of the intermediate imino-... 

Nucleophilic phosphanes can also be used for olefin isomerization. Nitroolefins having a substituent on the nitro group, readily available via the nitro aldol reaction followed by dehydration, often give a mixture of (E)- and (Zj-isomers. By adding catalytic amounts of polymer-supported triphenylphosphane, the (Z) -isomer could be isomerized to the corresponding (Ej-isomer, in most cases with total (E)-selectivity [30]. 

Another well-known process that utilizes a nucleophilic phosphane is the Mit-sunobu reaction, that is, the reaction between an acidic partner and an alcohol, typically facilitated by an azodicarboxylate and a phosphane. Two options are possible, anchoring of the electrophilic part to the solid support, dealt with in the next section, or anchoring of the nucleophilic phosphane. Georg et al. used polystyrene-bound triphenylphosphane and DEAD (diethyl azodicarboxylate) in their synthesis of aryl ethers [31]. Alcohols were reacted successfully with electron-rich and electron-deficient phenols, giving the desired products in good yield and purity. More recently, Wilhite and coworkers disclosed an efficient protocol for the synthesis of pyridine ethers using ADDP [l,l -(azodicarbonyl)dipiperidine] and polymer-supported triphenylphosphane (Scheme 6.9) [32], Both methods eliminate purification problems caused by triphenylphosphane oxide, but chromatography is still needed. 

The reactivity of fluoro(organyl)phosphanes depends on the nucleophilicity of phosphorus For mstance the phosphanes may add to the carbonyl carbon to form phosphiniio phosphoranes (equation 36) or may react with acid fluondes to form acyldifhiorophosphoranes [37] (equation 37)... 

Nucleophiles like alcohols [2, S], hydrogen sulfide [2], thiols [2,10], ammonia, amines, hydrazines, hydroxylamines [2 11, 12, 13, 14, 75], azides [2], other pseudohalides [2], phosphonates [2,16,17,18,19, 20], and phosphanes [2,19] add rapidly across the CO or CN double bond to yield stable adducts The phosphonate adduets undergo a subsequent aleohol—lester rearrangement [19, 20] (equation 2)... 

Reaction of the primary phosphane Bu3SiPH2 If with MgBu2 furnishes the solvent-free hexameric cluster 17 (Eq. 10) (47). Yellow crystals, have been isolated in 39% yield, which are thermochromic. The NMR spectrum, especially the 31P NMR signal at S = -263.8, suggested that the molecule prefers a high symmetry or dissociates rapidly on the NMR time scale. Since 15 is highly soluble in aromatic hydrocarbons even at low temperature and free of metal oxide, it can thus be regarded as a valuable source of phosphandiide, that is, for nucleophilic RP2 transfer reactions. 

Based on nucleophilic addition, racemic allenyl sulfones were partially resolved by reaction with a deficiency of optically active primary or secondary amines [243]. The reversible nucleophilic addition of tertiary amines or phosphanes to acceptor-substituted allenes can lead to the inversion of the configuration of chiral allenes. For example, an optically active diester 177 with achiral groups R can undergo a racemization (Scheme 7.29). A 4 5 mixture of (M)- and (P)-177 with R = (-)-l-menthyl, obtained through synthesis of the allene from dimenthyl 1,3-acetonedicar-boxylate (cf. Scheme 7.18) [159], furnishes (M)-177 in high diastereomeric purity in 90% yield after repeated crystallization from pentane in the presence of catalytic amounts of triethylamine [158], Another example of a highly elegant epimerization of an optically active allene based on reversible nucleophilic addition was published by Marshall and Liao, who were successful in the transformation 179 — 180 [35], Recently, Lu et al. published a very informative review on the reactions of electron-deficient allenes under phosphane catalysis [244]. 

Allenic esters such as 185 can act not only as dipolarophiles but also, at least formally, as 1,3-dipoles, which was shown by Xu and Lu during the phosphane-cata-lyzed reaction with N-tosylimines 387 (Scheme 7.52) [358, 359]. The heterocycles 388 are formed at least in moderate and mostly in excellent yields, if R1 is an aryl or a vinyl group. The formation of the products can be explained by reversible nucleophilic addition of the phosphane to 185 (cf. Section 7.3.1) followed by nucleophilic addition of the resulting intermediate to the imine 387. 

Treatment of propyne iminium triflate 258 with silylated phosphorus nucleophiles such as Me3SiPPhR affords (3-morpholinoallenyl)phosphanes 259 in high yield (Scheme 8.69) [150]. 

For the reaction of phosphane oxide with isocyanate, the rate-determining step is the formation of the oxazaphosphetane 45 via P—O—bond formation of the intermediate betaine (44), since the stable and energetically favorable P=0 double bond is broken here. Subsequent rapid decomposition of the oxazaphosphetane 45 into iminophosphorane and carbon dioxide occurs. Within the actual aza-Wittig step, the intermediate betaine (46) is generated in a rate-determining step by nucleophilic attack of the iminophosphorane nitrogen on the carbonyl C. By P —O-bond formation, betaine (46) is then converted into an oxazaphosphetane (47), which decomposes... 

Unlike phosphane oxide, the reaction rates of the irainophosphoranes exhibit no dependence on the P substituents. The initial step is a factor of 1(P-10 slower than the second step. However, the nucleophilicity of the iminophosphoranes can influence the reaction rate thus, electron-donating... 

In another approach, 2-(alkylamino)alcohol is employed as starting material for aziridine syntheses with the aid of dihalogenophosphoranes (70BCJ1185). Intramolecular transformation of 3-azidopropyloxirane 73 results in a simultaneous formation of a condensed aziridino[l,2-a]pyrrol-idine system (Scheme 39). The azide group is first transformed into imino-phosphorane 74, the nucleophilic N atom cleaves the oxirane to form betaine 75 [as in the Mitsunobu reaction (81S1)], and the phosphorus is shifted from N to O and then eliminated as phosphane oxide under simultaneous cyclization to bicyclic 76 (89JA7500). 

