Phosphines from phosphorus halides

Mono-, bis-, and tris-substituted A-pyrrolyl or /V-pyrrolidine phosphines have recently been described and prepared in excellent yields from pyrrole (or pyrrolidine), a phosphorus halide and base (NEt3, pyrrolidine, or DBU), as illustrated by the syntheses of (206) (Equation (49)) and (207) (Equation (50)) 451-453... 

Like the red solutions obtained from and NaOR, the red phosphides derived from phosphorus and organometallic reagents were found to react with alkylating agents to give tertiary phosphines s) Addition of butyl chloride to the reaction mixture from phenyllithium and (ratio 2 2 1) in ether gave di-butylphenylphospliine (37%) and butyldiphenylphosphine (44%). Similar products were obtained from the reactions of 4-methoxyphenyllithium, 3-trifluoro-methylphenyllithium or phenylsodium witli phosphorus and butyl halides ... 

Reactions with Alkyl Halides.— The in situ generation and reaction of chlorodi-phenylphosphine (2) with a-chloro-ethers gives good yields of a-alkoxyalkylphosphine oxides (20). The phosphine (2) is made from phosphorus trichloride and benzene, and the sequence looks like a very convenient one-pot procedure - the dangers of certain chloro-ethers aside ... 

Carbonyl-stabilized phosphorus ylides are less nucleophilic and hence do not react with (phosphine)gold(I) halides, but their gold(I) complexes can be generated from precursors such as [Au(acac)(PPh3)] or [AuCl(SC4Hg)] by reaction with phosphonium salts and ylides, respectively, and again both mono- and bis(yhde) complexes have been obtained (equation 48 and Scheme 8)206 207. The ylide carbon atoms in these complexes are centres of chirality, but no stereospecificity was observed in the coordination process and racemic mixtures are formed throughout. 

The organophosphides derived from phosphorus and organometallic compounds were found to react with alkyl halides in a manner typical of phosphides, to give unsymmetrical tertiary phosphines (6). Thus, phosphorus, plienyllithium, and butyl chloride gave dibutylphenyl-phosphinc and butyldiphenylphosphine in 37% and 44% yields, respectively. 

It will be recalled that substituted amino functions are displaced more slowly from phosphorus than halogen at low temperatures. An interesting case in the series of phosphinous halides involves the synthesis of phosphorus heterocycles having ultraviolet spectra that suggest aromatic character (46). Addition of Grignard reagents to the phos-... 

In fact, lithium diphenylphosphide can be reacted in situ with alkyl halides to give phosphines. Obviously, this reaction could be a serious side reaction in mixtures obtained from lithium reagents and phosphorus trichloride in which residual lithium was present. It should be noted also that metalation of triphenylphosphine with butyllithium occurred at the meta position on one ring to a small extent (58). Consequently, in the condensation of phosphorus halides with lithium reagents prepared by an exchange reaction employing butyllithium, an excess of the latter could result in mixtures. 

Tetravalent phosphorus halides are known to react with lithium reagents, but data is scarce. Aryllithium reagents easily displace chloride ion from phosphoryl chloride in the synthesis of tertiary phosphine oxides (143,144,174). A small quantity of the corresponding phosphinic acid (42) was isolated in the preparation of tris(p-dimethylamino-phenyl)phosphine oxide (43) (174). Choice of conditions and concentrations of reactants may well favor either the single or the double dis-... 

The well-known approach to functionalized phosphorus ylides based on the three-component reactions of triphenylphosphine (TPP), dialkyl acet-ylenedicarboxylates (DAAD) and various EH-nucleophiles (E = N, O, S, C) stabilizing by protonation a reactive intermediate generated from the reaction of TPP and DAAD followed by addition of a conjugated base to the vinyltriphenylphosphonium salt formed, has continued to find application. When 2-bromoacetamide was used as a nucleophile in this reaction, a-amido phosphorus ylides (52) were formed, even despite the high reactivity of P(III) atom of phosphines towards alkyl halides and a-halocarbonyl compounds. Ethyl phenylcarbamate reacted in a similar way ((52), Y = OEt). The other series of stable a-amido phosphorus ylides (53) was produced from the above reaction with l-benzylidene-2-phenylhydrazines. The reaction of TPP,... 

Phosphonium halides are produced by direct union of phosphine and hydrogen halide (4.139) or acid. A convenient preparation is from diphosphorus tetraiodide and white phosphorus (4.152). 

Phosphorus pentahalide complexes contain phosphonium cations and boron tetrahalide anions, for example, PCI4 BCI4 (Chapter 2.6). Phosphonium borohydrides, R4P BjH., can be prepared from phosphonium halides and sodium borohydride. On hydrolysis they give phosphine boranes. Salts with phosphonium cations and boron-containing anions are formed in other reactions (6.379) and (6.531). 

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]. 

In the Wittig reaction an aldehyde or ketone is treated with a phosphorus ylid (also called a phosphorane) to give an alkene. Phosphorus ylids are usually prepared by treatment of a phosphonium salt with a base, and phosphonium salts are usually prepared from the phosphine and an alkyl halide (10-44) ... 

B. By Hydrolysis Reactions.—Details have appeared of the synthesis of dibenzophosphorin oxides (15) from 5-alkyldibenzophospholes, by reaction with methyl propiolate in the presence of water, and of confirmatory syntheses from phosphinic acid chlorides, as shown below. Evidence for the suggested mechanism of the ring-expansion reaction is presented. The hydrolysis of enamine phosphine oxides is an efficient, although somewhat indirect, method for the preparation of j8-ketoalkylphosphine oxides (16) [see Section 3(iii), for the preparation of enamine oxides]. Reasonable yields (48—66%) of trialkylphosphine oxides (17) have been obtained by the alkaline hydrolysis of the products from the pyrolysis at 220 °C of red phosphorus with alkyl halides, in the presence of iodine. 

Heterocyclic phosphines 32 were prepared from base-induced condensation of a secondary 1,8-diamino-naphthalene with phosphorus trichloride (the corresponding As- and Sb-analogues were obtained analogously) and converted into cyclic phosphenium cations 33 by Lewis acid promoted halide abstraction using GaCl3 or trimethylsilyl triflate as reagents (Scheme 18) [15, 92],... 

Gusarova, N.K., Shaikhudinova, S.I., Reutskaya, A.M., Tartarinova, A.A., and Trofimov, B.A., One-step synthesis of unsymmetrical tertiary phosphine oxides from red phosphorus and organyl halides, Russ. Chem. Bull., 49, 1320, 2000. 

Miscellaneous. A number of reports of the synthesis of unusual heterocyclic phosphines have appeared. Improved procedures for the synthesis of l,3,5-triaza-7-phospha-adamantane (48) have been reported,40-41 and the triazaphosphahomo-adamantane (49) has also been prepared.42 Routes to the large ring phosphacyclo-alkanes (50) have been described,43 and the bicyclic diphosphine (51) has been isolated from the reaction of white phosphorus with o-dichlorobenzene in the presence of transition-metal halides.44... 

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