The range of carbon nucleophiles that have been successfully employed for 1,4-addition to -a,/i-unsaturated iron-acyl complexes is limited to simple alkyl- and aryllithium species. Grignard reagents and the 1,3-propanedioate anion are reported to fail to react with. E-complexes36. The effect of varying the phosphane ligand has been examined little effect upon... 

The conjugate addition of phosphorus nucleophiles of various oxidation states and in neutral or metallated form constitutes an efficient and well-known method for C—P bond formation [30]. In the case of phosphanes as nucleophiles especially, the corresponding phosphane-borane adducts have been used in 1,4-additions to Michael acceptors. Following the idea to use a chirally modified phosphorus nucleophile in asymmetric Michael additions to aromatic nitroalkenes, we synthesized the new enantiopure phospite 45 starting from TADDOL (44) with nearly quantitative yield. Due to the C2 symmetry, of the... 

Cyclobutanes were also obtained from metallacyclopentanes by simple thermal decomposition, by treatment with other nucleophiles (rather than alkenes) such as phosphanes, nucleophilic solvents or by reaction with oxygen. Byproducts of these reactions are the respective alkenes or linear dimers. The extent of the formation of byproducts depends on the temperature of the decomposition, on the solvent and the nucleophile and on the coordination number of the metal. 

Until 1998, only gold(III) was believed to be effective for catalyzing these processes because, as mentioned previously, only the gold(I) compound K[Au (CN)2] was tested and it was inert to catalysis. Fortunately, Teles et al. reported very strong activity in the addition of alcohols to alkynes when they used cationic gold( I) -phosphane complexes [14]. In this study, the aforementioned authors tested for the first time the suitability of nucleophilic carbenes that displayed even greater activity than other gold complexes, but they were unable to synthesize the subsequent cationic derivatives. 

Other routes to sulfonated phosphanes are the nucleophilic substitution of phosphides [Eq. (1)], which was first published in 1995 (26), and the reaction of halogenated arenesulfonates with PH derivatives (27) [Eq. (2)]. 

The telomerization of dienes in a two-phase system was first described in a patent (100). Water was used as the solvent for the catalyst, with sulfonated phosphane ligands providing the water solubility. Water, alcohols, phenols, acids, amines, and acetylacetic add were used as nucleophiles. 

Bromo-l,3-butadienes 62 can be coupled with nucleophiles to deliver allenylcarbinols and the related amines and phosphanes 63 [41]. In some cases even chloroprene can be used [42]-... 

Reactions of carbene complexes with phosphorous compounds are topics of current research.164-167 (l-Alkynyl)carbene complexes (CO)5M= C(OEt) —C=CR 1 (M = Cr, W R = Ph, r-Bu, SiMe3) readily add tertiary phosphanes PPhR2 (R = Ph, Me) and form stable zwitterionic phosphonium allenide complexes (CO)5M —C(OEt)=C=C(R)—P+PhR2 145, which have been characterized by X-ray diffraction (Scheme 57).55 In previous studies on Michael-type additions of nitrogen and oxygen nucleophiles to (l-alkynyl)carbene complexes 1, zwitterionic allenide complexes of type 145 have been postulated as intermediates.21,23,503 62 112,168,169 Unambiguous structural evidence of the tendency to form such intermediates is given by isolation of a stable zwitterionic adduct, such as compound 145. Zwitterionic... 

Fluorodenitration can be realized with the less reactive potassium fluoride when bromo(tetra-phenyl)-4 -phosphanc (Ph PBr) is used as a phase-transfer catalyst. - Bromo(tetraphenyl)-A -phosphane acts by enhancing the nucleophilicity of the fluoride anion in aprotic solvents of medium or high polarity, in which it is very soluble. The catalytic effect of bromo(tetraphenyl)-... 

Method B Trimcthyi(trilluoromethyl)silane was first synthesized in preparative amounts in i9j5424.28.29 tris(diethylamino)phosphane and bromotrifluoromethane for generation of the trifluoromethyi nucleophile suited to replace the chlorine in chlorotrimethylsilane almost quantitatively. 

The method has been further improved." Trimethyl(perfluoroalkyl)silanes RpTMS (Rp = c, -C, perfluoroaliphatic groups) are prepared by reaction of perfluoroalkyl halides RpX (X = Br, I) with chlorotrimethylsilane in the presence of tris(dialkylamino)phosphanes in acetonitrile. For example, chlorotrimethylsilane was treated with bromotrifluoromethane and tris(diethylamino)phosphane in acetonitrile at — 40"C for 1 hour to give trimethyl(trifluo-romethyl)silane in 90% yield. Bis(dimethylamino)(trifluoromethyl)silane is available from the reaction of chlorobis(dimethylamino)silane with the system bromotrifluoromethane/tris-(diethylamino)phosphane, while trichloro(trifluoromethyl)silane is prepared by nucleophilic trifluoromethylation of tetrachlorosilane with bromotrifluorornethane/tris(diethylamino)phos-phane. " ... 

The nucleophilic phosphorus atom in the bromopcntafluorobenzene/tris(diethylamino)-phosphane system attacks the bromine, affording a phosphonium cation and a carbanion. The subsequent reactions of these species depend on the presence of C-electrophiles. It has been shown that this system is convenient for the introduction of the polyfluoroaryl fragment into polyfluoro aromatic compounds and perfluoroalkenes examples are given by the formation of7-n. - - ... 

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